SOURCES AND EFFECTS
OF IONIZING RADIATION
United Nations Scientific Committee on the Effectsof Atomic Radiation
UNSCEAR 1994 Report to the General Assembly,
with Scientific Annexes

UNITED NATIONSNew York, 1994

NOTE
The report of the Committee without its annexcs appears as Official Records of the
Gencral Assembly, Forty-ninth Session, Supplemerlt No. 46 (A/49/46).
The designation employed and the presentation of material in this publication do not imply
the expression of any opinion whalsoever on the part of the Secretariat of thc United Nations
concerning the legal status of any country, territory, city or area, or of its authorities, or concerningh e delimitation of its frontiers or boundaries.
The country names used in this docurnent are, in most cases, those that were in use at thetime the data were collected or the lext prepared. In other cases, however, the names have been
updated, where this was possible and appropriate, to reflect political changes.

UNITED NATIONS PUBLICATION
Sales No. E.94.IX.11
ISBN 92-1- 142211-6

ANNEX B
Adaptive responses to radiation in cells and organisms

CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
I . ADAPTIVE PROCESSES IN MAMMALIAN CELLS . . . . . . . . . . . . . . 188
INTRODUCTION. EFFECTS 1N HUMAN LYMPHOCYTES ................... 188

A

Cllro~nosonleaberrations ............................ 188
Clone-forming ability and genomic stability . . . . . . . . . . . . . . 190
Cell survival and n~utationfrequency ................... 190
Interaction with chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
5. Repair of specific DNA lesions . . . . . . . . . . . . . . . . . . . . . . . 192
6 Sunlnlary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
EFFECTS IN MOUSE CELLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
1. Splenic lymphocytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
2. Bone marrow cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
3. Spermatocytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
4. Mammary carcinoma cells . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
5. Pre-implantation embryos . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
EFFECTS IN FIBROBLASTS FROM VARIOUS SPECIES . . . . . . 195
1. Human embryonic and skin fibroblasts . . . . . . . . . . . . . . . . . . 195
2. Chinese hamster cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
3. Mouse embryo cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
4. Derived human epithelial cell line . . . . . . . . . . . . . . . . . . . . . 197
ADAPTIVE RESPONSE TO CHEMICAL MUTAGENS ........ 197
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
1.
2.
3.
4.

B.

.

C

.
.

D
F

.

I1. MECHANISMS OF ADAPTIVE RESPONSE . . . . . . . . . . . . . . . . . . . . 198

A. CELL CYCLE CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
1 Protein synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
2. Tunlour suppressor genes . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
B GENE ACTIVATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
1. Cell growth arrest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
2. Radiation-induced gene expression . . . . . . . . . . . . . . . . . . . . . 200
3. Induced protein products and DNA repair . . . . . . . . . . . . . . . . 202
4. Stress-response proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . .204.

.

UNSCEAR 1994 REPORT

186

Page

C. OTHER MECHANISMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
1. Radical detoxification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
2 . Activation of membrane receptors . . . . . . . . . . . . . . . . . . . . . 206
3 Stimulated proliferation of splenocytes . . . . . . . . . . . . . . . . . . 206
D. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.

m . EFFECTS ON THE IMMUNE SYSTEM . . . . . . . . . . . . . . . . . . . . . . . 206
A. CELLS OF THE IMMUNE SYSTEM . . . . . . . . . . . . . . . . . . . . . 207

T-cell ontogeny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Apoptosis and radiation-induced interphase death . . . . . . . . . . . 208
3 . Signalling processes in thymocytes . . . . . . . . . . . . . . . . . . . . . 208
B RESPONSE IN THE ORGANISM ........................ 209
1 Effects in animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .209
2. Effects in humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
3 Effects on turnour growth . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
C. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
1.
2.

.

.

.
.

IV EXPERIMENTAL STUDIES OF RESPONSE IN MAMMALS ....... 214
A SHORT-TERM SURVIVAL FOLLOWINGACUTE. HIGH-DOSE EXPOSURE . . . . . . . . . . . . . . . . . . . . . . . 214
B. LONG-TERM SURVIVAL FOLLOWING
SUB-LETHAL EXPOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
1. Experiments with rodents . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
2 Experiments with beagle dogs . . . . . . . . . . . . . . . . . . . . . . . . 217
C. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.

.

V. EPIDEMIOLOGICAL STUDIES OF RESPONSE IN HUMANS . . . . . . 218
A. INHABITANTS OF HIGH-BACKGROUND AREAS . . . . . . . . . . . 219
B. OCCUPATIONALLY EXPOSED INDlVIDUALS
219
C. SURVIVORS OF THE ATOMIC BOMBINGS . . . . . . . . . . . . . . . 221
D. PATIENTS EXAMINED OR TREATED
WITH RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.............

CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

INTRODUCTION
1. The scientific cor~ilnunity has been aware formany years of the possibility that low doses ofradiation may result in changes in cells and organisms.
which reflect an ability to adapt to the effects ofradiation. In lower organisms. for example. enhanced
proliferation in the presence of radiation at doses of afew microgray per day to a few milligray per day has
been observed in experiments involvi~~gcultures ofprokaryotes and eukaryotic cells [Cl. C2. C3. C4. C5.
C6. 11. 12. L4. P2. P3. T l l ].

2. The biological expression of adaptive andstinlulatory responses in seeds and plants (e.g. [C14.
H9. H10. R6. R7. S431) has also been described The
extensive literature up to 1976 supporting radiationassociated adaptive effects was reviewed by Luckey[Ll] A more recent publication by h e same authorsummarizes the literature between 1976 and 1991.
involving about one thousand reports judged by him to
demonstrate beneficial responses in allimals and in
human populations [L2].

.

.

ANNEX B: ADAPTlVE RESPONSES TO RADIATlON IN CEUS AND ORGANISMS

3.
It has been suggested in recent years that theconventional estimates of stochastic effects following
exposure to low doses of ionizing radiation may have been
overstated because no allowance was made for the
possibility that small doses of radiation may condition cells
so as to induce processes that reduce either the natural
incidence of cancer in its various fomls or the likelihoodof excess cancers being caused by further radiation
exposure.

An important observation Goni mammalian cell
4.
studies in support of these processes is that mitogenstimulated human blood lymphocytes exposed in vitro
appear to suffer less damage than would be expeded
following acute exposure to a few gray of low-LET
radiation if they are fmt exposed to a dose of a few tensof milligray. This response to low-dose exposure, which
remains effedive for several hours, is referred to as an
adaptive response.

5.
Adaptive responses have been observed in othermammalian cell types, such as bone marrow cells andfibroblasts, but not consiste~~tlyin spennatocytes or at allin embryo cells exposcd in the pre-implantation stage.
Changes in the composition of the culture medium canalter the adaptive response. hl a wider context, it is known
that changes similar to those observed in radiation-induced
adaptive response can occur as a result of metabolic
disturbances and after damage resulting from exposure toa variety of physical and chemiciil agents. The consequences of these ccllular changes are referred tocollectively in the literature as stress response or response
to genotoxic stnrs.
6.
Evidence of adaptive resporae has also been
described UI studies using laboratory animals, in which theanimals were cxposed either to single acute doses from a
few tens of milligray to a few gray, or accumulated dosesof up to a few gray over a lifetime. Reported manifestations of this fornl of adaptive response described in
mammals after exposure to low doses of radiation include
an accelerated growlh rate in the young, an increase inreproductive ability, an extended life-span, stimulatory
effects on the immune systeril and a lower-than-expected
incidence of spontaneous tumours. A satisfactory
explanation of nlechanisrns that r n i g t be responsible forsuch effects, which have not been consistently observed indifferent investigations, is not obvious. It niay involve a
DNA repair mecbanus~nsimilar to that proposed for thecellular adaptive response, iml~lying its inmediate
availability if cellular damage rando~ulyoccurs during theanimal's lifetime. Ir~volvcnientoC tile h~miuilosurveillancesystem has also been proposed.
7.
Four conference. (one on radiation honncsk, held at
Oakland, Califonda, in 1985 [Sl];o ~ l one low-dose radiationand the immune system, held at Fra~lkfurtin 1987 [S21];
one on low-dose inadiation and biological defense

187

mechanisms, held at Kyoto in 1992 [S2]; and one on lowlevel exposures to radiation and related agents, held at
Changchun, China, in 1993 P8]) have provided an opportunity for scientists working m the fild of lowdose effeds topresent their experimental findings and debatc the possible
mechanisms uivolved in radiatior~induccdadaptive response.
8.
This Annex, based mainly on recently publisheddata, has been compiled by the Committee with a view to
identifying the cellular rncchar~isrrlsthat may be involvedin the adaptive response at low doses. It should bc
considered as a continuation of the discussions on radiation response contained in the UNSCEAR 1993 Report
PI]. One problen~in identifying common mechanisms of
response is that there are differences between the doses
and dose rates used in cellular studies and those used in invivo studies of laboratory animals. A further complicationis that there are few studies available in which doses of afew milligray per year above the natural backgroundradiation level have been used. Low doses were defined in
the UNSCEAR 1993 Report P I ] , Annex F, "Influence ofdose and dose rate on stochastic effects of radiation", withthe values depending on the level of investigation. At amicrodosirnetric level a low dose is defmed as about
0.0002Gy. In a similar context, the I~lternational
Commission on Radiological Protection P6] consideredthat low doses and low dose rates imply situations inwhich it is very unlikely that more than one event ofenergy deposition will occur in the critical parts of a cellwithin the tune during which repair mechanisms in the cell
can operate. For mammalian cells in culture, a low doseis defined as less than about 0.02 Gy. For the induction ofhuman tumours, a low dose is defined as less than about
0.2 Gy. The same criteria can be applied UI this Annex,
although it should be recognized that much of theexperimental data on effects in cells and animals is basedon doses in excess of about 0 5 Gy.
9.
hfanifestations of adaptive responses in animals andhi human populations are briefly addressed in this Annex.
Evidence for the expression of an adaptive response in
human populations exposed to low doses of radiation
above the natural background level has not until now beenclearly demonstrated nor has it been refuted. The
possibility that exposure to low doses of radiation may
affect the level of competence of imn~unosurveillancemecha~lisrnsUI carcinogenesis is discussed. Details of themechanisms of action of radiation UI inducing cancers andserious hereditary effects in humans are not discussed.
These aspects of the deleterious effcfects of radiation can befound in the UNSCEAR 1993 Report [Ul],Annex E,"Mechanisms of radiation o~~cogenesis",Annex G,"Hereditary effects of radiation", and in this Report in
Annex A, "Epidaniological studies of radiation carcinogenesis". These Annexes should be read in conjunction
with this Annex to achieve a balanced view of the overall
effects of low doses of radiation.

UNSCEAR 1994 REPORT188

I. ADAPTIVE PROCESSES IN MAMMALIAN CELLS
10. Efforts have been made over the past decade tocharacterize the adaptive response induced by niutagens inmammalian cells. A response has been demonstrated in
mitogen-stimulated, human blood T lymphocytes. Other
cell types investigated for evidence of a response include
proliferating lymphoblasts, bone marrow cells, spemiatocytes, pre-implantation enibryos and fibroblasts.
11. Cells respond to radiation-induced injury by the u p
regulation of proteins involved in cell signalling and by
the increased expressior~of genes involved in cell proliferation [Al, S3] and in the synthesis of DNA repair
enzymes [Ll, LS, M3, W2]. Qualitatively similar
responses have been d e s c n i d as a result of cellular
disturbance caused by temporary oxygen deprivation [B5,L7, M4, S9, SlO] and glucose starvation [HI, Sll].
1 2 The mechanisms i~~volvedin the adaptive response
to low doses of radiation have been linked to a moregeneral phenomenon UI which the cells are able torespond to damage fioni a variety of physical andchemical agents. These agents include overheating [ S ] ,W-radiation [B3], trace amounts of mutagenic chemicals[B4, Vl], local anaesthetics that alter membrane structure[L6] and heavy metals known to act as cellular poisorls[='I.
A. EFFECTS IN HUMAN LYMPHOCYTES

1. Cllron~osomeaberrations
13. It was reported in 1984 [ 0 2 ] that when phytohaemagglutinin-stimulated human lymphocytes weregrown in a culture medium contau~ingtritiated thymidine
and were exposed in the G, phase of the cell cycle to
15 Gy fioni x rays, the yieldif chromatid aberntions was
significantly less than the sum of yields of the aberrations
induced by tritiated thymidine and x rays separately
Fable 1). The responsc was observed to occur at aconcentration of tritiated thymidine low enough to give an
estimated one beta disintegration in each cell volunie
between exposure to the tritium and the x rays. The
reduction in the expected number of aberrations was notconsidered to be attributable to a radiation-induced delay
in cell cycle progression at this low concentration. Nor
was it considered to be due to the selective killing of aradiosensitivc population of lymphocytes that had
incorporated tritiated thymidine [W3].
14. When the tritiated thymidine was present in the
blood cultures throughout the entire culture period, theresults were quite variable. This was shown, hmvever, tobe attributable to the fact &at, UI blood, the amount oftritiated thymidine incorporated into cells is highly
dependen1 on the catabolism of thyniidine to a degraded

fornl which cannot be incorporated. Later experiments inwhict~the tritiated thymidh~ewas pulse-labelled while thecells were in the S phase markedly reduced thisvariability,
and the uptake of tritiated thymidine was maximized.

15. A similar response was shown to be induced byexposing phytohaemagglutinin-stimulated lymphocytes in
the S phase to a low dose from x rays (referred tovariously in the literature as the conditioning, inducing,priming or adapting dose), followed by exposure of thecells h~ the G2 phase to a high dose born x rays (caIled
the challe~~gedose). This response was subsequently
confinned by some investigators [B6, B11, K4, L25,M30,
03, S13, S14, W4, WS], although not consistently byothers who were using suiiilar culhue protocols p7, H8,
M21, S1.5. S16]. The lymphocyte cells from different
donors show variable sensitivity, as is shown in Table 2
16. It was postulated that the conditioning dose ofradiation activated genes and that this was quickly
followed by the synthesis of enzymes responsible for
DNA repair. If these enzymes were available in adequate
at the time the cells were exposed to aconccntnlio~~schallenge dose, the extent of the repair of DNA damage
was inlproved, so that fewer chromatid aberrations wereobserved than in cells receiving the challenge dose only.
It was presumed that the repair enzymes were notinmediately available to cells receiving the challenge dose
only and that, in these circumstances, much of the damage
was irreparable by tile time a sufficient quantity oferuynes became available. This hypothesis was supportedby the observation that the adaptive response could beblocked by the protein synthesis inhibitor cyclohexirnide(Table 3) and by 3-an~inobenzamide(Table 4), an inhibitorof poly(ADP-ribose) polymerase. which is known to be
induced during the repair of DNA strand breaks [A16].
17. Other characteristics of the in v h o lynphocyte
adaptive responsc have been reported:(a) the adaptive response to x rays requires a dose of atleast 0.005 Gy delivered at a rate of more than
(1.2 Gy mia-' [S14]. The implication of this fmdingis that a certain number of DNA lesions, perhaps ofa specilic type, need to occur within a fived time inorder to initiate the signal for expression of theadaptive responsc. In f a d , there is a window ofdose, 0.005 to 0.2 Gy, below which and above
which h e phenomer~onwas not observed. Such anarrow window has also been observed inexperuiients with radiomimetic compounds such asbleoniycin, which, like x rays, induces double-strand
breaks;@) the illduction of the repair mechanism takes place
between 4 and 6 hours afier exposure to theconditioning dose and remains effective for threecell cycles [S13];

ANNEX B: ADAPTIVE RESPONSES TO RADlATlON IN CELLS AND ORGANISMS(c)when the cells werc exposed to two conditioning
doses delivered within a few hours of each other,
the reduction in the amount of chromatid damage
was found to be similar to that observed after as~ngledose. The second dose thus provided no
additional protection against the damage caused by
the first conditioning dose within this time Fable 5):(d)it has recently been shown that a single dose of
0.005 Gy fromganuna rays did not create
conditions for the adaptive response, but two doses,
each of 0.005 Gy given in the same cell cycle, did
do so [B22]. The effect of the two conditioning
doses was optiniuni when they werc given at 36
hours and 42 hours and the challenge dose of 1 Gyor 1 5 Gy was given at 48 hours after mitogenstimulation. It is implied from this study that theacute dose to induce maximum activity of the repair
enzyme system is about 0.01 Gy.

18. The question why lymphocytes from sonicindividuals do not respond rc~llainsu~uesolved.In fact, thely~tlphocytesin some cultures exposed to 0.02 Gy fromx rays reacted synergistically to subsequent mutagenic
treatment [03]. The cells in this experiment were futed 24 hours after the challenge dose, in contrast to those inother experiments, where futation times were confined to
6 hours or more after the challenge dose. The
unpredictable nature of tlle rcsponse has been confirmed
using differences in niicronuclei frequency as an end-point[P4]. Changes in the hydrogen ion concentration of theculture medium can affect the yield of induced chromatidaberrations Fable 6). This finding was confinned when it
was shown that adjusting the hydrogen ion co~lcentrationof the culture medium to pH 6.4 just before the challengedose enhanced the effectiveness of the response 1031. It
was also shown that the response could be induced incultured lymphocytes from donors who had not previously
displayed the adaptive resporse, by adding conipounds tothe culture medium that could affkct the metabolis~nof thephytohaemagglutinin-stimulated lymphocytes (e.g.
intcrieukin-2, which sti~iiulates proliferation). It isconceivable that the rcpair systems induced may react
differently according to Ihc culture conditio~ls,a situationthat should not be ovcrlookcld when considcri~g thecoruequences of the co~~ditio~lingdose. Thus, theconlposition of the culture ~nediurnmay be nucii~l.
19. It has been pointed out that measurements of thefrequencies of aberrations induced in asynchronous cell
populations are likely to be misleading if expressed as asimple avcrage from a single furation tune IS23). The
reason for this lies in Ihc intercellular variability of thecell-cycle transition d~nes.I t is knoun that tllc inlri~rsic
cellular radiosensitivity varies as the cells pass thrc>u@thecell cycle, and the time of application of the conditionu~gor challenge doses of ediation may therefore be crucial.
In these circumstances, thc aberration score will alu'ays

189

refled the average of a mixture of cclls having different
radiosensitivities, and any shifts in the mixture ratios will
influence the aberration yields. A double-labelling
technique (Brd-U replication banding), which permits
identification of the cell cycle position occupied by eachscored ~netlphaseat the time of the conditioning andchallenge doses, has recently been described and may help
to solve this problem [NO]. Usuig this technique, it was
shown that a conditioning dose of 0.01 Gy from x raysdelivered at a rate of 0.05 Gy min-l, followed 6 hours
later by a challcnge dose of 1 5 Gy at a rate of
0.0044 Gy n i i ~ i l ,resulted in a transient decrease in thetiequency of total aberrations at 6 hours, but not at 9hours, after challenge. Furthennore, when the cohorts at 3,
6 and 9 hours after the challenge dose were combined,
there was no evidence of an adaptive response. This
preliminary experiment sen7esto demonstrate the complex
nature of the kinetics of cells in stimulated lymphocyte
cultures and the possibility that an adaptive response may
occur only in a narrow window of cell cycle when cells
are particularly radiosensitive.

20. The experiments descnied above refer to theapplication of UIC conditioning dose in the S phase and achallenge dose horn x rays in the G.2 phase of the cell
cycle. Studies in which phytohaenlagglutinin-stimulated
lymphocytes were exposed to the conditioning dose atother stages of the cell cycle have been reported, butdifferent laboratories have had different results, which has
yet to be explained. An adaptive response was reported
when the Go or GI phase cclls were exposed to aconditioning dose and challenged in dle late S or early G2phase [a,K4, K5] and when cells werc exposed to aconditioning dmc in the G1 phase and challenged in the
GI phase (S17, W7]. No response was reported by otherlaboratories if the conditioning dose was given in the Go
or the GI phase and the challer~gedose in the G1 phase[K4, S131. T h c x results arc presented in Table 7.
21. An adaptive response, indicated by a reduced
frequency of clromosorne aberrations, has also been
de~nonstratcdwith the conditioai~ydose given in vn.0.
Preli~ninary results of the cytogenetic monitoring ofchildren living in a region of Ukraine conta~ninatedafter
the Chen~ol~yl
accident indicate that the chron~oso~tie
aberration yield in lymphocytes to a challcnge dose inritro is less tlian that in control lymphocytes from achallenge dose alone [PlO]. This has to be confirmed byfurther studies, but there is supporting evidence f?om inviva studies in the rabbit [Dl.The response of lymphocytes to both cnndithling and challcnge doses in I&-ohad
earlier [C8]. hl the in vivo study, fourbeen der~io~lstrated
adult male rabbits were exposed to ganuna-radiation at adose n t e of about 6 mGy h-' for 9 hours each day for 36days, giving a daily dose of 0.05 Gy. Blood samples weretaken before the in viva imadiations and further samples
were collected at intervals of 6, 15, 18, 24. 30 and 36
days, the curt~ulativedoses being 0.3, 0.75, 0.9, 1.2, 1.5

190

UNSCEAR 1994 REPORTand 1.8 Gy, respectively. Six cultures were establishedfiom each blood sample. Two were analysed for baseline
chromosome aberrations; two were exposed to a challengedose of 15 Gy from x rays at a dose rate of 0.44 Gymhil, and phytohaeniagdutinin was added to them
immediately thereafter. The remaining two c d t u m wereincubated with the addition of phytohaemagglutinin at thestart of culture and exposed to a challenge dose of 15 Gy
fiom x rays 48 hours later. The results fioni the analysisof blood lymphocytes from individual rabbits showed thesame trend and are presented as average values in Table 8.
They show that an adaptive response can be induced inlymphocytes exposed to 0.05 Gy d-I in vivo when thechallenge dme to the phytohaemagglutinin-stimulatedcells
is given in vitro in either the Go or the G, phase of thecell cycle. This could imply that chronic-irradiation of
circulating blood lymphocytes induces the synthesis ofproteins in sufficient amounts to maintain a continuousand effedive reservoir of repair enzymes.

2. Clone-forming ability and genon~iestability
22. To study the effects of radiation on clone-forming
ability and karyotypic abnormalities in human peripheral
blood lymphocytes, cells were exposed to 3 Gy fromx rays in vino and either individual T-cell clones or longterm T-cell cultures were established m161. The karyotypes were analysed in G-banded chmmosorne preparations after proliferation for 9-34 days in vuro.

23.

T-cell clonal karyotype abnormalities were found in
24 of 37 (65%) irradiated clones and in 2 of 43 (5%)
control clones. Balanced reciprocal translocations anddeletions were the predominating types of clonal abenations. Complex aberrations and unstable karyotypes were
found in about half of the irradiated clones. Some of the
T-cell clones demonstrated sequential change from normal
to aberrant karyotype. Other clones seemed to develop
multiple, heterogeneous chmn~osonialaberrations duklg
growth in vuro.

24. T cells irradiated wiih x rays and grown in longterm culture displayed karyotype abnormalities in 60%80%of the cells, and the types of aberrations were similar
to those found in the individual irradiated T-cell clones.
An increasing number of cells with the same abnonnal
karyotype was observed when the cultivatio~~
time wasextended, indicating preferential clonal proliferation.
25. These rcsulls demonstrate that a surprisingly highproportion of T cells with stable and often complex
inadiation-induced chromosome aberrations are able toproliferate and fonn expanding cell clones in 1.itt-o.
Furthemiore, they indicate that x-inadiation induces latent
chromosome damage and geno~nicinstability in human
T lymphocytes. What would be interesting would be torepeat this study by giving a conditio~ungdose of a few

tells o l rnilligray before the challenge dose of 3 Gy andobserving if any reduction in proliferating T cells withstable aberration occurred.

3. Cell survival and mutation frwluency

26. Cell survival and chromosome aberration yield havebeen measured in phytohaemagglutinin-stimulated
lymphocytes exposed to 0.05 Gy kom x rays followed byacute exposure to 2 or 4 Gy, both exposures being in the
GI phase [SlJ. In studies on six donors, the yields ofchromosome exchanges and deletions were found to beless than in cells receiving the challenge d m only.
Lymphocytes 6om only two of the six donors tcsted
showed an adaptive response expressed as enhanced cellsi~rvivalwith a challenge dose of 2 Gy and none after achallenge dose of 4 Gy. A chromosome adaptive response,
therefore, docs not necessarily coincide with a cell survival
adaptive response. Reductions in the number of cells withseven1 aberrations (multiply aberrant cells) can be theR S U ~of a cylogenetic adaptive response, but if the proportion of non-aberrant cells is not increased, then asurvival adaptive response will not be seen.

27. In a subsequent study, a lower challenge dose wasused. Lymphocytes 601n the six donors were exposed to
0.05 Gy fiom x rays, followed by 1 Gy in the GI phase[S44]. Under these exposure conditions, most of theaberrant cells would be expected to contain only one
chromosonie aberration after the challenge dose. Cell
survival adaptive responses were seen in four of the six
donors, but the decrease in the numbers of singly aberrant
cells was not in itself sufficient to account for the increasein cell survival. It was proposed, therefore, that someincrease in cell survival could have been due to repair oflesions in cells that were at the level of the gene locus,
which would not be recognized by the cytological
techniques used to identify aberrations.

28. Cell survival has been measured concurrently withthe yield of mutations using 6-thioguanine (TG) selection
to detect clones mutated at the X-linked hypoxanthine
phosphoribosyl transfense (Ipn) locus [S18]. Tritiatedthymidine was added during the Go phase, followed byexposure to 1.5 or 3.0 Gy from x rays in the GI phase.
Cell survival was not affected (Table 9), but tritiatedthymidine at concentrations of 3.7 and 37 kBq ml-I i11 theculture 11iediun1produced a significant decrease in thenumber of mutations induced after the challenge dose
fioni x rays compared with cells receiving the challengedose only.
29. 111 support of this observation, the mutation
frequency was reduced by 70%, while cell survival was
not affected, when lyrnphoblastoid cells were exposed to
0.02 Gy from x rays, followed by a dose of 4 Gy in the
GI phase [R8]. This decreased mutation frequency was

ANNEX B: ADAPTVE RESPONSES TO RADlATON 1N CELLS AND ORGANISMS

considered to be the result of an induced repair system,
which was shown to be absent from mutant cells deficientin the Iprt locus. Lymphocytes exposed in the GI phase
to a conditioning dose of 0.01 Gy from x rays, followed
by a challenge dose of 3 Gy from x rays in the G2 phase,
also showed a reduced mutation frequency compared withcells exposed to the challenge dose only (Table 10).

function of the accumulated dose, regardless of theradiation source and the modalities of treatment, a linear
relationship was found, indicating that the mutagenic
effects of protracted exposure to tritiated water and acuteexposure to x rays were additive, as can be seen from thelower plot of Figure I.
4.

30. Reduced mutation Gequency was denionstrated withhuman HL60 cells exposed to a conditioning dose of~rays at a dose rate of
0.01 Gy Gom 6 0 gamma
0.078 Gy min-' and then exposed 18 hours later to achallenge dose of 2 Gy [El.After irradiation, the cells
were cultured for seven days in a non-selective RPM11640 medium to allow phenotypic expression of lpnmutants. The frequency of ilpn mutations resulting fromthe dose of 2 Gy was 26.9 10.~.Treatment with theconditioning dose reduccd the niutation frequency to
10.7

31. Mutant colonies exposed to the challenge dose
showed gene deletions and rearrangements in 15 out of 32
colonies (46%). This compared to 1 2 out of 46 colonies(26%) fnst exposed to a conditioning dose. Since genedeletions and reanangements are associated with
unrepaired or error-prone DNA double-strand breaks. it
could be concluded from this experiment that a DNA
double-strand fidelity repair niechanisni had been induced.
3 2 In contrast, the human lymphobiastoid cell line TK6,
which is heterozygous for the thymidine kinase genehas been used in studies of mutatio~~
induction at
two independent genetic loci. One of these is the Itprt
locus; the other is the autosomal thymidine kinase (7iY)
locus. The selective agents 6-thioguanine (TG) andtrifluorothymidine
were used to measure mutation
at the hprt and 1X loci, respectively. Cell survival andmutation rate were measured after protracted exposure totritiated water, follo\ved by exposure to x rays at the rateof 0.8 Gy min" [TI]. The results of this experiment are
illustrated in Figure I.

(mi-),

33. The cells were grown in a medium containing
0.74 MBq ml-' of tritiatcd water, the tritium irradiating thecells at a dose rate of about 0.05 Gy d-l. During theoverall period of incubation in the presence of tritiatedwater, the cloning efficiency, detenniried after 10, 20 and
30 days of exposure, reniained almost constant, and it wascomparable to that found for unhdiated cells. M e r thechallenge dose of up to 1.5 Gy from x rays, the survival
curves for TK6 cells, pretreated or not with tritiated water
for different lengths of ti~iie,were also similar, as shownin the upper plot of Figure I. These results showed thatwith a low-dose-rate, protracted conditioning exposurefroni incubation in tritiated water, no adaptive eKect oncell survival was detectable. Furthemiore, treatment withtritiated water had no significant effect on the i~~ductionofmutations. When the mutation frequency was plotted as a

191

Interaction with chemicals

34. A recent review of experiments involving theactivation of bacterial oxidative stress genes provides auseful background for understanding adaptive mechanisms
UI eukaryotic cells [Dj]. One of the mechanisms involved
in DNA repair after exposure to low-LET radiation isthought to be shnilar to that operating after exposure to
trace amounts of oxidizing radicals. In confirmation of thishypothesis, exposing lymphocytes to low concentrationsofhydrogen peroxide, followed by a dose of 15 Gy fromx rays, was found to induce the adaptive response(Table 11). Conditioning with a chemical and challengewith radiation is temied cross-adaptation.
35. Other studies (see also paragraph 74) havesubstantiated this Ending, in which the adaptive response
was shown to occur in donors whose lymphocytes weretreated with 25-75 ,&ofIhydrogen peroxide 24 hours
before a challenge dose of 15 Gy from x rays [C13].
However, when the cells were repeatedly exposed tohydrogen peroxide at intervals of 24,30 and 36 hours, theadaptive resprlse was not observed. The authors did notgive any explanation for this lack of response to repeateddoses [W3].
36. A reduction in niicronuclei frequency has beendernonsmted in lymphocytes conditioned with hydrogen
peroxide [D6]. Lymphocytes were exposed to a 30-nlinutepulse of hydrogen peroxide ( 2 5 - 2 5 0 m 24 hours aftcr
formation of the cultures and to a challenge dose of
1.5 Gy or 3 Gy froni x rays 48 hours later.
37. An adaptive response can be induced in the presenceof trace amounts of bleornycu~,which is known to
produce double-strand breaks during the G2 and M phasesof the cell cycle [V2, W8]. Thus, when lymphocytes
cultured in the presence of low concentrations of
bleomycit~(0.0l-0.1pg ml-l) for 48 hours were challenged
with a high concentration ( 1 5 pg ml-l) of bleomycin orwith 1.5 Gy lkoni x rays, lower than expected frequencies
of chromatid and isochromatid breaks were found. Thiscross-adaptation was not observed if cells were exposed toniethylating agents. In fact, radiation and methyl methanesulphor~ate act synergistically in the same way as a
combination of methylating agents (Table 12).
Conditioning with kiterferon (SO IF rnl-') has been
described p 3 0 ] . These experiments lend support to theview that cross-adaptationmay operate in lymphocytes toreduce the damage caused by some, but not all, DNAdamaging agents.

192

UNSCEAR 1994 REPORT

5. Repair of specific DNA lesions

38. A study to identify the molecular lesions associatedwith conditioning doses of several nu tag ens has recently
been reported [S19]. The end-points measured in thelymphocytes from two donors included chromatid andchromosome aberrations and sister chromatid exchanges.
39. To measure chromatid aberrations, the cells were
exposed to 0.05 Gy from x rays 24 hours after phytohaemagglutinin stimulation (i.e. in the GI phase) andchallenged with 2 Gy from x rays at 48 hours (ie. in late
SJearly G2 phasc). To measure chronlosome aberrations,the cells were exposed to 0.05 Gy from x rays 12 hours
after phytohaemagglutinin stirnulation and challenged with
2 Gy from x rays at 18 hours (i.e. both exposures in the
GI phase). Cells frorn one donor showed an adaptive
response when challenged in the late S or early G2 phase,in contrast to e l l s from the other donor, which showed
the adaptive response when challenged in the GI phase.
40. Three drugs were used to induce sister chromatid
exchanges: etoposide (VP16), 1,3-bis(2-chloroethyl)-lnitrosourea (BCNU) and cis-diamminedichloroplatinum(lI) (cis-platin). Etoposide, a topoisomerase II
inhibitor, prevents the creation and resealing of DNA
strand breaks, as opposed to the base modifications causedby cis-plah and inter-strand cross-links by BCNU. The
repair of DNA damage at specific sites from these drugs
is the result of the synthesis of enzymes involved inexcision and past-replication repair or the synthesis ofdamage-recognition proteins (esterases) that prevent crosslinking.

to the observation that a statistically significant decreased
number of sister chromatid exchanges was found in thelymphocytes of workers who had been occupationally
exposed to low doses of radiation and whose blood
were pres~lrt~ed
to be in the Go phase while
ly~r~phocytes
they were chronically irradiated [T2].

43. An adaptive response to low-LET radiation exposure
has been demonstrated in mitogen-stimulated human
lynlphocytes when they are acutely exposed to a conditioning dose within the range 0.005-0.2 Gy prior to achallenge dose of a few gray. The response has been
expressed as a reduction in the yield in chromatid orchro~nosornelesions, typically to about one half the yield
expected. The adaptive response has been demonstrated
when both the conditioning and challenge dases areapplied at late stages (S/G2 phases) of the cell cycle.
Howcver, Uiere is disageernent as to whether or not theadaptive response occurs if the conditioning dose isapplied in the resting or early stages (G&) of the cell
cycle. This important point needs to be clarified, since it
has inlplications for the circumstances in which cells arechronically irradiated in vivo.
44. The cellular response is transient, lasting for about
three cell cycles in culture. Since radiation-induced doublestrand breaks are repaired, this could imply the productionof specific repair enzymes in addition to those involved in
the process of repair of damage m cells occurring during
nonrlal ~t~etabolism.

41. Cells were exposed to 0.05 Gy from x rays at 40
hours after phytohaemagglutinin stimulation and exposedto drugs (05 ph4 VP16, 10 pM BCNU or 0.67 pM cisplatin) 6 hours later for 2 hours. At 48 hours, the drugs
were washed out and the cultures treated for 4 hours with
30pM bromodeoxyuridu~e (BrdUrd). This techniqueensured that only the cohort of cells that spent sufftcient
time in the S phase during the BrdUrd labelling would bescored. Small but statistically significant reductions insister chromatid exchanges, consistent with an adaptive
response, were observed (Table 13). Both donors
responded sinlilarly, showing reductions most ofien for
VP16-induced sister chromatid exchanges. Althoughsignificant reductions were also observed for chromatid
deletions, analysis of the data showed that they occurred
independently of those for sister chronlatid exchanges.
These results are consistent with the view that damage to
specific sites in DNA is repairable follo\vi~g a
conditioning dose of x rays.

45. There appears to be individual donor variation, withno evidence of an adaptive response in the lymphocytes ofsome blood samples tested even though the culture
procedures arc identical to those producing a response.
Why this is so is not lu~own.Several explanations havebeen proposed. One possibility is that the adaptive
Ksponse requircs the nlaintcnance of a narrow range ofpH and the presence of specific growth-stimulating factors
in the culture medium. Another possibility is that theadaptive response occurs at a precise time in the cell
cycle, so that cells outside this phase do not respond. A
third possibility is that in vivo factors such as the~lutritionalstatus or the inmlunocompetence of the livingorganis111may i~ffluencethe cellular response.

42. No adaptive response was obtained when cells from10 donors were exposed to mitomychl C, with and withouta prior conditioning dose of 0.01 Gy from x rays in theGOphase [MS]. This may be relcvant and in contradiction

46. The results of different studies with mousely~nphocyteshave been contradictory. In one experiment,
mice of the C57BlJ6 strain received a whole-body dose of
0.05 Gy from gamma rays, at the rate of 1.25 mGy min"13.

EFFECTS IN MOUSE CELLS
1. Splenic lymphocytes

ANNEX B: ADAPTIVE RESPONSES TO RADIATlON IN CELLS AND ORGANISMS

on four consecutive days [W9]. Groups of mice were
killed at intervals up to 26 days thereafter. Lymphocytes
isolated from the spleens of sham-irradiated arid irradiatednice were exposed in virro to W-radiation to induce
unscheduled DNA syntlicsis or to mitomycin-C to induce
sister chromatid exchanges. The results showcd a higher
rate of unscheduled DNA synthesis and lower sister
chromatid exchange frequencies ir, the irradiated mice thanin the sham-irradiated conlrols. Irradiation in vivo with low
doses of gamma rays was corlsistent with an inaease in
the rate of DNA repair, which is effective forapproximately 12days. The results support those publishedby Tuschl et al.
T3] arid Liu et al. [L9], whodemonstrated that it is possible to induce the adaptive
response in vivo.

m,

47. However, the adaptive response was not observed
when lymphocytes obtained fiom the spleens of female
mice of the Heiligenberger strain were exposed in vko.
either to O.Q5 Gy from x rays at 24 hours or 32 hours
after phytohaemaglutinin-stimulation, followed by achallenge dose of 2 Gy at 40 hours; or to 0.1 Gy at 32
hours or 42 hours with the challenge dose at 48 hours
p.5, W231. A reduction in the number of chromosome
aberrations as a result of exposure to conditioning doses
was seen in the lyniphocytes from o~lly1 of 14 micetested. Because of the high variability of the ndiationinduced break frequencies in the lymphocytes of thedifferent donors, the authors concluded that this one
positive result was due to chance and was not a genuine
adaptive response.
48. To determine if this lack of an adaptive response
was unique to the Heilignbcrgcr strain, spleen
lymphocytes were collcctcd froni C57B1/6 female mice inwhich, as discussed above, adaptive response to UVradiation-induced, u~ischeduled DNA synthesis andmitomycin-C-induced sister chromatid exchanges had been
observed P S I . A dose of 0.1 Gy from x rays was given
after 32 hours, followed by a challerge dose of 1.5 Gyafter 48 hours of culture Initial results indicated thepresence of an adaptive response in sorne of the CS7l3116
mice. However, subsequent analysis of the aberration
scores of parallel lymphocyte cultures revcaled a highintra-individual variability. The authors concludcd that theresults were a reflection of this variability nthcr than of
any induced adaptive response [W27].

49. Experiments have been reprtcd in which colonyfornling units (CFU-S) cells wcrc exln~sedto low doses ofradiation in the range 0.03-0.05 Gy [Sm, S321. The
adaptive resprtsc wiis obscrvcd from 4 hours until 28
days aner cach challcngc dose and was more pronounced
after high-dose-rate exposure. The response could be
potentiated by injecting Ihe niice with 5 0 p g ofpolynuclcotide Poly I-Poly C two days before thechallenge dose.

2.

193

Bone n i a m w c w k

50. Male Kunrning mice werc exposed to a whole-bodyconditioning dose of 0.1 Gy from x mys, followed 25-3
hours later by a challenge dose of 0.75 Gy fmrn x rays
[C8,LlO]. The combined exposure to the conditioning andchallenge doses resulted in a smaller nurnber of chromatidaberrations in bone marrow cells than in cells fromanimals receiving the challenge dose only. These results
aregiven in Table 14. The whole-body exposure of female
C57BV6 mice to a conditioning dose of 0.002-05 Gy
from x rays, followed by a challenge dose of 0.65 Gy
within 3 hours, also resultcd in an adaptive response at allconditioning doses (Table 14). A sirnilar adaptive response
was observed when the animals were exposed to these law
conditioning doses and then to a high dose of
mitomycin C (0.5-50 mg kg-') instead of the challengedose from x rays [Y2].
51. In a sequel to this experiment, mice were exposed
to a range of whole-body dases fromgammaradiation at a rate of 0.09 Gy niin-' and irradiated 3 hours
later with a challenge dose of 1 5 Gy horn x rays [J2].
SigniGcantly lower chroniosonle aberration frequencies
were observed in bone marrow cells aRer conditioning
doses of 0.05, 0.10 and 0.20 Gy, but not 0 5 0 Gy,
compared with animals receiving the challenge dose only.
The protracted whole-body exposure of male mice toganuna-ndiation at the rate of 0.014, 0.025, 0.06 or
0.23 Gy d-', followed by a challenge dose of 0.9 Gy fro111
x rays within 3 hours after protracted exposure had ceased,also resulted in adaptivc responses [Y2].
52. Using a different cnd-point, male white SHK mice
were given whole-body exposures to 13'C5 gammaradiation at the rate of 1.3 mGy h-' over periods up to 80
days and then exposed to a challenge dose of 1 Gy fromx rays within a few hours aftcr the protracted exposure
ceased [G2]. The frequency of micronuclei in polychromatic erythrocytes in chronically irradiated mice
exposed to the challenge dose was about one third of thatobserved in mice receiving the challenge dosc only. It wasalso shown that chronic exposure befort the challengedose resulted in a marked decrease in single-strand breaks
and an increase in DNA poly~neraseactivity in splenic andliver cells, consistent with the availability of a reservoir ofrepair enzymes during chronic irradiation.
53. In anotllcr experiment, 9-12-week-old male mice of
the Swiss albino strain wen. exposed in vivo togamma nys P I . The conditioning doses of cilhcr 0.025
or 0.05 Gy were given at a dosc ntc of 1.67 Gy min-l.
The cballengc dosc of 1 Gy was given at 2, 7 5 , 13, 1 8 5
or 24 hours after the conditioning doses. At a time intervalof 2 hours, both conditionulg doses reduccd thc frequencyof micronuclci in polychrolnatic erythrocytes and ofchroniosome abcrratio~tsin the bone rnannw cells. After
exposure to 0.025 Gy, tlic adaptive response remained for

UNSCEAR 1994 REPORT

194

24 hours. After exposure to 0.05 Gy, however, theadaptive response was not present when the challengedose was given 13 or more hours later.
54. These experiments indicate that the adaptive
rcsponse can be induced in bone marrow cells in somestrains of mice after acute or chronic exposure to low-LET
radiation in viva, provided that the challenge dose is given
within a few hours after the exposure to low doses hasceased. The results contrast, however, with those of
Jacobsen-Kram and Willianls [Jl], who were unable toelicit an adaptive response in the bone marrow cells frorn
their strain of mice irradiated in vivo. However, in thelatter experiments, the challenge dose was given 24 hours
after the conditioning dose, a time span possibly too longfor the DNA repair enzymes to remain effective in rapidly
dividing bone marrow cells.

55. Male Kunniing niice were exposed to a wholebody dose of 0.01 Gy from x rays, followed 2 5 - 3hours later with a challenge dose of 0.75 Gy fromx rays [Cg]. The nuniber of chromatid aberratio~lsin
the spermatocytes of conditioned mice was less thanin the sperniatocytes of niice receiving the challengedose only (Table 14).
56. In another experiment involving the whole-body
irradiation of male Kunniing mice, the adaptive
response was shown by reduced chromoso~iiedamage
and dominant lethal mutations [C17]. A conditionirlg
dose of 0.05-0.2 Gy resulted in a statisticallysignificant reduction (p < 0.01) of chromatid andisochro~natidbreaks in spcnn;~tocytesand in reciprocaltranslocatiorls in spernlatogonia, compared with cells
from animals receiving only the 1.5-2 Gy challengedose.
57. Cross-adaptation has been shown using x rays
and low concentrations of rnitornyci~lC, hydrogen
peroxide and cyclophosphamide as the conditioning
dose [M27]. Male Kunming mice were exposed to aconditioning dose of 0.05 Gy from x rays; 3 hours
later, 0.1-0.5 mg ml" of mitomycin C or 0.1-1 M ofhydrogen peroxide was injected intraperitoneally orhours later, thedirectly into the testis. Twe~~ty-four
mice were exposed to a challe~~gedose of 1.5 Gy fromx rays. The frequency of aberrations in primary
spermatocytes was markedly reduced with the use of
mitomycin C or hydrogen peroxide. In contrast,
cyclophosphaniide in the range 0.05-0.5 nig 1111.~acted
synergistically with the conditioning dose of x rays.
4.

Mammary careinonla cells

58. Exposing cultured mouse Inarnrnar carcinoma(SR-1) cells to a dose of 0.01 Gy from 'Co

gamma

rays, followed by a dose of 3 Gy from gamma rays
18-24 hours later, resulted in a decreased frequency of
induction of mutations at the hprt locus (Z5 Whencells were exposed to bleomycin (5-10 pg ml- ) for 1 2hours instead of 3 Gy from gamma rays, a similar
reduction in lnutageriic response was observed. Since
blconiycin acts to produce double-strand breaks, it waspresunied that the reduction in the frequency ofradiation-induced mutations was also attributable to
the repair of double-strand breaks.

I.

59. Mouse embryos of the Heiligenberger strain were
exposed to a conditioning dose of 0.05 Gy from x rays
at times correspondirig to the late G2/M phase of theSour-cell stage or the GI/S phase ofthe eight-cell stage
e~nbryos[M6, W5]. A challenge dose of 1.5 Gy fromx rays was applied 6 hours later, and cells werearrested in metaphase immediately thereafter. The
iriterval of 6 hours between the conditioning andchallenge doses was chosen because it was found tobe tlle appropriate tirne for the expression of theadaptive response in both human ly~iiphocytesand incultured Chinese hanister fibroblast cells [T5]. The
results of these experinients are summarized inTable 15. The yields of chromosomal break
Creqi~cnciesand the percentages of aberrant cells giveno indication of an adaptive response compared withcells receiving the challenge dose only.

60. It has been reported that rat mammary glandcells irradiated in vivo may have a higher repair
capacity than cells irradiated in virro, a phenomenon
called in siru repair [G4]. To examine the possible
influence of in sifrr repair on the adaptive response inemhryos. the conditioning dose was applied in vivo
arid the embryos were left in sit11 until shortly before
Uic challenge dose [W5 1. One group of embryos given
a conditio~iingdose of 0.05 Gy was irradiated in vivo
with 2 Gy from x rays at 50 hours after conception
arid isolated 4 hours later. Another group was isolated
at 48 hours after conception and irradiated with 2 Gy
fro111 x rays i~r virro at 50 hours after conception.
Colchicine was added at 55 hours and the metaphasesor the embryos io the 8-16-cell stage were harvested;it 62 hours after conception. The results of the in sit11
rcpair experiments, given in Table 15, indicate that insirrr repair was not associated with an adaptive
response. They suggest that the mouse embryos areeither in sitrr repair-deficient or that the optimal
conditions for the itiductio~iof an adaptive response
tlavc not been achieved.
61. Wojcik et al. [W5] pointed out that for an
adaptive response to occur in pre-iniplantation mouse
enibryos, they ~liustbe able to perform DNA repair.
Unsclleduled DNA syntllesis docs occur in both

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

pronuclei of the one-cell embryo as well as in cells of
the later developmental stages. Until the late two-cellstage, however, there is no gene expression in theembryo, and all proteins required are synthesized
constitutively from mRNA inherited from the oocyte
1531. A t the late two-cell stage, the embryonic genes
are switched on and much of the maternally inherited
mRNA is destroyed. There is, however, evidence that
despite the transcriptionally active genome, some
genes inducible in somatic cells do not respondinductively to the changing environment in e ~ i ~ b r y ofos
the preblastocyst stages. It is not clear whether
induced expression of repair genes in the embryo isnecessarily required for an adaptive response toradiation. However, the negative outcome of the above
experiment could be due to a general inability of the
preblastocyst ernbryo to adapt to changes in its
environment
6 2 T o investigate the points further, pre-implantationembryos were exposed to a conditioning dose of 0.030.1 Gy, with a challenge dose 6-24 hours later [M6].
Table 16 gives the results of an experiment in which
two-cell embryos were exposed to 0.05 Gy in the earlyG, phase and to 2 Gy when the embryos were in thelate G, phase of the same cycle. None of the endpoints-measured indicates a statistically significant
effect as a result of the conditioning dose.
63. It is recognized that up to the early two-cellstage, the absence of an adaptive response in early
embryonic development could depend on specific traitsof this system. Starting with the blastocyst, however,there is no reason why genes coding repair enzymes
should not respond to signals calling for additional
enzyme synthesis. A similar experiment to the one
described for the embryo in the two-cell stage wastherefore carried out using blastocysts in which theembryonic genome was active. No statisticallysignificant difference was seen between the effects
with and without the conditioning dose [M6].

195

exposure, but the authors pointed out that the different
conditions of exposure need to be examined before theabsence of an adaptive response can be conclusively
stated.

C. EFFECTS IN FIBROBIASTSIXOM VARIOUS SPECIES
1. Human embryonic and skin fibroblasts(a)Life-span and mutation fi-equency

66. The effect on the life-span of human embryo
gammafibroblast cells of chronic exposure toradiation delivered at a dose rate of about 0.001 Gy h" for10 hours per day has been investigated [S25]. The average
life-span, which was measured by the number of mean
population doublings, was 1.2-1.6 times longer in
irradiated than in unirradiated d l s . The number ofchromosomes in the unirradiated cells remained constantthroughout their life-span. Conversely. the irradiated cells
showed numerical abnomialities with increasing time.
These results indicated that the life-span of chronically
irradiated cells at low dose rates was prolonged, but thatthe cells showed chromosomal changes consistent withabnormal phenotypes.

67. In another study p 1 0 , W l l ] to determine the effecton the growth ability of human embryo fibroblast cells invkro, the expression of abnormal phenotypes wasmeasured after fractioriated low-dose gamma-radiation
Cells were assayed for cell su~vivalby their colonyCornling ability, for mutation at the tprt locus and fortransfom~ationby foci formation. After a dose of about
2 Gy had been accumulated, the mean population doublingtime was 1.3-1.6 times that of the con&ols. Althoughtransformed foci were not observed until the cells had
accumulated about 1 Gy, the numbers of cells withabnormal phenotypes increased thereafter with increasing
dose. No cells, howevcr, showed unlimited life-span invkro.
64. It niay be concluded that an adaptive response
cannot be induced in pre-implantation embryos, atleast with regard to the end-points measured, or thatthe conditions are entirely different from thosedetermined in other systems, in particular in human
lymphocytes.
65. The response of fetal tissue has also been
examined. Pregnant Sprague-Dawley-derived rats were
exposed to 0.02 Gy from 13'cs gamma-radiation at a
rate of 0.4 Gy min-I at various times on day 15 ofgestation, prior to receiving a challenge dose of
0.5 Gy. Fetuses were examined 6 hours and 24 hours
after the challenge dose for changes in the developing
cerebral cortex [H20]. There was no evidence of acellular adaptive response under these co~iditionsof

68. The mechanism responsible for the increased growthpotential of embryonic fibroblasts after fractionated lowdose gamma-radiation in vitro remains obscure. Although
the data suggest that some damage is repaired during these
exposures, it cannot be assumed that all of the damage
resulting in the transfonnation of cells is repaired. The
prolonged life-span may allow additional time for the
expression of an otherwise unexpressed lesion, perhaps
associated with the development of additional karyotypicchanges and aneuploidy. This proccss might be very rareamong human diploid fibroblasts grown in t~itro[K6, K7)
and might be specifically related to the imn~ortalizationof
human cells. The mechanism leading to the prolongationof their life-span remains to be shown, but calcium ion
may act as a signal transducer during e l l cycling PlO].

UNSCEAR 1994 REPORT196(b) Cell sumval and clone-forn~ingability
69. The hunian skin fibroblast cell line (AG1522) has
been used to determine Ule effects of low-dose gammaradiation, followed by a challcrye dose of x rays [MI.
Cell survival, colony growth rate and micronuclei
formation wcre measurcd to assess evidence of adaptive
response. Protracted exposure of plateau-phase cells to
gamma rays, delivered at a dose rate of 0.003 Gy mid1
over a period of 24 hours, reduced the effects of achallenge dose of 4.25 Gy fro111x rays given inunediately
after the chronic exposure. Figure Il shows that up to a
twofold improvement in cell survival and a twofold
reduction in micronuclei formation were observed.
compared with the results obtained when cells were
exposed to the challenge dose only. Furthermore, after 7
days: the size of colonies from cells surviving theconibined exposures was about four times as great as thesize of colonies horn cells given a challenge dose only.
70. The stiniulation of clonogenicity at doses below
0.4 Gy h n i gamma rays lias been observed in cultures ofhunian skin fibroblasts (strain GM 2185). The results,
illus~+ted
in Figure 111, are compatible with the hypothesisthat cells that do not I'onn clones in the absence ofradiation are stunulated to do so by low doses of radiation;that is, additional colony-fonniag cells are recruited fromformerly non-clonogenic cells. This enhanced
clonogenicity was not observed in fibroblasts (A-T strain
GM 2531) in which DNA repair was deficient, althoughtl~enumbers of non-clorogenic cells are siniilar to thoseobserved in Ule nonnal fibroblast strain. It can be implied
froni these results that cnl~anced clonogenicity isdependent on DNA repair competence, but othermechanisms could be i~lvolved[G5].

2. Chinese hamster cells(a)hlicronuclei fornli~tionfkquency

71. Proliferating Chinese hamster cells, cloned frorti the
V79-B310H cell linc, wcre cxposcd to beta- or gammaradiation 6orn tritiated thymidine or tritiated water,
followed by exposure to I ~y from *CO gamma rays [ij,17, Ill]. Ai adaptive response, expressed as a reduction in
micronuclei frequency, was observed. The adaptive
response was inhibited by 3-aminobe~uaniide(3AB) andwas not observed aftcr one cell division following the
cmnditioning dose. The opli~iialrangc of the conditioning
dose was estimated to be hctwecn 0.001 arid 0.1 Gy on
the basis of thc alnount of tritium hicorporated into DNA.
When tritiated thyniidinc \vi~sad~ni~listercd
at lower orhigher concentrations, a rcductio~~in niicronuclei induction
was not observed.
72. Acute exposure to 0.01 or 0.05 Gy from ganiniaradiation also induced all i~daptiveresponse to a challc~yedose of 1 Gy, but exposure to high-LET radiation did notThis dependency on the type of radiation might reflect thequality and quantity of chromosomal lesions that trigger
UIC adaptive response. The adaptive response did not fully
develop until 4 hours ancr Ulc challenge dose and was notobserved if the time intcrval between the conditioning dose
and the challenge dose wiis ex~cndedto 6 hours. The
adaptive response can be attributed to the induction of amechanism that repairs DNA daniage.

73. Chinese hamster V79 cells exposed to conditioning
doses (0.01-0.05 Gy) from ganima-radiation showed aossadaptation to challenge dmes of W-Bradiation (975195 J m-2) and mitomycin C (25-50% ml-') but not toethyl rilethane sulphonate (EMS) ( 1 0 0 ~or cisplatin (1 pg rnl-'), as evidenced by a reduction in thenumber of sister chrnmatid exchanges. This could imply
that the adaptive response observed after radiation could
be coupled to the repair network that copes with chromatinlesions induced by rnitomycb~C arid W - B [I7]. The
results observed after exposure to cis-platin were conhary
to those observed wl~enhun~anlymphocytes were exposedto this agent.
dml.')

74. The errects of sniall amounts of hydrogen peroxide
on tlic killing and mulation of Chinese hamster V79 cellsby different agents is sup~lortiveof an adaptive response
from daniage due to oxid;~tivefree radicals [Gll, S221. It
has been shown that low, I I O I I - ~ O X ~ concentrations
C(e.g.
0.9 ,ug ml-l) of hydrogen peroxide render W 9 cells moreresistant to subsequent killing by hydrogen peroxide (315 pg ml-l), gamma rays (1-6 Gy) and N-methyl-N'-nitroN-nitrosogu;~nidine (0.5-2.0 pg ml-'). However, such
pretreabnent with hydrogen peroxide increased theormutation yield by N-methyl-N'-nitro-N-nitrcsqyanidinc
garluna rays, suggesting error proneness of the induced
repair activity. Cyclohcxirnide or benzamide prevented theinductiori of repair, and they also suppressed the inaeasein mutation yield.
75. The treatment of Chinese hanister V79 cells or Ha
rat hepatonna cells wilh low concenwations of hydrogen
peroxide (1-5 $4) also resulted in an adaptive response,
exprcsscd as increased survival when the cells were
exposed to high dmes of hydrogen peroxide (0.1-15 mM)or to a challenge dose from garunia-radiation (up to 8 Gy)[L20]. This adaptivc rcslxmsc was observed in both
exponentially growing cells i111d plateau-phase cells, butthere was a reduced l~prtniuti~tionfrequency.

3.

blouse enll)ryo cells

76. C3HlOT!! platcau-phase niouse e~nbryocells wereconditio~~ed
wilt1 doses of 0.1, 0.65 or 1 5 Gy from * ~ ogamma rays at a rate of 0.0025 Gy mill-'. Three and a

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN C E U S AND ORGANISMS

half hours later they were exposed to a dose of 4 Gy h mgamma rays. The conditioning dose did not affed clonogenic survival, but it led to a reduction in micronucleus
frequency in binucleate cells and to a twofold reduction intransformation frequency per viable cell when cells were
subsequently exposed to 4 Gy fiom gamma rays. The datasuggest that a conditioning dose of low-LET radiationinduces an adaptive response in C3HlWA cells, resulting
in enhanced DNA double-strand break repair when thecells are exposed to the challenge dose. This enhanced
repair appears to be error-free, since the cells are lesssusceptible to radiation-induced neoplastic transfomlation~ 7 1 .

4.

Derived human epitlielial cell line

77. Adaptive response has been descnied it1 experiments
involving Hela cells [C21]. The cells were exposed to aconditioning dose of 0.03 Gy, followed by a challengedose of 2 or 3 Gy. A decrease in the number of induced
micronuclei occurred within 4 hours of the conditioning
dose and lasted for three cell cycles. If the conditioning
dose was increased to 0.4 Gy, the adaptive response
disappeared and the cells subsequently showed increased
radiosensitivity.

D. ADAPTIVE RESPONSE
TO CHEMICAL MUTAGENS
78.

An adaptive response in human keratinocytes
exposed to low doses of the mutagen N-methyl-N1-nitroN-nitrosoguanidinehas been described [Kg].Growing andconfluent human keratinocytes (Ha CaT cell line) were
exposed to different concentrations of N-methyl-N1-nitroN-nitrosoguanidine for one hour, and the number ofsingle-strand DNA breaks was determined by measuring
nucleoid sedimentation through neutral sucrose gradients.
Strand breaks cause the supercoiled DNA structure of thenucleoids to relax, leading to a reduction in thesedimentation rate. When the growing cells were treatedwith low doses of N-methyl-N'-nitro-N-nitrosoguanidine,
the nucleoids were found to sediment faster than in cells
in the confluent phase. Similar shifts have been reported
following mitogen activation of hu~nanlymphocytes [J4]and mouse splenic lymphocytes [MI. This effect was
attributed to the rejoining of DNA single-strand breaks
present in confluent cells.

79. The ADP-riiosylation system of chromatin responds
to radiation-induced damage by processing ADP-ribose
residues through a complex series of syl~thetic andcatabolic reactions. The key cornpollent of this multienzyme system is poly(ADP-ribose) polymerase, a zinccontaining protein that specilically binds to single- anddouble-stranded DNA breaks. Binding activates different
catalytic reactions that lead to the synthesis of polynlers
covalently bound to the polymerase [N3]. These polymers

197

then remove histones from the DNA, thereby allowing
access to other proteins, e.g. DNA helicase A andtopoisomerase I, to encourage DNA excision repair.
Inhibitors of poly(ADP-ribose) polymerase suppress theadaptive response in mammalian cells.

80. Further evaluation [B9],however: has shown thatdifferences in the nucleoid sedimentation rate might also
be explained by changes in the amount of RNA andproteins, which affect the sedimentation velocity of thenucleoids. To test this hypothesis, keratinocytes were
exposed to 0.005 ,uM of N-methyl-N1-nitro-Nnitrosoguanidine for 1 hour, followed by a challenge doseof 5 pM of N-methyl-Nf-nitro-N-nitrosoguanidine
6 hours
later. The results can be interpreted as reflecting fewer
DNA breaks in the pretreated cells than in cells exposedto the challenge dose only. The presence of 2 m M of
3-aminobenzamide blocked this response. Repau in thepresence of low doses of N-methyl-N1-nitro-Nnitrosoguanidi~~eis consistent with an adaptive response of
the cells to the mutagen. However, a synergistic rather
than an adaptive response was observed in human
lymphocytes pretreated with N-methyl-Nf-nitro-Nnitrosoguanidine, followed by a challenge treatment withmethyl methane sulphonate [W4].
81. Studies with hydrogen peroxide (0.1 pM
conditionin dose, 100 ph4 challenge dose) and bleomycin(0.1 ng ml-' conditionisg dose, 100 ng ml-' challengedose) are also consisterlt with the view that exposure to a
low dose of these mutagens results either in an overall
decrease in the number of single-strand breaks or changes
in the nucleoid cage of the DNA. They provide
complementary evidence of an adaptive DNA repair
process.

82. The adaptive r e s p o ~ ~hasc been demotlstrated inproliferating cultured lymphocytes and fibroblasts. In
addition lo a reduction in chromosome aberrations, theresponse has been measured as a reduction in the expected
number of sister chromatid exchanges, of induced
micronuclei and of specific locus mutations. An increased
survival rate and an increased proliferative capacity havebeen shown to be associated with increased mutation andtransformation hequency in some experinients.
83. Bone marrow cells and spematocytes from mice
exposed in vivo to low doses (0.01-0.2 Gy)fiom x rays a
few houn before challenge doses (0.75-2 Gy) to the cells
showed reductions in the number of chromosome aberrations compared to cells exposed to the challenge dosealone. No adaptive response was observed in pre-hiplantation mouse ernbryo cells, even though these embryoniccells were tested at a stage of development in which they
were considered to bc capable of synthesizing their own
DNA repair enzymes.

UNSCEAR 1994 REPORT198

There is evidence of cross-adaptation between sometoxic chemical agents arid low-LET radiation While it isreasonable to assume that some comnion repair pathways
exist depending on the category of damage (for example,
84.

damage caused directly by the ionizing events or indiredly
by induced hydroxyl radicals), the relation between random radiation-induced DNA damage and specific chernically induced DNA damage needs to be further resolved

11. MECHANISMS OF ADAPTIVE RESPONSE
85. Studies of cultures of lymphocytes, bone marrowcells, melanonu cells and fibroblasts have provided insight
into some aspeas of the mechanisms involved in theadaptive response. These include:

the effects of radiation on the upregulation of genes
and their influence on cell cycle kinetics;(b) the identification of activated genes and theirerlzyme products specifically involved in radiationinduced DNA repair;(c) the relationship between radiation-induced repair
genes and those activated by other mutagens;(d) the ability of ceUs to remove toxic radicals;(e) the activation of membrane receptors and the releaseof growth factors;(9 the effects of radiation on the proliferative responseto mitogens.
Other mechanisms may he involved, such as enhancedinln~unasurveillance,which is discussed in Chapter III.
(a)

A. CELL CYCLE CONTROL

86. Research into the mechanisms involved in cell
N1, N?, N5, SB].The
cycling is advancing rapidly [M23,division of a cell into a pair of genetically identicalprogeny depends on the precise timing of a sequence of
events. To divide successfully, the cell must havecompleted DNA replication and repaired any DNA
damage to the extent that allows the formation ofchromosomes and their correct segregation.
87. Control of cell cycling is influenced by feedback
mechanisms that can detect failure to complete the above
processes and arrest progress at various stages hi the cycle(e.g. progression from the G1 to the S phase and horn the
G2 to the M phase). Much of the basic knowledge of theniechanisms has been derived from studies with yeast cells
and sea urchin eggs. Elucidating the mechanisms in
mammalian cells is proving more complex than doing so
in primitive cells. It is clear that the understanding is as
yet incomplete, but there is sufEcient information to allow
speculating on the principles involved.
1. Protein synthesis

88. The key components in mammalian cell cycle
control are two classes of protein, the kinases and thecyclins, which are synthesized in a well-conserved
sequence. Cell-division-cycle(cdc) kinases are believed toact at several check-points, switching cell cycle
progression on and off principally by interacting withcyclins. Activation of the kinase-cyclin complexes requires
dephosphorylation of tyrosine phosphate, and w i b l y of
threonine phosphate, on the kinase molecule.
89. Passage from the Goto the GIphase is thought tobe triggered by low cell population density, cell size, thepresence of mitogens and the activation of protooncogenes. Progression in the GI phase seems to be
regulated by kuiases similar to, but not identical with, cdc2
kinase encoded by the p34 CdCZ gene
Cyclin Dl
accumulates during the GI phase and associates withmany cellular proteins, including cdk2, cdk4 and cdk5
kinases [M24, XI].

v].

90. The GI to S phase transition appears to involve thecomplexitg of cyclin E wilh cdk2 kinase and of cyclin D
with cdk4 kuiase. The cdc2-cyclin E complex may beparticularly important for the transition from the GI to the
S phase in human cells P O ] .
91. A gene encoding a cyclin-like protein has recently
been isolated from rat fibroblasts [T12]. It is referred to as
cyclin G.Cyclul G mRNA is induced within 3 hours ofgrowth stimulation, that is, during the transition from the
GI to the S phase, and its level remains elevated with noapparent cell cycle dependency, indicating its close
association with growth stimuli but not with the cell cycle.
The kinasc-cyclui G complex remains inactive until
dephosphorylation of the kinase occurs.

92. A cdc2 kuiase-cyclin A complex regulates S phaseprogression [G9,PI11. Essential accessory growth factors
during the S phase include platelet-derived growth factor(PDGF) and insulin-like grow& factor (IGF-1).
93. On passing through the G2 phase, proteins that
regulate the spindle assembly, chromosonle condensationand nuclear envelope breakdown are synthesized. If thespindle assembly is not completed, then the cell is arrested
in the M pk~se.A cdc2 kinase-cyclin B complex controls
the transition born the G," to the M phase [G9, Pll].
94. Cyclins A and B are rapidly dcgraded at the end ofmitosis. The process induces the synthesis of enzymes that
conjugate ubiquitin lo the cyclins and thereby targets themfor degradation by proteolytic enzymes. Degrading thecyclins negates the activity of the kinase-cyclin complexes,
and the cells proceed to interphase.

ANNEX B: ADAPTIVE RESPONSES M RADIATION IN CELLS AND ORGANlSMS

95. The effect of radiation on the levels of cyclin present
at different stages of the cell cycle has been studied. In
normal cell cycling of unirradiated cells, the levels of
cydin B protein inaease rapidly in d ~ G2
e and M phases
and decrease at the c~ld of mitosis. If the cells areirradiated in the G2 phase, cyclin B mRNA is readily
detectable, although at slightly lower levels than in theunirradiated controls. However, cyclin B protein ismarkedly decreased in amour14 as can be seen in
F i e IV, and this is associated with a delay in thecompletion of the G, phase, which is associated withdiminished levels of activated kinase-cyclin complex. This
Ending has been confiled in experiments with Chinese
hamster cells [L13].

2. Tumour suppressor genes%. As the role of tumour suppressor genes was
discussed in the UNSCEAR 1993 Report jUl]Annex E,
only the points relevant to their role in cell cycling arereferred to in this Annex. Current evidence indicates that
the Rb turnour suppressor gene protein plays multiple rolesin the control of the cell cycle, not only in regulating the
response to early mitogenic signals to the cell but also inmediating the transitional phases of the cycle itself. The
hndamental mechanism by which this is achieved is therepression of cell growth and division by the Rb bindingof regulatory nuclear proteins, such as E2F and Myc,
which drive proliferative rcspolscs. Mutational loss orinactivation of the Rb gcne in an appropriate target cell
may therefore be viewed as a principal means of relaxing
these controls.

97. The phosphoprotein product of the p53 tumour
suppressor gcne is also suspected of playing a role in cell
cycle regulation p 2 ] . It is thought to function as an
inhibitor of cell replication by delaying entry into the Sphase of the cell cycle througb influencing the assemblyof the late GI protein complexes that initiate DNA
replication. The inhibition of DNA synthesis is therefore
an active physiological process, and loss of the p53 gene
results in lass of this control.

98. Another possible mechanism of adion is that p53
protein, by virtue of its DNA-binding properties, may act
as a transcriptional betor uffluencing critical gene
expression controlling a cyclin-dependent protein kinase
inhibitor (CKI). This is a p21 protein that can bind to andAinhibit a wide variety of cyclin-dependent kinases
simple hypothesis for cell cycle progressio~~has been
proposed: cyclin-dcpenda~tprotei~~
kinases build up at the
GI phase and rhe G2/M trar~sitio~lowing to the presenceof cyclin-dependent protein kinase inhibitors. Surplus
cyclins then trigger the inactivation of cyclhl-dependent
protein kinase inhibitors, and the cell proceeds through thecycle. Inducible DNA damage may also cause the build-up
of cyclin-dependent protein kinase inhibitors, which may
be reversible or irreversible.

199

99. Proto-onmgenes, ongmally isolated as functional
genes supporting the pro life ratio^^ of tumour cells, e n d eproteins that are involved in normal cellular proliferation
Some of these proto-oncogenes are therefore mnccmed withcell cycling. They are invoked in signal bansdudion fiom
the cell surface to the nucleus, thercby integrating growthsignals so as to increase the biosynlhesis of DNA. These
oncoproteins include growth factors (e.g. c-sici encoding
platelet gowlh factor), membrane binding receptors (eg. cfms encoding macrophage-colony stimulating t?ctor
receptor), signal mediators by subsequent phosphoryl
reaction (eg. c-raf encoding protein, which can bephasphorylated during signal transduction), transcriptional
aczivatos (e.g. c-jicn and c-far encoding AP-1 transuiptional
activator protein) and replication-related proteins (cg. c-myc
encoding nuclear protein). Some oncoproteinspossess DNAbinding activity after phosphorylation.

100. As exanlplej, the transition h m the Gg to the GI
phase has been associated with the in&exprrsion ofc-fos, cjlm and c - ~ J C
and EGR-1 proboncogenes thatb e m e activated within minutes of a growth stimulus. Allof the products are d W y bound with DNA to activate
tmscription of the many genes necessary for entry into thegrowth cycle. The c-fos gene transiently expresses prior todifferentiation in a wide variety of premature blood cells.
After differentiation, several typcs of cell further express
different oncogenes, such as src [G7],c-sk [P5]and c-fms[S29], depending on the type of cell. Progression from the
GIto the S phase is thought to involve the upre~wlationof
the rus farnily genes.
GENE ACI'IVATION
101. The disruption of DNA structure is a amscquenoe of
exposure to many physical, chemical and biological toxins.
To a lesser degree, as d e s c n i earlier, it is also a consequence of the changes that can take place during normal
metabolism. It is not surprising, therefore, that cells have
evolved a complex system of defence against cirmrnstancesthat might irreversibly damage them A major role is playedby the activation of gcncs and gene products that initiate
DNA repair prooesses.

102 Evidence for the activation of genes associated withgrowth control and DNA repair came initially from studies

in prokaryotes. These studies provided an insight into themechanisms operating UI eukaryotic cells. For example,
genotoxic stress in the bacterium Escl~ericliiucoli induces
re-sponses in which regulator genes (reylons) participate.
These include the l~/rec4-mediatedSOS mponse p,
MI, P9, R1, SQ, W2, W241, h e adaptive response toalkylating agen& [Bl, K1, K2, K3, M2, 01,S4, SS, S6],
the myR-mediated hydrogen peroxide response, the sarRTmediated superoxide response, and the activation of heatshock protein (HSP) genes [Dl, D5,F18, GI,S7,W8,
w24, 241.

UNSCEAR 19194 REPORT

200103. The response of manunalian cells to mutagens,including radiation, is complex, but it is known that manyof the genes involved in nonilal cell cycling are activated.
These include genes responsible for growth stimulation,
growth control and differentiation [Rg]. Genes associatedwith growth control and activated by radiation exposure
were discussed in a recent review article p19). Siniilar
types of genes are activated by some alkylating agents andhydrogen peroxide.
1. Cell growth a m s t

104. An immediate reaction UI proliferating cells exposed
to a niutagen is delayed progression through cell division,and a number of genes have been identified that inhibit
cell cycle kinetics, among them the growth arrest andDNA-damage-inducible (DDI) genes PI. Delayed
progression tl~roughcell division is accon~paniedby anincrease in the rate of transcription of genes that encode
for the production of enzymes to repair the DNA damage
caused by the mutagen [Wl 1. The different types of repair
eruymes produced in response to different types ofgenotoxic stress are probably interrelated in the sense thatthey are the products of similar regulons [S3].
105. Cell cycle delay is a prixnary response to DNA
damage that represents active processes mediated bycertain genes, such as those involved in the expression of
the cyclins, p53 tumour suppressor gene, r s oncogenes,
and the g d (growth ~ e s andt QNA-d_aniage), gar(growth-zest-~pecific), spr (Small poline-gch), MyD(nlyeloid differentiation) and c/EBP growth arrest genes[F19]. Genotoxic stress has the punling effect ofconditioning genes associetcd with both growth stirnulatory
and inhibitory responses, but the main effect is inhibitory.
Many transcription factors and genes activated soon after
exposure to radiation are ;issodated with both responses.
Many of the genes involved in signal transduction havebeen implicated in both the initiation and progression
stages of carcinogenesis, and the same genes are oRen
induced by turnour promoters and DNA-damaging agents[C15, D5].
106. A summary of the DNA-damage-induced (DDI)
genes found by various invcstigators to be induced withina few hours of exposure is given in Table 17. The
complcx multi-gene reaction after irradiation makes it
difficult to characterize the molecular mechanisms of any
particular group of genes. However, most of the DDI
genes listed in Table17 are probably involved
immediately aRer DNA damage.
107. Expe~nentswith cultwed nonnal bone marrowprogenitor cells and with myeloblastic (ML-1) leukaenliccells have shown fiat the levels ofp53 tumour suppressor
gene protein transiently increase while the rate of DNA
syntllesis decreases after DNA damage, appare~~tly
occurring via a post-transcriptional mechanism [Ql].

Since cells with wild-type (wt) p53 genes exhibited
transient a m s t in both the GI and the % phases afterg;tmma-irradiation,while cells with absent or mutantp53
genes arrested only in the G2 phase, it was concluded that
wtp53 genes played a role in GI phase arrest
108. This observation was further supported byexperiments showing that the transfection of wtp53 genes
into malignant cells lacking endogenous p53 genes
partially restored the G I phase arrest after gammaimdiation and that overexpression of a transfected mutant
p53 gene in tumour cells with wild-type endogenous p53
gcnes abrogated the GI phase arrest after irradiation [K221
109. Because the tulnour cell lines used for thetransfection experiments had multiple genetic
abnomialities, the experunents were repeated in irradiated~ior~iialmurille embryonic fibroblasts in which the p53
genes had been disrupted by homologous recombination[K23]. Under these conditions, the loss of both p53 allelesin otherwise normal fibroblasts led to the loss of GIphase;I rrest.

110. Further studies showed that irradiated cells fromp;~tientssuffering fro111ataxia-telangiectasia were unable toinduce the gi1&5 gene. Finally it was shown that wildtype but not mutant p53 gene products bind strongly to aconserved elelnent in the gnddl5 gene. It was concluded
that in nonnal mammalian cells, p53 and gadd45 genes
participate UI a signal tralisduction pathway that controls
cell cycle arrest in the G I phase following DNA damage
arid that this check-point pathway is defective in ataxiatelangiectasia patients.
111. The effect of radiation on the expression of two
DNA-darnagc-induced genes, designated g d 4 5 andgnddl53, h;~s been examined in cultured human
lynlphoblasts p6]. Thesc genes had previously beenshown to be strongly induced by W-radiation andalkylaling agents in human and hanistcr cells. It was foundthat the gndd45 gene, but not the gaddl53 gene, was alsostrongly ulduccd by x rays. The level of g&5
mRNA
in~~eased
rapidly after x-ray exposure at doses as low as
2 Gy (Figure V). Alter 20 Gy, g&5
induction, as
rllcasured by illcreased amounts of mRNA, was similar tothat produced by the most effective dose of the alkylating
agent methyl methane sulphonate. No induction was seen
after treatment with 12-0-tetra-decanoylphorbol-lIacetate,a known activator of protein kinase C. Therefore, g d . 5
represents an x-ray-respo~lsivegene whose induction is not
rnediated by protein khlase C. However, induction was
blocked by ~ h cprotein kix~ase inhibitor H7, so thatir~ductioxiis likely to be mediated by some other kinase.

2.

Ibdiation-induced gene expxs.sion

112. The effccts on gene expression of low doses of lowand high-LET radiations have been studied in cultures of20 1

ANNEX B: ADAPTIVE RESPONSES TO RN)IATION IN CELLS AND ORGANISMS

Syrian hamster embryo (SHE) cells p 1 6 ] . These fibroblasts are normal diploid cells that can be transformed into
neoplastic cells by radiation Genes coding virus-like 30
S elements, c$m and $-protein kinase C have been shown
to be activated by exposure to x rays (0.75 Gy) or gamma
rays (0.9 Gy) but not by exposure to fission neutrons.
Further studies PI71 have revealed that the induction ofc-fos mRNA occurred within 3 hours of exposure, and aprotein-binding site has been identified that ~uediates
transcriptional response of the c f m gene to serum factors

WI113. Of particular interest was the response to radiationof members of the protein kinase C @KC) gene family,
which has been shown to play an unpornnt role in hmourpron~otionand in the regulation of cell growth. The resultsof these experiments showed that exposure to gamma rays
can induce increased expression of PKC mRNA within
1 hour of radiation exposure (Table 18). However, PKC
inhibitors prevented the expression of PKC in Chinese
hamster V79 cells pll]. Dose effects were evident, withinaeased accumulation of PKC I ~ R N Aat higher doses.
Levels of expression of PKC IIIRNA were increased
sixfold over uninadiated controls after exposure to0.75 Gy &om x rays (Figure VI).
114. The induction of PKC mRNA occurred at a time
when total cellular transcription was reduced following
inadiation. The activation of PKC directly stimulates
transcription of proto-oncogenes c$m and c-jlcn, which are
typical early immediate genes. Cellular levels of c-fos andc-jim mRNA also increase transiently afier irrddiation [I9,S48], and it has been reported that these oncogenes are
induced via the activation of PKC after irradiation [H12].
These results suggest that supplementation oC PKC afier
activation of the PKC gene is necessary for prolonged
expression of fosljltn genes, since depletion of PKC anddown-regulation of fosljun mRNA occur after theiractivation. On the other hand, several cytokine genes suchas interleukin &I$) and Nmour necrosis factor (TNF-a)
are found to be continuously expressed by irradiation
Fable 17). L I B is known as a radioprotector because thesurvival rate after a sublethal dose of radiation is increasedby the admu&&ation of L I B [N6]. Since there is apotential AP-1 (transcriptional activated protein, complexof fix and jlln protein) binding site at the 5'-upstream
region of these genes, it is considered that the genes arecontinuously stimulated by regulators containing the
produds of the eady immediate genes as a later response
against radiation damage at a whole-body level [W25].
However, transient expression of the L I B gene is also
observed together with transient expression of foslj~ltnearly
immediate genes within 1 hour of irradiation 1191. Thissuggests the activation of early protective mechanisms asa response to whole-body irradiation.
115. The effects of neutrons and gamma rays on theexpression of genes encoding the nucleus-associatedH4histone, c-jun, c-myc, Rb and p53 proteins have alsok e n reported w18]. Syrian hamster embryo cells wereinadiated at various doses and dose rates. After incubationof the cell cultures for 1hour following radiation
exposure, the induction of transcripts for c-jun and H 4
histone was shown to occur following gamma-ray
exposure Fable 19) but not foliowing neutron exposure.
The expression of p53 protein was unaffected by either
gamma-ray or neutron exposure. The increase in therelative amounts of Rb mRNA was marginal, and theexpression of c-myc mRNA was repressed following
exposure to gamma rays and was unaffecled following
exposure to neutrons.
116. These experiments provide support for the
hypothesis that radiation induces different cellularresponses to radiation-induced damage, be it DNA
damage, oxidative damage, protein denaturation or someother intracellular event Recent experiments implicatingoxidative damage as the inducing agent for c-fos, c-jun, cm y and other genes induced following DNA damage
would suggest that gamma-ray induction of' these genes
may involve oxidative damage as the modulating agent
117. The activation of oncogenes, including c-raf, c - m y ,v-src, Ki-ras, c-H-ras, v-H-ras, N-ras, v-k-ras and v-fms
genes, has been correlated with increased clonogenic
S45]. The
survival over the dose range 16 Gy
adaptive response appeared to be a s p d c consequenceof the ras gene mutation rather than transformation, since
revertant cells that contained functional ras genes retained
their clonogenic survival properties.

w,

118. The effect of oncogene expression on the sensitivity
to gamma-radiation of the haematopoietic (32DCl3) cellline has been measured P I ] . It was shown that thesehaen~atopoietic progerutor cells transfected with theoncogenes v-erbB, v-abl or v-src also showed increased
clonogenic survival when exposed at dose rates of
0.05 Gy min-' over the dose range 1-10 Gy. Exposure of
NlH3T3 fibroblast cells transfected with the oncogenes
v-abl, v-fms or H-ras also showed increased clonogenic
survival.
119. In a more recent experiment, rat embryo cells fromthe Fischer strain of rats and derived transfedants
containing the Ha-ras oncogenes were irradiated withgamma rays at dose rates between 0.018 and0.72 Gy mhi* [MI. The oncogene-containing cells
exhibited higher survival levels at all doses compared with
the non-transf-ed cells.
120. In contrast, the measurement of colony-forming
ability following exposure to gamma-radiation was madeon transformed human embryo retinoblast cell lines
containing mutant ras genes [GlO]. No correlation was
found between trdnsformation with activated r u ,adenovirus or SV40 genes arid increased radiation-

UNSCEAR 1994 REPORT

202

resistance. Nor was there any correlation between
donogenic survival and the level of expression of r a d l ,but two of the thee ras transformants that were leastsensitive to gamma radiation were h m cell lines
expressing the highest levels of ras21 polypeptide, whichplays a pivotal role in signal transduction and possibly
DNA repair. Notwithstanding the negative findings insome laboratories, it is generally accepted that radiationinduced oncogene activation can induce increased cell
survival in some circunlstances [W25].
121. A human XRCCl (x-ray repair crosscomplementing) gene has been isolated that affects thesensitivity of cells to radiation [C16, T131. The Chinese
hamster ovary cell mutant, EM9: exhibits extraordinarily
high sister chromatid exchanges and is unable toeffectively repair DNA breaks caused by radiation andcertain alkylating agents. Introduction of the human
XRCCl gene corrects the EM9 DNA-repair defect and is
the first human gene to be cloned that has an establishedrole in DNA strand-break repair. The gene is 33 kb inlength and encodes a 2 2 kb transcript and a corresponding
putative protein containing 633 amino acids. Constructs inwhich the open reading frame of the XRCCl gene weret r a n s c r i i from the SV40 promoter, or the genornic
promoter native to XRCCl gene, were compared withregard to their ability to correct the sister chromatid
exchange defed in the EM9 mutant These transfectants
displayed significantly fewer sister chromatid exchanges
than other transfectants. The results suggest thatoverexpression of the niinigene h m the SV40 promoter
may increase the repair capacity of EM9 mutant cells
relative to that of wild-type cells.

3. Induced protein products and DNA rrpair(a)Human melanoma cells

122. Induced gene products synthesized in response to
low doses of radiation in human melanoma (Ul-Me1
strain) cells and in a variety of other hunian normal
and cancer-prone cells have been identified using twodimensional gel electrophoresis [B12]. U1-Me1 cells
were chosen since they have a high capacity forpotentially lethal damage repair. Eight proteins were
induced by radiation, and two proteins were repressed.
They were not found after heat shock treatment or
exposure to UV-radiation or certain alkylating agents.
The expression of one protein tenned XIP269 (toindicate an &-ray-induced protein of approximately
269 kDa) at a dose of 0.05 Gy correlated very wellwith potentially lethal damage repair capacity. This
protein was found to be down-regulated by exposure
to caffeine or cyclohexirnide under conditions inwhich both potentially lethal darnage repair andsubsequent adaptive responses, expressed as cell
survival, were prevented [H3].

123. In addition to characterizing x-ray induced proteins,the levels of x-ray-inducible genes have been measured in
cDNA clones isolated by differential hybridizatioa Someof these genes were increased to over 20 times the
background levels by as little as 0.05-0.2 Gy;four havebeen identified as T-diphorase, tissue-type plasminogenactivator [B13, B14, H3], thymidine kinase and the protooncogene c-fislfes.
124. The first phase of potentially lethal damage repair
occurs very quickly (2-20 minutes), presumably toincrease the chances of survival of irradiated cells. It is
associated with a rapid resealing of single- and, at a laterstage, double-stranded DNA lesions that are either c~eatedinitially by x rays or produced as a result of the repair ofvarious types of base damage. The second slower phase of
potentially lethal damage repair proceeds over a period ofa few hours following irradiation, during which attempts
are made to repair the remaining double-stranded DNA
breaks. This second phase of repair closely corresponds to
the restructuring of gross chromosomal damage and canbe partially blocked in some human cells by inhibiting
protein synthesis p 3 ] . The rapid repair of potentiallylethal damage may be due to the immediate availability of
constitutively synthesized repair enzymes such as DNA
ligascs, topoisomerases or polyrnerases [BlS]. In contrast
it is proposed that the slow phase of potentially lethal
damage repair requires the induction on demand of
specific genes and gene products. These slow-phase,
potelltially lethal damage repair responses may be further
enhanced if the genes are stimulated with low doses ofradiation before a high challenge dose is given.

125. In a Curther experiment, coduence-arrested humannornial (GM2936B and GM2907A) and neoplastic(Ul-Mel, H e y 2 and -1.52)
cells were tested forevidence of adaptive survival recovery responses p26,
M9]. Cells were exposed to 0.05 Gy each day for fourdays at a rate of 1.13 Gy min'l and then challenged witha dose of x rays giving a 20% cell survival. Only H e p 2
and U1-Me1 cells pretreated with 0.05 Gy showed an
improvement in survival after 4 5 Gy, compared withuntreated cells. Two genes, XlP5 (human growthhom~one-related)and a gene transcript related to XIP12(human angiogenin-related), showed increased expression
over time ui these cells. Levels of cyclin A and, to a lesser
extent, cyclin B increased in the pretreated cells only after
the high challel~gedose and were not expressed duringexposure to the conditioning dose or in cells receiving
oidy the challenge dose. A slight increase in glutathione S
IransCerase mRNA was noted after the primary dose, but
p53 suppressor gene and 10lYIP genes were not activated.
126. Under the conditions of this experiment, U1-Me1
cells did not progress into the S phase as measured by theuptake of tritiated thymidine into DNA The indudion of
cycli11A under these co~~ditions
may thus indicate an
involvement of cyclin A in specifically stimulating DNA

ANNEX B: ADAPnVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

repair. Based upon these preliminary data, a model has
been proposed in which an adaptive response to low dosesof radiation may be achieved in mammalian cells w9].
Initially cells are assumed to be in the Go phase or atsome point in the GI phase. Upon repeated exposure to
low doses of radiation, for example 0.05 Gy, cells
progress to and pause at or near the GI phase or the
beginning of the S phase of the cell cycle. Gene transcriptsthat build up slowly in response to conditioning doses thenproduce proteins (e.g. cyclin A) that regulate or control thetranscripts that appear following a challenge dose. At thatpoint, cells are poised to stimulate various DNA repair
systems that are not inducible in the initial resting state.
127. In another experinlent, human melanonla (G361
strain) cells were exposed to gamma radiation [04].
Eleven induced proteins were extracted from cells withmolecular welghts between 43 and 98 kDa, while in P39
strain cells, 21 induced proteins were extracted after
exposing the cells to 3 Gy. Their molecular weights
ranged from 32 to 98 kDa, and four of these, withmolecular weights of 57, 58, 77 and 88 kDa, wereconsidered to be specific DNA repair enzymes. These
proteins are of a lower molecular weight than thoseisolated and characterized by Boothman et al. [B12].
@)

Human lymphocytes

128. Using twedimensional gel electrophoresis, a specificgroup of proteins was detected from human lymphocytes
exposed to a conditioning dose of 0.01 Gy fiom x rays
p 6 , W8]. Cellular extracts from u~lirradiatedlymphocytes
and from other cell types were separated by electrophoresis and then exposed to a mixture of 32~-labelled
nick-translated and non-radioactive plasmid pCHllO on
nitrocellulose membranes. Several bands that bind to thenick-translated DNA were detected, the protein binding
occurring as early as 1hour after irradiation and reachingits maximum by 6 hours. This binding was diminished bya prior proteinase K treatment of the extracts, indicatingthat the bands are related to proteins present in theextracts. The cellular extracts contained three proteins (ofmolecular weights 105 kDa, 35 kDa and 1 4 1 8 kDa) that
reproducibly bound to the labelled DNA. The binding of
the DNA probe to the 30-35 kDa and 1418 kDa bands
was twice as great as that found in uriirradiated cells, andthe 35 kDa band regularly separated into two bands.
129. The 30-35 kDa band proteins have been substantiallypurified by affinity chromatography. If enough of theproteins can be obtained, it should be possible to see if
their introduction into cells will lead to a reduction in theyield of chromosomal aberrations induced by a dose of
15 Gy fiom x rays, even though the cells are not preexposed to the conditioning dose of 0.01 Gy. An
alternative approach could be to introduce engineered
genes into cells and look for the adaptive response. It is
likely that the binding proteins are single-chain molecules

203

and that the binding site does not require a conformation
dictated by internal disulfides; and it is unlikely that the1418 kDa band protein is a subunit of the larger 34 kDaband protein. Further studies should confirm this.
130. The existence of a specific DNA-binding protein in
the nuclei of human lyrnphoblast cells exposed toradiation, which was not deteaed in nudear extracts fromunperturbed cells, has been reported [S33]. The effects ofthis binding protein were shown to be dose-dependent andtransient, reaching a maximum 1hour after irradiation anddisappearing fiom the nuclei by 9 hours. The protein was
induced in cells by a mechanism not requiring de w oprotein synthesis, and the response was specific forradiation and radiomimetic agents; neither W-radiation
nor heat shock invoked a response. The DNA-binding
protein was present in the cytoplasm of unirradiated cells,
apparently being translocated to the nucleus only afterradiation exposure. Analysis demonstrated that the nuclear
and cytoplasmic proteins were approximately the same
size, that is, 43 kDa.
131. Siniilar experiments with irradiated lymphocytes
from humans, mice and rabbits have been reported P I .
Human lymphocytes in vifro and mice in vivo wereinadiated with 200kV xrays at a rate of
0.0125 Gy min-'. Rabbits were exposed in vivo togamma-radiation at a dose rate of 0.0056 Gy h-' for 9hours, resulting in an accumulated dose of 0.05 Gy.
Extracts of cells or separated cytosolic and nuclear
fractions were subjected to two-dimensional
electrophoresis. Four protein spots not present in theunirradiated cells appeared in the extracts of humanly~nphocytes4 hours after in vuro exposure to 0.05 Gy,
with molecular weights of 25, 167, 168 and 174 kDa.
Nine spots were detected in the cytsolic extract frommouse lymphocytes 4 hours after in vivo exposure to0.075 Gy with molecular weights of 51, 69-70, 145 and160-179 kDa, and four spots were found in the nuclear
extract with ~nolecular weyhts of 70, 90, 230 and
247 kDa. F i e spots were detected in the extract fromrabbit lymphocytes with molecular weights of 105, 135,
138, 145 and 174 kDa. When compared to the protein
spots identified after exposure of cells to mitomycin C andheat (41°C), it was found that the proteins induced bythese treatments showed many aspects in common,
although there were some differences in theirelectrophoretic mobility.
132. Crude extracts of splenic lymphocytes frominadiated and sham-inadiated mice were subjected to gel
filtration with sephadex G-100 and aliquots tested forbiological activity. Both stirnulatory and suppressive
effects were noted when separate fractions were added tothenormal splenocytes exposed to concanavalinstirnulatory effect of one protein fraction being moremarked in the eluted Gaction from the irradiated mice.
These various proteins were found to have molecularUNSCEAR 1994 REPORT

204

we~ghts below 100kDa. When the fiaction withstirnulatory effeds was added ui 10 ng amounts tolymphocyte cultures, it was found that the addition 42
hours after phytohaemagglutini~istiniulation reduced thefrequency of chromatid and isochromatid breaks produced
by a dose of 15 Gy from x rays to a magnitude similar tothat observed when a conditioning dose of 0.05 Gy fromx rays was given 42 hours after phytohaeniagdutinin
stimulation.

4. Stress-response proteins133. There are several examples of genotoxic stresses
influencing the expression of proto-oncogenes and theirproducts. Temporary hypoxia or glucose deprivation, forexample, induces the expression of several proteins. The
increased expression of intracellular proteins termed"oxygen regulated proteins" in Chinese hamster ovary cells
has been descnied w19].
Thcse proteins are different
from the heat shock proteins, but two with molecularweights of 80 kDa and 100 kDa appear to be identical totwo proteins that are induced by glucose deficiency [S31].
134. Haemoxygcnase is a protein associated with oxidative stress. Increased levels of this 33 kDa proteintranscript have been obse~vedin human s k h ~fibroblasts
and can be induced by treatment with W-A-radiation,hydrogen peroxide arid sodiurn arsenite [Kg],heat shock[S8]and temporary hypoxia.
135. Changes in expression of protein kinase C canfollow exposure to physical or chemical agents. Protein
kinase C is often upregulated in proliferative cells
compared with quiescent cells in these circumstances.
Moreover, the intracellular distribution of protein kinase Cin cells is also affected [MI. Consistent with this, lowdoses of W-A-radiation have been shown to inmase
protein kinase C activity hi cultured nianlnialian fibroblasts
and also to inhibit EGF-binding WlO].
136. While some degree of homology between the effectsof various stresses has been reported, there are clear
differences.The expression of the c-fos and c-jltn genes,
both involved in the regulatory mechanisms of cell
progression, arc increased by heat shock [I3161 andradiation p 1 6 ] . However, hypoxia followed by reoxygenation has been shown to elevate only c-fos mRNA.
Radiation causes upregulation of the g a M 5 gene, whileboth UV-radiation and alkylating agents upregulatemRNA for gndd45 and gndd1.53. Upregulation of the
ppolymerase gene is an example of chemical agents thatcause DNA damage affecting transcription, whereas
x-radiation and W, both potent agents for DNA damage.
have no effect F6].
137. The possibility that low doses of radiation induce anadaptive increase in the antioxidant defence mechanism
has also been considered [N2]. The expression of stressproteins was given special attention, in view of the Endingtl~at these proteins are present in nionocytes whose
antioxidant activities have been elevated [C9,P7j. A
sunilar response has been obse~vedin mitogen-stimulated
lymphocytes p,H4]. Male C57B1/6 mice, six weeks ofage, were exposed to a dose rate of 0.04 Gy d-' fromx rays on five consecutive days each week for four weeks
w19]. Three days after the last exposure, their spleens
were assessed for the constitutive arid mitogen-stimulated
levels of heat shock protein (HSP) 70 mRNA and protein.
Glyceraldehyde->phosphate dehydrogenase (GAPD), a
housekeeping gene, was used as a reference. The results
indicate that low doses augment the constitutive levels of
HSP70 niRNA and HSP70 protein (Table 20). Thus, theniag~litudeof the proliferative response of sple~iocytesto
T-cell niitogen stimulation can be directly related to theconstitutive and niitogcn-stiniulatcd levels of HSP7O
niRNA and protein. These results are consistent with theview that splenocytes need to accu~nulatesonie minimal
constitutive level of HSP70 protein before they canundergo an augmented proliferative response to mitogenicstin~ulatiori and that T cells adapt to low doses byaugmenting their HSP7O gene expression
138. It was shown subsequently that the chronic
irradiation of mice increases the expression of HSWO
genes in tissues Mll]. n ~ micee were irradiated at a dose
rate of 0.03 Gy d-l, and the levels of HSP70 genes wereanalysed. Increased but transient expression of HSP70 inlung, spleen and intestinal cells was observed,
commenci~~gon day 5 of irradiation. In an.extension ofthis expcriment, the effect of dose rate was examined. The
data indicated Ulat chronic irradiation within the range
0.03-0.06 Gy d-' can activate the transcription of HSP70
genes and their respective protein products. Ln this respect,
the results were consistent with those of Nogami et al.
[N4], who observed the induction of HSP70 protein in
resting splenic T cells aRcr chronic irradiation at a dose
rate of 0.04 Gy d'l, but not at rates above 0.1 Gy d-' witha total dose not exceeding 0.2 Gy. However, increases in
HSP70 protein were not seen in Chinese hamster ovary
cells [A141 unless the dose was in the region of 400 Gy[S41.
139. In support of a coninion niechankm, the effects ofviral arid activated cellular orlcogenes on the sensitivity of
Syrian hamster (Osaka-Kanazawa) cells exposed to
gamma-radiation, W-radiation and heat shock haverecently been described [S41]. Greater tolerance toganinia-radiation was co~lrerred by the introduction ofv-rt~osand c-cot genes, which encode for serinehhreonine
kinase. Cells transfected with v-mos and c-cot genes werealso rnore tolerant to W-radiation and heat shock. Of theactivated ras genes, the N-ras gene developed a 1x11
phc~iotyperesistant to W-radiation and gamma-radiation.
The Ha-ras gene produced a cell type resistant to Wndiation alld heat shock, while introduction of the Ki-rus
gene did not affect sensitivity. The v-erb B gene wasANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANLSMS

found to be involved in the developnlent of resistance toheat shock. Transfection with wo, c-myc and v-fgr genes
had little or no effect on survival. The karyotypes of theoriginal cell type and the oncogene-containing cells werecompared, and no alterations were seen in the cells
carrying the foreign genes. These results suggest that
activation of serine/thre,onine kinase may be involved incommon processes occuuing after gamma-radiation, Wradiation and heat shock treatment, and that each oncogene
may have a difierent effect on the development of a
resistant phenotype. However, cDNA clones for a varietyof DNA-damage-inducible (DDI) transcripts have been
isolated that may represent more specific responses to
DNA damage r17].

1. Radical detoxification

140. In addition to cell cycle arrest and induced genes
and gene products to initiate DNA repair, an alternative
mechanism has been proposed to explain the adaptive
response [F8, F9, Fl0, F11, F12, F13, F14, F15, F16,
M12, Zl]. It relates to the ability of cells to remove toxic
radicals. Radicals are known to be generated in small
amounts and detoxified during normal metabolism. The
process of detox5cation involves the mobilization of
enzymes, such as catalase, peroxidase, superoxide
dismutase, from the cytosol [S34]. Membrane-boundvitamin E is thought to scavenge the radicals as they areformed; the latter are then detoxified by the cytosolic
enzymes. The purpose of this radical detoxification systenl
is to maintain the structural and fu~ictio~~al
integrity of thecell by preventing damage to cellular co~~stitue~lts
such asmembrane-bound DNA [S35].
141. Evidence in support of this hypothesis is based on
the results of a series of experiments in which rnale Witar
rats were exposed to x rays within the dose range 0.050.5 Gy. Levels of superoxide dkmutase were found to be
increased in spleen, thymus and bone marrow 4 hours
later, while lipid peroxides were decreased [Y4].
1 4 2 It has been reported that the concratration of scru111
thymidine ku~ase increases after acute exposure toradiation [H5]. This was associated with a decrease irl theconrentration of the enzyme in bone marrow cells and adelay in the incorporation of the radioactive thymidine
analogue, 5-iodo-3deoxyuridine (l2'1IJdr), ir~toDNA in
these cells. The function of thymidine kinase is to prepare
cxtracelluiar thymidine for its u~corporation into DNA.
Measuring charges in thymidine kinase activity has proved
to be a conve~lie~lt
probe for studying changes in radical
detoxification.
143. In one procedure of this kind, Sernale (NMRI strain)
mice received whole-body 1 3 7 ~gamma-irradiation,
s
and

205

Uie relative activity of thymidine kinase was measured inbone marrow cells after one or two exposures, each of
0.01 Gy. A dose of 0.01 Gy produced a reduction in
enzyme activity that reached a minimum about 4 hours
after the irradiation, with full recovery after 6-8 hours. If
a second exposure to 0.01 Gy was given within 30
minutes of the first exposure, the decrease in enzyme
activity was accelerated, as was the rate of recovery. If a
second exposure to 0.01 Gy was given 4 hours after the
first, there was no change in enzyme activity, and asecond exposure 12 hours after the first resulted in a
reduction of enzyme activity sinlilar to that observed after
a single dose of 0.01 Gy PI.
144. These reductions in thymidine kinase activity closely
followed the decreased rate of uptake of lE1IJdr into bonemarrow DNA, and there was a simultaneous increase in
the radical scavenger glutathione. These responses wereabsent in cells exposed to a strong magnetic field, whichtransier~tlyalters lipid membrane structure. A deficiency ofvitamin E. which is known to be a radical scavenger, also
prevented the response.
145. The effect of low-dose radiation on 1251Udr incorporation has also been measured in mouse intestines,
spleen and thymus w2.01.Young female BALBlc mice
were imdiatcd within the range 0.05-0.23 Gy with x rays
at a dose rate of 0.05-0.2 Gy min-', followed at various
times thereafter by an injection of lSmdr. The incorporation of ' % J d r was decreased for several hours after asingle exposure to x-radiation in a dosedependent mannerin spleen and thymus. At 4 hours a k r i~~adiation,forexample, the decrease relative to controls was 79% in
spleen and 86% in thymus. If the first irradiatio~lwas
followed 4 hours later by a second irradiation (0.05 Gy or
0.1 Gy, for example) the second irradiation did notenhance the inhibitory effect of the first exposure, thus
confirming the observations of Feinendegen et al. PI.

146. To put these studies into pcrspcctive, it has been
calculated that a radiation dose sutlicient to create an
average of one ionizing track per cell would produce
enough radicals to delay the rate of DNA synthesis inmetabolically active cells [F9]. This time delay was
sufficient to ellsure the availability of radical scavengers tocope with radicals produced by a second dose of radiationa few hours later.
147. Other calculations reveal that 0.01 Gy of low-

LET radiation could produce about 6 nM of oxidative
radicals in each cell [KlO]. This concentration should
be con~paredwith the cellular steady-state concentration of radicals from nornlal metabolic processes
involvi~lgoxygen, which is about 1 nM . Therefore, it
has to be assumed that a snlall transient increase inradical cco~lcenlrationabove that normally present in
the cell is able to cause a measurable activation of
11arrna1detoxification mechanisms.

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMSA.

CELLS OF THE IMMUNE SYSTEM

156. T cells are lymphocytes that develop in thethymus. They are primarily responsible for ensuringcellular immunity and delayed hypersensitivity
response. They mediate their acquired immune
responses first by activation of specific T cells, thenby a phase of clonal expansion and finally by a phasein which some of the lynlphocytes become effector
cells.

157. There are at least three functionally distinct
classes of T cells:
(a)
@)

(c)

cytotoxic T cells, which kill virus-infected cells
and tumour cells directly;
helper T cells (TH),which amplify responses bysecreting a variety of local chemical mediators(interieukins) that stimulate activated T cells to
proliferate, help B cells to make antibodies, andactivate macrophages;
suppressor T cells (Ts), which inhibit the
responses of helper T cells.

Helper and suppressor T cells are the principal
regulators of immune responses, and the ratio between
the two cell subsets is an important factor in ensuring
immunocompetence in the living organism.

1. T-cell ontogeny

158. Most T cells bear an antigen receptor consistingof a heterodimer of transmembrane a and $polypeptide chains. Both chains are required for
antigen recognition [D3]. These polypeptide molecules
resemble antibodies in structure and interact with
antigens that are presented to T cells as proteolytic
digestion fragments associated with Class I and ClassII major histocompatibility complex proteins on thesurface of antigen-presenting cells. The specificbinding of antigen histocompatibility complexes on thesurface of a target cell to antigen receptors on thesurface of the T cell is often not strong enough tomediate a hnctional interaction between the two cells.
Various cell-cell adhesion glycoproteins on T cells
help to stabilize such interactions by increasing theoverall strength of cell-cell binding. The characteristicsof these accessory glycoproteins are su~ntnarizedin
Table 21. Among the best characterized are the CD4
and CD8 glycoproteins, which are expressed on thesurface of helper and cytotoxic T cells, respectively.
159. The T-cell receptor is also associated with agroup of glycoproteins, collectively referred to as theCD3 complex, which is involved in receptor assembly[ClO]. The T-cell receptor CD3-a/$ heterodimer isexpressed on the surface of the vast majority ofmature CD4+ or CD8' cells in peripheral human blood

207

lymphocytes and lymphoid organs [A5, H6, M141.
(The presence or absence of accessory proteins on
T cells is designated by the superscripts + and -,e-g.
CD4+CD8-). A second group of glycoproteins consisting of y and 8 chains is also CD3-associated and isfound mainly in the double-negative (CD4-CD8')
T-cell population [B17]. According to current understanding, CD4-CD8 T cells are thought to be theprecursors of thymocytes, which differentiate into
CD~+CDT~ +cells, which in turn differentiate into
CD4+CD8or CD4dD8' T cells [S36]. These last twocell types become the antigen-positive mature T cells.
160. Spontaneous loss and alteration in antigen
receptor expression in mature human CD4+ T cells
obtained from healthy donors have been described[Kll]. The T-cell receptor CD3 complex plays acentral role in antigen recognition and activation ofnlature cells, so abnormalities in the expression of thiscol~lplexshould be related to the unresponsiveness ofT cells to antigen stimulus. Using flow cytometry,variant T cells with loss or alteration of T-cell receptor
CD3 expression among CD4' cells were detected andenumerated. Variance was demonstrated by defects inprotein expression and partial protein deletion. The
variant frequency in peripheral blood increased withage in normal donors and was highly elevated inpatients with ataxia telangiectasia. Thus, alterations inantigen-receptor expression may be induced by the
spontaneous somatic mutation of T-cell receptor genes,
and these alterations could be important factors related
to age-dependent, disease-associated T-cell dysfunction
and radiation-induced T-cell damage.
161. Over the past decade, knowledge of T-cell
renewal, differentiation and maturation in the mousehas been remarkably advanced by the development
and use of specific monoclonal antibodies that identify
T cells at the various stages of differentiation. Itshould be noted that a different terminology for
identifying glycoproteins is sometimes used in themouse. Thus, CD4' equates with U T 4 + , and CD8'equates with lyt2+. It is now generally agreed that asmall progenitor cell compartment exists in the thymusthat expresses neither L3T4 nor lyt2 surface antigens(i.e. it is double-negative). The progeny of these
cycling cells beconle the major cell population in thethymus and express both L3T4 and lyt2 antigens(double-positive). At present, there is insufficientevidence to determine whether the mature thymocytes,
which express either L3T4 or lyt2, differentiate froma subset of double-positive cells or whether they
derive directly from the double-negative cells. In either
case, the nirijority of double-positive cells are notselected because of inappropriate major histocompatibility complex reactivity. The single-positive
functional effector cells are exported to peripheral
lyn~phoidtissue, where, in contrast to their behaviour

208

UNSCEAIZ 1994 REI'ORT

in the thymus, they become the predominant cell
populations. A model for the various stages in T-cell
ontogeny, as defined by L3T4 and lyt2 antigen
expression, is schematically presented in Figure VIII.

2.

Apoptosis a n d radiation-induced
interphase death162. The mechanism responsible for producing T cells
is unusual in that the vast majority of differentiating
cells are destroyed prior to their complete
differentiation and release to the peripheral lymphoidtissues. This phenomenon, known as apoptosis, occurs
within the thymus and results in the death of most of
the developing thymocytes. The process is thought toensure that differentiating cells with potential forreacting against the host are eliminated, thereby
preventing an auto-inlmune response, and it essentiallyinvolves double-positive T cells. One feature of
apoptosis is then an alteration in the differentiati011
rate of developing T cells in the thymus [LlS].
163. Some types of lymphocytes die soon after
exposure to radiation and before entering the mitotic
phase of the cell cycle. The process is referred to asinterphase cell death. T o deterrtline any similarity
between apoptotic death and radiation-induced
interphase death, thymocytes were collected from male
C57B116 mice between five and six weeks old,
separated into CD4'CD8-, CD4+CD8+,CD4+CD8- andCD4CD8' T-cell subsets and exposed to gammaradiation w 1 9 ] . They were assayed 8 hours later for
evidence of cell death by measuring the amount ofDNA fragmentation. The results given in Table 22show that double-positive CD4+CDgt T cells are
extremely sensitive to radiation. With a 50%
fragnlentation index (J?DSO) at 0.22 Gy, it would
appear that a small but significant fraction of the
double-positive T cells die as a result of apoptosis
following exposure to low doses of radiation. Since
the double-positive T cells constitute the majority ofthe parenchymal cells in the thymus in an intermediatestage of differentiation, elimination of a fraction ofthem could conceivably alter the dynamic balance
between cells in different stages of differentiation.

sharp increase in mRNA polymerase I1 was observed.
This was followed within 2 hours by an increase in
intracellular calcium ion concentration and theappearance of newly synthesized polypeptides. In
particular, there was a sharp increase in thephosphorylation of three proteins with molecularweights of 20, 35 and 48 kDa [Z3].Different stressrelated proteins of molecular weights of 48, 70 and
90 kDa were also detected after heat shock or after the
addition of glucocorticoids to the culture medium[M16].

3.

Signalling processes in thymocytes

166. Some consensus has emerged regarding thenature of the signalling process that couples antigen
recognition to changes in lymphocyte behaviour. It is
postulated that the activation of T cells requires two
signals, one through the CD3 conlplex, the other fromantigen-presenting cells. Antigenic, allogenic,
niitogenic or n~onoclonalantibody stimulation of the
T-cell antigen receptor (TCRICD3 complex) leads toa series of biochemical processes, including theactivation of phospholipase C, with subsequenthydrolysis of phosphatidyl inositol-4,5-diphosphateto
generate two second messengers, inositol-1,4,5triphosphate (IP3) and diacylglycerol @G) p 7 , 112,
J5, T141. These two messengers cause an increase in
intracellular calcium ion concentration (Cat+) and theactivation of protein kinase, respectively. The two
events are considered essential in the expression of the"early immediaten gene, c-fos, to be followed later by
the exlxession of c-myc, gamma interferon,interleukins 1 and 2 (IL-1 and IL-2) and transferrin
receptor, which are crucial in the activation andproliferation of T cells [K26]. Activated T cells
secrete interleukin-2, which results in division in thosecells expressing interleukin-2 receptors. The T cells
produce a series of lymphokines that clonally expand
activated B cells and cause their maturation into
antibody-synthesizing cells [S37, W22]. Signals
derived from the T-cell receptor could also regulate
the maturation arid selection of immature T-cellprogenitors in the thymus [V5].

167. The kinases responsible for protein synthesis
have not yet been fully identified, but it is known that164. On this basis, interl)hase cell death caused by
T cells contain transcripts encoded by at least threeradiation may be considered similar to, if not identicalnlembers of the src family of protein-tyrosine kinase
with. apoptosis [D4,W20, W211. The elimination ofgenes: namely Ick, fjln and yes [Cl 1, S381. The p561ck
cells damaged by radiation ensures that the c l o ~ ~ a l protein was first identified by virtue of its overexpansion of renegade T cells is prevented.
expression in a murine lymphoma cell line. It is the
product of the Ick proto-oncogene, which is closely
165. A biochemical rllechanism responsible forrelated to the c-src gene, and hence is a potential
radiation-induced interphase cell death in lymphocytes
signal transduction element [P8]. Two pieces of
has recently been proposed [Z2]. Within tens ofevidence suggest the type of signalling event that may
minutes after exposing rat thymocytes to radiation, abe ~nediatedby p56Ick. First, expression of lck mRNA

ANNEX B: ADAP'llVE RESPONSES TO RADIA710N IN CELLS AND ORGANISMS

and of p561ck is altered by stimuli that induce
lym hokine release from T cells w 1 5 ] . Secondly,
p56PFkis associated with CD4 and CD8 glycoproteins[V6]. When p56bk is brought into proximity with the
T-cell antigen recognition unit by CD4 or CD8
glycoproteins, its activity may increase to reflect
receptor occupancy.
168. A second membrane-associated protein tyrosine
kinase, p59fyn, the product of the fin proto-oncogene,is also abundant in T cells [Cll]. Using transgenic
mice in which a lymphocyte-specific protein-tyrosine
kinase isoform, p59fyn0,was 20-fold overexpressedin developing T-lineage cells, it was found thatthymocytes from thcse animals were highly sensitive
to stimulation [C12]. Furthermore, the phenotypes
produced by overexpression of p59fyn were different
from those produced by overexpression of p561yk.
Although p59'yn may regulate early steps in the T-cell
receptor signalling, it cannot by itself confer a mature,
responsive phenotype upon otherwise refractory.
immature thymocytes. Thus, CD4+CD8+ thy~nocytes
from lyk-fyn transgenic mice exhibit enhanced calcium
ion accumulation following activation, but they do notrelease interleukin-2 or proceed to proliferate. Hence,components of the signalling cascade that are essential
for activation are apparently ul~availableor inactive in
immature thymocytes in these transgenic mice.

B. RESPONSE IN THE ORGANISM
169. The cell types involved in the immune response
exhibit a broad spectrum of radiosensitivity withconsequent effects in the organism [A6]. Some
populations of lylnphocytes are exceedingly
radiosensitive, while plasma cells and niacrophages
are, by comparison, relatively radioresistant. The basisof these differences in radiosensitivity is not wellunderstood, but the effects of radiation on the i~nrnurie
system have been extensively studied. Several reviews
have been published that provide coniprehensive
background information [A6, A7, A8, S39, T61.

1. Effects in animals
170. Irradiation at high doses is kllown to inhibit theimmune response. A dose-response relationship wasobserved almost three decades ago by Kennedy et al.
[K12]. They exposed mice to x rays within the dose
range 0.5-7 Gy and 10 days later injected the animals
with antigenic sheep red blood cells. Four days after
injection of the antigen, they measured the number of
splenic plaque-forming cells. The effect of exposure to
between 1 and 3 Gy from x rays was to reduce thenumber of splenic plaque-forming cells to about 30%
and 1%,
respectively, conlpared with the nunlbers of

209

plaque-forming cells observed in sham-irradiatedani~nals.The results are illustrated in Figure IX.
171. More recently, the immediate and long-tenn
effects of radiation on the immune response of
specific-pathogen-free mice were described after
exposing mice to a dose of 3 or 6 Gy horn x rays andlneasuririg the surviving fraction of T-cell subsets[S39]. At high doses (>1 Gy), Tfi and TS cells wereequally radiosensitive but there was a marked
difference in the radiosensitivity of T cells between
C3H, BALB/C, C57B1/6 and BlOBR strains of mice.
No long-tenn effect of radiation at these high doses on
the i~nmunesystem was found in terms of accelerated
ageing of the immune function in animals exposed as
young adults.
172. Other experiments have shown an enhancement of
Uie immune response following whole-body exposure to
low doses. As an example, rabbits wen exposed to small
doses of x rays (about 0.25 Gy) before or after
immunbation with antigenic sheep red blood cells
T8]. These small doses were able to stimulate theproliferation of plaque-fonning cells. This finding has been
confinned in experiments in which human and murine
T cells were exposed to low doses [A& A9, D8. L9, L16,
L17, M17, S40, S51, T9].

m,

173. In contrast, four different strains of pathogen-freemice (BlOISn, BlO/SgSn, C3HIHeMsNrs andC57B1/6JSlc) were exposed to doses of 0.025-0.25 Gy
from x rays [K13]. Nine hours later, they were
injected with sheep red blood cells; the number of
direct plaque-forming cells per spleen was assessed
after 4.5 days. There was no evidence of enhancementof the plaque-forming cells in any of the strains within
the dose range used. In an extension of thisexperiment, C57B1/6J mice were immunized withsheep red blood cells and exposed two days later tohigher doses (1.5-3.0 Gy) from x rays. Numbers ofindirect and direct plaque-forniing cells per spleen
were assessed at intervals thereafter. Mice exposed to
1.5 Gy were found to have a significant increase in the
nurnber of indirect plaque-forniing cells 11 days after
the il?jection of the sheep red blood cells. This was
highly correlated with an increase in the CD4+/CD8+
cell ratio during the first three days after radiation
exposure, followed by a rapid decline, as shown in
Figure X. These results suggest that the ratio of TH to
Ts subsets changes in favour of helper cells shortly
aflcr exposure, possibly contributing to the observed
enhancement of the indirect plaque-forming cell
response.
174. Anderson and Lefkovits [A91 proposed that theenhancing effect withill the dose range 1-7 Gy could
be due to the elimination of the more highly
radiosensitive Ts cells. These investigators questioned,

1994 REPORT

however, whether the sanie mechanism operated whendoses below this range were used. Under thesecircumstances, they postulated that TS cells could
proliferate. The enhancing effect on muririe splenic
T cells, which is illustrated in Figure XI, is however,effective over only a narrow range of doses [M18].
The maximum effect occurs at about 0.25 Gy.
175. To determine the fate of proliferating T cells,
animals from a normal C57B1/6J+/+ strain of mousewere chronically exposed to gamma-radiation in therange 0.005-0.04 Gy d-' during 20 days in a fourweek period [J7]. Aninials from an immunologicallydepressed C57BIj6J Ipr/lpr strain were exposed undersimilar conditions. A dose-related proliferation inthymocytes and splenocytes was noted in both strains
up to cumulative doses of about 0.8 Gy. This is
illustrated in Figure XII. The mitogen-responsive
L3T4'1yt2- and L 3 ~ 4 - 1 ~ 1 2T' cells increased with
dose, while the niitogen-unresponsive L3T41yt2' andL3T4qyt2' T cells decreased in both strains relative
to sham-irradiated animals.
176. However, the lnagl~itudes of the changes inthymic and splenic T cells .subsets were different,
according to whether or not the animals were fed ona calorie-restricted diet. The immunologicallydepressed niice were more sensitive to these dietarychanges. It was proposed that these experiments
support the hypothesis that the stress of continuous
low-dose irradiation is consistent with an adaptive
mechanism for cell rcrrcwal arid maintenance of
mitogen-responsive cells.

177. Two recent reviews [L16, M19] provide the basisof a hypothesis with which to explain a radiationinduced T-cell response to low doses of radiation. At
the cellular level, the question as to whether or notsonie subsets are more radiosensitive than others
remains unresolved. The evidence points to the needfor an intact thymus, in that thymectomy prevenled theadaptive response [J6]. Mitogen-responsive T cells
appear to be a prime target, and their stimulation isassociated with enhanced expression of the HSP7O
gene and its related proteins. There may be selective
destruction of niitogen-unresponsive T cells. Theinterpretation is complicated by the evidence that the
metabolicstatus of irradiated ariirnals can influence theresponse and that there is a marked difference inradiosensitivity betwee11 tlic strains of animals used in
the experiments.
178. Liu et al. [L8, L9, L161 have irrvestigated several
reactions of splelrocytes in two strains (C57B1/6 andKunming) of niice irradiated with x rays. The doseeffect relationships for antigenic (plaque-fornling cell)ability, mixed lymphocyte reaction, mutagenic(concanavalin A)-stimulation, antibody-dependent cell-

mediated cytotoxicity, natural killer cell activity,interleukin-2 and interferon secretions, and thelipopolysaccharide reaction are given in Table 23.
Interestingly, the maximum response in most of thesereactions occurs at 0.075 Gy.
179. Sorne specific features of the reactions occurringat n~aximumresponse are su~nniarizedin Table 24. An
analysis of cell-cycle progression by measuring theuptake of tritiated thymidine showed an increase in thenumber of thylnocytes entering the S phase, with acorresponding decrease in the nuniber of cells in the
Go phase 3-7 days after exposing mice to 0.075 Gy.
The T H n S ratio of thy~niclymphocytes was the samefor the first three days, with a lowering of the ratio
after seven days, which the authors claim was due toa decrease in the number of CD4'CDS'
cells(compared with CD4-CD8' cells) in the thymus.
180. A parallel examination of the phenotypic changesof the thyn~ocytesubsets, with flow cytometry using
fluorescence-labelled monoclonal antibodies against
surface antigens, showed a significant increase in thepercentage of the double-negative (CD4CD8-) cells in
the thymus after 0.075 Gy, implying an enhanced
renewal of thymocytes. These results are also includedin Table 24. At the same time, the secretion of colonystimulating factors by thymocytes was stimulated. It is
klrown tliat the colony-sti~nulatiligfactors secreted by
the thymocytes act on ~ni~crophages
to facilitate theproduction of interleukilr-1, which, in turn, serves asa signal for the ~naturation of immature thymic
lymphocytes. All these changes occurring in thethymus following low doses should increase thesilpply of mature lymphocytes.
181. Liu et al. [L26] proposed a niechanism to explain
their findings after the whole-body irradiation of miceat low doses. This is sulnliiarized in Figure XIII,
which outlines the changes in signal transduction of
T lymphocytes. It is a process similar to that
postulated for apoptosis and interphase death. How it
might be influenced by neuroendocrine factors is being
investigated. What is known is that exposure to0.075 Gy causes a decrease in serum corticosterone in
the course of a few weeks accompanied by an increasein 5-hydoxytryptan~inefrom the hypothalamus and adecrease in adrenocorticotropic hormone [L27]. It isriot kaown how these cha~rgesirr endocrine function
followi~rg low-dose irrildiation affect the signaltransductiolr process in T cells, but it is an area of
research worth pursui~ig.

2.

Effects in hunians

182. Scvcral parameters of cellular immune function
have been assessed for 168 persons who survived theANNEX B: ADAPTWE RESPONSES TO RADlAlON IN CELLS AND ORGANISMS

atomic bombings of Hiroshima and Nagasaki but who
now reside in the United States [B18, B19, 8201.
Persons exposed to doses between 0.01 and 1 Gy werecompared with persons exposed to less than 0.01 Gy.
Lymphocytes were isolated from the peripheral bloodof these individuals and assessed for the following
parameters of cellular inlnlunity: (a) mitogenic
response to phytohaemagglutinin; @) mitogenic
response to allogenic lymphocytes (mixed lymphocyte
response); (c) natural-cell-mediated cytotoxicity; (d)interferon production. 111 every case, the response of
the group exposed to 0.01-1 Gy was greater than thatof the group exposed to less than 0.01 Gy, although
only the difference for natural cell-mediatedcytotoxicity was statistically signific.ant (Figure XIV).
It is not possible to say whether the increase innatural-cell-mediated cytotoxicity observed in thesesurvivors of the atomic bombings exposed to very low
doses of radiation is a genuine adaptive response thatwas modulated by post-radiation environmental conditions or a chance finding.

183. In Inore recent studies carried out among 1,328
survivors of the atomic bombings and now living inJapan, there was an age-related decrease in the total
number of T cells (CDSf, CD4+, CD8') [K14].
Although the differences were not statisticallysignificant, the overall impression is that ageing of the
T-cell-related immune system is accelerated in older
persons receiving doses in excess of 1 Gy, comparedwith the control group, who received doses of lessthan 0.01 Gy.
184. The responsiveness of peripheral blood lymphocytes to allogenic antigens in mixed lymphocyte
culture was measured in 139 survivors of the atomic
bombings. In contrast to the findings in paragraph 182,
the study revealed a significant decrease in mixed
lymphocyte culture response with increasing dose ofprevious radiation exposure. This decline was marked
in the survivors who were older than 15 years at thetime of the bombings.. It suggests a possible relationship between the recovery of T-cell-related function
and the thymic function that processes mature T cells
for the immune system. Thus it may be that in the
persons who were older at the time of the bombings,
the thymus function had started to involute, allowing
less recovery of T-cell function than in younger
sunrivors, who had adequate proccssing T-cell activity[A19].
185. As indicated in paragraph 160, the spontaneous
loss and alteration of antigen receptor expression inmature CD4 cells has been found in blood cells takenhom 127 healthy donors who had not been exposed toother than natural background radiation [Kll]. The
mean frequency of mutant T cells in males withaltered T-cell receptor expression was 2.5
equal

211

to about 1.3 lo4 per single T-cell receptor locus
anlong the CD4 cells, increasing with age.
186. The mean frequency of mutant T lymphocytes
was measured in 203 survivors of the atomic bombings, 78 of whom received doses greater than 1.5 Gy
and 125 of whom received doses less than 0.005 Gy[K16]. The results were 1.39 2 0.63 lo4 mutants percell in exposed males compared with 1.20 2 0.35 lo4in unexposed males and 0.99 2 0.39 lo4 in exposed
females compared with 0.89 2 0.38
in unexposed
females. There was no statistical difference in mutant
Crequency between the two groups, although thefrequency was higher in males than females. The
smoking habits of the males may have contributed tothe higher values.

187. Antibody titres to Epstein-Barr virus antigens
were determined in the sera of 372 atomic bomb
survivors to evaluate the effect of the previous
radiation exposure on immune conlpetence against thelatent infection of the virus. The proportion of persons
with high titres (rl:40) of IgG antibodies to the early
antigen was significantly elevated in the exposed
survivors. Furthermore, the distribution of IgM titres
against the viral capsid antigen was significantly
affected by radiation dose, with an increased
occurrence of titres of 1:s and 1:10 in the exposed
survivors, although the dosc effect was only
marginally suggestive when persons with rheumatoid
factor were eliminated fiom the analysis. These results
suggest that reactivation of Epstcin-Barr virus in thelatent stage occurs more frequently in the survivors,even though this might not be affected by the radiation
dose. Otherwise, there was neither an increased trend
in the prevalence of high titres (>1:640) of IgG
antibodies to the viral capsid antigen among thesurvivors nor a correlation between the radiation
exposure and distributions of titres of IgA antibodies
to the viral capsid antigen or antibodies to the nuclear
antigen associated with anti-Epstein-Barr virus [ A l l ] .
188. The effects on the immune system of long-term
low-level radiation exposure were measured in twoareas in Gaungdong Province. China [Y8]. The annual
effective dosc in the area of low background radiation
in Enping County was about 2.0 mSv. In the area ofhigh background radiation in Yangjiang County, theannual effective dose was about 5.4 mSv. The annual
equivalent doses from external gamma-radiation to thered bone marrow were estimated to be about 0.77 mSv
and 2.1 mSv, respectively. Twenty-five healthy malesubjects from the high-background-radiation area and27 subjects from the control (low-backgroundradiation) area were divided into three age groups, and
Lhe frequency of interleukin-Zsecreting cells was~neasured as an index of immune conipetence inperipheral blood lymphocytes.

189. The results shown in Table 25 indicate that thefrequency of interleukin-2-secreting cells was significantly greater in subjects from the high-backgroundradiation area than in those from the control (lowbackground-radiation) area. The increased productionof interleukin-2 in lymphocytes after low-dose
irradiation has also been demonstrated [Z7], consistent
with the view that long-term exposure to low doses ofradiation may affect the immune system. However.
other factors, particularly differences in smoking
habits. a u l d also have contributed to the differences.
190. A study of the T-cell subsets in occupationally
exposed persons revealed no significant influence ofradiation on their profile [TlO]. Data were pooled into
two groups, one with individual exposures less than
0.5 nlSv and another with exposures in excess of
0.5 mSv in the previous three months. The average
doses for the two groups were 0.36 + 0.09 mSv and1.06 2 0.77 mSv, respectively. Natural backgroundradiation was estimated to be 0.06 mSv during theperiod. The results shown in Figure XV indicate nostatistically significant difference in the percentage ofCD~', CD4+, CD8' and HNK-1 (natural killer cells).
However, as indicated by the data given in Table 26,
significant differences were shown as an effect ofcigarette smoking.

3.

Effects on tumour growth191. The precise involvement of the immune systemin the natural course of cancer renlains uncertain. It is
known that white cells cultured in vitro in thepresence of the cytokine interleukin-2 acquire thecapacity to kill tumour cells [SSO]. The phenomenon
was termed lymphokine-activated killer activity. The
use of in vitro techniques to study cytokine kinetics
has given some insight into their role in tunlour
biology. Some cytokines (e.g. gamma-interferon) callrender tumour cells resistant to cell-mediated killing,
while others (e.g. transfomling growth factor b) can
enhance the growth of some tumour cells. Thus,
cytokines interact to generate immune responses andmodulate the outcome of effector mechanisms ontarget cells.
192. Thus, the response of a cell to a cytokine
depends on the context in which the cytokine signal isreceived. For example, if white cells are mixed wilh
tumour cells in culture, the ability of the white cells tokill the tumour cells in the presence of cytokines callbe measured. This is shown in Figure XVI. Interleukin-2 can profoundly increase the cytotoxicity of
the white cells. Conversely, if either interleukin-4 ortransfomling growth factor is added at Lhe sametime as the inter1euki11-2,the cytotoxicity is significantly reduced. However, if the white cells are firststimulated with interleukin-2 and the11interleukin-4 ortransforming growth factor 13 is added, the reduction
in cytotoxicity does not occur.
193. Low doses of radiation (0.25-1 Gy) have beenused to augment the effect of immunization of animals
to reduce tunlour growth [A4]. The immunization
procedure involved injecting animals with an antigen
of non-active tunlour cells before exposing them tolive tunlour cells. The antigen was prepared bytreating the ascitic form of a methylcholanthreneinduced fibrosarcoma (SaI cells) with mitomycin andparaformaldehyde. These mitomycin-treated cells werethen injected subcutaneously into the A/J strain ofmouse and, to assess immunity. the mice were injectedsubcutaneously with an amount of living SaI cells
known to induce subcutaneous tumours. The effect ofirradiation upon this immunization process can be~neasured.Figure XVII shows tlle effect of wholebody exposure to 0.15 Gy from x rays on the responseof A/J mice to mitonlycin-treated SaI cells.
Irnrnediately after irradiation, the mice were injectedwith varying numbers of treated SaI cells, as indicatedin the Figure. Twenty-one days later, they received a
subcutaneous injection of lo4 viable SaI cells into theleft flank, and the size of the growing tumour wasmeasured over a period of 26 days. The non-irradiatedcoritrol group (solid line) did not receive themitomycin-treated cells. hljection with 103 to 1d
mitomycin-treated tumour cells resulted in variable
degrees of immunity in both sham-irradiated andirradiated groups, expressed in terms of smaller
tumour size than in the control group. However, thedegree of i ~ n ~ ~ l u rwas
~ i t yalmost always greater in theirradiated mice. Low-dose augmentation was less~xonouncedin recipients of thymus-derived T cells.
From these results it was suggested that exposure to
low doses of radiation reduces the number of Ts cells,
wt~ich~~ornlally
suppress tunlour rejection.
194. In a follow-up to these studies, the effect ofradiation was shown in an in vitro system in which theeffect of irradiating donor spleen cells could be~neasured [A18]. One procedure ( W i m assay)
involved injecting viable Sal cells into NJ mice andkilling them two days later. The spleens were shamirradiated or irradiated with 0.15 Gy, and lo4 spleencells were mixed with lo4 SaI cells. This mixture wasinjected subcuta~~eously
into NJ mice and tumour size
measured over 18 days. Figure XVIII shows theinhibitory affect of the radiation.
195. The effects of low-dose radiation on another typeof experimental tunlour, the Lewis cell carcinoma,
have been measured [L29]. C57B1/6 mice received
whole-body x-irradiation giving doses in the range
0.05-0.15 Gy at a dose rate of 0.0125 Gy min-l. All
mice were injected intravenously with 7 105 cells of

ANNEX B: ADAPTWE RESPONSES TO RAI)IATlON IN CELLS AND ORGANISMS

Lewis lung carcinoma 24 hours after the irradiation
and were killed 1 4 days later. The lungs weregremoved and the tumour nodules on the l u ~ ~surface
were counted. The mean number of lung tumour
nodules was 16 in the 0.05 Gy dose group, 27 in the
0.075 Gy group, 20 in the 0.1 Gy group and 27 in
0.15 Gy group, all significantly lower than the 85
nodules counted in the sham-irradiated group(p < 0.01-0.001). This supports the view that there
may be an inhibitory effect of low-dose radiation on
the pulmonary dissemination of Lewis lung carcinoma
in mice.
196. Miyamoto and Sakamoto [MB] demonstrated
the anti-tumour effects of low doses of radiation inmice of the WHT/Ht strain. Mice were exposed to
250 kV x rays in the dose range 0.05-1 Gy at a dose
rate of 1.23 Gy min-l. They were then injected withsquamous carcinoma cells, and the effect of theradiation on subsequent tunlour growth was measured.
For example, whole-body irradiation of 0.1 Gy to micebearing primary leg tumours followed 12-24 hours
later by localized tumour irradiation delayed thegrowth of the tumours more than did localized
irradiation alone. The results for various times andamounts of local irradiation are given in Table 27. The
in virro immune responses of splenocytes fromtumour-bearing mice exposed to 0.1 Gy are comparedto those from sham-irradiated tumour-bearing mice i11
Figure XIX.The selective depression of Ts cells may
have been responsible for this low-dose effect197. Immune response and tumour growth have also
been studied in humans. In a study of non-Hodgkin's
lymphoma patients, the effect of whole- or half-body
x-irradiation on the various T-cell subsets wasmeasured [T16]. Patients received 0.1-0.15 Gy per
fraction, delivered two or three times per week, until
the cumulative dose was 1.5 Gy. The changes in the
T-cell subsets are shown in Table 28. A statisticallysignificant increase in helper T cells and helperinducer T cells was found, with no change in the
suppressor cells or natural killer cells. The direct antitumour effect was evaluated in 10 patients. Twopatients showed complete remission, seven partial
remission and one, no change. In four patients given
half-body irradiation, the tumours showed complete oralmost complete remission even though the primary
tumours in the tonsils or neck lymph nodes wereoutside the irradiation field. Anti-tumour activity in theother patients was obscured by chemotherapy received
after the irradiation. The changes in T-cell subsets andtumour responses could be consistent with an adaptive
feedback control signal that up-regulates stem cells,with preferential proliferation of differentiating TH
cells. These studies need to be substantiated toeliminate the possibility of spontaneous remission.

213

198. Studies to characterize the role of the immune
response to low doses of radiation are continuing. The
mechanisms responsible for T-cell selection during normal
differentiation in the thymus and activation of thesignalling process that couples antigen recognition tochanges UI lymphocyte behaviour are gradually being
elucidated. A sequential role for phospholipase C,
intracellular calcium ion and protein kinase C, followed bytranscription of genes such as c-fos, and interleukin-2
production in the activation of T cells has been proposed.
Sinlilar sequences of events appear to be associated with
apoptosis and in low-dose-radiation-induced interphase
death, which causes enhanced DNA replication andproliferation of T cells. Whole-body irradiation of mice
results in a dose-related enhancement of the T-cell
response to antigenic, allogenic and mitogenic stimuli atdoses below about 0.1 Gy.
199. As an alternative explanation to radiation-induced
interphase death, experimental studies using mice haveshown selective depression of radiosensitive suppressor
T cells within the dose range 0.025-0.25 Gy, with an
optirnurn response at 0.075 Gy. This needs to beinvestigated hurther as a possible mechanism of theadaptive response.

200. The evidence for changes in the TS& ratio ofT cells in humans exposed to radiation remains equivocal.
Reported changes in the ratio of these cells in the blood of
atomic bomb survivors over 40 years after exposure are
dificult to interpret, the effects of the long time intervaland of changes in the environment and cigarette smoking
being confounding and inexplicable factors. A Chinese
study of the chronic exposure of a large population to
background levels of external radiation of about
5.4 nlGy a-I indicated that levels of interleukin-2-secreting
cells were significantly increased in persons h n this~ areacon~paredwith persons living in an area of lower radiation
background where the annual effective dose from external
exposure was about 2.0 mSv; the authors acknowledged,
however. that differences in geochemical and othere~lvirorunental factors provide an equally plausible
explanation. A study of workers chronically exposed to
low doses of radiation showed 110 statistical difference inthe percentage of helper or suppressor T cells or of naturalkiller cells in groups with average d w of 0.36 and1.06 mSv, however significant differences were found in
relation to cigarette smoking.
201. A role for the neuroendocrir~esystem in influencing
T-ccll proliferation after low doses of radiation has
recently been proposed. The blood vessels in mostlymphoid tissues are innervated with sympathetic nerves,
and !he ly~nphoid tissues are under the control ofhormonal factors via the hypothalamus. There is evidence
to support the view that radiation can activate theneuroendocril~esystem and enhance the immune response.

UNSCEAR 1994 REPORT

214

202 A cytotoxic effect of irradiated T cells on tumour
cells has been demonstrated. It is postulated that low dosesof radiation act by modulating antigen-stinlulated clonal
growth. There is evidence of a down-regulating effect onIV.

tumours in animals, but the evidence for a similareffect on human tumours is sparse. There is a need toinvestigate these effects, which could be of clinicalsignificance.

EXPERIMENTAL STUDlE:S OF RESPONSE IN MAMMALS

203. The effects of radia tion in animals have been studiedin numerous experiments. Evidence of possible adaptive
responses have sometimes emerged in lifetime studies ofanimals exposed to acute or chronic low-LET radiation atdoses well below those associated witb bone marrow
failure. Life-span and incidence of neoplastic diseases havebeen assessed. Other experiments have been done withanimals exposed to non-lethal conditioning doses prior toacute exposures to potentially lethal doses. It should be
noted that in many of these studies the conditioning doses
were well above the range of doses producing the adaptive
response in cellular systems.

207. Agc at exposure was shown to be an importantfactor influencing survival. Female mice of the BDF1/J(C57B1/6J x DBAl2.J) strain were exposed to 0.8, 2.4
or 3.2 Gy from 250 kV x rays at 90 days of age, andLDSono values were determined at various ages
thereafter [S55]. The results, given in Table 29,
showed that there was no statistically significant
difference in LDS0 values between controls and those
pretreated with 0.8 Gy in aninials below the age of
550 days. With higher conditioning doses, however,there was residual damage in the aninlals resultix~gin
lower resistance to a lethal dose (expressed as reduced
LDSOvalues).

A. SHORT-TERM SURVIVAL FOLLOWINGACUTE, HIGH-DOSE EXPOSURE

208. As a recent example of these short-term survival
studies, two-month-old SPF mice of the C57B1 strain
were acutely exposed to a range of doses from x rays
between 0.025 and 0.1 Gy [Y9]. Two months later,
they were acutely exposed to 7.75 Gy, and 30-day
survival was measured. The results, given in Table 30,
showed a marginally significant increase in the lifespan of animals receiving the lowest conditioning doseand a definite inlprovenlent in survival at conditioning
doses of 0.05 and 0.1 Gy compared with animals not
exposed to a conditioning dose. The improvement insurvival rate coincided with an increase in endogenous
colony-forming units, consistent with increased
proliferation of haematopoietic stem cells following
the conditioning doses.

204. Experiments were carried out in the 1950s and1960s to investigate the hypothesis that stimulating
haematopoietic stem cells to proliferate before exposing
animals to a potentially le~haldose of radiation could
improve their chances of recovering from acute bonemarrow failure. A historical review of these experinlents
was given by Dacquisto and Major [D2].

205. In one of these early experiments, adult female
Swiss white mice (Bethesda Naval Medical ResearchInstitute strain) were acutely exposed to a dose of aboutover a
1.2 Gy from 250 kV x rays at weekly it~te~vals
period of three weeks [C18]. Thirty days after the third
exposure, the mice were acutely exposed to a challengedose of about 5.6 Gy, which was known to be the dose
approximating the LDSORO.
Of the animals in this group,
26% died aAer 28 days, compared with 41% in the control
group, which received only the challenge dose.
7 f i . This observation was confirmed by another study inwhich adult female Swiss white mice (Walter Reed strain)
were acutely exposed to a conditioning dose of about
0.4 Gy from x rays, either 10 or 15 days before determining IDSOm
values [D2]. The LDNm values for thetwo irradiated groups were about 4.48 + 0.25 Gy and4.94 ? 0.25 Gy, respectively, compared with 3.90 2
0.21 Gy for animals not exposed to the conditior~ingdose.
There was no evidence of splenic or thymic hypert~ophy
in animals that received the condithung doses, in contrast
to an earlier observation that localized splenic irradiation
to a dose of about 0.16 Gy caused transient hypemophy
P131.

209. In a subsequent experiment, niice were irradiatedwith x rays to doses of 0.025-0.5 Gy at six weeks ofage and exposed two months later to a dose of 7 Gy
from x rays [Y7].
A dose of 0.025 Gy was insufficientlo affect survival after exposure to the high dose, but
pretreatment with 0.05-0.1 Gy produced a significantly
increased survival rate. However, the response to
pretreatment with 0.05 Gy after two months wasstrain-specific. It occurred in C57B1 but not in
BALBIc mice. Surprisingly, an increase in survival
was not observed in animals pretreated with 0.2 Gy if
exposure to the challenge dose occurred up to 1.5
months after the conditioning dose; and pretreatment
with 0.5 Gy resulted in an increase in survival if thechallenge dose was given two weeks later but not after
two months. These findings persuaded the authors to
postulate different mechanisms involving time-related
stimulation of haematopoiesis, although they were notspecified.

ANNEX B: ADAPnVE RESPONSES TO RADIAION IN CELLS AND ORGANISMS& LONGTERM SURVIVAL FOLLOWING

SUB-LETHAL EXPOSURE
210. Studies using rodents and beagle dogs have provided
some insight into the long-term effects of acute exposure
to low doses and of chronic exposure at low dose ratcs.
They date From the early pioneering work of Russ andScott [R2.R31.

1. Experiments with rodents
211. The effect of chronic irradiation of niice was
dcm'bed by Lorenz et al. p 1 4 , L19] in an earlyexperiment in which both survival and tumour incidence
were measured. Male and female niice of the (C57BI x
A)F1 stram, refened to as LAF1, were exposed Gom theage of one month for the duration of life to gamma rays
From n6Ra delivered at the rate of about 1 n ~ G yfor 8hours each day. Control mice were housed in a room
adjacent to the exposure room. Almost a year aftcr thestart of the experiment, the control mice developed
dermatitis and had to be replaced by mice not directly
related to the irradiated mice but from crosses of the same
inbred strains.
2 1 2 The mean survival times of the irradiated male mice
was sigmficantly higher than those of the control mice, butthere was no statistical difference between the two groupsof females, although there was a tendency for the females
to live longer than the males Fable 31). However, thedifferences in life-span in the males cannot be acceptedwithout reservation, since the replacement control group
may have been subject to different enviro~uriental
conditions and may have possessed genetic characteristics
slightly different from those of the original group.
213. Although no single cause of death predominated,
pyelonephritis appeared to be a major contributing factor.
Its m m e n c e is Gquently associated with dennatitis,
particularly among males. There was an increase in theincidence of lymphosarcon~asand other turnours of thereticular tissues in both male arid female irradiated mice,and mammary carcinoma incidence was also higher in theirradiated females @ c 0.1). The irradiated females
showed an increase in ovarian lun~ours@ < 0.05), and theirradiated males showed an inncase in lung tulnours@ < 0.05). These results were essentially confinned in astudy in which guinea igs of the Tumble Brook Fanns
strain were exposed to &L Co garnnia rays from the age of
100 days for the duration of life at a dose rate of about
1 mGy d-' [Rl11.
214. Sacher ar~dGralin [S52], in a study of the survivalof mice exposed for the duration of life, also reported an
inaease in the life-span of animals exposed to
gamma rays at a dose rate of up to about 30 times that of
the background radiation. Male al~dfemale mice of the
LAF, strain were exposed to a wide range of doses at

215

different dose rates. Non-irradiated animals serving as
controls were placed either in a corridor adjacent to tbe
irradiation facility or hi an adjoining room. It was
subsequently discovered that the control group m thecorridor were in bd exposed to stray radiation From theirradiatiol~ hcility at a rate of behveen 1.6 and4.9 mGy a-l. This comparcd to about 0.14 niGy ad in thecontrol group in the adjoining room The mean survival
times are shown in Table 3 2 For comparison, the results
for animals irradiated at the rate of 40 mGy a-' are given.
There was a statistically significant inaease in the mean
survival hnes of males but not of females exposed to
between 1.6 and 4.9 mGy a-l compared with those
exposed to d w rates of 0.14 mGy a-l.
215. One interpretation of these studies is that any increase hi survival for male niice receiving the higher dosesof radiation reflects a decreased number of deaths in earlylife. A possible explanation could be that minimal injury
to the haematopoietic system causes a rebound in stancell proliferation. This regenerative hyperplasia could thencreate a larger mass of tissues devoted to the defence
against intercurrent and potentially lethal infection. Thismechanism, however, does not prevent the occurrence oftuniours that appear hi late life, which are not neclessarily
the cause of death. Why this response is confined to males
cannot be explained.
216. Upton et a]. [U12,U13] studied the late effects of
low-LET radiation in RF/Un mice. Life-span and theincidence of neoplastic diseases were assessed. The effectsof mean accumulated doses up to about 3 Gy at varying
dose rates between 0.05 Gy d-' and 0.8 Gy m i d l are
shown UI Table 33. Several interesting features emerge
from these studies. In males, there was little effed on lifespan (mean age at death) at dose rates of 0.8 Gy min-'until the accumulated dose approached about 1 Gy, there
was little effect of dose rate in the range 0.05-0.77 Gy d"at an accuriiulated dose of about 1 5 Gy; and, overall,gamma rays were less effective at low dose rates than athigh dose rates at acculi~ulateddoses of about 3 Gy. In
females, there was no significant change in the mean age
at death at dase rates of 0.067 Gy d-' until theaccumulated dose reached about 2 Gy; reducing the dose
rate to 0.01 Gy d-' increased the mean age at death ataccumulated doses of about 3 Gy.
217. The mean age at death of animals with neoplasms
was also influenced by dose rate. Thus in males, irradiatedanimals died earlier than controls at dose rates of
0.8 Gy min", even at the lowest accumulated dose of
0.25 Gy, but there was no significant difference comparedwith controls at dose ratcs of 0.15-0.77 Gy d" at anaccumulated dose of about 15 Gy, with a inarginal
difference at a dme rate of 0.05 Gy d-l. In females, earlier
death Goni neoplasnls occurred at dase rates of
0.067 Gy d-' after an accumulated dose of about 2 Gy,
and there was no difference From controls at doses of

UNSCEAR216

3 Gy, if the dose rate was reduced to 0.01 Gy d-l. In
summary, these results support the view that at low dose
rates and accumulated doses of a few gray there is noapparent life shortening or early appearance of neoplastic
diseases causing death of the irradiated animals comparedwith unirradiated controls. There is, as well, no support for
an apparent inaease in life-span or decrease in tunlour
incidence due to the radiation exposures at the lowest
doses.
218. Ullrich and Storer [U14, U15] also d e s c r i i theinfluence of radiation on life-span and tumour induction inniice of the RFM and BALB/c strains. S cifically, a
study was made of thc efIccts produced by 7~ ammaradiation delivered at 0.4 Gy min-' or 0.083 Gy d- .within
the dose range 0.1-4 Gy for RFM mice and 0.5-4 Gy for
BALBJc mice. At the lower dose rate, the life-shortening
effect in BALBJc mice could be described as a linear or
linear-quadratic function of dose, although the lowest doseused was 0 5 Gy. The influence of dose at a dose rate at
0.083 Gy d.' on the incidence of neoplastic disease infemale BALB/c mice is shown in Table 34. For RFM
mice, thymic lympbon~aswere the predominant reticular
tissue neoplasm, tbe solid tumours being lung adenomas
or endocrine-related tumours. The incidence of tumoun
was at all doses higher than in the uninadiated controls.

rP

219. Sato et al. [S42, S53] ex ed male and female
mice of the CSWlMJ strain to
gamma rays at rates
of 0.029-038 Gy d-l. Exposures at the rate of
0.029 Gy d-I started at four weeks of age. The mean lifespan of female mice was 628 % 10 days, with a mean
accumulated dose of 16.4 Gy; for male mice, the mean
life-span was 723 5 10 days, with a mean accumulated
dose of 18 Gy. The mean life-spans of unirradiatedfemales and males were 693 % 11 days and 725 % 15days, respectively. III the irradiated females, this life
shortening was statistically significant in the males, it was
not In a follow-up study, life shortening at the higher dose
rates was associated with the occurrence of thymic
lymphomas, which octuncd more bequently in exposed
younger mice [05]. At the highest dose rate, and ataccumulated doscs of 39 Gy over a period of 105 days,
life shottening was also associated with haemorrhage andinfectious diseases owing to depletion of the sten) cells ofbone marrow.

l3E

220. Covelli et al. [(JZO]studied the effects of x rays onlife-span and tuniour induction as a function of age at
exposure. Male and fernale mice of the BC3Fl strain were
acutely exposed to 250 kV x rays, either in lrfero at 17days after coitus, at 3 months, or at 19 months of age. The
doses varied from 0.3 to 2.1 Gy for in utero irradiationand fiom 0 5 to 7 Gy at 3 months or 19 months of age.
Prenatal irradiation or irradiation at 19 months of age did
not result in clearly measurable life shortening Fable 35).
There was, however, a trend suggestive of life shortening
in animals exposed at 3 months of age at doses in excess

of about 2 Gy, albeit h e confidence limits were extremely wide. There was a non-significant trend suggesting
an increase in life-span in animals exposed at 19 monthsof age at a dose of 2 Gy. Life shortening was associatedwith an increased incidence of reticulum cell sarcoma (aIIOII-thymicmalignant lymphoma that infiltrates the spleen,
liver and rnesenteric lyrnpll nodes). Primary tumours of
the lung and liver, mostly benign adenomas, andsubcutar~eousfibrosarcomaswere also found However, nodifference could be detected in the patterns of total tumour
ulcidencc for irradiated and non-irradiated (control)
animals.
221. Sasaki and Kasuga IS541 compared the effects of
1 3 7 ~ ganutlasrays on fcmale mice of the B6C3F1strain
exposed under specific-pathogen-free conditions until
natural death. Mice were irradiated at 17 days in utero, orat birth, or at 15 weeks of age with doses of 1.9, 3.8 or
5.7 Gy. There was a decrease in life-span at 1.9 Gy in allgroups, but no statistically significant increase in total
tumour incidence between irradiated and control p u p s
was observed (Table 36). Mice in the fetal period were
found to be susceptible to pituitary tumours and liver andlung tumours. There was an excess of malignant
lymphomas at a dose of 5.7 Gy, and Ihe total time until
incidence was less than with controls. The exposure ofyoung adults was associated with the indudion of myeloid
leukaenlias and Harderian gland tumours.
222. Maish et al. w 2 9 ] rneasured life-span and disease
incidence in the C57BIfCnb strain of mouse exposed toacute and fractionated doses of 1
3'cs gamma rays.
Twelve-week-old mice were exposed to doses ranging
frorn 0.25 to 6 Gy at a dose rate of 0.3 Gy min-l in asingle scssion or in 10 sessiorls delivered 24 hours apart,or in 8 sessions, delivered 3 houn apart The results of anacute cxposure are shown in Table 37. There was no
indicqtioa of an increase in life-span at these doses;
decreases in life-span were not statistically evident until
the dose approached 1 Gy. A fractionated exposure wasless effective in reducing survival time than an acuteexposure, and life shortelling was not observed m the 8a~ld10 fraction protocols until the dose approached 2-3 Gy
and 4 Gy, respectively.
223. The causes of death in urlirradiated mice could besegregated into late degenerative changes in lung andkidney (glomerulosclerosis) (a%),
leukaemias (-21%)and carcinomas (mainly liver adenocarcinoma) andsarcomas (-16%). The incidence of thymomas was low(-1 %), and no radiation-induced excess of lymphnma was
obscrvcd until the doses approached 2-4 Gy, but U I ~tunlours did result in deatli at an earlier age than inunirradiated animals. The incidence of all malignancies
was less U~an the uninadiated mice after acute doses
bctween 0.25 Gy and 1 Gy, with no significant change in
the alpha parameter of the Cox linear propottional halardmodels within this dose range. Fractionation increased theANNEX B: ADAPTlVE RESPONSES M RADIATION IN CELLS AND ORGANISMS
incidence of all malignancies: thus their incidence was
45% and 52% at 1 Gy and 2 Gy, respectively, for the
Sbaction protocol and 40%, 32% and 36% at 0.25 Gy,
0 5 Gy and 1 Gy, respectively, for the 10-fradion
protocol. The authors concluded that these differences
between fractionated and acute exposures were small andnot well enough established Gorn a statistical viewpoint
224. The effec3s of gamma rays and fission neutrons on
the life-span of mice has been studied for many years at
the A r g o ~ eNational Laboratory in the United States.
Earlier studies of low-LET radiation principally involved
gamma mys delivered either as acute exposures orcontinuously [C19, T15). For the most part, the acuteexposures were delivered over a 20-minute period at dose
rates ranging Gorn 0.0083 to 0.094 Gy Inin-'. The
exposure regime began when the animals were 110 daysof age.

225. The results obtained on the mean survival after
irradiation of male mice of the B6CFI strain exposed for
22 hours each day, fwe days each week have beenreported p15]. The exposures were continued for either
23 or 59 weeks, the accumulated doses ranging Gom 2.1
to 24.6 Gy.The effects of these exposure conditions areshown in Table 38. There was no indication of an increasein life-span at any dose in this range. Life shortening fromdeaths due to all causes did not beconle significant
until
the total dose approacl~ed4 Gy for a =week exposure or
5 Gy for a 59-week exposure. These values were notsignificantly altered when the analysis was restricted tomice dying from turnours. Above -4 Gy, the doseresponse relationship was linear and inversely dependent
on the protraction period. The life-shortening coefficientsfor the %week continuous arid 59-week continuous
protocols were 0.16 and 0.08 days lost per 0.01 Gy,compared with 0.39 days for an acute suyle exposure,thus showing a marked dose-rate effect

2. Experiments with beagle d o g
226. The effects on life-span of external whole-body
exposure of beagle dogs to x or gamma rays has beenstudied In one study, dogs were exposed to 0.16 Gy or
0.83 Gy fromganuna rays at 8, 28 or 55 days inurero or 2 days after birth. In addition, some dogs were
exposed to 0.83 Gy at 70 days or 365 days after birth. The
status of these studies in 1982 is shown in Table 39.
Through 10 years of age, no differences in survival were
evident in any of the cxposure groups [B23]. Irradiation
during the fetal period was, however, associated withabnormalities of skeletal, dental and central nervous
system develop~ncnt Perinatal irradiation resulted in
kidney dysplasia and, in,alimals receiving higher doses, inchronic renal disease. The thymus gland, particularly thethymic epithelium, was found to be highly radiosensitive
during fetal developme~it.

217

227. In another study, dogs were exposed bilaterally
to 3-50 kV x rays, delivered in different numbers offractions and different fractionation intervals, to total
doses of 1-3 Gy. The dogs were exposed between 8
and 15 months of age. Some dogs were bred after
exposure, distinguished as parous or nulliparous. The
dogs listed in each group shown in Table 40 are thosesurviving at least 90 days after the irradiation. Two
general summaries of the data have been published,
one before all the animals were dead [A13], the otheremphasizing the effects on life-span and tumour
induction [R12].

228. There was no increase in survival time, expressed as
median survival after exposure, of any of the irradiateddogs compared with the unurradiated controls. Although
life shortening was only marginal in animals given acuteor hctionated doses up to 1 Gy, it occurred in somegroups of animals given 2 or 4 fractionated doses ofbetween 0.75 and 1 5 Gy total dose and bactionated dosesof 3 Gy. The main causes of death were similar in
irradiated and unirradiated dogs. The development of nonneoplastic diseases (essentially fibrosis) at an earlier age in
irradiated animals at the higher dose explained, in large
pafi, the observed life shortening. However at 1 Gy,theincidence of non-neoplastic diseases, mammary tumours
and non-nianimary tuniours was broadly similar to thatobserved in the unirradiated group.
229. In a third study, dogs were exposed to 6 0 gamma~
mys continuously until death or, in a companion
experiment, until they had received a predetermined total
dose P I , F22, G13). Dose rates raryed from 0.003 to
0.054 Gy d-l, and the accumulated doscs at ternination of
exposures ranged from 4 5 to 30 Gy. At dose rates greaterthan 0.019 Gy d-l, the responses were dose-rate-dependentand limited primarily to damage of the haematopoietic
system (Table 40). At dose rates between 0.003 and0.008 Gy d-l, myeloprolifemtive diseases ultimately
expressed as myelogenous leukaemia were the limiting
factor for survival [K25].

230. Observations of adaptive responses in in vuro
cellular studies cannot be readily extrapolated to postulate
adaptive response in the irradiated animal. The different
exposure patterns in animal studies (acute versus chronic
lifetime exposure) could involve mecha~lismsdifferent
Gom those involved in the cellular adaptive response to a
low conditioning dose followed by a high challenge dose.
The complexity of multicellular organisms, including theand endocrine factors
crucial role of irru~iu~losurveillancein maintaining the healthy state, must be taken into
account. The careful managenient of the animal colonies
to avoid infections and stress and the need to recognize
strain-specificity of tumours should not be overlooked infuture experiments.

218

UNSCEAR l 9 W REPORT

accumulated doses up to a few gray, at dose rates
231. Stiniulating the haerilatopoietic system tobetween 0.005 and 0.3 Gy d-I, or on the time ofproliferate by exposing the bone marrow in vivo to
between about 0.025 and 0.1 Gy has been shown toappearance of tumours or on tumour incidence among
improve the short-term survival (expressed as LDSOl3()) irradiated animals. Why some experiments resulted in
an increase in life-span is not easily explained. Whileof mice subsequently exposed to a potentially lethal
the observed increase in life-span could be due todose of radiation. Whether a similar mechanism israndom variability, it is possible that the effect is real.
responsible for improving the longer tenn survival of
If so, it is important to understand the precise conanimals chronically exposed at low dose rates isditions under which life-span is increased.
unclear. It is plausible to suggest that improvement inlong-term survival could be a result of chronic
234. More recent experiments using mice have conminimal injury to the bone marrow, causing a reboundfirmed that there is no statistically significant change
in stem cell proliferation and protection against
in tunlour incidence in iradiated mice compared to
infections, but occurring along with this effect is anunirradiated controls below about 2 Gy, depending on
increased risk of malignancy due to the proliferation
the strain of mouse used. At higher doses there is aof potentially malignant cells.
dose-related increase in several tumour types causing
232. Experiments in the 1950s indicated that the mean
death and a corresponding decrease in mean life-span.
life-span of male, but not female, mice could be
235. The results of experiments using beagle dogs are
increased if the animals were exposed daily to lowin general agreenient with those obtained using mice.
LET radiation from a few rnilligray to several hundredI n addition, they confirmed the increased sensitivity of
milligray per year above the level of backgroundthe fetus arid young animals. Observed life shortening
radiation. A feature of these observations was that theat accuniulated doses greater than a few gray could bemean increase in life-span reflected a decreased
related to the development of non-neoplastic diseases
number of deaths in younger irradiated animals. Whyat an earlier age than in unirradiated animals.
the response was confined to niales is not apparent
Irradiated animals were susceptible to the developmentof rnyeloproliferative disorders, which were frequently
233. Other experiments related life-span to theexpressed as myelogenous leukaemia at dose rates
incidence of neoplastic diseases. Taken together, theabove about 0.003 Gy d-' and after accumulated doses
results of these experiments could bc interpreted asof a scvcral gray. Error-prone DNA repair mechanisms
demonstrating that, compared with the patternwere proposed to explain the onset of myeloproobserved in unirradiated controls, there was no signiliferative disorders.
ficant effect on mean life-span following exposure to

V. EPIDEMIOLOGICAL STUDIES OF RESPONSE IN HUMANS
236. The effectiveness of a cellular adaptive response
in humans, expressed ill ternis of a reduced rate of
spontaneously occurring cancers or of a reduction in
the expected numbers of radiation-induced cancers,
would be most convincirigly demonstrated if it were
the outconie of epidemiological studics involving
exposure to low doses. The general results of thesestudies are discussed in Annex A, "Epideniiologicalstudies of radiation carcinogenesis", most of whichindicate steadily increasing cancer incidence withincreasing dose. Only those cases in which exposures
were only marginally above the natural backgroundlevel are re-examined in this Chapter. For inherent
reasons, the evidence of an i~lcreasein the sporltalieous
incidence of cancer is in these cases equivocal.

237. There are theoretical reasons based solely on the
nam of DNA daniage and repair to expea that cancer canoccur at the lowest doses without a threshold in the

response, although this effect would perhaps not be
statistic;llly demo~atrablcThe dose-response rclation9hip has
been judged to be linear without threshold for all cancers
excluding leukaernia. For leukaemia, the relationship thatbest fits the data is linear-quadratic and l i n m at low dases.
kl increase in total cancer mortality has been statisticallydcmoostrated at doses above 4 . 2 Gy oflow-LET radiation
but not at lower doses, exepl in special circumstances suchas caner in childhood following in luero inadiation andthyroid cancer after acute exposure of the thyroid to lowLET radiation during childhood.

238. k n o n g tl~elirnibtio~lson the confidence of lowdose
epideniiological studies, by far the most consistent problem
has bee11the lack of sblislical power. This has been due toa co~iibinationof factors, including insufficient numbers in
the irradiated population, inadequate follow-up and doses
hilt are colleaively too snlall to have any chance ofproviding a dose-respor~wrelationship.

ANNEX B: ADAPTIVE RESPONSES TO RADIATON IN CELLS AND ORGANISMS

k IN1;IW[3ITANTSOF HIGH-BACKGROUNI)

AREAS
239. Examples of background radiation studies UI France,
Japan, Sweden, the United Kmgdonl and the United States
are reviewed in Annex A, "Epidemiological studies ofradiation carcinogencsis". The conclusion from thesestudies is that there is no demonstrable association
between leukaemia and other cancers and backgroundradiation.

240. Updated estimates of the cancer risk for a populationof about 80,000 persons continuously exposed to natural
background radiation at a dose rate about three times
higher than the world average have recently been reported[W29, WM].This population lives in two areas in
Yiangjiang County of Guangdong Province, China. A
comparison is being made with a population of similar
size and age structure in a nearby control area of low
badgmund radiation in Enping County. Details of thedoses are given in paragraph 188. These populations arestable in that there is little movement into and out of thearcas. Their age structure is biased towards younger age
groups compared with the rest of China. Ascertainment ofcause of death is of a high standard, and the dose
measurements, based on several different techniques, arein good agreement The rates of site-specific cancer
mortality and estimates of excess risk in the highbackground-radiation arca, relative to the control arca, aregiven in Table 41 [W29]. The high incidences of prir~laryliver cancer and nasopharyngeal cancer are peculiar to thewhole of Guangdong Province and are probably related to
local environmental factors, which ir~cludeinfection with
hepatitis B virus and smoking, respectively. These twocancer types comprise the largest number of cancers in the
two areas and are highest in the low background area. The
totals of all cancers other than leukaemia are not strictly
comparable with these cancers included.
241. While there are slight differences in the site-specificcancer mortality rates between the two populations, theoverall differences in leukaemia and other cancers
combined are not statisticaliy significant, and the results so
fir do not provide clear evidence of the presence orabsence of deleterious effects due to low doses ofradiation in the environment This may not be surprising,considering the difference in cu~i~ulative
dose between the
two areas, based on a 50-year exposure, of about 60 mSv.
The problem, then, is the lack of statistical power to detect
an effect on risk at such low doses.
242 Thyroid riodularity followi~y:continuous low-dae
exposure in China was deternlined in about 1,000 women
aged 50-65 years living in the hidi-bacwund-radiation
area and in a similar number of controls l i v i i in the lowbackground control area [WB]. Cu~~lulative
doses to thethyroid were estimated to be about 0.14 Gy and 0.05 Gy,
respectively. For mul tiple nodular disease, the prevalences219

in the high-background-radia tion area and in the control
area were 95% and 9.3%, respectively. For smgle
nodules, the prevalences were 75% in the highbackground area and 6.6% in the m n m l area (prevalence
iatio = 1.13; 95% CI: 0.82-155). No differences were
found in serun~levels of thyroid hormones. Women in thehigh-background region, however, had significantly lower
concentratiore of urinary iodine. The prevalena of mild
diffuse goitre was higher in the high-background-radiation
region, perhaps related to a low dietary intake of iodine.
The authors suggested that continuous exposure throughout
life to a total dose of about 0.1 Gy in excess of the low
background level did not influence the risk of thyroid
nodular disease; however, this study did not provide
statistically significant results.

Ii.

OCCUPATIONALLY EXPOSEDINIINIDUALS

243. Studies of the effeds of radiation following
occupational exposures are useful in clarifying the possible
relationship between relatively low doses of gammaradiation arid the risk of cancer. One relevant study was of
nuclear shipyard workers in the Unitcd States w131.
From a database of almost 700,000shipyard workers,
including about 108,000 nuclear workers, three study
groups were sclectcd, consisting of 28342 nuclear workers
with working lifetime doses ZS mSv (many of themreceived doses well in excess of 5 mSv), 10,462 nuclear
workers with doses 4 mSv and 33,352 non-nudear
workers. The type of work carried out by the three groups
was identical, except that the nudear workers were
exposed additionally to 6 0 ~ ogamma-radiation. The
median age of entry into c~iiploymentfor the three groups
was similar, that is, about 34 years. The study included
exposures received from the beginning of nuclear ship
overhauls in the 1960s until the end of 1981. All groups
worked in areas where intakes of asbestas were possible.
244. Deaths in each of IIICgroups were classified as due
to all causes, leukaen~ia,lymphatic and haematopoietic
cancers, nlesothelio~na and lung cancer. The results,
summarized in Table 42, demonstrate a statisticallysignificant decrease in the standardized mortality ratio forthe two groups of nuclear workers for "death from allcauses" cornpared with tl~enon-nuclear workers. This wasdue in part to a higher incidence in the non-nuclear
workers of deaths from diseases other than cancer, which
included cardiovascular disease and respiratory, genitourinary and digestive tract disorders. Both groups of
nuclear workers had lower death rates from leukaemia andfrom lymphatic and hac~natopoieticcancers than the nonnuclear workers, but this was not statistically significant
All three goups of workers had lower death rates hom
lymphatic and haernatopoietic cancers than the general
population in the United States. This has been referred toas the healthy worker effect. Mesothelioma was the only

220

UNSCEARcancer that showed a significantly higher incidence forall groups. The slightly higher, but non-significant,incidence of lung cancer for all three groups comparedto the general population of the United States could
have been associated with asbestos exposure.

245. Two features of this study need to beemphasized. First, the collective lifetime doses fromoccupational exposure in the two nuclear worker
p u p s were estimated to be 1,450 man Sv and26 man Sv, respectively. The estimated collective
doses from natural background radiation in the same
periods were 1,067 lriarl Sv and 409 man Sv,
respectively. The collective dose to the non-nuclear
workers from background radiation was estimated tobe 1,275 man Sv. It is difficult to draw conclusions
about the incidence of diseases that might beassociated with low-level occupational radiation
exposures when the doses are comparable to, or lessthan, the doses from natural background radiation.
Also, the statistically significant decrease instandardized mortality ratio for deaths from all causes
cannot be due to the healthy worker effect alone, since
the non-nuclear workers and UIC nuclear workers weresimilarly selected for employment and were afforded
the same health care thereafter.
246. A study of about 95,000 radiation workers in the
United Kingdom has rece~itly been reported. The
cohort received a collective lifetime dose of
3,200 man Sv, with an average individual dose of
34 mSv [KlS]. Up to 1988, 6,600 workers had died.
The standardized mortality ratio for all causes of death
after excluding the first 10 years following the start ofradiation work was 0.85 (p < 0.001). The standardizedmortality ratios for all malignant neoplasms in 23
organs or tissues and for all known, non-violent causes
other than malignant neoplasms were 0.86 (p < 0.001)
and 0.84 (p c 0.001), respectively. For most othertissue-specific cancers, the standardized mortality
ratios were below unity, but they were not statisticallysignificant. The only cancer for which an elevatedstandardized mortality ratio reached statisticalsignificance was thyroid cancer (SMR = 3.03). It is
not unexpected that one organ or tissue showed anincreased standardized ~nortalityratio by chance. The
excess relative risks for all cancers and for leukaemia,
excluding chronic lymphocytic leukaemia, were 0.47
(90% C1: -0.12-1.20) and 4.3 (0.4-13.6), respectively.
A confounding factor in this study was that cancers
could have been associated with exposure to chemical
carcinogens.
247. Since the healthy worker effect complicates theinterpretation of standardized mortality ratios, greater
importance was attached by the authors to internal
analysis or to testing for the trend in risk with dose, inwhich steps are taken to co~npensatefor the factors

thiit lead to the healthy worker effect. Positive trends
with dose were found for all malignant neoplasms
taken together and for Ieukaemias, excluding chronic
lymphatic leukaemia (Figure XX). The former trend
did not reach statistical significance (p = 0.10, onesided test), while t l ~ elatter was statistically significant(1) = 0.03). Because it was considered possible thatcigarette srnoking may have influenced the results,
Figure XX also shows the relative risk for themalignant ~~eoplasms,
excluding both lung cancer andleukacmia. The scatter of the points showing the
avcrilgc relative risk and the wide confidence intervals
011 these points provide no reliable information on therisks at doses below about 0.2 Gy.
248. Updated intenla1 analyses of mortality in 33,000
workers ~nonitoredfor six months or longer at theHi~ofordsite in the U ~ ~ i t eStatesdprovide no evidenceof a correlation between cumulative occupational
external dose and mortality from leukaemia and fromother cancers [G12]. The relative risks and theirconfidence intervals are summarized in Table 43. Of
24 tissue-specific cancer categories evaluated, only
cancer of the pancreils and Hodgkin's disease showed
positive correlations with dose that approachedstatistical significance (one-tailed p-values of 0.03 and
0.04, respectively). These correlations were interpretedby the authors as probably spurious. A significant
correlation (1) < 0.05) was obtained at doses above
50 mSv but not at 10 mSv. Earlier analysis ofnlortality from nlultiple myeloma had shown asignificant excess risk [G14], but the extended analysisof thcse data now show that the excess relative risk
for this fonn of cancer is no longer statisticallysignificant [PI, R101.
249. A study has been under way since 1980 on the~r~ortalityof past and present employees of Atomic
Energy of Canada Ltd. [G8]. The study population
co~~sistsof 13.491 persons, 9,997 males and 3,494
fen~ales,for a total of 262,403 person-years at risk
until 1985. The number of female deaths (121) was
too small for detailed analysis, but the 1,178 deaths inthe male population gave a limited basis for study.
Mortality pattenu in the cohort between 1950 and1985 were examined by comparing the observedmortality with that expecled in the general population
for three groups of workers: those with nooccupational exposure, those with up to about 5 0 mSv
and those with more than 50 mSv. The number ofdeaths was fcwcr than would have been expected on
the basis of ge~leralpopulation statistics for males inh e three groups. The lindings were similar for thegroups "all cancer deaths" and "all other causes ofdeath". In the occupationally exposed males, elevatedstaridardized mortality ratios were seen for nonHodgkin's lymphoma arid for buccal cavity, rectum,
rectosigmoid and prostate cancers. But in the

ANNEX B: ADAPTIVE RESI'ONSES TO RADlAnON IN CELLS AND ORGANISMS

unexposed male group. there were elevatedstandardized mortality ratios for lymphatic andmyeloid leukaemias and for large intestine, prostate,brain and biliary system cancers. The nunlber of cases
identified of all these cancers was srnall and theconfidence limits were wide, such that none of theelevated standardized mortality ratios were statisticallysignificant.

C. SURVn70RS OF THE
ATOhrIC BOhiBINGS
250. The epidemiological study of the survivors of theatomic bombings in Japan has up to now been the
primary source of data from which to estimate theeffects of radiation on humans. A dose-response
analysis of these data for doses less than 0.5 Sv wasrecently presented [S30]. The end-points measured
were cancer mortality, cancer incidence and noncancer mortality. The relative risks with 95%
confidence intervals and the dose-response
relationships fitted by the authors are illustrated in
Figure XXI.
251. For mortality from leukaemia, the relative risks
varied among the five dose groups (0.010-0.019,
0.020-0.049,0.050-0.099, 0.100-0.199, 0.20-0.49 SV),but they did not differ statistically from the control
group, which received less than 0.010 Sv (11 > 0.10).
The relative risks for the three dose groups less than
0.1 Sv wcre less than unity but still within the rangeof what the authors considered to be rando~nvariation
about a value equal to unity. For leukaenlia mortality.
a linear-quadratic model fitted marginally better thana linear model (p = 0.07 compared with 0.06).
252. For all cancers other than leukaemia, the relative
risks generally increased with dose, as shown by thedose-response curve, although lhc lowest four dosegroups had relative risks not significantly different
froni unity. The highest dose interval (0.20-0.49 Sv)
showed a statistically significant increase in mortality.
253. Mortality from lung cancer and incidence of
thyroid cancer by dose group, based on data from theHiroshima and Nagasaki tumour registries during
1958-1987, were also analyscd. A pattern similar tothat observed for mortality from all cancers except
leukaemia was seen, that is, the relative risk variedamong comparison groups with wide confidcncc limits
but did not differ statistically fron~unity within thelowest dosc intervals.
254. For mortality froni all diseases other than cancer,
a significantly elevated risk was observed at higher
doses (estimated threshold dose: 1.5 Sv) for younger
survivors of the atomic bombings (age at tllc tirnc of

22 1

bombings <40 years). However, the relative risks forthe various low-dose groups (<0.5 Sv) did not differ
and were close to unity with the exception of one
significant point at the dose interval 0.20-0.49 SV (RR= 0.83). It is interesting to note that the decrease inrelative risk at this point corresponds to a significant
increase in relative risk for n~ortalityfrom all cancers
except leukacmia.

D.

PATIENTS EXAhiINED OR TREATED
WITH RADIATION

255. There arc several examples in clinical practice where
low doses have been used for diagnostic purposes. Theseare x-ray examinations to detect fetal abnormalities, x-ray
fluoroscopy to check the efficacy of artificial pncumothorax in the Ircahnent of pulmonary tuberculosis, (eg.
[B2]), x-ray examinations to assess the progress of skeletal
development during treatment for scoliosis and 1 3 1 ~diagnostic t a t s to dctcct thyroid abnormalities.
256. The available studies [Q,H19, M8, M22, M26,
S24] of in rtrero exposure arc discussed in detail in Annex
A, "Epidemiological studies of radiation carcinogenesis".
The main conclusion is that the low-dose exposure of the
fetus in diagnostic examinations is associated with apositive risk of cancer induction, but quantification of therisk is subject to much uncertainty. There is nothing tosupport the assu~iiptionthat adaptive processes could be
operati~lgafter irradiation that could reduce the incidenceof radiation-induced cancers.

257. The evidence for radiation-induced breast cancer isdiscussed UI Annex A, "Epidemiological studies of radiation carcinogcnesis". Although exposure to radiation athigh doses and high dose rates is associated with excess
breast cancer, the potential hazard from low-dose,
fractionated exposures during early breast development has
not been thoroughly evaluated. The failure to detectincreased brcnst cancer in several large studies issurprising, and no satisfactory explanation is forthcomirg.
However, Inany of thc women were over 35 years of age
at exposure.
258. A retrospective study of 35,074 Swedish patients
receiving 13'1 for suspected thymid disorders between
1951 and 1969 has been reported p 1 7 , H18, H211. It is
not possible to be precise about the doses delivered toindividual thyroids because of differences in
uptakeand variatio~~sin Inass of the thyroids However, theavenge anlou111 of 13'1 activity administcrcd was
1.92 MBq, delivering an estimated average dosc of
approximately 0.5 Gy to the thyroid. The data are givcn inTable 31. Patie11ts give11 13'1 for reasons other than asu5pected tumour wcre not at increased risk (standardized
incidence ratio = 0.62; n = 16 Overall, the data provide
for diagnostic purposes
no indication that expmure to I'

i n m s e d the incidence of thyroid cancer in the follow-up
period after 10 years. It was concluded by the authors thatthe observed increase in the 5-9 year period was most
likely to be due to a high level of medical surveillance,
leading to an increased detection of indolent tumours.

E SUMMARY
259. The human epideniiological studies following
exposures at low doses and low dose rates to low-=radiation do not at present provide evidence of an adaptive response expressed as a decrease in the prevalenceoccurring human cancers. This is n d surof sp~~tatieously
prising in view of the low statistical power of thesestudies. The results have been interpreted variously as
being consistent with the upper bound on the confidence
limits of total cancer risk at low doses obtained by
extrillmlating from high-dose and high-dose-rate data; or
as i~ldicathigno additional risk at low doses comparedwith the spontaneously occurring rate. Statistical limitations do not pemiit a decisive choice at the present time.
Cautio~~is necessary when using isolated examples in theepidemiological literature to justify either an increased ora dccrcascd risk at doses of a few hundred milligray,bearing in mind the statistical limitations of the data.

CONCLUSIONS
260. Adaptive response is the collective term used todesaibe the results of expcrinlcnts in which a small doseof radiation can condition cells so as to indue repair
procases and/or to stimulate proliferation. One
consequence of DNA repair might be to reduce the natural
incidence of cancer in its various forms or the likelihoodof excess cancers being caused by further radiation
exposure. A great deal of effort is being directed into
characterizing these processes, and in r a n t years resultsof research especially at the cellular level have bccorrie
available.

261. There is convincing evidence that the number ofradiation-induced chroniosonie aberrations and mutations
that occur in proliferating niam~naliancells after an acutedose of low-LET radiation in the range 1-3 Gy can be
reduced by exposing the cells to an acute dose of between
a few milligay and a few tcns of miIligray several hours
before the high dose. These experiments involving a low
conditioning dose and a high challenge dose were
designed to demonstrate the adaptive response as alaboratory phenomenon They were carried out underclearly defined conditions using n~itogen-stimulated
lymphocytes, proliferating bone marrow cells, spermatocytes and fibroblasts. The response has not been
demonstrated so far in other cell systems or convincingly
in cells under conditions of chronic exposure.

262 The evidence that is becoming available indicatesthat followuy radiation-induced damage to cells, a nuniberof changes occur. Anlong these changes are the activationof several classes of genes, including those coding for thesynthesis of enzymes iwolvcd in the control of cell
cycling, proliferation and repair. It is not entirely clear
how these changes may specifically improve repair
capacity. There is some evidence to indicate that radiationinduced enzymes, which rcniain to be isolated andcharacterized,are relatcd to stress-response proteins. Theresecnis to be some similarity ill the types of damage

induced by radiation and other toxic agents. The adaptive
resporlse may therefore be a common feature of cellularresponse to damage.

263. A multi-step process has been proposed to explain
the cellular adaptive response. After acute doses of several
hundreds of milligray. cell cycling in proliferating cells
may be delayed. The period of delay allows enzymes
induced by the radiation to repair damage before the cells
procccd through ccll cycle and undergo mitosis rY5, Y6].
The adaptive response at these hlgher dases may therefore
depend on whether or not the cells in cyde areten~porarilyblocked. There is no direct evidence, however,to suggest that ccll cycle delay occurs after acute dasesn ~ g i o gfrom a few rnilligny to a few tens of milligray,eve11 though the adaptive response has been observed inthis range of doses. The fate of cells exposed to aradiation dose in the resting phase remains to beestablished.

264. 111 evaluatulg the cfkctiveness of the adaptive
reslxmsc in cells exposed to a conditioning dose of up toa few t e ~ aof ~nilligrayor to concentrations of toxic agents
below that concentration known to produce a toxic
reaction, it is important to recognize the unstable nature of
DNA in living cells during normal metabolism (H2, L11,
L21, V3, V4]. It has been estimated that the DNA
molcculc within each nucleus undergoes several thousand
detectable changes evcry hour as a result of metabolism[BlO, L12, S27, W12, W13, W14, W151.Dcspite thishigh rate of spontaneous n~olecularchange, few stable
mutations accuniulate in the genome. Thus, cells havecvolvcd efficient prorcsscs for the cmrrection of metabolically uiduced changes.
265. This inherent ability to repair DNA needs to betaken illto account in assessing the ability of ails to repair

die dxnage caused by doses of radiation in the wide range
of ;I fcw milligray per year to a few tcns of milligray

ANNEX B: ADAPTlVE RESPONSES TO RADIATION IN C E U AND ORGANISMS

delivered in minutes. Just how capable the existingmechanisms are of coping with the additional radiationinduccd damage is not readily obvious. But it would bereasonable to assume from the evidence that damage
caused by natural background radiation, in which theenergy deposition events in a particular nucleus are
separated by weeks or months [B21], should bc readily
reparable by the available metabolically driven
mechanisms.

266. However, errors in repair do occur, even duringmetabolism, sucb as small base-sequence changes w i t
mutations), gene deletions or rearrangements, although theoverall DNA integrity may be retained p,F4, FS]. It
needs to be recogruzed, therefore, that the effectiveness of
DNA repair in irradiated mammalian cells is not absolute,
some Gaction of the cells retaining stable mutiltions. Thus,
the same low conditioning doses that result in iln adaptive
response are likely also to result in nlalig~antcellulartransformations by the mechanisms discussed in Annex E,"Mechanisms of radiation onm-genesis" in the UNSCEAR
1993 Report [Ul]. It would seem important to judge thebalance between the fidelity of repair, residual damage andmalignant transformationsand whether indeed these effects
interact with each other. The Committee hopes that moredata will become available in the near futurc to address
this point.
267. Alternative cellular mechanisms have bee11proposed
to explain the adaptive response. These include thedetoxification of reactive radicals, thereby reducing thepotential for damage, and the activation of membranebound receptors stimulating cell proliferation. Efforts
should be made to characterize the possible role of theseprocnrses.

268. It remains doubtful whether the immune system
plays a significant role in any of the adaptive processes at
low doses. In the UNSCEAR 1993 Report [Ul], theCommittee concluded that the inlniune systeni niay notplay a major role in noder rating hu~nanradiation oncogenesis, although immune function in certain organs may
ensure that sonlc early neoplastic cells are eli~ninatedbefore they become established. The data hi this Annex
are not in conflict with this generalized conclusion. Sonie
transient effects on the ratio of subsets of T cells and inaccelerating programmed cell death in damaged lymphocytes have been identified. It is interesting in this respect
to note that a dose of a few hundreds of rriilligay can
influence tumour growth kinetics, expressed as a transient
reduction in turnour size in experuncn~alani~~ials.
The
evidence for changes in the hunlan im~nunesyste~nlong
after exposure is not convincing.

269. Animal experiments in the 1950s arid 1%0s showedthat chronic exposure of rodents at doses of up to a few
milligay per day from low-LET radiation could result inincreased life-span compared to co~itrolsexposcd to only223

background radiation. However, some anomalies in theseexperiments need to be explained. Why was the response
confined to male mice, and why was it not observed
consistently in pathogen-Gee mice?
270. More recent experiments witb rodents and beagle
dogs exposed at various ages to low dose rates of lowL J 3 radiation have generally been unable to demonstrate
any statistically significant difference in life-span ofirradiated and control groups after accumulated doses of
up to about a gray. However, tumour incidence did notincrease until the dose was in excess of about a gray,depending on the mouse strain and the susceptibility of theanimals to developing spontaneous tumours. In somestudies there was a non-statistical trend towards a lowerthan-expected incidence of tissue-specific tumours, but inother studies there was a non-statistical trend towards ahigher-than-cxlxcted incidence at doses of 22 Gy. A
reduction hi life-span or an increase in tumour incidence
after fractionated exposures was not of statisticalsignificance until accumulated doses exceeded a few gray.
271. The low statistical power of most human epidemic^
logical cancer surveys with exposures at low doses makes
it difficult to rcach a decisive conclusion on the existenceor absence of an adaptive response. Studies of exposure tohigher-than-average levels of natural background radiation
have made little contribution so h r to estimating the riskof canccr lioin low-dose-rate, low-LET radiation. Studiesof occupational exposures have recently sbown more
promise of yielding positive results. especially after
moderate doses, but in the low-dose region the confidence
limits are so broad that tlie results are still equivocal. The
Life Span Study of survivors of the atomic bombings
shows no sig~ilicantexcess of total cancer mortality below
about 0.2 Gy. All cancers other than leukaemia are inexcess but not statistically significant down to a dose
range of 0.01-0.05 Gy. Leukaemia shows a deficit at doses
less than 0.1 Gy, which again is not statisticallysignificant At present no coriclusion can be drawn about
the dose response below 0.2 Gy because of statislical
limitations.
272. 11conclusion, there is substantial evidence of an
adaptive respolae in selected cellular systems following
acute expasure to conditioning doses of low-LET radiation. The precise n~olecularprocesses involved in theadaptive response are riot well understood at present, but
cellular repair is likely to play a role by mechanisms
siniilar to those involved hi the generalized stress response.
The prcsencc of an adaptive response is not rcadily
evident from tlic rcsults of experiments in mammalianorganisms in [enils of reduced tumour induction. Interpretation of lhcse experinlents is complicated by variationsin the susceptibility of different animal strains tospontaneous tumour induction The low statistical powerof the epidemiology studies also prevents a clear statementon the presencc of an adaptive response in humans

221

UNSCEAR 1994 REPORT

exposed to low doses. It is to be hoped that better
understanding of mechanisms of radiation effects
obtained in molecular studies might provide a basis
upon which to judge thc role of adaptive resporise in
the organism. In the meantime, it would be premature
to conclude that cellular adaptive responses could con-vey possiblc beneficial effects to the organism thatwould outweigh the detrirnental effects of exposures
to low doses of low-LET radiation. The Committeer e c o r ~ i ~ n e ~that~ d thiss research be continued in order toclarify the nature and iniportance of the effects ofradiation-induced adaptive response.

225

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

Table 1
Adaptive response In human lyniphocytcs conditioned with tritiated thynlidine
lo21
Chromaromc a k r r a i o n s in 100 cells
Challenge rrcalrnenl

Conduioning rrcalmetu

Ere&

Exchanges

Deldionr '

3

0

0

3

0
0

2

6

1.5 Gy (x rays)

12

I

36

1.5 Gy (x rays)
1.5 Gy (x rays)

9
10

3
3

23 (38)13 (41)

None (control)

Tritia~cdhymidinc
Tritiatd hymidine

Tritiatd ( h y m i d k
Tritiartd hymidim(370Bq ml.')(37W Bq ml-I)(370 Bq ml-')(3700 Bq rn1.l)

5

Table 2
Adaptive response in human lynlphocytes conditioned with x rays

w51-

C h r o m o m e aburuions in 100 c d k (fadonors 1, 2, 3)
Condirioning trcamenr

Challcngc treamcni'

BreaksExchanges

Deletiom

Total '

X m c (conrrol)

1 1, 1

Q 0. 00,0,01, 1, 1

0.1 Gy (x rays)

7. 1, 1

Q 0, 1

0,0,0

7. 1, 3

1.5 Gy (x rays)

240, 34, 41

27. 5, 8

3. 1. 2

Mq 54, 61

1.5 Gy (x rays)

181, 18, 23

18. 7. 7

3. 0. 00.01 Gy (x rays)

223', 32 37

Exchanges m d delctioos counted as two breaks

p < 0.05.

Table 3
Adaptive response in human lyn~phocytesinhibited by cycloheximide

ryll
Chromaid dclctiarr in 200 celL
Conditioning rrcnrmenl

Challenge rrcnrmau,Male donor

F d c donor

Smr (control)

200.01 Gy (x rays)
10 pg ml-' oE cydoheximidc
0.01 Gy (x rays) and cyclohcldrnidc

4

0
2

1
0
0

1.5 Gy (x rays)

74

94

1.5Gy (x rays)
1.5 Gy (x rays)

39 "
75

59

0.1 Gy (x rays)
0.1 Gy (x rays) and cyclohcxiaide

78b.

UNSCEAR 1994 REPORT

226

Table 4
Inhihition of adaptive response in human lyn~phocytesby 3-aminobenlamlde

1s121
Chromaromc oburarions in 200 cdis "Condirioning rrerumcni

Challenge rrurrmenr
Break without 3-aminobcmmidc

None (control)

440.005 Gy (x rays)
0.01 Gy (x rays)

4

6

6

6

1.5 Gy (x rays)

81

79

1.5 Gy (x rays)
1.S Gy (x rays)

45 (6 1)69 (81)

4t3 b(83)?3 (81)0.005 Gy (x rays)
0.01 Gy (x rays)*

Breaks 4 3C-

Expected n u m b in parentheses.
p < 0.005.

Table 5Adaptive response in humiin lymphocytes lollowing successivc conditioning treatmcnk[ElCondiiwning rrearmmr

Chdcngc rrcamau

Told breaks in 400 cdis 'Nooe (control)

30.01 Gy (x rays)
0.01 Gy (x rays) afta 4 h
0.01 Gy + 0.01 Gy (x rays) afier 4 h

6
7
9

0.01 Gy (x rays)
0.01 Gy (x rays) afta 4 h
0.01 Gy t 0.01 Gy (x rays) afrcr 4 h

Expected number in parcnlhtses.
p < 0.005.

1 Gy (x rays)

117

1 Gr (X rays)
1 Gy (x rays)
1 Gy (x rays)

64 *(l20)
71 (121)75 b [ l n )*ANNEX B: ADAFTlVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

227

Table 6
Influence of extracellular pH on adaptive response in human lymphocytes[B81
Chromaid delerions for challcngc dare ar 5 0 hours
Conditioning trcntment

Challenge rrcamcnl

PI{ a1 rime of uenlmcnl@I at rinu of lreormcnl

Z2-7.4

7.57.2pH ar time of aealmurl
62-6.9N m e (control)

10

10

13

0.02 Gy (x rays)

8

9

12

0.3 Gy (x rays)

372

518

1219

0.3 Gy (x rays)

400

593 "

1155

0.02 Gy (x rays)

Chromatid d d c l i w for challenge darc or 78 bs

p l l or r i m of rreatmenr

pH or rime o/ treormcnr

pH or rime of lrrarnrmr

7.2-8.2

6.8-6.9

6.4-6.8

N m e (coatrol)

14

9

11

0.02 Gy (x rays)

7

11

15

0.3 Gy (x rays)

732

642

1137

0.3 Gy (x rays)

696

572

983 '

0.02 Gy (x rays)
Synergistic respame.
p c 0.5.
p<o.001.

Table 7
Influence of cell cycle phase on adnptive response in human lymphocytes~ 4 1

Conditioning rrecumcnr"

Chdlcngc rredmenr

Cliromaromc o k r a t i m u in 100 cclk '?

0.03 Gy (x rays) in Go phase
0.03 Gy (x rays) in GI phax
0.03 Gy (x rays) in S phax

4

Tritiated water

6

6
3

3 Gy ( x rays) in G,phase
1.5 Gy (x rays) in G2 phav
1.2 Gy (x rays) in G2 phaw

880.03 Gy (x r a p ) ~n Go phax
0.03 Gy (x rays) in G, phase
0.03 Gy (x rays) in Go phase
0.03 Gy (x rays) in G, phasc
0.03 Gy (x rays) in S phase

3 Gy (x rays) ~n GIphaw
3 Gy (x rays) in GIphase
1.5 Gy (x rays) in G2 phase
1.5 Gy ( x rays) in G2 phaw
1.5 Gy (x rays) in G2 phase107 (92)
96 (96)14 (26)20 (28)12 (24)

Triti at& u a t a

1.5 Gy (x rays) i n G2 phase

20 (28)

Expected numbn in parentheses.
p c 0.05.

ZZ

11

UNSCEAR 1994 REPORT

228

Tahle 8Adaptive response in rabbit lymphocytes conditioned in vivo and chrrllenged in vifro

P I
Challenge rrcatnunr

in vivoin viuo

Challenge dose in Go phnre

Challcqc dose in G2phnrc

1.S Gy128 :
3.2

173 :1.3

Xmc (cwbd)

0.30 Gy (gunma rays)
0.75 Gy (gnmma nys)0.90 Gy (pmrna rays)
1.20 Gy (gprnma rays)
1.50 Gy (gnmma rays)
1.80 Gy (gamma rays)"

Cells wirh uberrariom (%) *Condifiuning rreatmutr

1 5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)

7.8 2 2.2
6.3 r 1.9
7.5 r 1.7
8.0 r 2.2
10.5 :4.1* (14.1)(14.3)(15.0)(16.5)(16.5)

11.8 :1.9 b(18.6)
13.3 ? 2 0 (18.8)
11.8 r 3.5 (19.5)
13.5 ? 4.9 (21.0)
17.8 + 5.0 (21.0)
23.5 r 3.3 (725)

Lnduder all types d d u a n m m e abcnatiws; $00 d l s soacd; expeaed number of abcrratims in parenthcrcr.
p < 0.01.
p < 0.05.

Table 9Relative survivnl and muhtion frequency in human lyniphocylcs conditionrd with tritintcd thymidine[SlSI

Conduwning r r c a t m

ChaUargc truumau

Relafile s w i t n l of clone-furw~ingcclls

Muration fregrouy (104)1.00

22: 0.5

0.86 r 0.07
0.99 5 0.07
1.00 r 0.1
1.00 r 0.1

2.3 r 0.7
3.2 r 0.9
2 2 ~ 0 5
3.3 r 0.5

Smc (cmtrd)

Tritiated thymidine (37 Bq ml'l)
Tritiated thymidine (370 Bq oll")
Tiitiated thymidine (3700 Bq rn1.l)
Tritiatcd thymidiac(37000Bq ml-I)

Tritiatcd thyrmmnc (3700 Bq ml-I)
Tritiated thymidiae(37000Bq ml-')

1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)

0.80 2 0.05
0.82 :0.0.1
0.84 r 0.06

152 r 2 0
3.9 r 0.9 '6.3 r 1.8 "Tritiatcd thymidine (37 Bq rnl-')
Tritiatcd thymidine (370 Bq m1.l)
Tritiatcd thymidine (3700 Bq ml-')
Tritiatcd thpdine(37000 Bq rnl.')

3.0 Gy (x rays)
3.0 Gy (x rays)
3.0 Gy (x rays)
3.0 Gy (x rays)
3.0 Gy (x rays)

0.52 r 0.03
0.65 + 0.06
0.56 r 0.06
0.55 z 0.08
0.57 :0.05

19.7 r 2 8
14.4 f 6.2
21.5 r 7.8
7.2 r 3.7
9.5 r 1.7 "Signiticant dffcrencc.

Table 10
Mutation frequency in hunlr~nlymphocytes conditioned with x rilys

PI
1

Cloning flcciutc?; (94).~utationfreqrauy (104)

Smt (mnlrd)

24.4 2 7.9

2 6 :0 3

0.01 Gy (x rap)

24.0 f 12.0

4.5 r 2.3

3.0 Gy (x rays)

21 .O + 8.4

15.5 r 8.0

3.0 Gy ( x rays)

18.4 2 6.6

5.2 r 2.8 "Conduwning rrenrmou

0.01 Gy (x rays)
Significant &!Terence, p < 0.5.

Chdlcngc wcatmenr

ANNEX U: ADAPTIVE KESPONSES TO RADIATION IN CELLS AND ORGANISMS

229

Table 11Adaptive response in human lymphocytes conditioned with hydrogen peroxide
F81

-

1

Chdlcngc lrearmcnr

Condirioning rrcamnr

AboTarions in 100 cells

Nme (conuol)

0.5

Hydrogen peroxidc (0.1 pM)
Hydrogen peroxide (1 p,H)
Hydrogen peroxide (10 pM)
Hydrogen peroxide (25 pH)
Hydroga peroxide (50 ,phi)

1.0
0
0.5
1.0
0.5

Hydroga pcroxide (0.1 pM)
Hydrogen peroxide (1 pH)
Hydrogen peroxide (10 pM)
Hydrogen paoxide (25 FM)Hydrogen peroxide (50 pM)

1.5 Gy (x rays)

3.0

1.5 Gy (x nys)
1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x rays)
1.5 Gy (x nys)21.5 '
20.4
21.5
20.5 '
25.0

Table 12
Synergistic response In human lymphocytes conditloncvl with x rays or niethylritcd chemicals~

41
Cordirioning rrcormcnr

Challenge rrcatmcnr

A b m a i w in 200 cdL

Nme (control)

30.01 Gy (x rays)
0.01 Gy (x rays)

Methyl methane sdphonate (0.42 rnM)
Methyl mahane sulphmatc (0.42 mM)

3
114
169 "

Melhyi methane sulphonatc (0.42 mM)
Methyl methane sdphooatc (0.42 mM)

2
97
133 "

Methyl mahanc sulphonatc (0.42 mM)
Mcthyl mdhanc sulphonatc (0.42 mM)

1
97
147

Methyl mclhanc sulphmate (0.018 mM)
M w l mcchurc rulphmatc (0.018 in..
N-mahylN'-rlltr-N-nimguanidine(600 ng d m ' )N-methyl-N'-nitro-N-ninosoganidine (600 ng ml-')aSynmgistic response. p c 0.01.
Synergistic rcspociy p < 0.001.

Table 13Adaptive response in human lymphocytes exposed to drugs
1~191
Chromarid exchanges (96)
Condirioning rrearrnau

Chdlmgc rrcormnr
Donor A

D m B

Nme (coaud)

3.58 :
0.6

4.2 2 0.2

0.05 Gy (x rays)

3.7 % 0.3

4.5 2 0.2

0.05 Gy (x rays)

VP-16 (etopcside)
VP- 16 (etopasidc)

11.1 r 1.3
9.8 :1.2

13.0 2 0.7
10.7 2 0.8

0.05 Gy (x rays)

BCNU (1,3+is (2-chloroethyl)-1-nitrourca)
BCNU (1.3-bis (2shlaoethyl)-l-ni1rowu)

8.7 2 0.4
8.0 r 0.5

0.4
10.1 :
9.0 :1.2

cis-R(cis-diaminodichlaoplr~~num(Ir)

12.6 :1.2
11.9 :1.1

143 :1.3
U.8 2 L4

0.05 GY(x m y 4

cis-R (as-diaminodichlaOP(atinum(n)UNSCEAR 1994 KI:I1ORT

230

Table 14Adaptive response in nlouse bone n l a m w cells and spern~utocytes
Chromatome u h n a i m r (%jConditioning rrnvmmr
in vivo

Chdenge rreanrau

I

Bone marrow c d b*-ocyr-Stale I<unming mouse [C8]0.75 Gy (x r a p )0.75 Gy (x r a p )Cmbd
0.01 Gy (x rays)

12.6
8.4 '

38.5
19.5 "

Female C57B116 moune (YZ]

0.5

Nme (control)

0.002 Gy (x rays)
0.005 Gy (x rays)
0.010Gy (x rays)
0.050Gy (x rays)

0.65 Gy (x r a p )27.1

0.65 Gy (x r a p )0.65 Gy (x rays)
0.65 Gy (x rays)
0.65 Gy (x r a p )

28
8.8
3.5
9.5

Table 15
Investigation of response in pre-implantation mouse emhryos
PSI
Conditioning r r c a m w

Challenge
nealmaal

Nmc (culbol)

0.05 Gy (x rays) in vitro
0.05 Gy (x rays) i n vino

1.5 Gy (x rays) in via0
1.5 Gy (x rays) in r h o

N m c (control)

0.05 Gy (x rays) in vito
0.05 Gy ( x rays) in v i w

1.5 Gy (x rays) in viao
1.5 Gy (x rays) in r w o

Abarmr c c hAberraiotrr per 100 mcraphmes
BreaksF-rchonger

Rcm~gonuus

rod

(46)

9.4

0

0

9.1

6.9

7.0
39.7
27.1

0
0
5

0
0
0.5

7.0
39.7
37.8

228

7.3

0

0.6

7.9

6.4

10.2
24.3
252

0

6.8
6.2

1.3
1.7
27

11.5
39.6
40.3

7.6
27.0
28.0

6.4
26.4

Repair in silu
N m c (cootrd)
0.05 Gy (x rays) in v i w

2 Gy (x rays) in viva

12.2
50.7

0
32.3

0
10.7

12.2
126.0

4.9
52.3

N m c (coatrol)
0.05 Gy (x rays) in vino

9.4
2 Gy (x rays) in t w o

58.2

0
20.0

0
16.4

9.4
114.6

6.9
56.4

Table 16
Investigation of m p o n s e in two-cell mouse embryos[M61
R u u i ~ ta 144 hows qrer conccprion
Conditioning
weasmau a

Challengenea~muu'

N~~ (-lrd)

0.05 Gy (x rays)
0.05 Gy (x rays)''

2 Gy ( x rays)
2 Gy (x rays)

R d r r ar 192 hows rsfm c m c c p i m'

Inno
cdlmnrs

1%)

TrophoMm
wrgronrh(46)(%)(dodcmadeclodmn) (%)

79

n

92

88

a

87
40

81
20
29 (21)84
31
31 (28)71
22
18 (18)

36
8
7 (6)

C&

Ilarchcd

F

Murrory~u'embryo44 P 4 )Coaditiooing treatment given in the early GI phasf, challenge treatment givm in ~ h latec G2 phase.
Rerulu for 144 hours .Her mnceptioa and 192 horns anex m~cptiollurrc obtained in i n d c p d e n t cxperimmtal series.
Expected r d u in pumthcses.

Tuo-cell layers

.rt8bl~17
Some DNA-damage-induced genes ldcntlfled In mrrmmcilinn cclls[I:19]

I h c i n g ogcnfs

'

Dose

Genc

For positiu response

Detection

For i u g a f h r response

Dercerion rims
off- aposwc

Species

CdI

R4

Syrinn hamster
IIumanMouse
Human
Chinem hamster
Chinere hamster
IIumanllumanIlumanl lumanI lumnnIlumanSyrian hamsta
llumanIturnanIlumnnIlumanllumanllunian1luninn

SllE fibroblast cell line
l e a
Myelad cell
Epithelium cell lines
CIIO-Kl
CIIO-K1
I IcLa -3s
I leLa -3s
IIL-60llU37
AG 1522
Epilheliurn ccll lines
SHE-fihoblast c d l line
HcLa-3S
IU-60
I IcLa-3s
Epithelium dl lines
KG-]
KG-I
Uurkatt T

IW161
IS481
[I91
IH12l
lHlsl
Ilils]ID71
1~71
IS'+fJIIS481
1~481[1*12]
IW6l
ID71
ISMI
[D~I
IH121
18241
lR241
IS471

IlumanIlumanIfurnanCdon carcinunn
Cdon carcinuna~.ymphocytccell line

[=2l
1=21

3-24

Moue
Moue
llumanMoue
Rat(Transfcctant) NIII73T3
NIIIBT3
Rctinoblasb
32Dd3, NIlWT3
Embryo cdls

1~241
IGlOl
IGlOI
IGlOl
[Glol

3
05
24-48
3
3

Syrian hamsta
Mouc
Mouse
IlumnnllumanSHE-fibroblast a l l line
M y d a d cell
SpleenIIL-60 dnivativc
Sarcomn a l l linc

lW6l
1191
1191
[HI41
[If131(hours)cod in^ transcripli~mruetorc-(06x raysx raysHzo:0.75-0.9 Gy
20 Gy
2 0 (320 Gy
100 /cg ml-'
0.4 mM
0.25 rnM
0.25 mU
20 Gy
20 Gy
20 Gy
20 Gy
2 GY
0.25 mM

x rays

20 Gy

Hz0:
x raysGamma rays
Gamma rays
Il2O2

0.25 mM
20 Gy
20 Gy
20 Gy
0.1 mMx raysx rays
MMS
f120~

c-jun

H2°2
H~02
x raysx raysx raysx ray5Gamma rays

junB
junU
EGR 1
h T t B gene

mRNA
mRNA
mRNA
mRNA
mKNA
mRNA
Activity
mRNA
mRNA
mRNA
mRNA
mRNA
mRNA
mKNA
mRNA
mRNA
mRNA
Activity
Activity

3
0.5
2-8
3
0.75
1-6
3-6
1-4
~0.5
1
0.75
3-6
0.75
3-6
0.5-6
0.5-1

Codin8 nuclcnr prutein
p53 gene

Gamma rnys
Gamma rays
Gamma rays

4 GY
4 GY
2 GY

ProteinGI -arrest
Protein

1
1

IK231

Other m e g n c r
MoMuSV -LTR
N,K and 11-rnr
N,Kiasv-ab, B, v-sib v-nbl, v-svc
Ha-rasx raysx raysGamma rnys
Gamma rays
Gamma rays

0.7 GyI-LOGY
1-5 Gy1-40 Gy

Activity
Survival
Survival
Survival
Survival
Cali118 cytukine o r receptor

IL-Ip gcne

'IWP-a gene

Ncutrms
x raysGamma raysx rnysx raya0.021 Gy
20 Gy
8.5 Gy
20 Gy
5 G~

mRNA
mRNA
mRNA
mRNA
ndNA

233

ANNEX 13: ADAPTIVE RESPONSFS TO RADIATION IN CELLS AND ORGANISMS

Table 18
Accumulation of a-interferon mKNA and protein kinase C following gamma-ray exposure of Syrian hamster
embryo fibroblasts

W161
Dose "

ffe1a1it.e amowr

3 hours 'I hours '(GY~a-interferon mRNA

0.02
0.12
0.25
0.5
1.0
20

1.0
1.0
1.0

1.0
1.5
3.9
6.9
3.7
3.8

1.5
0.9
p p m t e i n kinilse C

0.02
0.12
0.25
0.50
1.0
20

1.0
1.7
21

1.0
1.9
24
24
3.4
4.3

2.9
3.5

"

Gamma r a p administered at a dase rate d 0.14 Gy min.'.
* Amountof ainterferon mRNA in untreated cells was set at 1.0. All Mhcr valua are expressed relative to that. Standard de\iation fa all mlucs u a s r0.1.
Incubation rime fdlouing completion of h e radiation exposure.

Table 19
Relative expression of transcripts encoding nuclear proteins following gamma-my exposure a

W181
Dare

Dme rue~GYJ(Gy min.')

c-jun

Xb

H4-hLonc

N3

c-myr

0

0

1.0 (0.04)

1.0 (0.01)

1.0 (0.04)

1.0 (0.11)

1.0 (0.03)

0.06
0.25
0.50
0.75

0.01

1.6 (0.04)
22 (0.07)
1.8(0.12)'
1.7 (0.17)

0.9 (0.a)1.3 (0.03)
1.7 (0.03)'
1.3 (0.06)

1.4 (0.08)
1.4 (0.03)
1.7 (0.08)'
2 0 (0.07)C

1.1 (0.09)
1.3 (0.09)
1.S (0.06)
1.4 (0.02)

HND
HN3

0.25
0.50
0.75
200

0.11

1.5 (0.11)
0.8 (0.21)
1.1 (0.12)
4.7 (0.03)'

0.9 (0.09)
0.7 (0.I 1)
1.3 (0.06)
1.7 (0.19)'

1.4 (0.02)
1.6 (0.04)
1.1 (0.05)
1.4 (0.09

1.1 (0.m)
1.3 (0.07)
1.3 (0.02)
0.9 (0.11)

HND
HND

Relative amwnr ofHN.4 for rranscrip~r

HND
HND

HND
HND

Cyding cells were irradiated uith m ~ prnmorays at the doses or dase rates indicated 1 h prior to KNA harvest.
Standard de\iaticos are in parenthcsa.
Hh?) = Hytridizatioas not detected.
Significantly different from contrd, p < 0.05.

Table 20
Relative constitutive levels of mRNAs and proteins in splenocytes of mice conditioned with x rays
[MI91
Relative I&of c 0 n ~ l ~ u N

CON!UUCIUS
Controls

HSP70 (heat shock protein) mKSAGAPD (glycenldehyde-3-phosphatedehydrogenasc) rnRNAIISP70 (heat shock protcin)a

T d dose was 0.8 Gy from 0.04 Gy d-I for 20 days.

0.38
1.98
0.24

Irr&rufrdls "

0.n
201
0.54

UNSCEAR 1994 REI'ORT

234

Table 21
Accessory glycoproteins on the surface or T cells in the blood[A121
Approximale m o ~ e c d a r
wugh ( m a )fiprrssed on

Putative fvncrwn

T11
Thy 1in mice50

All Tcells

Promotes adhcsion bdwm T cells sad tbdr tare
cells by tinding to LFAJ cm target cells

l3

y chain: 25; b chain: 20
r chain: 20; 5 chain: 16

All T cells

I f d p tranrduce & g a l when m t i g e n - W C complex
binds to T cell receptors

50

l lclper 1' cells

60 (homodimn)
70 (hetcrod~ma)

Cyldoxic T cellso chain: 190; p chain: 95

Most white blood cells

Protein "Alranaih~ename

CD2

CD3

Thy 1in micea 4

T4 in humans
WT4 in m i a

TB in humans

CD8

LytZ L y 3 in mice
LFA-1

"

I

Prunotes adhesion to antigen-prucnting d l s and B
cell* probaMy by tinding to d a u I1 MHC
molecul a
Promotes adhuioa to v i ~ s i n f e d atar*l
cdls,
probably by binding to darr I MHC mdecules
I'runotes ccll-all and dl-matrix adhesioa

CD stands for duster ddifferentiatios as c a d d the CD prateinr was aiginally dctincd as T cell "differcntiatim antigen' rtcogtlizod by multiple m m d m a lantibodies. 'Ihdr identification depended on l a r g e s a l e d l a b u a t i v e studies in whch hundreds of such antibodies, generated in many laborataicr w a ccompared and f a d to a n s i s t of relatively few groups (a'dustas'k each rccogni7jng a dngle dl-surface protein.

Table 22
Gamma-ray-induced DNA fragmentation of thymic T cells" Chmma-radiation dohe to induce 50% f r a w t a t i o n .

Table 23
Dose-eflkcl relationship for l ~ l l n ~ u nfunctionse
In mouse splcnocytcs nfter x-irradlatlon aIL161
t'orcnragc of control

dare

Immundogic paranuicr

PFC reaction
MU3 reaction
Reaction to 6 n A
hK acti\ity
ADCC aaivity
LPS rcaclion
IF'+ m e t i o n
ILZ secretion

0.025 Gy

0.05 Gy

0.075 Gy

0.10 Gy

0.25 Gy

109.6
108.8
19L1
111.8
109.0
129.4
103.8

113.4
133.3 '
254.6
109.0
127.6
171.9
110.8

173.8
1222
529.7
118.8
131.7
169.5
130.3
166.0

61.3
1248
104.9
115.4
150.3
65.9
130.9

84.1
110.7
44.6
120.1
llL7
54.5
873

The i m m u n d o ~ cpanmeters were examined on s p l m ~ d
u rmce &cr u-hdc-body irradiation explcued as a pcrccniap d cmtrdr.
The palr rtimul~tionuas found at 0.5 Gy,u % a c the rdatrw n l u c was 145.0% d cmtrd.

' p c 0 5 oomparcd to rham-irradiated contrd.

p c 0.01 uxnpued to sham-irradiated wnnd.

235

ANNEX B: ADAPTIVE RESPONSES TO RADIATlON IN C E U S AM) ORGANISMS

Table 24
Response of mouse splenic and thymic lymphocytes to whole-body x-irradiation o l 0.075 Cy[L16,L181
Cell cycle progre~sionTime 4ffo i r r d h i o n(dcrysJ~ercenmgein
Go a d GI phases

Percenlage
insphase

Parauagc
inG2andMpher

Shamzoatrd
347

86.0 (0.6)"
82.1 (0.7)
81.9 (0.7)
822 (0.5)

10.8 (0.3)
14.7 (0.7) '14.8 (0.8)'
14.4 (0.6)

3.3 (0.3)
3.1 (0.3)
3.4 (0.2)
3.4 (0.3)*

Percuvage change in rhymocyrc subseu

Tinu 4f1o tradhim(dcr~sj

CDJCDK

CD4+CD8'

CD1'CDB-

CD4CD8'

Shmsmud3
4
7

2W (0.06)a

80.89 (143)80.25 (1.20)
80.68 (1.33)
63.64 (1.06)

1265 (0.98)
11.84 (1.22)
12.14 (0.94)
9.36 (0.73)

4.37 (0.45)
4.37 (0.61)
3.68 (0.33)
3.84 (0.m3.56 (0.29)
3.50 (0.15)
3.16 (0.16)

Table 25Comparison belween frequency or intcrleukin-2-secreting cells from human lymphocyles in inhabitants of a highbackground-radiation area end u control (low-background-iadiation) area in China
F81
I n h a b i r ~of high-background-rrdioh area
(Yany'i~Counry.
~Gmgdong P n k c China)
Age FouP&N

analysed

Frepmcy (%)

20-50 yaur
> 50 years

9
9
7

Total

25.

c20years

inhabit an^^ of lom~bruk~wnd-radiation
area(Enping Counry, China)(Conwd popularion)&N

P b*alu?

andysedFrep-cy

20.11 r 0.66
19.89 + 0.58
20.71 r 032

99917.02 r 0.69
17.17 r 0.79
15.78 r 0.52

A.05
c0.05
<0.01

20.20 r 032

27

16.63 r 0.53

4.01

(%)

UNSCEAR 1994 REPORT

236

Table 26
Analysis of the effect of cigarette smoking on the percentage of lyniphocytic suhscts 111 occupaUonally exposed
persons[TI01
Nwnber of

CD2*

CI>Ji

CD8'

'

(46)

('7n)

(sbl

/INK-1 '(96)

CDJICD8

77.6 r 5.7
n . 3 r 6.7

39.9 2 8.1
39.1 + 8.6

27.2 2 9.5
30.3 .c 8.9

17.7 r 5.1
5.3
18.4 :

1.7
1.4

0.63

0.45

0.03

0.59

0.05

PUSON

Nm-rmolrcrs
Smdtas120
39

p-value (Wilmxcm two-sample test)

Raio

Data w u c p d e d f a all pusolu tested in each calcgay.

Table 27
Influence o l a whole-body pre-irradiation of 0.1 Gy on the growth of primary muririe squamous carcinoma
subjectfd to loceliutd irradiation[M281

Table 28
Change In the percentage o r lunctional subsets of peripheral blood lyniphocytes in non-tfodgkin's lymphoma
patients before and after low-dose whole-body o r half-body irradiation

[TI61
1

Subs& of 1,vmphoryrec

Befme b r d o r i o n (5% :SEJ

A/lc. Lraiiorim (% z S!$

Supprrwr-induccr T (CDt2H4')t I c l p a T (CD4*21143
f i d p a - i n d u c n T (CD4*4B4')Suppram T (CD8'CDll')~ y l d & c T ( ~ ~ 8 ' 1031
A a i v c h d p a h n d u c t r T (CD4*lLA-DW+)
A a i v c supprcucx/cytdoxic T (CDB'HLA-DR')hX raivity (+t)
(CD16*Leu7')hX activity (+) ( C D 1 6 h 7 ' )hX aaivity (+) (CDl6'Lcu7')
Namalizcd ratio T ~ T S

6.9 r 4 3
27.1 z 7.7
Z-7 r 6.8
9.7 z 6.6
21.0 r 8.5
4.1 :1.6
8 3 r 5.6
5.9 r 2.4
14.3 :9.4
21.0 r 9.2

7.5 2 5.7
33.1 7.7
28.7 :7.2
9.3 r 4.9
21.4 2 6.9
6.8 2 2.5
10.8 r 7.4
5.4 r 2.5
14.0 .c 7.6
20.0 :8.0
1.42 2 0.86

1.0

*

237

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANlSMS

Table 29
LDSolMfor mice pretreated with non-lethal doses of 250 kV x rdys
[SSSI
Treatment group~ g acrcning a

Nwnbcr

(4
120
150
240
430
550
670
730
760
820
930
%O

"

LDm13

(GY)

90
40
40
40

6.10 + 0.12
6.42 r 0.11
6.80 + 0.14
6 . n t 0.13
6.58 2 0.27

40

Numberof mice

2 YEof mice40

6.55 2 0.1550

5.96 + 0.15

57

4.53 + 0.23

LDY),*

t .YE

(GY)

* SE

Numberof mice

LDm 2 SE
(GY)

Numberof mice5.90 t 0.13
6.65 2 0.16
6.60 t 0.06

89
40
40

5.67 t 0.10
6.60 0.13
6.40 + 0.10+

58

6.08 0.22
5.69 + 0.19

40
58

5.18 + 0.34
5.18 2 0.30

4.86 + 0.26

45

4.33 -C 0.24

49

YO

6.31 + 0.09

40

6.74 + 0.17

90
40
40

40

6.53

+ 0.1940

4.% 2 034

48

3.2 Gy (500 R)

2.4 Gy (300 R) "0.8 Gy ( I 00 R)

No wealmenr (chnwolsJ

LD,{,

(GY)

=

4.16 2 0.2150

'Ihe mice were pre-treated at age 90 days.
Convezled to S l units: 100 R = 0.8 Gy.

Table 30
Short-term survival and acquired resistance in mice conditioned with low-dose x-irradiation

P I
Numberof miceGroup

Challengerrea~menr

70
60
60
60

0
0.025 (x rays)
0.05 (x rays)
0.10 (x rays)

7.75 (x rays)
7.75 (x rays)
7.75 (x ~ y s )7.75 (x rays)

Control
1
2

JO
40
39
39

0
0.025 (x rays)
0.05 (x rays)
0.10 (x mys)

7.0 (x rays)
7.0 (x rays)
7.0 (x rays)
7.0 (x rays)

Colony-faming u n h

30-&y s u r ~ i v d
Percerllage

Control
1
2
3

3

'

Condilioningtrea~mem
(GY)

14.3
16.7
42.4
40.0

SInrirtualsigm~uance

Avcragemouse r SE

R& toconwolp > 0.1
p c 0.001
p r 0.01+

1.58 0.39
1.98 + 0.50
2.46 2 0.53
2.51 2 0.50

1.3
1.7
1.7

Cnvm at two of age.
Givcn at four month d agc.

Table 31
Mean survival time of LAF1 mice exposed to gamma rays from a 2 2 6 ~ sourceaat a dose rate of about 1 mGyeach day for tlle duration of life

~ 1 9 1
IrradiatedComolsNwnk
of mice
110
116

Male

Female,1tean sunival timet SE (days)

Xumberof miceSa

Mean suniral timer SE ( d q s )683.5 r 14.3
8029 + 16.1

111
120

Male
Fcmalc783.1 + 11.0
820.3 + 17.6

Diflerer~ccbeween
irradinred ad comrol
groupsp Valuecomparing urdiared~ i r hconrrols

99.6
17.4

Nd s~gnificant

0.01

UNSCEAR 1994 REPORT238

Table 32
Survival of IAFI micc nfter lifetime irmdiation[S521
NumberDmc rue(mGy a*')Maleof micein snmple

0.14
1.6-4.9

90
90

40

120

Fcdc

Mean s m i v d rime

Srandard deviarion(days)

Mean sunival rime
r SE (dtiys).FInndnrd dasiarionr SE ( d q s )464 :23
528 + 22501 + 16

222
213
178

662: 17630 r 20
518: I 1

164
193
125

(dwJ

Table 33
Life-span and neoplasms in RF mice exposed to x and ganlnla rays
PI31
A t e a g e doserare

Dwaion.Y&accwnviolod d i mof a p a t w eof mice

Sun it ing
irrdiaion

ICY 6'1

(GY)

(hs)

npamd

I%)

Mean

Numba
of micencrropsiad

hfeon agea~deah(days)

Mire tdh ~ o p l n s n u
Incidmcc
unecropry

Mean agea d d

2 SE (%)

t SE (days)

ifales

0
0.25
0.50
0.75
1.00
1.50
1.48
1.53
1.55
3.00
3.29
3.03
3.08
3.05
3.15

11%)"
1150"
1150"
1150'"
1150'
0.052
0.15
o.n
1150 "
0.05
0.14
0.22
0.3 1
0. r)

30
10
2
63

22
14
10
4

623
20 1
189
188
197
427
98
176
80
241
118
119
79
117
79

100
100
100
100
100
97
100
100
100
99
100
100
100
100

612
198
183
186
194
417
06
175
79
238
118
116
76
109
79

578
565
550
548
494
484
606
58 1
590
408
619
573
538
610
536

52 r 264 r 365 r 471 r 363 r 475 r 267 r 568 r 475 r 581 r 376 r 47224
7225
72 r 463 + 5606% 8568 + 13562 .r 15
571 + 15514 r 14
485 r 8651 :20594 r 13611 + 174 1 5 r 11
638 1 16580% 16552 + 19629 r 20568 + 23

53 7
94
95
95
95
117
92
98
92
124
87
122
107
97
97
97

586
603
599
55 1
578
599
520
576
470
61 1
595
54 '1
564
504
587
575

66 r 270 :5

6 0 8 ~8597 r 13612 + IS549 r 15592 r 14605-8
525 r 20587 z 17473 r 18625 r 14609 r 14549 + 16571 r 14534 r 18597 r 16582 + 17

Fcmala

0
0.25
0.50
1.00
1.W
1-01
200
240
3.00
3.06
3.06
3.13
3.10
3.13
3.05
3.06

"

0.067
0.067
0.067
0.052
0.15
0.067
0.005
O.M7
0.010
0.01 1
0.051
0.15
0.21
0.31
1.02

554
95
95
95

20

99

7

119

516

94
99

300
300
61
21
15
10
3

X rays; all other p u p s exposed to ganima rays.

92
125
89
125
110
99

99
99

100
100
100
100
100
100
48
100
93
92
98
100
100
100
100

n: J
6624
75 r 474 :487 r 479 + 489 3
82 r 479 f 479 r 486 t 38424
80 r 48014+

ANNEX B: ADAPnVE RESPONSES TO RADlATION IN CELLS AND ORGANISMS

Table 34
Influence of dose on induction of nmplastic disuses in fenlale DALlllc mice exposed lo gamma rays
[U141
Dare " (Gy)t\ge-odjrrsted incidence (96 t SE)

Ovarian tmuu

0
0.5
1.0
2.1)

6.4 t 1.4
9.9 r 1.8
21.9 t 26
42.5 t 28

Mammary admoolrcinana

0
0.5
1.0
20

7.6 :0.9
9.0 t 0.9
13.2 r 1.2
13.9 r 1.3

LMg adamcarcinoma

0
0.5
1.0
20

128 r 2 2
14.5 r 1.8
16.5 t 21
21.4 t 26~ P ofC ~~w

Table 35
Survival of male BC3F1 mice after exposure to x rays

tn o 1Dare(GY)

f i m b a of mice

GY)

Mean long-ram sunival= .m (4M i c e irradiated in utem

0.0
0.3
0.9
1.5
21

34'
48 "

61 '
46"

45 "

052 r 247
798 t 180
824 2 212
897 t 173832 r 167

Micc irradiated at 3 munU~ror age

0
0.5
1.0
20
3.0
4.0
5.0
6.0
7.0

M3

w
48

50
50
18

72
95
249

827 r 188
828 r 182
797 t 238
767 r 225
731 :176
792 t 166
701 z 210
718 z 175682 r 222

hlice irradiated a1 19 months of age

0
0.5
1.0
20
3.0
4.0
5.0
6.0
7.0
Numba ci mice at weaning

56
58
46

18
50

SO
72
95
I42

849 r 170865 r 170865 r 141893 r 160
859 125834 r 134
6.51 t 167
662 r 183759 2 184

239

UNSCEAR 1994 REPORT

230

Table 36
Life-span and devclopn~enlof neoplasms in irradiated mice
[S541
/)are

Numbcrof mice

Meon li/e;pw
SE (days)

Mice beari~cgneoplasms

(GY)

(%)

Mean number of neoplasms pernunue SE

Gmtrol

0

198

a928

90.4

1.09 r 0.W

Far

1.9
3.8
5.7

93
81
65

831 r 14 "741 r 18564-21 "

91.4
86.0
70.8

1.30 r 0.08
1.18 r 0.09
0.95 2 Ck08

Neoaatc

1.9
3.8
5.7

85
81
91

784% 1 7 "M 2 r 16"453 r 16 *

90.6
96.3
91.2

1.38 r 0.09
1.49 r 0.08 '1.21 r 0.07

Adult

1.9
3.8
5.7

81
UI

799 r 17 '723~19'
5S6 r 1 9 "

95.1
91.3
91.6

1.44 r Ll08 '1.56 r 0.10 '1.28 r 0.09

Y a g c in l f iof m o u eTable 37
We-span and dl-

83

+

+

incidcnm aRCr a single exparun! of t h - n ~ o n t h s u l dC571H mice lo '''(3gamma-radialion

[M291
Dare

(GY)

Gmtrol
0.25
0.5
1
2
4
6

Ihym~ma

SunivalNlrnbcrof mice

473
242
239
246
217
143
188

Li/e.s~m
2 .YE "

(da~rr)

606 r 20
9 8 r 38
558 r 38
540 2: 36
532 r 38
478 t 43
400 r 32

T d ,mrrcsid for competing risks.

f%J

1.27
1.65
1.26
0
23
U.29
3032

Life-spm
2 SE '(doysJ

420: 204
500 :304
405 z 303
174 r 95
190 r 46
253 r 36.411 1eJioeminr

(96)

20.93
18.18
15.48
15.04
13.82
357
45.68

Liff-span+ SF''

Carcinoma nrtd sarcoma

Incidence(I)

All mulignmcicr

Life-span

lncidencc

r SE '(46)

Lfe-spanr SE '

676 r 78636 r 113
626 r 143593 r 134
584 r 109594 r 129538 2 108

33.19
28.51
23.01
21.95
26.27
39.16
55.32

648 r 53598 r 74599 1 8 4566 r 80543 r 76453 z 67352 r 39(day)

624 2 65581 r 92
582 2 100546 r 93513 r 102
375 +- 72
305 + 37

16.3
14.04
8.79
8.94
14.29
16.08
14.36

ANNEX B: ADAPTlVE USI'ONSES TO RADIATION IN CELLS AND ORGANISMS

24 1

Table 38
Survival of male B6CFI mice after acute, 2 3 - w i ~ kand 59-week exposures to gamma-radiation a[C19,TlS]
Totd doseA ~ w a g cdose rate

ICY)

(Gy we&')Mean survival t SE (dnys)
D e a h from d l coures

D c n h from cancers

Single acute cxpmurc

0
0.9
1.4
21
27

863 r 10834 t 12827 r 16807 r 15727 ? 13
C r ~ ~ ~ t i n u ocxpimureur[or 23 uccks

0857 r 15830: 13806 r 22675 :23
579 :32

0
0.09
0.18
0.42
0.83

21
4.2
9.6
192

893 r 15871 ? 15842 r 21732 r 24622 r 35

Corttinuws cxpmure Tor 59 w e e k

o

0
5.3
10.7
24.6
a

803 r 16768 r 15719 r 16616 r 21

0.09
0.18
0.42

844 r 14829 ? 15750 r 16656 r 20

Mice W a c 107-114 days old at the b c g i ~ i n gd irradiation.

Table 39
Survival of beagle dogs expmed to whole-body gamma-irradiation
IB231

Agc a!a p a r w c

Dose group

(4

IGY)

Controls (all ages) '

0
0.16
0.83
0.16
0.83
0.16
0.83
0.16
0.83
0.83
0.83

8 (in u t a o )28 (in w o o )55 (in urao)
2@an-P~m)
70 (past-pu-rum)
365 @an-pwtum)

T d

Age ofswviwrs bears)
Number in group

Paceniage dcod in
1982

360
120
120
120
120
120
120
120
120
120
240

66
47
51
67
50
63
68
67

1680

63

60

65
73

Meon

Range

12.6
11.5
11.4
11.8
11.7
12.2
12.1
12.2
11.9
12.2
12.5

9.9-15.0
10.6-13.6
10.4-13.4
10.5-13.9
10.7-13.6
113-14.1
11.3-14.2
10.2-13.8
11.2-14.2
113-14.2
11.3-lS.0

UNSCEAR 19% REPORT

242

Table 40
Survival and disease incidence in beagle dogs exposed to x- and gamma-irmdintion~ 4 1
Acute and rrulionated whole-body irrudiution

m=ve

N&

4doHs
Dnse

Frarriart

Inravol bamn
fiacrionr (&sJ

~GY)

n
22
25
20
21
21
20
23

22
23
26
25
21
23
11

4
4
4

0.75
0.75
0.75
1.50
1.50
1.50
3.00

4
4
4
2
2
2
1

2
2
2
1

Incidence 1%)
Non-ncoplmh
disemes

M

W

IWWS

Non-mommcry

lumours

11.6

44

21

35

28
14
7
28
14
7

11.0
10.0
11.3
10.6
9.8
10.7
10.8

46

23

31

28
14
7

10.3
9.3
9.0
9.2
8.5
8.7
10.4

54

17

29

N C ~ C( C ~ W O I S )

0.25
0.25
0.25
0.50
0.50
0.50
1.00

Medi~
past-orpaswe
nvriwl &cars)

28
14
7

Continuous gsmmu-i~rudiution

Numba
4 dogsDarerme(GY 6')

46

None

92
46
46
24
16
13
16
8
4

0.003
0.008
0.019
0.036
0.075
0.013
0.m
0.038
0.054

N&
oldogs
d.wd

12
33
28
42
24
16
13
16
8
4

-

Mean s u n h i d (years)

C a u e of & a ~ h (% incidence in p a r o u h w )Of &ad dogs

Of l i b i n 8 d o ~ s

Sepruaemia

Anaemia

8.4
6.2
8.0
7.3
5.2
1.9
0.8
0.U
0.10
0.M

10.0
9.7
10.0
8.9

0 (0)
0 (0)
0 (0)
0 (0)
O (0)
0 (0)
7 (54)
16 (100)0 (0)8 (100)4 (loo)

0 (0)
0 (0)
1 (Z)
2 (8)
7 (44)
4 (31)
0 (0)
0 (0)
0 (0)

Mydopdif~afiw
disadcr

0 (0)
0 (0)
1(4)
7 (17)
1 1 (46)
7 (44)
2 (12)
0 (0)
0 (0)
0 (0)

ANNM B: ADAPTlVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

243

Table 41
Cancer mortality rates and estiniates of excess relative risk of cancer for a high-background-radlaUonarea anda control (low-background-rndiation) area in China~ 2 9 1
Number of cancer cares in 80,OWperson~'Sire of cancer(0)Iligh-hckgrwnd
a r e a (5.4 n 6 v t i 1 )Leukacmia
Nm-lculuania
Nm-lculucmia
N~topharynx

049
10-79
0-39
10-79

ogophag~

50-89

St-&
Li%u
Htcstinc

20-79
20-79
30-79
20-79
30-79
40-79

31
412
40
94
12
52
113
16

BreastGxGx uteri

Boae
0-89

Olheraa

Age cdjusred rnorrdiry r a t 0 (ID' PY')

Age range
Lo~bockgrwnd
a r m (2 mFv a*')Jligfr-backgroundmeas

Lowbackgramd
are=

32

3.0

3.4

9.8
1.4
5.6
12.5
17
27
0.75
1.4
0.52

10.5
1.5
4.5
13.9
23
3.3
0.59
1.1
0.45

464

29
108
16
47
138
23
35
13
5
3
99

25
7
13
4
95

Evus relativerirk
PO% CI)

4.08 (4.40.0.39)
4.06 (4.16.0.05)
0.44 (4.03.1.17)
4.07 (4.2b.O.l8)
4.16 (4.56.0.56)
0.21 ((4.13.0.68)
4.13 (-0.30.0.07)
4.24 (4.56,0.29)
4.21 (4.49.0.21)
4 3 7 (4.720.34)
2 12 (037,6.96)
0.03 (-0.19.0.31)

Latent paid assumed is 10 ycarr f a solid turnours and 2 years f a lurkaemia.
AdNed with the cunbi~cdpopulation of both high- and low-badrgramd radiation areas.
1,W8,769 person-yearswcre o b d in high-backgrcund radiation area.
995,070 pasm-years wcre obacrvcd in the control Ow-tackgormd) area.

Table 42
Standardized mortality raUm for selected causes of death among shipyard workers in the United States[MI31
Yandurd m a i d *ratio (95% C I )Cause of dea~h

AIIO ~ U S C ~Lsukacmia
Lymphatic and haanopuaic cancas
Mewthelioma
h g canca>5 mSv

4 mSv

Non-nuclear rcrdiaion wcrkcrs

0.76 (0.73,0.79)
0.91 (0.56.1.39)
0.82 (0.6 1.1.08)
5.11 (3.03.8.08)
1.07 (0.94.1.21)

as1 (0.76,0.86)

1.00 (0.97.1.03)
0.97 (0.65.1.39)
1.10 (0.88.1.37)
241 (1.16.4.43)
1.15 (1.02 1.29)

0.42 (0.lL 1.07)
0.53 (0.28,0.9 1)
5.75 (24811.33)
L l l (0.9Q 1.35)

Table 43
Relative risk of mortality for workers who were employed for at least six months at the Hanford nuclear
materials produclion plant in the United States
[GI21

&mnd

"

Rdafibe risk (90% C I )

dare

(64

All cancers

0-9
10-49
50-99
100-199,200

I.(X)
1.04 (0.9,1.2)
1.01 (0.8.1.3)
1.17 (0.9.1.5)
0.93 (0.7.1.3)

All ditenrc; a c q r CMCW

1.00.89 (0.8,l.O)
0.85 (0.7,l.O)
0.83 (0.7,l.O)
0.96 (0.8.1.2)

Leukarmia

Mult+le myeloma

1.0
0.8 (0.4-1.6)
0.3 (0.03-1.6)
1.5 (0.4-4.8)
0.3 (0.02-1.3)

0.4 (0.1.1.3)
4.2 (0.7,19)
5.9 (0.5.41)
21 (21.270)

The rdative risk is the ratio of the risk for thc indicated dose categcry rdative !o that for thc lowcsl dose category (0-9 mSv).
Mainly deaths from cardiovascular dixases, gmito-urinary diseases and diseases of the respiratory Iran.
Exdudhg chranic lymphatic Icukacmia.

1.0

UNSCEAR 1994 REPORT

244

Table 44
Incidence of thyroid cancer aRer administration of '"1[HI81
Acrivjr
mimini-In medial diagnmtic examinations

Fdlowuprrad

1 M l years

S-9 years

15-19 years

yaps

(ME4

O h s dSR

95% CIO b r dSR

95% CI

ObsawedSR

95% CIO b s d

SR

95%CI

d.9
0.9-2.2
>2.2
All

8
5
10
23

1.90
1.22
4.88
222

0.82-3.76
0.40-285234-8.97
1.14-334

2
7
2
11

0.39
1.47
0.85
0.90

3.05-1.42
0.59-3.03
0.10-3.07
0.45-1.62

3
3
3

0.85
0.R
1.44
0.92

0.18-250
0.14-2.10
0.30-4.22
0.42-1.75

1
4
2
7

0.56
1.16
LO8
0.99

(X01-3.10
0.32-296(XU-3.88
0.6-203

9

245

ANNEX B: ADAPTIVE RESPONSES M RADIATION IN CELLS AND ORGANISMS-I1

w

x rays, v.0 v y rrlrri-

HTO,0.05 Gy d-1
HTO for 10 days, then x rays
- B HTO for 20 days, then x rays
HTO for 30 days, then x rays

0

I

0

1

0.5

\

I
1O
.

I

I

1.5

2.0

Irradiated with x rays
Irradiated for 10, 20 and 30 daysin the presence of HTO

DAYS

Figure I.
No evidence of adaptive response in human lymphoblastoid ceUs
conditioned with tritiated water (HTO).

frll

UNSCWR 1994 REPOIIT246

Control Chronic Acute Chronic Chronic
gamma-ray x-ray plus acute plus acuteexposure exposure exposure exposure(observed) (expccaed)

Control

Chronic
gamma-ray
exposure

Acute
x-ray
exposure

Chronic
plus acuteexposure

Figure 11.
Adaptive response of sWn fihmblnst (AG1522) cells.
The cells were exposed to 4 3 5 Gy of chronic gamnia-mdiation and/or 4.25 Gy of acute x-radiation.

(A21

A I

GM218S (normal strain cells)

DoSE (Gy)4

GM2531 (AT-derived cells)

DOSE (GY)

Figure 111.
Colony-fomiing ability of human fibmbl1~5b:normal GhI2185 strain cells
c o r t ~ b r e dwiih ahda-te~an~iectasiaaerived[Gh12531 (AT)] strain cells.
IS261

ANNEX 8: ADAenVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS'"1CONTROL CELLS'" 1

IRRADMED CEUS
after irradiation with 6 Gy

TIME (hour)

Figure 1%'.
Cyclin B protein levels in HeLa cells after in-adinlion in G 2 phase.
PI71

,
6

EXPOSURE 1 0 X RAYSl81

To MMSTIME (hour)

TIME (hour)

Figure V.
Relative levels of induced gadd45 and gaddl53 mRNA in human lyrnphoblast (CMOS-t6) cells
following exposure to x rays or to methyl methane sulphonate (MMS, 100 pg mi-1)

[S261

247

UNSCEAR 1994 REPORT

248

TIME FOLLOWING II~RADIATION(h)Figure VI.
I n c m s e d expmsion of fJ-prolein kinase C in Syrinn hamster embryo cells
at various times following acute exposure to 0.75 Gy fron~x rays.
[W171

z0

1

ENHANCEMENT OF RESPONSE
150

0
lo3

10.~

10-I

18

i

NO ENHANCEMENT OF RESPONSE

0

lo1

DOSE (Gy)Figure VII.
Concanavnlin-A-induced proliferaUon with small doses of whole-body x-irmdiation
leading to enhancement of m p o n s e in rat splenocytes and no enhancen~entof response in rat thymocytes.
[I31

ANNEX B: ADAPnVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

249

--

BONE MARROWSPLEENTHYMUS:&- Cycling alls*-

Noncyciing cellsdI

Figure VIII.
A model of T-cell ontogeny from bone marrow and thymic Tcell precursors
to fully dfierentiated peripheral T cells in terms of WT4 and lyt2 surface antigen expression.

[J7

Figure IX.
Relationship between whole-body dose from x-inadiatlon and plaque-forming capacity in mice.
Antigenic sheep 1-4hlood cells (4 109 were iqjected 10 days after the irradiation,
and assays for plaque-forming spleen cells were performed 4 days later.
[K121

UNSCEAR 1994 REPORT

250

3.0

-

2.5

-

3

Control
1.5 Gy of x rays
0 3.0 Gy of x rays

San~plcs i z : 2 4 micc per pointo...

.: ....

a

,

:

.

.

U

......................... -----0.............................

TlME FOLLOWING INJECTION OF BUIOD CELLS (d)Figure X.
Effects or radiation given two days after iqjection of antigenic sheep red blood cellron the CDJt/CDSt cell ratios in the spleens of C57BVCJ mice.

~131

Figure XI.
Effect or ri~diirtion on mouse splenic cells primed wilh antigenic sheep red blood cells.
Results a r t expressed as the menn per cent change in peak antigen response relative lo the hlghest rcsponder gmup.
[MI81

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

251

C57B116.J Ipr~lprstrain mia:

C57BU6J +/+ strain mice
90

90

Figure MI.
EFTect of low dose on the percentage distribution or mitogen-responsive and mitogen-unresponsive splenic cells
in normal (C57BU6J +/+ strain) and lmn~unologicallydeficient (C57BUG.J Iprnpr s h i n ) mice.

[J 7

m
m
Motecular changes at the T all mcmbrancRciliution of signal mmduaion

T

Ccll acriwlinn and ctir proliferation

Figure XIII.
Proposed scheme or signal transduction In lymphocytes after low-dose radiation.
L26j

252

UNSCEAR 1994 REPOKTNATURAL CELL-MEDIATED
C(TOTOXIcm

No
E x p a r e tocxpaarrc 4.01-1 Gy

Mde

Fandc

MIXED LYMPHOCYTE REACnONNo
ErpoRne to
expaarre 4.01-1 Gy

Mdc

Fmdc

Figure XIV.
Changes in inimunologlcal function in atomic bonib survivors rfslding in the United States.
[El91

ANNEX B: ADAPTIVE RESPONSES TO RADIA710N IN CELLS AND ORGANISMS

80

0

70

@%

3m
u
W
>

E

Radiation uposure: A.5 mSv in three rnonlhs(numba d tat pasons: 118)
Radiation uposure: c0.5 mSv in lhree rnoaihs(numba d test p a s m s : 78)

60

40

30

8 20
10

0

C D ~ ' cells

C D ~ ' cells

C D ~ ' cells

HNK-1' cells

Figure XV.
Percentage of CD~', CD~', C D ~ ' and HNK-1' cells
within the peripheral lymphocytes of persons occupalionaliy exposed to low-dose radiation.
frl01

No cytokines
added

Inrerleukin-2

Interleukin-:!
plus interleukin-4

Interleukin-? plustransforming
growth factor fi

Figure XVI.
Cytotoxicity of while blood cells against tumour cells in Ule presence of cytoklnes.

[sw

253

UNSCEAR 1994 REPORT

254

"1

12

14

16

18

20

26

cdls
00 Gy; heated00.15 Gy; ld treated tlmm cdls
IUDM

cultrol group

12

14

16

18

20

26

Days after inoculation of viable [umour cells

Days after inoculation of viable tumour cells

00 Gy; 1@ trcated tumw cclh

00 Gy; 16 bated turnan cdlr

"10.15 Gy; lo4 ncated rumour alb
Canlrd gwp

12

14

16

18

20

26

0.15 Gy; ld treatcd IUDM cdir
Control group

12

14

16

18

20

26

Days after inoculation of viable rumour cells

Days afier inoculation of viable tumour cells

Figure XVII.

Effect of 0.15 G y upon rerponse of NJ mice to varying numbers of mitoniycin-treated S a l cells.
Groups of 60 mice were exposed to whole-body irradiation o r sham-irradiated arid Inoculated subcutaneouslywith the lndicatcd n u m b e r s of niitoniycin-hated t u m o u r cells. Twenty-one days later, all animals
received 104 untreated S a l cells a n d were followed f o r t u m o u r size.
A control g r o u p did not receive mitomycin-treated cells.
[AJIANNEX B: ADMTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

255

TIME AFTER INITIATION OF ASSAY (d)Figure XVIII.
EfTect of in vim irradialion of donor spleen cells on turnour size.
hlice were inoculated subcutaneously with lo4 SaI cells; after two days they were killed
and their spleens irradiated o r sham-irradiatedand then used in the Wlnn assay technique with an equal number of Sal cells.
[A181

Concanavalin A(5.0 pg ml-l)

Phytohaema lutinioInterleukin-:!

(0.8%) (400 units rnl-1)

hlixcd lymphocyte

reaction(R:S = ,:I)

Figure MX.
I n vitro immune rcsponsc of splenocytes from tumour-bearing mice. The control value of 100% represents theamount of l 3 ~ ] ~ incorporated
drInto the splcnocytes of non-tumour-bearing mice.

PlBl

UNSCEAR 1994 REPORT

?.56

1

0.8

ALL MALIGNANT NEOPLASMS

;

I

I

I

I

0

0.1

0.2

0.3

.,.'...-

I

I

0.4

I
0.5

0.6

I
0.4

1
0.5

1
0.6

DOSE (Sv)

0

I

I

I

0.1

0.2

0.3

DOSE (Sv)1

0.8

MALIGNANT NEOPLASMS
EXCLUDING LUNG CANCER

1

I

I

I

0

0.1

0.2

0.3

+ LEUKAEMIA

I
0.4

I

1

0.5

0.6

DOSE (Sv)
Figure XX.
Relative risk compared with dose lor radialion workers in the United Klngdom.
The solid line shows the mean, the dashed lines W % CIS.
~ 1 5 1

257

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

%

3.0

-

2.5

-

1.3

-

2.0

-

1.2

-

0.9

-

d

d

MORTALITY FROM CANCERS
OTHER THAN LEUKAEMIAMORTALITY FROM LEUKAEMM

c)2
Lkm-quadraric modcl for c0.5 Sv

0

I
0.1

0

I
0.2

I
0.3

(

0.8

0.4

0

Linem modd for <0.5 Sv

I
0.1

DOSE (Sv)

%
a

I
0.2

I
0.3

1
0.4

DOSE (Sv)

MORTAUTY FROM LUNG CANCER

3.0

-

1.6 -

2.5 -

1.4 -

2.0 1.5

INCIDENCE OF THYROID CANCER

-

0.8

-

0.6

1
0
1

Linenr model for cO.5 Sv

0.5 -L i n e modd for cJ.0 Sv

0

0

0.1

0.2

0.3

0.4

0

0.1

DOSE (Sv)

1

0.7

1
0

0.2

0.3

0.4

I

I

0.6

0.7

I
0.8

DOSE (Sv)

MORTAJ-ITY FROM CAUSES OTHER THAN CANCER

I
0.1

I
0.2

I

I

0.3

0.4
DOSE (Sv)I
0.5

Figure XXI.
Relative risk and fitted dwe-response curves for mortality and incidence from various causes.
IS301

ANNEX B: ADAP71VE RESPONSES M RADIAl'ION IN CELLS AND ORGANISMS

25 9

References
Adams, G.E., W.S. Chan and I.J. Stratford. Radiationand other stress responses and their relevance tocancer: some general features. p. 389-397 in: Low
Dose Irradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers, The Netherlands, 1992.
A2 Anam, E.I., S.M. de Toledo, G.P. Raaphorst et al.
Radiation-induced radioresistance in a normal humanskin fibroblast cell line. p. 291-294 in: Low DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers, The Netherlands, 1992.
A3 Adamo, S., C. Caporale, S. Aguamo et al. Proliferating and quiescent cells exhibit different
subcellular distribution of protein kinase C activity.
FEBS Lett. 195: 352-356 (1986).
A4 Andewon, R.E., S. Tokuda, W.L. Williams et al. Low
dose irradiation permits immunization of AIJ micewith subimmunogenic numbers of SaI cells. Br. J.
Cancer 54: 505-509 (1986).
M Allison, J.P. and L.L. Lanier. The structure, hnction
and serology of the T cell antigen receptor complex.
Annu. Rev. Immunol. 5: 503-540 (1987).
A6 Anderson, R.E. and N.L. Warner. Ionizing radiationand the immune response. Adv. Immunol. 24: 215-335(1976).
A7 Anderson, R.E. Effects of low-dm radiation on the
immune response. p. 95-112 in: Biological Effects of
Low Level Exposures to Chemicals and Radiation. (EJ.
Calabrcse, 4.Lewis) Publishers, Bcca Raton, 1992.
A8 Anderson, R.E., J.C. Standifer and S. Tokuda. The
structural and functional assessment of cytotoxic
injury of the immune system with particular reference
to the effect of radiation and cyclophosphamide. Br.
J. Cancer 53: 140-160 (1986).
A9 Anderson, R.E. and I. Lefkovits. In vitro evaluation ofradiation-induced augmentation of the immune
response. Am. J. Pathol. 97: 456-472 (1979).
A10 Aghamohammadi, S.Z. and J.R.K. Savage. A BrdU
pulse double-labelling method for studying adaptive
response. Mutat. Res. 251: 133-143 (1991).
All Akiyama, M., Y. Kusunoki, S. Kyoizumi et al. Studyof the titers of anti-epstein-barr virus antibodies in thesera of atomic bomb survivors. Radiat. Res. 133: 297302 (1993).
A12 Alberts, B., D. Bray, J. Lewis et al. p. 1051 in:Molecular Biology of the Cell. Second edition.
Garland Publishing Co.,New York, 1989.
A13 Andersen, kc.and L.S. Rosenblatt. The effect of wholebody x-irradiation on the median lifespan of female dogs
@eagles). Radiat. Res. 39: 177-200 (1%9).
A14 Anderson, R.L. E. Shiu, G.A. Fisher et al. DNA
damage does not appear to be a (rigger forthermotolerance in mammalian cells. Int. J. Radiat.
Biol. 54: 285-298 (1988).
A15 Applegate, L.A., P. Luscher and R.M. Tyrrell.
Induction of heme oxygenase: a general response tooxidant stress in cultured mammalian cells. Cancer
Res. 51: 974-978 (1991).

A1

A16 Nthaus, F.R., H.E. Kleizkowska, P.L. Panzeter et al.
Molecular mechanisms of low dose adaptation: therole of the poly ADP-ribosylation system. p. 68 in:International Symposium on Biological Effects of
Low Level Exposures to Radiation and Related
Agents (Isbelles '93), Akstracts, Changchun, China,
1993. P o be published in the Chinese Medical
Journal (1994))
A17 Azzam, E.I., G.P. Raaphorst and R.EJ. Mitchel.
Radiation-induced adaptive response for protedion
against miaonucleus formation and neoplastictransformation in C3H 1 0 m mouse embryo cells.
Radiat. Rcs. 138 (1): S28-S31 (1994).
Anderson, R.E., W.L. Williams and S. Tokuda. Effectof low-dose irradiation upon T a l l subsets involvedin the response of primed AIJ mice to SaI cells. Int.
J. Radiat. Biol. 53 (1): 103-118 (1988).
Akiyama, M., O.L. Zhou, Y. Kusunoki et al. Age anddose related alteration of in vitro mixed lymphocyte
culture response of blood lymphocytes from A-bomb
survivors. Radiat. Res. 117: 26-34 (1989).
Brennand, J. and G.P. Margison. Reduction of the
toxicity and mutagenicity of alkylating agents in
mammalian cells harboring the Escherichia coli
alkyltransferase gene. Proc. Natl. Acad. Sci. (USA)83: 6292-6296 (1986).
Boice. J.D., D. Preston. F.G. Davis et al. Frequent
chest x-ray fluoroscopy and breast cancer incidence
among tuberculosis patients in Massachusetts. Radiat.
Res. 125: 214-222 (1991).
Brunet, S. and P.U. Giacomoni. Heat shock mRNA inmouse epidermis after UV irradiation. Mutat. Res.
219: 217-224 (1989).
Burdon, R.1-I., V. Gill and C. Rice-Evans. Cell
proliferation and oxidative stress. Free Radic. Kes.
Commun. 7: 149-159 (1989).
Benjamin, I.J., B. Kr6ger and R.S. Williams.
Activation of the heat shock transcription factor byhypoxia in mammalian cells. Proc. Natl. Acad. Sci.
(USA) 87: 6263-6267 (1990).
Bosi, A. and G. Olivieri. Variability of the adaptive
rcsponse to ionizing radiations in humans. Mutat. Res.
211: 13-17 (1989).
Bauchinger, M., E. Schmid, H. Braselmann et al.
Absence of adaptive response to low-level irradiationfrom tritiated thymidine and X-rays in lymphocytes of
two individuals examined in serial experiments.
Mutat. Res. 227: 103-107 (1988).
Bosi, A., A. Micheli, S. Pietrosanti et al. Effect of pli
shifts on radiosensitivity of human lymphocytes
irradiated in the G2 stage. Mutat. Res. 250: 325-329(1991).
Boerrigter, M.E. DNA strand break metabolism inhuman lymphocytes: a reevaluation. Exp. Cell Rcs.
196: 1-5 (1991).
Billen, D. Spontaneous DNA damage and its significance for the "negligible dose" controversy inradiation protection. Radiat. Res. 124: 242-245 (1990).

260

UNSCEAR1311 Bouzyk, E., 0. Rosick and M. Wojew6dzka. Smalldoses of x-rays make human peripheral blood
lymphocytes less sensitive to induction of chromatidaberrations by a subsequent large dose of thisradiation. Nukleonika 34: 10-12 (1989).
B12 Boothman, D.A., 1. Bouvard and E.N. Hughes. Identification and characterization of x-ray-induced proteinsin human cells. Cancer Res. 49: 2871-2878 (1989).
B13 Boothman, D.A., M. Wang and S.W. Lee. Inductionof tissue-type plasminogen activator by ionizing
radiation in human malignant melanoma cells. Cancer
Res. 51: 5587-5595 (1991).
B14 Boothman, D.A., S. Lee, D.K. Trask et al. X ray
induced proteins and genes in human cells. p. 136 and309-317 in: UCLA Symposia On Molecular andCellular Biology: Ionizing Radiation Damage to DNA.
New series. (S. Wallace and R. Painter, eds.) WilcyLiss, Inc., 1990.
B15 Boothman, D.A., D. Trask and A.B. Pardee. Inhibitionof potentially lethal DNA damage repair in humantumor cells by beta-lapachone, an activator of
topoisomerase 1. Cancer Res. 49: 605-612 (1989).
B16 Bukh, A., H. Martinez-Valdez. S.J. Freedman et al.
The expression of c-fos. c-jun and c-myc genes isregulated by heat shock in human lymphoid cells. J.
Immunol. 144: 4835-4840 (1990).
B17 Brenner, M.B., J. McLcan. D.P. Dialynas et al.
Identification of a putative second T-cell receptor.
Nature 332: 145-149 (1986).
B18 Bloom, E.T., E.L. Korn, M. Takasugi et al. Immune
function in aging atomic bomb survivors residing in
the United States. Radiat. Res. 96: 399-410 (1983).
B19 Bloom, E.T., M. Akiyama, Y. Kusunoki et al.
Delayed effects of low-dose radiation on cellularimmunity in atomic bomb survivors residing in the
United States. Health Phys. 52: 585-591 (1987).
B20 Bloom, E.T., M. Akiyama, E.L. Kom et al.
Immunological responses of aging Japanese A-bomb
survivors. Radiat. Rcs. 116: 343-355 (1988).
B21 Burkart, W., P. Ileusser and Vijayalaxmi. Microdosimetric constraint. on specific adaptation
mechanisms to reduce DNA damage caused byionising radiation. Radiat. Prot. Dosim. 31: 269-274(1990).
B22 Bai, Y. and D. Chcn. Accumulative effect of two low
doses of irradiation in inducing an adaptive response
in human lymphocytes. Mutat. Res. 302: 191-196(1993).
8 2 3 Benjamin, S.A., A.C. Lee, C.M. Angleton et al. Lifespan radiation effects studies in prenatally andpostnatally exposed beagle dogs at Colorado Slate
University. p. 1-13 in: Life-Span Radiation Effects
Studies in Animals: What Can They Tell Us? (R.C.
Thompson and J.A. Mahaffcy, eds.) CONF-830951(1986).
B24 Brach. M.A., R. Hass, M.L. Sherman el al, Ionizing
radiation induces exprcssion and Pd binding activityof the nuclear factor kappa B. J. Clin. Invest. 88: 691695 (1991).
B25 Brooks. B. Immunology and cancer. Biologist 40 (4):162-166 (1993).
I326 Boothman, D A . Role of x-ray-inducible genes andproteins in adaptivc survival responses. p. 14 in:lnternatior~al Symposium on Biological Effects of
Low Level Exposures to Radiation and Related
Agents (Isbelles '93), Abstracts. Changchun, China.
1993. [To be published in the Chinese Medical
Journal (1994)l.
Conter, A., D. Dupouy and H. Planel. Demonstrationof a biological effect of natural ionizing radiation. Int.
J. Radiat. Biol. 43: 421-432 (1983).
Conter, A., D. Dupouy, M. Murat et al. Radiation
stimulation during the early stationary growth phasein Syncchoccus lividus and its correlation with photooxidativc stress occurring before the stationary phase.
Environ. Exp. Bot. 27: 21-28 (1987).
Conter, A., D. Dupouy
and H. Planel. Effects of dose.
.
rate on response of Synechococcus lividus to very low
doses of chronic gamma-radiation: influence of
enzymatic equipment of starting cells. Radiat. Res.
105: 379-386 (1986).
Conter, A. Prc-irradiation of medium induces a
subsequent stimulation or inhibition of growthaccording to the physiological state in synechocouxls
lividus in culture. Radiat. Res. 109: 342-346 (1987).
Conter, A., D. Dupouy, C. Vincent et al. Radiation
stirnulalion during the early stationary growth phasein synechococcus lividus and its correlation withphotooxidative stress occurring before the stationary
phase. Health Phys. 53: 281-286 (1987).
Croute, F., J.P. Soleilhavoup. S. Vidal et al.
Paramecium tetradurelia growth stimulation under
low-level chronic irradiation: investigations on a
possible mechanism. Radiat. Res. 92: 560-567 (1982).
Calabrese, E.J., M.E. McCarthy and E. Kenyon. The
occurrence of chemically induced hormesis. HealthPhys. 52: 531-542 (1987).
Cai, L. and S.Z. Liu. Induction of cytogenetic
adaptive response of somatic and germ cells in vivo
and in vitro by low-dose X-irradiation. Int. J. Radiat.
13iol. 58 (1): 187-194 (1990).
Clerget, M. and B.S. Polla. Erythrophagoqtosis
induces heat shock protein synthesis by humanmonocytcs-maaophages. Proc. Natl. Acad. Sci. (USA)87: 1081-1085 (1990).
Clevers, I I., B. Alarcon, T. Wileman et al. The T cell
rcceptor/CD3 complex: a dynamic protein ensemble.
Annu. Rev. Immunol. 6: 629-662 (1988).
Cooke. M.P. and R.M. Perimutter. Expression of anovel form of the fyn proto-oncogene in hematopoietic cells. New Biol. 1: 66-74 (1989).
Cooke, M.I'., K.M. Abraham, K.A. Forbush el al.
Ikgulation of T cell receptor signalling by a src
hmily protein-tyrosine kinase (p59fyn). Cell 65: 281291 (1991).
CortCs, F.. I. Dominguez, J. Pinero et al. Adaptive
response in human lymphocytes conditioned withhydrogen peroxide before irradiation with x rays.
Mulagenesis 5: 555-557 (1990).
Cortbs, F., I. I>ominguez, S. Matcos et al. Evidence
lor an adaptive response to radiation damage in plant
cells conditioned with x-rays or incorporated tritium.
Int. J. Radiat. Biol. 57: 537-541 (1990).
Cerutti, P.A. and B.F. Trump. Inflammation andoxidativc strcss in carcinogenesis. Cancer Cells 3: 1-7(1991).

ANNEX B: ADAYnVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS
C16 Caldecott, K.W., J.D. Tucker and L.H. Thompson.
Overcorrection of the CIIO EM9 DNA repair mutant
by overexpression of a human XRCCl minigene. Mol.
Cell. Biol. 14 (1): 68-76 (1994).
C17 Cai, L., J. Jiang, B. Wang et al. Induction of an
adaptive response to dominant lethality and tochromosome damage of mouse genn cells by low
dose radiation. Mutat. Res. (1994, in press).
C18 Cronkite, E.P., C.R. Sipe, D.C. Eltholtz et al.
Increased tolerance of mice to lethal x radiation as aresult of previous sublethal exposures. Proc. Soc. Exp.
Biol. Med. 73: 184-186 (1950).
C19 Carnes, B.A., D. Grahn and J.F. Thomson. Doseresponse modeling of life shortening in a retrospective
analysis of the combined data from the JANUS
program at Argonne National Laboratory. Radiat. Res.
119: 39-56 (1989).
CU) Covelli, V., V. Di Majo, B. Bassani et al. Influence ofage on life shortening and tumor indudion after x-ray andneutron irradiation. Radiat. Res. 100: 348-364 (1984).
Q1 (3bemikova,S.V., V.Ya. Gotlib and 1.1. Pelevina. lnfluencc
of low dme radiation on the radimsitivity.
RadiatsionnayaBiologia Radioekologia33: 537-541(1993).
D l Demple, B. and J. tlalbrook. Inducible repair ofoxidative DNA damage in Escherichia coli. Nature
304: 466-468 (1983).
D2 Dacquisto, M.P. and M.C. Major. Acquilad radioresistance. A review of the literature and report of aconfirmatory experiment. Radiat. Res. 10: 118-129 (1959).
D3 Davis, M.M. and PJ. Bjorkman. T-cell antigen
receptor genes and T-cell recognition. Nature 334:
395-402 (1988).
D4 Duvall, E., A.H. Wyllie and R.G. Morris. Macrophage
recognition of cells undergoing programmed cell death(apoptosis). Immunology 56 (2): 351-358 (1985).
D5 Demple, B. Regulation of bacterial oxidative stressgenes. Annu. Rev. Genet. 25: 315-337 (1991).
D6 Dominguez, I., E. Panneerselvam, P. Escalza et al.
Adaptive response to radiation damage in human
lymphocytes conditioned with hydrogen peroxide asmeasured by the cytokinesis-block micronucleus
technique. Mutat. Res. 301: 135-141 (1993).
D7 Devary, Y., R.A. Gottlieb, L.F. Lau et al. Rapid andpreferential activation of the c-jun gene during the
mammalian UV response. Mol. Cell. Biol. 11: 28042811 (1991).
D8 Dixon, FJ. and PJ. McConahey. Enhancement ofantibody formation by whole body x-irradiation. J.
Exp. Med. 117: 833-848 (1963).
F1 Fritz, T.E.. T.M. Seed, D.V. Tolle et al. l a t e effects
of protracted whole-body irradiation of beagles bycobalt-60 gamma rays. p. 116-141 in: Life-Span
Radiation Effects Studies in Animals: What Can They
Tell Us? (R.C. Thompson and J.A. Mahaffey, eds.)
CONF-830951 (1986).
F2 Fan. S., Vijayalaxmi, G. Mindek et al. Adaptive
response to two low doses of X-rays in human blood
lymphocytes. Mutat. Res. 243: 53-56 (1990).
F3 Frankenberg-Schwager, M., D. Frankenberg and R.
Harbich. Exponential or shouldered survival curves
result from repair of DNA double-strand breaks
depending on post-irradiation conditions. Radiat. Res.
114: 54-63 (1988).

F4

261

Frankenberg-Schwager, M. Review of repair kinetics
for DNA damage induced in eukaryotic cells in vitro
by ionizing radiation. Radiother. Oncol. 14: 307-320(1989).
F5 Frankenberg-Schwager, M. and D. Frankenberg. DNA
double-strand breaks: their repair and relationship tocell killing in yeast. Int. J. Radiat. Biol. 58: 569-575(1990).
F6 Fornace, AJ., B. Zmudzka, M.C. Hollander et al.
Induction of mammalian fi-polymerase mRNA by
DNA damaging agents in Chinese hamster ovary oclls.
Mol. Cell. Biol. 9: 851-853 (1989).
F7 Ferris, D.K., A. Harel-Bellan, R.I. Morimoto et al.
Mitogen and lymphokine stimulation of heat shockproteins in T lymphocytes. Proc. Natl. Acad. Sci.
(USA) 85: 3850-3854 (1988).
F8 Feinendegen, L.E., V.P. Bond, J. Vooz et al.
Biochemical and cellular mechanisms of lowdose
radiation effects. Int. J. Radiat. Biol. 53: 23-27 (1988).
F9 Feinendegen, L.E. Radiation risk of tissue late effects,
a net consequence of probabilities of various cellularresponses. Eur. J. Nucl. Med. 18: 740-751 (1991).
F10 Feinendegen, L.E., H. Muhlensiepen, H. Lindberg et
al. Acute and temporary inhibition of thymidine
kinase in mouse bone marrow after lowdose
exposure. Int. J. Radiat. Biol. 45: 205-215 (1984).
F11 Feinendegen. L.E. and fl. Muhlensiepen. In vivo
enzyme control through a strong stationary magnetic
field - the case of thymidine kinase in mouse bonemarrow cells. Int. J. Radiat. Biol. 52: 469-479 (1987).
F12 Feinendegen, L.E. The cell dose concept; potential
applications in radiation protection. Phys. Med. Biol.
35: 597-612 (1990).
F13 Feinendegen, L.E., J. Booz, V.P. Bond et al.
Miaodosimetric approach to the analysis of cell
responses at low dose and dose rate. Radiat. Prot.
Dosim. 13: 299-306 (1985).
F14 Feincndcgen, L.E., 1.1. Muhlensiepen, V.P. Bond et al.
Intraccllular stimulation of intracellular control
mechanisms by low-dose, low-LET irradiation. HealthPhys. 52: 663-669 (1987).
F15 Feinendegen, L.E. and H. Muhlensiepen. Effect ofstatic magnetic field on cellular metabolism in theliving mouse. Endeavour 12: 119-123 (1988).
F16 Fornace, A.J.J., D.W. Nebert, M.C. Hollander et al.
Mammalian genes coordinately regulated by growtharrest signals and DNA-damaging agents. Mol. Cell.
Biol. 9: 4196-4203 (1989).
F17 Fornace, A.J. Jr., 1. Alamo Jr. and M.C. Hollander.
DNA damage-inducible transcripts in mammaliancells. Proc. Natl. Acad. Sci. (USA) 85: 8800-8804(1988).
F18 Farr, S.B. and T. Kogoma. Oxidative stress responses
in Escherichia coli and Salmonella typhimurium.
Micro. Rev. 55 (4): 561-585 (1991).
F19 Fornace, A.J. Mammalian genes induced by radiation:
activation of genes associated with growth control.
Annu. Rev. Genet. 26: 507-526 (1992).
F20 Fang, F. and J.W. Newport. Evidence that the GI-S
and G2-M transitions are controlled by different cdc2
proteins in higher eukaroytes. Cell 66: 731-742(1991).

262

UNSCEAR 1994 REPORTFZ1 Fitzgerald, TJ., S. Henault, M. Sakakeeny et al.
Expression of transfected recombinant oncogenes
increases radiation resistance of clonal hematopoietic
and tibroblast cell lines selectively at clinical low
dose rate. Radiat. Res. 122: 44-52 (1990).
F22 Fritz, T.E., D.V. Tolle and T.M. Seed. The preleukemicsyndrome in radiation-induced myelogenous
leukemia and related myeloproliferative disorders.
Chapter 7. p. 87-100 in: The Preleukemic Syndrome(Hemopoietic Dysplasia). (G.C. Bagby, ed.) CRC
Press. Cleveland, 1985.
F23 Farooqi, Z. and P.C. Kesavan. Low-dose radiationinduced adaptive response in bone marrow cells of
mice. Mutat. Res. 302: 83-89 (1993).
R4 Fritz, G. K Tano, S. Mitra et al. Inducibility of the DNA
repair gene e n d i n g 06-methylguanine-DNA methyltransferase in mammalian &Is by DNA-damaging
mtments. Mol. Cell. Biol. 11: 660-4668(1991).
F25 Fornace, A.J.J., B. Zmudzka, M.C. Hollander et al.
Induction of beta-polymerase mRNA by DNAdamaging agents in Chinese hamster ovary cells. Mol.
Cell. Biol. 9: 851-853 (1989).
G1 Greenberg, J.T., P. Monach, J.H. Chou et al. Positive
control of a global antioxidant defense regulo~lactivated by superoxide-generating agents inEscherichia coli. Proc. Natl. Acad. Sci. (USA) 87:
61816185 (1990).
G2 Gaziev. A.I., L.A. Fomenko, I.K. Kozhanowskaja etal. Radio-adaptive response in mice chronically
exposed to low dose rate of gamma-rays. p. 259-262
in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama. eds.) Elsevier Science Publishers, The
Netherlands, 1992.
G3 Gibson, R., S. Graham, A.M. Lilicnfeld et al.
Irradiation in the epidemiology of leukaemia among
adults. J. Natl. Cancer Inst. 38: 301-311 (1972).
G4 Gould, M.N. and K.1 I. Clifton. Evidence for a uniquein situ component of the repair of radiation damage.
Radiat. Res. 77: 149-155 (1979).
G5 Gentner, N.E. Commentary 3 to Schull and Weiss
Increased definition of abnormal sensitivity using low
dose rate testing. Adv. Radiat. Biol. 16: 293-302(1992).
G6 Greer, W.L. and J.G.Kaplan. Early nuclear events inlymphocyte proliferation. The role of DNA strand
break repair and A D P ribosylation. Exp. Cell Res.
166: 399-415 (1986).
G7 Gee, D.E., J. Griffin, L. Sastre et al. Differentiation of
myeloid cells is accompanied by increased levels of
p60C'S" protein and kinase activity. Proc. Natl. Acad.
Sci. (USA) 83: 5131-5135 (1986).
G8 Gribbin, M.A., G.R. IIowe and J.L. Weeks. A studyof the mortality of AECL employees. V. The second
analysis: mortality during the period 1950-1985.
AECL-10615 (1992).
G9 Girard, F., U. Stransfeld, A. Fernandez et al. Cyclin
A is required for the onset of DNA replication in
mammalian fibroblasts. Cell 67: 1169-1179 (1991).
G I 0 Grant, M.L., R.K. Bruton, P.J. Byrd et al. Sensitivity
to ionising radiation of transformed human cells
containing mutant ras genes. Oncogene 5: 1159-1164(1990).

-

GI1 Gupta, S.S. and S.B. Bhattachajee. Induction of repair
fundiom by hydrogen peroxide in Chinese hamster ells.
Int. J. Radiat. Biol. 53 (6): 935-942 (1988).
G I 2 Gilbert, E.S., E. Omonhundro, J.A. Buchanan et al.
Mortality of workers at the Hanford site: 1945-1986.
Health Phys. 64 (6): 577-590 (1993).
G13 Crahn, D. and T.E. Fritz. Chronic radiation injury
with mice and dogs exposed to external whole-body
irrddiation at the A r g 0 ~ NationaleLaboratory. p. 1431 in: Life-Span Radiation Effects Studies in Animals:
What Can They Tell Us? (R.C. Thompson and J.A.
Mahaffey, eds.) CONF-830951 (1986).
G14 Gilbert, E.S., G.R. Petersen and J.A. Buchanan.
Mortality of workers at the Hanford site, 1945-1981.
Health Phys. 56: 11-25 (1989).
Ill Hasan, N.M., R.B. Cundall and G.E. Adams. Effectsof hypoxia and reoxygenation on the conversion ofxanthine delydrogenase to oxidase in Chinese hamster.
Free Radic. Biol. Mcd. 11: 179-185 (1991).
H2 Hart, R., M. Chou, R. Feuers et al. DNA repair: As
influenced by age, nutrition and exposure to toxic
substances. p. 53-58 in: Biological Effects of Low
Level Exposures to Chemicals and Radiation. (E.J.
Calabrese, ed.) Lewis Publishers, Boca Raton, 1992.
1.13 Ilughes, E.N. and D.A. Boothman. Effect of caffeineon the cxprcssion of a major x ray induced protein inhuman tumor cells. Radiat. Res. 125: 313-317 (1991).
1-14 Haire, R.N., M.S. Peterson and J J . O'Leary. Mitogenactivation induces the enhanced synthesis of two heatshock proteins in human lymphocytes. J. Cell Biol.
106: 883-891 (1988).
H5 Hohn-Elkarirn, K., 11. Muhlensiepen, K.I. Altman etal. Modification of effects on radiation on thymidine
kinase. Int. J. Radiat. Biol. 58: 97-100 (1990).
H6 Haskins, K., R. Kubo, J. White et al. The major
histocompatibility complex-restricted antigen receptor
on T cells. I. Isolation with a monoclonal antibody. J.
Exp. Med. 157: 1149 (1983).
H7 Hsi, E.D., J.N. Siegel, Y. Minami et al. T cell
activation induces rapid tyrosinc phosphorylation of alimited number of cellular substrates. J. Biol. Chem.
264: 10836-10842 (1989).
M8 Ilain, J., R. Jaussi and W. Burkart. Lack of adaptive
response to low doses of ionizing radiation in human
lymphocytes from five different donors. Mutat. Res.
283: 137-144 (1992).
H9 Heindorff, K., R. Rieger, A. Schubert et al. Clastogenic adaptation of plant cells reduction of the yieldof clastogen-induced chromatid aberrations by various
pretreatment procedures. Mutat. Res. 181: 157-171(1987).
1-110 Ileindorff, K., R. Rieger, A. Michaelis et al. Clastogenic adaptation triggered by S-phase-independent
clastogens in Vicia faba. Mutat. Res. 190: 131-135(1987).
HI1 Herrlich, P., H. Ponta and H.J. Rahmsdorf. DNA
damage-induced gene expression: signal transduction
and relation to growth factor signaling. Rev. Physiol.
Hiochem. Pharmacol. 119: 187-223 (1992).
1112 Itallahan, D.E., V.P. Sukhatme, M.L. Sherman et al.
Protein kinase C mediates x-ray inducibility of nuclear
signal transducers EGRl and JUN. Proc. Natl. Acad.
Sci. (USA) 88: 2156-2160 (1991).

-

ANNEX B: ADAPTIVE RESPONSES TO RADIATlON IN CELLS AND ORGANISMS
H13 Hallahan, D.E.. D.R. Spriggs, M.A. Beckett et al.
Increased tumor necrosis factor alpha mRNA after
cellular exposure to ionizing radiation. Proc Natl.
Acad. Sa. (USA) 86: 10104-10107 (1989).
H14 Hallahan. D.E., S. Virudachalam, M.L. Sherman et al.
TNF gene expression is mediated by PKC following
activation by ionizing radiation. Cancer Res. 51:
4565-4569 (1991).
I115 Hollander, M.C.and A.J.J. Fornace. Induction of fos
RNA by DNAdamaging agents. Cancer Res. 49:
1687-1697 (1989).
H16 Holmberg, K, S. Falt, A. Johanssen et al. Clonal
chromosome aberrations and gcnomic inslability in xirradiated human T lymphocyte cultures. Mutat. Res.
286: 321-330 (1993).
H I 7 Holm. L.E. Cancer risks after diagnostic doses of 13'1
with special reference to thyroid cancer. Cancer
Detect. Prev. 15 (1): 27-30 (1991).
H18 Holm, L.E., K.E. Wiklund, G.E. Lundell et al.
Thyroid cancer aRer diagnostic doses of iodine-131:
a retrospecZive cohort study. J. Nall. Cancer Inst. 80:
1132-1138 (1988).
1419 Harvey, E.B., J.D. &ice Jr.. M. Honeyman et al.
Prenatal x-ray exposure and childhood cancer intwins. N. Engl. J. Med. 312: 541-545 (1985).
H20 Hays, S.R., X. Li and B.F. Kimler. Is then: an
adaptive response to radiation in the developing brainof the fetal rat. Radiat. Res. 136: 293-296 (1993).
HZ1 Holm, L.E.. K.E. Wiklund, G.E. Lundell et al. Cancer
risk in population examined with diagnostic doses of
13'l. J. Natl. Cancer Inst. 81: 302-306 (1989).
I1
Imlay. J.A. and S. Linn. DNA damage and oxygen
radical toxicity. Science 240: 1302-1309 (1988).
12
M a y , J A , S.M. Chin and S. Linn. Toxic DNA damage
by hydrogen peroxide through the Fenton reation in vivo
and in vitro. Science 240: 640642 (1988).
13
Ishii, K.. N. Muto and I. Yamamoto. Augmentation in
mitogen-induced proliferation of rat splenocytes bylow dose whole body X-irradiation. Nippon Acta
Radiologica 50 (10): 1262-1267 (1990).
14
Ishii, K., J. Misonoh, Y. Hosoi et al. Effects of lowdose irradiation on proliferative response and IL-1
production of mouse splenocytes. p. 191-194 in: Low
Dose Irradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyarna, eds.)
Elsevier Science Publishers, The Netherlands, 1992.
15
Ikushima, T. Chromosomal response to ionizing
radiation reminiscent of an adaptive response incultured Chinese hamster cells. Mutat. Res. 180: 215221 (1987).
16International Commission on Radiological Protection.
1990 Recommendations of the International Commission
on Radiological Protection. ICRP Publication 60. Annalsof the ICRP 21(1-3). P e r p o n Pms, Oxford, 1991.
Ikushima, T. Radio-adaptive response: a novel
17
chromosomal response in Chinese hamster cells in vitro.
151-161 in: Chromosome Ahcmtions. (G. Obe and
AT. Natarajan, eds.) Springer Verlag, Berlin, 1990.
18
International Symposium on Biological Effects of
LOW Level Exposures to Radiation and Related
Agents (Isbelles '93), Abstracts, CEangchun. China,
1993. [TO be published in the Chinese Medical
Journal (1994)l.

263

Ishihara, H., K. Tsuneoka, A.B. Dimchev et al.
Induction of the exprcssion of the interleukin-1 beta
gene in mouse spleen by ionizing radiation. Radiat.
Res. 133: 321-326 (1993).
Ishii, K., J. Misonoh, Y. Hosoi et al. Acquiredradioresistance on human embryo cells by low dose
x ray irradiation. p. 49 in: International Symposium
on Biological Effects of Low Level Exposures to~ a d i a t i o n and Related Agents (lsbelles '93),
Abstracts, (3hangchun. China, 1993. [To be publishedin the Chinese Medical Journal (1994)].
Ikushima, T. Radio-adaptive response. Involvement of
induction of specific gene expression by low doses ofionising radiation. p. 255-258 in: Low Doselrradiation and ~iological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers, The Netherlands, 1992.
Isakov, N., W. Scholtz and A. Altman. Signaltransduction and intracellular events in T-lymphocyte
activation. Immunol. Today 7: 271-277 (1986).
Jacobsen-Kram, D. and J.R. Williams. Failure toobserve adaptive response to ionizing radiation inmouse bone marrow cells in vivo. Environ. Mol.
Mutagenesis 2 (Suppl. 11): 49-50 (1988).
Jiang. T., D. Chen and C. Wang. Adaptive response
in mouse bone marrow cells to chronic gamma- andbeta-rays. p. B-2 in: International Conference on Low
Dose Irradiation and Biological Defense Mechanisms.
Abstracts, Kyoto, Japan, 1992.
Johnson, M.H. The molecular and cellular basis ofpreimplantation mouse development. Biol. Rev. 56:
463-498 (1981).
Johnstone, A.P. and G.T. Williams. Role of DNA
breaks and ADP-ribosyl transferase activity ineukaryotic differentiation demonstrated in bumanl y mphocytes. Nature 300: 368-370 (1982).
June, C.H., M.C. Fletcher, J.A. Ledbetter et al.
Increases in tyrosine phosphorylation are detectable
before phospholipase c activation after T cell receptor
stimulation. J. Immunol. 144: 1591-1599 (1990).
James, S.J., S.M. Enger, WJ. Peterson et al. Immune
potentiation after fractionated exposure to very low
doses of ionizing radiation and/or caloric restriction in
autoimmune-prdne and normal C57B1/6 mice. Clin.
Immunol. Immunopathol. 55: 427-437 (1990).
James, S J . and T. Makinodan. T cell potentiation innormal and autoimmune-prone mice after extended
exposure to low doses of ionizing radiation and low
caloric restriction. Int. J. Radiat. Biol. 53 (1): 137-152(1988).
Karran. P., T. Lindahl and B. Griffin. Adaptive
response to alkylating agents involves alteration insitu of ~"meth~lguanineresidues in DNA. Nature
280: 76-77 (1979).
Karran, P., T. Hjelmgren and T. Lindahl. Induction of
a DNA glycosylase for N-merhylated purines is par1of the adaptive response to alkylating agents. Nature
296: 770-773 (1982).
Katoaka, Ii., J. liall and P. Karran. Complementationof sensitivity to alkylating-agents in E.Coli andChinese hamster ovary cells by expression of doned
bacterial-DNA repair gene. EMBO J. 5: 3195-3200(1986).

264

K4

UNSCEAR 1994 REPORT

Khandogina,E.K.,G.R.Mutovin,S.V.Zverevaetal.

Adaptive response in irradiated human lymphocytes:
radiobiological and genetical aspeds. Mutat. Res. 251:
181-186 (1991).
K5 Kelsey, KT., A. Memisoglu, D. Frenkel et al. Humanlymphocytes exposed to low doses of X-rays are lesssusceptible to radiation-induced mutagenesis. Mutat.
Res. 263: 197-201 (1991).
K6 Kano, Y. and J.B. Little. Mechanisms of human cell
neoplastic transformation: relationship of specificabnormal clone formation to prolonged lifespan in Xirradiated human diploid fibroblasts. Int. J. Cancer 36:
407-413 (1985).
K7 Kano, Y. and J.B. Little. Mechanisms of human cell
neoplastic transformation: X-ray-induced abnormal
done formation in long-term cultures of human
diploid fibroblaslc. Cancer Res. 45: 2550-2555 (1985).
K8 Kleakowska, H.E. and F.R. Althaus. Adaptive
response of human keratinocytes to low doses of
MNNG. p. 275-278 in: Low Dose Irradiation and~ i o l o ~ i cDefensealMechanisms. (T. Sugahara, L.A.
Sagan and T. Aoyama, eds.) Elsevier Science
Publishers, The Netherlands, 1992.
K9 Keyse, S.M. and R.M. Tyrrell. lnduction of the heme
oxygenase gene in human skin fibroblasts byhydrogen peroxide and UVA (365 mn) radiation:evidence for the involvement of the hydroxyl radial.
Carcinogenesis 11: 787-791 (1989).
K l 0 Koppewl, W.11. and P.L. Bounds. Hormesis. Science
245: 311 (1989).
K11 Kyoizumi, S., M. Akiyama, Y. Hirai et al.
Spontaneous loss and alteration of antigen receptor
expression in mature CD4' T cells. J. Exp. Med. 171:
1981-1999 (1990).
K12 Kennedy, J.C., J.E. Till, L. Simonovitch et al.
IZadiosensitivity of the immune response to shcep red
cells in the mouse, as measured by the hemolytic
plaque methods. J. Immunol. 94: 715-722 (1965).
K13 Kamisaku, H.. T. Sado, P. Pongpiachan et al. Low
dose irradiation does not stimulate in vivo prima
response in specific-pnthogen-free mice. Yokohama
Med. Bull. 42: 3-4 (1992).
K14 Kusunoki, Y., M. Akiyama, S. Kyoizumi et al. Agerelated alteration in the composition of immunommpetent blood cells in atomic bomb survivors. Int.
J. Radiat Biol. 53: 189-198 (1988).
K15 Kendall, G.M., C.R. Muirhead, B.H. MacGibbon el al.
First analysis of the national registry for radiation
workers: occupational exposure to ionising radiationand mortality. NRPB-R251 (1992).
K16 Kyoizumi, S., S. Umeki, M. Akiyama et al. Frequencyof mutant T lymphocytes defective in the expressionof the T-cell antigen receptor gene among radiationexposed people. Mutat. Res. 265: 173-180 (1992).
K17 Kuzin, A.M., L.V. Slozhenikina and T.E. Ushakova.
Effect of gamma-irradiation of isolated biomembranesof rat embryo cells on the activity of adenylate
cyclase. Dokl. Akad. Nauk SSSR 233: 978-980(1977). (in Russian)
K18 Kuzin, A.M., V.P. Ruda and E.G. Mozgovoi. The roleof receptors in radiation hormesis. Radiat. Environ.
Biophys. 30: 259-266 (1991).

Kusen, S.I. and R.S. Stoika. Molecular mechanisms in
the influence of polypeptide growth factors. Nauka
Moscow: 240 (1985).
Koff, A., F. Cross, A. Fisher et al. Human cydin E,
a new cyclin that interacts with two members of the
CDC2 gene family. Cell 66: 1217-1228 (1991).
Kastan, M.R., 0.Onyekwere, D. Sidransky et al.
Participation of p53 protein in the cellular response to
DNA damage. Cancer Res. 51: 6304-6311 (1991).
Kuerbitz, SJ., B.S. Plunkett, W.V. Walsh et al. Wildtype p53 is a cell cycle checkpoint determinantfollowing irradiation. Proc. Natl. Acad. S a . (USA) 89:
7491-7495 (1992).
Kastan, M.B., Q. Zhan, W.S. El-Deiry et al. A
mammalian cell cycle checkpoint pathway utilizing
p53 and GADD45 is defective in ataxia-telangiectasia.
Cell 71: 587-597 (1992).
Kaina, B., 11. Lohrer, M. Karin et al. Overexpressed
human metallothione in IIA gene protects Chinese
hamster ovary cells from killing by alkylating agents.
Proc. Natl. Acad. Sd. 87: 2710-2714 (1990).
Klein, A.K., J.A. Dyck. J.A. Shimizu et al. E k t ofcontinuous, whole-body gamma irradiation uponcanine lymphohematopoietic (CFU-GM, CRI-L)
progenitors and a possible hematopoietic regulatory
population. Radiat. Res. 101: 332-350 (1985).
Karanta, A., E. Konitny, M. Jondal et al. Mitogenstimulation increases c-fos and c-jun protein levels,
AP-1 binding and AP-1 transcriptions activity. Cell
Signal 4: 275-286 (1992).
1-uckcy, T.D. Hormesis with Ionizing Radiation. CRC
Press, B o a Raton, 1:lorida. 1980.
Luckey, T.D. Radiation tlormesis. CRC Press. Boca
Raton, Florida, 1991.
Lavin, M.F. and A.L. Schroeder. Damage-resistant
DNA synthesis in eukaryotes. Mutat. Res. 193: 193206 (1988).
Luckey, 'l'.D. Ionizing radiation promotes protozoan
reproduction. Radiat. Res. 108: 215-221 (1986).
Lindquist, S. The heat shock response. Annu. Rev.
Biochem. 55: 1151-1191 (1986).
Lepock, J.R., K.H. Chcng, 11. Al-Qysi et al. Thermotropic lipid and protein transitions in Chinese hamsterlung cell membranes: relationship to hyperthermic cellkilling. Can. J. Biochem. Cell Biol. 61: 421-427(1983).
Luk, C.K., 1,. Veinot-Ilrebot, E. Tjan et al. Effect oftransient hypoxia on sensitivity to doxorubian in
human and murine cell lines. J. Natl. Cancer Inst. 82:
684-692 (1990).
I,iu, S.Z., L. Cai and S.Q. Sun. lnduction of cytogenetic adaptive response by exposure of rabbits tovery low dose-rate gamma-radiation. Int. J. Radiat.
Biol. 62 (2): 198-190 (1992).
Liu. S.Z.. W.H. Liu and J.B. Sun. Radiation hormesis:
its expression in the immune system. IIealth Phys. 52:
579-583 (1987).
Liu. S.Z., L. Cai and J.B. Sun. Effect of lowdose
radiation in repair of DNA and chromosome damage.
Ada Biol. Ilung. 41 (1-3): 149-157 (1990).
Lindahl, T. and B. Nyberg. Rate of depurination ofnative deoxyribonuclcic acid. Biochemistry 11: 36103621 (1972).

ANNEX B: ADAPnVE RESPONSES TO RADIATION IN CELLS AND ORGANISMS

Leadon, S.A. Production and repair of DNA damage
in mammalian cells. Health Phys. 59: 15-22 (1990).

Lock, R.B. and W.E. Ross. Inhibition of p34cdc2
kinase activity by etoposide or irradiation as amechanism of G2 arrest in Chinese hamster ovary
cells. Cancer Res. 50: 3761-3766 (1990).
Lorenz, E., L.O. Jambson, W.E. Henston et al.
Effects of long-continued total-body gamma
irradiation on mice, guinea pigs and rabbits. 111.
Effects on lifespan, weight, blood picture andcarcinogenesis and the role of the intensity ofradiation. p. 24-148 in: Biological Effects of External
X and Gamma Radiation. National Nuclear Energy
Series IV-22B. (R.E. Zirkle, ed.) McGraw-Hill, New
York, 1954.
Lubinski, J.M., A. Serrano-Williams, J. Chung et al.
Varying susceptibility of thymicT cell subpopulations
to radiation-induced DNA fragmentation. p. 365 in:
Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
Liu, S.Z. Multilevel mechanisms of stimulatory effectof low dose radiation on immunity. p. 225-232
in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
Liu, W.H. and S.Z. Liu. Effect of continuous low
level gamma-irradiation on plaque forming cells inmouse spleen and its mechanism. Chin. J. Radio].
Med. Prot. 7: 336-340 (1987).
Liu, S.Z., Y.C. Zhang and J J . Qi. Low dose ionisingradiation does not cause ratio changes in regulatory T
subsets in mouse spleen. 1. Norman Bethune Univ.
Med. Sci. 18: 209-213 (1992).
Lorenz, E., J.W. fiollcroft, E. Miller et al. Long-term
effects of acute and chronic irradiation in rnice. I.
Survival and tumor incidence following chronic
irradiation of 0.11 r per day. J. Natl. Cancer Inst. 15(4): 1049-1057 (1955).
Laval, F. Pretreatment with oxygen species increases
the resistance of mammalian cells to hydrogen
peroxide and gamma-rays. Mutat. Res. 201: 73-79(1988).
Lindahi, T. Instability and decay of the primarystructure of DNA. Nature 362: 709-715 (1993).
Levine, AJ., J. Momand and C.A. Finlay. The p53
tumour suppressor gene. Nature 351: 543-456 (1991).
Laval, F. Increase of 06-methylguanine-DNA methyltransferase and N3-methyladenine glycosidase RNAtranscripts in rat hepatoma cells treated with DNA
damaging agents. Biochcm. Hiophys. Res. Commun.
176: 1086-1092 (1991).
Lin, C.S., D.A. Goldthwait and D. Samols. Indudonof transcription from the long terminal repeat ofMoleney murine sarcoma provirus by UV-irradiation,
x-irradiation, and phorbor ester. Proc. Natl. Acad. Sci.
(USA) 87: 36-40 (1990).
Lu, C. and S.Z. Liu. Study on the mechanisms ofcytogenetic adaptive response induced by low doseradiation. Chin. Med. J. 105 (4): 277-283 (1992).

265

Liu, X.Z., S. Xu, Y.C. Zhang et al. Signaltransduction in lymphocytes after low dose radiation.
p. 15 in: International Symposium on Biological
Effects of Low Level Exposures to Radiation and
Related Agents (Isbelles '93), Abstracts, Changchun,
China, 1993. [To be published in the Chinese Medical
Journal (1994)l.
Liu, S.Z., Y. Zhao, Z.B. Han et al. Role of changes infunctional status of hypothalamic-pituitary-adrenocortical axis in immunoenhanccment alter low doseradiation. p. 8 3 in: International Symposium on
Biological Effects of Low Level Exposures to
Radiation and Related Agents (Isbelles '93),
Abstracts, Changchun, China, 1993. [To be publishedin the Chinese Medical Journal (1994)l.
Liu, S.Z. and X.K. Li. Induction of proteins inlymphocytes by in vitro and in vivo irradiation withlow dose x- and gamma rays. p. 28 in: International
Symposium on Biological Effects of Low Level Exposures to Radiation and Related Agents (Isbelles '93),
Abstracts, Changchun, China, 1993. [To be publishedin the Chinese Medical Journal (lW4)I.
Li, X.Y., Y J . Li, H.Q. Fu et al. Effects of low doseradiation on pulmonary dissemination of Lewis m11
carcinoma in rnice. p. 103 in: International
Symposium on Biological Effects of Low Level
Exposures to Radiation and Related Agents (Isbelles'93). Abstracts, Changchun, China, 1993. [To be
published in the Chinese Medical Journal (1994))
Miller, R.V. and T.A. Kokjohn. General microbiology
of =A; environmental and evolutionary significance.
Annu. Rev. Microbial. 44: 365-394 (1990).
Morohoshi, F. and N. Munakata. Two classes ofBacillus subtilis mutants deficient in the adaptive
response to simple alkylating agents. Mol. Gen.
Genet. 202: 200-206 (1986).
McClintock, B. The significance of responses of the
genome to challenge. Science 226: 792-801 (1984).
Murphy, B.J., K.R. Laderoute, S.M. Short et al. The
identification of heme oxygenase as a major hypoxic
stress protein in Chinese hamster ovary cells. Br. J.
Cancer 64: 69-73 (1991).
Moquet, J.E., D.C. Lloyd, J.S. Prosser et al. Sisterchromatid exchanges induced by mitomycin C after
exposure of human lymphocytes in Go to a low doseof X-radiation. Mulat. Res. 176: 143-146 (1989).
Mfiller, W.U., C. Streffer and F. Niedereichholz.
Adaptive response in mouse embryos?. Int. J. Radiat.
Biol. 62 (2): 169-175 (1992).
Muschel, RJ., L1.H. Zhang, G. lliakis et al. Effeds ofionizing radiation on cyciin expression in HeLa cells.
Radiat. Res. 132: 153-157 (1992).
MacMahon, B. Prenatal x-ray exposure and childhood
cancer. J. Natl. Cancer Inst. 28: 1173-1191 (1962).
Meyers, M., R.A. Schea, A.E. Pettrowski et al. Roleof x-ray-inducible genes and proteins in adaptive
survival responses. p. 263-266 in: l o w DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers, The Netherlands, 1992.
Matsui, M.S. and V.A. DeLeo. Induction of protein
kinase C activity by ultraviolet radiation.
Carcinogenesis 11: 229-234 (1990).

266

UNSCEAR 1994 REPORTM I 1 Melkonyan, H.. T. Ushakova and S. Umansky.
Chronic irradiation increases the expression of hsp70
genes in mouse tissues. p. 243-246 in: Low DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers. The Netherlands. 1992.
M12 Miihlensiepen, tl., K.I. Ntman and L.E. Feinendegen.
The effect of low dose gamma irradiation andmagnetic field exposure on the caution transport inbone marrow cells of mice (Abstract). 23rd Annual
Meeting. European Society for Radiation Biology,
Dublin, 1990.
M13 Matanoski, G.M. Ilealth effects of low-level radiationin shipyard workers final report, June 1991. DOE DEAC02-79 EV10095 (1991).
M14 Meuer. S.C., K.A. Fitzgerald, R.E. Hussey et al.
Uonotpic structures involved in antigen-specifichuman T cell function: relationship to the T3
molecular complex. J. Exp. Med. 157: 705 (1983).
MI5 Marth, J.D., J.A. Cooper, C.S. King et al. Neoplastictransformation induced by an aaivated lymphocytespecific protein tyrosine kinase (p56kk). Mol. Cell.
Biol. 8: 540-550 (1988).
M16 Margulis. B A , B.D. Zhivotovski. T.V. Pospelova el
al. Patterns of protein synthesis in various cells after
extreme heat shock. Exp. Cell Rcs. 193: 219-222(1991).
M I 7 Makinodan. T.. J.M. Lubinski and T.C. Fong.
Cellular, biochemical and molecular basis of T all
senescence. Arch. Pathol. Lab. Med. 111: 910-914(1987).
M18 Makinodan, T. and S.J. James. T cell potentiation by
low dose ionizing radiation: possible mechanisms.
Health Phys. 59 (1): 29-34 (1990).
M19 Makinodan, T. Cellular and subcellular alterations i nimmune cells induced by chronic, intermittent
exposure in vivo to very low doses of ionizing
radiation (LDR), and its ameliorating effects on
progression of autoimmune disease and mammary
tumor growth. p. 233-237 in: Low Dose Irradiation
and Biological Defense Mechanisms. (T. Sugahara,
L.A. Sagan and T. Aoyama, eds.) Elsevier Science
Publishers, The Netherlands, 1992.
M20 Misonoh. J., M. Yoshida, Y. Okumura et al. Effeds of
lowdose irradiation of x-rays on lUdR incorporation
into mouse tissues. p. 323-326 in: Low DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers. The Netherlands, 1992.
M21 Mindek, G. No adaptive response in G2 phase xirradiated human lymphocytes and adenocarcinoma
cells. Int. J. Radiat. Biol. (1994, in press).
M22 Monson, R.R. and B. MacMahon. Prenatal x-ray
exposure and cancer in children. p. 97-106 in:Radiation Carcinogenesis:
Epidemiology andBiological Significance. (J.D. Boice Jr. and J.F.
Fraumeni Jr., eds.) lii~venPress, New York, 1984.
M23 Murray. A.W. Crcative blocks: cycle checkpoints andfeedback controls. Nature 359: 599-604 (1992).
M24 Mabushime. H., M.E. Ewen, D.K. Strom et al.
Identification and roperties of an atypical catalytic
subunit (p34m~-~$cdd) for mammalian D type G lcylcins. Cell 71: 323-334 (1992).

M25 McKenna, W.G.. M.C. Weiss, B. Endlich et al.
Synergistic effect of the v-myc oncogene with H-ras
on radioresistancc. Cancer Res. 50: 97-102 (1990).
M26 Mole, It.11. Childhood cancer after prenatal exposure
to diagnostic x ray examinations in Britain. Br. J.
Cancer 622: 152-168 (1990).
M27 Meng, Q.Y. and Y.K. Jin. Cross induction of adaptive
response by low level radiation and chemical
mut3gens in mouse germ cells. p. 43 in: International
Symposium on Biological Effects of Low Level
Exposures to Radiation and Related Agents (Isbelles'93), Abstracts. Changchun, China, 1993. [To be
published in the Chinese Medical Journal (1994)l.
M28 Miyamoto, M. and K. Sakamoto. Anti-tumour effectof total body irradiation of low doses in WHTHt
mice. Jpn. J. Canccr Clin. 33 (10): 1211-1220 (1987).
M29 Maisin. J.R., A. Wambersie. G.B. Gerber et al. Lifeshortening and disease incidence in C57B1 mice after
single and fractionated y and highenergy neurron
exposure. Radiat. Rcs. 113: 300-317 (1988).
M30 Makedonov, G.P.. N.I. Alekhina, L.V. Tskhovrebova
et al. Comparison of expression of anticlastogenic
action of interferon and radioadaptive response.
Radiatsionnaya Biologia Radiwkologia 33: 259-264(1993).
N1 Nurse, P. Universal control mechanism regulating
onset of M-phase. Nature 344: 503-508 (1990).
N2 Norburg, C. and P. Nunc. Animal cell cycles and theircontrol. Annu. Rev. Uiochem. 61: 441-470 (1992).
N3 Naegeli, 11. and F.R. Allhaus. Regulation ofpoIy(ADP-ribose) polymerase. Ilislonc-specificadaptations of reaction products. J. Biol. Chem. 266(1 6): 10596-10601 (1991).
N4 Nogami, M., J.T. Iluang, S.J. James' et al. Micechronically exposed to low dose ionizing radiation
possess splenocytes with elevated levels of HSP70
mliNA. IISC70 and 11SP72 and with an increased
capacity to proliferate. Int. J. Radiat. Biol. 63 (6):775-783 (1993).
N5 Nasmyth, K. and T. Ilunt. Dams and sluices. Nature
366: 634-635 (1993).
N6 Neta, R., S. Douches and JJ. Oppmheim. Interleukin-1
is a radioprotedor. J. Immunol. 136 (7): 2483-2485(1986).
0 1 Olsson, M, and T. Lindahl. Repair of alkylated DNA
in Escherichia coli. Methyl group transfer from 06methylguanine to a protein cysteine residue. J. Biol.
Chem. 255: 10569-10571 (1980).
0 2 Olivieri, G., J. Bodycote and S. Wdff. Adaptive responseof human lymphocytes to low concentrations ofradioactive thymidine. Science 223: 594-597 (1984).
0 3 Olivieri, G., A. Bosi. R. Grillo et al. Interadion of low
dose irradiation with sutsequent mutagenic treatment
Studies with human lymphocytes. p. 279-282 in: Low
Dose Irradiation and I3iological Defense Mechanisms.
('r. Sugahard. L.A. Si~gi~nand T. Aoyama, eds.) EIsevier
Science Publishers, The Netherlands, 1992.
0 4 Ohnishi, T., M. lhara and 11. Utsumi. Induced proteinsin hurnan melanomas by gamma-ray. p. 247-249
in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.

ANNEX B: ADAPTIVE RESPONSES TO RADIATION IN CELLS AND ORGANlSMS

Otsu, H., S. Kobayashi, T. Furuse et al. Age and sex
dependence in tumorigenesis in mice by continuous
lowdose-rate gamma-ray whole-body irradiation.
p. 211-216 in: International Conlerence on Radiation
Effects and Protection, Mito, 1992. Japan Atomic
Energy Research Institute, Tokyo, 1992.
Ong, A., W.X. Li and C.C. Ling. Low-dose-rateirradiation of rat embryo cells containing the ha-ras
oncogene. Radiat. Res. 134: 251-255 (1993).
Owens, G.P., W.E. Hahn and J J . Cohen. Identification of mRNA associated with programmed cell
death in immature thymocytes. Mol. Cell. Biol. 11:
4177-4188 (1991).
Preston, D.L., S. Kusumi, M. Tomonaga et al. Cancer
incidence in atomic bomb survivors. Part Ill:leukaemia, lymphoma and multiple myeloma, 195087. RERF TR/24-92 (1992) and Radiat. Res. 137:
S68-S97 (1994).
Planel, H., J.P. Soleilhavoup, R. Tixador et al.
Influence on cell proliferation of background radiation
or exposure to very low, chronic gamma radiation.
Health Phys. 52: 571-578 (1987).
Planel, H., C. Caratero, F. Croute et al. Investigations
on the biological effects of very low doses of ionizing
radiations. p. 13-20 in: Low Dose Irradiation and
Biological Defense Mechanisms. (T. Sugahara, L.A.
Sagan and T. Aoyama, eds.) Elsevier Science
Publishers, The Netherlands, 1992.
Pereira Luis, J.H. and V.L. Povoa. Individual
variability of adaptive response of human lymphocytes
primed with low dose gamma rays. p. 315-317
in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
Pantazis, P., E. Sariban, D. Kufe et al. Induction ofc-sis gene expression and synthesis of plateletderived
growth factor in human myeloid leukaemia cells
during monocytic differentiation. Proc. Natl. Acad.
SQ. (USA) 83: 6455-6459 (1986).
Papathanasiou, M.A., N.C.K. Kerr, J.H. Robbins et al.
Induction by ionizing radiation of the gadd45 gene incultured human cells: lack of mediation by protein
kinase C. Mol. Cell. Biol. 11: 1009-1016 (1991).
Polla, B.S., A.M. llealy, W.C. Wojno et al. Hormone
1 alpha, 25-dihydroxyvitamin D3 modulates heatshock response in monocytes. Am. J. Physiol. 252:
-40-C649 (1987).
Perlmutter, R.M.. J.D. Marth, S.F. Ziegler et al.
Specialized protein tyrosine kinase proto-oncogenes inhematopoietic cells. Biochem. Biophys. Acta 948:245-262 (1988).
Peterson, K.R., N. Ossanna, A.T. Thliveris et al.
Derepression of specific genes promotes DNA repair
and mutagenesis in Escherichia coli. J. Bacterial. 170:
1-4 (1988).
Pilinskaya, M A , S.S. Dibskiy and L.P. Pedan. Modification by dirnatyph of cytogenetic damages in blood
lymphocytes of children exposed to constant low-rateirradiation. Cytology and Genetics 27 (4): 87-90 (1993).
Pines, J. and T. Hunter. Human cyclin A is adeno-virus
EIA-associated protein p60 and behaves differently fromcyclin B. Nature 346: 760-763 (1990).

267

Panozzo, J., D. Bertoncini, D. Miller et al. Modulationof expression of virus-like elements following
exposure of mice to high- and low-LET radiations.
Carcinogenesis 12: 801-804 (1991).
Pape, R. New obsewations and experimental findingson the effect of very small roentgen doses. Radiol.
Austriaca 4: 35-51 (1951).
Radman, M. SOS repair hypotheses. Phenomenology ofan inducible DNA repair which is accompanied bymutagenesis. p. 355-367 in: Molecular Mechanisms for
DNA Repair, Part A. (P. Hanawalt and R.B. Setlow, eds.)
Plenum Publishing Co.,New York (1975).
Russ, S. and G.M. Scott. Biological effects of gamma
radiation (series 11). Br. J. Radiol. 12: 440-441 (1939).
Russ, S. and C.M. Scott. Some biological effects ofcontinuous gamma radiation, with a note onprotection. Br. J. Radiol. 10: 619-628 (1937).
Ruda, V.P. and A.M. Kuzin. Effed of chronic lowlevel gamma-irradiation on the activity of plasma
membrane adenylate cyclase from rat lung tissue.
Radiobiologiya 31: 743-746 (1991).
Ruda, V.P., A.A. Narimanov and A.M. Kuzin. The
motivation of sensitivity of membrane receptors tonatural effectors by low dose gamma-radiation.
p. 327-329 in: Low Dose Irradiation and Biological
Defense Mechanisms. (T. Sugahara, L.A. Sagan and
T. Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
Rieger, R.A., A. Michaelis and H. Nicoloff.
Clastogenic adaptation of the Vicia faba root tip
meristem as affected by various treatment parameters.
Mutat. Res. 140: 99-102 (1984).
Rieger, R., A. Michaelis and S. Takehisa. Low
temperature between conditioning and challenge
treatment prevents the "adaptive response" of Vicia
faba root tip meristem cells. Mutat. Res. 282: 69-72(1992).
Rigaud, 0.. D. Papadopoulo and E. Monstacchi.
Decreased deletion mutation in radioadapted human
lymphoblasts. Radiat. Res. 133: 94-101 (1993).
Ron, D., A.R. Brasier and J.F. Habener. Transcrip
tional regulation of hepatic angiotensinogen gene
expression by the acute-phase response. Mol. Cell.
Endocrinol. 74: 0 7 - C 1 0 4 (1990).
Ron, E., D.L. Preston, K. Mabuchi et al. Cancer
incidence in atomic bomb survivors. Part IV:
Comparison of cancer incidence and mortality. RERF
111/11-93 (1993) and Radiat. Res. 137: S98-S112(1994).
Rust, J.H., R J . Robertson, E.F. Staffeldt et al. Effects
of lifetime periodic gamma-ray exposure on thesurvival and pathology of guinea pigs. p. 217-244 in:Radiation & Ageing, Proceedings of a Colloquium,
Scmmering, Austria. (P.J. Lindop and G.A. Sacher,eds.) Taylor & Francis, London, 1966.
Rosenblatt, L.S., S.A. Book and M. Goldman. Effectsof x-irradiation of young female beagles on life span
and tumor incidence. p. 628645 in: Life-Span
Radiation Effects Studies in Animals: What Can They
Tell Us? (R.C. Thompson and J.A. Mahalfey, eds.)
CONF-830951 (1986).
Sagan, L.A. Special issue on radiation hormesis.
Ilcalth Phys. 52 (5): 517678 (1987).

19N REPORT

Sugahara, T., L.A. Sagan and T. Aoyama (eds.).Low
Dose lrradiation and Biological Defense Mechanisms.
Elsevier, The Nethcrlands, 1992.
Smith-Sonneborn, J. The role of the "stress protein
response" in hormcsis. p. 41-52 in: Biological Effects
of Low Level Exposures to Chemicals and Radiation.
(E.J. Calabrese, ed.) Lewis Publishers, Boca Raton,
1992.
Sekiguchi, M. and Y. Nakabeppu. Adaptive response:
induced synthesis of DNA repair enzymes byalkylating agents. Trcnds Genet. 3 (2): 51-54 (1987).
Samson, L. and J. Cairns. A new pathway for DNA
repair in Escherichia coli. Nature 267: 281-283(1977).
Samson, L., B. Derfler and EA. Waldstein.
Suppression of human DNA alkylation-repair defects
by Escherichia coli DNA-repair genes. Proc. Natl.
Acad. Sci. (USA) 83: 5607-5610 (1986).
Storz, G., L.A. Tartaglia and B.N. Arnes. Transcriptional regulator of oxidative stress-inducible genes:
direct activation by oxidation. Science 248: 189-194(1990).
Shibahara, S., R.M. M6ller and H. Taguchi. Transcriptional control of rat heme oxygenase by heatshock. J. Biol. Chem. 262: 12889-12892 (1987).
Storch, T.G. and G.D. Talley. Oxygen concentration
regulates the proliferative response of humanfibroblasts to serum and growth factors. Exp. Cell
Res. 175: 317-325 (1988).
Sakata, K., T.T. Kwok, BJ. Murphy et al. Hypoxiainduced drug resistance comparison to P-glycoproteinassociated drug resistance. Br. J. Cancer 64: 809-814(1991).
Shen, J.W., J.R. Subjeck, R.B. Lock et al. Depletionof topoisomerase 11 in isolated nuclei during a
glucose-related stress response. Mol. Cell. Riol; 9:3284-3291 (1989).
Shadley, J.D. and S. Wolff. Very low doses of X-rays
can cause human lymphocytes to become lesssusceptible to ionizing radiation. Mutagenesis 2: 95-96(1987).
Shadley, J.D., V. Afzal and S. Wolff. Characterizationof the adaptive response to ionizing radiation induced
by low dmes of x rays to human lymphocytes. Radiat.
Res. 111: 511-517 (1987).
Shadley, J.D. and J.K. Wiencke. Induction of theadaptive response by X-rays is dependent on radiation
intensity. Int. J. Radial. Biol. 56: 107-118 (1989).
Sankaranarayanan, K., A.v. Duyn, M.J. Loos et al.
Adaptive response of human lymphocytes to low-level
radiation from radioisotopes or X-rays. Mutat. Res.
211: 7-12 (1989).
Schmid. E., M. Riiuchinger and U. Nahntedt.
Adaptive response from X-irradiation of human
lymphocytes. Mutagcnesis 4 (2): 87-89 (1989).
Shadley, J.D. and G. Dai. Cytogenetic and survival
adaptive responses in GI phase human lymphocytes.
Mutat. Res. 265: 273-281 (1992).
Sanderson. BJ.S. and A.A. Morley. Exposure ofhuman lymphocytes to ionizing radiation reduces
mutagenesis by subsequenl ionizing radiation. Mutat.
Res. 164: 347-351 (1986).

Shadley, J.D. and G. Dai. Low dose x-ray-induced
cytogenetic adaptivc response in human lymphocytes.
p. 283-286 in: Low Dose Irradiation and Biological
Defense Mechanisms. (T. Sugahara, L.A. Sagan and
T. Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
Semenetc, T.N., O.V. Semina and A S . Saenko.
Adaptive response of colony forming units (CFUS)
alter preirradiation: the condition of manifestation in
exotest. RadiaLsionnaya Biologia Radioekologia 33:
525-528 (1993).
Sagan, L.A.. L.E. Feinendegen and G.B. Gerber(eds.). Low dose radiation and the immune system.
Int. J. Radiat. Biol. 53 (1): 1-200 (1988).
Sengupta, S. and S.B. Bhattacharjee. Effects of lowdose hydrogen peroxide treatment of V79 cells on
killing and mutation by different agents. Mutat. Res.
243: 81-85 (1990).
Savage, J.R.K. and D.G. Papworth. The effect ofvariable G2 duration upon the interpretation of yieldtimc curves of radiation-induced chromatidaberrations. J. Theor. Riol. 38: 17-38 (1973).
Stewart, A., J. Webb and D. Hewitt. A survey ofchildhood malignancies. Br. Med. J. 1: 1495-1508(1958).
Suzuki, M., K. Nakano. K. Suzuki et al. Effect oforays inchronic low dose irradiation of m ~ gamma
human embryo cells. p. 307-310 in: Low DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, ],.A. Sagan and T. Aoyama, eds.)
Elsevier Science Publishers, The Nethcrlands, 1992.
Smith, B.P., K.L. Gi~le, M. Einspenner et al.
Stimulated human fibroblast cell survival1
clonogenicity in response to low doses of ionizing
radiation. p. 299-302 in: Low Dose lrradiation and
Biological Defense Mechanisms. (T. Sugahara, L.A.
Sagan and T. Aoyama, eds.) Elsevier Scienoe
Publishers, The Netherlands. 1992.
Shapiro, R. Damage to DNA caused by hydrolysis.
p. 3-18 in: Chromosome Damage and Repair. (E.
Seeberg and K. Kleepe, eds.) Plenum Press, New
York, 1981.
Studzinski, G.P. Invited review - oncogenes, growth,and the cell cycle: an overview. GI1 Tissue Kinet. 22:405-424 (1989).
Sariban, E., T. Mitchell and D. Kufe. Expression of
the c-fms proto-oncogene during human monocytic
differenliation. Nature 316: 64-66 (1985).
Shimizu, Y., H. Kato. W.J. Schull et al. Doseresponse analysis among atomic-bomb survivors
exposed to low-level radiation. p. 71-74 in: Low DoseIrradiation and Biological Defense Mechanisms.
(T. Sugahara, L.A. Sagan and T. Aoyama, eds.)
Elsevier Science I'ublishers. The Nethcrlands, 1992.
Sciandra, J.J., J.R. Subjeck and C.S. Hughes.
lr~duction of glucose-rcgulatcd proteins during
anaerobic exposure and of heat-shock proteins after
re-oxygcnation. Proc. Natl. Acad. Sci. (USA) 81:
4843-4847 (1984).
Semenetc, T.N., O.V. Semina, A.M. Poverenny et al.
Adaptive rcsponse i n vivo: the reasons of CFU-S
radioresistance increase. Radiatsionnaya Biologia
Radioekologia 33: 812-815 (1993).

ANNEX B: ADAPTIVE RESPONSES TO KADIATION IN CELLS AND ORGANISMS

Singh, S.P. and M.F. Lavin. DNA-binding protein
activated by gamma radiation in human cells. Mol.
Cell. Biol. 10: 5279-5285 (1990).
Sies, H. (ed.). Oxidative Stress. Academic Press,
London, 1985.
Slater, T.F. and K.H. Cheesemann. Free radical
mechanism and tissue injury and mechanism ofprotection. p. 1-14 in: Reactive Oxygen Species in
Chemistry, Biology and Medicine. (A. Quintaniha,ed.) Plenum Press, New York, 1988.
Shortman K., M. Egerton, G.J. Spangrude et al. The
generation and fate of thymocytes. Semin. Immunol.
2: 3-13 (1990).
Schwartz, R.H. A cell culture model for T lymphocyte
clonal energy. Science 248: 1342-1347 (1990).
Samelson, L.E., A.F. Philips, E.T. Loung et al.
Association of the fyn protein tyrosine kinase with the
T cell antigen receptor. Proc. Natl. Acad. Sci. (USA)87: 4358-4362 (1990).
Sado, T., H. Kamisaku, Y. Ikarashi et al. Immediateand long-term effects of radiation on the immune
system of specific-pathogen-free mice. Int. J. Radiat.
Biol. 53: 177-187 (1988).
Sato, K., J.F. Flood and T. Makinodan. Influence ofconditioned psychological stress on immunological=very
in mice exposed to low-dose X irradiation.
Radiat. Res. 98: 381-388 (1984).
Suzuki, K., M. Watanabe and J. Miyoshi. Differencesin effects of oncogenes on resistance to gamma rays,
ultraviolet light, and heat shock. Radiat. Res. 129:
157-162 (1992).
Sato, F., N. Kawashima, K. Fukutsu et al. Influence ofphysical and biological factors on radiation
carcinogenesis: some delayed effects of continuous
irradiations in mice. p. 29-35 in: Annual Report April
1982 - March 1983. National Institute of Radiological
Sciences, Japan (1983).
Stepanyan, N.S., G.F. Krupnova and V. Zhestyanikov.
Reparation of cytogenetical damage in plant cells
upon an unequal fractionation of injurious action. I.
'Treatment by nitrogen mustard. Tsitologiya 25: 958964 (1983). (in (Russian)
Shadley, J.D. and G. Dai. Evidence that the adaptive
response of human lymphocytes to ionizing radiation
sets on lethal damage in nonaberrant cells. Mutat. Res.
301: 171-176 (1993).
\,
Sklar, M.D. The ras oncogenes increase the intrinsic
resistance of NIH 3T3 cells to ionizing radiation.
Science 239: 645-647 (1988).
Sierra-Rivera, E., G.J. Vourhees and M.I.. Freeman.
Gamma irradiation increases hsp-70 in CIIO cells.
Radiat. Res. 135: 40-45 (1993).
S47 Schreck, R., P. Rieber and P.A. Baeuerle. Reactive
oxygen intermediates as apparently widely usedmessengers in the activation of the NF-kappa B
transcription factor and HIV-1. EMRO J. 10: 22472258 (1991).
S48 Sherman, M.L., K. Datta, D.E. Hallahan et al.
Ionizing radiation regulates expression of the c-jun
protooncogene. Proc. Natl. Acad. Sci. (USA) 87:
5663-5666 (1990).

T6

~7

'1'8

T9

269

Sherman, M.L., R. Datta, D.E. Hallahan et al.
Regulation of tumor necrosis fador gene expression
by ionizing radiation in human myeloid leukemia cells
and peripheral blood monocytes. J. Clin. Invest. 87:
1794-1797 (1991).
Smith, K.A. Interleukin 2. Sci. Am. 262 (3): 26-33(1990).
Schmidtke, J.R. and FJ. Dixon. Effects of sublethal
irradiation on the plaque-forming cell response inmice. J. Immunol. 111: 691-697 (1973).
Sacher, G.A. and G. Grahn. Survival of mice under
duration-of-life exposure to gamma rays. I. The
dosage-survival relation and lethality function. J. Natl.
Cancer Inst. 32: 277 (1964).
Sato, F., S. Sasaki and N. Kawashima. Late effects ofwhole- or partial-body x-irradiation on mice. Causesof death. p. 59-70 in: Late Biological Effects of
Ionizing Radiation. Volume 11. 1AEA-SM-2241210.
IAEA, Vienna, 1978.
Sasaki, S. and T. Kasuga. Life shortening andcarcinogenesis in mice irradiated at the perinatal
period with gamma rays. 357-367 in: Life-Span
Radiation Effects Studies in Animals: What Can They
Tell Us? (R.C. Thompson and J.A. Mahaffey, eds.)
CONF-830951 (1986).
Storer, J.H. Radiation resistance with age in normal
and irradiated populations of mice. ~ a d i a t Res.
.
25:
435-459 (1965).
Tabocchini, M.A.. J.B. Little and H.L. Liber.
Mutation induction in human lymphoblasts after
protracted exposure to low doses of tritiated water.
p. 439-445 in: Low Dose Radiation: Biological Basesof Risk Assessment. (K.F. Baverstock and J.W.
Stather, eds.) Taylor and Frances, London, 1989.
Tuschl, I-I., R. Kovac and H. Ntmann. UDS and SCE inlymphocytes of persons occupationally exposed to lowlevels of ionizing radiation. Health Phys. 45: 1-7 (1983).
Tuschl, II., 11. Ntmann, R. Kovac et al. Effeds of
low-dose radiation on repair processes in human
lymphocytes. Radiat. Res. 81: 1-9 (1980).
Thompson Roy. C. Life-span effects of ionizing
radiation in the beagle dog. A summary a m u n t offour decades of research funded by the US
Department of Energy and its predecessor agencies. p.
1-323 in: PNL-6822 UC-408 (1989).
Treisman, R. Identification of a protein-binding sitethat mediates transcriptional response of the c-fos
gene to serum factors. Cell 46: 567-574 (1986).
Taliaferro, W.H.. L.G. Taliaferro and B.N. Jaroslow.
Radiation and immune Mechanisms. Academic Press.
New York, 1964.
~ ~ l i W.H.
~ f and~ ~L.G.
~ ~, ~ l i ~~ f f ~ of ~ f ~radiation on the initial and anamnestic IgM hemolysin
responses in rabbits: antigen injection after x-rays. J.
Immunol. 103: 559-569 (1969).
Taliaferro, W.I.1. and L.G. Taliaferro. Effects ofirradiation on initial and anarnnestic hemolysin
responses in rabbits: antigen injection before x-rays.
J. lmmunol. 104: 1364-1376 (1970).
Troup. G.M. and R.E. hderson. Radiation-induced
augmentation of mitogenic responsiveness in murine
spleen cells. Fed. Proc., Fed. Am. Soc. Exp. Riol. 4:335 (1982).

.~

~

~

UNSCEAR 1994 REPORT

Tuschl, H., R. Kovac and A. Wottawa. T-lymphocyte
subsets in occupationally exposed persons. Int. J.
Radiat. Biol. 58: 651-659 (1990).
Takizawa, Y., J. Yamashita, A. Wakizaka et al.
Background radiation can stimulate the proliferationof mouse-L-5178Y cells. p. 234-236 in: International
Conference on Radiation Effects and Protection, Mito,
1992. Japan Atomic Energy Research Institute, Tokyo,
1992.
Tamura, K., Y. Kanaoka, S. Jinno et al. Cyclin G: a
new mammalian cyclin with homology to fission yeast
Cig 1. Oncogene 8: 2113-2118 (1993).
Thompson, L.H., K.W. Brookman, N.J. Jones et al.
Molecular cloning of the human XRCCI gene, whichcorrects defective DNA strand break repair and sister
chromatid exchange. Mol. Cell. Biol. 12: 6160-6171(1990).
Tomita, Y., S. Hashimoto, S. Sawadi et al. Regulatoryrole for T cell activation. Nihon Univ. J. Med. 32:
207-221 (1990).
Thornson, J.F. and D. Grahn. Life shortening in mice
exposed to fission neutrons and y radiation. Radiat.
Res. 118: 151-160 (1989).
Takai, Y., S. Yamada, K. Nemoto et at. Anti-tumour
effect of low dose total (or half) body irradiation andchanges of the functional subset of peripheral
lymphocytes in non-1,lodgkin's lymphoma patients
after TBI (IIBI). p. 113-116 in: International
Conference on Low Dose Irradiation and Biological
Defense Mechanisms, Abstracts, Kyoto, Japan, 1992.
United Nations. Sources and Effects of Ionizing
Radiation. United Nations Scientific Committee on the
Effects of Atomic Radiation, 1993 Report to theGeneral Assembly, with scientific annexes. United
Nations sales publication E.94.IX.2. United Nations,
New York, 1993.
Upton. A.C., M.L. Randolph, J.W. Conklin et al. Lateeffects of fast neutrons and gamma rays in mice asinfluenced by the dose rate of irradiation: life
shortening. Radiat. Res. 32: 493-509 (1967).
Upton, A.C., M.L. Randolph, J.W. Conklin et al. Lateeffects of fast neutrons and gamma-rays in mice asinfluenced by the dose rate of irradiation: induction ofneoplasia. Radiat. Res. 41: 467-491 (1970).
Ullrich, R.L. and J.B. Storer. Influence of dose, dose
rate and radiation quality on radiation caranogenesis
and life shortening in RFM and BALBIc mice. p. 95113 in: Late Biological Effects of Ionizing Radiation.
Volume 11. IAEA-SM-2241210. IAEA, Vienna, 1978.
Ullrich, R.L. Tumor induction in BALBlc mice after
fractionated or protracted exposures to fissionspectrum neutrons. Radiat. Res. 97: 587-597 (1984).
Vichi, P. and T.R. Tritton. Stimulation of growth inhuman and murine cells by adriamycin. Cancer Res.
49: 2679-2682 (1989).
Vijayalaxmi and W. Burkart. Resistance and crossresistance to chromosome damage in human blood
lymphocytes adaptcd to bleomycin. Mutat. Res. 211:
1-5 (1989).
Vilenchik, MJ. Spontaneous DNA damage and repair.
p. 266-267 in: Mechanisms of DNA Damage andRepair. Biological Centre of the Academy of
Saences, Puschcino, 1971.

Vilenchik, M.M. DNA Instability and Late Radiation
Effect. Energoatomizdat, Moscow, 1987.
V5 von Boehmer, H. The developmental biology of
T lymphocytes. Annu. Rev. Immunol. 6: 309-326(1988).
V6 Veillelte, A., M.A. Bookman, E.M. Horak et al. The
CD4 and CD8 T cell surface antigens are associatedwith the internal membrane tyrosine-protein kinase
p56'Ck. Cell 55: 301-308 (1988).
W1 Wilson, V.L. and P.A. Jones. Inhibition of DNA
methylation by chemical carcinogens in vitro. Cell 32:
239-246 (1983).
W2 Walker, G.C. Inducible DNA repair systems. Annu.
Rev. Uiochem. 54: 425-457 (1985).
W3 Wiencke, J.K., V. Alzal, G. Olivieri et al. Evidence]
adaptive response ofthat the [ 3 ~ thymidine-induced
human lymphocytes to subsequent doses oT X-rays
involves the induction of a chromosomal repair
mechanism. Mutagenesis 1: 375-380 (1986).
W4 Wolff, S., V. Afzal, J.K. Wiencke et al. Humanlyn~phocytes exposed to low doses of ionizing
radiation become refractory to high doses of radiation
as well as chemical mutagens that induce doublestrand breaks in DNA. Int. J. Radiat. Biol. 53: 39-48(1988).
W5 Wojcik, A,, K. Bonk, W.U. Muller et al. Absence ofadaptive response to low doses of X-rays in preimplantation embryos and spleen lymphocytes of an
inbred mouse strain as compared to human peripheral
lymphocytes: a cytogenetic study. Int. J. Radiat. Biol.
62 (2): 177-186 (1992).
W6 Wolff, S. Low-dose exposures and the induction ofadaptation. p. 21-28 in: Low Dose Irradiation and
Biological Defense Mechanisms. (T. Sugahara, L.A.
Sagan and T. Aoyama, 4 s . ) Elsevier Science
Publishers, The Netherlands, 1992.
W7 Wang. Z.Q., S. Saigusa and M.S. Sasaki. Adaptive
response to chromosome damage in cultured human
lymphocytes primed with low doses of X-rays. Mutat.
Res. 246: 179-186 (1991).
W8 Wolff, S.. J.K. Wiencke, V. Afzal et al. The adaptive
response of human lymphocytes to very low doses ofionizing radiation: a case of induced chromosomal
repair with the induction of specific proteins.
p. 446-454 in: Low Dose Radiation: Biological Basesof Risk Assessment. (K.F. Baverstock and J.W.
Slather, eds.) Taylor and Frances, London, 1989.
W9 Wojcik, A. and H. Tuschl. Indications of an adaptive
response in C57BL mice pre-exposed in vivo to low
doses of ionizing radiation. Mutat. Res. 243: 67-73(1990).
W10 Watanabe, M.,M. Suzuki, K. Suzuki et al. Effect ofmultiple radiation with low doses of gamma rays on
growth ability of human embryo cells in vitro. p. 303306 in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
W11 Watanabe, M., M. Suzuki, K. Suzuki et al. Effect ofmultiple irradiation with low doses of gamma-rays onmorphological transformation and growth ability ofhuman embryo cclls in vitro. Int. J. Radiat. Biol. 62(6): 71 1-718 (1992).

V4

ANNEX B: ADAPTIVE RESPONSES TO K A D I A ~ O NINCEU,S AND ORGANISMS

W12 Ward, J.F. Some biological consequences of thespatial distribution of ionizing radiation-produced free
radicals. Radiat. Res. 86: 185-195 (1981).
W13 Ward, J.F. Biochemistry of DNA lesions. Radiat. Res.
104: S103-Slll (1985).
W14 Ward, J.F. DNA damage produced by ionisingradiation in mammalian cells: identies, mechanisms offormation and repairability. Prog. Nudeic Acid Res.
Mol. Biol. 35: 95-125 (1988).
W l 5 Ward, J.F. Response to commentary by D. Rillen.
Radiat. Res. 126: 385-387 (1991).
W16 Woloschak, G.E. and C.M. Chang-Liu. Difrerenlial
modulation of specific gene expression following
high- and low-LET radiations. Radiat. Res. 124: 183187 (1990).
W17 Woloschak, G.E., C.M. Chang-Liu and P. ShearinJones. Regulation of protein kinase C by ionizing
radiation. Cancer Res. 50: 3963-3967 (1990).
W18 Woloschak, G.E. and C.M. Chang-Liu. Effects of lowdose radiation on gene expression in Syrian hamster
embryo cells: comparison of JANUS neutrons andgamma rays. p. 239-242 in: Low Dose Irradiation and
Biological Defense Mechanisms. (T. Sugahara, L.A.
Sagan and T. Aoyama, eds.) Elsevier Science
Publishers, The Netherlands. 1992.
W19 Wilson, R.E. and R.M. Sutherland. Enhanced
synthesis of specific proteins, RNA, and DNA causedby hypoxia and reoxygenation. Int. J. Kadiat. Oncol.
Biol. Phys. 16: 957-961 (1989).
W20 Wyllic, A.Il., J.F.R. Ken and A.R. Currie. Cell death:the significance ofapoptosis. Int. Rev. Cytol. 68: 251306 (1980).
W21 Wyllie, AIL, R.G. Morris, A.L. Smith et al.
Chromatin cleavage in apoptosis: association withcondensed chromatin morphology and dependence onmacromolecular synthesis. J. Pathol. 142: 67-77(1984).
W22 Weiss, A., J. Imboden, K. Hardy et al. The role of
T31antigen receptor complex in T cell activalion.
Annu. Rev. Immunol. 4: 593-619 (1986).
W23 Wojcik, A., K. Bonk and C. Streffer. Indications ofstrain specificity for the induction of adaptive
response to ionizing radiation in mice. p. 311-314 in:
Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L.A. Sagan and T.
Aoyama, eds.) Elsevier Science Publishers, The
Netherlands, 1992.
W24 Walker, G.C. Mutagenesis and inducible responses todeoxyribonucleic acid damage in Eschcrichia coli.
Microbial. Rev. 48: 60-93 (1984).
W25 Weichselbaum. R.R., D.E. Hallahan, V. Sukhatme etal. Biological consequences of gene regulation after
ionizing radiation exposure. J. Natl. Cancer Inst. 83:
480-484 (1991).
W26 Woloschak, G.E., C.M.L. Liu, S.P. Jones et al.
Modulation of gene expression in Syrian hamster
embryo cells rollowing ionizing radiation. Cancer Res.
50: 339-344 (1990).
W27 Wojcik, A., K. Bonk and C, Streffer. Is there an
adaptive response in spleen lymphocytes of C57B1/6
mice as assessed by chromosomal aberrations. Radiat.
Res. 135 (2): 249-256 (1993).

ni

W28 Wang, Z., J.D. Boice Jr., L. Wei et al. Thyroid
nodularity and chromosome aberrations amongwomenin areas of high background radiation in China. J.
Natl. Cancer Inst. 82: 478-485 (1990).
W29 Wei, L. Re-analysis of some dab related lo therelationship between dose and cancer mortality rate in
the high background radiation areas of Yangjiang,
China. p. 1-11 in: Proceedings of Workshop on
Radiological Biology, Medicine and Protection. (Zhao
Ru and Tao Zufan, eds.) China-Japan Medical
Conference, Beijing, 1992.
W30 Wei, L., Y. Zha, Z. Tao et al. Epidemiologicalinvestigation of radiological effects in highbackground radiation areas of Yangjiang, China. J.
Radiat. Res. 31: 119-136 (1990).
X1 Xiong, Y., H. Zhang and D. Beach. D type cyclins
associate with multiple protein kinases and the DNA
replication and repair factor PCNA. Cell 71: 505-514(1992).
Y1 Youngblom, J.H., J.K. Wiencke and S. Wolff.
Inhibition of the adaptive response of human
lymphocytes to very low doses of ionizing radiationby the protein synthesis inhibitor cycloheximide.
Mutat. Res. 227: 257-261 (1989).
Y2 Yu, W.R., M.D. Wang, L. Cai et al. Preexposure ofmice to low-dose or low-dose-rate ionizing radiations
reduces chromosome aberrations by subsequent highdose of radiation or mitomycin C. p. C2-10 in:
International Conference on Low Dose Irradiation and
Biological Defense Mechanisms, Abstracts, Kyoto,
Japan, 1992.
Y3 Yezzi, M.J., E.A. Blakely and C.A. Tobias. Splitdose
recovery and protein synthesis in X-irradiated CHO
cells. Radiat. Res. 114: 281-296 (1988).
Y4 Yamaoka, K.. R. Edamatsu and M. Akitane. Effeds oflow dose x-ray irradiation on old rats - SOD activity,liquid peroxide level and membrane Fluidity. p. 419422
in: Low Dose Irradiation and Biological Defense
Mechanisms. (T. Sugahara, L A Sagan and T. Aoyama,eds.) Elsevier Saence I'ubliskrs, The Nethedands, 1992.
Y5 Yi. PN. and C. Rha. Kinetics of repair in mouse
lymphoma cells in the low dose rate range. p. 431-434
in: l o w Dme Irradiation and Biological Defense
Mechanisms. (T. Sugahara, LA. Sagan and T. Aoyama,eds.) Elsevier Science Publishers, The Netherlands, 1992.
Y6 Yi, P.N., W.S. Stanley and W. Lee. Relationshipbetween mitotic delay and the minimum dose rate ofx irrddiation required to stop cell proliferation. Radiat.
Res. 133: 163-169 (1993).
Y7 Yonezowa, M., J. Misonoh and Y. Hosokawa. Radioresistance acquired after low doses of x-rays in mice.
p. 48 in: International Symposium on Biological
Effects of Low I,evel Exposures to Radiation and
Related Agents (Ishellcs '93). Abstracts. Changchun,
China, 1993. [To be published in the Chinese Medical
Journal (1994)l.
Y8 Yao, J., Y.R. Cha and Z.X. Lin. Effects of long term
low-level radiation on the immune system in humanbeings. p. 64 in: International Symposium on
Biological Effects of Low Level Exposures to
Radiation and Related Agents (Isbelles '93).
Abstracts, Changchun, China. 1993. fTo be publishedin the Chincse Medical Journal (1994)l.

272

23

24

UNSCEAR 1994 REPORT

Yonezawa, M., A. Takeda and J. Misonoh. Acquiredradioresistance after low dose x-irradiation in mice. J,
Radiat. Res. 31: 256-262 (1990).
Zamboglou, N., W. Porschen, H. Miihlensiepen et al.
Low dose effect of ionizing radiation on incorporationof iododeoxyuridine into bone marrow cells. Int. J.
Radiat. Biol. 39: 83-93 (1981).
Zhivotovsky, B.D., K. Hanson, P. Nicotera ct al.
Involvement of protein synthesis and intracellular ca2'changes in the early stages of radiation-induced interphase
death of rat thymocytes. p. 251-254 in: h w Dose
lnadiation and Biological Defense Mhanisms.
p.Sugahara. LA Sagan and T. Aoyama, &.) Elsevier
Science Publishers, The Netherlands. 1992.
Zhivotovsky, B.D., L. Perlaky, k Fonagy et al. Nuclear
protein synthesis in thymocytes of Xirradiated rats. Int.
J. Radiat. Biol. 54: 999-1006 (1988).
Zhang, Q.M.,S. Yoncl and M. Kalo. Multiple
pathways for repair of oxidative DNAdamages causedby x rays and hydrogen perioxide in escherichia coli.
Radiat. Res. 132: 334-338 (1992).

Zhou. P.K., X.Y. Liu, W.Z. Sun et al. Cultured mouse
SIi-1 cells exposed to low dose of gamma-rays
become less susceptible to the induction ofmutagenesis by radiation as well as bleomycin.
Mulagenesis 8 (2): 109-111 (1993).
Zhou, P.K., W.Z. Sun, X.Y. Liu et al. Adaptive
response to mutagenesis induced by low dose y-rays
i n human HL-60 cells and its molecular basis. p. 67
in: International Symposium on Biological Effects of
IAW Level Exposures to Radiation and Related
Agents (Isbclles '93), Abstracts, Changchun, China,
1993. [To be published in the Chinese Medical
Journal (1994)l.
27

Zhang, L.S., N.H. Wang and J.C. Miao. Effect of low
dose radiation on IL-2 production and DNA synthesis
by human lymphocytes. p. 51 in: International
Symposium on Biological Effects of Low Level
Exposures to Radiation and Related Agents (Isbelles'93). Abstracts, Changchun, China, 1993. [TO be
published in the Chinese Medical Journal (1994)l.