RADIATION RESEARCH 174, 870–876 (2010)0033-7587/10 $15.00
g 2010 by Radiation Research Society.
All rights of reproduction in any form reserved.
DOI: 10.1667/RR1847.1

T-Cell Immunosenescence and Inflammatory Response in Atomic
Bomb Survivors
Yoichiro Kusunoki,a,1 Mika Yamaoka,a Yoshiko Kubo,a Tomonori Hayashi,a Fumiyoshi Kasagi,b Evan B. Douplec
and Kei Nakachia
Departments of a Radiobiology/Molecular Epidemiology and b Epidemiology and c Associate Chief of Research, Radiation Effects Research
Foundation, Hiroshima, Japanand 0.14, respectively (1). While the estimated ERR for
noncancer disease death is clearly low, the death toll has
risen to about 32,000, representing approximately 70% of
the total recorded deaths in the cohort (1). Mechanisms forradiation-related cancer, although not totally understood,
are much clearer than those for radiation-related noncancer diseases, about which almost nothing is known. An
interesting hypothesis is that radiation effects on the
immune system may be involved in part in radiationrelated diseases, especially for noncancer diseases.
Advancing age is accompanied by a variety ofalterations in the immune system, many of which willtend to increase the susceptibility of elderly people to awide range of diseases. Thus, for example, age-dependent decreases in T-cell numbers and/or function arealmost certain to lead to increases in vulnerability todisease-causing pathogens as well as to several adverse
manifestations of chronic inflammation. In A-bomb
survivors, dose-dependent increases in morbidity havebeen associated with a variety of inflammatory diseases,
such as chronic liver diseases, thyroid diseases and heartdiseases (2). To gain further insights into the mechanisms of radiation-related noncancer diseases, we havebeen focusing on aging- and radiation-related alterations
in T-cell immunity. In this paper, we first summarize thelong-term effects of A-bomb radiation on the T-cellsystem, including current study results on regulatory T
cells, and then we discuss a possible involvement ofattenuated T-cell immunity in the development ofdiseases frequently observed in A-bomb survivors.

Kusunoki, Y., Yamaoka, M., Kubo, Y., Hayashi, T., Kasagi,F., Douple, E. B. and Nakachi, K. T-Cell Immunosenescenceand Inflammatory Response in Atomic Bomb Survivors. Radiat.
Res. 174, 870–876 (2010).
In this paper we summarize the long-term effects of A-bombradiation on the T-cell system and discuss the possible
involvement of attenuated T-cell immunity in the diseasedevelopment observed in A-bomb survivors. Our previous
observations on such effects include impaired mitogen-dependent
proliferation and IL-2 production, decreases in naive T-cell
populations, and increased proportions of anergic and functionally weak memory CD4 T-cell subsets. In addition, we recently
found a radiation dose-dependent increase in the percentages of
CD25+/CD1272 regulatory T cells in the CD4 T-cell populationof the survivors. All these effects of radiation on T-cell immunity
resemble effects of aging on the immune system, suggesting thationizing radiation might direct the T-cell system toward acompromised phenotype and thereby might contribute to an
enhanced immunosenescence. Furthermore, there are inverse,
significant associations between plasma levels of inflammatory
cytokines and the relative number of naı̈ve CD4 T cells, alsosuggesting that the elevated levels of inflammatory markers
found in A-bomb survivors can be ascribed in part to T-cell
immunosenescence. We suggest that radiation-induced T-cell
immunosenescence may result in activation of inflammatory
responses and may be partly involved in the development ofaging-associated and inflammation-related diseases frequently
observed in A-bomb survivors. g 2010 by Radiation Research Society

INTRODUCTION

Epidemiological studies of A-bomb survivors havesuggested a relationship between radiation dose and themortality or morbidity rates for various noncancer diseases(1, 2). Risk estimates made for the years from 1950 to 1997
were found to be elevated for death from all solid cancers
combined and also for death from all noncancer diseases
combined, with excess relative risks (ERRs) per Gy of 0.47

MATERIALS AND METHODS
Blood Donors
A total of 1,035 study subjects were randomly selected from
Hiroshima participants in the Adult Health Study (AHS) at theRadiation Effects Research Foundation (RERF) (3). For the present
study, blood samples from the subjects were obtained with informed
consent when they participated in the AHS health examination program
between 2006 and 2008. The study protocol has been approved by the
Human Investigation Committee of RERF (the RERF Institutional
Review Board). Cancer prevalence within the study subjects by dose

1 Address for correspondence: Department of Radiobiology,
Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami
Ward, Hiroshima, 732-0815 Japan; e-mail: ykusunok@rerf.or.jp.

870

T-CELL IMMUNOSENESCENCE IN A-BOMB SURVIVORS871

TABLE 1
Characterization of the Study Population
Age (years)b
70–79

,70

80z

Dose (Gy) Male Female Male Female

Male Female Total,0.005a0.005–0.5
0.5–1.0
1.0–4.0
Total

14
22
19
17
72

29
11
18
28
86

26
34
23
32
115

73
62
19
29
183

102
86
41
40
269

97
133
48
32
310

341
348
168
178
1,035

a
Individuals in this dose category were exposed at distances inexcess of 3 km from the hypocenter and hence received doses that areequivalent to zero.
b
Age at the time of the examinations that were conducted between
2006 and 2008.

category was 14% at ,0.005 Gy, 16% at 0.005–0.5 Gy, 22% at 0.5–
1.0 Gy, and 24% at $1.0 Gy and tended to be higher in survivors
exposed to higher doses, in accord with a recent observation in the AHS
population (4). The age-, gender- and radiation dose-specific distributions of the 1,035 study subjects are listed in Table 1. Radiation doses
are based on Dosimetry System 02 (DS02) estimates (5).
Flow Cytometry
Mononuclear cell fractions separated by the Ficoll-Hypaque
gradient technique were analyzed by three-color flow cytometry
using a FACScan flow cytometer (BD Biosciences, San Jose, CA) as
described previously (6). For assessment of regulatory T (Treg) cells,
approximately 100,000 mononuclear cells were stained with Alexa
FluorH 488-labeled CD25 mAb (Serotec Ltd, Oxford, UK), PElabeled anti-CD127 mAb (BD Biosciences), and PerCP-labeled CD4
mAb (BD Biosciences). Analyses of naı̈ve and effector/memory cellsubsets in the CD4 T-cell population involved staining mononuclear
cell fractions with FITC-labeled anti-CD45RA mAb (Beckman
Coulter, Inc., Fullerton, CA), PE-labeled anti-CD62L mAb (BDBiosciences), and PerCP-labeled CD4 mAb.
TNF-a Measurement
Of the 1,035 subjects examined for their T-cell subsets, we selected
69 subjects whose DS02 doses exceeded 1 Gy as well as 86 age- andgender-matched subjects who were exposed to less than 5 mGy andanalyzed their plasma TNF-a levels. Since the sample selection was
originally made for the purpose of examining associations between
inflammatory responses and mutant frequency at the glycophorin A
locus in erythrocytes (4), all subjects were all heterozygous for bloodtype MN at that locus. TNF-a levels were analyzed using a highly
sensitive enzyme-linked immunosorbent assay kit (Quantikine HS,
R&D systems, Minneapolis, MN). The minimum detectable concentration was 0.05 pg/ml.
Data Analysis
Associations of the percentage (Y) of each CD4 T-cell subpopulation with age at time of examination (age), gender (gender) andradiation dose (dose) were analyzed using a multiple regression model(7). This model assumes that the percentage of each T-cell
subpopulation, or level of TNF-a, is related to each variable in an
exponential manner with adjustment for age, gender and otherparameters (V) measured for the same individuals:
log Y ~azb1 |agezb2 |genderzb3 |dosezb4 |V,
where gender is an indicator of female sex, i.e., gender 5 0 for male

FIG. 1. Age- and radiation-associated alterations in the T-cellsystem in humans. Left panel: An outline of aging of the T-cell systemfrom a review by Weng (8). Right panel: Alterations in the T-cellsystems we have observed in association with radiation exposure
among A-bomb survivors (6, 9–12).
and gender 5 1 for female, and dose is radiation dose in grays. The a
is a constant term, and b1, b2, b3 and b4 are regression coefficients forvariables to be estimated. The age term was subtracted by 70 years sothat a corresponds to log-transformed percentage of CD4 T-cell
subset, i.e., the subset percentage is calculated to be ea (5 exponential[a]), for nonirradiated males at 70 years of age. The percentage changeof subset percentage was estimated to be 100(e10b1 – 1) per 10 years
increment of age and 100(eb3 – 1) per 1 Gy radiation dose. All
statistical analyses were carried out using the SAS program (SASInstitute Inc., Cary, NC).

RESULTS AND DISCUSSION

Evidence for T-Cell Immunosenescence from Previous
Studies on A-Bomb Survivors
Age-associated changes in T-cell populations areprimarily characterized as (1) decreases in cell numbers
and functions such as proliferative responses to T-cell
receptor (TCR) stimulation and T-helper function innaı̈ve T-cell populations, (2) increases in memory T-cell
populations, (3) decreased TCR repertoire diversity
along with a reduced antigen recognition, and (4)frequent emergence of an oligoclonally expanded
population of memory T cells (Fig. 1, left panel) (8).
Radiation effects on the human immune system that are
in accordance with the age-associated changes in T-cell
populations are also depicted in Fig. 1 (right panel).
Among A-bomb survivors, we have observed radiationassociated alterations such as (1) decreases in naı̈ve CD4
and CD8 T cells (6, 9–11), (2) increases in memory CD4
and CD8 T cells (6), and (3) decreased repertoire
diversity in memory CD4 T cells (11). We also observed(4) clonal chromosome aberrations of memory T-cellorigin in heavily exposed survivors, suggesting clonal
expansion of memory T cells (12). Thus the effects ofradiation on T-cell immunity mostly resemble the effects
of aging on the immune system.
Although other studies have reported that clonal
expansion of a subset of memory T cells, CD282 or
CD57z, frequently occurred in older unirradiated872

KUSUNOKI ET AL.

FIG. 2. Flow cytometry patterns of regulatory T (Treg) andconventional T (Tconv) cells that were discriminated with CD25
expression levels alone (left panel) or with both CD25 and CD127
levels (right panel) in the peripheral blood CD4 T-cell fractions froma typical A-bomb survivor.

individuals (8, 13), no significant radiation-associatedchange in percentages of such cells in either CD4 (14) or
CD8 (6) T-cell subsets was observed among A-bomb
survivors. To further evaluate the maintenance of T-cell
memory in A-bomb survivors, we recently analyzed
memory CD4 T-cell subsets using HSCA-2 (recognizing
the low-molecular-mass glycoform of CD43), a monoclonal antibody that we established to classify humanmemory T cells (15). We found that functionally weak
(CD43middle) and anergic (CD43low) memory CD4 T-cell
subsets dose-dependently increased among A-bomb survivors, suggesting that attrition of the competent memory
T-cell population is related to radiation exposure (16).
Immunosenescence in the T-cell system may be involved
in long-lasting impairments in T-cell functions among
A-bomb survivors. In fact, our previous observations
indicated that previous radiation exposure dose-dependently induced deleterious effects on T-cell functions in A-bomb
survivors. In vitro T-cell proliferative responses to PHA (17)and alloantigens (18) and the frequency of IL-2-producing
T cells (19) were all found to decrease in association withradiation dose. Also noted were dose-dependent decreases
in the proliferative responses of A-bomb survivors’ T cells
that were exposed to superantigen staphylococcal enterotoxins (10). The superantigen responses correlated well with
the naı̈ve CD4 T cell percentages, suggesting that theimmunosenescence in naı̈ve CD4 T cells that we consistently observed in A-bomb survivors might account in partfor their deficits of T-cell proliferative function (10). In
addition, the other T-cell functions, which were inversely
related to radiation, also tended to decrease in association
with aging. Taken together, there is accumulating evidenceof T-cell immunosenescence being associated with aging
and previous radiation exposure in A-bomb survivors andconsequently leading to diminished functions in theiradaptive immune systems.
Radiation Effects on Regulatory T Cells (Current Study)
CD4z regulatory T (Treg) cells express CD25 andsuppress T-cell activation and function, and their

number increases with age (20). Our previous measurement of Treg, which were identified by their high CD25
expression level, did not find any effect of age orradiation on these cells, probably due to the difficulty inaccurately discriminating Treg from conventional T(Tconv) cells (data not shown). Recently, however, Treg
cells were shown to be clearly identified by their CD25z/
CD1272 phenotype (21, 22), allowing us to make moreaccurate measurements. Figure 2 shows representative
flow cytometry patterns of Treg cells that were identified
by the CD25z phenotype alone and by the CD25z/
CD1272 phenotype in an A-bomb survivor. We could
not find a significant effect of age on Treg cells(Table 2). This is probably due to the advanced agesof our study subjects; all subjects were 60 years old orolder. As for radiation effects, there was a dosedependent increase in the percentages of Treg cells in
the CD4 T-cell population. The same trend wassuggested for the ratio between Treg and Tconv cells.
Those results suggest that A-bomb radiation might
direct T-cell immunity toward suppressor phenotypes inrelation to immunosenescence. It has been demonstrated
that Treg cells have a strong influence in suppressing
pathological immune responses in autoimmune diseases(23). Clinical studies in A-bomb survivors thus far havefound no evidence that supports the idea that there is anincrease in autoimmune diseases (24). Therefore, thecurrent observation for Treg cell counts is not contradictory to the absence of an excess prevalence ofautoimmune diseases in A-bomb survivors.
Radiation Effects on Naı̈ve and Memory CD4 T-Cell
Subsets (Current Study)Naı̈ve and memory T cells are mature T cells that havenot previously experienced antigen encounter and thatmediate recall responses to second and subsequent
exposure to antigens, respectively. Memory T-cell populations are produced by antigen stimulation of naı̈ve T
cells and survive for many years and are classified basedon the expression of other surface markers including
CD62L into central and effector memory T cells andeffector T cells with several differences in their functions,migration capacities and proliferation abilities. Our
previous examinations of the peripheral blood lymphocyte
populations of A-bomb survivors using CD45RO and
CD62L as markers showed decreased percentages of naı̈ve
CD4 and CD8 T cells and increased percentages ofmemory CD8 T-cell subsets in a dose-dependent manner(6). In the present study, we discriminated naı̈ve andmemory CD4 T-cell subsets by using CD45RA and
CD62L as markers and assessed the percentages of these
subsets in the peripheral blood CD4 T-cell population
among A-bomb survivors. We observed a dose-dependent
decrease in the percentage of CD45RAz/CD62Lz (naı̈ve,Tn) cells within the CD4 T-cell population, confirming

873

T-CELL IMMUNOSENESCENCE IN A-BOMB SURVIVORSTABLE 2Age, Gender and Radiation Effects on the Percentages of T-Cell Subpopulations in the Peripheral Blood CD4 T-Cell
Populations among a Total of 1,035 A-Bomb Survivorsa

T-cell subpopulation

Estimated
percentage fornonirradiatedmales at 75 yearsof ageAge (10 years)b

Regulatory T (Treg) andconventional T (Tconv) cells
CD25z/CD127– (Treg)
25.9CD25–/CD127z (Tconv)
Ratio (Treg/Tconv)

6.3
89.7
7.0

1.2 (–1.2, 3.5)e P 5 0.34
– 0.8 (–1.2, –0.5) P 5 0.0001
2.0 (–0.5, 4.6) P 5 0.13

Naı̈ve and memory
CD45RAz/CD62Lz (Tn)
CD45RA–/CD62Lz (Tcm)
CD45RA–/CD62L– (Tem)
CD45RAz/CD62L– (Teff)

25.9
44.5
19.6
0.4

– 18.7 (–23.5, –13.9) P 5 0.0001 5.6 (–2.2, 13.8) P 5 0.16
– 5.6 (–10.9, –0.3) P 5 0.040
0.4 (–1.6, 2.5) P 5 0.68
0.3 (–3.0, 3.7) P 5 0.85
4.5 (2.3, 6.8) P 5 0.0001
17.3 (13.4, 21.2) P 5 0.0001 – 2.1 (–8.5, 4.3) P 5 0.51
2.5 (–1.8, 6.7) P 5 0.26
8.6 (–3.0, 20.2) P 5 0.15
– 22.3 (–42.1, –2.6) P 5 0.036 – 8.0 (–21.1, 5.0) P 5 0.23

Percentage change of T-cell subpopulation percentage per unit
Genderc

Dose (Gy)d–7.3 (–11.7, –5.3) P 5 0.0004 2.7 (0.1, 5.3) P 5 0.044
0.9 (0.3, 1.5) P 5 0.0046– 0.1 (–0.5, 0.3) P 5 0.67
–8.2 (–12.4, –4.0) P 5 0.0002 2.7 (–0.1, 5.5) P 5 0.052

Note. Treg, regulatory T cells; Tconv, conventional T cells; Tn, naı̈ve T cells; Tcm, central memory T cells; Tem; effector memory T cells; Teff,
effector T cells.
aPercentages of CD4 T-cell subpopulations for age, gender and dose were obtained by the multiple regression model, using the following
formula: log (percentage T cells) 5 a z b1 3 age z b2 3 gender z b3 3 dose, where the value showing zero for the percentage of T cells was
replaced with 0.01 when the value was transformed into natural log.
b
Effects of age were estimated for 10 years.
c
Gender 5 0 for male and 5 1 for female.
dEffects of dose were estimated for 1 Gy.
e
95% confidence interval.

our previous findings (Table 2). As for memory T-cell
subsets, the percentage of CD45RA2/CD62Lz (central
memory, Tcm) cells appeared to increase with radiationdose, whereas there was no significant radiation effecton CD45RA2/CD62L2 (effector memory, Tem) or
CD45RAz/CD62L2 (effector, Teff) cells (Table 2). Those
results clearly indicate that radiation exposure generated a
reduction of Tn cell populations but an increase of Tcm
cell populations among A-bomb survivors. Because Treg
cells are known to suppress differentiation of resting naı̈ve
and memory T cells into effector cells (24), we analyzed
the associations between the percentages of Treg cells with
the CD25z/CD1272 phenotype and those of Teff cellswith the CD45RAz/CD62L2 phenotype. A multiple
regression analysis showed an inverse association between Treg and effector cell percentages (r 5 0.14, P 5
0.0001) after adjusting for age, gender and radiation dose.
Although it needs to be determined whether the increasein the proportion of Treg cells is actually responsible for a
suppression of the effector functions of T cells, elevated
Treg cell levels in A-bomb survivors may be partly
involved in the diminished T-cell responsiveness that wehave observed among the survivors.
T-Cell Immunosenescence and Inflammation
A link between alterations in T-cell immunity andelevated inflammation among A-bomb survivors issuggested (24). We found that plasma levels of
inflammatory cytokines such as IL-6, TNF-a and IFNc increased with radiation dose (26). Kim et al. (27)reported that treatment of T-cell-deficient nude andRag1-knockout mice with poly I:C led to a lethal
cytokine storm, whereas similar doses of poly I:C did
not kill wild-type mice, which possess abundant T
lymphocytes. They also showed that T cells, either Tn orTreg, were sufficient to control this cytokine response by
the adoptive transfer of T cells prior to poly I:Ctreatment of Rag1-knockout mice, which resulted indecreased pro-inflammatory cytokine production. Those
results suggest that T cells suppress the cytokine stormthat occurs during the initial innate immune response. In
A-bomb survivors, there were dose-dependent increases
in plasma levels of inflammatory cytokines and CRP,
and such enhanced inflammatory responses might becaused by alterations in the T-cell system of thesurvivors. For example, we found that plasma IL-6
and CRP levels were significantly elevated in thesurvivors with low percentages of peripheral blood
CD4 T cells (26). A similar trend was also apparent in
the survivors with low percentages of Tn (YK and TH,
unpublished observation).
To seek a further link of T-cell immunosenescence toinflammatory responses among A-bomb survivors, in thepresent study we analyzed associations between percentages of T-cell subsets (that we currently examined) andplasma TNF-a levels. TNF-a concentration has alreadybeen measured among a large number of subjects foranother study and purpose; 1.50 pg/ml was estimated fornonirradiated males at 75 years of age, and the effects(percentage increases) of age, gender and radiation dose

874

KUSUNOKI ET AL.

TABLE 3
Partial Correlation Coefficients between TNF-a Levels and Percentages of T-Cell Subsets in the Peripheral Blood
CD4 T-Cell Population
T-cell subset
TNF-a

Treg

Tn

Tcm

Tem

Teff

20.08 (P 5 0.36)

20.20 (P 5 0.014)

0.04 (P 5 0.67)

0.23 (P 5 0.005)

0.12 (P 5 0.15)

Notes. Partial correlation coefficients adjusted for sex, age and radiation dose were calculated after TNF-a levels and percentages of T-cell
subsets were naturally log-transformed. Each P value in parentheses is a significant level of partial correlation coefficient between natural logtransformed percentage of the T-cell subset and the log-transformed of TNF-a level. The value showing zero for the percentage of T cells was
replaced with 0.01 when the value was transformed into natural log. Treg, regulatory T cells; Tn, naı̈ve T cells; Tcm, central memory T cells; Tem;
effector memory T cells; Teff, effector T cells.

on TNF-a concentration were 15% for 10 years, 15% forfemales relative to males, and 7% for 1 Gy, respectively(28). In this study, we remeasured the TNF-a concentration with a subset (155 survivors) of the current study
subjects, whose T-cell data are available in Table 2, andwe used these data (1.14 pg/ml being estimated fornonirradiated males at 75 years of age) for the calculationof partial correlation coefficients in Table 3. Plasma
TNF-a levels were inversely associated with the percentages of Tn but not Treg cells, suggesting an involvementof Tn but not Treg cells in suppression of innate
inflammatory responses manifested by increased TNF-alevels (Table 3). This may explain why we observed longlasting inflammatory responses despite an increase in therelative number of immunosuppressive Treg cells in Abomb survivors. It was also noted that plasma TNF-alevels were positively associated with the percentage of
Tem cells (Table 3). There was a negative correlation
between percentages of Tn and Tem cells (r 5 20.71, P 5
0.0001) but not between those of Treg and Tem cells (r 50.05, P 5 0.13). Thus T-cell immunosenescence manifested by a reduction in the relative number of Tn cells
might be linked to the development and/or expansion of
Tem cells, involving enhanced inflammatory responses.
Implications of T-Cell Immunosenescence in Disease
Development among A-Bomb Survivors
We found previously that the CD4 T-cell percentages
were significantly lower in survivors with a history of
myocardial infarction (MI) than in survivors with nosuch history (28). We also noted that the T cells ofsurvivors with a history of MI tended to be poor
responders to several superantigens of S. aureus toxins
and that these same individuals had proportionallyfewer naı̈ve CD4 T cells than survivors with no MI
history (10). As suggested for a link between alterations
in T-cell immunity and inflammation among A-bomb
survivors, both IL-6 and CRP levels were significantly
higher in survivors with a history of MI than in those
without such a history (26). We thus believe that the Tcell immunosenescence associated with inflammatory
reactions will prove to be a cause of increased risk ofcardiovascular disease among A-bomb survivors, inmuch the same way as seen in other epidemiologicalstudies of unirradiated individuals (29–31). However,
because it is still possible that the disease itself or somemedication might be responsible for such immunosenescence, prospective studies are needed to provide
definitive information on the causal link between T-cell
immunosenescence and inflammatory diseases.
Noncancer diseases frequently observed in A-bomb
survivors include circulatory, respiratory and digestive
diseases, especially cardiovascular disease, pneumonia
and liver disease (1, 2). One possible explanation
involves the failure of aging immune systems to control
microbial infections, since infections might lead tochronic inflammation and hence to increased susceptibility to such noncancer diseases in heavily exposed
survivors, resulting from unregulated and hence longlasting inflammatory responses. In A-bomb survivors,
however, no significant long-term effects of radiation on
the antimicrobial functions of blood monocytes or
granulocytes (e.g., phagocytosis, in vitro migration,etc.) have been noted (32). There is a growing interestin the role of pathogen recognition molecules, such as
Toll-like receptors (TLRs), in the pathogenesis ofchronic inflammatory diseases: TLRs play a key rolein the host defense against exposure to microbial
pathogens and also in the development and progressionof atherosclerotic lesions (33, 34). It may be importantand possible to conduct an integrated and systematic
examination of the A-bomb survivors’ innate immune
systems in the future, including the analyses of TLRmediated signaling as well as interaction of the signaling
with T-cell immunity.
Conclusions and Perspectives
In summary, A-bomb radiation may have induced Tcell immunosenescence, resulting in attenuation of Tcell-mediated immunity. Such decrements in the T-cellsystem may cause chronic inflammation and in turn may
be partly responsible for cardiovascular disease andother aging-associated diseases of importance. Although
there is accumulating evidence of T-cell immunosenescence among A-bomb survivors, how ionizing radiation
causes T-cell immunosenescence and how radiation-

T-CELL IMMUNOSENESCENCE IN A-BOMB SURVIVORS

induced T-cell immunosenescence interacts with ordinary aging remain to be explained. Mechanistic approaches using appropriate animal models will benecessary to depict a complete picture of radiobiologicalinvolvements in host immunological aging. Longitudinal
analyses of the changes in the various immunologicalparameters may provide a suitable vehicle for a better
understanding of the interaction between radiationrelated and aging-associated immunological changes
and for exploring causal relationships between these
immunological changes and various noncancer diseases
in A-bomb survivors.
ACKNOWLEDGMENTS
The authors thank Ms. Mika Yonezawa for her excellent assistancein the data analyses. The Radiation Effects Research Foundation(RERF), Hiroshima and Nagasaki, is a private nonprofit foundation
funded by the Japanese Ministry of Health, Labour and Welfare(MHLW) and the United States Department of Energy (DOE), thelatter in part through the National Academy of Sciences. Thispublication was based on RERF Research Protocols RP 1-93 and RP
4-02 and supported in part by Grants-in-Aid for Scientific Researchfrom Japan’s Ministry of Education, Culture, Sports, Science, andTechnology and MHLW.
Received: April 1, 2009; accepted: December 6, 2009; published online:
September 10, 2010

REFERENCES
1. D. L. Preston, Y. Shimizu, D. A. Pierce, A. Suyama and K.
Mabuchi, Studies of mortality of atomic bomb survivors. Report
13: Solid cancer and noncancer disease mortality: 1950–1997.
Radiat. Res. 160, 381–407 (2003).
2. M. Yamada, F. L. Wong, S. Fujiwara, M. Akahoshi and G.
Suzuki, Noncancer disease incidence in atomic bomb survivors,
1958–1998. Radiat. Res. 161, 622–632 (2004).
3. K. Kodama, H. Sasaki and Y. Shimizu, Trend of coronary heartdisease and its relationship to risk factors in a Japanese
population: A 26-year follow-up, Hiroshima/Nagasaki study.
Jpn. Circ. J. 54, 414–421 (1990).
4. S. Kyoizumi, Y. Kusunoki, T. Hayashi, M. Hakoda, J. B.
Cologne and K. Nakachi, Individual variation of somatic genemutability in relation to cancer susceptibility: prospective study
on erythrocyte glycophorin A gene mutations of atomic bomb
survivors. Cancer Res. 65, 5462–5469 (2005).
5. H. M. Cullings, S. Fujita, S. Funamoto, E. J. Grant, G. D. Kerrand D. L. Preston, Dose estimation for atomic bomb survivor
studies: its evolution and present status. Radiat. Res. 166, 219–
254 (2006).
6. M. Yamaoka, Y. Kusunoki, F. Kasagi, T. Hayashi, K. Nakachi
and S. Kyoizumi, Decreases in percentages of naı̈ve CD4 and
CD8 T cells and increases in percentages of memory CD8 T-cell
subsets in the peripheral blood lymphocyte populations of Abomb survivors. Radiat. Res. 161, 290–298 (2004).
7. G. Armitage, G. Berry and J. N. S. Matthews, Statistical
Methods in Medical Research. Blackwell Science, Oxford, 2002.
8. N. P. Weng, Aging of the immune system: how much can theadaptive immune system adapt? Immunity 24, 495–499 (2006).
9. Y. Kusunoki, S. Kyoizumi, Y. Hirai, T. Suzuki, E. Nakashima,
K. Kodama and T. Seyama, Flow cytometry measurements ofsubsets of T, B and NK cells in peripheral blood lymphocytes ofatomic bomb survivors. Radiat. Res. 150, 227–236 (1998).

875

10. Y. Kusunoki, M. Yamaoka, F. Kasagi, T. Hayashi, K. Koyama,
K. Kodama, D. G. MacPhee and S. Kyoizumi, T cells of atomic
bomb survivors respond poorly to stimulation by Staphylococcus
aureus toxins in vitro: does this stem from their peripheral
lymphocyte populations having a diminished naive CD4 T-cell
content? Radiat. Res. 158, 715–724 (2002).
11. Y. Kusunoki, M. Yamaoka, F. Kasagi, T. Hayashi, D. G.
MacPhee and S. Kyoizumi, Long-lasting changes in the T-cell
receptor V beta repertoires of CD4 memory T-cell populations in
the peripheral blood of radiation-exposed people. Br. J. Hematol.
122, 975–984 (2003).
12. M. Nakano, Y. Kodama, K. Ohtaki, M. Itoh, A. A. Awa, J.
Cologne, Y. Kusunoki and N. Nakamura, Estimating thenumber of hematopoietic or lymphoid stem cells giving rise toclonal chromosome aberrations in blood T lymphocytes. Radiat.
Res. 161, 273–281 (2004).
13. J. K. Morley, F. M. Batliwalla, R. Hingorani and P. K. Gregersen,
Oligoclonal CD8z T cells are preferentially expanded in the CD57z
subset. J. Immunol. 154, 6182–6190 (1995).
14. Y. Kusunoki, S. Kyoizumi, Y. Hirai, T. Suzuki, E. Nakashima,
K. Kodama and T. Seyama, Flow cytometry measurements ofsubsets of T, B and NK cells in peripheral blood lymphocytes ofatomic bomb survivors. Radiat. Res. 150, 227–236 (1998).
15. T. Ohara, K. Koyama, Y. Kusunoki, T. Hayashi, N. Tsuyama,
Y. Kubo and S. Kyoizumi, Memory functions and death
proneness in three CD4zCD45ROz human T cell subsets. J.
Immunol. 169, 39–48 (2002).
16. S. Kyoizumi, M. Yamaoka, Y. Kubo, K. Hamasaki, T. Hayashi,
K. Nakachi, F. Kasagi and Y. Kusunoki, Memory CD4 T-cell
subsets discriminated by CD43 expression level in A-bomb
survivors. Int. J. Radiat. Biol. 86, 56–62 (2010).
17. M. Akiyama, M. Yamakido, K. Kobuke, D. S. Dock, H. B.
Hamilton, A. A. Awa and H. Kato, Peripheral lymphocyte
response to PHA and T cell population among atomic bomb
survivors. Radiat. Res. 93, 572–580 (1983).
18. M. Akiyama, O-L. Zhou, Y. Kusunoki, S. Kyoizumi, N. Kohno,
S. Akiba and R. R. Delongchamp, Age- and dose-related
alteration of in vitro mixed lymphocyte culture response ofblood lymphocytes from A-bomb survivors. Radiat. Res. 117, 26–
34 (1989).
19. Y. Kusunoki, T. Hayashi, Y. Morishita, M. Yamaoka, M.
Maki, M. Hakoda, K. Kodama, M. A. Bean and S. Kyoizumi,
T-cell responses to mitogens in atomic bomb survivors: A
decreased capacity to produce interleukin 2 characterizes the
T cells of heavily irradiated individuals. Radiat. Res. 155, 81–88(2001).
20. R. Gregg, C. M. Smith, F. J. Clark, D. Dunnion, N. Khan, R.
Chakraverty, L. Nayak and P. A. Moss, The number of humanperipheral blood CD4z CD25high regulatory T cells increases withage. Clin. Exp. Immunol. 140, 540–546 (2005).
21. W. Liu, A. L. Putnam, Z. Xu-Yu, G. L. Szot, M. R. Lee, S. Zhu,
P. A. Gottlieb, P. Kapranov, T. R. Gingeras and J. A. Bluestone,
CD127 expression inversely correlates with FoxP3 andsuppressive function of human CD4z T reg cells. J. Exp. Med.
203, 1701–1711 (2006).
22. N. Seddiki, B. Santner-Nanan, J. Martinson, J. Zaunders, S.
Sasson, A. Landay, M. Solomon, W. Selby, S. I. Alexander andB. Fazekas de St Groth, Expression of interleukin (IL)-2 and IL7 receptors discriminates between human regulatory andactivated T cells. J. Exp. Med. 203, 1693–1700 (2006).
23. L. Chatenoud, B. Salomon and J. A. Bluestone, Suppressor T
cells – they’re back and critical for regulation of autoimmunity!
Immunol. Rev. 182, 149–163 (2001).
24. Y. Kusunoki and T. Hayashi, Long-lasting alterations of theimmune system by ionizing radiation exposure: Implications fordisease development among atomic bomb survivors. Int. J.
Radiat. Biol. 84, 1–14 (2007).
25. S. Sakaguchi, T. Yamaguchi, T. Nomura and M. Ono, Regulatory
T cells and immune tolerance. Cell 133, 775–787 (2008).

876

KUSUNOKI ET AL.

26. T. Hayashi, Y. Kusunoki, M. Hakoda, Y. Morishita, Y. Kubo,
M. Maki, F. Kasagi, K. Kodama, D. G. Macphee and S.
Kyoizumi, Radiation dose-dependent increases in inflammatory
response markers in A-bomb survivors. Int. J. Radiat. Biol. 79,
129–136 (2003).
27. K. D. Kim, J. Zhao, S. Auh, X. Yang, P. Du, H. Tang and Y. X.
Fu, Adaptive immune cells temper initial innate responses. Nat.
Med. 13, 1248–1252 (2007).
28. Y. Kusunoki, S. Kyoizumi, M. Yamaoka, F. Kasagi, K. Kodama
and T. Seyama, Decreased proportion of CD4 T cells in the bloodof atomic-bomb survivors with myocardial infarction. Radiat. Res.
152, 539–543 (1999); Errata, Radiat. Res. 154, 119 (2000).
29. P. M. Ridker, N. Rifai, M. J. Stampfer and C. H. Hennekens,
Plasma concentration of interleukin-6 and the risk of future
myocardial infarction among apparently healthy men.
Circulation 101, 1767–1772 (2000).

30. J. Danesh, P. Whincup, M. Walker, L. Lennon, A. Thomson, P.
Appleby, J. R. Gallimore and M. B. Pepys, Low grade
inflammation and coronary heart disease: prospective study
and updated meta-analyses. Br. Med. J. 321, 199–204 (2000).
31. A. Armani and R. C. Becker, The biology, utilization, andattenuation of C-reactive protein in cardiovascular disease: part
II. Am. Heart J. 149, 977–983 (2005).
32. M. Akiyama, Late effects of radiation on the human immune
system: an overview of immune response among the atomicbomb survivors. Int. J. Radiat. Biol. 68, 497–508 (1995).
33. K. Takeda, T. Kaisho and S. Akira, Toll-like receptors. Annu.
Rev. Immunol. 21, 335–376 (2003).
34. K. Edfeldt, J. Swedenborg, G. K. Hansson and Z. Q. Yan,
Expression of toll-like receptors in human atherosclerotic lesions:a possible pathway for plaque activation. Circulation 105, 1158–
1161 (2002).