Evening star., 1952-05-02
New Technique Found
In Research on Viruses
Scientist Produces Areas
Of Destruction on Cultures
By Thomos R. Henry

By Thomas R. Henry
A new technique designed to simplify
research on animal viruses, ultramicro-
scopic disease producing organisms which
attack man and animals. has peen oe.
veloped at the California Institute OF
Technology in Pasadena by DR.. Renato
Dulbecco, senior research fellow In ol-
ology.
He outlined the technique. which re-
sembles that developed three decades
ago for study of bacterial viruses, at the
annual spring meeting of the National
Academy of Sciences. With it he has
been able to produce plaques, or areas
of destruction, on culture OF chicken
fibroblasts in flask with the virus OF
western equine encephalomyelitis and
thus easily determine the activity of the
virus.
This phenomenon" he said, appears
to provide an animal-viruS assay superior
to any other assay now in use. 1t affords
hundredfold saving in time, labor and
materials, and the accuracy obtained
with only one flask equals that obtained
from at least 100 chicken embryoS in
uoCu
1--WE do not know whether many other
viruseS will exhibit this property of pro-
ducing plaques under our conditions. So
far, we have tried only one other virus,
the Newcastle disease virus and the re-
suits here were positive"
New Technique for Study.
DR.. Dulbecco plans to use the tech
nique as means of studying the growth
of virus on animal tissue. Relatively
little is known about the basic properties
of animal viruseS because of the techni-
cal difficulties involved in their study.
In some cases their chemical and physi-
cal properties have been established, but
little or nothing is known about their
Unbeatable characteristics, the inter-
relation between the virus and the host
cell, the manner of growth of the virus
and the conditions affecting that growth.
The main interest in animal viruSes,
which cause such diseases as influenza,
poliomyelitiS, shingles and smallpox, has
been with an eye to therapeutic pur-
poses, DR.. Dulbecco said. However he
added, little progress has been made
because the manner in which the viruSeS
grow is not yet understood.
Research on these ViruSeS has been
done primarily with animals or chicken
embryoS as experimental subjects. The
virus is lost from the moment it is in
troGuced into the animal and the effects
are observed on the animal as q whole,
rather than on specific type of cell,
only when radical change has taken
place after the virus multiplies perhaps
a millionfold. Tissue cultures have also
been used, but here again infectivity is
determined by some final effect pro-
duced on the whole culture.
Localized effects are produced in the
technique developed by DR.. Dulbecco for
the western equine encephalomyelitis
virus. The technique permits the use of
a uniform type of host cell and pro-
vides an accurate method of determine
ing virus activity, he reported. With it
he hopes also to be able to- isolate the
progeny of single virus particle, which
might pave the way toward development
of special virus strains useful as vac
cineS. Ability to isolate progeny also
would make it possible to study the
factors influencing hereditary changes
in virus characteristics.
DR.. Dulbecco's technique involves the
formation of a continuous layer Of
chicken embryo fibrobaSt connective
tiSSue) cells ON the bottom of a round.
fiat glass flask according to a method
devised by DR.. W. r. Earle of the Ma
tional Institutes Of Health, Bethesda,
Md.
Small Islands Formed.
The layer grows in two days of in
cubation and the virus is applied on it.
The virus particles attack the fibro-
blasts, multiply and continue Destroy
ing fibroblasts in the immediate vicin-
ity until-after two or three days Of
incubation-small islands of destroyed
tissue (plaques) are formed.
About one hundred plaques visible
under microscope and sometimes to
the naked eye may form in a single
flask. They provide information su-
perior to that which would be OBJ
tanned with an equal number of expert
mental animals or embryos, DR.. Dull
becco said.
BY statistical analysis DR.. Dulbecco
has shown that each plaque represents
an area Of destruction initiated orig
inally by only one virus particle. He
has also introduced the virus In the
same concentration directly into chicken
embryos and found that the number Of
plaque producing particles and infect
ing particles is virtually identical. This
establishes that infection in the animal
can be produced by one virus particle.
he reported.
The virus Of western equine enceph-
alomyelitis, disease relatively common
in horses but rare in man, produces
only areas of destruction on the fibro-
blast cultures. The virus of Newcastle
disease, a paralyzing disease of chick
ems, acts differently. Around the plaques
it forms, DR.. Dulbecco reported, are
halos of abnormal cell growth This
indicates, he said, that it may also be
possible to study viruses which do not
kill the cells they infect but rather
cause increased cell growth.
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