LIVE POLIO IRUS VACCINES

DISCUSSION
CHAIRMAN BURNET: The paper presented by
Dr. Koprowski is now open for discussion. Dr.
Dick.
DR. DICK: I would like to request some information.
In using this intratypic serological
marker, how can one determine that the virus
has not undergone an antigenie change in multiplication
in the gut?
The other question concerns the T marker:
Generally, what experience have people had in
finding T negative viruses in wild paralytic
strains? We have not done very much of this
yet, but we do have some evidence that some wild
paralytic strains are T minus. Therefore, if you
find T- wild paralytic strains, and if you get an
antigenie change neither the T marker nor the
intratypic serologic marker is of much use in
sorting things out.
DR. KOPROWSKI: The number of wild strains
studied in our laboratory for the T marker is
relatively small, and of all strains examined one
showed intermediate T characters and the remaining
strains were all "hot."
As far as antigenic stability of CHAT strain
is concerned, viruses isolated from the healthy
infants and children fed CHAT virus either in
the Belgian Congo or in the U.S.A. were identical
serologically (in the intratypic serodifferentiation
test) with the CHAT virus. We found no
exception to this observation. This obviously
refers to a study in which anti-CHAT serum was
employed in the test. We have not as yet explored
the use of a serum prepared against a
wild strain in a test with CHAT-virus-derived
human passage strains. However, results published
by McBride suggest that a specific reaction
may also be encountered.
DR. MELNICK: I would like to refer Dr. Dick
to Table 9 of our paper.* In it I have indicated
the results of such T tests on wild viruses. We
found that, of 64 wild viruses tested, 8 were
negative for the T characteristic; 5 were plusminus,
and 51 were positive. Dr. Sabin has also
carried out such tests.
*See p. 23.
66
I should like to address a question to Dr.
Koprowski in connection with the antigenic typing
of viruses. Would he say a word about the
number of bottles or plates which he used per
dilution? In order to get significant differences,
it is important to know the total number of
plaques counted, and one could not determine
this from the averages which Dr. Koprowski
showed in his paper.
I should also like to know the number of
plaques that were counted in order to determine
the average size, and how these plaques were
followed during the incubation period. If
plaques are counted only on day 5, then some
plaques are three or four days old and others
are perhaps only one day old. This will greatly
influence the results.
DR. KOPROWSKI: We used three to five plates
with a predetermined dilution of serum. The
number of plaques counted varies, let us say
from 40 to about 60 or 70, and from this we obtain
an average value.
Dr. Wecker, who originally developed the use
of serum in the overlay, has counted plaques at
different days after infection of monolayers and
found little difference in plaque counts between
the third and fifth day.
DR. SABIN: Since the question of the reproductive
capacity of naturally occuring poliovirus at
higher temperatures has been raised several
times, I should like to call attention to the results
of a rather extensive study shown in Table 1.
These are results of tests on a total of about
260 strains derived from patients with disease,
without disease, and under various other circumstances.
To summarize, while the majority of naturally
occurring polioviruses do possess the capacity for
multiplying at 40 ° C., there are exceptions to the
rule, even in the central nervous system of the
fatal cases. I should point out that I went back
and studied the original central nervous system
tissue suspensions-thinking that the virus might
have undergone a change after one passage in
monkey-kidney tissue culture-and found that
the virus in the original central nervous system