LIVE POLIO IRUS VACCINES

Development and Persistence of Polio Antibodies in Young Adults 235
taneously against Types 2 and 3, and once simultaneously
against Types 1 and 3. In most cases,
the antibody rises to Type 1 were observed later
than to Type 2.
The appearance of heterotypic antibodies in
subjects lacking detectable levels of Type 1 and
Type 2 antibodies in the pre-immunization sample
of sera was of special interest to us. Type 1 antibodies
appeared in three out of six cases without
homologous serological immunity, persisting in
two cases for a short period of time; in the remaining
case they were demonstrated in a very
low titer only in pH/6 after 12 weeks. A Type
2 antibody increase was observed in four out of
five subjects lacking Type 2 antibodies prior to
immunization. In two of these subjects, the antibodies
persisted after 12 weeks. The appearance
of heterotypic antibodies repeatedly had the
character of biphasic process.
Differences in the titers of Type 1 and Type 2
antibodies, estimated by means of different tests,
were similar to those observed in Type 3 antibodies.
Some preliminary results concerning the possible
difierences in antibody avidity.
(a) As already mentioned, the results of CP/1
and CP/6 were read on the second, third, fifth,
and seventh day after inoculation, the IIT on the
third, fifth, and seventh day. Between the titers
estimated in the second and seventh-day readings
considerable differences were observed, varying
from case to case. We tried to establish the
following: (1) whether the magnitude of such
differences in antibody titers was in any relation
to the pre-immunization immunity state; and
(2) whether these differences changed in the
course of poliomyelitic infection.
For this purpose we divided the subjects investigated
in two groups according to their prevaccination
state of immunity. Geometric mean
titers were computed from the antibody titers
estimated in corresponding serum specimens.
The results presented in Fig. 6 show: (1) In
all three CP tests used, a more considerable difference
between the antibody titers estimated in
the first and the last readings was observed in
subjects lacking pre-existing antibodies, being
usually three to fourfold in CP/1 and CP/6 and
threefold in IIT. In subjects possessing preexisting
antibodies it was twofold or less in all
three tests. The analogical decrease of GMT
of Type 3 antibodies found in the standard human
serum tested simultaneously with non-immune
subjects, was 4.5-fold for CP/1, 3.5-fold for
CP/6 and 2.4-fold for IIT. The corresponding
data obtained when subjects with pre-existing
immunity were investigated were 4.3, 3.7, and
2.5, respectively.
(2) In the course of the infection the differences
between the second and seventh and the
third and seventh-day readings, respectively, remained
nearly unchanged. Only in the group of
non-immunes a slight decrease of the differences
can be found in samples of sera taken at the end
of the observation period in CP/1 and IIT, but
not in CP/6 tests.
(b) The most pronounced difference between
the antibody titers in pH and CP tests was estimated
in subject 9/HB.
The serum samples taken on the 14th day
(S-5) and on the 84th day (S-10) were tested
against virus dilution 10 - ' to 10 -5 in CP/1 and
pH/1, using four tubes (cups) per every dilution.
The results of this experiment are given in
Table 4.
In order to obtain more knowledge of this
interesting discrepancy we followed the residual
virus activity (RVA) in mixtures containing approximately
103.5 TCD 50 of virus per 0.1 ml. and
the final dilution 1:100 of S-5 and S-10, respectively.
The mixtures were incubated at 37 ° C.
and after one, three, six, and 24 hours, samples
were drawn and diluted in several tenfold steps
in pre-cooled medium. Immediately after it, 10
tissue-culture tubes were inoculated with 0.1 ml.
from each dilution. The five-day readings of
two consecutive experiments are presented in
Table 5.
The results indicate that in the test system
used almost no neutralizing effect by S-5 in the
dilution tested could be demonstrated even after
24-hour incubation, although, as previously
demonstrated, the same serum in the dilution
1:256 "neutralized" about 103' . TCD,, of virus in
the pH test.
On the other hand, S-10, having a lesser neu
tralizing potency in pH test, reduced the virus
titer during the incubation period of 24 hours by
1.4 log 10 .