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A new method for intratypic antigenic differentiation of poliovirus strains has been developed. The method is based on the use of cross-absorbed sera in neutralization tests where virus is titrated by the cytopathic effect. Qualitative differences between the antigenic structure of vaccine and "wild" strains as well as between some "wild" strains of the same serologic type have been found. The method may be used in practical laboratories.
Two methods for the detection of antibodies to the bovine leukemia virus (BLV) in infected animals were compared for their suitability for the early diagnosis of bovine leukemia - pseudotype neutralization test (PNT) employing vesicular stomatitis virus - bovine leukemia virus pseudotypes (VSV-BLV), and radioimmunoassay test (RIA) for major internal viral protein p24 of the BLV. The comparison was made using more than 300 sera from cows of the herds with high incidence of bovine leukemia. In infected animals the presence of antibodies against virus envelope glycoprotein detected by PNT and antibodies against major structural viral protein p24 detected by RIA were found always coincidentally. Both methods were found highly comparable and suitable for early detection of bovine leukemia virus infected animals.
Sixteen lots of rabies immune globulin (RIG) and six lots of rabies immune horse serum (RIS) from different producers were examined for rabies antibody by the standard mouse neutralization test (MNT) and the rapid fluorescent focus inhibition test (RFFIT). An equine rabies standard serum was assayed in parallel. In comparisons of RIS with this standard the MNT and RFFIT gave comparable results. In comparisons of RIG the antibody values in the MNT was two to ten times higher than that in the RFFIT in 15 out of 16 lots. The MNT and RFFIT are thus not fully comparable when measuring rabies antibodies in RIG. The choice of the titration method is obviously important in the measurement of the antibody concentration in RIG or RIS in IU against an equine rabies reference preparation. The described differences could have consequences for the use of RIG.
The causative agents of Ockelbo disease in Sweden, Pogosta disease in Finland, and Karelian fever in the USSR have been attributed to alphaviruses (family Togaviridae) related to Sindbis virus. We compared prototypes Sindbis, Ockelbo, and Karelian fever viruses by neutralization tests. We also analyzed oligonucleotide fingerprint maps of prototypes Ockelbo and Karelian fever viruses and a strain of Sindbis virus from Czechoslovakia. The results indicate that Ockelbo and Karelian fever viruses are essentially identical and suggest that Ockelbo disease, Pogosta disease, and Karelian fever are synonyms for the same disease.
The antibody response of rabbit to infectious bovine rhinotracheitis (IBR) virus was examined. Two rabbits were inoculated with IBR virus strain Los Angeles into the trachea and intravenously, and intravenously two times, respectively. The patterns of antibody titers in the rabbits measured by neutralization test and ELISA were similar to those in the case of bovine. The antibody was detected after the inoculation, and much more antibody was detected after the second inoculation. The fact suggests that rabbits are a very useful laboratory animal for IBR virus infection studies.
Heretofore, the most reliable way of measuring yellow fever virus antibody was to use the mouse neutralization (MN) test employing either suckling or weanling mice. Certain disadvantages (e.g., expense both of animals and of maintaining a mouse colony, allergic reactions of many laboratory workers, and the relatively long time, 21 days, before end points are reached) are inherent in any program with mice or other laboratory animal species and have discouraged the use of the MN test by many laboratories. A previously reported plaque neutralization (PN) test with primary chick embryo cell cultures could not be consistently reproduced by later investigators. We have developed a convenient and reproducible PN test employing the MA-104 embryonic rhesus monkey kidney cell culture and a single agar-overlay procedure. When compared with MN tests with newborn (1 to 3 days old) and weanling (16 to 20 g, 24 to 28 days old) mice inoculated by the intracranial route, the PN test was the most sensitive for measuring neutralizing antibody; it was also less variable, less costly, and it achieved results in the shortest period of time. End points could be determined in 5 to 6 days for the PN test as compared to 21 days for the MN test.
Antisera prepared against 16 strains of hantaviruses isolated from patients with hemorrhagic fever with renal syndrome (HFRS) or from rodents captured in HFRS-endemic and nonendemic regions were titrated against Hantaan virus strain 76-118, Puumala virus strain Sotkamo, and Prospect Hill virus strain Prospect Hill-I by using the indirect immunofluorescent antibody and plaque reduction neutralization tests. Isolates fell into one of four distinct groups or serotypes. Serotype 1 included Apodemus-derived strains, serotype 2 included Rattus-derived strains, serotype 3 included Clethrionomys-derived strains, and serotype 4 included Microtus-derived strains. Serotypic classification of hantavirus infections was possible for humans and rodents in widely varied geographical areas, but in a few instances, sera from patients with HFRS did not conform to any of the four serotypes, suggesting the existence of as yet unidentified serotypes. A definitive serological classification of hantaviruses must await analysis of additional virus isolates.
Neutralizing antisera to human cytomegalovirus were produced in rabbits with alkaline-buffered extracts of infected cell cultures. The antibody activity was complement dependent and associated primarily with the 7S immunoglobulin fraction. Antisera with homologous K values greater than 10.00 were shown to be suitable for neutralization kinetic studies and were so used to examine the antigenic relatedness of strains AD169, Davis, Esp, C-87, Kerr, and Towne. Based upon the degree of relationship as determined by normalized K values, antisera to the Davis or AD169 strains discriminated three antigenic groups, and an antiserum to strain Esp discriminated two groups.
A three day serum neutralization (SN) test for the detection of antibodies to bovine viral diarrhea virus (BVDV), which is an improvement on the existing five day test, is described. The improved test results in a more rapid viral cytopathic effect and utilizes Madin Darby kidney (MDBK) cells, and horse serum as a medium supplement. A comparison of tests utilizing the NADL and the Singer strains of BVDV and the use of either secondary bovine kidney cells with calf serum (BKCS) or continuous MDBK cells with horse serum (MDHS) was performed. Analysis of the SN results of 685 serum samples from 445 Quebec and Ontario cattle showed that there was no difference, as expected, in the means of the SN antibody titers when the NADL strain was used in either the BKCS or MDHS system but SN antibody titers were elevated (p less than 0.01) when the Singer strain was used in the MDHS system. The SN test with the Singer strain also yielded significantly higher titers for sera from 200 Alberta cattle.
A test for the titration of B. pertussis toxin with antisera on Chinese hamster ovary (CHO) cells has been worked out. B. pertussis protective antigenic cell-free complex containing 48-54% of B. pertussis toxin has been used as antigen. The specificity of the effect of this complex on CHO cells has been confirmed in the toxicity neutralization test with antisera. CHO cells have been adapted to reagents and culture media made in the USSR. The titration of B. pertussis toxin and antisera on CHO cells did not require the use of highly purified antigen.
Statistical analysis of the results of tumor-cell neutralization (Winn) tests has been presented in a refined manner using three variables: tumor incidence, time to palpable tumor, and growth rate. The concept of relative risk and the Z statistic were used to describe the latter two variables. This analysis is then applied to a particular experiment. Lymphocytes sensitized in vitro were compared with specifically immune lymphocytes and were found to facilitate the growth rate. Further applications of this analysis are discussed.
The correlation between skin reaction, exhibited by vaccinees immunized against smallpox, and antibody titer determined by plaque neutralization and ELISA, was evaluated. Twenty eight out of 35 young adults (vaccinated at infancy and at the age of 8 years), who were injected with vaccinia virus, displayed a major skin reaction a week later. An increase of four-folds and more, in antibody titer against vaccinia virus, is generally considered positive immunization take-up against smallpox. According to this criterion, only 17 of the vaccinees were found positive by plaque neutralization, while 25 by the indirect micro-ELISA. Thus, there were eight vaccinees who were considered immunized by the ELISA, (seven of them also according to the skin reaction), but not by the plaque neutralization test.
An improved micromethod for infectivity assays and neutralization (N) tests of dengue (DEN) type 1-4 viruses was developed, using 96-well plates and the PAP (peroxidase-antiperoxidase) staining technique. The foci formed on BHK-21 cell monolayers in wells of the plate were readily countable under an ordinary stereomicroscope. This micromethod has the advantages over the micromethod of the Lab-Tek 8 chamber slide system of lower cost, requirement for smaller volumes of test sera and applicability to larger number of serum specimens for N tests of DEN viruses.
Weekly oral chloroquine prophylaxis for malaria has been associated with impaired antibody response to intradermal rabies vaccination. Experimental data indicate that chloroquine may inhibit yellow fever virus in vitro, yet there has been no clinical evidence to suggest that antibody response to yellow fever vaccine is impaired by concomitant oral administration of chloroquine. A prospective trial was undertaken to evaluate the antibody response to yellow fever 17D vaccine (Connaught Laboratories) of volunteers who were randomized to taking either chloroquine or no drug. Of fifty subjects, 28 were randomized to taking chloroquine, 22 were randomized to taking no drug. Yellow fever 17D vaccine was administered on day 0 and blood sampled on days 0, 14, 35 and 210. Chloroquine was administered weekly for four weeks. There was no significant difference in peak antibody titer by plaque reduction neutralization testing (PRNT) between the group that took chloroquine (mean log peak of reciprocal titer 1.43 +/- SD 0.60) with vaccine subcutaneously compared to vaccine-only group (mean log peak of reciprocal titer = 1.21 +/- 0.55). All fifty subjects seroconverted to yellow fever vaccine by day 210. ELISA testing was also performed on all subjects. The two tests showed good correlation (Spearman r = 0.675), although ELISA readings were positive by day 14 in significantly more subjects (p = .01). We conclude that routine anti-malarial doses of chloroquine do not affect antibody response to yellow fever 17D vaccine. ELISA testing, a less complex and less time-consuming test, correlates well with PRNT and is proposed for additional trials to measure yellow fever 17D vaccine response in flavivirus non-immune subjects.
When assessed by a conventional plaque neutralization (NT) test, about one third of recipients of live mumps vaccine were found to have failed to seroconvert, although the majority of them became seropositive by the complement-mediated neutralization (CNT) test. The discrepancy between the conventional NT and CNT was found to result from two factors. First, the predominant production of antibodies to the fusion (F) protein during the early phase of antibody response, and second, a low efficiency of NT of the early antibodies in the absence of complement. These features of antibody response were also seen in natural mumps infection and in experimental infection of monkeys, but were particularly prominent in vaccinees because of the limited extent of antibody response in the latter. The discrepancy between conventional NT and CNT diminished with time after vaccination, after natural infection, and also after experimental infection of monkeys. The CNT test was therefore considered better suited than the conventional NT test for assessment of the outcome of vaccination, at least until 6 to 9 weeks after vaccination. The protective role of the antibody in vivo, which requires the addition of complement for neutralization, was inferred from the observation that the antibody incorporated in the agar overlay significantly reduced the size of plaques formed by mumps virus.
The effect of altering the strain of the test virus used in the standardized pseudorabies virus neutralization (VN) test on the sensitivity of the assay was evaluated. Comparative VN tests were performed using 4 different strains: the avirulent Bartha parental, the avirulent recombinant Bartha gIIIKa, the moderately virulent Shope (currently used for the VN test at the National Veterinary Services Laboratory, Ames, IA), and the highly virulent P2208 (Funkhauser). A radioimmunoassay and a Western immunoblotting technique were employed to verify the presence of anti-pseudorabies virus (PrV) antibodies in sera. Statistical analysis indicated that replacement of the Shope strain by the Bartha gIIIKa or the P2208 strain resulted in VN titers that were 4.23- and 2.00-fold higher, respectively. Despite these differences, specificity with regard to PrV diagnosis was unaltered. This apparent enhancement of the sensitivity of the PrV VN test would be beneficial for the serologic identification of PrV-infected animals during an eradication effort.
The RAST, originally developed for the assay of reaginic IgE antibodies, was applied for the detection of blocking antibodies. Sera taken ante- or post-hyposensitization were incubated with solid phase coupled allergen which neutralized reaginic IgE antibodies in the serum. The remaining activity of the reaginic IgE antibodies was measured by the RAST. When blocking antibodies were present in the serum they competed with the reaginic IgE antibodies and the amount of reaginic antibodies that was neutralized by the solid phase coupled allergen was decreased. The blocking antibodies were found in the IgG fraction of the serum taken post-hyposensitization. Blocking antibodies to various allergens were detected in 25 out of 26 tests on sera taken post-hyposensitization. The results were compared with those of Prusnitz-Küstner neutralization tests and/or patient self-neutralization tests. There was no correlation between semi-quantitative results of these in vivo tests and those of the RAST neutralization tests. However, cases with subjectively a strong improvement had a significantly higher mean value for RAST neutralization index than those with subjectively a weak improvement. The method is suggested as a supplement to clinical tests for evaluation of hyposensitization treatments.