Comparison of Neutralization Rate and Agar Diffusion Methods for Intratypic Sero-Differentiation of Polioviruses.

Abstract
Discussion and summary Although these data are derived from examination of only 5 strains of type 1 poliovirus they are representative of the results of a larger number of similar observations(6). It is evident that when antigenic differences were detected by the agar diffusion method they were confirmed by the neutralization rate test. Thus, the results obtained with these 2 methods of determining intratypic antigenic differences would appear to be highly comparable. When these findings are considered with those of Nakano and Gelfand(4), who showed that the neutralization rate test and their modification of the method of Wecker gave similar results, it can be concluded that in spite of the potential differences, the 3 technics are in remarkable agreement. Our results are at variance with those of McBride(2) in that a clear difference could be demonstrated between the Mahoney and LSc-2ab strains, the latter being derived from the former, whereas he found no such distinction, but employed only antiserum prepared against Mahoney. Nakano and Gelfand(4) did find the 2 viruses to be antigenically distinct, but this was most evident in tests with the antiLSc serum. The discrepancy in results in the 3 laboratories might be explained by differences in the viruses tested or more likely by differences in specificity of the antisera employed. That the latter is the probable explanation is demonstrated by the results of tests in our laboratory with anti-Mahoney serum kindly supplied by Dr. Gelfand, which were in agreement with those of Nakano and Gelfand(4) and failed to differentiate clearly LSc and Mahoney viruses. However, with suitable technics not only can the related Mahoney and LSc strains be distinguished one from the other, but alterations which occur during multiplication in the human intestine can be detected. Changes during passage in the human intestine are shown by the few data given here and further documented by more extensive observations in our laboratory(6).† Nakano and Gelfand(4) indicate that they too have demonstrated antigenic differences between the viruses excreted by vaccinated persons and the vaccine virus. Similar observations have been made by Wassermann and Fox(7). Thus, it is apparent that the antigenicity of polioviruses is not such a stable trait as had been hoped.