[Antigenic anachronism of influenza viruses A(H2N2) in Leningrad in 1980. II. The laboratory characteristics of influenza A/Leningrad/80 viruses].

As indicated by the results of the hemagglutination inhibition (HAI) test, influenza viruses A/Leningrad/80 contain hemagglutinin (HA), similar to that of virus A/Singapore/1/57 (H2N2). Neuraminidase contained in viruses A/Leningrad/80 belongs to serological subtype N2 and is similar to that of virus A/Singapore/1/57 (H2N2). No differences in the polypeptide composition of the virus-induced proteins of viruses A/Leningrad/527/80, A/Leningrad/549/80, A/Leningrad/553/80 and virus A/Singapore/1/57 used as reference have been detected in the study of their electrophoretic mobility in polyacrylamide gel, as well as the mobility of duplexes obtained by the hybridization of the virion and complement RNA of viruses A/Leningrad/553/80 and A/Singapore/1/57. The results of the HAI test with antisera to purified HA indicate that virus A/Leningrad/549/80 contains HA similar to that of viruses A(H2N2) isolated in 1957, but not in 1964. The HAI test with the sera of polecats having the infection permits the differentiation of viruses A/Leningrad/80 from epidemic viruses A(H2N2) isolated in 1957-1965, including reference virus A/Singapore/1/57. In relation to the latter, the isolates of 1980 are older antigenic mutants. The isolates of 1980 are distinguished from virus A(H2N2), isolated in 1975 from the system of persisting influenza infection in a tissue culture, by mutation in NS-gene and the properties of RNA-polymerase. The authenticity of the isolation of viruses A(H2N2) in Leningrad in 1980 has been proved.