Comparative studies on influenza B virus. I. Biological properties and polypeptide composition of strains isolated in different years.

Influenza B viruses isolated in 1940, 1950 and 1970 belonged to antigenically remote subgroups according to the antigenic composition of haemagglutinin (HA). Antigenically related strains isolated in 1972-1976 differed by their reproduction capability, by their sensitivity to inhibitors in mammalian sera and by affinity to specific antibodies in human sera. Certain correlation between these properties was observed by strains of the Hong Kong variant. Polyacrylamide gel electrophoresis (PAGE) showed that the viruses under study differed in the mobility of the major HA chain (HA1). Molecular weights (MW) of HA1 of antigenically similar influenza B viruses isolated in 1972-1976 revealing different biological properties varied from 52.5 K to 58 K. Neuraminidase (NA) of influenza B/Leningrad/369/75 virus purified by electrophoresis in acetate cellulose consisted of 2 polypeptides with apparent MW of 62 K and 57 K. All viruses examined showed similar mobility of the NA polypeptide MW 57 K; the mobility of the former polypeptide was similar to that of nucleoprotein (NP).