[Evolution of H3 antigen of influenza viruses isolated during 1968-1976].

Influenza viruses type A isolated in 1968--1976 were found to have changes in the content of the antigenic determinant H3. The experiments showed that while in the viruses isolated in 1968--1972 the H3 antigen was dominating, in the A/Port Chalmers/1/73 virus and some viruses isolated in 1975--1976 this antigen became more and more minor. A correlation was observed between the content of H3 antigen in viruses and the capacity of anti-H3 antiserum to inhibit the infectious activity of viruses. The prepared monospecific serum to H3 antigen contained no antibody to the other two antigenic determinants of virus or to neuraminidase and host cell antigen and was completely free from inhibitors. The serum could be used in HI, CFT, and immunodiffusion tests for the analysis of the antigenic composition of newly isolated influenza viruses.