Antigenic analysis of H2 influenza virus haemagglutinin with monoclonal antibodies.

Antigenic analysis of human and avian H2 influenza virus was carried out with monoclonal antibodies to the HA molecules of H2 influenza viruses isolated in the early stage of an H2 pandemic. The study revealed antigenic differences between inhibitor sensitive (Japan+/57, RI+57) and inhibitor resistant strains (Japan-/57, Ri-/57). This indicates that the receptor-binding specificity of the haemagglutinin can markedly influence the antigenic analysis obtained with monoclonal antibodies in HI test. Minor antigenic differences (microheterogeneity) could be detected between different H2 influenza viruses isolated in 1957. Minor antigenic variation continued in the H2 viruses until 1961, but significant antigenic drift occurred in 1962 so that viruses isolated after that date reacted with few monoclonal antibodies. Analysis of avian H2 influenza viruses suggested antigenic differences between the different avian H2 haemagglutinin, but no correlation between the year of isolation and the progressive antigenic drift similar to that seen in the human strains was found.