Antigenic mapping of an avian H1 influenza virus haemagglutinin and interrelationships of H1 viruses from humans, pigs and birds.

Monoclonal antibodies to the haemagglutinin (HA) of the avian H1 influenza virus A/duck/Alberta/35/76 were used to construct an operational antigenic map of the HA molecule and to study the interrelationships of H1 viruses from different hosts. Haemagglutination inhibition tests between the monoclonal antibodies and variants selected by them provided evidence of four antigenic regions which overlap to varying degrees. Avian H1 influenza viruses displayed a spectrum of reactivities to the monoclonal antibody panel. Representatives of the epidemic strains of human H1 influenza viruses and early swine influenza viruses showed little or no reactivity with the monoclonal antibodies but swine influenza-like viruses isolated from pigs and humans in the last decade reacted with 11 of 17 antibodies. The antigenic similarity of these viruses to many avian isolates suggests that there has been a transfer of HA genetic information between mammalian and avian H1 influenza viruses.