Haemagglutinin Relationships of Hong Kong(H3) and Asian(H2) Influenza Strains Delineated by Antigen-Specific Recombinants

Abstract

Reports by others have described the haemagglutinins of Hong Kong (H3N2) strains and the Asian (H2N2) strains as being antigenically unrelated. Cross reactions seen by the haemagglutination-inhibition (HI) test have been attributed to antibodies to a second major surface antigen, the neuraminidase, which is common to both subtypes. However, observations on human anamnestic antibody responses suggest the two haemagglutinins are related. In the present study we reexamined the antigenic relationship of these viruses using haemagglutinin specific virus recombinants, chicken and ferret antisera, antibody equilibrium filtration methods, and cross-infection in ferrets. Data from these studies consistently demonstrated an asymmetric relationship, independent of the neuraminidase, between the H2 and H3 strains.