Antigenic analysis of intraepidemic variants of influenza A (H3N2) viruses by hyperimmune rat antisera.

Hyperimmune rat antisera prepared against 5 recent antigenic variants of influenza A (H3N2) viruses were studied for haemagglutination inhibiting (HI) antibodies to the homologous and the heterologous viruses. The ratios of homologous to heterologous reactions varied from one animal to another in immunizations with each of the immunogens. Some antisera exhibited a ratio high enough to allow differentiation of the epidemic variants and demonstration of an intraepidemic heterogeneity of field strains isolated during the outbreak of 1985/86. The variation of cross-reactions of polyclonal antisera may reflect differences in the range of specificities of anti-haemagglutinin antibodies produced by individual animals. The significance of this finding in the classification of influenza A (H3N2) viruses is discussed. Lack of nonspecific inhibitors interfering with the HI test is an additional advantage of hyperimmune rat antisera in typing influenza A and B virus isolates.