CHARACTERIZATION OF THE HEMAGGLUTININ RECEPTOR SPECIFICITY AND NEURAMINIDASE SUBSTRATE-SPECIFICITY OF CLINICAL ISOLATES OF HUMAN INFLUENZA-A VIRUSES

Six clinical isolates of influenza A viruses were examined for hemaggl utinin receptor specificity and neuraminidase substrate specificity. A ll of the viral isolates minimally passaged in mammalian cells demonst rated preferential agglutination of human erythrocytes enzymatically m odified to contain NeuAc alpha2, 6Gal sequences, with no agglutination of cells bearing NeuAc alpha2, 3Gal sequences. This finding is consis tent with the hemagglutination receptor specificity previously demonst rated for laboratory strains of influenza A viruses. The neuraminidase substrate specificities of the clinical isolates examined were also i dentical to that described for the N2 neuraminidase of recent laborato ry strains of human influenza viruses. The H3N2 viruses all displayed the ability to release sialic acid from both alpha2, 3 and alpha2, 6 l inkages. In addition, two clinical isolates of H1N1 viruses also demon strated this dual neuraminidase substrate specificity, a characteristi c which has not been previously described for the NI neuraminidase. Th ese results demonstrate that complementary hemagglutinin and neuramini dase specificities are found in recent isolates of both H1N1 and H3N2 influenza viruses.