PURIFICATION AND CHARACTERIZATION OF INFLUENZA A VIRUS INHIBITORS IN ANIMAL SERA

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Normal horse and guinea pig sera contain a2-macroglobulin which inhibits the infectivity and hemagglutinating activity of influenza A viruses of the H2 and H3 subtypes. On the other hand, normal bovine serum contains a component termed beta inhibitor that inhibits the infectivity and hemagglutinating activity on influenza A viruses of the H1 and H3 subtypes. To investigate the nature of the beta inhibitor of influenza A virus, we purified the conglutinin and examined its characteristics. The conglutinin , purified from bovine serum, had neutralizing-activity as well as HI activity on influenza A viruses of the H1 and H3 subtypes. The HI activity of conglutinin was heat stable, Ca^<++>-dependent, and resistant to both neuraminidase and periodate treatments. The HI activity of purified conglutinin was blocked by N-acetylglucosamine but not by D- mannose. The conglutinin was bound to hemagglutinin which had high mannose and complex sugar chains and its binding was inhibited by N- acetylglucosamine and dependent on devalent cations. These data indicate that the beta-like inhibitor activity of bovine serum is mainly dependent on conglutinin which inhibits hemagglutination and neutralizes the virus infectivity by its binding to a carbohydrate site at the HA. Nextly, we tried to clone the cDNA coding for bovine conglutinin. cDNA clones encoding the bovine conglutinin were isolated from a bovine liver cDNA library using a specific probe obtained from the PCR product. These cDNAs carry an insert of 1113 bp coding for a protein of 371 amino acid residues with a signal peptide of 20 residues. Southern blot analysis of total bovine genomic DNA indicated that there is only one copy of the gene encoding bovine conglutinin. Northern blot analysis of bovine tissues showed that conglutinin mRNA of about 1.5 kb is expressed in the liver and also slightly in the lung.