Antigenic drift in type A influenza virus: Sequence differences in the hemagglutinin of Hong Kong (H3N2) variants selected with monoclonal hybridoma antibodies

Abstract

Three monoclonal hybridoma antibodies, designated H14/A2, H14/A20, and H14/A21, which appeared to bind to different sites on the hemagglutinin of A/Mem/1/71 (H3N2) virus, were used to select a total of 10 antigenic variants of this virus. The variants occurred with a frequency of about 1 per 100,000 infectious wild-type virus particles and were isolated after a single passage of the virus in the presence of the monoclonal antibody. Hyperimmune rabbit antisera did not distinguish wild-type and variant viruses, but the monoclonal antibodies, which reacted with the wild-type virus to titers of the order of 1 100,000, did not react at all (or to very low titer) with thevariants they selected. This dramatic change in antigenicity appeared to be associated with a single change in the amino acid sequence of the large hemagglutinin polypeptide, HA1. Four variants selected with H14/A2 monoclonal antibod showed the same antigenic properties and the same sequence change (asparagine to lysine) in the N-terminal half of HA1. Of three variants selected with H14/A20 monoclonal antibody, two showed a different change at a locus also in the N-terminal region of HA1 (a proline was replaced by serine in one variant and by leucine in the other). Of the other three variants (selected with H14/A21 monoclonal antibody) one showed a change in HA1 of serine to tyrosine. This change occurred in residue number 37 of cyanogen bromide fragment 2 (CN2). In the other two variants the change in HA1 has not been determined, but in these a tryptic peptide comprising residues 49–56 of CN2 was missing. No changes were found in the HA2 polypeptide from any of the variants.