Inhibition of influenza virus haemolytic and haemagglutination activities by monoclonal antibodies to haemagglutinin glycopolypeptides HA1 and HA2.

Acid treatment of influenza virus enhanced haemagglutination inhibiting (HI) activity of some anti-HA1 monoclonal antibodies (MoAbs). These changes in the HI-activity could be either due to alteration in the mutual orientation of MoAb (e.g. IC8, IB8) binding epitope to receptor site or to an increase in the number of epitopes accessible to the corresponding MoAbs (e.g. IVA1). HI test with pH 5-virus revealed similar (although not identical) antigenic differences among related virus strains as the HI test with pH 7-virus. Anti-HA2 MoAbs were negative in the HI test with both pH 5- and pH 7-virus. Anti-HA1 MoAbs showed a HI activity with pH 5-treated BHA similar to that with pH 5-treated virus. Surprisingly one out of eight anti-HA2 MoAbs (IIF4) exhibited a relatively high HI activity to pH 5-BHA-mediated haemagglutination. Virus-induced red blood cell haemolysis was efficiently inhibited with several anti-HA1 MoAbs (e.g. IC8, IB8, and IIB4) while other anti-HA1 antibodies, including IVA1 and IVG6 with preferential reactivity with pH 5-treated antigens in RIA, gave no inhibition. As a rule, anti-HA2 MoAbs were poor haemolysis inhibitors.