Monoclonal antibodies demonstrate accessible HA2 epitopes in minor subpopulation of native influenza virus haemagglutinin molecules.

Haemagglutinin (HA) was detected on the surface of influenza virus infected cell with monoclonal antibodies (MAbs) against both HA glycopolypeptides, HA1 and HA2, however, the reactivity of HA2-specific MAbs was remarkably lower as compared with HA1-specific MAbs. Quantitative analysis with two MAbs, IB8 (anti-HA1) and IIF4 (anti-HA2) respectively, revealed that HA2 epitope was reachable for antibody only in minor subpopulation of the HA representing approximately 7% of all molecules (spikes). The basis of the HA heterogeneity is discussed.