Biological activity of a monoclonal antibody to a measles virus haemagglutinin epitope detected late in infection.

A hybrid cell line secreting monoclonal antibody 2H9c (mAb 2H9c) with measles virus haemagglutinin (HA) specificity was produced. The mAb 2H9c was non-reactive in haemagglutination inhibition and neutralization assays. A protein of apparent mol. wt. 79000 was immune-precipitated using a Triton X-100/SDS/sodium deoxycholate detergent buffer and two proteins with mol. wt. of 79000 and 69000 were immune-precipitated using 1% Nonidet P40/sodium deoxycholate buffer in SDS-PAGE assays. Similar results were obtained with other anti-HA monoclonal antibodies, supporting the assumption that mAb 2H9c was directed against the HA polypeptide. The indirect immunofluorescence (IFA) staining pattern of acetone-fixed infected cells with mAb 2H9c differed substantially from that with other HA-specific monoclonal antibodies. Kinetic studies revealed that the reactivity of mAb 2H9c lagged behind other HA-specific monoclonal antibodies by 18 to 36 h post-infection in IFA assays. This suggests that mAb 2H9c may be directed against a binding site that arises late in infection, possibly as a result of a conformational alteration of the HA polypeptide.