Topographical analysis of bovine herpesvirus type-1 glycoproteins: use of monoclonal antibodies to identify and characterize functional epitopes.

Monoclonal antibodies, specific for two of the major bovine herpesvirus type-1 (BHV-1) glycoproteins, GVP 3/9 and GVP 6/11a/16, have been previously produced and characterized. The reactivity of each monoclonal antibody was determined by enzyme-linked immunosorbent assay (ELISA), the ability to neutralize viral infectivity, and the capacity to mediate complement-dependent (AbC') lysis of virus-infected cells. The topography of epitopes on GVP 3/9 and GVP 6/11a/16 was analyzed, using selected monoclonal antibodies in a competitive antibody binding assay (CBA). Nine epitopes were identified on GVP 3/9. Comparison of the biological activities and epitope specificities of the monoclonal antibodies against GVP 3/9 showed that one epitope was involved in virus neutralization, whereas six epitopes mediated AbC' lysis of the virus-infected cell. Of the seven epitopes identified on GVP 6/11a/16, six were involved in neutralization and three participated in AbC' lysis. In some cases, partial competition between monoclonal antibodies was observed, indicating that they were directed against overlapping or closely adjacent epitopes. In other instances, asymmetrical competition between monoclonal antibodies suggested conformational changes in the glycoprotein molecule induced by antibody binding. Mixtures of two monoclonal antibodies with different epitope specificities resulted in higher neutralizing activity than either antibody alone, suggesting that multiple monoclonal antibodies can exert a synergistic effect on virus neutralization.