Immunobiologic heterotypic activity associated with viral and soluble components of bovine virus diarrhea virus

Summary The V and S antigens of bovine virus diarrhea (BVD) virus were studied by pig inoculation experiments to determine the basis for the bovine virus diarrheahog cholera heterotypic relationship. BVD virus infected tissue cultures were harvested and separated by ultracentrifugation and ultrafiltration. V antigen was prepared by Tween-ether-urea inactivation of virus. S antigen was quantitated in filtration samples and in density gradients by specific complement fixation. Pigs inoculated with crude, concentrated V antigen survived virulent hog cholera (HC) virus exposure. However, V antigen partially purified by ultracentrifugation failed to protect pigs. Neutralizing antibody to BVD, but not to HC, was synthesized in inoculated pigs following HC exposure. S antigen separated by 10 m, ultrafiltration and purified by potassium tartrate density gradient ultracentrifugation protected pigs from virulent HC. No BVD or HC antibody was detected at the time of HC virus exposure but HC antibody was produced at an accelerated rate following exposure. It thus appeared that an S antigen less than 10 m in size having a density between 1.05 and 1.10 g/ml which was produced during BVD virus replication in cells initiated the potential for a protective response.