Abstract
Single radial immunodiffusion (SRID) using convalescent cattle sera was developed to evaluate the potency of foot-and-mouth disease inactivated vaccine. The complete virion (140S antigen) was collected by sucrose-gradient centrifugation of inactivated virus. The 12S subunit antigen was prepared by heat treatment of purified 140S antigen. Convalescent cattle sera produced diffusion ring with 140S antigen alone, while hyperimmunized guinea pig sera produced with both 140S and 12S antigens. In SRID of mixed viral antigen (140S and 12S) tested against hyperimmunized guinea pig sera, diffusion rings of the former was affected by contamnination of the latter. When the same samples were tested in SRID using convalescent cattle sera, 12S antigen did not affect the quantitation of 140S antigen. Area of diffusion rings of purified 140S antigen clearly correlated with concentration of proteins measured by optical density, as well as by complement fixation tests using hyperimmunized guinea pig sera. SRID using convalescent cattle sera is more practical than conventional SRID using immunized guinea pig sera, because cattle sera react with effective component (140S antigen) alone, and not with ineffective 12S antigen, in the vaccine, and because infected cattle is more suitable to make large amount of pooled sera for the routine assay.
