Indirect complement fixation test with foot-and-mouth disease virus antigen concentrated by polyethylene glycol precipitation.

To a BHK-21 cell culture fluid infected with the O, A, or Asia 1 type of foot-and-mouth disease (FMD) virus was added polyethylene glycol 16000 to a concentration of 10% (w/v). Then the fluid was concentrated to one-tenth of the original volume. The resulting concentrated virus antigens showed a complement fixation (CF) titer ranging from 12 to 14. The rate of recovery of CF activity was in a range of 40 approximately 80%. Each antigen was applied to the indirect complement fixation (ICF) test with serum from cattle infected experimentally with the respective type of virus to estimate antibody titers. When antibody was examined for a rise and fall, it began to be detected 4 approximately 7 days after inoculation and was detectable even 63 days after inoculation. It showed a tendency to exhibit a rise and fall parallel with that of neutralizing antibody, although it was always lower in titer than this antibody. ICF antibody corresponding to one type of virus was type-specific, presenting little crossing with a heterologous antigen. As a result, it was clarified that such antigen as prepared from an infected cell culture fluid after concentration with polyethylene glycol was applicable to the ICF test for the estimation of the titer of antibody against FMD virus.