The effects of IgG2 and of antigen concentration on prozoning in the complement fixation test for bovine brucellosis.

Addition of Brucella-specific IgG2 to solutions of Brucella-specific IgG1 initially induced prozoning and at higher concentrations prevented all reaction in the complement fixation test (CFT) for bovine brucellosis. Some infected cattle may be diagnosed as brucellosis-free due to a high ratio of specific IgG2 to IgG1. Increasing the concentration of antigen in the CFT reduced the tendency to prozone.