Significance of the Blocking Antibody in Experimental Brucellosis

Hyperimmunization of rabbits with heat-killed Brucella abortus called forth blocking antibodies which appeared late and only if the antigenic dose was very large. The blocking antibody was shown to have a shifting electrophoretic mobility in rabbit and human serum proteins, varying with the duration of antigenic stimulation. Early, the blocking phenomenon appeared in the slow moving γ-globulins; with continued stimulation, the blocking antibodies migrated in the serum proteins with the mobility of the β-globulins. The blocking phenomenon in a B. abortus hyperimmunized rabbit disappeared 14 weeks after the cessation of heavy antigenic stimulation. It reappeared after a single injection of the same antigen. These findings suggest that in the rabbit blocking antibody indicates continued antigenic stimulation or active infection by Brucella.