Antibody response in rabbits to Mycobacterium bovis BCG

The specificity of the immune response after immunization with Mycobacterium bovis BCG was studied by crossed immunoelectrophoresis with intermediate gel in a BCG/anti-BCG system, in which the reaction against thirty distinct components of BCG was recorded. After a single injection of total sonicate of 3 mg (dry weight) bacilli, the antibody response was markedly similar in eight rabbits. Th earliest and strongest response was directed against nine components of BCG; all but one of these belonged to the group of thirteen components that cross-react extensively with other mycobacteria. After repeated immunization with sonicate from about 0.8 microgram of BCG bacilli, five components still induced a marked antibody response. All but one of these components are among the most widely cross-reacting BCG components, and the observations made after subsequent challenge with the higher dose of BCG indicate that low-zone tolerance was induced against other components of the bacilli. The implication of these findings concerning formation of anti-mycobacterial antibodies in normal individuals and during mycobacterial infection is discussed.