The patterns of complex and partially purified mycobacterial antigens in macrophage migration inhibition testing.

In rabbits immunized intratarsally by M. tuberculosis, M. kansasii and M. avium the responses to homologous and heterologous antigens were assessed by direct and indirect macrophage migration inhibition tests. Complex cytoplasmic antigens were obtained by disruption of bacterial mass and by ultracentrifugation of the supernatants. The partially purified antigens were prepared by gel chromatography of the complex antigens on a Sephadex G 150 column. The middle fraction (260/280 ratio approx. 1, molecular weight approx. 32 KD) was employed as partially purified antigen. In the direct tests the migration activity of immune spleen macrophages was significantly reduced by homologous complex and partially purified antigens (MI = 0.63 to 0.72) and it differed significantly from responses obtained with heterologous antigens (MI = 0.75 to 0.92); however, these were still lower than those in nonimmunized control animals where MI ranged from 0.89 to 1.01. In the indirect tests, the strongest responses were recorded again with homologous complex and partially purified antigens (MI = 0.43 to 0.53). The responses in heterologous systems differed even more markedly than in direct tests (MI = 0.65 to 0.81); and, these were again still significantly lower than in control animals (MI = 0.89 to 0.98). In both direct and indirect tests, the complex and partially purified antigens did not vary substantially in their immunogenic capacity. The presence of cross-reacting responses in heterologous systems can be explained by a close relatedness of mycobacteria used in the immunization schedule and by the presence of common epitopes in complex and purified testing antigens.