Comparative study of immunizing and delayed hypersensitivity eliciting antigens of Mycobacterium leprae, M. tuberculosis, M. vaccae, and M. bovis (BCG).

A variety of mycobacterial antigens have been associated with the delayed-type hypersensitivity (DTH) reactions in human beings and animals. An attempt has been made in the present study to identify the major antigen fractions of Mycobacterium leprae and M. tuberculosis responsible for the elicitation of DTH and to evaluate their specificity by a comparison with the antigens of two closely related mycobacteria, BCG and M. vaccae. Guinea pigs and mice were sensitized with native or heat-killed M. leprae, M. tuberculosis, M. vaccae, and BCG. Four fractions each of the latter three mycobacteria, obtained by preparatory polyacrylamide slab gel electrophoresis, were used for elicitation of DTH. Three fractions of M. leprae (MY1, MY2, and MLSE) were obtained by affinity chromatography using monoclonal antibodies. Heat-killed M. leprae and M. vaccae proved to be better sensitizers for DTH compared to their native counterparts, whereas there were no significant differences between the efficacies of autoclaved and unautoclaved M. tuberculosis or BCG. The best DTH responses were recorded with a 16-24 kD fraction of M. tuberculosis, a 20-27 kD fraction of BCG, and MLSE of M. leprae. The purified molecules of M. leprae, MY1 (12 kD) and MY2 (35 kD), did not elicit a DTH reaction. Although none of the fractions of M. tuberculosis or BCG exhibited species specificity, fraction II (15-24 kD) of M. vaccae and MLSE might be comprised of species-specific determinants.