Protective immunity and delayed-type hypersensitivity in C57BL mice after immunization with live Mycobacterium lepraemurium and sonicated bacilli.

The immunizing effects of live Mycobacterium lepraemurium (MLM) and bacillary sonic extract (MLMSon) were compared in C57BL mice. MLMSon-immunized mice developed a delayed-type hypersensitivity (DTH) reaction when tested in the footpad with diluted MLMSon. The ability to develop a DTH reaction was transferable with immune cells but not with serum. Footpad testing with live MLM and MLMSon indicated that the specificity of the DTH response induced by MLMSon was different from that induced by infection with live bacilli. Two weeks after footpad inoculation with live MLM, MLMSon-immunized mice developed a strong local reaction to the bacilli. No local reaction developed in these mice after injection of the same number of heat-killed MLM. Studies of bacillary growth after inoculation with live MLM indicated that the bacilli did not multiply in micr previously inoculated with live MLM, but that they multiplied for about 2 weeks in LMLSon-immunized mice versus 4 weeks in the controls. The results suggest that immunization with MLMSon does not by itself induce a protective immune response, but creates a state in which the development of protective immunity is accelerated.