A single subcutaneous inoculation of 10⁷ armadillo-derived irradiated Mycobacterium leprae evokes different immunological behavior in C57Bl/6 and C3H mice

Following subcutaneous injection in the footpad with 6.7 x 10³ living Mycobacterium leprae, it was observed that locally, at the injection site, more microorganisms were destroyed after the sixth month in C57BL/6 mice than in C3H/HeN mice. The specific and non-specific immune responses after inoculations of Armadillo-derived, irradiated killed M. leprae (IML) was then investigated in these two strains of mice and also in Biozzi's HL and LL mice. One single injection of 1 x 10⁷ IML into the hind footpad of C57BL/6 and Biozzi's HL mice was able to elicit a state of cell-mediated immunity (CMI) to M. leprae antigens or to cross-reacting mycobacterial antigens, such as BCG antigens. The selected parameters of CMI were as follows. Development of an immune granuloma at the injection site and in the draining lymph node which corresponds to the accumulation of macrophages and lymphoid cells. Development of a systemic delayed-type hypersensitivity (DTH) to both living BCG and IML. Specific acquired protection against infection with M. bovis strain BCG. Immunopotentiation of the DTH response to an unrelated antigen, such as sheep red blood cells. In low responder strains (C3H/HeN and low-antibody producer mice selected by Biozzi) no such parameters developed at all after immunization. The mechanisms and relevance of these observations to the efficacy of an antileprosy vaccine for man is discussed.