Influence of Route of Mycobacterium lepraemurium Injection on Susceptibility to Mouse Leprosy and on Lymphoblastic Transformation

Groups of female C57BL/6 and C3H/St mice were inoculated intraperitoneally (i.p.) with 10 9 , 10 7 , and 10 5 bacilli and into the right hind footpad with 10 7 and 10 5 bacilli of Mycobacterium lepraemurium . The incidence of death from leprosy and the mean survival time of leprous mice were recorded. In addition, the blastogenic responses to the T-cell mitogens phytohemagglutinin and concanavalin A and to the B-cell mitogens lipopolysaccharide and dextran sulfate were evaluated at various times during the course of infection in the spleen and peripheral lymph nodes of mice infected with 10 7 bacilli. When M. lepraemurium was administered i.p., the two strains of mice succumbed to the disease at about the same time, except for the C57BL/6 mice infected with 10 9 bacilli, which died earlier than the C3H/St mice. Moreover, in both strains of mice, a progressive depression of blastogenesis, first to the T-cell mitogens and then to the B-cell mitogens in the spleen, and to the T-cell mitogens in the peripheral lymph nodes, occurred during the course of the infection, whereas the response to the B-cell mitogens in the nodes increased slowly during the advanced stage of the disease. When 10 7 and 10 5 bacilli were injected into the footpad, the C3H/St mice succumbed to the disease at 298 and 344 days, respectively, and the modifications of blastogenesis were similar to those observed in i.p.-infected C3H/St mice. In contrast, the C57BL/6 mice appeared resistant to footpad inoculation of M. lepraemurium , since they lived until the end of the observation period (466 days postinfection) and the depression of blastogenesis was not detectable until 1 year after the infection. Thus, it is concluded that for the C57BL/6 mice (but not for the C3H/St mice), the route of administration of M. lepraemurium can markedly influence the susceptibility or resistance to leprosy.