RESUMO
C3H mice were immunized subcutaneously with water soluble antigens of ultrasonicated Mycobacterium lepraemurium bacilli (MLMSon-S) in Freund's incomplete adjuvant (FIA) and challenged with 1 X 10(6)-1.25 X 10(8) live MLM bacilli inoculated into the foot pad. No swelling of the infected foot pad and no differences in bacillary multiplication and dissemination between the immunized mice and the control animals were observed in the first nine weeks. From nine weeks on, a small foot pad swelling developed in the immunized mice. Twenty weeks after inoculation, the number of bacilli in the foot pad, the popliteal lymph node, and the spleen was significantly lower in the immunized mice than in the normal controls after challenge with the lowest bacillary doses. Cyclophosphamide (CY) pretreatment did not increase the effect of immunization. The addition of MLM cell wall fragments to the emulsion used for immunization tended to increase the difference between immunized and normal animals, while no further increase of the immunization effect was obtained by the use of Freund's complete adjuvant (FCA). A tendency toward a plateau phenomenon for the multiplication of MLM bacilli was observed in the normal mice. In nonimmunized mice, CY treatment caused some reduction in bacillary numbers in the foot pads, and reinfection experiments suggested that a small reduction in susceptibility had been induced by the priming infection. Although unable to prevent a progressive course of the infection, genetically low-resistant C3H mice were able to modify the development of the infection by mechanisms that were activated by the infection itself. Similar mechanisms were facilitated by immunization with MLMSon-S.