Host immunological mechanisms in the resistance of mice to leptospiral infections.

Several serovars of Leptospira virulent for hamsters and guinea pigs caused acute lethal leptospirosis in mice immunosuppressed with cyclophosphamide. Neither BCG vaccine nor Corynebacterium parvum suspension influenced the course of leptospiral infection in either immunosuppressed or normal BALB/c mice. Nude athymic mice produced anti-leptospiral antibody and were therefore resistant to infection with leptospires. Nude mice were made susceptible with cyclophosphamide but were immune if they had acquired antibody from previous infection or immunization. The evidence suggests that mechanisms of resistance to primary infection and immunity to reinfection are exclusively humorally mediated in mice. The roles of host and microbial factors in the outcome of infection are discussed.