Susceptibility of selected inbred strains of mice to Encephalitozoon cuniculi.

Selected inbred strains of mice were examined for susceptibility to peritoneal infections with Encephalitozoon cuniculi. Marked differences in susceptibility and resistance among mouse strains were not controlled by loci within the mouse major histocompatibility (H-2) complex, but resistance in BALB/c mice was influenced by a dominant gene(s) outside the H-2 complex. The lethality of peritoneal infections in hypothymic nude mice suggested that resistance to encephalitozoonosis is dependent on thymus-derived lymphocytes. Peritoneal infection with E. cuniculi was associated with slightly enhanced proliferative spleen cell responses to mitogens in BALB/c mice and significantly depressed responses in C57Bl/6 mice. Infection in BALB/c mice was accompanied by normal antibody responses to sheep erythrocyte immunogens, but C57Bl/6 mice had depressed antibody responses. The results indicate that the immune system plays a major role in determining the course of peritoneal infections with E. cuniculi and that encephalitozoonosis can modulate the host's immune system.