Mechanisms of resistance to the intracellular protozoan Encephalitozoon cuniculi in mice.

Mechanisms of resistance to the obligate intracellular protozoan Encephalitozoon cuniculi were studied in BALB/c mice. Resistance to lethal disease was T cell-dependent because transfer of T-enriched, but not T-depleted, spleen cells from sensitized BALB/c donors would protect infected BALB/c-nu mice. A modified focus-forming assay was utilized to measure effects on E. cuniculi infectivity in vitro. The results show that antibodies exert an opsonization effect and may block parasite entry into nonphagocytic cells. No cytotoxic T cells were demonstrated. Supernatants from E. cuniculi-sensitized spleen cells incubated with E. cuniculi in vitro could induce adherent PEC to kill E. cuniculi.