IL-12 protects immunocompetent and immunodeficient neonatal mice against infection with Cryptosporidium parvum

The protozoan parasite Cryptosporidium parvum (Cp) causes diarrhea that can be acutely severe in immunocompetent persons and can become chronic and life-threatening in immunocompromised individuals. Because studies in mice have implicated IFN-γ in protection against this parasite, and IL-12 can induce IFN-γ production, we examined the ability of IL-12 to prevent or cure Cp infection in neonatal BALB/c and SCID mice. Treatment of both immunocompetent and immunodeficient mice with IL-12 before experimental inoculation with Cp oocysts prevented or greatly reduced the severity of infection. Intestinal epithelial cell invasion and/or early intracellular development of Cp was inhibited by exogenous IL-12. The protective effect of IL-12 was completely blocked by anti-IFN-γ mAb. Established infections were associated with elevated IFN-γ gene expression and were not ameliorated by IL-12 treatment, even though such treatment further enhanced IFN-γ gene expression. The severity of Cp infection was, however, exacerbated by treatment with anti-IL-12 Ab. These observations provide the first evidence that treatment with exogenous IL-12 can prevent Cp infection through an IFN- γ-dependent, specific immune system-independent mechanism, and that endogenous IL-12 production has a role in limiting Cp infection.