Cryptosporidium parvum: the contribution of Th1-inducing pathways to the resolution of infection in mice

The contribution of cytokines IL-12, IL-18, IL-23, and IFN-γ, and Stat1 signaling molecules involved in Th1 responses associated with host resistance to Cryptosporidium parvum infection was investigated in adult IL-12p40^−/−mice. Host resistance to C. parvum infection was assessed in different mouse strains lacking IL-12, IL-18, and IL-23 genes. We found that as in IL-12p40^−/− mice (which lack both IL-12 and IL-23), IL-12p35^−/− mice (which lack IL-12) and IL-18 deficient mice were also susceptible to infection with C. parvum. Varied levels of resistance were observed when mice were treated with cytokines like IL-18, IL-23 and IFN-γ. Mice treated with IL-12, as expected, were completely resistant to infection until day 5 post infection, and had significantly decreased (85%) parasite loads at peak infection (day 7), whereas rIL-23 had a lesser effect, decreasing parasite load by approximately 45%. Interestingly, IL-18 appears to play a significant role in initial immune response, even in the absence of IL-12, since treatment with IL-18 in IL-12p40^−/− knockout mice decreased parasite load by approximately 70%. In addition, the establishment of C. parvum infection in mice lacking the Stat1 gene demonstrated the involvement of this pathway in resolution of infection. These observations indicate a strong requirement for Th1 response in the development of immunity to C. parvum in the adult IL-12p40^−/− mice, information that will be essential to further investigate the immune responses during infections and in the development of potential vaccine candidates.