Lymphocytes and not IFN-gamma mediate expression of iNOS by intestinal epithelium in murine cryptosporidiosis.

We hypothesized that unrecognized differences in epithelial expression of inducible nitric oxide synthase (iNOS), resulting from engineered immunodeficiency, could explain the contradictory findings of prior studies regarding the importance of nitric oxide (NO) in murine models of Cryptosporidium parvum infection. Severe combined immunodeficient mice (SCID) failed to constitutively or inducibly express epithelial iNOS or increase NO synthesis in response to C. parvum infection. In contrast, mice lacking IFN-gamma alone induced both epithelial iNOS expression and NO synthesis in response to infection. Accordingly, lymphocytes mediate epithelial expression of iNOS and NO synthesis independent of IFN-gamma in response to C. parvum infection. These findings in large part explain the contradictory conclusions of prior studies regarding the role of iNOS in C. parvum infection.