Susceptibility of major histocompatibility complex (MHC) class I- and MHC class II-deficient mice to Cryptosporidium parvum infection.

Major histocompatibility complex (MHC) class I-deficient and MHC class II-deficient mice lack functional CD8 T cells and CD4 T cells, respectively. These mice were evaluated for infection following oral administration of 10(7) Cryptosporidium parvum oocysts. MHC class II-deficient (but not MHC class I-deficient) mice dosed with C. parvum oocysts at 3 to 5 days of age remained infected 8 weeks postexposure. MHC class II-deficient mice exposed to C. parvum oocysts at 5 to 6 weeks of age were significantly more susceptible to infection than control mice (P < 0.0001).