CD4+ T cells are not essential for control of early acute Cryptosporidium parvum infection in neonatal mice

Cryptosporidiosis is an important diarrheal disease of humans and neonatal livestock caused by Cryptosporidium spp. that infect epithelial cells. Recovery from Cryptosporidium parvum infection in adult hosts involves CD4(+) T cells with a strong Th1 component, but mechanisms of immunity in neonates are not well characterized. In the present investigation with newborn mice, similar acute patterns of infection were obtained in C57BL/6 wild-type (WT) and T and B cell-deficient Rag2(-/-) mice. In comparison with uninfected controls, the proportion of intestinal CD4(+) or CD8(+) T cells did not increase in infected WT mice during recovery from infection. Furthermore, infection in neonatal WT mice depleted of CD4(+) T cells was not exacerbated. Ten weeks after WT and Rag2(-/-) mice had been infected as neonates, no patent infections could be detected. Treatment at this stage with the immunosuppressive drug dexamethasone produced patent infections in Rag2(-/-) mice but not WT mice. Expression of inflammatory markers, including gamma interferon (IFN-γ) and interleukin-12p40 (IL-12p40), was higher in neonatal WT mice than in Rag2(-/-) mice around the peak of infection, but IL-10 expression was also higher in WT mice. These results suggest that although CD4(+) T cells may be important for elimination of C. parvum, these cells are dispensable for controlling the early acute phase of infection in neonates.