Dietary nucleosides and nucleotides reduce Cryptosporidium parvum infection in dexamethasone immunosuppressed adult mice

Numerous studies have demonstrated that dietary sources of nucleosides and nucleotides are important for the maintenance of cellular and humoral immune responses. To determine the immunological effects of feeding a nucleoside-nucleotide mixture to dexamethasone-immunosuppressed C57BL/6 adult mice infected with Cryptosporidium parvum, we examined fecal oocyst shedding, lymphoproliferative responses to concanavalin (Con) A, and C. parvum antigen, interleukin (IL-2), and gamma-interferon (IFN-γ) production by cultured spleen cells. Mice were fed a nucleotide-free 20% casein diet (control group) or this diet supplemented with a 0.5% nucleoside-nucleotide mixture before and after inoculation with C. parvum. Spleens from mice receiving the supplemented diet had higher (P < 0.05) Con A and antigen-specific induced cell proliferation than those from control mice. In addition to the increased cell proliferation, the spleen cells from the supplemented mice produced significantly more IL-2 (P < 0.002) and significantly more IFN-γ (P < 0.004) than cells from the control mice. Mice fed the supplemented diet excreted fewer (P < 0.05) C. parvum oocysts in the feces than control mice. The cumulative survival rate in the nucleoside-nucleotide mixture-fed group was higher compared with the control group (P < 0.05). We conclude that nucleosides and nucleotides may partially counteract the immunosuppressive effects of dexamethasone in C. parvum-challenged mice.