Development of cellular immune functions in neonatal to weanling mice: relationship to Cryptosporidium parvum infection.

Lymphocyte phenotypes and cellular immune responses (blastogenesis and production of cytokines) to Cryptosporidium parvum were determined for spleen cells taken from BALB/c mice. These parameters were measured in mice at 1, 2, 3, and 4 wk of age, either exposed or not exposed to C. parvum in vivo. The percentage of T cells and the T-helper subset increased from weeks 2 to 4; B cells reached a peak percentage at 2 wk. Blastogenic responses were elevated at 1 wk and declined to a low level during weeks 2 to 4. Interferon-gamma production was maximal at 4 wk. No interleukin-5 production was seen. Data obtained were similar for cells from mice either exposed or not exposed to C. parvum in vivo. These data indicate that age-related changes, particularly the increased percentage of T cells and increased interferon-gamma production, are temporally related to the acquisition of resistance to colonization of mice with C. parvum. The data also indicate that these age-related changes occur in the absence of specific exposure to parasite antigens.