Gastrointestinal cellular and humoral immune responses in BALB/c mice infected with Cryptosporidium parvum.

Abstract

Immunohistochemical analysis of intestinal tissue from infected and uninfected neonatal mice was performed to determine immune responsiveness to Cryptosporidium parvum at the gut level. Infected mice showed a significant increase in T cell (T helper/T cytotoxic/suppressor) populations (p < 0.001), macrophages (p < 0.001), IL-2R positive cells (p < 0.001 at 16 days PI), and IgA positive cells (p < 0.001 at 16 days PI) compared to control (uninfected) animals. No differences between the two groups of animals existed for B cell populations of the IgG (p = 0.264) and IgM (p = 0.646) isotype. Cellular immunity seems to be primarily responsible for clearing cryptosporidial infection from infected animals. Humoral immunity mediated by B cells of the IgA isotype could be a secondary (delayed) factor which aids in the recovery of the animal. Neonatal mice were also infected with C. parvum to describe the susceptibility dynamics in this animal model. Percent infectivity of the animals (infected at various days of age beginning on day 4 and ending at day 18) began to decrease at 10 days of age (33% infectivity). Infectivity percentages varied up until 14 days of age and older when all of the animals inoculated were refractory to infection. Why this refractiveness to infection occurs as the animals age is still unknown. In another study neonatal mice infected at 4 days of age continued to be positive for parasites up until 25 days of age (21 days PI). Percent infectivity began to vary at 20 days of age (16 days PI) which meant that only a certain percentage of the mice tested at that time point were positive for C. parvum. Prior to 20 days of age 100% of the animals tested were infected. Proliferative responses of spleen cells from infected and control mice to C. parvum antigen were measured. Spleen cells from infected animals responsed to C. parvum antigen in vitro (stimulation index (SI) = 14.52 (infected mouse #1); 14.23 (infected mouse #2)) whereas cells from uninfected mice did not (SI = 1.12 (control mouse #1); 1.07 (control mouse #2)). The spleen seems to be one organ involved in the immune circuitry responsible for clearance of cryptosporidiosis in neonatal mice.