Accumulation of mucosal T lymphocytes around epithelial cells after in vitro infection with Cryptosporidium parvum

We had previously shown that ileal intraepithelial lymphocytes isolated fro m calves with cryptosporidiosis include significantly increased numbers of CD8(+) T lymphocytes and activated CD4(+) cells. These increases could resu lt from redistribution of resident mucosal lymphocytes or from homing of pe ripheral T cells to ileal mucosa. To determine whether resident mucosal lym phocytes can redistribute to Cryptosporidium parvum-infected epithelium, oo cysts were inoculated in vitro onto ileum explants taken from 1-2-wk-old no ninfected calves. After 24 hr of incubation, the explants were collected an d frozen in liquid nitrogen. Immunohistochemical analysis of T-lymphocyte s ubpopulations was performed on sections, and labeled lymphocytes adjacent t o villous epithelial cells were counted. Compared with uninoculated explant s. there was a statistically significant increase in the number of CD8(+) T lymphocytes per 100 epithelial cells in oocyst-inoculated tissue. In addit ion, there were increased numbers of CD4(+) T cells and activated (CD25(+)) lymphocytes adjacent to C. parvum-infected epithelium. These results show that resident mucosal T lymphocytes can accumulate at the epithelium during C. parvum infection.