Role of intraepithelial lymphocytes in mucosal immune responses of mice experimentally infected with Cryptosporidium parvum

In order to investigate the role of intestinal intraepithelial lymphocytes (IELs) in host defense against Cryptosporidium parvum infection, convention ally bred immunocompetent (ImCT) ICR mice and immunosuppressed (ImSP) litte rmates were infected orally with 10(6) C. parvum oocysts. Then fecal oocyst excretion, the number and location of IELs, and their T lymphocyte subsets were observed on days 4, 7, 10, 13, 16, and 20 postinfection (PI). Uninfec ted ImCT and ImSP mice were used as controls. The starring point of oocyst excretion was day 4 PI in both ImCT- and ImSP-infected mice. The highest oo cyst excretion occurred on day 7 PI in both groups, though the number of oo cysts excreted was 3 times greater in ImSP than in ImCT mice. In ImCT mice, IELs greatly increased in number on days 16 and 20 PI (P < 0.05), but the increase was minimal in ImSP mice. IELs changed their location from the bas al area to intermediate and apical areas of villous epithelial cells during the early stage of infection. In ImCT-infected mice, IEL phenotypes also c hanged: whereas CD4(+) cells increased temporarily on day 7 PI (P < 0.05), CD8(+) cells increased significantly on days 16 and 20 PI (P < 0.05). The r esults strongly suggest that IELs play a significant role in host defense a gainst C. parvum infection, with helper T cells initiating control of the i nfection and cytotoxic T cells eliminating the parasites.