PRIMARY INFECTION WITH CRYPTOSPORIDIUM PARVUM

Changes in intraepithelial (IEL), lamina propria (LPL), and draining lymph node (LNL) lymphocytes were assessed in 9-day-old calves during primary infection with Cryptosporidium parvum and in similarly aged noninfected calves. A very low percentage of both CD4+ and CD8+ T cells were found in IEL and LPL of noninfected calves. In infected compared to controls, percentages of CD2 +, CD3 +, CD4+, and CD8 + T cells in IEL exhibited a significant increase (P < 0.05), whereas the percentage of IL2R+ increased and the percentage of IgG+ cells decreased, but neither of these changes were statistically significant. In LPL, percentages of CD2+, CD3+, CD8+, and IL2R+ T cells were increased in infected compared to noninfected calves, whereas the percentage of IgG-bearing cells decreased; but only the increase in CD3+, CD8+, and IL2R+ cells was significant (P - 0.05). In LNL only minimal changes were seen. In fact, the percentage of CD2+ T cells increased whereas the percentage of CD8 + T cells decreased, but neither of these differences was statistically significant. These findings indicate that T cell subsets in the ileal mucosa of naive neonatal calves are different than those of adult cattle, and that the immune response to C. parvum infection differs in ileal mucosa when compared to the regional lymph nodes. Cryptosporidium parvum is a parasitic protozoan recognized as a common cause of intestinal illness in humans and animals throughout the world. The disease, characterized by fluid diar- rhea and abdominal pain, is generally mild and self-limiting in adults and immunocompetent hosts, but clinical signs can be severe in young animals, and can become chronic and life- threatening in immunocompromised hosts (Fayer and Ungar,