Effects of Cryptosporidium parvum infection on lymphocyte phenotype and reactivity in calves.

Cryptosporidium parvum is a protozoan parasite now recognized as a significant cause of neonatal diarrhea in calves, and infection is also widespread in both immunocompetent and immunocompromised humans. No effective treatment or preventive measures against C. parvum infection are available, owing largely to the lack of understanding of immunologic mechanisms of resistance to and recovery from this parasite. In the present study, we compared phenotypes of lymphocytes from peripheral blood, spleen, mesenteric, and prescapular lymph nodes of calves infected or not infected with C. parvum. We also compared reactivity of these lymphocytes to mitogens and C. parvum antigen in vitro. There were more non-T, non-B (null) lymphocytes in all tissues of infected compared with control calves. The percent of CD8+ lymphocytes was significantly increased in spleens of infected compared with control calves, and there were markedly less CD4+ than CD8+ cells in spleens of both groups (i.e. low CD4/CD8 ratios). Splenic lymphocytes showed significantly decreased in vitro proliferation to pokeweed mitogen and C. parvum antigen stimulation compared with lymphocytes from other tissues. These findings suggest that null lymphocytes and CD8+ lymphocytes may be important in the expression and regulation of bovine immune responses to C. parvum in vivo.