EFFECTS OF CRYPTOSPORIDIUM-PARVUM INFECTION ON LYMPHOCYTE PHENOTYPE AND REACTIVITY IN CALVES

Cryptosporidium parvum is a protozoan parasite now recognized as a sig nificant cause of neonatal diarrhea in calves, and infection is also w idespread in both immunocompetent and immunocompromised humans. No eff ective treatment or preventive measures against C. parvum infection ar e available, owing largely to the lack of understanding of immuno-logi c mechanisms of resistance to and recovery from this parasite. In the present study, we compared phenotypes of lymphocytes from peripheral b lood, spleen, mesenteric, and prescapular lymph nodes of calves infect ed or not infected with C. parvum. We also compared reactivity of thes e lymphocytes to mitogens and C. parvum antigen in vitro. There were m ore non-T, non-B (null) lymphocytes in all tissues of infected compare d with control calves. The percent of CD8(+) lymphocytes was significa ntly increased in spleens of infected compared with control calves, an d there were markedly less CD4(+) than CD8(+) cells in spleens of both groups (i.e. low CD4/CD8 ratios). Splenic lymphocytes showed signific antly decreased in vitro proliferation to pokeweed mitogen and C. parv um antigen stimulation compared with lymphocytes from other tissues. T hese findings suggest that null lymphocytes and CD8(+) lymphocytes may be important in the expression and regulation of bovine immune respon ses to C. parvum in vivo.