The objective of this study was to determine whether changes in the ileal intraepithelial lymphocyte (IEL) phenotype and function occurred prior to development of diarrhea in Cryptosporidium parvum–infected calves. Calves were orally inoculated with 108 oocysts and maintained in enteric pathogen-free conditions until their use in experiments. Age-matched uninfected calves were used for comparisons. Ileal IELs were isolated and phenotyped to determine whether changes in lymphocyte population dynamics had occurred by 3 days postinoculation (PI). Ex vivo reverse transcriptase–polymerase chain reaction of messenger ribonucleic acid (mRNA) from IELs from infected calves was compared with controls to determine whether changes in cytokine expression had occurred by 3 days PI. No significant changes in lymphocyte population dynamics were documented; however, IELs isolated from 4 out of 8 infected calves, but not from 8 out of 8 control calves, expressed mRNA for interleukin-10 (IL-10). IL-10 expression by IELs was associated with the expression of a significantly larger (P < 0.001) proportion (0.75) of monoclonal antibody–defined C. parvum epitopes within infected ileal epithelium, as compared with a much smaller proportion (0.30) of epitopes with IL-10 lymphocytes. The results suggest that a temporal association exists between the expression of IL-10 by ileal IELs and the expression of C. parvum antigens in infected calf epithelium prior to development of cryptosporidiosis.

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