Immunity to Eimeria tenella in chickens: Phenotypical and functional changes in peripheral blood T-cell subsets

The changes in peripheral blood leukocyte (PBL) T-cell subsets following Eimeria tenella infection in outbred white leghorn chickens were studied, using a panel of murine monoclonal antibodies specific for the chicken homologues of the mammalian CD3, CD8, and CD4 markers on day-to-day samples of PBLs. Both flow cytometric analysis (FCA) and immunofluorescence microscopy with fixed cells on slides were used as read-out systems. The changes in the composition of the T-cell subsets measured with both techniques were similar. Ar 8 days post primary infection, a sharp transitory increase in the proportion of CD8-expressing cells was found. With FCA, CD8-expressing cells could be discriminated in CD8(Dim+) and CDSBright+ populations, which have not been described before. The proportion of CD4-expressing cells was decreased at days 9-10 after primary infection, which coincided with a less marked decrease in CD3-expressing cells. Such effects were not seen after secondary infection. When PBLs collected at day 8 post primary infection were stimulated in vitro with E. tenella sporozoite antigen, the response was higher than that in uninfected control chickens. The effects we observed coincide with the onset of recovery from primary infection. We speculate that the increase in CD8-expressing PBLs is the result of stimulation and expansion of a specific subset involved in the induction of protective immunity against Eimeria tenella.