Eimeria tenella: sporozoites rarely enter leukocytes in the cecal epithelium of the chicken (Gallus domesticus).

In this study, the intraepithelial leukocytes supposedly involved in the transportation of Eimeria tenella sporozoites through the cecal lamina propria were phenotypically characterized. The ceca of naive and immune chickens were examined at various times after inoculation by light microscopy and immunocytochemical techniques. The distribution of sporozoites within the villus differed markedly between both groups. From 16 hr postinoculation, significantly fewer sporozoites had reached the crypts in immune chickens, and schizont formation was inhibited. In the villus epithelium of both naive and immune chickens, few sporozoites were found within a leukocyte. Using anti-sporozoite and anti-CD45 monoclonals, we showed that even when intraepithelial leukocytes are abundantly present, only a few sporozoites were inside them. In the lamina propria of immune chickens significantly more sporozoites were found within leukocytes than in the lamina propria of naive chickens. The phenotype of the few leukocytes that harbored sporozoites was similar in naive and immune chickens. A few sporozoites were detected in B cells, 10% in macrophages, and 50% in T cells, especially CD8+ cells. These results show that E. tenella sporozoites rarely enter intraepithelial leukocytes and therefore their putative role in transporting sporozoites through the lamina propria is doubtful.