IN-SITU CHARACTERIZATION OF LEUKOCYTE SUBPOPULATIONS AFTER INFECTION WITH EIMERIA-TENELLA IN CHICKENS

We characterized the leucocyte subpopulations after infection with Eim eria tenella in both naive and immune chickens. Immunocytichemical sta ining was used to characterize the cells in situ, so that the interact ion between host and parasite could be studied. More leucocytes were d etected in the lamina propria of immune chickens, and leucocytes infil trated the ceca more rapidly than in naive chickens, but the infiltrat ion was less pronounced than in naive chickens. In naive chickens, mos t infiltrated leucocytes were macrophages and T cells. Two days after inoculation the number of CD4(+) cells had increased greatly. In immun e chickens, mainly T cells (CD4(+) and CD8(+)) infiltrated the lamina propria, and in contrast to naive chickens, the number of CD8(+) cells exceeded the number of CD4(+) cells. Furthermore, we characterized wh ich cells contained a parasite and which cells were detected next to t he parasites, because these cells are probably involved in the arreste d development of the parasites. In naive chickens, sporozoites were si gnificantly more often located within or next to macrophages than in i mmune chickens. In immune chickens, sporozoites were significantly mor e often located, within or next to CD3(+), CD8(+), and TCR2(+) cells. In conclusion, the marked increase of CD4(+) cells after primary infec tion suggests that these cells are involved in the induction of the im mune response, whereas the increase of CD8(+) cells after challenge in fection suggests that these cells act as effector cells.