Changes in intestinal intra-epithelial and systemic T-cell subpopulations after an Eimeria infection in chickens: comparative study between E acervulina and E tenella.

During chicken coccidiosis, the growth of the parasite in the intestinal epithelium cells leads to the development of host immune response. Cell-mediated immune mechanisms appear to be mainly responsible for the acquired resistance to disease. The action of two species of Eimeria, with two different intestinal localizations, on T-lymphocyte subsets was followed by fluorescent antibody cell-sorter analysis, locally at the intestinal site of the parasitic development and systemically in spleen and blood. An Eimeria acervulina infection, localized in duodenum, induced a significant increase in the proportion of CD4+ (up to 15%), CD8+ (up to 12%) and TCR gamma/delta (up to 6%) in the duodenal intraepithelial leucocytes (IEL) from day 4 to day 8 Pl, and an increase in the proportion of IgM+ cells (12%) on day 8. At the same time, the proportion of CD8+ cells dropped significantly in the blood and spleen (-5 to -10%) on days 4 and 6 Pl and then increased with the proportion of CD4+ cells on day 8. An E tenella infection, localized in caecum, increased the proportion of CD4+ cells on day 8 Pl (20%) and of CD8+ cells (10%) on days 6 and 8 Pl in caecal IEL. A negative or zero effect on the proportion of TCR gamma/delta + cells was observed as well as on the IgM+ cells. At the same time, the proportion of CD4+ cells dropped in the spleen on day 8 Pl (-10%) and that of CD8+ cells dropped in the blood on day 6 (-15%). In conclusion, Eimeria infection seems to rapidly induce, locally at the site of the parasite development, a dramatic modification of the proportion of T-cell subsets in IEL, accompanied by systemic variations that are generally opposing, in the lymphocyte populations. The timing of the changes seems to follow the phases of the parasitic cycle for the Eimeria species considered.