Lymphocyte subpopulations in the caecum mucosa of rats after infections with Eimeria separata: early responses in naive and immune animals to primary and challenge infections.

This study aimed to characterise the local (intestinal) immune response of rats after primary and challenge infections with Eimeria separata. Naive rats and rats which had been immunised by two moderate infections were exposed to a heavy infection with 100000 oocysts per animal. Necropsies were performed 0, 24 and 48 h after infection and lymphocyte subpopulations were microscopically quantified in the caecum mucosa after marking by immunohistological techniques. There was no difference between naive and immune rats concerning the number of CD45R(+) (B) cells, whereas significantly more CD3(+) (T) cells were found in the caecum wall of the immune rats. CD4(+) T cells predominated in animals after primary infection, whereas CD8(+) T cells represented the major T-cell subset in challenged rats. The proportion of TCRgammadelta(+) T cells did not differ in the mucosa between the groups examined, whereas challenged rats showed significantly increased numbers of TCRalphabeta(+) T cells in the caecum wall when compared with animals after a primary infection. Thus, CD4(+) T cells may be particularly involved in the immune response to a primary infection of rats with E. separata whereas immunity to a challenge infection seems to be mediated predominantly by CD8(+) and TCRalphabeta(+) T cells.