Increase of intestinal intraepithelial lymphocytes expressing CD8 antigen following challenge infection with Eimeria acervulina.

Eimerian infection-induced changes in the intestinal intraepithelial lymphocyte (IEL) subpopulations expressing CD8 antigen (cytotoxic/suppressor T cells) or antigen-specific T cell receptor (TCR) heterodimer alpha beta (TCR2) or gamma delta (TCR1) were investigated in F2 crosses of 15I5 B-congenic chickens differing for the major histocompatibility complex (MHC). Duodenum TCR2+ IEL were increased in B2 B2 and B5 B5 chickens 7 days following secondary infection. Two-color immunofluorescence revealed that the majority of CD8+ cells in the duodenum intraepithelium of immune chickens expressed TCR2. A significant increase in the duodenum TCR2+CD8+ and TCR1+CD8+ IEL occurred in B2 B2 chickens, which developed significantly less oocyst production than the B5 B5 chickens following challenge infection. The results suggest that a significant increase in the duodenum CD8+ IEL may reflect an enhanced acquired immunity of B2 B2 chickens.