Analysis of Eimeria acervulina-induced changes in the intestinal T lymphocyte subpopulations in two chicken strains showing different levels of susceptibility to coccidiosis.

The major T lymphocyte subpopulations expressing CD8, CD4, or antigen-specific T cell receptor (TCR) heterodimer alpha beta (TCR2) or gamma delta (TCR1) were assessed in duodenum intraepithelium of two inbred chicken strains, SC and TK, by single- and double-label immunofluorescence (IF) at various times after oral inoculation with Eimeria acervulina. The duodenum intraepithelial T lymphocytes (IEL) expressing the CD8 antigen (cytotoxic/suppressor T cells) increased in the SC and TK chickens following primary infection. However, a significant increase in the duodenum CD8+ IEL occurred in the SC chickens which manifested as a lower level of oocyst production compared to the TK chickens following primary and challenge infections. The CD4+ (T helper) cells increased seven days after primary infection in SC and TK chickens, and in TK chickens seven days after challenge infection. Two colour immunofluorescence analysis of duodenum IEL at 10 days after challenge infection revealed that the majority of CD8+ IEL expressed the TCR2 antigen. Furthermore, the SC chickens showed increased TCR2+CD8+ cells shortly following challenge with E acervulina. These results suggest that variations in T cell subpopulations may reflect eimerian infection-related changes in the gut-associated lymphoid tissues and that a significant increase in CD8+ IEL in SC chickens may reflect enhanced acquired immune status in SC chickens compared to TK chickens.