Abstract
The integrin CD103 and the chemokine receptor CCR9 are co‐expressed on small intestinal CD8^+^ intraepithelial lymphocytes (IEL), naïve murine CD8^+^ T cells and by a small population of effector/memory CD8^+^ T cells, indicating a potential role for CCR9 in regulating CD103 expression and function. Here, we demonstrate that CD103, in contrast to CCR9, is down‐regulated on CD8^+^ T cells following their activation in mesenteric lymph nodes and that effector CD8^+^ T cells upon initial entry into the small intestinal epithelium are CCR9^+^CD103^–^. CD103 was rapidly induced on wild‐type CD8^+^ T cells subsequent to their entry into the small intestinal epithelium, however, CCR9^–/–^ CD8^+^ T cells exhibited a significant delay in CD103 induction at this site. In addition, the CCR9 ligand, CCL25, that is constitutively expressed in the small intestinal epithelium, induced transient, dose‐dependent and pertussis toxin‐sensitive CD103‐mediated adhesion of CD8^+^ small intestinal IEL to a murine E‐cadherin human Fc (mEFc) fusion protein. Together, these results demonstrate a role for CCR9/CCL25 in promoting the induction and function of CD103 on CD8^+^ IEL and suggest that this chemokine receptor/chemokine pair may function to regulate lymphocyte‐epithelial interactions in the small intestinal mucosa.