Gut-associated lymphoid tissue-primed CD4+ T cells display CCR9-dependent and -independent homing to the small intestine.

CD4(+) T-cell entry to the intestinal mucosa is central to the generation of mucosal immunity as well as chronic intestinal inflammation, yet the mechanisms regulating this process remain poorly defined. Here we show that murine small intestinal CD4(+) lamina propria lymphocytes express a heterogeneous but restricted array of chemokine receptors including CCR5, CCR6, CCR9, CXCR3, and CXCR6. CD4(+) T-cell receptor transgenic OT-II cells activated in mesenteric lymph nodes acquired a distinct chemokine receptor profile, including expression of CCR6, CCR9, and CXCR3 that was only partially reproduced in vitro after priming with mesenteric lymph node dendritic cells. A subset of these effector CD4(+) T cells, expressing CD69 and alpha(4)beta(7), entered the intestinal lamina propria and the majority of these cells expressed CCR9. CCR9(-/-) OT-II cells were disadvantaged in their ability to localize to the intestinal lamina propria; however, they were readily detected at this site and expressed alpha(4)beta(7), but little CCR2, CCR5, CCR6, CCR8, CCR10, CXCR3, or CXCR6. Thus, whereas CD4(+) T cells activated in gut-associated lymphoid tissue express a restricted chemokine receptor profile, including CCR9, targeting both CCR9-dependent and CCR9-independent entry mechanisms is likely to be important to maximally inhibit accumulation of these cells within the small intestinal mucosa.