T-cell homing to the gut mucosa: general concepts and methodological considerations.

Effector/memory T cells can migrate to most extra-lymphoid tissues in the body. However, migration to the intestinal mucosa requires the expression of very specific homing receptors on T cells, integrin α4ß7 and chemokine receptor CCR9. These receptors are induced by all-trans retinoic acid (RA), a vitamin A metabolite that is specifically synthesized by gut-associated dendritic cells (DC), but not by extra-intestinal DC. Here we summarize some general concepts on T cell homing with an emphasis on the gut mucosa. We also discuss experimental strategies to generate gut-homing T cells in vivo and in vitro and the techniques to track gut-homing T cells.