Chemokine receptor CCR7 required for T lymphocyte exit from peripheral tissues.

Lymphocytes travel throughout the body to carry out immune surveillance and participate in inflammatory reactions. Their path takes them from blood through tissues into lymph and back to blood. Molecules that control lymphocyte recruitment into extralymphoid tissues are well characterized, but exit is assumed to be random. Here, we showed that lymphocyte emigration from the skin was regulated and was sensitive to pertussis toxin. CD4(+) lymphocytes emigrated more efficiently than CD8(+) or B lymphocytes. T lymphocytes in the afferent lymph expressed functional chemokine receptor CCR7, and CCR7 was required for T lymphocyte exit from the skin. The regulated expression of CCR7 by tissue T lymphocytes may control their exit, acting with recruitment mechanisms to regulate lymphocyte transit and accumulation during immune surveillance and inflammation.