The Majority of Human Peripheral Blood CD4+CD25highFoxp3+ Regulatory T Cells Bear Functional Skin-Homing Receptors

CD4+CD25+ T regulatory cells (Treg) are thought to be important in the peripheral tolerance. Recent evidence suggests that human peripheral blood CD4+CD25+ T cells are heterogeneous and contain both CD4+CD25(high) T cells with potent regulatory activity and many more CD4+CD25(low/med) nonregulatory T cells. In this study, we found that virtually all peripheral blood CD4+CD25(high)Foxp3+ Treg expressed high levels of the chemokine receptor CCR4. In addition, 80% of Treg expressed cutaneous lymphocyte Ag (CLA) and 73% expressed CCR6. These molecules were functional, as CLA+ Treg showed CD62E ligand activity and demonstrable chemotactic responses to the CCR4 ligands CCL22 and CCL17 and to the CCR6 ligand CCL20. The phenotype and chemotactic response of these Treg were significantly different from those of CD4+CD25(med) nonregulatory T cells. We further demonstrated that blood CLA+ Treg inhibited CD4+CD25- T cell proliferation induced by anti-CD3. Based on homing receptor profile, CLA+ Treg should enter normal skin. We next isolated CD4+CD25(high) T cells directly from normal human skin; these cells suppressed proliferation of skin CD4+CD25- T cells. Therefore, the majority of true circulating Treg express functional skin-homing receptors, and human Treg may regulate local immune responses in normal human skin.