Unique Chemotactic Response Profile and Specific Expression of Chemokine Receptors Ccr4 and Ccr8 by Cd4⁺Cd25⁺ Regulatory T Cells

Chemokines dictate regional trafficking of functionally distinct T cell subsets. In rodents and humans, a unique subset of CD4⁺CD25⁺ cytotoxic T lymphocyte antigen (CTLA)-4⁺ regulatory T cells (Treg) has been proposed to control peripheral tolerance. However, the molecular basis of immune suppression and the trafficking properties of Treg cells are still unknown. Here, we determined the chemotactic response profile and chemokine receptor expression of human blood-borne CD4⁺CD25⁺ Treg cells. These Treg cells were found to vigorously respond to several inflammatory and lymphoid chemokines. Treg cells specifically express the chemokine receptors CCR4 and CCR8 and represent a major subset of circulating CD4⁺ T cells responding to the chemokines macrophage-derived chemokine (MDC)/CCL22, thymus and activation-regulated chemokine (TARC)/CCL17, I-309/CCL1, and to the virokine vMIP-I (ligands of CCR4 and CCR8). Blood-borne CD4⁺ T cells that migrate in response to CCL1 and CCL22 exhibit a reduced alloproliferative response, dependent on the increased frequency of Treg cells in the migrated population. Importantly, mature dendritic cells preferentially attract Treg cells among circulating CD4⁺ T cells, by secretion of CCR4 ligands CCL17 and CCL22. Overall, these results suggest that CCR4 and/or CCR8 may guide Treg cells to sites of antigen presentation in secondary lymphoid tissues and inflamed areas to attenuate T cell activation.