Dual expression of chemokine receptor CCR4 and E-selectin ligand is characteristic of skin-tropic CD4 T cells from blood, lymphoid organs, and the skin itself. A strong and specific correlation exists among CCR4, its ligand CCL17/TARC, and the cutaneous lymphocyte-homing process. Nevertheless, whether CCR4 function is required for skin-specific trafficking remains an open question, which we address in this study. We developed an Ag-specific, TCR-transgenic, murine CD4 T cell adoptive transfer model that induces a mixed Th1 and Th17 cutaneous response. Within the hosts, both CCR4(+/+) and CCR4(-/-) donor CD4 T cells contribute equally well to the circulating E-selectin ligand(+) pool in response to Ag. However, only CCR4(+/+) donor cells accumulate efficiently within the skin. CCR4(-/-) cells home normally to the peritoneum, showing that they do not have a general defect in lymphocyte trafficking. We conclude that under physiological conditions, CCR4 is a nonredundant, necessary component of skin-specific lymphocyte trafficking.
