CCR4 (C-C chemokine receptor type 4) is a high affinity receptor for the C-C type chemokines CCL17/TARC and CCL22/MDC. CCR4 receptors express in the thymus, peripheral blood leukocytes and the spleen. CCR4 functions as a chemoattractant homing receptor on circulating memory lymphocytes and as a coreceptor for some primary HIV-2 isolates. In the CNS, CCR4 mediates hippocampal-neuron survival. CCR4 is one of the type 2 T helper cell (Th2) markers. Th2 cells are recruited to the asthmatic lung in response to allergen challenge and CCR4 has been therefore considered as a therapeutic target of lung inflammation, including eosinophilic inflammation of the lung and asthma. In addition, CCR4 has been reported as a potential independent and significant prognostic factor for adult Tcell leukemia/lymphoma (ATLL).