Identification of CCR8: A Human Monocyte and Thymus Receptor for the CC Chemokine I-309

The human CC chemokine I-309 is a potent monocyte chemoattractant and inhibits apoptosis in thymic cell lines. Here, we identify a specific human I-309 receptor, and name it CCR8 according to an accepted nomenclature system. The receptor has seven predicted transmembrane domains, is expressed constitutively in monocytes and thymus, and is encoded by a previously reported gene of previously unknown function named, alternatively, CY6, TER1, and CKR-L1. After transfection with the CY6 open reading frame, a mouse pre–B cell line exhibited calcium flux and chemotaxis in response to I-309 (EC(50) = 2 nM for each), whereas 20 other chemokines were inactive. Signaling was sensitive to pertussis toxin, suggesting coupling to a G(i)-type G protein. These properties parallel those of endogenous I-309 receptors expressed in an HL-60 clone 15 cell line model. The apparent monogamous relationship between I-309 and CCR8 is unusual among known CC chemokines and known CC chemokine receptors. CCR8 may regulate monocyte chemotaxis and thymic cell line apoptosis.