An orphan seven transmembrane G protein-coupled receptor called GPR5 was identified as a specific functional receptor for Lptn/SCM-1/ATAC and is now termed XCR1. Lymphotactin (Lptn)/single C-motif 1 (SCM-1)/activation-induced, T cell-derived and chemokine-related molecule (ATAC) belongs to theCor subfamily of chemokines.XCR1is expressed in tissues such as placenta, thymus, and spleen in humans. Few, if any, transcripts are, however, detected
in peripheral blood leukocytes. Therefore, the exact types of cells that express XCR1 are still not known. Ltpn/SCM-1/ATAC induces chemotaxis and calcium flux in murine L1.2 cells transfected with XCR1. XCR1 and its murine counterpart mXCR1 have no N-glycosylation sites and have a sequence of HRYLSVVSP in the second intracellular domain instead of the standard DRY (Asp-Arg-Tyr) motif highly conserved in many chemokine receptors.