The function of ENSG00000154165 (GPR15, G protein-coupled receptor 15) is as follows. G protein-coupled receptor that plays an important role in immune homeostasis (PubMed:33758080, PubMed:38918398). Acts via its natural ligand GPR15LG, a chemokine-like polypeptide strongly expressed in gastrointestinal tissues. GPR15-GPR15LG signaling axis regulates intestinal homeostasis and inflammation through the migration of immune cells (PubMed:33758080, PubMed:38918398). Controls thereby the specific homing of T-cells, particularly FOXP3+ regulatory T-cells (Tregs), to the large intestine lamina propria (By similarity). Also required for skin localization of thymus-derived dendritic epidermal T-cells (By similarity). Plays an important role in mediating cytoprotective function as well as angiogenesis of thrombomodulin (By similarity). Mechanistically, preferentially signals through the Gi/o pathway to inhibit adenylate cyclase activity and activate a phosphatidylinositol- calcium second messenger system that regulates the release of Ca(2+) ions from intracellular stores (PubMed:35510660). {ECO:0000250|UniProtKB:Q0VDU3, ECO:0000269|PubMed:33758080, ECO:0000269|PubMed:35510660, ECO:0000269|PubMed:38918398}. (Microbial infection) Acts as an alternative coreceptor with CD4 for HIV-1 infection. .