CXCR4/CD184/LESTR/fusin/NPY3R is a G protein-coupled receptor for the CXC chemokine SDF-1. Binding of SDF-1 induces CXCR4 phosphorylation by Ser/Thr kinases, leading to CXCR4 internalization via clathrin-coated pits. CXCR4 functions include co-stimulation in pre-B cell proliferation, induction of apoptosis, and HIV entry, since CXCR4 is one of the 2 major HIV/SIV co-receptors. Early infection with HIV-1 is dominated by CCR5-tropic (R5) viruses. The evolution of CXCR4-tropic (X4) viruses occurs later in the infection and is associated with rapid disease progression. CXCR4 mediates chemotaxis in mature and progenitor blood cells and is essential for B lympho- and myelopoiesis, cardiogenesis, blood vessel formation and cerebellar development. Although ubiquitously expressed in blood and tissue cells, its role in blood and tissue homeostasis is not fully understood. CXCR4 is predominantly stored intracellularly, and may contribute to the inefficiency in transmission and propagation of X4-tropic viruses.Synonyms: C-X-C chemokine receptor type 4, CXC-R4, CXCR-4, FB22, Fusin, HM89, LCR1, LESTR, Leukocyte-derived seven transmembrane domain receptor, NPYRL, SDF1 receptor, Stromal cell-derived factor 1 receptor