CD184, also known as CXCR4 or Fusin, is a seven-transmembrane G protein-coupled receptor that plays a crucial role in various physiological processes. It is widely expressed on hematopoietic cells, including lymphoid and myeloid precursor cells, megakaryocytes, and endothelial cells. Its natural ligand is stromal cell-derived factor-1 (SDF-1), a C-X-C chemokine that induces chemotaxis and enhances intracellular signaling through calcium ion influx and MAPK activation.