Chemokines are molecules that control the migration and positioning of the immune system cells. In addition to their function as chemo-attractants they have various other roles in the maturation of immune cells such as T-cell development in the thymus and homeostatic retention of immune cells in the bone marrow¹.

Chemokines bind to chemokine receptors, members of the G-protein coupled receptor superfamily. They are comprised of seven transmembrane receptors with extracellular N-terminus, three extracellular and three intracellular loops and an intracellular C-terminus. One of the intracellular domains of the receptor couples with G proteins and begins a cascade of signal transduction².

Until recently the CXCR-7 was an “orphan” receptor with its endogenous ligand unknown. This receptor is encoded by the CXCR7/RDC-1 gene which was mapped to mouse chromosome 1 and human chromosome 2. Homology has been shown with the viral gene ORF74 suggesting the receptor might signal without the binding of a ligand. Currently it is known that the chemokines CXCL12 and CXCL11 bind to CXCR-7³.

CXCR-7 is tightly linked to the regulation of B cell development and differentiation indicating it might have a role in the formation of B memory cells⁴. CXCR-7 was also found to be associated with tumors where its levels are elevated in many tumor cell lines such as endothelial cells, fetal liver cells and placenta cells⁵. Despite this suggested role, there is growing evidence that this receptor does not function as a regular GPCR⁶.