CXCR1 and CXCR2 are closely related receptors that recognize CXC chemokines that possess an E-L-R amino acid motif immediately adjacent to their CXC motif. CXCL8 (otherwise known as interleukin-8) and CXCL6 can both bind CXCR1 in humans, while all other ELR-positive chemokines, such as CXCL1 to CXCL7 bind only CXCR2. They are both expressed on the surface of neutrophils in mammals.
CXCR3 is expressed predominantly on T cells (T lymphocytes), and also on other lymphocytes [some B cells (B lymphocytes) and NK cells] and is highly induced following cell activation. There are two isoforms, CXCR3-A and CXCR3-B. It has three highly related ligands in mammals, CXCL9, CXCL10 and CXCL11.
CXCR6 was formerly called three different names (STRL33, BONZO, and TYMSTR) before being assigned CXCR6 based on its chromosomal location (within the chemokine receptor cluster on human chromosome 3p21) and its similarity to other chemokine receptors in its gene sequence. CXCR6 binds the ligand CXCL16. However, CXCR6 is more closely related in structure to CC chemokine receptors than to other CXC chemokine receptors.
CXCR7 was originally called RDC-1 (an orphan receptor) but has since been shown to cause chemotaxis in T lymphocytes in response to CXCL12 (the ligand for CXCR4) prompting the renaming of this molecule as CXCR7. There is no information publicly available to confirm whether this designation has been accepted by the IUIS/WHO Subcommittee on Chemokine Nomenclature at this time. This receptor has also been identified on memory B cells.
^Tsai, H.-H., Frost, E., To, V., Robinson, S., ffrench-Constant, C., Geertman, R., Ransohoff, R.M., Miller, R.H. The chemokine receptor CXCR2 controls positioning of oligodendrocyte precursors in developing spinal cord by arresting their migration. Cell 110: 373-383, 2002.
^Pelus LM, Fukuda S. Peripheral blood stem cell mobilization: the CXCR2 ligand GRObeta rapidly mobilizes hematopoietic stem cells with enhanced engraftment properties. Exp Hematol. 2006 Aug;34(8):1010-20. PMID = 16863907
^Lasagni L, Francalanci M, Annunziato F, Lazzeri E, Giannini S, Cosmi L, Sagrinati C, Mazzinghi B, Orlando C, Maggi E, Marra F, Romagnani S, Serio M, Romagnani P. An alternatively spliced variant of CXCR3 mediates the inhibition of endothelial cell growth induced by IP-10, Mig, and I-TAC, and acts as functional receptor for platelet factor 4. J Exp Med. 2003 Jun 2;197(11):1537-49.
^Tensen et al. Human IP-9: a keratinocyte derived high affinity CXC-chemokine ligand for the IP-10/Mig receptor (CXCR3). J. Invest. Dermatol. 112:716-722, 1999.
^Booth et al. The CXCR3 binding chemokine IP-10/CXCL10: structure and receptor interactions. Biochemistry 41: 10418-10425, 2002.
^Legler D.F., Loetscher M., Stuber Roos R., Clark-Lewis I., Baggiolini M., Moser B.; B cell-attracting chemokine 1, a human CXC chemokine expressed in lymphoid tissues, selectively attracts B lymphocytes via BLR1/CXCR5. J. Exp. Med. 187:655-660, 1998. PubMed : 9463416
^Balabanian et al., The chemokine SDF-1/CXCL12 binds to and signals through the orphan receptor RDC1 in T lymphocytes, J Biol Chem, 2005, 280:35760-35766.