CC chemokine receptors (orbeta chemokine receptors) areintegral membrane proteins that specifically bind and respond tocytokines of theCC chemokine family. They represent one subfamily ofchemokine receptors, a large family ofG protein-linked receptors that are known as seven transmembrane (7-TM) proteins since they span the cell membrane seven times. To date, ten true members of the CC chemokine receptor subfamily have been described. These are named CCR1 to CCR10 according to the IUIS/WHO Subcommittee on Chemokine Nomenclature.

The CC chemokine receptors all work by activating theG proteinG_i.^[1]

CCR1 was the first CC chemokine receptor identified and binds multipleinflammatory/inducible (seeinducible gene) CC chemokines (includingCCL4,CCL5,CCL6,CCL14,CCL15,CCL16 andCCL23).^[2][3][4] In humans, this receptor can be found onperipheral blood lymphocytes andmonocytes. There is some suggestion that this chemokine receptor is restricted tomemory T-cells within thelymphocyte pool. This receptor is also designatedcluster of differentiation marker CD191.

CCR2 can interact withCCL2,CCL8 andCCL16 and has been identified on the surface ofmonocytes, activatedmemory T cells,B cells, andbasophils in humans, and also inperitonealmacrophages in mice.^[4][5] CCR2 is also designated CD192.

CCR3 is a receptor for multiple inflammatory/inducible CC chemokines, includingCCL11,CCL26,CCL7,CCL13,CCL15,CCL24 andCCL5 that attracteosinophils, andCCL28 that attracts B and Tlymphocytes tomucosal tissues.^{[3][6][7][8][9]} It is most highly expressed in botheosinophils andbasophils, but can also be found inTh1 andTh2 cells and airwayepithelial cells. Thus CCR3 plays a role in allergic reactions. CCR3 is also known asCD193.

CCR4 is expressed on Th2T lymphocytes and is up-regulated byT cell receptor activation. However, some reports suggest a role for this receptor also in trafficking ofdendritic cells. The CC chemokinesCCL3,CCL5,CCL17 andCCL22 signal through this receptor.^[10][11]

CCR5 is expressed on several cell types including peripheral blood-deriveddendritic cells, CD34+hematopoieticprogenitor cells and certain activated/memoryTh1 lymphocytes. This receptor is well defined as a major coreceptor implicated in susceptibility toHIV-1 infection and disease. This receptor has several CC chemokine ligands includingCCL2,CCL3,CCL4,CCL5,CCL11,CCL13,CCL14 andCCL16.^{[4][5][12][13]}

CCR6, a receptor forCCL20, is expressed on unactivatedmemory T-cells and somedendritic cells. CCR6 is also expressed on Th17 cells.^[14] CCR6 is down-regulated in activated T-cells.^[15]

CCR7 is a highly important receptor with a role in trafficking of B and T lymphocytes anddendritic cells to and acrosshigh endothelial venules and positioning those cells correctly in T cell zones of secondarylymphoid organs. Its ligands include the related chemokinesCCL19 andCCL21, (previously called ELC and SLC).^[16]

CCR8 is associated with Th2 lymphocytes and is therefore found predominantly in thethymus (in humans) although some expression can be found in the brain,spleen,lymph node, and monocytes at thenucleotide level. The ligands for this receptor areCCL1 andCCL16^[17]

CCR9 was previously calledorphan receptor GPR 9-6 and is very highly expressed in thymus (on both immature and mature T-cells) while low in lymph nodes and spleen. CCR9 is also abundant in the gut, with its expression associated with T cells of theintestine. The specific ligand of this receptor isCCL25^[18] To note, the chemokine binding protein D6 had previously been named CCR9, but this molecule is ascavenger receptor not a true (signaling) chemokine receptor.

CCR10 is receptor forCCL27 andCCL28 that was originally called orphan receptor GPR2.^{[8][19][20][21]} CCR10 has been implicated in inflammation of the skin, and has been shown to recruitregulatory T cells (Tregs) to mucosal layers.

This molecule was originally designated CCR11 due to its ability to bind several CC chemokines (includingCCL19,CCL21 andCCL25) and its structural similarity to chemokine receptors. However, due to the inability of this molecule (also known asCCRL1 and CCX CKR) to generate a signal following ligand interaction, it has been suggested that it is a scavenger receptor for chemokines and not a bona fide chemokine receptor. Thus CCRL1 should not be called CCR11 under the guidelines of the IUIS/WHO Subcommittee on Chemokine Nomenclature.

• "Chemokine Receptors".IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived fromthe original on 2016-03-03. Retrieved2008-11-25.

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• Chemokine receptors
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