CCR (Chemokine receptors) are G-protein-coupled receptors with 7 α helical transmembrane region structures rich in hydrophobic amino acids. They are mainly expressed in various leukocyte subpopulations from bone marrow, and also in epithelial cells, vascular endothelial cells, nerve cells and other types of cells. Chemokine receptors are also divided into four subfamilies according to the ligands they bind: CCR, CXCR, XCR and CX3CR. There are 11 species of CCR subfamily (CCR1-CCR11), 6 species of CXCR subfamily (CXCR1-CXCR6), and 1 species of XCR1 and CX3CR1, respectively.
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