The chemokine family is divided into four classes based on the number and spacing of their conserved cysteines: 2 Cys residues may be adjacent (the CC family), or separated by an intervening residue (the CXC family), or have only one of the first two Cys residues (C chemokines), or contain both cysteines separated by three intervening residues (CX3C chemokines).This entry includes beta-chemokines (CC chemokines), in addition to gamma (C chemokines) and delta-chemokines (CX3C chemokines). CC chemokines stimulate mainly monocytes, but also basophils, eosinophils, T-lymphocytes, and natural killer (NK) cells. C-C motif chemokine 2 (CCL2) stimulates chemotaxis of monocytes and several cellular events associated with chemotaxis. Two other chemokines structurally related to CCL2 are CCL8 (MCP-2) and CCL7 (MCP-3) [].The C chemokine subfamily is composed of two members, XC chemokine ligand 1 (XCL1), also known as lymphotactin or SCM-1 alpha, and XC chemokine ligand 2 (XCL2), also known as SCM-1 beta []. The cognate receptor for these chemokines is XCR1 []. The only CX3C chemokine identified to date is CX3C chemokine ligand 1 (CX3CL1), also known as fractalkine or neurotactin. With its unique CX3CR1 receptor [], it is involved in adherence to the endothelium of the inflammatory monocyte population [].
