Chemokines are a family of small cytokines, or signaling proteins secreted by cells. They form a superfamily of secreted proteins involved in immunoregulatory and inflammatory processes. Their name is derived from their ability to induce directed chemotaxis in nearby responsive cells; they are chemotactic cytokines. Proteins are classified as chemokines according to shared structural characteristics such as small size (they are all approximately 8-10 kilodaltons in size). The superfamily is divided into four subfamilies based on the arrangement of the N-terminal cysteine residues of the mature peptide, which are key to forming their 3-dimensional shape. Chemokines are all about 8�10_kDa in mass and have 4 cysteine residues in conserved positions However, these proteins have historically been known under several other names including the SIS family of cytokines, SIG family of cytokines, SCY family of cytokines, Platelet factor-4 superfamily or intercrines. Chemokines have been classified into four main subfamilies : CXC, CC, CX3C and XC. Chemokines are found in all vertebrates, some viruses and some bacteria, but none have been described for other invertebrates.
Some chemokines are considered pro-inflammatory and can be induced during an immune response to recruit cells of the immune system to a site of infection. Others are considered homeostatic and are involved in controlling the migration of cells during normal processes of tissue maintenance or development. They exert their biological effects by interacting with G protein -linked transmembrane receptors called chemokine receptors, that are selectively found on the surfaces of their target cells. CXC chemokines are potent promoter of angiogenesis.
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