Chemokines are a family of small
cytokines, or
proteins secreted by
cells. Proteins are classified as chemokines according to shared structural characteristics such as small size (they are all approximately 8-10
kilodaltons in size), and the presence of four
cysteine residues in conserved locations that are key to forming their 3-dimensional shape. Their name is derived from their ability to induce directed
chemotaxis in nearby responsive cells; they are chemotactic cytokines. 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. Some chemokines are considered
pro-inflammatory and can be induced during an immune response to promote cells of the
immune system to a site of
infection, while others are considered
homeostatic and are involved in controlling the migration of cells during normal processes of tissue maintenance or
development. Chemokines are found in all
vertebrates, some
viruses and some
bacteria, but none have been described for other
invertebrates. These proteins 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.
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