Authors: Carolina Tafalla, Alí Alejo, Centro de Investigación en Sanidad Animal (CISA-INIA), Valdeolmos, Madrid, Spain
Abstract: Chemokines are chemoattractant cytokines defined by the presence of four conserved cysteine residues which in mammals can be divided into four subfamilies depending on the arrangement of the first two conserved cysteines in their sequence: CXC (), CC (), C and CX3C classes. Evolutionarily, fish can be considered as an intermediate step between species which possess only innate immunity (invertebrates) and species which depend greatly on their adaptive immunity such as mammals. Therefore, the functionality of their different immune cell types and molecules is sometimes also intermediate between innate and adaptive responses. The first chemokine gene identified in fish was an interleukin 8 (IL-8) homologue characterized in lamprey (Lampetra fluviatilis) in 1999. Since then, many different chemokine genes have been identified in several fish species evidencing the great differences that exist between mammalian and fish chemokines. In this group of animals, only chemokines belonging to CC and CXC classes have been identified in most species, while in zebrafish (Danio rerio) some C chemokines have been reported, as well as a new CX group with four members of unknown function. Moreover, extensive intrachromosomal gene duplications have considerably increased the number of genes in most species, and while twenty-eight CC members have been identified in mammals, at least eighty-one CC chemokine genes are present in zebrafish. The role of these molecules in homeostasis and immune response remains largely unknown.
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