Genomics of fish cytokines

Cytokines are important regulators of immune system and finding these genes in fish have potential applications for the development of vaccines and or immunostimulants for aquaculture. Major hurdle in discovering cytokines from fish is the low identities of these molecules when compared to its mammalian counterparts. In fish, prior to pufferfish (Fugu rubripes and Tetraodon nigroviridis) and zebrafish (Danio rerio) genome sequencing, only a handful of cytokines like IL-1β, TNF-α, TGFβ, some CXC (including IL-8) and CC chemokine genes were identified. Post genome release of pufferfish and zebrafish, the rate of discovery of fish cytokines has accelerated tremendously. Fish and human share a certain degree of synteny in genomes. Exploiting this characteristic, cytokines have been searched for in the genome databases of pufferfish (http://fugu.hgmp.mrc.ac.uk) and zebrafish. Pro-inflammatory cytokines like TNF's, IL-6 and IL-17 family have been cloned. A new TNF gene has been found adjacent to TNFα gene from fugu and zebrafish. Among the TH1 type interleukins, IL-2, IL-15, IL-12α, IL-12β, IL-18 have been cloned. Among IL-10 and its family members, IL-10, IL-19/20, IL-22 and IL-26 have been discovered. Interferon genes have also been identified by from fish. However, TH2 cytokines (IL-4, IL-5 and IL-13), IL-3, IL-7 and IL-9 are yet to be discovered from fish. This study shows that the type and diversification of fish cytokines are very similar to that found in mammals.