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As the adaptive immune system arose in jawed vertebrates, a reasonable working hypothesis is that cytokines involved exclusively in controlling the adaptive immune system, e.g. T1 and T2 cytokines, will only be found in jawed vertebrates whilst those with a role in innate responses, e.g. type I IFNs or pro-inflammatory cytokines, will be universal, or have functional equivalents in ‘lower’ animals.Progress to date in cloning cytokines, including interleukins, in vertebrates outside of mammals is limited and non-existent in invertebrates. T1 and T2 interleukins have only been cloned in birds. Receptors for T1 and T2 interleukins have been cloned in fish, however, suggesting the presence of the corresponding interleukins. Pro-inflammatory interleukins have been cloned in birds, fish and amphibia, but not reptiles. Cross-reactive bioassays, polyclonal antisera and mAbs suggest that an IL-6-like factor exists in starfish, as yet the only evidence for innate immune response cytokines in ‘lower’ animals. [Copyright &y& Elsevier]

Type I interferon (IFN) exerts its pleiotropic effects mainly through the JAK–STAT signaling pathway, which is presently best described in mammals. By subtractive suppression hybridization, two fish signaling factors, JAK1 and STAT1, had been identified in the IFN-induced crucian carp Carassius auratus L. blastulae embryonic (CAB) cells after treatment with UV-inactivated grass carp hemorrhagic virus (GCHV). Further, the full-length cDNA of STAT1, termed CaSTAT1, was obtained. It contains 2926 bp and encodes a protein of 718 aa. CaSTAT1 is most similar to rat STAT1 with 59% identity overall and displays all highly conserved domains that the STAT family possesses. Like human STAT1β, it lacks the C-terminus acting as transcriptional activation domain in mammals. By contrast, only a single transcript was detected in virus-induced CAB cells. Expression analysis showed that CaSTAT1 could be activated by stimulation of CAB cells with poly I:C, active GCHV, UV-inactivated GCHV or CAB IFN, and displayed diverse expression patterns similar to that of mammalian STAT1. Additionally, the expression of an antiviral gene CaMx1 was also induced under the same conditions, and expression difference between CaSTAT1 and CaMx1 was revealed by induction of CAB IFN. These results provide molecular evidence supporting the notion that the fish IFN signaling transduction pathway is similar to that in mammals. Fish IFN exerts its multiple functions, at least antiviral action, through a JAK–STAT pathway. [Copyright &y& Elsevier]