Abstract
As an important immune regulatory molecule, interleukin (IL)-22 has been reported in several species of fish, but its soluble receptor, IL-22 binding protein (IL-22BP), discovered as a natural antagonist of IL-22 in mammals, has not been functionally characterized in fish to date. In the present study, IL-22 and IL-22BP genes were cloned in mandarin fish Siniperca chuatsi. They all exhibited a high basal expression level in mucosa-enriched tissues, implying their possible roles in mucosal immunity. The IL-22 was found to show a potent response to LPS stimulation, acting as an inducer of antimicrobial peptide (AMP) genes, such as hepcidin and Liver-expressed antimicrobial peptide-2 (LEAP-2) in intestinal cells. IL-22BP, via co-incubation with IL-22, inhibited completely the induction of downstream genes by IL-22. Through a yeast two-hybrid assay, the interaction between IL-22BP and IL-22 was confirmed, which may account for the inhibitory effect of IL-22BP. Moreover, two hot spot residues for IL-22 binding, as reported in mammalian IL-22BP, were found to be conserved both in sequence location and function in mandarin fish IL-22BP, indicating that the interaction mode between IL-22 and IL-22BP may be also conserved in fish and mammals. In conclusion, the mandarin fish IL-22 and IL-22BP are conserved in their interaction and function with their mammalian orthologues, and these findings provide basis for future research on IL-22-IL-22BP axis in fish immunity.
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