Expression and Function Analysis of Interleukin-17A/F1, 2, and 3 Genes in Yellow Catfish (): Distinct Bioactivity of Recombinant IL-17A/F1, 2, and 3.

In mammals, Interleukin-17 cytokine family plays critical roles in both acute and chronic inflammatory responses. In fish species, three Interleukin-17A/F (IL-17A/F) genes have been identified to be homologous to mammalian IL-17A and IL-17F, but little is known about their functional activity. In this study, _IL-17A/F1, 2 and 3 genes were cloned from yellow catfish () and they differed in protein structure and exon length, implying that they may have divergent bioactivity. Real-time quantitative PCR analyses revealed that three _IL-17A/F genes were highly expressed in blood and mucosal tissues (skin+mucus and gill) from healthy adult fish. The mRNA expressions of _IL-17A/F1, 2 and 3 genes were significantly up-regulated in the gill, skin+mucus, head kidney and spleen after challenge with and in the isolated peripheral blood leucocytes (PBLs) of yellow catfish after stimulation with phytohaemagglutinin (PHA), lipopolysaccharides (LPS), peptidoglycan (PGN) and polyinosinic-polycytidylic acid (Poly I:C). These results indicate that _IL-17A/F1, 2 and 3 genes may play a vital role in the regulation of immune against pathogens. Additionally, the recombinant (r) _IL-17A/F1, 2 and 3 proteins significantly induced the mRNA expressions of proinflammatory cytokines, chemokines and antibacterial peptides genes, and the r_IL-17A/F 2 and 3 proteins promoted phagocytosis of PBLs more powerfully than the r_IL-17A/F1. Furthermore, the r_IL-17A/F1, 2 and 3 proteins might activate the NF-κB and MAPK signal pathways by IL-17RA, ACT1, TRAF6, TRAF2, TRAF5 and TAK1, indicating that the three _IL-17A/F proteins may play different roles in promoting inflammatory response.