Molecular characterization, expression and function analysis of interleukin-17B, C and D genes in yellow catfish (Pelteobagrus fulvidraco)

In mammals, Interleukin-17B, C and D (IL-17B, C and D) play critical roles in the inflammatory responses. In fish, IL-17C and D have been found in various species, and IL-17B has only been reported in channel catfish, but there is little information about the functional activities of IL-17B, C and D in fish. In this study, the protein structure and exon length of Pf_IL-17B, C and D genes in yellow catfish (Pelteobagrus fulvidraco) were similar to those of mammalian IL-17B, C and D, implying that the IL-17B, C and D in fish may have similar bioactivities to those in mammals. Moreover, NJ phylogenetic tree and syntenic analysis showed that the IL-17B, C and D genes were highly conserved in tetrapods, but the IL-17B gene was lost in some teleosts. Pf_IL-17B, C and D genes were highly expressed in blood and gonad from healthy yellow catfish. After infection with Edwardsiella ictaluri, Pf_IL-17C and D transcripts were notably up-regulated in all six tissues and five tissues (except skin) detected, respectively, whereas Pf_IL-17B transcript was only markedly up-regulated in the gill. Moreover, lipopolysaccharides (LPS), polyinosinic-polycytidylic acid (Poly I:C), peptidoglycan (PGN), and phytohaemagglutinin (PHA) distinctly induced the expressions of Pf_IL-17B, C and D mRNAs in the isolated peripheral blood leucocytes (PBLs) of yellow catfish. These results reveal that Pf_IL-17C and D genes may play more important roles than Pf_IL-17B in the immunoregulation against pathogens. Moreover, recombinant (r) Pf_IL-17B, C and D proteins could remarkably induce the expressions of inflammatory cytokines, chemokines and antimicrobial peptide genes mRNAs in the PBLs and gill leukocytes (GLs), and they also notably promoted the phagocytosis and chemotaxis of the PBLs. Besides, the rPf_IL-17B, C and D proteins could induce ACT1, TRAF6, TAK1, IKK alpha, NF kappa B1 and NF kappa B2 mRNAs to activate the NF-kappa B and p38 MAPK signal pathways. These results uncover that the Pf_IL-17B, C and D genes may mediate inflammatory response to eliminate invasive pathogens.