title: Molecular and functional identification of three interleukin-17A/F (IL-17A/F) homologues in large yellow croaker (Larimichthys crocea).
abstract: The interleukin-17 (IL-17) cytokine family plays a central role in the coordination of inflammatory responses. In fish species, three genes that have a similar homology to both IL-17A and IL-17F were designated IL-17A/F1, 2, and 3. In this study, we identified three IL-17A/F homologues (LycIL-17A/F1, 2, and 3) from large yellow croaker (Larimichthys crocea). The deduced LycIL-17A/F1 and 3 had four cysteine residues conserved in teleost IL-17A/F1 and 3 homologues and shared a domain similar to the B chain of human IL-17F. The deduced LycIL-17A/F2 possessed the unique arrangement of six cysteine residues as teleost IL-17A/F2 (except Fugu IL-17A/F2) and higher vertebrate IL-17A and F, and shared a domain similar to the D/E chain of human IL-17A. Phylogenetic analysis showed that teleost IL-17A/F1 and 3 fall into a major clade, whereas IL-17A/F2 forms a separated clade and is clustered with IL-17N. Based on structural and phylogenetic analyses, we suggest that teleost IL-17A/Fs may be classified into two subgroups: one consisting of IL-17A/F1 and 3, and the other composed of IL-17A/F2. The three LycIL-17A/Fs were constitutively expressed in all tissues examined although at a different level. Following challenge with Aeromonas hydrophila, expression of these three LycIL-17A/Fs was rapidly increased in head kidney and gills. The in vivo assays showed that recombinant LycIL-17A/F1, 2, and 3 all were able to enhance the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α2), chemokines (CXCL8 and CXCL13), and antimicrobial peptide hepcidin in head kidney. Furthermore, LycIL-17A/Fs appeared to mediate pro-inflammatory responses via NF-κB signalling. These results therefore reveal similar functions between the two subgroup members，LycIL-17A/F1 and 3 and LycIL-17A/F2, in promoting inflammation and host defences.
authors.affiliation: College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, PR China; Key Laboratory of Marine Biogenetic Resources, Third Institute of Oceanography, State Oceanic Administration; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen 361005, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Ding
authors.affiliation: Key Laboratory of Marine Biogenetic Resources, Third Institute of Oceanography, State Oceanic Administration; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen 361005, PR China.
authors.forename: Jingqun
authors.initials: J
authors.lastname: Ao
authors.affiliation: College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, PR China. Electronic address: chunxai@xmu.edu.cn.
authors.forename: Chunxiang
authors.initials: C
authors.lastname: Ai
authors.affiliation: Key Laboratory of Marine Biogenetic Resources, Third Institute of Oceanography, State Oceanic Administration; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen 361005, PR China. Electronic address: chenxinhua@tio.org.cn.
authors.forename: Xinhua
authors.initials: X
authors.lastname: Chen
mesh_terms: D016980:Aeromonas hydrophila / Q000276:immunology*; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D016905:Gram-Negative Bacterial Infections / Q000276:immunology*; D064451:Hepcidins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D020381:Interleukin-17 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010473:Perciformes / Q000276:immunology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D064451:Hepcidins; C508717:IL17A protein, human; D018836:Inflammation Mediators; D020381:Interleukin-17; D011994:Recombinant Proteins
keywords: Bioactivity analysis; IL-17A/F; Large yellow croaker (Larimichthys crocea); Structural analysis; Tissue expression pattern