Characterization and mucosal responses of interleukin 17 family ligand and receptor genes in channel catfish Ictalurus punctatus

Identification and functional characterization of fish IL-17 receptors suggest important roles in the response to nodavirus infection

Th17 is a lymphocyte T helper (Th) subpopulation relevant in the control and regulation of the immune response characterized by the production of interleukin (IL)-17. This crucial cytokine family acts through their binding to the IL-17 receptors (IL-17R), having up to six members. Although the biology of fish Th17 is well-recognized, the molecular and functional characterization of IL-17 and IL-17R has been limited. Thus, our aim was to identify and characterize the IL-17R repertory and regulation in the two main Mediterranean cultured fish species, the gilthead seabream (Sparus aurata) and the European sea bass (Dicentrarchus labrax). Our in silico results showed the clear identification of six members in each fish species, from IL-17RA to IL-17RE-like, with well-conserved gene structure and protein domains with their human orthologues. All of them showed wide and constitutive transcription in naïve tissues but with highest levels in mucosal tissues, namely skin, gill or intestine. In leucocytes, T mitogens showed the strongest up-regulation in most of the il17 receptors though il17ra resulted in inhibition by most stimulants. Interestingly, in vivo nodavirus infection resulted in alterations on the transcription of il17 receptors. While nodavirus infection led to some increments in the il17ra, il17rb, il17rc and il17rd transcripts in the susceptible European sea bass, many down-regulations were observed in the resistant gilthead seabream. Our data identify the presence and conservation of six coding IL-17R in gilthead seabream and European sea bass as well as their differential regulation in vitro and upon nodavirus infection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00225-1.

Transcriptome analysis and immune gene expression of channel catfish (Ictalurus punctatus) fed diets with inclusion of frass from black soldier fly larvae

The larval waste, exoskeleton shedding, and leftover feed components of the black soldier fly and its larvae make up the by-product known as frass. In this study, we subjected channel catfish (Ictalurus punctatus) to a 10-week feeding trial to assess how different dietary amounts of frass inclusion would affect both systemic and mucosal tissue gene expression, especially in regard to growth and immune-related genes. Fish were divided in quadruplicate aquaria, and five experimental diets comprising 0, 50, 100, 200, and 300 g of frass per kilogram of feed were fed twice daily. At the end of the trial, liver, head kidney, gill, and intestine samples were collected for gene expression analyses. First, liver and intestine samples from fish fed with a no frass inclusion diet (control), low-frass (50 g/kg) inclusion diet, or a high-frass (300 g/kg) inclusion diet were subjected to Illumina RNA sequencing to determine global differential gene expression among diet groups. Differentially expressed genes (DEGs) included the upregulation of growth-related genes such as glucose-6-phosphatase and myostatin, as well as innate immune receptors and effector molecules such as toll-like receptor 5, apolipoprotein A1, C-type lectin, and lysozyme. Based on the initial screenings of low/high frass using RNA sequencing, a more thorough evaluation of immune gene expression of all tissues sampled, and all levels of frass inclusion, was further conducted. Using targeted quantitative PCR panels for both innate and adaptive immune genes from channel catfish, differential expression of genes was identified, which included innate receptors (TLR1, TLR5, TLR9, and TLR20A), proinflammatory cytokines (IL-1β type a, IL-1β type b, IL-17, IFN-γ, and TNFα), chemokines (CFC3 and CFD), and hepcidin in both systemic (liver and head kidney) and mucosal (gill and intestine) tissues. Overall, frass from black soldier fly larvae inclusion in formulated diets was found to alter global gene expression and activate innate and adaptive immunity in channel catfish, which has the potential to support disease resistance in this species in addition to demonstrated growth benefits.

Transcriptomic Analysis Reveals Functional Interaction of mRNA-lncRNA-miRNA in Trachinotus ovatus Infected by Cryptocaryon irritans

The skin of Trachinotus ovatus is a crucial component of the mucosal immune system and serves as the primary site of infection by Cryptocaryon irritans. In order to investigate the significant role of skin in C. irritans infection, a comprehensive transcriptome analysis was conducted on skin tissues from the infection group, infection-adjacent group, and infection group compared with the infection-adjacent group (ATT_vs_PER, ADJ_vs_PER, ATT_vs_ADJ). This study identified differentially expressed long non-coding RNAs (DE lncRNAs), microRNAs (DE miRNAs), and differentially expressed genes (DEGs). The prediction of lncRNA target genes was accomplished by utilizing positional relationship (co-location) and expression correlation (co-expression) with protein-coding genes. Subsequently, functional enrichment analysis was conducted on the target genes of differentially expressed lncRNAs, revealing their involvement in signaling pathways such as tight junction, MAPK, and cell adhesion molecules. This study describes the regulatory network of lncRNA-miRNA-mRNA in T. ovatus skin tissue infected with C. irritans. Functional prediction analysis showed that differentially expressed lncRNA and miRNA may regulate the expression of immune genes such as interleukin-8 (il8) to resist the infection of C. irritans. Conducting additional research on these non-coding RNAs will facilitate a deeper understanding of their immune regulatory function in T. ovatus during C. irritans infection. The study of non-coding RNA in this study laid a foundation for revealing the molecular mechanism of the immune system of T. ovatus to respond to the infection of C. irritans. It provided a choice for the molecular breeding of Trachinotus ovatus against C. irritans.

Molecular characteristics of interleukin (IL)-17A/F3 and its immune response on the pathogen and functional regulation on cytokines in common carp Cyprinus carpio L

Fish interleukin (IL)-17A/F is homologous with mammalian IL-17A and IL-17F, which plays a key role in regulating inflammatory responses and autoimmune diseases. In fish, IL-17A/F1, 2, and 3 have been identified and described. However, IL-17A/F3 has received little attention in fish. In this study, a homolog of IL-17A/F3 was identified in common carp (Cyprinus carpio L.), which was termed as Cc_IL-17A/F3. The deduced amino acid sequence of Cc_IL-17A/F3 has four conserved cysteine residues, which could form two intrachain disulfide bonds. Homology comparison showed that the Cc_IL-17A/F3 was in the range of 31.7-71.9% of sequence similarity with these of other fishes. The Cc_IL-17A/F3 gene was constitutively expressed in various tissues, with higher expression levels in the skin and gills. After common carp were infected by Aeromonas. hydrophila, the mRNA expression levels of Cc_IL-17A/F3 were significantly up-regulated in the spleen, head kidney, gills, and intestine. Based on the indirect immunofluorescence assay, Cc_IL-17A/F3 proteins were found to be obviously increased in the intestine and spleen upon A. hydrophila infection at 24 h post-infection. The recombinant protein rCc_IL-17A/F3 could enhance the gene expression levels of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, and TNF-α) as well as chemokines (CXCL8 and CXCL20) in primary head kidney leukocytes. In vivo and in vitro experiments have similar stimulatory effects. When Cc_IL-17A/F3 was overexpressed in common carp, the expressions of pro-inflammatory cytokines and chemokines were significantly up-regulated in head kidney and spleen. In summary, the results derived from the present study suggested that the Cc_IL-17A/F3 plays an important role in defending against bacterial infections, and probably participates in mucosal immunity of the host.

Sub-lethal concentration of metamifop exposure impair gut health of zebrafish (Danio rerio)

Previous studies have demonstrated that sublethal metamifop exposures induce hepatic lipid metabolism disorder in zebrafish. Whether metamifop will cause adverse effects in zebrafish gut is unknown. In the present study, effects of metamifop on gut heath of zebrafish were investigated after sublethal concentration (0.025, 0.10 and 0.40 mg/L) exposure. Histopathology analysis showed that metamifop induced inflammation and reduction of goblet cells in the gut, indicating that gut health may be impaired. Metamifop exposure could reduce activities of digestive enzymes (lipase and alkaline phosphatase), indicating the capacity of lipid absorption were impaired. Meanwhile, the content of fatty acid-binding protein 2 (FABP2) and mRNA levels of related genes (apoa-1a, apoe-b, fatp4, lpl and fabp2) were reduced in zebrafish gut after exposure to metamifop, suggesting the lipid transportation were decreased. The transcripts of genes associated with inflammation (il-17c, tnf-α and nf-kb) were significantly increased in 0.40 mg/L metamifop treatment group, which were 1.90-, 1.53- and 2.77-fold of the control group, respectively, confirming that metamifop induced inflammatory response in zebrafish gut. Moreover, reduction of mRNA levels of cldn-15 and elevation of lipopolysaccharides (LPS) content were observed in metamifop-treated groups, which suggested that metamifop exposure increased the intestinal permeability. Furthermore, metamifop exposure decreased the relative abundance of beneficial bacteria (Psychrobacter and Aeromonas) and elevated the abundance of pathogenic bacteria (Rhodobacter and Ralstonia) in zebrafish intestine. These results indicated that metamifop exposure at sublethal concentrations would impair zebrafish gut health, via reduction of lipids absorption, inflammatory response, elevation of permeability and microbiota disorder.

Molecular characterizations, immune modulation, and antibacterial activity of interleukin-17A/F1a and interleukin-17A/F1b in common carp Cyprinus carpio

Interleukin-17 (IL-17), as a pro-inflammatory cytokine family, mediates different pro-inflammatory mediators in various cell types (e.g., epithelial cells, macrophages, endothelial cells, and fibroblasts), which play an important role in defending against pathogens. The IL-17A/F1 genes have recently been reported in fish. However, the functions of these genes are still unclear. In this study, we identified two duplicated IL-17A/F1 genes in common carp (Cyprinus carpio L.), namely, CcIL-17A/F1a and CcIL-17A/F1b. Sequence analysis showed that CcIL-17A/F1a and CcIL-17A/F1b proteins had four conserved cysteine residues, which could form two intra-chain disulfide bridges. Homology comparison displayed that the deduced amino acid sequences of CcIL-17A/F1a and CcIL-17A/F1b shared 31.1%-77.3% and 32.5%-75.7% of sequence similarity to IL-17A/F1 homologues from other fish species, respectively. The mRNA expression levels of CcIL-17A/F1a and CcIL-17A/F1b were obviously increased in gill and head-kidney of fish challenged with A. hydrophila. The recombinant protein rCcIL-17A/F1a and rCcIL-17A/F1b could enhance the expression levels of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, and TNF-α) and chemokines (CXCL8 and CXCL20). The 3 × Flag eukaryotic expression vectors to express protein rCcIL-17A/F1a (or rCcIL-17A/F1b) were constructed and intramuscularly injected in common carp. The rCcIL-17A/F1a (or rCcIL-17A/F1b) could be successfully expressed in vivo. Four immune-related genes, namely, CD4, CD8, TNF-α, and IgM, were also significantly induced to be expressed at higher mRNA levels compared with the control. The pretreatment with CcIL-17A/F1a or CcIL-17A/F1b could markedly increase the survival rate of common carp challenged with A. hydrophila. Our results demonstrated that CcIL-17A/F1a or CcIL-17A/F1b plays an important role in immune responses and immune defense against bacteria. CcIL-17A/F1a or CcIL-17A/F1b could also be potentially used as an immunopotentiator to prevent diseases in common carp.

Identification of two interleukin 17 receptor C (IL-17RC) genes and their binding activities to three IL-17A/F ligands in the Japanese medaka, Oryzias latipes

In mammals, interleukin (IL)-17 receptor C (IL-17RC) and IL-17RA mediate IL-17A and IL-17F signaling to produce mucin, antimicrobial peptides, and maintain healthy intestinal flora. However, IL-17RC signaling in fish remains unclear. In this study, three il17rc transcripts (il17rca1, il17rca2, and il17rcb) from the Japanese medaka (Oryzias latipes) were cloned; il17rca1 and il17rca2 mRNAs were alternatively spliced from il17rca pre-mRNA as transcript variants. The il17rca and il17rcb genes were located on chromosomes 7 and 5, respectively. Teleost clades containing medaka il17rca and il17rcb clustered separately from the tetrapod clade. In adult tissues, il17rca1 expression was significantly higher than il17rca2 and il17rcb. Conversely, il17rcb expression was significantly higher in embryos and larvae. These expression patterns changed following infection with Edwardsiella piscicida and Aeromonas hydrophila. Furthermore, an immunoprecipitation assay using recombinant IL-17RCs and rIL-17A/Fs suggested that, in teleosts, three ligands could function in signaling through two IL-17RCs.

Genome-wide identification of interleukin-17 (IL-17) / interleukin-17 receptor (IL- 17R) in turbot (Scophthalmus maximus) and expression pattern analysis after Vibrio anguillarum infection

Interleukin-17 (IL-17) is a cytokine secreted by a variety of immune cells that plays an important role in host defense against pathogens. IL-17 usually activates downstream immune signaling pathway by binding to heterodimeric or homodimeric complex formed by IL-17 receptors (IL-17R). Describing the characteristics, tissue distribution of IL-17 and IL-17 receptor family members and their expression after pathogen infection will provide a reference for host defense against disease of turbot. In this study, six IL-17 family members and nine IL-17 receptor family members were identified by analyzing the turbot (Scophthalmus maximus) genome. Different from other vertebrates, most members of the IL-17 receptor family own two copies. Protein structure analysis showed that the six IL-17 family members contained typical "IL-17" domains, and the nine IL-17 receptor family members contained typical "SEFIR domain" or "IL17_R_N domain". Syntenic analysis revealed that all IL-17s and IL-17Rs were chromosomally conserved compared with other fish. The phylogenetic analysis further confirmed the evolutionary conservatism of different copies of IL-17C and IL-17Rs. Tissue distribution results showed that IL-17 and IL-17R genes were highly expressed in immune-related tissues. The expression of IL-17C and its receptor in the mucosal immune tissues after infection with V. anguillarum were analyzed subsequently, which were significantly increased in the skin. The results are consistent with previous studies showing that IL-17 and IL-17 receptor play an important role in promoting innate immune response.

Expression and Function Analysis of Interleukin-17A/F1, 2, and 3 Genes in Yellow Catfish (Pelteobagrus fulvidraco): 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, Pf_IL-17A/F1, 2 and 3 genes were cloned from yellow catfish (Pelteobagrus fulvidraco) and they differed in protein structure and exon length, implying that they may have divergent bioactivity. Real-time quantitative PCR analyses revealed that three Pf_IL-17A/F genes were highly expressed in blood and mucosal tissues (skin+mucus and gill) from healthy adult fish. The mRNA expressions of Pf_IL-17A/F1, 2 and 3 genes were significantly up-regulated in the gill, skin+mucus, head kidney and spleen after challenge with Edwardsiella ictaluri 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 Pf_IL-17A/F1, 2 and 3 genes may play a vital role in the regulation of immune against pathogens. Additionally, the recombinant (r) Pf_IL-17A/F1, 2 and 3 proteins significantly induced the mRNA expressions of proinflammatory cytokines, chemokines and antibacterial peptides genes, and the rPf_IL-17A/F 2 and 3 proteins promoted phagocytosis of PBLs more powerfully than the rPf_IL-17A/F1. Furthermore, the rPf_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 Pf_IL-17A/F proteins may play different roles in promoting inflammatory response.

Identification, expression and pro-inflammatory effect of interleukin-17 N in common carp (Cyprinus carpio L.)

Two interleukin (IL)-17 N genes (CcIL-17Na and b) present on different linkage groups were identified in the common carp (Cyprinus carpio) genome and confirmed by polymerase chain reaction (PCR) and real time (RT)-PCR in this experiment. Synteny analysis revealed that IL-17 N is transcribed by the complement sequence of TOP3B's intron 2. It is flanked by SDF2L and PPM1F in all fish studied to date, except fugu (Takifugu rubripes). The open reading frames of the two CcIL-17Ns are 411 base pairs long and encode 136 amino acids. The amino acid identity/similarity between CcIL-17Na and b is 91.2%/97.1%. The CcIL-17Ns share identity (46.8-90.4%) with their orthologs from other teleosts. Identities/similarities to other members of the IL-17 family in common carp were low at 21.4-30.2%/31.4-51.4%. In the phylogenetic tree, IL-17Ns from spotted gar (Lepisosteus oculatus, the ancestor of teleosts) and coelacanth (Latimeria chalumnae, the ancestor of tetrapods) were grouped within the same branch with a high bootstrap value of 97%, which indicates that IL-17 N is an ancient and conserved gene. Quantitative RT-PCR results showed that CcIL-17Ns were most highly expressed in the brain of healthy individuals. The expression in brain was significantly induced at 6 h post Aeromonas hydrophila infection; at 1 day post infection, expression in liver, muscle, skin, spleen, and head kidney was up-regulated. In addition, the upregulated expression of proinflammatory cytokines IL-1β, IFN-γ, IL-6, chemokine CCL20, NF - κ B and TRAF6 in kidney tissue by ccIL-17 N recombinant protein also indicate that IL-17 N can promote inflammation through NF-κB pathway and induce the expression of chemokines and inflammatory factors.

Histone Deacetylase 3-Mediated Inhibition of microRNA-19a-3p Facilitates the Development of Rheumatoid Arthritis-Associated Interstitial Lung Disease

Histone deacetylase (HDAC) has been implicated in rheumatoid arthritis (RA) progression. We investigated the roles of histone deacetylase 3 (HDAC3) involved in RA-associated interstitial lung disease (ILD) fibrosis. Firstly, we measured the expression of HDAC3 and interleukin 17 receptor A (IL17RA) in lung tissue samples from normal controls, idiopathic pulmonary fibrosis (IPF) patients, and RA-ILD patients. Next, chromatin immunoprecipitation (ChIP) and dual luciferase reporter assay were employed to detect the interaction between HDAC3 and microRNA-19a-3p (miR-19a-3p) and between miR-19a-3p and IL17RA. Further, immunohistochemistry was used to localize HDAC3 and IL17RA expression in lung tissues. Additionally, functional assays were conducted followed by expression determination of HDAC3, miR-19a-3p, and IL17RA with reverse transcription quantitative PCR (RT-qPCR) and Western blot analysis. The effect of HDAC3 on RA-ILD in the constructed RA-ILD mouse model was also studied based on arthritis assessment. We found overexpressed HDAC3 and IL17RA as well as silenced miR-19a-3p in RA-ILD mouse model and RA-ILD patients. In the mouse model, HDAC3 downregulated miR-19a-3p in lung fibroblasts to promote the progression of RA-ILD fibrosis. In lung fibroblasts of RA-ILD mice, IL17RA was a target gene of miR-19a-3p. miR-19a-3p negatively regulated IL17RA, thereby increasing the expression of fibrosis markers, COL1A1, COL3A1, and FN, in lung fibroblasts of mice. Taken together, HDAC3 upregulated IL17RA expression by targeting miR-19a-3p to facilitate the RA-ILD fibrosis development, which sheds light on a new HDAC3/miR-19a-3p/IL17RA axis functioning in RA-ILD fibrosis.

RNA-Seq analysis of the guppy immune response against Gyrodactylus bullatarudis infection

Gyrodactylids are ubiquitous ectoparasites of teleost fish, but our understanding of the host immune response against them is fragmentary. Here, we used RNA-Seq to investigate genes involved in the primary response to infection with Gyrodactylus bullatarudis on the skin of guppies, Poecilia reticulata, an important evolutionary model, but also one of the most common fish in the global ornamental trade. Analysis of differentially expressed genes identified several immune-related categories, including IL-17 signalling pathway and Th17 cell differentiation, cytokine-cytokine receptor interaction, chemokine signalling pathway, NOD-like receptor signalling pathway, natural killer cell-mediated cytotoxicity and pathways involved in antigen recognition, processing and presentation. Components of both the innate and the adaptive immune responses play a role in response to gyrodactylid infection. Genes involved in IL-17/Th17 response were particularly enriched among differentially expressed genes, suggesting a significant role for this pathway in fish responses to ectoparasites. Our results revealed a sizable list of genes potentially involved in the teleost-gyrodactylid immune response.

Effects of Vibrio harveyi infection on serum biochemical parameters and expression profiles of interleukin-17 (IL-17) / interleukin-17 receptor (IL-17R) genes in spotted sea bass

Vibrio harveyi is regarded as serious pathogen for marine fishes. To evaluate the physiological responses of spotted sea bass (Lateolabrax maculatus) after V. harveyi infection, four biochemical biomarkers including alanine amino transferase (ALT), albumin (ALB), total protein (TP) and glucose (GLU) were measured in serum. Our results showed that V. harveyi infection significantly influenced the concentration of ALT, ALB and GLU. Additionally, five interleukin-17 (IL-17) and five IL-17 receptors (IL-17R) genes were identified in spotted sea bass and their gene structures were characterized. Furthermore, the expression patterns of IL-17 and IL-17R genes were determined by qPCR in liver, intestine, spleen and head kidney after V. harveyi infection. All IL-17 and IL-17R genes exhibited time- and tissue-dependent expressions. Several tested genes were dramatically induced by V. harveyi treatment, particularly IL-17A/F1 in liver and head kidney, IL-17A/F2 in head kidney, IL-17RC in spleen with more than 10-fold increases, which suggested their potential essential roles against bacterial infection.

Interleukin-17A/F1 from Japanese pufferfish (Takifugu rubripes) stimulates the immune response in head kidney and intestinal cells

In mammals, interleukin (IL)-17A and IL-17F, mainly produced by Th17 cells, are hallmark inflammatory cytokines that play important roles in the intestinal mucosal immune response. In contrast, three mammalian IL-17A and IL-17F counterparts (IL-17A/F1-3) have been identified in teleosts, and most of their functions have been described in the lymphoid organs. However, their function in the intestinal mucosal immune response is poorly understood. In this study, a recombinant (r) tiger puffer fish fugu (Takifugu rubripes) IL-17A/F1 was produced and purified using a mammalian expression system, and was used to stimulate cells isolated from fugu head kidney and intestines. The gene expression levels of TNF-α, IL-1β, IL-6, and β-defensin-like protein-1 (BD-1) genes were evaluated at 0, 3, 6 and 12 h post-stimulation (hps). Phagocytic activity and superoxide anion production were evaluated at the same time points using an NBT assay. The rIL-17A/F1 protein was shown to induce the expression of pro-inflammatory cytokines and antimicrobial peptides in both head kidney and intestinal cells. Expression levels for IL-1β, TNF-α, and IL-6 were all up-regulated between 3 and 12 hps. In addition, stimulation with rIL-17A/F1 enhanced phagocytic activity at 24 hps. Superoxide anion production was increased at 48 hps in the head kidney cells and moderately increased at 48 hps in intestinal cells. This study suggests that fugu IL-17A/F1 plays an important role in promoting the innate immune response and may act as a bridge between innate and adaptive immunity in the head kidney and intestine.

Biological filters regulate water quality, modulate health status, immune indices and gut microbiota of freshwater crayfish, marron (Cherax cainii, Austin, 2002)

Water quality has significant impacts on the health and immune responses of aquaculture species. This study aimed to analyse and compare the effects of two biological filters namely, gravel and, Bio-Ball with a recently developed filter called Water-cleanser on regulation of water quality parameters, health and immune response of marron reared in plastic tanks for 60 days. Results showed that addition of Bio-Ball significantly (P < 0.05) reduced the concentration of ammonia, nitrate and phosphate while Water-cleanser showed the ability to reduce ammonia and nitrate from water in aquaculture tanks. Although the biological filters had no significant effect on marron growth but inclusion of Bio-Ball and Water-cleanser positively influenced the biochemical composition of tail muscle and some haemolymph parameters of marron. The next generation sequence data demonstrated higher bacterial diversity in the hindgut of marron with Water-cleanser, followed by Bio-Ball and gravel, respectively. In addition, the predicted metabolic pathways revealed a significantly higher bacterial activity and gene function correlated to metabolism and biosynthesis of protein, energy and secondary metabolites in Bio-Ball and Water-cleanser. Bio-Ball and Water-cleanser were also associated with up-regulation of innate immune responsive genes of marron gut. Overall, Bio-Ball and Water-cleanser proved to have higher water remediation and immune response modulation capabilities, and therefore could be used as preferred filters for growth of beneficial bacteria in crayfish culture.

Interleukin-17 suppresses grass carp reovirus infection in Ctenopharyngodon idellus kidney cells by activating NF-κB signaling

The grass carp accounts for a large proportion of aquacultural production in China, but the hemorrhagic disease caused by grass carp reovirus (GCRV) infection often causes huge economic losses to the industry. Interleukin 17 (IL-17) is an important cytokine that plays a critical role in the inflammatory and immune responses. Although IL-17 family members have been extensively studied in mammals, our knowledge of the activity of IL-17 proteins in teleosts in response to viral infection is still limited. In this study, the role of IL-17 in GCRV infection and its mechanism were investigated. The expression levels of IL-17AF1, IL-17AF2, and IL-17AF3 in Ctenopharyngodon idella kidney (CIK) cells gradually increased from 6 h after infection with GCRV. The nuclear translocation of p65, which acts in the NF-κB signaling pathway, was also increased by GCRV infection. The overexpression of IL-17AF1, IL-17AF2, or IL-17AF3 also promoted the nuclear translocation of p65 and the levels of phospho-IκBα in CIK cells, and reduced the expression of the viral structural protein VP7. An NF-κB signal inhibitor abolished the inhibition of GCRV infection by IL-17 proteins. These results suggested that the NF-κB signaling pathway was activated by the overexpression of IL-17 proteins, resulting in the inhibition of viral infection. In conclusion, in this study, we demonstrated that IL-17AF1, IL-17AF2, and IL-17AF3 acted as immune cytokines, exerting an antiviral effect by activating the NF-κB signaling pathway.

Genomic Signatures After Five Generations of Intensive Selective Breeding: Runs of Homozygosity and Genetic Diversity in Representative Domestic and Wild Populations of Turbot (Scophthalmus maximus)

Massive genotyping of single nucleotide polymorphisms (SNP) has opened opportunities for analyzing the way in which selection shapes genomes. Artificial or natural selection usually leaves genomic signatures associated with selective sweeps around the responsible locus. Strong selective sweeps are most often identified either by lower genetic diversity than the genomic average and/or islands of runs of homozygosity (ROHi). Here, we conducted an analysis of selective sweeps in turbot (Scophthalmus maximus) using two SNP datasets from a Northeastern Atlantic population (36 individuals) and a domestic broodstock (46 individuals). Twenty-six families (∼ 40 offspring per family) from this broodstock and three SNP datasets applying differing filtering criteria were used to adjust ROH calling parameters. The best-fitted genomic inbreeding estimate (F_ROH) was obtained by the sum of ROH longer than 1 Mb, called using a 21,615 SNP panel, a sliding window of 37 SNPs and one heterozygous SNP per window allowed. These parameters were used to obtain the ROHi distribution in the domestic and wild populations (49 and 0 ROHi, respectively). Regions with higher and lower genetic diversity within each population were obtained using sliding windows of 37 SNPs. Furthermore, those regions were mapped in the turbot genome against previously reported genetic markers associated with QTL (Quantitative Trait Loci) and outlier loci for domestic or natural selection to identify putative selective sweeps. Out of the 319 and 278 windows surpassing the suggestive pooled heterozygosity thresholds (ZHp) in the wild and domestic population, respectively, 78 and 54 were retained under more restrictive ZHp criteria. A total of 116 suggestive windows (representing 19 genomic regions) were linked to either QTL for production traits, or outliers for divergent or balancing selection. Twenty-four of them (representing 3 genomic regions) were retained under stricter ZHp thresholds. Eleven QTL/outlier markers were exclusively found in suggestive regions of the domestic broodstock, 7 in the wild population and one in both populations; one (broodstock) and two (wild) of those were found in significant regions retained under more restrictive ZHp criteria in the broodstock and the wild population, respectively. Genome mining and functional enrichment within regions associated with selective sweeps disclosed relevant genes and pathways related to aquaculture target traits, including growth and immune-related pathways, metabolism and response to hypoxia, which showcases how this genome atlas of genetic diversity can be a valuable resource to look for candidate genes related to natural or artificial selection in turbot populations.

Dietary supplementation of lemon verbena (Aloysia citrodora) improved immunity, immune-related genes expression and antioxidant enzymes in rainbow trout (Oncorrhyncus mykiss)

The use of veterinary drugs for the treatments of fish diseases has often health and environmental side effects and thus alternative more sustainable strategies are needed. In this study we have explored the effect of dietary administration of lemon verbena (Aloysia citrodora) leaves powder on growth, immune parameters and antioxidant enzyme activity of rainbow trout (Oncorrhyncus myskiss). The results show that adding lemon verbena (LV) leaves powder (0.5, 1 and 2%), as feed supplement does not affect significantly rainbow trout growth, but increases the levels of some immune parameters. All enriched-diets induced an increase in the levels of lysozyme activity and total immunoglobulin in rainbow trout serum (P < 0.05), whilst 1 and 2% enriched-diets increased lysozyme and immunoglobulin in skin mucus. Expression of interleukin-1β (IL-1β) was enhanced in all fish supplemented with LV leaves powder (0.5, 1 and 2%) whilst only the diet with the highest dose (2%) induced a significantly higher expression of IL-8 and tumour necrosis factor (TNF-α). Fish fed with LV leaves powder at 1 and 2% had significantly lower expression of transforming growth factor (TGF-β, P < 0.05). Furthermore, all enriched-diets significantly increased the activity of super oxide dismutase (SOD, P < 0.05) and diets containing 1 and 2% of LV leaves powder also increased activity of glutathione-S-transferase (GST) and glutathione peroxidase (GPx). In conclusion, LV leaves powder administered as feed supplement at 2% enhances the expression of some immune-related genes (IL-1β, IL-8 and TNF- α), rises the levels of lysozyme and total immunoglobulin in serum and skin mucus and increases the activity of antioxidant enzymes (SOD, GST and GPx) in rainbow trout.

Identification and Regulation of Interleukin-17 (IL-17) Family Ligands in the Teleost Fish European Sea Bass

Interleukin-17 (IL-17) cytokine comprises a family of six ligands in mammals with proinflammatory functions, having an important role in autoimmune disorders and against bacterial, viral, and fungal pathogens. While IL-17A and IL-17F ligands are mainly produced by Th cells (Th17 cells), the rest of the ligands are expressed by other immune and non-immune cells and have different functions. The identification of IL-17 ligands in fish has revealed the presence of six members, counterparts to mammalian ones, and a teleost-specific form, the fish IL-17N. However, tissue distribution, the regulation of gene expression, and scarce bioactivity assays point to similar functions compared to mammalian ones, though this yet to be investigated and confirmed. Thus, we have identified seven IL-17 ligands in the teleost European sea bass (Dicentrarchus labrax), for the first time, corresponding to IL-17A/F1, IL-17A/F2, IL-17A/F3, IL-17C1, IL-17C2, IL-17D, and IL-17N, according to the predicted protein sequences and phylogenetic analysis. They are constitutively and widely transcribed in sea bass tissues, with some of them being mainly expressed in the thymus, brain or intestine. Upon in vitro stimulation of head-kidney leucocytes, the mRNA levels of all sea bass IL-17 ligands were up-regulated by phytohemagglutinin treatment, a well-known T cell mitogen, suggesting a major expression in T lymphocytes. By contrast, the infection of sea bass juveniles with nodavirus (NNV), a very pathogenic virus for this fish species, resulted in the up-regulation of the transcription of IL-17C1 in the head-kidney and of IL-17C1 and IL-17D in the brain, the target tissue for NNV replication. By contrast, NNV infection led to a down-regulated transcription of IL-17A/F1, IL-17A/F2, IL-17C1, IL-17C2, and IL-17D in the head-kidney and of IL-17A/F1 and IL-17A/F3 in the brain. The data are discussed accordingly with the IL-17 ligand expression and the immune response under the different situations tested.

Interleukin-17A/F1 Deficiency Reduces Antimicrobial Gene Expression and Contributes to Microbiome Alterations in Intestines of Japanese medaka (Oryzias latipes)

In mammals, interleukin (IL)-17A and F are hallmark inflammatory cytokines that play key roles in protection against infection and intestinal mucosal immunity. In the gastrointestinal tract (GI), the induction of antimicrobial peptide (AMP) production via Paneth cells is a fundamental role of IL-17A and F in maintaining homeostasis of the GI microbiome and health. Although mammalian IL-17A and F homologs (referred to as IL-17A/F1-3) have been identified in several fish species, their function in the intestine is poorly understood. Additionally, the fish intestine lacks Paneth cells, and its GI structure is very different from that of mammals. Therefore, the GI microbiome modulatory mechanism via IL-17A/F genes has not been fully elucidated. In this study, Japanese medaka (Oryzias latipes) were used as a teleost model, and IL-17A/F1-knockout (IL-17A/F1-KO) medaka were established using the CRISPR/Cas9 genome editing technique. Furthermore, two IL-17A/F1-deficient medaka strains were generated, including one strain containing a 7-bp deletion (-7) and another with an 11-bp addition (+11). After establishing F2 homozygous KO medaka, transcriptome analysis (RNA-seq) was conducted to elucidate IL-17A/F1-dependent gene induction in the intestine. Results of RNA-seq and real-time PCR (qPCR) demonstrated down-regulation of immune-related genes, including interleukin-1β (IL-1β), complement 1q subunit C (C1qc), transferrin a (Tfa), and G-type lysozyme (LyzG), in IL-17A/F1-KO medaka. Interestingly, protein and lipid digestive enzyme genes, including phospholipase A2, group IB (pla2g1b), and elastase-1-like (CELA1), were also downregulated in the intestines of IL-17A/F1-KO medaka. Furthermore, to reveal the influence of these downregulated genes on the gut microbiome in IL-17A/F1-KO, 16S rRNA-based metagenomic sequencing analysis was conducted to analyze the microbiome constitution. Under a non-exposed state, the intestinal microbiome of IL-17A/F1-KO medaka differed at the phylum level from wild-type, with significantly higher levels of Verrucomicrobia and Planctomycetes. Additionally, at the operational taxonomic unit (OTU) level of the human and fish pathogens, the Enterobacteriaceae Plesiomonas shigelloides was the dominant species in IL-17A/F1-KO medaka. These findings suggest that IL-17A/F1 is involved in the maintenance of a healthy gut microbiome.

Metabolites-Enabled Survival of Crucian Carps Infected by Edwardsiella tarda in High Water Temperature

Temperature is one of the major factors that affect the outbreak of infectious disease. Lines of evidences have shown that virulence factors can be controlled by thermo-sensors in bacterial pathogens. However, how temperature influences host's responses to the pathogen is still largely unexplored, and the study of this might pave the way to develop strategies to manage pathogenic bacterial infection. In the present study, we show that finfish Carassius carassius, the crucian carp that is tolerant to a wide range of temperatures, is less susceptible to bacterial infection when grown in 20°C than in 30°C. The different responses of C. carassius to bacterial infection could be partially explained by the distinct metabolisms under the specific temperatures: C. carassius shows elevated tricarboxylic acid cycle (TCA cycle) but decreased taurine and hypotaurine metabolism as well as lower biosynthesis of unsaturated fatty acids at 30°C. The decreased abundance of palmitate, threonine, and taurine represents the most characteristic metabolic feature. Consistently, exogenous palmitate, threonine, or taurine enhances the survival of C. carassius to bacterial infection at 30°C in a dose-dependent manner. This effect could be attributed to the inhibition on the TCA cycle by the three metabolites. This notion is further supported by the fact that low concentration of malonate, a succinate dehydrogenase inhibitor, increases the survival of C. carassius at 30°C as well. On the other hand, addition of the three metabolites rescued the decreased expression of pro-inflammatory cytokines including TNF-α1, TNF-α2, IL-1β1, IL-1β2, and lysozyme at 30°C. Taken together, our results revealed an unexpected relationship between temperature and metabolism that orchestrates the immune regulation against infection by bacterial pathogens. Thus, this study shed light on the modulation of finfish physiology to fight against bacterial infection through metabolism.

Sequence characterization and expression pattern analysis of six kinds of IL-17 family genes in the Asian swamp eel (Monopterus albus)

Interleukin-17 (IL-17) is an important cytokine that plays a critical role in the inflammatory response and host defense against extracellular pathogens. In the present study, six novel IL-17 family genes (MaIL-17) were identified by analyzing Asian swamp eel (Monopterus albus) genome. Sequence analysis revealed that the MaIL-17 family genes shared similar features, comprising a signal peptide, an IL-17 superfamily region, and four conserved cysteines. Phylogenetic analysis showed that the MaIL-17 genes were clustered together with their corresponding IL-17 genes from other species. The similarity and identity of all IL-17 family genes indicated that the MaIL-17 genes are conserved among teleosts, while Ma-IL-17D is more conserved than the other Ma-IL-17s. Except for MaIL-17A/F3 and MaIL-17D, all MaIL-17s shared the same genomic structure as the genes from other fish, namely three exons and two introns. The MaIL-17s showed conserved synteny among fish, and we found that the MaIL-17D locus has a more conserved syntenic relationship with the loci from other fish and humans. These results demonstrated that MaIL-17D and human IL-17D might have evolved from a common ancestral gene and subsequently diverged. The analysis of swamp eel reference genes revealed that EEF1A1 (encoding eukaryotic translation elongation factor 1 alpha 1) was an ideal reference gene for accurate real-time qRT-PCR normalization in the swamp eel. The MaIL-17 genes are widely distributed throughout tissues, suggesting that MaIL-17s carry out their biological functions in immune and non-immune tissues compartments. The transcript of Ma-IL17s exhibited different fold changes in head kidney cells in response to Aeromonas veronii phorbol 12-myristate 13-acetate (PMA) and polyinosinic:polycytidylic acid (poly I:C) challenge, showing that MaIL-17A/F1 has stronger antiviral activities compared with other MaIL-17 family genes, and that MaIL-17A/F3 and MaIL-17A/F2 possess stronger effects against extracellular pathogens compared with the others; however, MaIL-17C2 and MaIL-17D may play vital roles during pathogen infection. The differential immune responses of these genes to Aeromonas veronii, PMA and poly I:C implied distinct mechanisms of host defense against extracellular pathogens.

Evolution and function analysis of interleukin-17 gene from Pinctada fucata martensii

Interleukin-17 (IL-17) is a proinflammatory cytokine that plays an important role in immune responses. In this study, we identified 57 IL-17 genes from the genomes of six marine invertebrates, including Pinctada fucata martensii, Crassostrea gigas, Lottia gigantea, Capitella teleta, Mizuhopecten yessoensis, and Mytilus galloprovincialis. Phylogenetic analysis showed that all invertebrate IL-17 genes were clustered into one group, implying that invertebrate IL-17 evolved from one common ancestral gene. From the extron-intron analysis, we found many intronless IL-17 genes in mollusks, which may be caused by retroposition. Tissue and development transcriptomic analysis showed that the expression of PmIL-17 was tissue and developmental stage-specific. Moreover, we cloned the full length of the IL-17-2 gene from P. f. martensii (PmIL-17-2) and explored its function in the immune response. The full-length cDNA of PmIL-17-2 is 719 bp, containing an open reading frame of 564 bp, a 5' -untranslated region (UTR) of 31 bp, and a 3' -UTR of 124 bp with a 30 bp poly (A) tail. PmIL-17-2 had a strong response to lipopolysaccharide (LPS), indicating that the PmIL-17-2 participates in innate immune responses. In situ hybridization of hemocytes showed that PmIL-17-2 was mainly produced by granulosa cells, and the number of the stained granulosa increased after LPS stimulation. These results lay the foundation for the research of IL-17 family in marine invertebrates.

Genome-wide identification of interleukin-17 (IL17) in common carp (Cyprinus carpio) and its expression following Aeromonas hydrophila infection

Interleukin-17 (IL17) family cytokines are well known for having pro-inflammatory actions as important mediators of mucosal immune responses and are tightly regulated by various kinds of signals. However, most studies of IL17 genes have focused on mammals, and much less is known about IL17 genes in fish species. To better understand the scope and actions of the IL17 gene family in common carp, we characterized seven IL17 gene homologs from genomic and transcriptomic databases that could be classified into three subclasses according to different comparative genomic analyses. Phylogenetic analysis revealed that most IL17s are highly conserved, though recent gene duplication and gene loss events do exist. Through observation, we found that IL17D has undergone gene duplication in common carp and that all the IL17E genes were lost in vertebrates except mammals. The expression patterns of IL17 genes in common carp were examined during early developmental stages and in various healthy tissues, and the results indicated that most IL17 genes are ubiquitously expressed during early development and show particular tissue-specific expression in various healthy tissues, with relatively high levels in the spleen, liver, and kidney. To gain insights into the mucosal actions of inflammatory processes, the expression profiles of IL17 genes in gills from common carp were investigated after experimental challenge with Aeromonas hydrophila. After A. hydrophila infection, most IL17 genes were upregulated at 4 h postinfection in the gill and then gradually declined, while IL17A/F2 and IL17N were generally upregulated at 12 h postinfection, and IL17D2 maintained an increasing tendency. In contrast, IL17D showed the third phenomenon, rising expression, suggesting that immunogenes have different response strategies to bacterial invasion. Overall, the expression of IL17 in unstimulated tissues and toxicity attack test results demonstrated that these genes play critical roles under normal conditions and during bacterial infection. Moreover, this common carp IL17 gene family research provides a genomic resource for future studies on IL17 gene evolution, fish disease management and immune regulation.

Molecular characterization and expression analysis of IL-22 and its two receptors genes in yellow catfish (Pelteobagrus filvidraco) in response to Edwardsiella ictaluri challenge

Interleukin (IL)-22, as a member of the interleukin (IL)-10 family, is an important mediator between the immune cells and epithelial tissues during infection and inflammation. This study reported the characterization and mRNA expression patterns of Pf_IL-22 gene and its cell surface-associated receptors Pf_IL-22RA1 and soluble Pf_IL-22RA2 genes in yellow catfish (Pelteobagrus filvidraco). The open reading frames (ORFs) of the Pf_IL-22, Pf_IL-22RA1 and Pf_IL-22RA2 genes were 546 bp, 1740 bp and 690 bp in length, encoding 181, 579 and 229 amino acids, respectively. Alignments of the deduced amino acid sequences present that the Pf_IL-22 has a conserved IL-10 family signature motif, and the Pf_IL-22RA1 and Pf_IL-22RA2 have two conserved fibronectin type-III domains. Quantitative real-time PCR (qPCR) analyses showed that the Pf_IL-22 and Pf_IL-22RA1 mRNAs were highly expressed in mucosal tissues such as the fin, gill, intestine, skin mucus and stomach, and were weakly expressed in the kidney, liver and head kidney of adult yellow catfish, indicating that the Pf_IL-22 transcripts may be mainly produced by mucosal immune cells/tissues in healthy yellow catfish. The mRNA expression levels of the Pf_IL-22RA2 gene were high in the muscle and liver, and were relatively low in the spleen and kidney. The mRNA expression levels of the Pf_IL-22 and its two receptor genes were significantly up-regulated in both mucosal tissues (gill, hindgut, and skin mucus) and systemic immune tissues (spleen, head kidney and blood) after Edwardsiella ictaluri challenge. These results indicated that the Pf_IL-22 and its two receptors genes might play an important role in the innate immune defense against bacterial invasion.

A Review of Molecular Responses of Catfish to Bacterial Diseases and Abiotic Stresses

Catfish is one of the major aquaculture species in the United States. However, the catfish industry is threatened by several bacterial diseases such as enteric septicemia of catfish (ESC), columnaris disease and Aeromonas disease, as well as by abiotic stresses such as high temperature and low oxygen. Research has been conducted for several decades to understand the host responses to these diseases and abiotic stresses. With the development of sequencing technologies, and the application of genome-wide association studies in aquaculture species, significant progress has been made. This review article summarizes recent progress in understanding the molecular responses of catfish after bacterial infection and stress challenges, and in understanding of genomic and genetic basis for disease resistance and stress tolerance.

Comparative study of interleukin-17C (IL-17C) and IL-17D in large yellow croaker Larimichthys crocea reveals their similar but differential functional activity

Interleukin 17 (IL-17) family members are key players in regulating the immune response in mammals. Here, we identified the IL-17C and IL-17D homologs from large yellow croaker (Larimichthys crocea), named LcIL-17C and LcIL-17D, respectively. The deduced LcIL-17C and LcIL-17D proteins possessed the typical IL-17 domain and shared a conserved arrangement of eight cysteine residues. Both LcIL-17C and LcIL-17Dc genes were constitutively expressed in all tissues examined, although at different levels. After challenge with Aeromonas hydrophila, the expression of LcIL-17C and LcIL-17D was significantly increased in gills, head kidney, and spleen. In the peripheral blood leukocytes (PBLs), the recombinant LcIL-17C (rLcIL-17C) could strongly promote the expression of chemokines (CXCL8, CXCL12, and CXCL13), proinflammatory factors (TNF-α, IL-1β, IL-6, and IFNg), and antibacterial peptide hepcidin, whereas rLcIL-17D induced a weaker expression of these chemokines. Consistently, the culture supernatants from the PBLs treated by rLcIL-17C showed a stronger ability to induce the migration of PBLs than those treated by rLcIL-17D. Furthermore, both rLcIL-17C and rLcIL-17D could activate the NF-κB signalling in the epithelioma papulosum cyprini (EPC) cells. Taken together, these results indicated that LcIL-17C and LcIL-17D, although differing in their ability to mediate chemotaxis for PBLs, may promote the inflammatory response and host defence via activating NF-κB signalling. To our knowledge, this is the first report on functional identification of a IL-17C in teleost.

Characterization and expression analysis of six interleukin-17 receptor genes in grouper (Epinephelus coioides) after Cryptocaryon irritans infection

Interleukin-17 receptors (IL17Rs) mediate the activation of several downstream signal pathways to induce inflammatory response and contribute to the pathology of many autoimmune diseases. In this study, six IL17Rs (IL17RA1, RA2, RB, RC, RD and RE) were cloned and characterized from Epinephelus coioides, an orange-spotted grouper. Multiple sequence alignment and structural analysis revealed that all members of IL17Rs were low in sequence identity with each other. But their structures were conservative in grouper, which contain signal peptide, extracellular FNIII domain (IL17RA1/RA2/RB) or IL-17_R_N domain (IL17RC/RD/RE), transmembrane domain and SEFIR domain in their intracellular region. The analysis of tissue distribution showed these six genes were ubiquitously and differentially expressed in all major types of tissues. What's more, it is interesting to find their high expression in immune tissues (liver, gill, skin and thymus). IL17RA1 and IL17RA2 were significantly down-regulated at all time-points in gill and spleen after Cryptocaryon irritans infection, however, there was no significant change in other grouper IL17Rs. It suggests that the C. irritans may escape from the host immunity or the host prevents serious inflammation by inhibiting the expression of ILl7Rs.

Peritoneal bacterial infection repressed the expression of IL17D in Siberia sturgeon a chondrostean fish in the early immune response

IL17s are pro-inflammatory cytokines that play important roles in host fighting against extracellular bacteria and auto-immune and allergic diseases. IL17D is believed to be the most ancient IL17 member and its functions are far from clarity. Although it has been found in invertebrates, jawless fish, teleosts, and tetrapods, it has not been described in chondrostean fish. Moreover, there are discrepancies concerning its expression pattern in these animals. In this study, we cloned and characterized the cDNA of il17d in Siberia sturgeon (Acipenser baerii), a chondrostean fish and commercially important species in aquaculture. The sturgeon il17d cDNA encodes a deduced protein of 210aa. The classical characteristics of IL17, such as IL17 domain, cysteine and serine residues importantly for cystine-knot formation, and signal peptide, were observed in sturgeon IL17D. Phylogenetic analysis and multiple alignment suggest it is a counterpart of mammalian IL17D. However, in vivo studies demonstrated that the expression pattern of sturgeon il17d mRNA is different from that of other teleosts and jawless fish, and in most cases its expression was down-regulated at the early time points and gradually increasing at late time points when sturgeon were challenged with bacteria (Aernomas hydrophila or Staphylococcus aureus). The In vitro study by using primary spleen cells stimulated with polyI:C revealed a similar expression pattern to that in vivo studies, while the stimulation with β-glucan or LPS, which normally induced expression of il17d mRNA in target cells in vitro in other animals, did not show apparent changes in the expression of il17d mRNA. The results of present study indicated sturgeon IL17D may possess some different characteristics from its counterparts of other fish and invertebrates in the immune response, and may contribute to the understanding of IL17D functions in evolution as well as the potential use in sturgeon aquaculture.

Transcriptomic profiling revealed the signatures of intestinal barrier alteration and pathogen entry in turbot (Scophthalmus maximus) following Vibrio anguillarum challenge

The mucosal immune system serves as the frontline barriers of host defense against pathogen infection, especially for the fishes, which are living in the pathogen rich aquatic environment. The intestine constitutes the largest surface body area in constantly contact with the external pathogens, and plays a vital role in the immune defense against inflammation and pathogen infection. Previous studies have revealed that fish intestine might serves as the portal of entry for Vibrio anguillarum. To characterize the immune actors and their associated immune activities in turbot intestine barrier during bacterial infection, here we examined the gene expression profiles of turbot intestine at three time points following experimental infection with V. anguillarum utilizing RNA-seq technology. A total of 122 million reads were assembled into 183,101 contigs with an average length of 1151 bp and the N50 size of 2302 bp. Analysis of differential gene expression between control and infected samples at 1 h, 4 h, and 12 h revealed 2079 significantly expressed genes. Enrichment and pathway analysis of the differentially expressed genes showed the centrality of the pathogen attachment and recognition, antioxidant/apoptosis, mucus barrier modification and immune activation/inflammation in the pathogen entry and host immune responses. The present study reported the novel gene expression patterns in turbot mucosal immunity, which were overlooked in previous studies. Our results can help to understand the mechanisms of turbot host defense, and may also provide foundation to identify the biomarkers for future selection of disease-resistant broodstock and evaluation of disease prevention and treatment options.

Molecular characterization and evolution analysis of five interleukin-17 receptor genes in large yellow croaker Larimichthys crocea

Interleukin-17s (IL-17s) play critical roles in inflammatory response and host defense against extracellular pathogens. IL-17s induce the immune response signaling through the specific IL-17 receptors (IL-17Rs) that consist of five members (IL-17RA to E). In the present work, we have identified the five IL-17R orthologs (LycIL-17Rs) from large yellow croaker Larimichthys crocea. The deduced protein of each LycIL-17R exhibits a typical IL-17R domain architecture, including a signal peptide, the extracellular FNIII domain (IL-17RA/RB/RD) or IL-17_R_N domain (IL-17RC/RE), a transmembrane domain, and a SEFIR domain in cytoplasmic region. In particular, the extracellular regions of teleost IL-17RB are much shorter than those in mammals and lack an FNIII domain (FN2). Phylogenetic tree shows that IL-17Rs are classified into two main groups: IL-17RA/RB/RD group and IL-17RC/RE group, which is distinct from previous proposal that grouped IL-17RB into IL-17RC/RE. The surrounding genes of IL-17Rs are conservatively aligned in genomes between teleosts and mammals. The five LycIL-17Rs were constitutively expressed in all tissues examined, but with different expression patterns. Aeromonas hydrophila infection significantly upregulated LycIL-17RA, RC, RD and RE in both mucosal tissue (gills) and systemic immune tissues (head kidney and spleen), while the increase of LycIL-17RB expression could be detected in gills, indicating that LycIL-17Rs may be involved in host defense against bacterial infection. Thus, these results suggest that teleost IL-17Rs may function in mediating immune response as their mammalian orthologs. To our knowledge, this is the first report of molecular characterization of the five IL-17Rs (IL-17RA/RB/RD and IL-17RC/RE) in teleost fish.

The Function of Fish Cytokines

What is known about the biological activity of fish cytokines is reviewed. Most of the functional studies performed to date have been in teleost fish, and have focused on the induced effects of cytokine recombinant proteins, or have used loss- and gain-of-function experiments in zebrafish. Such studies begin to tell us about the role of these molecules in the regulation of fish immune responses and whether they are similar or divergent to the well-characterised functions of mammalian cytokines. This knowledge will aid our ability to determine and modulate the pathways leading to protective immunity, to improve fish health in aquaculture.

Missing the target: DNAk is a dominant epitope in the humoral immune response of channel catfish (Ictalurus punctatus) to Flavobacterium columnare

Vaccination remains a viable alternative for bacterial disease protection in fish; however additional work is required to understand the mechanisms of adaptive immunity in the channel catfish. To assess the humoral immune response to Flavobacterium columnare; a group of channel catfish were first immunized with F. columnare LV-359-01 cultured in iron-depleted media, before being challenged with wild type F. columnare LV-359-01. The immunization protocol did not confer increased protection against F. columnare; however both control and immunized responders generated serum and skin IgM antibodies against F. columnare proteins. Western blot analyses of individuals from both groups showed that IgM antibodies were generated to the same 70 kDa extracellular protein, which was identified to be the bacterial chaperonin protein DNAk. Antibodies generated were cross reactive to DNAk proteins found in other gram negative bacteria. Our data suggests that DNAk is the dominant epitope in the channel catfish B-cell response to F. columnare.

Cloning and characterization of two duplicated interleukin-17A/F2 genes in common carp (Cyprinus carpio L.): Transcripts expression and bioactivity of recombinant IL-17A/F2

Interleukin-17 (IL-17) plays an important role in inflammation and host defense in mammals. In this study, we identified two duplicated IL-17A/F2 genes in the common carp (Cyprinus carpio) (ccIL-17A/F2a and ccIL-17A/F2b), putative encoded proteins contain 140 amino acids (aa) with conserved IL-17 family motifs. Expression analysis revealed high constitutive expression of ccIL-17A/F2s in mucosal tissues, including gill, skin and intestine, their expression could be induced by Aeromonas hydrophila, suggesting a potential role in mucosal immunity. Recombinant ccIL-17A/F2a protein (rccIL-17A/F2a) produced in Escherichia coli could induce the expression of proinflammatory cytokines (IL-1β) and the antimicrobial peptides S100A1, S100A10a and S100A10b in the primary kidney in a dose- and time-dependent manner. Above findings suggest that ccIL-17A/F2 plays an important role in both proinflammatory and innate immunity. Two duplicated ccIL-17A/F2s showed different expression level with ccIL-17A/F2a higher than b, comparison of two 5' regulatory regions indicated the length from anticipated promoter to transcriptional start site (TSS) and putative transcription factor binding site (TFBS) were different. Promoter activity of ccIL-17A/F2a was 2.5 times of ccIL-17A/F2b which consistent with expression results of two genes. These suggest mutations in 5'regulatory region contributed to the differentiation of duplicated genes. To our knowledge, this is the first report to analyze 5'regulatory region of piscine IL-17 family genes.

Molecular and functional identification of three interleukin-17A/F (IL-17A/F) homologues in large yellow croaker (Larimichthys crocea)

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.

Th17 master transcription factors RORα and RORγ regulate the expression of IL-17C, IL-17D and IL-17F in Cynoglossus semilaevis

The RAR-related orphan receptors (RORs) are members of the nuclear receptor family of intracellular transcription factors. In this study, we examined the regulatory properties of RORα (CsRORα) and RORγ (CsRORγ) in tongue sole (Cynoglossus semilaevis). CsRORα and CsRORγ expression was detected in major lymphoid organs and altered to significant extents after bacterial and viral infection. CsRORα enhanced the activities of CsIL-17C, CsIL-17D, and CsIL-17F promoters, which contain CsRORα and CsRORγ binding sites. CsRORγ also upregulated the promoter activities of CsIL-17D and CsIL-17F but not CsIL-17C. CsRORα and CsRORγ proteins were detected in the nucleus, and overexpression of CsRORα in tongue sole significantly increased the expression of CsIL-17C, CsIL-17D, and CsIL-17F, whereas overexpression of CsRORγ significantly increased the expression of CsIL-17C and CsIL-17F but no CsIL-17D. These results indicate that RORα and RORγ in teleost regulate the expression of IL-17 members in different manners.

Galectins in channel catfish, Ictalurus punctatus: Characterization and expression profiling in mucosal tissues

Galectins, a family of β-galactoside-binding lectins with conserved CRDs, which can recognize the glycans on the surface of viruses, bacteria and protozoan parasites, are emerging as key players in many important pathological processes, including acute and chronic inflammatory diseases, autoimmunity and apoptosis. Although galectins have attracted great interest in mammals, they are still poorly-characterized in teleost. Previously, several studies have reported their high expression levels in mucosal tissues before and post infection. Given the important roles for galectins in mucosal immunity, therefore, we characterized the galectin gene family and profiled family member expression after challenge with two different Gram-negative bacterial pathogens. Here, twelve galectins genes were captured in channel catfish (Ictalurus punctatus), and phylogenetic analysis showed the strongest relationship to zebrafish and salmon, which is consistent with their phylogenetic relationships. Furthermore, the galectin genes were widely expressed in catfish tissues, while most of the galectin genes were strongly expressed in mucosal tissues (skin, gill and intestine). In addition, the expression profiles of galectins after bacterial infection varied depending on both pathogen and tissue type, suggesting that galectins may exert disparate functions or exhibit distinct tissue-selective roles in the host immune response to bacterial pathogens. Further studies are needed, however, to expand functional characterization and examine whether galectins may also play additional physiological roles in catfish immunity.

Expression profile analysis of two cathepsin S in channel catfish (Ictalurus punctatus) mucosal tissues following bacterial challenge

Cathepsin S belongs to the papain family of cysteine protease, and is considered to play key roles in immune responses after bacterial challenge. However, despite the recognized importance of Cathepsin S in immunity, no studies have systematically characterized Cathepsin S in catfish. In this regard, here, we characterized the Cathepsin S gene family in channel catfish, and investigated their expression patterns following two different Gram-negative bacterial challenge. In the present study, two Cathepsin S genes (ctss and ctssa) were captured in channel catfish. In comparison to other species, the catfish Cathepsin S genes are highly conserved in their structural features. Phylogenetic analysis indicated the strongest phylogenetic relationship with zebrafish, which is consistent with their evolutional relationships. Tissue distribution analysis revealed that Cathepsin S genes were ubiquitously expressed in catfish tissues. Following bacterial infection, the Cathepsin S genes were significantly up-regulated at most time-points in mucosal surfaces, with an acute response post Edwardsiella ictaluri infection. Obviously, the expression profiles were quite distinct between two Cathepsin S genes, across the tissues and between pathogens, suggesting that Cathepsin S genes may exert disparate roles in mucosal immune responses. Our findings here, provide early insight into the immune functions of Cathepsin S in catfish; however, further studies are needed to determine the mechanisms of Cathepsin S for antigen presentation during inflammatory processes and innate host defense.

Characterization of Lamprey IL-17 Family Members and Their Receptors

IL-17 is an ancient cytokine implicated in a variety of immune defense reactions. We identified five members of the sea lamprey IL-17 family (IL-17D.1, IL-17D.2, IL-17E, IL-17B, and IL-17C) and six IL-17R genes (IL-17RA.1, IL-17RA.2, IL-17RA.3, IL-17RF, IL-17RE/RC, and IL-17RD), determined their relationship with mammalian orthologs, and examined their expression patterns and potential interactions to explore their roles in innate and adaptive immunity. The most highly expressed IL-17 family member is IL-17D.1 (mammalian IL-17D like), which was found to be preferentially expressed by epithelial cells of skin, intestine, and gills and by the two types of lamprey T-like cells. IL-17D.1 binding to rIL-17RA.1 and to the surface of IL-17RA.1-expressing B-like cells and monocytes of lamprey larvae was demonstrated, and treatment of lamprey blood cells with rIL-17D.1 protein enhanced transcription of genes expressed by the B-like cells. These findings suggest a potential role for IL-17 in coordinating the interactions between T-like cells and other cells of the adaptive and innate immune systems in jawless vertebrates.

Identification and mucosal expression analysis of cathepsin B in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish (skin, gill and intestine) constitute the primary line of defense against pathogen invasion. Although the importance of fish mucosal surfaces as the first barriers against pathogens cannot be overstated, the knowledge of teleost mucosal immunity are still limited. Cathepsin B, a lysosomal cysteine protease, is involved in multiple levels of physiological and biological processes, and playing crucial roles for host immune defense against pathogen infection. In this regard, we identified the cathepsin B (ctsba) of channel catfish and investigated the expression patterns of the ctsba in mucosal tissues following Edwardsiella ictaluri and Flavobacterium columnare challenge. Here, catfish ctsba gene was widely expressed in all examined tissues with the lowest expression level in muscle, and the highest expression level in trunk kidney, followed by spleen, gill, head kidney, intestine, liver and skin. In addition, the phylogenetic analysis showed the catfish ctsba had the strongest relationship to zebrafish. Moreover, the ctsba showed a general trend of up-regulated in mucosal tissues following both Gram-negative bacterial challenge. Taken together, the increased expression of ctsba in mucosal surfaces indicated the protective function of ctsba against bacterial infection, and the requirement for effective clearance of invading bacteria. Further studies are needed, indeed, to expand functional characterization and examine whether ctsba may play additional physiological and biological roles in catfish mucosal tissues.

Comparative study of four interleukin 17 cytokines of tongue sole Cynoglossus semilaevis: Genomic structure, expression pattern, and promoter activity

The interleukin (IL)-17 cytokine family participates in the regulation of many cellular functions. In the present study, we analyzed the genomic structure, expression, and promoter activity of four IL-17 members from the teleost fish tongue sole (Cynoglossus semilaevis), i.e. CsIL-17C CsIL-17D, CsIL-17F, and IL-17F like (IL-17Fl). We found that CsIL-17C, CsIL-17D, CsIL-17F, and CsIL-17Fl share 21.2%-28.6% overall sequence identities among themselves and 31.5%-71.2% overall sequence identities with their counterparts in other teleost. All four CsIL-17 members possess an IL-17 domain and four conserved cysteine residues. Phylogenetic analysis classified the four CsIL-17 members into three clusters. Under normal physiological conditions, the four CsIL-17 expressed in multiple tissues, especially non-immune tissues. Bacterial infection upregulated the expression of all four CsIL-17, while viral infection upregulated the expression of CsIL-17D and CsIL-17Fl but downregulated the expression of CsIL-17C and CsIL-17F. The 1.2 kb 5'-flanking regions of the four CsIL-17 exhibited apparent promoter activity and contain a number of putative transcription factor-binding sites. Furthermore, the promoter activities of CsIL-17C, CsIL-17D, and CsIL-17F, but not CsIL-17Fl, were modulated to significant extents by lipopolysaccharide, PolyI:C, and PMA. This study provides the first evidence that in teleost, different IL-17 members differ in expression pattern and promoter activity.

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.