The interleukins of fish

Assessing the impact of acidifiers on growth performance, innate immune capacity, response to ammonia nitrogen stress, digestive enzyme activity, intestinal histology, and gene expression of Nile tilapia (Oreochromis niloticus)

This study investigated the effects of acidifiers (ACD) supplementation level on the growth, immune response, intestinal histology and gene expression of Nile tilapia (Oreochromis niloticus). The experimental diets included three different levels of ACD concentrations: 0 g/kg (CTRL) as the control, 1 g/kg (ACD1), and 2 g/kg (ACD2). These ACD were sprayed onto the diets and fish were fed to Nile tilapia (7.12 ± 0.47 g) for 56 days. The results indicated that increasing the dietary content of ACD significantly enhanced growth performance, as reflected in higher final body weight, specific growth rate, average daily gain, and feed efficiency. The ACD2 diet showed improved outcomes compared to the CTRL diet. Fish fed ACD diets showed significantly higher antioxidant enzyme activity compared to the CTRL diet and were able to maintain their antioxidant status throughout the experiment. The activity of digestive enzymes, including protease, amylase, and lipase, was significantly increased in fish fed diets supplemented with varying levels of 1 and 2 g/kg diet compared to the CTRL diet (P < 0.05). Additionally, significant increases were observed in the thickness of the intestinal muscularis and the width of the intestinal villi in fish fed ACD at concentrations of 1 and 2 g/kg of the diet, compared to the CTRL diet (P < 0.05). Moreover, dietary supplementation with ACD at concentrations of 2 g/kg of the diet significantly upregulated the expression of immune-related genes (P < 0.05). Overall, the use of ACD in fish diets has shown improvements in growth performance, immune responses, and intestinal histology, indicating their potential as a beneficial feed additive for Nile tilapia aquaculture. To the best of our knowledge, recent evaluations of dietary ACD supplementation in practical diets also highlight the influence of ACD supplementation as a feed additive, which could benefit the aquaculture industry.

Transcriptome analysis of head kidney and liver in grass carp (Ctenopharyngodon idella) symptomatically or asymptomatically infected with Flavobacterium columnare

Flavobacterium columnare is an important pathogen causing columnaris disease, which can result in high mortality in freshwater fish worldwide. Understanding the immune response in infection status of fish may be essential for developing effective prevention and treatment strategies. In this study, transcriptomes of liver and head kidney tissues in grass carp (Ctenopharyngodon idella) were compared under symptomatic and asymptomatic statuses following the immersion infection of F. columnare. Significant differences in expression of genes were observed between fish showing disease symptoms and those without symptoms. The number of differentially expressed genes (DEGs) between infected and control groups ranged from 4752 to 8,277, while the DEGs between exposed and control groups ranged from 272 to 1,751, suggesting a strong acute inflammatory response in infected groups. KEGG pathway enrichment analysis of infected groups revealed that among the top 30 enriched pathways, liver and head kidney shared 22 and 16 common pathways, respectively. These common enriched pathways are involved in various functions such as metabolism, diseases, cellular processes, biological systems, and information processing, indicating their roles in the immune response to F. columnare. Notably, we investigated in detail the gene expression profiles associated with complement molecules and three classes of cytokines (interleukin, tumor necrosis factor, and interferon) in different organs/tissues and disease states during the pathogenesis of columnaris disease. The findings highlight the importance of inflammatory responses and complement pathways in the pathogenesis of columnaris disease and suggest potential targets for future research and disease management strategies. The present study thus provides valuable insights into the transcriptomic changes and immune responses in grass carp infected with F. columnare, and sheds light on how highly virulent strains of F. columnare cause morbidity and mortality in the host.

Unraveling the Bioactivities and Immunomodulatory Potential of Postbiotics Derived from Bacillus subtilis and B. amyloliquefaciens for Aquaculture

Postbiotics are molecules or soluble factors released as a result of a probiotic's metabolic activity. Their use in enhancing the growth, health, and disease resistance of aquatic animals has gained considerable attention in aquaculture. The present investigation was designed to assess the beneficial effects of postbiotic products derived from two probiotic strains, Bacillus subtilis and B. amyloliquefaciens. Postbiotics from B. subtilis exhibited significantly greater (p < 0.05) antibacterial activity against various pathogenic bacterial strains, more robust antagonistic growth kinetics, stronger anti-virulence potential, enhanced inhibition of biofilm formation, and increased antioxidant activity compared to those from B. amyloliquefaciens. Additionally, B. subtilis postbiotics triggered a significant (p < 0.05) cellular immune response, including higher myeloperoxidase activity, leucocyte proliferation, and production of nitric oxide and superoxide anions, along with a notable upregulation of immune-related gene expression (IL-1β, IL-10, IFN-γ, and TNF-α) in the head kidney leucocytes of Labeo rohita. A challenge test on L. rohita fingerlings confirmed the safety of B. subtilis postbiotics. These findings highlight the anti-pathogenic, immunostimulatory, and disease-resistant properties of B. subtilis postbiotics, suggesting their promising application in aquaculture.

Contribution of interleukins in the regulation of teleost fish immunity: A review from the perspective of regulating macrophages

Interleukins (ILs) are potent secreted regulators of a wide range of cell types and cellular activities, particularly in the immune system. They are able to participate in intercellular communication in homeostasis and disease, thereby exerting immune functions. Macrophages serve as the innate immune cells of vertebrates and play a pivotal role in defending against and eliminating external pathogens. In mammals, the immune response mounted by macrophages is intricately linked to ILs. Given the fact that teleost fish have evolved an innate immune system that closely resembles those of mammals, particularly in terms of the functionality of macrophages, raises the intriguing possibility that the regulatory function of ILs in macrophage-mediated immunity might be evolutionarily conserved across both mammal and teleost fish lineages. Consequently, from the perspective of interleukin regulation of macrophages, this review outlines the relationship between ILs and macrophages in teleost fish, and elucidates the regulatory role of ILs of immune cell function in teleost fish, thereby contributing to our understanding of the key role of these cytokines in the prevention and control of aquaculture diseases.

Reproductive Benefits of Dietary Selenium Nanoparticles (SeNPs) in Asian Seabass (Lates calcarifer) Male Broodstock

Selenium (Se), a critical trace element for human and animal health, is essential for numerous physiological processes, including antioxidant defense, immune function, and reproduction. This study investigated the effects of dietary selenium nanoparticles (SeNPs) at 2 mg/kg on the reproductive performance, Se deposition, antioxidant status, and gene expression in male Asian seabass (Lates calcarifer). Over 120 days before spawning, the male broodfish were fed either a control diet (CD) or a SeNP-supplemented diet (SeD) in triplicate tanks per group. The SeD group exhibited significantly higher gonadosomatic index (GSI), fertilization rate, and hatching rate, along with lower rates of abnormal embryogenesis compared to the CD group (P < 0.05). Selenium accumulation was significantly elevated in the liver and testis tissues of the SeD group, corresponding with increased expression of the hepatic selenop gene. Reproduction-related genes, including ar, p450scc, and cdk1, were significantly upregulated in the testis of the SeD group, indicating enhanced reproductive processes. Antioxidant-related genes, including catalase (cat), superoxide dismutase (sod), and glutathione-s-transferase (gst) were also upregulated in both liver and testis tissues, while catalase activity increased in the testis. In terms of sex steroid hormones, the SeD group displayed significantly higher serum levels of testosterone and progesterone (P < 0.05), suggesting enhanced steroidogenesis. The absence of adverse effects further demonstrates the efficacy and safety of SeNP supplementation at 2 mg/kg. This study highlights the potential of SeNPs to enhance reproductive performance, regulate molecular pathways, and optimize broodstock management in aquaculture.

Roles of S100A1 and S100A10 from hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀) in immune response to Vibrio infection

The S100 proteins are highly conserved EF-hand calcium-binding proteins found only in vertebrates. In the current study, two S100 genes (S100A1 and S100A10) were successfully identified and characterized from hybrid grouper Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀. The deduced S100A10 protein contained two EF-hand domains, and S100A1 only possessed the N-terminal EF-hand. Phylogenetic analysis revealed that S100A1 and S100A10 from hybrid grouper were evolutionarily closely related to their counterparts in other selected vertebrates. Quantitative real-time PCR results revealed that the transcripts of S100A1 and S100A10 mRNA were ubiquitously distributed in all the examined tissues. After Vibrio alginolyticus infection, the expression of S100A1 and S100A10 in the spleen increased significantly. Moreover, overexpression of S100A1 and S100A10 could not only regulate the expression of interleukin 8 (IL-8), IL-10, and IL-16 in the head kidney, liver, and spleen, change the activities of acid phosphatase, catalase, lysozyme, and superoxide dismutase in serum, but also reduce the promoter activities of interferon 3 and nuclear factor kappa-B in vitro. Taken together, this study indicated that S100A1 and S100A10 participate in the immune response of hybrid grouper against bacterial infection.

Ameliorative role of camel protein hydrolysates diet against alkaline stress in Oreochrmis niloticus: Hematology, immune responses and their regulating genes expression, and histopathological assays

This investigation looked at the ameliorative role of camel whey protein hydrolysates-diet (PH) in Oreochromis niloticus stocked under alkaline conditions. One hundred sixty fish (16.02 ± 0.14 g) were allocated equally into four groups with four replications for 30 days. The first (control) and second (alkaline) groups were fed basal diets and maintained in fresh and alkaline water, respectively. The third and fourth groups were fed on a PH diet (basal diet containing 75 g PH/kg) and maintained in fresh water and alkaline water, respectively. The hematology, immune-antioxidant indices, immune-regulatory genes, histopathological investigation of the spleen, and resistance to Aeromonas sobria were investigated. The results showed that the alkaline condition induced hematological disorders (lowered red blood cells, hemoglobin, packed cell volume, and white blood cell count) and immunosuppression (lowered phagocytic activity and index, lysozyme, nitric oxide, and complement 3) in the exposed fish. Alkaline exposure induced oxidative stress through elevation of the malondialdehyde and reduction in the antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione S-reductase, and reduced glutathione). The immune modulatory genes (tolls like receptor-5, interleukin-1beta, interleukin-6, interleukin-8, interleukin-10, interleukin-17, nuclear factor kappa beta, and tumor necrosis factor-alpha) were down-regulated by exposure to alkaline conditions. The microscopic section of the spleen of the fish subjected to alkaline conditions showed notable hyperplasia of the melanomacrophage centers, besides vascular congestion, endothelial cell hypertrophy, and mild hypercellularity in the erythroid and lymphoid elements. In addition, few sections manifested more pronounced erythroid hyperplasia than the lymphoid one. The survival of the fish subjected to alkaline conditions was reduced during the A. sobria challenge. Feeding on a PH diet, the hematology was restored and the immune-antioxidant functions were modulated. Modulation of the immune-regulatory genes and increased survivability of the alkaline-exposed fish were noticed when fed on the PH diet. Consequently, we can recommend enriching the Nile tilapia diet with a 75 g PH/kg diet especially when reared under alkaline conditions to support the immune functions of the fish.

Characterization and functional analysis of interleukin-6 and its receptor subunits (IL-6Rα and IL-6Rβ) in the yellow drum, Nibea alibiflora

Interleukin 6 (IL-6) is one of the cytokines found to be multifunctional and biologically effective, regulating immune and inflammatory response by interacting with receptors to transmit signals. In this study, the full-length cDNAs of IL-6 (named as NaIL-6) and its receptors IL-6R and gp130 (named as NaIL-6Rα and NaIL-6Rβ) of Nibea albiflora were acquired and they possessed the typical symbolic motifs similar to its teleost orthologues in multiple sequence comparisons. The phylogenetic trees showed that NaIL-6 and its receptors clustered with their counterparts in bony fish, and had the closest affinity to Larimichthys crocea. Real-time PCR indicated that NaIL-6, NaIL-6Rα and NaIL-6Rβ were widely expressed in different tissues, among which NaIL-6 was highly expressed in the liver, NaIL-6Rα showed the highest expression in the kidney and NaIL-6Rβ was reflected in the liver. Following stimulation by Vibrio parahaemolyticus, Vibrio alginolyticus, or Polyinosinic-polycytidylic acid (Poly (I:C)) infection, the mRNA expression of all three genes were greatly up-regulated over time. The cell localization analysis showed that NaIL-6 distributed in cytoplasm and cell membrane, and NaIL-6Rα located on the cell membrane. After co-transfection of NaIL-6- mCherry and NaIL-6Rα-EGFP, they co-expressed as orange at the same position for their possibility of spatial interactions on the cellular membrane. By GST-Pull down with the purified target proteins, the association between NaIL-6-His and NaIL-6Rα-GST was confirmed, which may be utilized for further functional study. Taken together, the results indicated that the biological functions of NaIL-6 and its receptors NaIL-6Rα and NaIL-6Rβ involved in the immunologic mechanism in N.albiflora, which would provide a basis for the research of immune functions and signaling pathway of IL-6 and its receptors in fish.

Effects of dietary Hericium erinaceus extract on growth, nutrient utilization, hematology, expression of genes related immunity response, and disease resistance of Nile tilapia (Oreochromis niloticus)

In recent years, there has been a growing focus on using herbal extracts as immune enhancers for aquatic species, replacing antibiotics. In the present study, the effects of dietary supplementation of Hericium erinaceus extract (HE) on growth, feed utilization, hematology, expression of immunity-related genes, and immune responses in Nile tilapia infected by Streptococcus agalactiae were examined. A total of 240 Nile tilapia with an average body weight of 17.28 ± 0.01 g were fed diets enriched with different levels of HE: 0 (HE0), 0.1 (HE0.1), 1.0 (HE1.0), and 5.0 (HE5.0) g/kg. The results showed that growth parameters, feed conversion ratio, and organosomatic indexes were not linearly or quadratically affected by HE supplementation. Fish fed HE0.1 and HE1.0 increased protein efficiency ratio and protein productive values with significant linear and quadratic effects of HE enrichment. In addition, dietary supplementation of HE quadratically increased whole-body protein content. Red blood cell, white blood cell, and hematocrit were linearly and quadratically increased by HE supplementation. HE also linearly and quadratically decreased LDL cholesterol and linearly decreased the total cholesterol levels. Stress markers, serum glucose, and cortisol levels were linearly and/or quadratically decreased in HE-fed fish. The relative mRNA expression of tnf-α, il-1β, il-6, and il-10 were upregulated in the HE0.1 and HE1.0 groups, while dietary supplementation of HE significantly decreased hsp70cb1 mRNA expression in all groups. After feeding dietary HE supplementation for 10 weeks, fish were intraperitoneally injected with pathogenic S. agalactiae. A high survival after challenge was found in all HE supplementation groups with the highest percent survival observed in the HE1.0 and HE5.0 groups. Our findings represent that supplementation of 1 g/kg of HE (HE1.0) could obtain the greatest effects on immunity and survival of Nile tilapia. In addition, the present study also showed that dietary supplementation of HE can improve protein utilization, hematology, expression of genes related to immunity, stress markers, and resistance of Nile tilapia against pathogenic bacterial infection.

Passive protection of chicken egg yolk immunoglobulin (IgY) against Streptococcus agalactiae infection in Nile tilapia (Oreochromis niloticus)

IgY is an immunoglobulin primarily found in the serum and egg yolk of birds, amphibians, and reptiles. Recent years, IgY is considered to have a good application prospect in the immunodiagnostics and passive immunotherapy of aquatic diseases. In this study, we prepared a specific IgY against Streptococcus agalactiae in tilapia after immunizing the hens for 4 times. The result of ELISA detection showed that the IgY titers in water-soluble fraction (WSF) after 6 weeks of immunization reached 1:51200 and last for 4 weeks. Western blot (WB) analysis data showed that the specific IgY could recognize the target band, the specific IgY showed a concentration-dependent inhibitory effect on the growth of S. agalactiae, altered cell wall structure and aggluted of S. agalactiae. The quantitative reverse transcription PCR (qRT-PCR) analysis data suggested that the specific IgY downregulated the expression of pro-inflammatory factors (IL-8, TNF-α), upregulated the anti-inflammatory factors (IL-10, TGF-β). In addition, the histopathological results showed that the specific IgY significantly decreased the pathological manifestations, dramatically improved the survival rates of tilapia in injection, feeding, and immersion experiments. Collectively, our findings demonstrated that the broad potential of specific IgY for the prevention and treatment of S. agalactiae infection in tilapia.

Lactobacillus delbrueckii ameliorates Aeromonas hydrophila-induced oxidative stress, inflammation, and immunosuppression of Cyprinus carpio huanghe var NF-κB/Nrf2 signaling pathway

Aeromonas hydrophila (A. hydrophila) is one of the most pathogenic disease-causing bacteria, and causes massive death of animals including fish. Thus, strategies are being sought to ameliorate the impact of A. hydrophila. In this study, we have evaluated the ameliorative potential of dietary Lactobacillus delbrueckii (L. delbrueckii). The fishes were divided into the control group, an A. hydrophila group (A. hydrophila), and an L. delbrueckii group (A. hydrophila + 1*107 CFU/g L. delbrueckii). The results showed that A. hydrophila increased reactive oxygen species (ROS) content. However, dietary supplementation with L. delbrueckii prevented oxidative damage caused by elevated levels of ROS. The toxic effects of A. hydrophila on superoxide dismutase (SOD) activity, glutathione-S-transferase (GST), glutathione peroxidase (GPx), and glutathione reductase (GR), along with the levels of glutathione (GSH), were mitigated by dietary L. delbrueckii (P < 0.05). Also, Dietary L. delbrueckii induced the expression of antioxidant-related genes (sod, cat, gpx, gst, NF-E2-related factor 2 (nrf2), Kelch-like-ECH-and associated protein 1a (keap1a)) in the intestine of fish (P < 0.05). Furthermore, L. delbrueckii increased A. hydrophila-induced lysozyme, ACP, C3, and C4 decline. The mRNA expression levels of interleukin 1β (il-1β), interleukin 8 (il-8), tumour necrosis factor α (tnf-α), and nuclear transcription factor-κB p65 (nf-κb p65) were significantly elevated by A. hydrophila. In contrast, the relative mRNA expression levels of inhibitor factor κBα (iκbα) in the intestine were decreased by A. hydrophila (P < 0.05). However, L. delbrueckii prevented A. hydrophila-induced the relative mRNA expression changes. These present results demonstrate that dietary L. delbrueckii alleviated A. hydrophila-induced oxidative stress, immunosuppression, inflammation, and apoptosis in common Cyprinus carpio.

The dynamic immune response of the liver and spleen in leopard coral grouper (Plectropomus leopardus) to Vibrio harveyi infection based on transcriptome analysis

Leopard coral grouper (Plectropomus leopardus) is one of the most important cultured fish in the Pacific and Indian oceans. Vibrio harveyi is a serious pathogen causing serious skin ulceration and high mortality in P. leopardus. To gain more insight into the tissue-specific and dynamic immune regulation process of P. leopardus in response to V. harveyi infection, RNA sequencing (RNA-seq) was used to examine the transcriptome profiles in the spleen and liver at 0, 6, 12, 24, 48, and 72 h post-infection. The upregulated differentially expressed genes (DEGs) were predominantly involved in the immune response in the spleen and liver at the early infection stage (6-12 h), and downregulated DEGs were mainly involved in metabolic processes in the liver at the early and middle infection stage (6-48 h). Moreover, an overview of the immune response of P. leopardus against V. harveyi was exhibited including innate and adaptive immune-related pathways. Afterwards, the results of WGCNA analysis in the spleen indicated that TAP2, IRF1, SOCS1, and CFLAR were the hub genes closely involved in immune regulation in the gene co-expression network. This study provides a global picture of V. harveyi-induced gene expression profiles of P. leopardus at the transcriptome level and uncovers a set of key immune pathways and genes closely linked to V. harveyi infection, which will lay a foundation for further study the immune regulation of bacterial diseases in P. leopardus.

Effects of Aeromonas infection on the immune system, physical barriers and microflora structure in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is an intensively cultured and economically important herbivorous fish species in China, but its culture is often impacted by Aeromonas pathogens such as Aeromonas hydrophila and Aeromonas veronii. In this study, healthy grass carp were separately infected with A. hydrophila or A. veronii for 12, 24, 48 or 72 h. The results showed that the mRNA expression levels of intestinal inflammatory factors (tnf-α, il-1β and il-8), complement factors (c3 and c4), antimicrobial peptides (hepcidin, nk-lysin and β-defensin-1), immunoglobulins (igm and igt), and immune pathway-related signaling molecules (tlr1, tlr2, tlr4, myd88, irak4, irak1, traf6, nf-κb p65 and ap-1) were differentially upregulated in response to A. hydrophila and A. veronii challenge. Additionally, the expression levels of the intestinal pro-apoptotic genes tnfr1, tnfr2, tradd, caspase-8, caspase-3 and bax were significantly increased, whereas the expression of the inhibitory factor bcl-2 was significantly downregulated, indicating that Aeromonas infection significantly induced apoptosis in the intestine of grass carp. Moreover, the expression of intestinal tight junction proteins (occludin, zo-1, claudin b and claudin c) was significantly decreased after infection with Aeromonas. Histopathological analysis indicated the Aeromonas challenge caused severe damage to the intestinal villi with adhesions and detachment of intestinal villi accompanied by severe inflammatory cell infiltration at 12 h and 72 h. The 16S rRNA sequencing results showed that Aeromonas infection significantly altered the structure of the intestinal microflora of the grass carp at the phylum (Proteobacteria, Fusobacteria, Bacteroidetes and Firmicutes) and genus (Proteus, Cetobacterium, Bacteroides, and Aeromonas) levels. Take together, the findings of this study revealed that Aeromonas infection induces an intestinal immune response, triggers cell apoptosis, destroys physical barriers and alters microflora structure in the intestine of juvenile grass carp; the results will help to reveal the pathogenesis of intestinal bacterial diseases in grass carp.

Salmonid Rickettsial Septicemia (SRS) disease dynamics and Atlantic salmon immune response to Piscirickettsia salmonis LF-89 and EM-90 co-infection

In Chile, Piscirickettsia salmonis contains two genetically isolated genogroups, LF-89 and EM-90. However, the impact of a potential co-infection with these two variants on Salmonid Rickettsial Septicemia (SRS) in Atlantic salmon (Salmo salar) remains largely unexplored. In our study, we evaluated the effect of P. salmonis LF-89-like and EM-90-like co-infection on post-smolt Atlantic salmon after an intraperitoneal challenge to compare changes in disease dynamics and host immune response. Co-infected fish had a significantly lower survival rate (24.1%) at 21 days post-challenge (dpc), compared with EM-90-like single-infected fish (40.3%). In contrast, all the LF-89-like single-infected fish survived. In addition, co-infected fish presented a higher presence of clinical lesions than any of the single-infected fish. The gene expression of salmon immune-related biomarkers evaluated in the head kidney, spleen, and liver showed that the EM-90-like isolate and the co-infection induced the up-regulation of cytokines (e.g., il-1β, ifnγ, il8, il10), antimicrobial peptides (hepdicin) and pattern recognition receptors (PRRs), such as TLR5s. Furthermore, in serum samples from EM-90-like and co-infected fish, an increase in the total IgM level was observed. Interestingly, specific IgM against P. salmonis showed greater detection of EM-90-like antigens in LF-89-like infected fish serum (cross-reaction). These data provide evidence that P. salmonis LF-89-like and EM-90-like interactions can modulate SRS disease dynamics in Atlantic salmon, causing a synergistic effect that increases the severity of the disease and the mortality rate of the fish. Overall, this study contributes to achieving a better understanding of P. salmonis population dynamics.

Climate change can impair bacterial pathogen defences in sablefish via hypoxia-mediated effects on adaptive immunity

Low-oxygen levels (hypoxia) in aquatic habitats are becoming more common because of global warming and eutrophication. However, the effects on the health/disease status of fishes, the world's largest group of vertebrates, are unclear. Therefore, we assessed how long-term hypoxia affected the immune function of sablefish, an ecologically and economically important North Pacific species, including the response to a formalin-killed Aeromonas salmonicida bacterin. Sablefish were held at normoxia or hypoxia (100% or 40% air saturated seawater, respectively) for 6-16 weeks, while we measured a diverse array of immunological traits. Given that the sablefish is a non-model organism, this involved the development of a species-specific methodological toolbox comprised of qPCR primers for 16 key immune genes, assays for blood antibacterial defences, the assessment of blood immunoglobulin (IgM) levels with ELISA, and flow cytometry and confocal microscopy techniques. We show that innate immune parameters were typically elevated in response to the bacterial antigens, but were not substantially affected by hypoxia. In contrast, hypoxia completely prevented the ∼1.5-fold increase in blood IgM level that was observed under normoxic conditions following bacterin exposure, implying a serious impairment of adaptive immunity. Since the sablefish is naturally hypoxia tolerant, our results demonstrate that climate change-related deoxygenation may be a serious threat to the immune competency of fishes.

Comparative studies on the intestinal health of wild and cultured ricefield eel (Monopterus albus)

Fish intestinal health under intensive aquaculture mode plays an important role in growth, development, and immune function. The present study was aimed to systematically investigate the differences of intestinal health between wild and cultured Monopterus albus by biochemical parameters, histomorphology, and molecular biology. A total of 15 healthy M. albus per group, with an average body weight of 45 g, were sampled to analyze intestinal health parameters. Compared with wild fish, the cultured M. albus in the foregut had lower trypsin, lipase, SOD, CAT, T-AOC, and GSH-Px activities (P < 0.05) and higher amylase activity and MDA content (P < 0.05). The villus circumference and goblet cells in the cultured group were significantly lower than those in the wild group (P < 0.05). In addition, the cultured fish showed lower relative expression levels of occludin, zo-1, zo-2, claudin-12, claudin-15, mucin5, mucin15, lysozyme, complement 3, il-10, tgf-β1, tgf-β2, and tgf-β3 (P < 0.05) and higher il-1β, il-6, il-8, tnf-a, and ifnγ mRNA expressions than those of wild fish (P < 0.05). In terms of gut microbiota, the cultured group at the phylum level displayed higher percentages of Chlamydiae and Spirochaetes and lower percentages of Firmicutes, Bacteroidetes, Actinobacteria, Cyanobacteria, and Verrucomicrobia compared to the wild group (P < 0.05). At the genus level, higher abundances of Pseudomonadaceae_Pseudomonas and Spironema and lower abundances of Lactococcus and Cetobacterium were observed in the cultured group than in the wild group (P < 0.05). To our knowledge, this is the first investigation of the intestinal health status between wild and cultured M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, the present study showed significant differences in intestinal health between wild and cultured M. albus and the main manifestations that wild M. albus had higher intestinal digestion, antioxidant capacity, and intestinal barrier functions than cultured M. albus. These results would provide theoretical basis for the subsequent upgrading of healthy aquaculture technology and nutrient regulation of intestinal health of cultured M. albus.

Discovery and Characterization of the ddx41 Gene in Atlantic Salmon: Evolutionary Implications, Structural Functions, and Innate Immune Responses to Piscirickettsia salmonis and Renibacterium salmoninarum Infections

The innate immune response in Salmo salar, mediated by pattern recognition receptors (PRRs), is crucial for defending against pathogens. This study examined DDX41 protein functions as a cytosolic/nuclear sensor for cyclic dinucleotides, RNA, and DNA from invasive intracellular bacteria. The investigation determined the existence, conservation, and functional expression of the ddx41 gene in S. salar. In silico predictions and experimental validations identified a single ddx41 gene on chromosome 5 in S. salar, showing 83.92% homology with its human counterpart. Transcriptomic analysis in salmon head kidney confirmed gene transcriptional integrity. Proteomic identification through mass spectrometry characterized three unique peptides with 99.99% statistical confidence. Phylogenetic analysis demonstrated significant evolutionary conservation across species. Functional gene expression analysis in SHK-1 cells infected by Piscirickettsia salmonis and Renibacterium salmoninarum indicated significant upregulation of DDX41, correlated with increased proinflammatory cytokine levels and activation of irf3 and interferon signaling pathways. In vivo studies corroborated DDX41 activation in immune responses, particularly when S. salar was challenged with P. salmonis, underscoring its potential in enhancing disease resistance. This is the first study to identify the DDX41 pathway as a key component in S. salar innate immune response to invading pathogens, establishing a basis for future research in salmonid disease resistance.

Role of alternative splicing in fish immunity

Alternative splicing serves as a pivotal source of complexity in the transcriptome and proteome, selectively connecting various coding elements to generate a diverse array of mRNAs. This process encodes multiple proteins with either similar or distinct functions, contributing significantly to the intricacies of cellular processes. The role of alternative splicing in mammalian immunity has been well studied. Remarkably, the immune system of fish shares substantial similarities with that of humans, and alternative splicing also emerges as a key player in the immune processes of fish. In this review, we offer an overview of alternative splicing and its associated functions in the immune processes of fish, and summarize the research progress on alternative splicing in the fish immunity. Furthermore, we review the impact of alternative splicing on the fish immune system's response to external stimuli. Finally, we present our perspectives on future directions in this field. Our aim is to provide valuable insights for the future investigations into the role of alternative splicing in immunity.

Exploration of the immune response of grass carp (Ctenopharyngodon idellus) erythrocytes during bacterial infection

In teleost blood, red blood cells (RBCs) are the most common type of cell, and they differ from mammalian RBCs in having a nucleus and other organelles. As nucleated cells, teleost RBCs contribute to the immune response against pathogens, but their antibacterial mechanism remains unclear. Here, we utilized RNA-Seq to analyze gene expression patterns of grass carp (Ctenopharyngodon idellus) RBCs (GcRBCs) stimulated by Aeromonas hydrophila, Escherichia coli, and Staphylococcus aureus. Our transcriptomic data showed that bacterial stimulation generated many differentially expressed genes (DEGs). Furthermore, several inflammatory pathways responded to bacterial activation, and the TLR, IL-17, and tumor necrosis factor (TNF) signaling pathways were significantly activated based on Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Furthermore, the findings of qRT-PCR showed markedly elevated expression of various cytokines, including IL-1β, IL4, IL6, IL8, IL12, and TNFα, in GcRBCs after incubation with bacteria. Reactive oxygen species (ROS) production in GcRBCs was markedly increased after the cells were stimulated with the three bacteria, and the expression of superoxide dismutase, glutathione peroxidase, and antioxidant enzymes, including catalase, was altered. Flow cytometry analysis showed that the apoptosis rate of GcRBCs was enhanced after stimulation with the three bacteria for different times. In summary, our findings reveal that bacterial stimulation activates the immune response of GcRBCs by regulating ROS release, cytokine expression, and the antioxidant system, leading to apoptosis of GcRBCs.

Gut physiology of rainbow trout (Oncorhynchus mykiss) is influenced more by short-term fasting followed by refeeding than by feeding fishmeal-free diets

Supplementing a fishmeal-free diet with yeast extract improves rainbow trout (Oncorhynchus mykiss) growth performance and modulates the hepatic and intestinal transcriptomic response. These effects are often observed in the long term but are not well documented after short periods of fasting. Fasting for a few days is a common practice in fish farming, especially before handling the fish, such as for short sorting, tank transfers, and vaccinations. In the present study, rainbow trout were subjected to a 4-day fast and then refed, for 8 days, a conventional diet containing fishmeal (control diet) or alternative diets composed of terrestrial animal by-products supplemented or not with a yeast extract. During the refeeding period alone, most of the parameters considered did not differ significantly in response to the different feeds. Only the expression of claudin-15 was upregulated in fish fed the yeast-supplemented diet compared to the control diet. Conversely, fasting followed by refeeding significantly influenced most of the parameters analyzed. In the proximal intestine, the surface area of villi significantly increased, and the density of goblet cell tended to decrease during refeeding. Although no distinct plasma immune response or major signs of gut inflammation were observed, some genes involved in the structure, complement pathway, antiviral functions, coagulation, and endoplasmic reticulum stress response of the liver and intestine were significantly regulated by refeeding after fasting. These results indicate that short-term fasting, as commonly practiced in fish farming, significantly alters the physiology of the liver and intestine regardless of the composition of the diet.

The cytokine genes of Oncorhynchus masou formosanus include a defective interleukin-4/13A gene

Oncorhynchus masou formosanus (Formosa landlocked salmon) is a critically endangered salmonid fish endemic to Taiwan. To begin to understand how its drastic change in lifestyle from anadromous to exclusively river-dwelling is reflected in its immune genes, we characterized the genes encoding six cytokines (IL-2A, IL-2B, IL-4/13A, IL-4/13B1, IL-4/13B2, and IL-17A/F2a) important for T cell responses as no genomic data is available for this fish. Interestingly, all genes appeared homozygous indicative of a genetic bottleneck. The IL2 and IL17A/F2a genes and their products are highly similar to their characterized homologs in Oncorhynchus mykiss (rainbow trout) and other salmonid fish. Two notable differences were observed in IL4/13 family important for type 2 immune responses. First, O. m. formosanus carries not only one but two genes encoding IL-4/13B1 proteins and expansions of these genes are present in other salmonid fish. Second, the OmfoIL4/13A gene carries a 228 bp deletion that results in a premature stop codon and hence a non-functional IL-4/13A cytokine. This suggests a reduced ability for T cell responses against parasitic infections in this species.

Vegetable omega-3 and omega-6 fatty acids differentially modulate the antiviral and antibacterial immune responses of Atlantic salmon

The immunomodulatory effects of omega-3 and omega-6 fatty acids are a crucial subject of investigation for sustainable fish aquaculture, as fish oil is increasingly replaced by terrestrial vegetable oils in aquafeeds. Unlike previous research focusing on fish oil replacement with vegetable alternatives, our study explored how the omega-6 to omega-3 polyunsaturated fatty acid (PUFA) ratio in low-fish oil aquafeeds influences Atlantic salmon's antiviral and antibacterial immune responses. Atlantic salmon were fed aquafeeds rich in soy oil (high in omega-6) or linseed oil (high in omega-3) for 12 weeks and then challenged with bacterial (formalin-killed Aeromonas salmonicida) or viral-like (polyriboinosinic polyribocytidylic acid) antigens. The head kidneys of salmon fed high dietary omega-3 levels exhibited a more anti-inflammatory fatty acid profile and a restrained induction of pro-inflammatory and neutrophil-related genes during the immune challenges. The high-omega-3 diet also promoted a higher expression of genes associated with the interferon-mediated signaling pathway, potentially enhancing antiviral immunity. This research highlights the capacity of vegetable oils with different omega-6 to omega-3 PUFA ratios to modulate specific components of fish immune responses, offering insights for future research on the intricate lipid nutrition-immunity interplay and the development of novel sustainable low-fish oil clinical aquaculture feeds.

Identifying transcriptomic indicators of tertiary treated municipal effluent in longnose dace (Rhinichthys cataractae) caged under semi-controlled conditions in experimental raceways

To evaluate effects of tertiary treated wastewater treatment plant effluent (MWWE) on transcriptomic responses in longnose dace (Rhinichthys cataractae; LND) we conducted a semi-controlled study in experimental raceways (Advancing Canadian Water Assets facility) imbedded in the Pine Creek treatment plant (Calgary, AB). LND collected from a reference site in the Bow River (REF) were caged in raceways containing either 5 % Pine Creek effluent (PC) or Bow River water (BR; control) over 28 d. Liver transcriptomes were analyzed in males and females sampled on days 7, 14 and 28 from BR and PC, and compared to REF fish on day 0. Concurrent with the caging, selected environmental substances of concern were analyzed in the BR and PC. Significantly different unigenes (SDUs) in females (vs males) within both BR and PC raceways increased over time and compared to REF fish. Moreover, SDUs in females and males within the same treatment (i.e., BR, PC) showed a temporal increase as well as compared to REF fish. Time was the dominant factor affecting SDUs, whereas sex and treatment had less of an impact on the transcriptome profiling. Gene Set Enrichment Analysis of BR vs PC over time revealed effects on genes involved in growth, metabolism of carbohydrates and lipids, and immune system on day 7; however, by day 28, 80-100 % of the transcripts localized to enriched biomarkers were associated with tissue immune responses in both sexes. Exposure to 5 % effluent had significant effects on female liver somatic index but no effects were observed on other phenotypic health indices in either sex. BR was used as the source of reference water, but analyses showed trace amounts of ESOCs. Analyses did not point towards definitive response patterns that could be used in field-based ecotoxicogenomic studies on the impacts of well-treated MWWE but suggested compromised adaptive immune responses.

Effects of Dietary Supplement of Basil Extract on Biochemical and Immunological Parameters and Growth Performance in Oncorhynchus mykiss

Ocimum basilicum has antioxidant, anti-inflammatory, and antimicrobial effects. The present study was conducted to evaluate the effects of O. basilicum extract on growth yield, safety, and marinating physiologic functions of the rainbow trout. The fish were fed with food rations containing 0%, 1%, 2%, and 3% of basil extract. Basil extract, especially at 1% concentration food ration, significantly increased the growth parameters compared with the control group (p < 0.05). The biochemical parameters of hepatic function, renal function, glucose, triglyceride, and cholesterol level were significantly reduced in the treatment groups compared with the control group (p < 0.05). Feeding with basil extract led to a significant increase in Ig, lysozyme, and respiratory burst assay, with the most prominent elevation at 2% concentration food ration. The mucosal antibacterial activity was improved. The mortality rate after exposure to Yersinia ruckeri was lower in the treatment groups compared with the control group. The results of the present study suggest that adding 2% basil extract to the food rations of the fish may improve their physiologic function and growth yield and reinforce their immune system.

Pathogenicity of Streptococcus iniae causing mass mortalities of yellow catfish (Tachysurus fulvidraco) and its induced host immune response

The outbreak of mass mortality occurred in Tachysurus fulvidraco farm in Hubei province of China. The pathogenic strain of Streptococcus iniae (termed 2022SI08) was isolated and identified from diseased T. fulvidraco, based on morphological, physiological, and biochemical characteristics, as well as 16S rRNA gene sequence and phylogenetic analysis. Further, the whole genome of isolate S. iniae was sequenced and predicted to contain one single circular chromosome of 1,776,777 bp with a GC content of 37.14%. The genomic sequence analysis showed that 2022SI08 was positive for 204 virulent and 127 antibiotic resistant genes. The experimental challenge demonstrated the high pathogenicity of the retrieved isolate of S. iniae, with a median lethal dosage (LD50) 9.53 × 105 CFU/g. Histopathological examination indicated that the 2022SI08 strain could induce extensive tissue cell degeneration, necrosis, hemorrhage, and inflammation in the skin, gill, fin, spleen, liver, kidney, intestine, eye, and brain. Moreover, the innate immune enzyme activities in serum such as acid phosphatase and alkaline phosphatase were increased significantly at 24 and 48 h post infection (hpi) and then decreased at 168 hpi. The transcriptional profile of immune associated gene in T. fulvidraco following bacterial infection was detected at each point of time, and the results revealed clear transcriptional activation of those genes, which proving their reacting and regulatory role during the response of the host against S. iniae infection. The results revealed that S. iniae was an etiological agent in the mass mortalities of T. fulvidraco and this research will be conducive for increasing our understanding on pathogenesis and host defensive system in S. iniae invasion.

Mechanism of sturgeon intestinal inflammation induced by Yersinia ruckeri and the effect of florfenicol intervention

The mechanism by which Y. ruckeri infection induces enteritis in Chinese sturgeon remains unclear, and the efficacy of drug prevention and control measures is not only poor but also plagued with numerous issues. We conducted transcriptomic and 16 S rRNA sequencing analyses to examine the differences in the intestinal tract of hybrid sturgeon before and after Y. ruckeri infection and florfenicol intervention. Our findings revealed that Y. ruckeri induced the expression of multiple inflammatory factors, including il1β, il6, and various chemokines, as well as casp3, casp8, and multiple tumor necrosis factor family members, resulting in pathological injury to the body. Additionally, at the phylum level, the relative abundance of Firmicutes and Bacteroidota increased, while the abundance of Plesiomonas and Cetobacterium decreased at the genus level, altering the composition of the intestinal flora. Following florfenicol intervention, the expression of multiple apoptosis and inflammation-related genes was down-regulated, promoting tissue repair. However, the flora became further dysregulated, increasing the risk of infection. In conclusion, our analysis of the transcriptome and intestinal microbial composition demonstrated that Y. ruckeri induces intestinal pathological damage by triggering apoptosis and altering the composition of the intestinal microbiota. Florfenicol intervention can repair pathological damage, but it also exacerbates flora imbalance, leading to a higher risk of infection. These findings help elucidate the molecular mechanism of Y. ruckeri-induced enteritis in sturgeon and evaluate the therapeutic effect of drugs on intestinal inflammation in sturgeon.

A Novel Postbiotic Product Based on Weissella cibaria for Enhancing Disease Resistance in Rainbow Trout: Aquaculture Application

Postbiotics are innovative tools in animal husbandry, providing eco-friendly solutions for disease management within the industry. In this study, a new postbiotic product was evaluated for its impact on the health of rainbow trout (Oncorhynchus mykiss). In vivo studies were conducted to assess the safety of the Weissella cibaria strains used in postbiotic production. Additionally, this study evaluated the impact of diet supplementation with 0.50% postbiotics on growth performance during a 30-day feeding trial; the gut microbial communities, immunomodulation, and protection against Yersinia ruckeri infection were evaluated. The strains did not harm the animals during the 20-day observation period. Furthermore, the effect of postbiotics on growth performance was not significant (p < 0.05). The treated group showed a significant increase in acid-lactic bacteria on the 30th day of the feeding trial, with counts of 3.42 ± 0.21 log CFU/mL. Additionally, there was an up-regulation of the pro-inflammatory cytokine IL-1β in head kidney samples after 48 h of feed supplementation, whereas cytokines IL-10, IL-8, INF-γ, and TNF-α were down-regulated. The findings indicate that rainbow trout fed with postbiotics saw an improvement in their survival rate against Y. ruckeri, with a 20.66% survival improvement in the treated group. This study proves that incorporating postbiotics from two strains of W. cibaria previously isolated from rainbow trout into the diet of fish has immunomodulatory effects, enhances intestinal microbial composition, and improves fish resistance against Y. ruckeri.

Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation

Smoltification was found to impact both immune and stress responses of farmed Atlantic salmon (Salmo salar), but little is known about how salinity change affects salmon months after completed smoltification. Here, we examined (1) the effect of salinity change from brackish water to seawater on the stress and immune responses in Atlantic salmon and (2) evaluated if functional diets enriched with microalgae can mitigate stress- and immune-related changes. Groups of Atlantic salmon were fed for 8 weeks with different microalgae-enriched diets in brackish water and were then transferred into seawater. Samples of the head kidney, gill, liver and plasma were taken before seawater transfer (SWT), 20 h after SWT, and 2 weeks after SWT for gene-expression analysis, plasma biochemistry and protein quantification. The salmon showed full osmoregulatory ability upon transfer to seawater reflected by high nkaα1b levels in the gill and tight plasma ion regulation. In the gill, one-third of 44 investigated genes were reduced at either 20 h or 2 weeks in seawater, including genes involved in cytokine signaling (il1b) and antiviral defense (isg15, rsad2, ifit5). In contrast, an acute response after 20 h in SW was apparent in the head kidney reflected by increased plasma stress indicators and induced expression of genes involved in acute-phase response (drtp1), antimicrobial defense (camp) and stress response (hspa5). However, after 2 weeks in seawater, the expression of antiviral genes (isg15, rsad2, znfx1) was reduced in the head kidney. Few genes (camp, clra, c1ql2) in the gill were downregulated by a diet with 8% inclusion of Athrospira platensis. The results of the present study indicate that salinity change months after smoltification evokes molecular stress- and immune responses in Atlantic salmon. However, microalgae-enriched functional diets seem to have only limited potential to mitigate the related changes.

JunD functions as a transcription factor of IL-10 to regulate bacterial infectious inflammation in grass carp (Ctenopharyngodon idella)

IL-10 is a key anti-inflammatory mediator ensuring the protection of a host from excessive inflammation in response to pathogen infections, whose transcription or expression levels are tightly linked to the onset and progression of infectious diseases. An AP-1 family member called CiJunD was shown to be a transcription factor of IL-10 in grass carp (Ctenopharyngodon idella) in the current study. CiJunD protein harbored the conserved Jun and bZIP domains. Mutant experiments demonstrated that CiJunD bound to three specific sites on IL-10 promoter, i.e., 5'-ATTATTCATA-3', 5'-AGATGAGACATCT-3', and 5'-ATTATTCATC-3', mainly relying on the bZIP domain, and initiated IL-10 transcription. Expression data from the grass carp spleen infected by Aeromonas hydrophila and lipopolysaccharide (LPS) challenged spleen leukocytes indicated that the expressions of CiJunD and IL-10 were positively correlated, while the expression of pro-inflammatory cytokines, such as IL-1β, IL-6, IL-8, IFN-γ, and TNF-α, showed an overall downward trend when CiJunD and IL-10 peaked. The ability of CiJunD to down-regulate the production of pro-inflammatory cytokines and up-regulate the expression of IL-10, both with and without LPS stimulation, was confirmed by overexpression experiments. Meanwhile, the subcellular fractionation assay revealed that the nuclear translocation of CiJunD was significantly enhanced after the LPS challenge. Moreover, in vivo administration of grass carp with Oxamflatin, a potent agonist of JunD activity, could promote IL-10 but suppress the expression of pro-inflammatory cytokines. Intriguingly, tissue inflammation lesions and the survival rates of grass carp infected with A. hydrophila were also significantly improved by Oxamflatin administration. This work sheds light on the regulation mechanism by JunD of IL-10 expression and bacterial infectious inflammation for the first time, and it may present a viable method for preventing infectious diseases in fish by regulating IL-10 expression and inflammatory response.

A review of soluble factors and receptors involved in fish skin immunity: The tip of the iceberg

The immune system of fish possesses soluble factors, receptors, pathways and cells very similar to those of the other vertebrates' immune system. Throughout evolutionary history, the exocrine secretions of organisms have accumulated a large reservoir of soluble factors that serve to protect organisms from microbial pathogens that could disrupt mucosal barrier homeostasis. In parallel, a diverse set of recognition molecules have been discovered that alert the organism to the presence of pathogens. The known functions of both the soluble factors and receptors mentioned above encompass critical aspects of host defense, such as pathogen binding and neutralization, opsonization, or modulation of inflammation if present. The molecules and receptors cooperate and are able to initiate the most appropriate immune response in an attempt to eliminate pathogens before host infection can begin. Furthermore, these recognition molecules, working in coordination with soluble defence factors, collaboratively erect a robust and perfectly coordinated defence system with complementary specificity, activity and tissue distribution. This intricate network constitutes an immensely effective defence mechanism for fish. In this context, the present review focuses on some of the main soluble factors and recognition molecules studied in the last decade in the skin mucosa of teleost fish. However, knowledge of these molecules is still very limited in all teleosts. Therefore, further studies are suggested throughout the review that would help to better understand the functions in which the proteins studied are involved.

CsIL-20, a tongue sole interleukin-20, negatively mediates leucocyte activity and antibacterial defense

Interleukin-20 (IL-20), as an essential member of IL-10 family, plays vital roles in mammalian immunological response such as antimicrobial, inflammation, hematopoiesis, and immune diseases. In teleost, the study about immune antimicrobial function of IL-20 is largely scarce. In this article, we revealed the expression profiles and the immunological functions of the IL-20 (CsIL-20) in tongue sole Cynoglossus semilaevis. CsIL-20 is composed of 183 amino acid residues, with seven cysteine residues and a typical IL-10 domain which comprises six α-helices and two β-sheets, and shares 34.4-71.2 % identities with other teleost IL-20. CsIL-20 was constitutively expressed in a variety of tissues and regulated by bacterial invasion, and the recombinant CsIL-20 (rCsIL-20) could bind to different bacteria. In vitro rCsIL-20 could interact with the membrane of peripheral blood leukocytes (PBLs), leading to the attenuation of reactive oxygen species (ROS) production and acid phosphatase activity in PBLs. In line with In vitro results, In vivo rCsIL-20 could obviously suppressed the host immune against bacterial infection. Furthermore, knockdown of CsIL-20 in vivo could markedly enhance the host antibacterial immunity. Collectively, these observations offer new insights into the negative effect of CsIL-20 on antibacterial immunity.

Exploring the impact of nano-Se and nano-clay feed supplements on interleukin genes, immunity and growth rate in European Sea Bass (Dicentrarchus labrax)

This study aimed to investigate the effects of adding Nano-Selenium (NSe) and Nano-clay (NC) as feed supplements on European Sea Bass (Dicentrarchus labrax). Two separate experiments were conducted, one with NC and the other with NSe. Each experiment consisted of four sub-groups with varying concentrations of NC or NSe. The expression levels of five immune-related genes (TNF-α, TNF-β, IL-2, IL-6 and IL-12) were measured using Real-time Quantitative PCR (Rt-PCR) Assay. The results showed an increase in the expression of interleukins (IL-2, IL-6 and IL-12) and pro-inflammatory cytokines (TNF-α and TNF-β) after exposure to NC and NSe. TNF-α gene expression was significantly higher with both 1 mg and 10 mg concentrations of NC and NSe. TNF-β gene expression was highest with the 5 mg concentration of NC. The concentrations of 1 mg and 10 mg for NC, and 1 mg, 5 mg, and 10 mg for NSe, led to the highest (p < 0.05) levels of IL-2 expression compared to the control. Similar trends were observed for IL-6 and IL-12 gene expression. Understanding the impact of these concentrations on gene expression, growth rate, biochemical indices, and antioxidant status can provide valuable insights into the potential applications of NC and NSe supplements on European Sea Bass.

Molecular cloning, characterization and gene expression analysis of twelve interleukins in obscure puffer Takifugu obscurus

Interleukins (ILs) are a subgroup of secreted cytokines, which are molecules involved in the intercellular regulation of the immune system. In this study, 12 IL homologs were cloned and functionally identified from obscure puffer Takifugu obscurus, and they were termed as ToIL-1β, ToIL-1, ToIL-6, ToIL-10, ToIL-11, ToIL-12, ToIL-17, ToIL-18, ToIL-20, ToIL-24, ToIL-27, and ToIL-34. Multiple alignment results showed that except for ToIL-24 and ToIL-27, other deduced ToIL proteins shared typical characteristics and structure with other known fish ILs. Phylogenetic analysis revealed that 12 ToILs were evolutionarily closely related to their counterparts in other selected vertebrates. Tissue distribution assay demonstrated that the mRNA transcripts of most ToIL genes were constitutively expressed in all tissues examined, with relatively high expression in immune tissues. Following Vibrio harveyi and Staphylococcus aureus infection, the expression levels of 12 ToILs in the spleen and liver were significantly upregulated, and their response over time varied. Taken together, these data were discussed accordingly with the ToIL expression and the immune response under the different situations tested. The results suggest that the 12 ToIL genes are involved in the antibacterial immune response in T. obscurus.

Structural and immunohistochemical characterization of pancreas of Molly fish (Poecilia sphenops), with a special reference to its immune role

Recently, teleost species have been considered important model systems for investigating different research areas including immunologic one. The available literature provides poor data about the localization and the structure of pancreas in Molly fish. Moreover, little attention has been paid to the immunologic role of pancreatic tissue of teleost, particularly Molly fish; therefore, this study aimed to highlights the description of pancreatic tissue in Molly fish using light- and electron- microscopy, focusing on the role of pancreatic immune cells and pancreatic acinar cells in immune responses. Microscopic analysis revealed that the pancreas of Molly fish was composed of intrahepatic, disseminated and compact parts. Exocrine pancreatic tissue was diffusely extended within the hepatic tissue forming hepatopancreas. The disseminated pancreas appeared as several irregular nodules of pancreatic tissue localized within the mesenteric adipose tissue. The compact pancreas appeared as an oval shaped body embedded within the mesenteric adipose tissue between the spleen and the intestinal loops. Several telocytes and melanomacrophages were detected within the disseminated pancreatic nodules. Moreover, dendritic cells were found in a close association to the exocrine pancreatic acini. The pancreatic acinar cells showed strong immunoreactivity to APG5, TGF-β, IL-1β, NF-κB, Nrf2, and SOX9 in both hepatopancreas and disseminated pancreas of Molly fish. S100 protein revealed a strong expression in the exocrine pancreatic acinar cells of disseminated pancreas and also in the endocrine cells of the compact pancreas. In conclusion, findings of this study suggest the potential role of the pancreas of the Molly fish in cell proliferation and differentiation, proinflammatory cytokines stimulation, and regulation of both innate and adaptive immunity. RESEARCH HIGHLIGHTS: Telocytes and melanomacrophages were detected in the disseminated pancreatic nodules of the Molly fish. In Molly fish, dendritic cells were found in a close association to the exocrine pancreatic acini. Strong immunoreactivity of the pancreatic acinar cells of the Molly fish to APG5, TGF-β, IL-1β, NF-κB, Nrf2, SOX9, and S100.

Expression of Interleukin-1β protein in vitro,exvivo and in vivo salmonid models

Interleukin-1β (IL-1β) is one of the first cytokines expressed during immune responses, and its levels are affected by many factors, including stress. To date, it has only been possible to measure IL-1β transcript (mRNA) expression quantitatively in fish using qPCR. This is because previous studies that measured IL-1β protein concentrations in these taxa used western blotting, which only provides qualitative data. To advance our knowledge of fish IL-1β biology, and because post-translational processing plays a critical role in the activation of this molecule, we developed a quantitative enzyme-linked immunosorbent assay (ELISA) to accurately measure the concentration of IL-1β protein in several cell cultures and in vivo in salmonids. We compared changes in IL-1β protein levels to the expression of its mRNA. The developed ELISA was quite sensitive and has a detection limit of 12.5 pg/mL. The tools developed, and information generated through this research, will allow for a more accurate and complete understanding of IL-1β's role in the immune response of salmonids.The assay described here has the potential to significantly advance our ability to assess fish health and immune status.

Effect of dietary gamma aminobutyric acid (GABA) modulated the growth performance, immune and antioxidant capacity, digestive enzymes, intestinal histology and gene expression of Nile tilapia (Oreochromisniloticus)

Dietary GABA plays an important role in a variety of physiological functions in animals, but this has been rarely reported in fish. This study investigated the effects of dietary supplementation with GABA on growth, serum antioxidant indicators, digestive enzyme activities, intestinal morphology, and the gene expression of Nile tilapia. Diets containing three different GABA concentrations, 0 (control), 200 mg/kg (GABA200), and 500 mg/kg (GABA500), were fed to Nile tilapia (6.97 ± 0.34 g) for 56 days. The present study found that increasing dietary GABA content could increase the fish growth performance including final body weight, weight gain, specific growth rate, average daily gain, protein efficiency ratio, and feed efficiency compared to the control diet. Interestingly, the feed conversion ratio was improved by dietary GABA supplementation. The antioxidant enzyme activities against ammonia stress of fish fed the GABA diets were significantly higher than the corresponding control group throughout the 96-h ammonia exposure. Moreover, significant increases in digestive enzyme activities including protease, amylase and lipase were found in fish fed the GABA diets. Intestinal morphology analysis revealed increased heights and widths of intestinal villi as well as thickness of the intestinal muscularis in fish fed the GABA diets compared to the control diet. The supplementation of diets with GABA significantly increased the expression level of immune- and growth-related genes. The above results indicate that dietary GABA can modulate the growth, improve their immune response and antioxidant status, gut health and morphology and gene expression of Nile tilapia. Therefore, GABA is a promising feed additive for Nile tilapia aquaculture.

Regulatory roles of cytokines in T and B lymphocytes-mediated immunity in teleost fish

T and B lymphocytes (T and B cells) are immune effector cells that play critical roles in adaptive immunity and defend against external pathogens in most vertebrates, including teleost fish. In mammals, the development and immune response of T and B cells is associated with cytokines including chemokines, interferons, interleukins, lymphokines, and tumor necrosis factors during pathogenic invasion or immunization. Given that teleost fish have evolved a similar adaptive immune system to mammals with T and B cells bearing unique receptors (B-cell receptors (BCRs) and T-cell receptors (TCRs)) and that cytokines in general have been identified, whether the regulatory roles of cytokines in T and B cell-mediated immunity are evolutionarily conserved between mammalians and teleost fish is a fascinating question. Thus, the purpose of this review is to summarize the current knowledge of teleost cytokines and T and B cells as well as the regulatory roles of cytokines on these two types of lymphocytes. This may provide important information on the parallelisms and dissimilarities of the functions of cytokines in bony fish versus higher vertebrates, which may aid in the evaluation and development of adaptive immunity-based vaccines or immunostimulants.

Impact of polystyrene microplastic exposure on gilthead seabream (Sparus aurata Linnaeus, 1758): Differential inflammatory and immune response between anterior and posterior intestine

Plastics are the most widely discharged waste into the aquatic ecosystems, where they break down into microplastics (MPs) and nanoplastics (NPs). MPs are ingested by several marine organisms, including benthic and pelagic fish species, contributing to organ damage and bioaccumulation. This study aimed to assess the effects of MPs ingestion on gut innate immunity and barrier integrity in gilthead seabreams (Sparus aurataLinnaeus, 1758) fed for 21 days with a diet enriched with polystyrene (PS-MPs; 1-20 μm; 0, 25 or 250 mg /kg b.w./die). Physiological fish growth and health status were not impacted by PS-MPs treatments at the end of experimental period. Inflammation and immune alterations were revealed by molecular analyses in both anterior (AI) and posterior intestine (PI) and were confirmed by histological evaluation. PS-MPs triggered TLR-Myd88 signaling pathway with following impairment of cytokines release. Specifically, PS-MPs increased pro-inflammatory cytokines gene expression (i.e., IL-1β, IL-6 and COX-2) and decreased anti-inflammatory ones (i.e., IL-10). Moreover, PS-MPs also induced an increase in other immune-associated genes, such as Lys, CSF1R and ALP. TLR-Myd88 signaling pathway may also lead to the mitogen-activated protein kinases (MAPK) signaling pathway activation. Here, MAPK (i.e., p38 and ERK) were activated by PS-MPs in PI, following the disruption of intestinal epithelial integrity, as evidenced by reduced gene expression of tight junctions (i.e. ZO-1, Cldn15, Occludin, and Tricellulin), integrins (i.e., Itgb6) and mucins (i.e., Muc2-like and Muc13-like). Thus, all the obtained results suggest that the subchronic oral exposure to PS-MPs induces inflammatory and immune alterations as well as an impact on intestinal functional integrity in gilthead seabream, with a more evident effect in PI.

Chromosome-Level Genome Assembly Provides Insights into the Evolution of the Special Morphology and Behaviour of Lepturacanthus savala

Savalani hairtail Lepturacanthus savala is a widely distributed fish along the Indo-Western Pacific coast, and contributes substantially to trichiurid fishery resources worldwide. In this study, the first chromosome-level genome assembly of L. savala was obtained by PacBio SMRT-Seq, Illumina HiSeq, and Hi-C technologies. The final assembled L. savala genome was 790.02 Mb with contig N50 and scaffold N50 values of 19.01 Mb and 32.77 Mb, respectively. The assembled sequences were anchored to 24 chromosomes by using Hi-C data. Combined with RNA sequencing data, 23,625 protein-coding genes were predicted, of which 96.0% were successfully annotated. In total, 67 gene family expansions and 93 gene family contractions were detected in the L. savala genome. Additionally, 1825 positively selected genes were identified. Based on a comparative genomic analysis, we screened a number of candidate genes associated with the specific morphology, behaviour-related immune system, and DNA repair mechanisms in L. savala. Our results preliminarily revealed mechanisms underlying the special morphological and behavioural characteristics of L. savala from a genomic perspective. Furthermore, this study provides valuable reference data for subsequent molecular ecology studies of L. savala and whole-genome analyses of other trichiurid fishes.

The acute inflammatory response of teleost fish

Acute inflammation is crucial to the immune responses of fish. The process protects the host from infection and is central to induction of subsequent tissue repair programs. Activation of proinflammatory signals reshapes the microenvironment within an injury/infection site, initiates leukocyte recruitment, promotes antimicrobial mechanisms and contributes to the resolution of inflammation. Inflammatory cytokines and lipid mediators are primary contributors to these processes. Uncontrolled or persistent induction results in delayed tissue healing. The kinetics by which inducers and regulators of acute inflammation exert their actions is essential for understanding the pathogenesis of fish diseases and identifying potential treatments. Although, a number of these are well-conserved across, others are not, reflecting the unique physiologies and life histories of members of this unique animal group.

Spleen Transcriptome Profiling Reveals Divergent Immune Responses to LPS and Poly (I:C) Challenge in the Yellow Drum (Nibea albiflora)

The yellow drum (Nibea albiflora) is a marine teleost fish with strong disease resistance, yet the understanding of its immune response and key functional genes is fragmented. Here, RNA-Seq was used to investigate the regulation pathways and genes involved in the immune response to infection with lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (poly (I:C)) on the spleen of the yellow drum. There were fewer differentially expressed genes (DEGs) in the LPS-infected treatment group at either 6 or 48 h. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these DEGs were mainly significantly enriched in c5-branching dibasic acid metabolic and complement and coagulation cascades pathways. The yellow drum responded more strongly to poly (I:C) infection, with 185 and 521 DEGs obtained under 6 and 48 h treatments, respectively. These DEGs were significantly enriched in the Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway, Jak-STAT signaling pathway, NOD-like signaling pathway, and cytokine-cytokine receptor interaction. The key functional genes in these pathways played important roles in the immune response and maintenance of immune system homeostasis in the yellow drum. Weighted gene co-expression network analysis (WGCNA) revealed several important hub genes. Although the functions of some genes have not been confirmed, our study still provides significant information for further investigation of the immune system of the yellow drum.

Novel insights into the cytokine network of rainbow trout Oncorhynchus mykiss using cell lines and primary leukocyte populations

Cytokines are small proteins that regulate innate and adaptive immune responses and are released by both immune and non-immune cell types. In the current study, the constitutive and induced gene expression profiles of a suite of proinflammatory and regulatory cytokines was examined comparatively in eight rainbow trout (Oncorhynchus mykiss) cell lines, in order to establish the cytokine repertoires of these different cell types, especially the understudied non-immune cells. They included three epithelial cell lines (RTgut, RTgill, and RTL), one endothelial cell line (RTH), one fibroblast cell line (RTG-2), two stromal cell lines (TSS and TPS-2) and one monocyte/macrophage-like cell line (RTS-11). Three types of primary leukocytes (derived from blood, spleen and head kidney) of trout were also included in the analysis, to allow comparison to the repertoires expressed in T cells, as a major source of cytokines in immune responses. The major findings are: 1) IL-2A, IL-2B, IL-4/13B1, IL-4/13B2, IL-10b, P40B1, P28B, IL-17A/F1b, TNF-α3, TNF-α4, IFNγ1, CCL20L2b and CCL20L3a are expressed mainly in leukocytes but IL-17 N, IL-17D, IL-20 and CCL20L1b2 are not expressed in these cells. Hence future studies in these cell lines will help establish their function in fish; 2) Some of the cytokines were differentially expressed in the cell lines, revealing the potential role of these cell types in aspects of trout mucosal and inflammatory immune responses, 3) Similar cell types grouped together in the cell cluster analysis, including the leukocyte cluster, stromal cell cluster, and epithelial and endothelial cell cluster. Taken together, this investigation of these trout cell lines forms a good database for studying the function of cytokines not expressed in isolated leukocytes or that are preferentially expressed in the cell lines. Furthermore, the cytokine expression analysis undertaken confirmed the phenotypic relationship of these cell types at the molecular level.

Cytokine networks provide sufficient evidence for the differentiation of CD4+ T cells in teleost fish

Cytokines, a class of small molecular proteins with a wide range of biological activities, are secreted mainly by immune cells and function by binding to the corresponding receptors to regulate cell growth, differentiation and effects. CD4⁺ T cells can be defined into different lineages based on the unique set of signature cytokines and transcription factors, including helper T cells (Th1, Th2, Th17) and regulatory T cells (Treg). In teleost, CD4⁺ T cells have been identified in a variety of fish species, thought to play roles as Th cells, and shown to be involved in the immune response following specific antigen stimulation. With the update of sequencing technologies, a variety of cytokines and transcription factors capable of characterizing CD4⁺ T cell subsets also have been described in fish, including hallmark cytokines such as IFN-γ, TNF-α, IL-4, IL-17, IL-10, TGF-β and unique transcription factors such as T-bet, GATA3, RORγt, and Foxp3. Hence, there is increasing evidence that the subpopulation of Th and Treg cells present in mammals may also exist in teleost fish. However, the differentiation, plasticity and precise roles of Th cell subsets in mammals remain controversial. Research on the identification and differentiation of fish Th cells is still in its infancy and requires more significant effort. Here we will review recent research advances in characterizing the differentiation of fish CD4⁺ T cells by cytokines and transcription factors, mainly including the identification of Th and Treg cell hallmark cytokines and transcription factors, the regulatory role of cytokines on Th cell differentiation, and the function of Th and Treg cells in the immune response. The primary purpose of this review is to deepen our understanding of cytokine networks in characterizing the differentiation of CD4⁺ T cells in teleost.

Interleukin-2 family cytokines: An overview of genes, expression, signaling and functional roles in teleost

The interleukin-2 (IL-2) family cytokines include IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21, which share γ chain (γc) subunit in receptors. The IL-2 family cytokines have unique biological effects that regulate differentiation, survival and activation of multiple lymphocyte lineages. Deficiency of IL-2 family signaling pathway in mammals prevents CD4⁺ T cells from developing effector functions and CD8⁺ T cells from developing immunological memory. In the present review, we addressed available information from teleost IL-2 family cytokines and discussed implications in teleost immunity. Also, we described and discussed their expression profiles, receptors, signaling transductions and functions. In teleost, IL-2 family has 5 members (IL-2, IL-4/13, IL-7, IL-15, IL-21) without IL-9, and their receptors share a common γc subunit and include other 6 subunits (IL-2Rβ1/2, IL-4Rα1/2, IL-13Rα1/2, IL-7Rα, IL-15Rα, and IL-21Rα1/2). Some paralogues have changes in domain structure and show differential expression, modulation, functions. IL-2 family cytokines constitutively express in many immune associated tissues and are largely induced after pathogenic microbial stimulation. In general, there are relatively conserved functions in the IL-2 family throughout vertebrates, and many of the key IL-2 family members are important in lymphocyte proliferation and differentiation, development, inflammation from fishes to mammals. This review will give an update on the effective information of teleost IL-2 family cytokines. Thus, it will provide a source of reference for other researchers/readers and inspire further interest.

From a cell model to a fish trial: Immunomodulatory effects of heat-killed Lactiplantibacillus plantarum as a functional ingredient in aquafeeds for salmonids

Paraprobiotics (dead/inactivated probiotics) are promising candidates in functional feeds to promote growth performance, modulate intestinal microbiota and enhance immune response of fish. During industrial production, fish are exposed to several stressful conditions such as handling, sub-optimal nutrition and diseases that can lead to reduced growth, increased mortalities and large economical losses. Such problems can be mitigated by use of functional feeds, leading to more-sustainable aquaculture and improved animal welfare. Lactiplantibacillus plantarum strain L-137 is a common bacterium found in fermented Southeast Asian dish made from fish and rice. The benefits of its heat-killed form (HK L-137) related to growth performance and immunomodulation have been studied in farmed fish such as Nile Tilapia (Oreochromis niloticus), striped catfish (Pangasianodon hypophthalmus) and bighead catfish (Clarias macrocephalus). To study if such benefits can also be observed in salmonids, we worked both at in vitro level using an intestinal epithelium cell line from rainbow trout (Oncorhynchus mykiss; RTgutGC) stimulated with HK L-137 (Feed LP20™) and at in vivo level with pre-smolt Atlantic salmon (Salmo salar) fed HK L-137 at different inclusion levels (20, 100 and 500 mg of Feed LP20™ kg-1 feed). In RTgutGC, the results showed that the barrier function of the cell monolayer was strengthened along with an increased production of IL-1β and a decreased production of Anxa1, indicating a modulation of the immune response. Interestingly, a similar trend was detected at the in vivo level in distal intestine from fish fed the highest inclusion level of HK L-137. Here, a lower production of Anxa1 was also detected (after a 61-day feeding period) in addition to an increase of total plasma IgM in the same group. Furthermore, the RNA-seq analysis showed that HK L-137 was able to modulate the gene expression of pathways related to molecular function, biological process and cellular component in distal intestine, without compromising fish performance and gut microbiota. Taken together, our study has shown that HK L-137 can modulate physiological response of Atlantic salmon, making fish more robust against stressful conditions during production.

Comparative study of the effects of Montanide™ ISA 763A VG and ISA 763B VG adjuvants on the immune response against Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae is regarded as a major bacterial pathogen of farmed fish, with outbreaks in Nile tilapia causing significant losses. Vaccination is considered the most suitable method for disease control in aquaculture, with the potential to prevent such outbreaks if highly efficacious vaccines are available for use. Several vaccines have been produced to protect against S. agalactiae infection in tilapia, including inactivated vaccines, live attenuated vaccines, and subunit vaccines, with variable levels of protection seen. Two commercial adjuvants, Montanide™ ISA 763A VG and ISA 763B VG, have been developed recently and designed to improve the safety and efficacy of oil-based emulsions delivered by intraperitoneal injection. In particular, their mode of action may help identify and stimulate particular immunological pathways linked to the intended protective response, which is an important tool for future vaccine development. Therefore, this study aimed to characterize the potential of two adjuvanted-bacterial vaccines against S. agalactiae (SAIV) comparatively, to determine their usefulness for improving protection and to analyse the immune mechanisms involved. Nile tilapia were divided into four groups: 1) fish injected with PBS as a control, 2) fish injected with the SAIV alone, 3) fish injected with the SAIV + Montanide™ ISA 763A VG, and 4) fish injected with the SAIV + Montanide™ ISA 763B VG. Following immunization selected innate immune parameters were analysed, including serum lysozyme, myeloperoxidase, and bactericidal activity, with significantly increased levels seen after immunization. Cytokines associated with innate and adaptive immunity were also studied, with expression levels of several genes showing significant up-regulation, indicating good induction of cell-mediated immune responses. Additionally, the specific IgM antibody response against S. agalactiae was determined and found to be significantly induced post-vaccination, with higher levels seen in the presence of the adjuvants. In comparison to the protection seen with the unadjuvanted vaccine (61.29% RPS), both Montanide™ ISA 763A VG and Montanide™ ISA 763B VG improved the RPS, to 77.42% and 74.19% respectively. In conclusion, Montanide™ ISA 763A VG and Montanide™ ISA 763B VG have shown potential for use as adjuvants for fish vaccines against streptococcosis, as evidenced by the enhanced immunoprotection seen when given in combination with the SAIV vaccine employed in this study.

Nigericin treatment activates endoplasmic reticulum apoptosis pathway in goldfish kidney leukocytes

Nigericin has been reported to induce apoptosis and pyroptosis in mammalian models. However, the effects and mechanism underlying the immune responses of teleost HKLs induced by nigericin remain enigmatic. To decipher the mechanism after nigericin treatment, the transcriptomic profile of goldfish HKLs was analyzed. The results demonstrated that a total of 465 differently expressed genes (DEGs) with 275 up-regulated and 190 down-regulated genes were identified between the control and nigericin treated groups. Among them, the top 20 DEG KEGG enrichment pathways were observed including apoptosis pathways. In addition, the expression level of selected genes (ADP4, ADP5, IRE1, MARCC, ALR1, DDX58) by quantitative real-time PCR showed a significant change after treatment with nigericin, which was generally identical to the expression patterns of the transcriptomic data. Furthermore, the treatment could induce cell death of HKLs, which was confirmed by LDH release and annexin V-FITC/PI assays. Taken together, our results support the idea that nigericin treatment might activate the IRE1-JNK apoptosis pathway in goldfish HKLs, which will provide insights into the mechanisms underlying HKLs immunity towards apoptosis or pyroptosis regulation in teleosts.

Effects of Cryptocaryon irritans infection on the histopathology, oxidative stress, immune response, and intestinal microbiota in the orange-spotted grouper Epinephelus coioides

Cryptocaryon irritans is a parasitic ciliate of marine fish, causing serious mortality and economic loss of grouper. In this study, the orange-spotted grouper (Epinephelus coioides) were separately exposed to C. irritans infection for 72 h at a dose of 5000 or 10000 active theronts per fish, and we evaluated the changes in histopathology, oxidative stress, immune response, and intestinal microbiota composition. The results showed that C. irritans infection caused pathological alteration on the skin, gills, and liver of E. coioides. Oxidative stress responses occurred in the liver and gills, reflected in the corresponding antioxidant enzyme and gene indexes. The mRNA expression levels of inflammation-related genes (IL-1β, IL-6, and IL-8) and the mediators of apoptosis (casp3, casp9, and cytc) were increased in the liver and gills of the fish. C. irritans infection also affected the diversity and composition of intestinal microbiota. Specifically, the relative abundance of Firmicutes was increased, whereas that of Proteobacteria was decreased. Several potentially beneficial bacteria (Pandoraea, Clostridium sensu stricto 1, Christensenellaceae R-7 group, and Weissella) were decreased, whereas pathogenic bacteria (Streptococcus and Acinetobacter) were increased. In conclusion, this study reveals that C. irritans infection caused histopathology, immune disorders, and intestinal microbial community variation in E. coioides.

Evolutional perspective and functional characteristics of interleukin-17 in teleosts

Interleukin (IL)-17 is a proinflammatory cytokine and plays essential roles in adaptive and innate immune responses against bacterial and fungal infections. Especially in mammalian mucosal tissues, it is well known that innate immune responses via IL-17A and IL-17F, such as the production of antimicrobial peptides, are very important for microbiota control. In contrast, interesting insights into the functions of IL-17 have recently been reported in several teleost species, although little research has been conducted on teleost IL-17. In the present review, we focused on current insights on teleost IL-17 and speculated on the different or consensus parts of teleost IL-17 signaling compared to that of mammals. This review focuses on the role of teleost IL-17 in intestinal immunity. We expect that this review will encourage a further understanding of the roles and importance of IL-17 signaling in teleosts.