Phylogeny of cytokines: molecular cloning and expression analysis of sea bass Dicentrarchus labrax interleukin-1beta

Hepatic transcriptome profiling of largemouth bass (Micropterus salmoides Lacépède) injected with Flavobacterium covae or lipopolysaccharide

Flavobacterium covae (columnaris) is the most detrimental bacterial disease affecting the largemouth bass (Micropterus salmoides Lacépède) aquaculture industry. In the current study, fish received an intraperitoneal injection of either 1× PBS (100 μL), LPS in PBS (100 μL, 10 μg/mL), or F. covae (100 μL, 2.85 × 1011 CFU/mL) to simulate immunological challenges. After 24 h post-injection, liver tissue from the control and treated groups were then collected for transcriptome analysis. Results of the Gene Ontology (GO) and KEGG pathway analyses for the F. covae and LPS-injected groups found differentially expressed genes (DEGs) enriched primarily in toll-like receptors (TLRs), cytokine-cytokine receptors, complement and coagulation cascades, and the PPAR signalling pathways. This suggests that the liver immune system is enhanced by these five combined pathways. Additionally, the DEGs TLR5, MYD88, and IL-1 were significantly upregulated in F. covae and LPS-injected fish compared to the controls, whereas IL-8 was downregulated. The upregulation of TLR5 was unexpected as F. covae lacks flagellin, the protein that binds to TLR5. Additionally, it is unknown whether the TLR5 is upregulated by LPS. Further research into the upregulation of TLR5 is warranted. These results provide insight into immune responses and associated pathways contributing to the immune system in the liver during columnaris infection and induced response to LPS in largemouth bass.

Sexual dimorphism in NLR transcripts and its downstream signaling protein IL-1ꞵ in teleost Channa punctata (Bloch, 1793)

Nucleotide-binding oligomerization domain-like receptors (NOD-like receptors or NLRs) are a family of intracellular pattern recognition receptors (PRRs) that initiates as well as regulate inflammatory responses. NLRs are characterized by a centrally located nucleotide binding domain and a leucine rich repeat domain at the C-terminal responsible for the recognition of intracellular microbe-associated molecular patterns (MAMPs) and danger-associated molecular patterns (DAMPs). In the present study in adult spotted snakehead we have investigated the sex-dependent tissue distribution of NLRs known to be associated with inflammation in teleost namely NOD1, NOD2, NLRC3, NLRC5, and NLRX1. Further, the sexual dimorphism in the expression of NLR transcript as well as the pro-inflammatory protein IL-1β was explored in fish under normal conditions, and in fish exposed to bacterial lipopolysaccharide (LPS). The NLRs show ubiquitous and constitutive expression in all the tissues. Moreover, a prominent disparity between males and females was observed in the basal expression of these genes in various tissues. The sexual dimorphism in NLR expression was also prominent when fish were exposed to LPS. Similarly, IL-1β exhibited sexual dimorphism in both normal as well as LPS-exposed fish.

Exploring bacterial community composition and immune gene expression of European eel larvae (Anguilla anguilla) in relation to first-feeding diets

European eel (Anguilla anguilla) is a commercially important species for fisheries and aquaculture in Europe and the attempt to close the lifecycle in captivity is still at pioneering stage. The first feeding stage of this species is characterized by a critical period between 20 to 24 days post hatch (dph), which is associated with mortalities, indicating the point of no return. We hypothesized that this critical period might also be associated with larvae-bacterial interactions and the larval immune status. To test this, bacterial community composition and expression of immune and stress-related genes of hatchery-produced larvae were explored from the end of endogenous feeding (9 dph) until 28 dph, in response to three experimental first-feeding diets (Diet 1, Diet 2 and Diet 3). Changes in the water bacterial community composition were also followed. Results revealed that the larval stress/repair mechanism was activated during this critical period, marked by an upregulated expression of the hsp90 gene, independent of the diet fed. At the same time, a shift towards a potentially detrimental larval bacterial community was observed in all dietary groups. Here, a significant reduction in evenness of the larval bacterial community was observed, and several amplicon sequence variants belonging to potentially harmful bacterial genera were more abundant. This indicates that detrimental larvae-bacteria interactions were likely involved in the mortality observed. Beyond the critical period, the highest survival was registered for larvae fed Diet 3. Interestingly, genes encoding for pathogen recognition receptor TLR18 and complement component C1QC were upregulated in this group, potentially indicating a higher immunocompetency that facilitated a more successful handling of the harmful bacteria that dominated the bacterial community of larvae on 22 dph, ultimately leading to better survival, compared to the other two groups.

Aeromonas hydrophila inhibits autophagy triggering cytosolic translocation of mtDNA which activates the pro-apoptotic caspase-1/IL-1β-nitric oxide axis in headkidney macrophages

The molecular mechanisms underlying Aeromonas hydrophila-pathogenesis are not well understood. Using head kidney macrophages (HKM) of Clarias gariepinus, we previously reported the role of ER-stress in A. hydrophila-induced pathogenesis. Here, we report that PI3K/PLC-induced cytosolic-Ca²⁺ imbalance induces the expression of pro-apoptotic ER-stress marker, CHOP in A. hydrophila-infected HKM. CHOP promotes HKM apoptosis by inhibiting AKT activation and enhancing JNK signaling. Elevated mitochondrial ROS (mtROS) was recorded which declined significantly by ameliorating ER-stress and in the presence of ER-Ca²⁺ release modulators (2-APB and dantrolene) and mitochondrial-Ca²⁺ uptake inhibitor, Ru360, together suggesting the role of ER-mitochondrial Ca²⁺ dynamics in mtROS generation. Inhibiting mtROS production reduced HKM death implicating the pro-apoptotic role of mtROS in A. hydrophila-pathogenesis. The expression of autophagic proteins (LC3B, beclin-1, and atg 5) was suppressed in the infected HKM. Our results with autophagy-inducer rapamycin demonstrated that impaired autophagy favored the cytosolic accumulation of mitochondrial DNA (mtDNA) and the process depended on mtROS levels. Enhanced caspase-1 activity and IL-1β production was detected and transfection studies coupled with pharmacological inhibitors implicated mtROS/mtDNA axis to be crucial for activating the caspase-1/IL-1β cascade in infected HKM. RNAi studies further suggested the involvement of IL-1β in generating pro-apoptotic NO in A. hydrophila-infected HKM. Our study suggests a novel role of ER-mitochondria cross-talk in regulating A. hydrophila pathogenesis. Based on our observations, we conclude that A. hydrophila induces ER-stress and inhibits mitophagy resulting in mitochondrial dysfunction which leads to mtROS production and translocation of mtDNA into cytosol triggering the activation of caspase-1/IL-1β-mediated NO production, culminating in HKM apoptosis.

Fish Meal Replacement by Mixed Plant Protein in the Diets for Juvenile Yellow Catfish Pelteobagrus fulvidraco: Effects on Growth Performance and Health Status

Increasing dietary replacement levels of fish meal by alternative plant proteins are of value for aquaculture. Here, a 10-week feeding experiment was undertaken to explore the effects of fish meal replacement by mixed plant protein (at a 2 : 3 ratio of cottonseed meal to rapeseed meal) on growth performance, oxidative and inflammatory responses, and mTOR pathway of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (2.38 ± 0.1 g, mean ± SEM) were randomly divided into 15 indoors fiberglass tanks, 30 fish each tank, and fed five isonitrogenous (44% crude protein) and isolipidic (9% crude fat) diets with fish meal replaced by mixed plant protein at 0% (the control), 10% (RM10), 20% (RM20), 30% (RM30), and 40% (RM40), respectively. Among five groups, fish fed the control, and RM10 diets tended to have higher growth performance, higher protein content, and lower lipid content in livers. Dietary mixed plant protein substitute increased hepatic free gossypol content and damaged liver histology and reduced the serum total essential amino acids, total nonessential amino acids, and total amino acid contents. Yellow catfish fed the control, and RM10 diets tended to have higher antioxidant capacity. Dietary mixed plant protein replacement tended to promote proinflammatory responses and inhibited mTOR pathway. Based on the second regression analysis of SGR against mixed plant protein substitutes, the optimal replacement level of fish meal by mixed plant protein was 8.7%.

Red sea bream interleukin (IL)-1β and IL-8 expression, subcellular localization, and antiviral activity against red sea bream iridovirus (RSIV)

Interleukin-1 beta (IL-1β) is transcribed by monocytes, macrophages, and dendritic cells in response to activation of toll-like receptors (TLRs) by pathogen-associated molecular patterns (PAMPs) or cytokine signalling and causes a rapid inflammatory response to infection. IL-8, also known as chemokine C-X-C motif ligand (CXCL)-8, is regulated by IL-1β and affects the chemotaxis of macrophages and neutrophils upon pathogen infection. In healthy red sea bream, rsbIL-1β is most highly distributed in the liver, and rsbIL-8 is most highly distributed in the head kidney. In response to RSIV infection, rsbIL-1β and rsbIL-8 mRNA are significantly upregulated in the kidney and spleen. This may be because the primary infection targets of RSIV are the kidney and spleen. In the gills, both genes were significantly upregulated at 7 days after RSIV infection and may be accompanied by a cytokine storm. In the liver, both genes were significantly downregulated at most observation points, which may be because the immune cells such as macrophages and dendritic cells expressing rsbIL-1β or rsbIL-8 migrated to other tissues because the degree of RSIV infection was relatively low. Using a GFP fusion protein, it was confirmed that rsbIL-1β and rsbIL-8 were localized to the cytoplasm of Pagrus major fin (PMF) cells. RsbIL-1β overexpression induced the expression of interferon gamma (IFN-γ), myxovirus-resistance protein (Mx) 1, IL-8, IL-10, TNF-α, and MyD88, while rsbIL-8 overexpression induced the expression of IFN-γ, Mx1, rsbIL-1β and TNF-α. In addition, overexpression of both genes significantly reduced the genome copies of RSIV and significantly reduced the viral titers. Therefore, rsbIL-1β and rsbIL-8 in red sea bream play an antiviral role against RSIV through their normal signalling.

Stress responses of the intestinal digestion, antioxidant status, microbiota and non-specific immunity in Songpu mirror carp (Cyprinus carpio L.) under starvation

Songpu mirror carp, Cyprinus carpio L., is a new variety of common carp that has become an economically important freshwater fish in China. However, it remains unknown how its metabolism is regulated under starvation. Here, we investigated how intestinal digestion, antioxidant status, microbiota and immune activities were affected under starvation stress. The feeding regimes were designed as follows: ST0 comprised fish allowed to feed continuously; ST1 comprised fish starved for 1 week; ST2 comprised fish starved for 2 weeks; ST3 comprised fish starved for 3 weeks; ST4 comprised fish starved for 4 weeks. Our results showed a significant decrease in the level of intestinal amylase, lipase, and protease activities in the group ST4 (P < 0.05). Compared with the control group, intestinal antioxidant enzyme activities were significantly increased during short-term starvation. The gene expression levels of interleukin 1β (IL-1β), interleukin 8 (IL-8) and tumor necrosis factor-alpha (TNF-α) were elevated in the groups ST3 and ST4. We also detected the reduction in the expression levels of interleukin 10 (IL-10) and transforming growth factor β (TGF-β2) compared with those of the group ST0. Notably, the gut microbial composition was dominated by Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Firmicutes. The relative abundance of the dominant microbial phyla changed significantly under starvation stress. Taken together, our results suggest that starvation can induce the change of intestinal digestion, non-specific immunity and microbiota in Songpu mirror carp, and provide new insights into its habitat selection and adaptation to environmental changes.

microRNA-148 is involved in NF-κB signaling pathway regulation after LPS stimulation by targeting IL-1β in miiuy croaker

The inflammatory response is a protective process to clear detrimental stimuli, constitutes the defense against infectious pathogens. Clearing pathogen infection requires appropriate immune and inflammatory response, but excessive inflammatory response can lead to uncontrolled inflammation, autoimmune disease, or pathogen transmission. Accumulating evidences show that miRNAs are important and multifunctional regulators of innate immunity and inflammation. However, in the inflammatory response of lower vertebrates, the miRNAs regulatory networks are largely unknown. In this study, a combination of bioinformatics and experimental techniques were used to investigate the functions of miR-148. IL-1β is a hypothetical target gene of miR-148 predicted by bioinformatics. In addition, dual-luciferase reporter gene experiment was used to verify the targeting effect of miR-148 on IL-1β-3'UTR. miR-148 inhibits IL-1β expression in a dose-dependent manner at protein and mRNA levels. It is important that miR-148 participates in regulation of LPS-induced the NF-κB signaling pathway by inhibiting IL-1β. These results will improve our understanding of the regulation of miRNAs in fish on the immune response.

microRNA-132 as a negative regulator in NF-κB signaling pathway via targeting IL-1β in miiuy croaker

The innate immune system is the first line of defense against the invasion of pathogens. It can make a rapid immune response to the invading pathogenic microorganisms, thereby eliminating the invading pathogens and protecting the body from harm. microRNAs are a family of small non-coding ribonucleic acid molecules, which are important and multifunctional regulator of immune response. In this study, we studied the role of miR-132 as a key regulatory factor of IL-1β-mediated inflammation. The seed region of miR-132 can regulate gene expression by binding to the 3'UTR of IL-1β, and inhibit the expression of IL-1β at the post-transcriptional level. More importantly, miR-132 inhibits LPS-induced NF-κB signaling pathway by targeting IL-1β, thereby preventing excessive inflammatory response from causing autoimmune diseases. These results will help to better understand the complex regulatory mechanisms of teleost fishes.

Extreme winter cold-induced osmoregulatory, metabolic, and physiological responses in European seabass (Dicentrarchus labrax) acclimatized at different salinities

Despite climate-change challenges, for most aquaculture species, physiological responses to different salinities during ambient extreme cold events remain unknown. Here, European seabass acclimatized at 3, 6, 12, and 30 PSU were subjected to 20 days of an ambient extreme winter cold event (8 °C), and monitored for growth and physiological performance. Growth performance decreased significantly (p < 0.05) in fish exposed at 3 and 30 PSU compared to 6 and 12 PSU. During cold stress exposure, serum Na+, Cl-, and K+ concentrations were significantly (p < 0.05) increased in fish exposed at 30 PSU. Serum cortisol, glucose, and blood urea nitrogen (BUN) were increased significantly (p < 0.05) in fish exposed at 3 and 30 PSU. In contrast, opposite trends were observed for serum protein, lactate, and triglycerides content during cold exposure. Transaminase activities [glutamic-pyruvate transaminase (GPT), glutamic oxaloacetic transaminase (GOT), lactic acid dehydrogenase (LDH), gamma-glutamyl-transaminase (γGGT)] were significantly higher in fish exposed at 3 and 30 PSU on days 10 and 20. The abundance of heat shock protein 70 (HSP70), tumor necrosis factor-α (TNF-α), cystic fibrosis transmembrane conductance (CFTR) were significantly (p < 0.05) increased in fish exposed at 3 and 30 PSU during cold shock exposure. In contrast, insulin-like growth factor 1 (Igf1) expression was significantly lower in fish exposed at 3 and 30 PSU. Whereas, on day 20, Na+/K+ ATPase α1 and Na+/K+/Cl- cotransporter-1 (NKCC1) were significantly upregulated in fish exposed at 30 PSU, followed by 12, 6, and 3 PSU. Results demonstrated that ambient extreme winter cold events induce metabolic and physiological stress responses and provide a conceivable mechanism by which growth and physiological fitness are limited at cold thermal events. However, during ambient extreme cold (8 °C) exposure, European seabass exhibited better physiological fitness at 12 and 6 PSU water, providing possible insight into future aquaculture management options.

Black soldier fly (Hermetia illucens) larvae meal in diets of European seabass: Effects on antioxidative capacity, non-specific immunity, transcriptomic responses, and resistance to the challenge with Vibrio alginolyticus

Black soldier fly larvae meal (BSFLM) has been successfully demonstrated as a promising fish meal (FM) replacer in diets of several fish species including European seabass (Dicentrarchus labrax). However, its impacts on antioxidant capacity, and immune responses of treated fish are still poorly understood. A 60-day feeding trial was carried out to evaluate the effects of partial substitution of FM with different levels of dry BSFLM on the antioxidative status, non-specific immunity, transcriptomic responses, and resistance of European seabass to the challenge with Vibrio alginolyticus. Four isoproteic (45%) and isolipidic diets were formulated by replacing 0.0%, 25%, 35%, and 50% of the dietary FM. Each diet was randomly assigned to four fish groups (in triplicates) (initial mean body weight, 12.1 ± 0.21 g) (20 fish per aquarium) (n = 240). Fish were fed three times daily to the apparent satiation. At the end of the feeding trial, serum antioxidant biomarkers such as malondialdehyde levels, and catalase, superoxide dismutase, and glutathione peroxidase enzyme activities were significantly increased in all BSFLM groups in a dose-dependent manner compared to the control group (P < 0.05). The non-specific immune indices, including phagocytic activity, phagocytic index, serum lysozyme and respiratory burst activities were significantly elevated in BSFLM groups compared to those in the control group (P < 0.05). Significant upregulation of the mRNA expression levels of hepatic heat shock protein 70, interleukin-1beta and interleukin-10 genes were observed in all BSFLM groups compared to the control group (P < 0.05). Additionally, after the challenge with V. alginolyticus, the relative percent of survival was significantly elevated in fish groups fed on diets containing graded levels of BSFLM over the control group (P < 0.05). Conclusively, the present study suggests the potential efficacy of partial replacement of dietary FM protein for up to 50% by BSFLM without negative effects on fish health with possible potentiation of the antioxidative status, and the immune responses of the European seabass.

Molecular characterization and gene expression analysis of the pro-inflammatory cytokines IL-1β and IL-8 in the South American fish Piaractus mesopotamicus challenged with Aeromonas dhakensis

In the present study, the complete characterization of cDNA and genomic sequences of IL-1β and IL-8, as well as the expression profile of these genes in the South American fish pacu (Piaractus mesopotamicus) is provided. The full-length pmIL-1β cDNA was composed of 1208 nucleotides that would produce a precursor peptide with 273 amino acid residues. A putative caspase-1 cleavage site, similar to what is found in mammalian IL-1β, was identified producing a mature peptide with a theoretical molecular weight of 17.21 kDa. The pmIL-8 cDNA sequence consisted of 1019 nucleotides which encoded a 95-amino acid protein with a theoretical molecular weight of 10.43 kDa that showed all typical CXC chemokine features, including a 20-residue signal peptide and four conserved cysteine residues. Constitutive mRNA expression was detected for both genes in the liver, head kidney, gill, intestine, skin and spleen. After a bacterial challenge, up-regulation was detected for both pmIL-1β and pmIL-8 in the spleen and head kidney at 12 h post-infection. At 24 h post-infection there was a decrease in the expression of both genes, with pmIL-8 showing a significant down-regulation in the liver and head kidney when compared to the control groups.

Identification of an IgD/IgT chimera in the European sea bass (Dicentrarchus labrax L.)

Three classes of immunoglobulins have been identified in Teleosts: IgM, IgT/Z and IgD. They are fundamental for fish immune responses and, therefore, their functional activities are heavily investigated. In this paper, we describe the identification of a new IgD/IgT chimera in sea bass (Dicentrarchus labrax) from a gills transcriptome. This transcript joined the first six constant domains of the IgD chain with the two terminal constant domains of IgT, generating a long in-frame coding sequence with a junction between the canonical δ6 exon splicing donor site and the τ3 exon splicing acceptor site. Studies performed on genomic DNA confirmed the presence of the sequence and identifies and intronic region of 656 bp within this joining region. The basal expression of the IgD/IgT chimera was investigated both in silico and in vivo: high level of expression was found in gills, gut and head kidney. Moreover, IgD/IgT transcripts were up-regulated after in vitro stimulation of sea bass HK leukocytes with LPS. The IgD/IgT chimera was found also in two congener species, Morone saxatilis and Morone chrysops. It is not possible to have a precise idea on the evolutionary scenario that lead to the appearance of this sequence due to the lack of genomic information, but we could speculate that an ancestral duplication of the entire IgH locus was followed by the chimerization of Cδ/Cτ in one of the two loci. Finally, the IgD/IgT high basal expression in tissues and organs fundamental for sea bass immune response and its modulation after LPS stimulation provide a very preliminary indication that this unusual Ig variant could have a functional activity.

Effects of extreme ambient temperature in European seabass, Dicentrarchus labrax acclimated at different salinities: Growth performance, metabolic and molecular stress responses

Extreme weather events are becoming more intense and frequent as a result of climate change. The modulation of hemato-physiological potential as a compensatory response to extreme warm events combined with different salinities is poorly understood. This study aimed to assess the hemato-physiological and molecular response of European seabass, Dicentrarchus labrax exposed to extreme warm temperature (33 °C) after prior acclimatization at 32 psu, 12 psu, 6 psu, and 2 psu water. Fish were acclimated to 32 psu, 12 psu, 6 psu, and 2 psu followed by 10 days extreme warm (33 °C) exposure. Along with growth performance and survival, hemato-physiological response and molecular response of fish were recorded. Fish held at 32 psu and 2 psu exhibited significantly lower growth performance and survival than those at 12 psu and 6 psu (p < 0.05). Red blood cells (RBC), hematocrit, and hemoglobin content were significantly decreased, while white blood cells (WBC), erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) were found to increase significantly in 32 psu and 2 psu fish (p < 0.05). Plasma lactate was found to increase significantly in 32 psu fish on day 10 (p < 0.05). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and TNF-α expression increased significantly in 32 psu and 2 psu fish (p < 0.05). Most of the repeated measured parameters indicated limited acclimation capacity during the extreme warm exposure at all four salinity groups. However, overall results indicate that European seabass acclimatized at 12 psu and 6 psu salinities, can cope better during extreme warm exposure (33 °C).

Effect of Yucca schidigera extract on the growth performance, intestinal antioxidant status, immune response, and tight junctions of mirror carp (Cyprinus carpio)

The current study was designed to evaluate the effect of Yucca schidigera extract (YSE) on the growth performance, intestinal antioxidant status, immune response, and tight junctions of mirror carp (Cyprinus carpio). A total of 450 mirror carp (45.21 ± 0.43 g) were fed diets supplemented with 0, 200, or 400 mg/kg YSE for 8 weeks. Compared with the control (0 mg/kg), the final body weight and weight gain rate were significantly higher in the 400 mg/kg YSE group (P < 0.05), and the serum ammonia concentration was significantly lower in both YSE groups (P < 0.05). Additionally, the total antioxidant capacity was significantly higher in the 400 mg/kg YSE group (P < 0.05), and the malondialdehyde content was significantly lower in both YSE groups (P < 0.05). Complement 3 and 4 contents were significantly higher in the 400 mg/kg YSE group (P < 0.05), and lysozyme was significantly higher in both YSE groups compared to the control group (P < 0.05). The relative mRNA levels of copper zinc superoxide dismutase, catalase, glutathione peroxidase1a, and nuclear factor erythroid 2-related factor 2 as well as transforming growth factor β were significantly higher in both YSE supplemented groups compared to the control (P < 0.05), whereas the relative mRNA level of Kelch-like ECH-associated protein 1 was significantly lower in both YSE supplemented groups (P < 0.05). The relative mRNA levels of interleukin 1β and interleukin 6 were significantly lower in the 400 mg/kg YSE supplemented group compared to the control (P < 0.05). Additionally, both YSE levels decreased the relative mRNA expression of tumour necrosis factor-α (P < 0.05). The relative mRNA levels of ZO-1 and claudin 11 were significantly higher in both YSE supplemented groups (P < 0.05), and the relative mRNA level of occludin was significantly higher in the 200 mg/kg YSE group than the control and 400 mg/kg YSE groups (P < 0.05). In conclusion, dietary supplementation with 400 mg/kg YSE improved the growth, intestinal antioxidant status, immune response, and tight junctions of mirror carp.

Bacteria-induced IL-1β and its receptors in snakehead (Channa argus): Evidence for their involvement in antibacterial innate immunity

As a central pro-inflammatory cytokine, interleukin-1β (IL-1β) plays critical roles in the inflammatory response, pathogen infection, and immunological challenges in mammals. Although fish IL-1β has been confirmed to participate in inflammatory response to pathogen infection, few studies have been performed to characterize the antibacterial and bactericidal functions of fish IL-1β. In this study, snakehead (Channa argus) IL-1β (shIL-1β) and its receptors, shIL-1R1 and shIL-1R2, were cloned and functionally characterized. ShIL-1β contained the IL-1 family signature domain, and a potential cutting site at Asp⁹⁶ that presented in all vertebrate IL-1β sequences. ShIL-1R1 had three extracellular IG-like domains and one intracellular signal TIR domain, while shIL-1R2 had three extracellular IG-like domain but lacked the intracellular signal TIR domain. ShIL-1β, shIL-1R1, and shIL-1R2 were constitutively expressed in all tested tissues, and their expressions could be induced by Aeromonas schubertii and Nocardia seriolae in the head kidney and spleen in vivo, and by LTA, LPS, and Poly (I:C) in head kidney leukocytes (HKLs) in vitro. Moreover, recombinant shIL-1β upregulated the expression of endogenous shIL-1β, shIL-R1, and shIL-R2 in snakehead HKLs, and enhanced intracellular bactericidal activity. Taken together, this study found that, like IL-1β and its receptors in mammals, shIL-1β and its receptors play crucial roles in antibacterial innate immunity. This provides new insight into the evolution of IL-1β function in vertebrates.

Molecular characterization and complement activating functional analysis of a new collectin(TfCol-11) from Trachidermus fasciatus

The complement system is a crucial component of the innate immune system that links innate and adaptive immunity. CL-11, a protein similar to Mannose-binding lectin (MBL), plays significant role in the innate immune system in mammals and fish, serving as an initiator of the lectin pathway of complement activation. In this study, a CL-11 homolog (TfCol-11) was identified in roughskin sculpin (Trachidermus fasciatus), and its expression and role in immune responses were characterized. The open reading frame of TfCol-11 is 795 bp long, encoding a 264 amino acid polypeptide. The deduced amino acid sequence of this protein is highly homologous to sequences in other teleosts, and is similar to vertebrate CL-11, containing a canonical collagen-like region, a carbohydrate recognition domain, and a neck region. Recombinant TfCol-11 purified from Escherichia coli(E.coli) was able to bind to different microbes in a Ca²⁺-independent manner. Meanwhile, a 993 bp-long of partial MASP cDNA with a 96 bp 5' untranslated region (UTR) was also cloned from roughskin sculpin, containing 299 amino acids and consisting of three domains (CUB-EGF-CUB). qRT-PCR indicated that TfCol-11 and MASP mRNAs were predominately co-expressed in the liver. The temporal expression of TfCol-11 and MASP were both drastically up-regulated in the liver, skin, and blood by LPS challenge. Recombinant TfCol-11 purified from E.coli BL21(DE3) was able to agglutinate some bacteria in a Ca²⁺-dependent manner. In addition, an in vitro pull-down experiment demonstrated that TfCol-11 was able to bind to MASP, and in vivo experiments showed that TfCol-11 was associated with increased membrane attack complex (MAC) levels. It is therefore possible that TfCol-11 may plays a role in activating the complement system and in the defense against invading microorganisms in roughskin sculpin.

Scophthalmus maximus interleukin-1β limits Edwardsiella piscicida colonization in vivo

Interleukine-1β (IL-1β) is the first identified pro-inflammatory cytokine, which is cleaved by caspase-1 following the inflammasomes activation, playing critical roles in innate immunity. However, few studies have been performed to characterize the IL-1β in lower vertebrates. Herein, we distinguished the Scophthalmus maximus IL-1β (SmIL-1β) from three IL-1β like sequences and found that SmIL-1β was cleaved by S. maximus caspase at a non-conserved Asp⁸⁶, then targeted to the plasma membrane. Moreover, during the immersion infection of Edwardsiella piscicida, we found that E. piscicida were mainly colonized in gills at early time points and invaded to systemic sites after 5 days post infection, which was consistent with the dynamic up-regulated transcription of SmIL-1β. Furthermore, knockdown of SmIL-1β promotes the bacterial colonization in gills at early time points and result into systemic colonization, while overexpression of SmIL-1β hampers the bacterial colonization in both spleen and kidney. Taken together, these data provide new insights into the molecular mechanisms of SmIL-1β and reveal its role in limiting bacterial infection in vivo, which will support the idea for better understanding the evolutionary of IL-1β functions in teleost.

Identification, molecular characterization and functional analysis of interleukin (IL)-2 and IL-2like (IL-2L) cytokines in sea bass (Dicentrarchus labrax L.)

In mammals, interleukin (IL)-2, initially known as a T-cell grow factor, is an immunomodulatory cytokine involved in the proliferation of T cells upon antigen activation. In bony fish, some IL-2 orthologs have been identified, but, recently, an additional IL-2like (IL-2L) gene has been found. In this paper, we report the presence of these two divergent IL-2 isoforms in sea bass (Dicentrarchus labrax L.). Genomic analyses revealed that they originated from a gene duplication event, as happened in most percomorphs. These two IL-2 paralogs show differences in the amino acid sequence and in the exon 4 size, and these features could be an indication that they bind preferentially to different specific IL-2 receptors. Sea bass IL-2 paralogs are highly expressed in gut and spleen, which are tissues and organs involved in fish T cell immune functions, and the two cytokines could be up-regulated by both PHA stimulation and vaccination with a bacterial vaccine, with IL-2L being more inducible. To investigate the functional activities of sea bass IL-2 and IL-2L we produced the corresponding recombinant molecules in E. coli and used them to in vitro stimulate HK and spleen leukocytes. IL-2L is able to up-regulate the expression of markers related to different T cell subsets (Th1, Th2 and Th17) and to Treg cells in HK, whereas it has little effect in spleen. IL-2 is not active on these markers in HK, but shows an effect on Th1 markers in spleen. Finally, the stimulation with recombinant IL-2 and IL-2L is also able to induce in vitro proliferation of HK- and spleen-derived leukocytes. In conclusion, we have demonstrated that sea bass possess two IL-2 paralogs that likely have an important role in regulating T cell development in this species and that show distinct bioactivities.

Effects of dietary tryptophan levels on antioxidant status and immunity for juvenile blunt snout bream (Megalobrama amblycephala) involved in Nrf2 and TOR signaling pathway

Dietary administration of tryptophan has been proved improving growth performance of fish. An 8-week feeding trial was conducted to investigate the effects of dietary tryptophan level on antioxidant capacity and immune response through Nrf2 and TOR signaling pathway. The results showed that, 0.08% tryptophan level significantly increased plasma aspartate aminotransferase (AST), while immunoglobulin M (IgM) and alkaline phosphatase (ALP) were strikingly increased by 0.40% level. The level of plasma complement component 3 (C3), alanine aminotransferase (ALT) and albumin (ALB) were independent of tryptophan supplementation. Total superoxide dismutase (T-SOD), catalase (CAT), total antioxidant capacity (T-AOC) and glutathione (GSH) activity were increased with increasing dietary tryptophan level until 0.40% and then decreased, while the level of malondialdehyde (MDA) showed a reverse trend. 0.19% and 0.28% tryptophan level significantly improved the glutathione peroxidase 1 (GPx-1) activity. Compared with 0.08% dietary tryptophan level, 0.40% level significantly improved nuclear factor erythroid 2-related factor 2 (Nrf2), GPx, manganese superoxide dismutase (Mn-SOD), CAT and transforming growth factor-β (TGF-β) mRNA level, while Kelch-like ECH-associated protein 1 (Keap1) and interleukin 1β (IL-1β) mRNA level were significantly decreased. The relative expression of copper zinc superoxide dismutase (Cu/Zn-SOD), heme oxygenase-1 (HO-1), target of rapamycin (TOR), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), protein kinase B (Akt) and interleukin 10 (IL-10) were significantly improved by 0.28% diet, while the mRNA level of tumor necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were increased by 0.08% diet. Interleukin 8 (IL-8) mRNA level was not significantly affected by dietary tryptophan. Based on MDA and T-SOD value, the optimal dietary tryptophan level of juvenile blunt snout bream was determined to be 0.33% (1.03% of dietary protein) and 0.36% (1.13% of dietary protein), respectively, using quadratic regression analysis.

The zebrafish: A research model to understand the evolution of vertebrate immunity

The zebrafish has unique advantages for understanding the evolution of vertebrate immunity and to model human diseases. In this review, we will firstly give an overview of the current knowledge on vertebrate innate immune receptors with special emphasis on the inflammasome and then summarize the main contribution of the zebrafish model to this field, including to the identification of novel inflammasome components and to the mechanisms involved in its activation, assembly and clearance of intracellular bacteria.

Molecular characterization, phylogenetic analysis and adjuvant effect of channel catfish interleukin-1βs against Streptococcus iniae

Channel catfish is one of the most extensively cultured species worldwide, which is widely used as a classical model for comparative immunology. Interleukin-1β (IL1β) is an immunoregulatory cytokine with the potential to enhance the immune response induced by vaccines in many animals. To characterize the molecular characterization and identify the immunoadjuvant role of channel catfish IL1β, molecular cloning, phylogenetic analysis, and expression of two IL1β genes were performed, the bioactivity of their recombinant proteins (rIL1β1 and rIL1β2) were detected in vitro and their adjuvant effects on a subunit vaccine encoding C5a peptidase (pSCPI) of Streptococcus iniae were evaluated. The results indicated that two IL1βs remained highly conserved possessing five conserved motifs compared with other fish IL1βs, although there were 28 nucleotide differences and 16 amino acid differences between channel catfish IL1β1 and IL1β2. Analysis of the ratios of nonsynonymous (dN) and synonymous (dS) substitutions revealed that fish IL1β genes were subjected to negative/purifying selection with global dN/dS ratios value 0.425. The results of adjuvant effect showed that compared with injection of pSCPI alone, co-injecting pSCPI with both rIL1β1 and rIL1β2 significantly enhanced antibody levels, serum bactericidal activity, lysozyme activity, alternative complement hemolytic activity, and the expression of endogenous IL1β and TNF-α in head kidney and spleen. Although vaccination with rIL1β1 or rIL1β2 failed to offer immunoprotection against S. iniae infection, the RPS (relative percent survival) of pSCPI+rIL1β1 and pSCPI+rIL1β2 groups were both higher than pSCPI alone (RPS, 50%), with 64.26% and 60.71%, respectively. Moreover, pSCPI+rIL1β1+rIL1β2 offered significantly higher (P < 0.05) immunoprotection (RPS, 75%) against S. iniae infection than pSCPI alone. Our present results not only enrich the molecular structure study of fish IL1βs but also signify that two recombinant channel catfish IL1βs can be used as potential adjuvants in a subunit vaccine model against bacterial infection, which are of profound importance to prevent and control bacterial disease in channel catfish.

Histopathological analysis and the immune related gene expression profiles of mandarin fish (Siniperca chuatsi) infected with Aeromonas hydrophila

Hemorrhagic septicemia of mandarin fish (Siniperca chuatsi) was mainly caused by Aeromonas hydrophila which was an opportunistic pathogen. In recent years, the disease has caused tremendous economic loss with high morbidity and mass mortality in the mandarin fish breeding industry. Histopathological analysis and the immune related gene expression profiles of mandarin fish (S. chuatsi) infected with A. hydrophila were investigated in this study. Transmission electron microscopy (TEM) images showed that the cells of A. hydrophila densely covered with a mass of fimbriae. Histopathological analysis revealed that inflammation, vacuolization and extensive necrosis existed in the gill, liver, spleen and head kidney of the diseased fish. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune related genes in mandarin fish after A. hydrophila infection. The transcriptional analysis of these immune related genes demonstrated that the expression levels of major histocompatibility complex class II (MHC II), T cell receptor α (TCRα), tumor necrosis factor α (TNFα), CC chemokine 3, interleukin 8 (IL-8) and Hepcidin were strongly up-regulated in spleen and head kidney of mandarin fish post-infection. These results will contribute to further study on the pathogenesis and host defensive system in A. hydrophila infection.

Molecular characterization and expression analysis of the interleukin 1b gene in Pacific cod (Gadus macrocephalus)

Interleukin 1b (IL-1b) is a member of the cytokine family that serves as major mediators for early pro-inflammatory responses. During artificial breeding of Pacific cod (Gadus macrocephalus), outbreaks of NNV in the early development stages could lead to high mortality. Recent research reported that IL-1b participated in the host-virus interaction against NNV infection, however, no IL-1b gene has been identified from Pacific cod so far. In this study, we described the identification and characterization of a IL-1b from Pacific cod transcriptome at both transcript and protein level. Sequence alignment and phylogenetic analysis were conducted to determine and confirm their evolutionary relationship. Expression analysis revealed that IL-1b was expressed in all tested tissues and the western blot analysis confirmed the same expression profiles using purified recombinant IL-1b protein. In addition, significant up-regulation was detected in IL-1b transcripts during early development stages at 30dph and 50dph. After challenged with poly I:C, IL-1b was significantly induced after 24 h. Taken together, these results strongly suggested that IL-1b might play an essential role in innate defense mechanism of Pacific cod.

Effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream, Megalobrama amblycephala

The present study assessed the effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream. Fish were fed three practical diets with graded arginine levels (0.87%, 1.62% and 2.70%) for 8 weeks. Compared with the control group (0.87%), the counts of white blood cell (WBC), red blood cell (RBC) and hemoglobin (HGB) content were significantly improved at dietary arginine levels of 1.62% (P<0.05). Plasma albumin (ALB) levels and alkaline phosphatase (ALP) activities were significantly improved at dietary arginine levels of 1.62% and 2.70% (P < 0.05). Alanine transaminase (ALT) activity was decreased in fish fed with 1.62% dietary arginine level (P<0.05). Plasma glutathione peroxidase (GPx) activities, copper-zinc superoxide dismutase (Cu/Zn-SOD) activities, total antioxidant capacity (T-AOC) activities and glutathione (GSH) levels were significantly increased at dietary arginine levels of 1.62% and 2.70% (P<0.05). Plasma total superoxide dismutase (T-SOD) activities and catalase (CAT) activities were significantly improved in fish fed with 1.62% dietary arginine level. Significantly higher manganese superoxide dismutase (Mn-SOD) activity was observed in fish fed with 1.62% dietary arginine level compared with 2.70% dietary arginine level (P<0.05). 1.62% and 2.70% dietary arginine levels significantly lowered malondialdehyde (MDA) levels. The relative expression of nuclear factor erythroid 2-related factor 2 (Nrf2) was significantly increased in fish fed with 1.62% dietary arginine level, inversely, the relative expression of Kelch-like ECH-associated protein 1 (Keap1) showed a converse trend. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of Cu/Zn-SOD, GPx and CAT. Furthermore, 2.70% dietary arginine level significantly lowered the relative expression of Mn-SOD compared with the control group and 1.62% dietary arginine levels. The relative expressions of Interleukin 1β (IL-1β), tumour necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were lowered in fish fed with 1.62% dietary arginine level. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of transforming growth factor-β (TGF-β). Hematocrit (HCT), aspartate aminotransferase (AST) activities, interleukin 8 (IL-8) and interleukin 10 (IL-10) expressions were not significantly affected by the graded dietary arginine levels. These results suggest that the optimal dietary arginine level plays an important role in enhancing antioxidant and immune status to maintain the intestinal health of juvenile blunt snout bream.

Evolution of Th2 responses: characterization of IL-4/13 in sea bass (Dicentrarchus labrax L.) and studies of expression and biological activity

Th2 immunity is a primary host defence against metazoan pathogens and two of the important cytokines involved in this immune response in mammals are IL-4 and IL-13. Recently the origin and evolution of Th2 immune responses have been investigated in fish where a molecule with relatedness to both IL-4 and IL-13 is present, termed IL-4/13. Different IL-4/13 paralogues (IL-4/13 A and IL-4/13B) exist in teleost fish. In this paper, we have focused on the IL-4/13 isoforms found in the European sea bass (Dicentrarchus labrax L.). Two tandem duplicated but divergent IL-4/13 A isoforms and one IL-4/13B are present, a unique situation compared to other teleosts. These genes were studied in terms of their in vitro and in vivo transcript levels after different treatments and their biological activities after production of the recombinant isoforms. The results show that the presence of these three paralogues is associated with different activities, both in terms of their expression profiles and the ability of the proteins to modulate the expression of immune genes in head kidney leukocytes. It is clear that the initiation and control of type-2 responses in seabass is complex due to the presence of multiple IL-4/13 isoforms with overlapping but distinct activities.

Immunoglobulin T from sea bass (Dicentrarchus labrax L.): molecular characterization, tissue localization and expression after nodavirus infection

Background

Immunoglobulins (Igs) are fundamental components of the adaptive immune system of vertebrates, with the IgT/IgZ isotype specific of Teleosts. In this paper we describe the identification of an IgT heavy chain from the European sea bass (Dicentrarchus labrax L.), its molecular characterization and tissue mRNA localization by in situ hybridization.

Results

Sea bass IgT consists of 552 aa (Accession Number KM410929) and it contains a putative 19 amino acids long signal peptide and one potential N-glycosylation site. The C-region consists of four C_H domains; each contains the cysteine and tryptophan residues required for their correct folding. Based on the recent sequencing of sea bass genome, we have identified five different genomic contigs bearing exons unequivocally pertaining to IgT (C_H2, C_H3 and C_H4), but none corresponded to a complete IgH locus as IgT sequences were found in the highly fragmented assembled genomic regions which could not be assigned to any major scaffold. The 3D structure of sea bass IgT has been modelled using the crystal structure of a mouse Ig gamma as a template, thus showing that the amino acid sequence is suitable for the expected topology referred to an immunoglobulin-like architecture. The basal expression of sea bass IgT and IgM in different organs has been analysed: gut and gills, important mucosal organs, showed high IgT transcripts levels and this was the first indication of the possible involvement of sea bass IgT in mucosal immune responses. Moreover, sea bass IgT expression increased in gills and spleen after infection with nodavirus, highlighting the importance of IgT in sea bass immune responses. In situ hybridization confirmed the presence of IgT transcripts in the gut and it revealed a differential expression along the intestinal tract, with a major expression in the posterior intestine, suggesting the hindgut as a site for the recruitment of IgT⁺ cells in this species. IgT transcripts were also found in gill filaments and parallel lamellae and, for the first time, we identified scattered IgT positive cells in the liver, with a strong signal in the hepatic parenchyma.

Conclusions

In conclusion, we performed a full molecular characterization of IgT in sea bass that points out its possible involvement in mucosal immune responses of this species.

Preliminary study on the relationship between dexamethasone and pathogen susceptibility on crucian carp (Carassius auratus)

Dexamethasone, a known immunosuppressant, can inhibit the immune response and increase the amount of pathogen in body, but the role of dexamethasone affecting susceptibility of crucian carp (Carassius auratus) to pathogen is unclear. The effects of dexamethasone on susceptibility of crucian carp to Aeromonas hydrophila were investigated in this study. The fish were divided into four groups randomly and injected intraperitoneally by dexamethasone for 0 day (group D), 3 days (group C), 6 days (group B), and 9 days (group A), respectively. The serum lysozyme activity was significantly declined in group A, B and C. Relative immune gene expression such as il-1β, cxcl-8, tnfα and crp in kidney were down-regulation compared to group D. After that crucian carp were infected with A. hydrophila, crucian carp treated by dexamethasone had higher mortality (group A 95%, group B 76%, group C 31%) when compared to group D (4% mortality); the amount of pathogen in was significantly increased (P < 0.05) in liver, kidney and spleen of fish in group A-C compared to group D. These results implicated that higher susceptibility caused by dexamethasone may be induced by the decrease of lysozyme activity and the down-regulation of some immune genes.

miR-192 targeting IL-1RI regulates the immune response in miiuy croaker after pathogen infection in vitro and in vivo

Activation of innate and acquired immune responses is regulated by detailed mechanisms to control their onset and termination. MicroRNAs have been implicated as negative regulators controlling the diverse of biophysical and biochemical processes at the post-transcriptional level. However, the physiological roles of miRNAs in aquatic organisms are largely unclear. In this study, we explored the potential roles of mmi-miR-192 in regulating interleukin 1 receptor type I (IL-1RI) involved in immune and inflammatory response in miiuy croakers. This was further evaluated by negative expression profiles in both LPS exposure macrophages and Vibrio anguillarum challenged miiuy croaker. By means of promoter analysis, mmi-miR-192 was found to be an AP-1 dependent gene. Importantly, the dual luciferase reporter assay presented the regulation between mmi-miR-192 and IL-1RI. The result of miiuy croaker miR-192 reduced the wild-type IL-1RI but not the mutant one luciferase levels suggested that mmi-miR-192 modulated IL-1RI expression by directly targeting the 3'UTR of IL-1RI mRNA. Overall, our study revealed the mechanism that the miR-192-IL1RI pathway regulated bacteria infection in miiuy croakers.

Grass carp TGF-β1 impairs IL-1β signaling in the inflammatory responses: Evidence for the potential of TGF-β1 to antagonize inflammation in fish

In the present study, effects of TGF-β1 on IL-1β signaling during inflammatory response were examined in grass carp. In grass carp head kidney leukocytes (HKLs), LPS significantly induced the mRNA expression of grass carp TGF-β1 (gcTGF-β1) and IL-1β, indicating the involvement of TGF-β1 and IL-1β in inflammatory process. Using anti-IL-1β antibody to neutralize the endogenous IL-1β, we found that stimulation of IL-1β mRNA expression by LPS was independent on IL-1β itself. Interestingly, recombinant gcTGF-β1 (rgcTGF-β1) suppressed basal and LPS-stimulated IL-1β mRNA expression in spite of immunoneutralizing endogenous IL-1β or not. Given that IL-1β receptor signaling molecule and natural IL-1β inhibitors are the important regulators in IL-1β signaling and activity, the effect of LPS on these molecules' expression was determined in HKLs. Results showed that LPS significantly enhanced the mRNA levels of IL-1 receptor type I (IL-1RI) and II (IL-1RII), IL-1R accessory protein (IL-1Racp) and novel IL-1 family member (nIL-1F). Moreover, the induction of IL-1RII, IL-1Racp and nIL-1F by LPS was IL-1β-dependent since IL-1β immunoneutralization abolished these inductions, implying the involvement of IL-1β auto-induction in these effects. Consistently, TGF-β1 could block basal IL-1RI and nIL-1F mRNA expression, and LPS-induced IL-1RI, IL-1Racp and nIL-1F mRNA expression, suggesting these molecules as the regulatory sites for TGF-β1 to modulate IL-1β signaling. Subsequent in vivo studies showed that bacterial challenge significantly up-regulated IL-1β mRNA expression with a rapid and transient pattern and TGF-β1 mRNA expression with a relatively time-delayed kinetics in head kidney. These expression patterns coincide with their pro-inflammatory and anti-inflammatory roles, respectively. As expected, rgcTGF-β1 could suppress bacterial-induced IL-1β mRNA expression, strengthening the anti-inflammatory role of TGF-β1 in vivo. Taken together, these results to our knowledge provide the first evidence for inducible TGF-β1 expression in inflammatory process, as well as the induction of inflammatory stimuli on IL-1β expression and signaling. In turn, TGF-β1 suppressed the proinflammatory process in vitro and in vivo presumably via interfering IL-1β expression and signaling in inflammatory response, highlighting the potential of TGF-β1 in the control of inflammation in 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.

Identification and Functional Analysis of Interleukin-1β in the Chinese Soft-Shelled Turtle Pelodiscus sinensis

Chinese soft-shelled turtle (Pelodiscus sinensis) is commercially cultured in East and Southeast Asia for its nutritional and medicinal values. In this study, we identified interleukin-1β (IL-1β) from Chinese soft-shelled turtle. The full-length cDNA of Pelodiscus sinensis IL-1β (tIL-1β) consists of 1529 base pairs with an 831-base-pair open reading frame, encoding 277 amino acids. The guanine-cytosine (GC) content in the coding sequence and 3' untranslated region of tIL-1β is considerably higher than that of other vertebrates. Its mRNA expression level increased significantly during Aeromonas hydrophila infection. The tIL-1β lacks the typical IL-1β-converting enzyme (ICE) cut site found in mammalian IL-1β, but still could be cleaved by turtle caspase-1. By mutating the potential cleavage sites, we identified aspartic acid (Asp/D) 130 as the ICE cut site in tIL-1β. The peptide truncated at D130 was expressed using the baculovirus expression system; its bioactivity is confirmed by the ability to induce cyclooxygenase-2 (COX-2) and tIL-1β itself in peripheral blood monocytes. In conclusion, we characterized IL-1β from Chinese soft-shelled turtle and identified its D130 as a non-typical ICE cut size.

Molecular characterization and comparative expression analysis of two teleostean pro-inflammatory cytokines, IL-1β and IL-8, from Sebastes schlegeli

Interleukin 1β (IL-1β) and interleukin 8 (IL-8) are two major pro-inflammatory cytokines which play a central role in initiation of inflammatory responses against bacterial- and viral-infections. IL-1β is a member of the interleukin 1 family proteins and IL-8 is classified as a CXC-chemokine. In the current study, putative IL-1β and IL-8 counterparts were identified from a black rockfish transcriptomic database and designated as RfIL-1β and RfIL-8. The RfIL-1β cDNA sequence consists of 1140 nucleotides with a 759bp open reading frame (ORF) which encodes a 252 amino acid (aa) protein, whereas the RfIL-8 cDNA sequence (898bp) harbors a 300bp ORF encoding a 99 aa protein. Furthermore, the RfIL-1β aa sequence contains an IL-1 super family-like domain and an N-terminal IL-1 super family propeptide, while the amino acid sequence of RfIL-8 consists of a typical chemokine-CXC domain. Analysis of sequenced BAC clones containing RfIL-1β and RfIL-8 showed each gene to contain 4 exons interrupted by 3 introns. Pairwise comparison and phylogeny analysis of these cytokine sequences clearly revealed their closer relationship with other corresponding members of teleosts compared to birds and mammals. Constitutive differences in RfIL-1β and RfIL-8 mRNA expression were detected in a tissue-specific manner with the highest expression of each mRNA in spleen tissue. Two immune challenge experiments were conducted with Streptococcus iniae and polyinosinic:polycytidylic acid (poly I:C; a viral double stranded RNA mimic), and transcripts were quantified in spleen and peripheral blood cells. Significantly increased RfIL-1β and RfIL8 transcript levels were detected with almost similar profile patterns, further suggesting a putative involvement of these pro-inflammatory cytokines in the rockfish immunity.

Characterization of interleukin-1β as a proinflammatory cytokine in grass carp (Ctenopharyngodon idella)

Interleukin-1β (IL-1β) is a well-characterized cytokine that plays key roles in cellular responses to infection, inflammation, and immunological challenges in mammals. In this study, we identified and analyzed a grass carp (Ctenopharyngodon idella) ortholog of IL-1β (gcIL-1β), examined its expression patterns in various tissues in both healthy and lipopolysaccharide (LPS)-stimulated specimens, and evaluated its proinflammatory activities. The gcIL-1β gene consists of seven exons and six introns. The full-length cDNA sequence contains an open reading frame of 813 nucleotides. The deduced amino acid sequence exhibits a characteristic IL-1 signature but lacks the typical IL-1β converting enzyme cleavage site that is conserved in mammals. In the phylogenetic tree, IL-1βs from grass carp and other members of the Cyprinidae family clustered into a single group. Expression pattern analysis revealed that gcIL-1β is constitutively expressed in all 11 tissues examined, and LPS stimulation leads to significant up-regulation in muscle, liver, intestine, skin, trunk kidney, head kidney, and gill. Recombinant grass carp IL-1β (rgcIL-1β) was generated prokaryotically as a fusion protein of Trx-rgcIL-1β. An anti-rgcIL-1β polyclonal antibody (rgcIL-1β pAb) was raised in mice against the purified Trx-rgcIL-1β. Western blot analysis confirmed that rgcIL-1β pAb reacted specifically with gcIL-1β in C. idella kidney (CIK) cells. Quantitative real-time PCR data indicated that intestinal mRNA expression levels of endogenous IL-1β, IL-1R2, and TNF-α were significantly up-regulated following Trx-rgcIL-1β exposure. The inhibitory activities of rgcIL-1β pAb against the inflammatory response were confirmed in a model of Aeromonas hydrophila-induced intestinal inflammation. Our immunohistochemical study revealed that the degree and intensity of inflammatory cell infiltration are fully consistent with the observed mRNA expression patterns of these key inflammatory genes. Taken together, these data suggest that gcIL-1β plays a critical role in the proinflammatory response in the grass carp intestine.

Differential innate immune response of European seabass (Dicentrarchus labrax) against Streptococcus iniae

Streptococcus iniae is a Gram-positive bacteria that causes invasive infections with severe septicemia and meningitis, producing high economic losses in marine and continental aquaculture. Head kidney leukocytes of European sea bass (Dicentrarchus labrax) were used to measure the differential innate immune response upon infection with S. iniae. The complete inhibition in the production of intracellular superoxide radicals and total peroxidase content was observed in infected cells. This study also elucidates changes in the relative expression of some immune-related genes. Interleukin 1β, tumor necrosis factor-α and interleukin-6 reached a peak of expression at 4-8 h post-infection, subsequently decreasing significantly up to 48 h post-infection. However, interleukin-10 and Mx protein increased over time, reaching the pick of expression at 48 h post-infection, whereas caspase-3 showed down regulation until 48 h post-infection. The in vivo study of immune related genes show the same kinetics of mRNAs expression as in vitro experience. The proinflammatory cytokines mRNA transcription levels peaked at an earlier time in vivo than in vitro system. Our findings indicate that there is a direct relationship between the dissemination of bacteria and the resulting infection-associated inhibition of respiratory burst, apoptosis, and the pro- and anti-inflammatory gene expression profiles.

Immunization of sea bream (Sparus aurata) juveniles against Photobacterium damselae subsp. piscicida by short bath: Effect on some pro-inflammatory molecules and the Mx gene expression

Cytokines are a family of proteins derived from macrophages, lymphocytes, granulocytes, mast cells and epithelial cells and can be divided into interferons (IFNs), Interleukins (ILs) and Tumor Necrosis factors (TNFs) among others. The presence of cytokines in a wide number of fish species has been proved and several molecules types have been already cloned and sequenced. In this work some proinflamatory molecules and Mx gene were detected in the liver of vaccinated sea bream juveniles with an average body weight of 5 g. The method of immunization was by short bath and three different bacterins against the marine pathogen Photobacterium damselae subsp. piscicida were designed and used to immunize fish. Five genes encoding for five different molecules were analyzed by real time PCR: IL-1β, IL Ir-2, Cox-2, Mx and TNFα. Gene expression was quantified along four days after fish immunization and results were compared among groups. Results show that the heat-inactivated vaccine stimulates the up-regulation of IL-1β, IL Ir-2, Cox-2 and TNFα genes whereas the UV-light inactivated vaccine was the unique vaccine which stimulates the expression of Mx gene. The present is a novel study that shows by the first time the effect of the inactivation process of vaccines on the expression levels of genes involved in the defense against Photobacterium damselae subsp piscicida.

Expression analysis of the Atlantic bluefin tuna (Thunnus thynnus) pro-inflammatory cytokines, IL-1β, TNFα1 and TNFα2 in response to parasites Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea)

Pro-inflammatory cytokines play an important role in teleost defence against numerous types of pathogens, therefore are often used as biomarkers during various infections. In order to evaluate Atlantic bluefin tuna IL-1β, TNFα1 and TNFα2 induction by PAMPs, we quantified their expression during in vitro stimulation of peripheral blood leukocytes by LPS and Poly I:C. Furthermore, their role in acute and chronic parasitic infection was examined during natural infection of Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea), as well as during leukocyte exposure to total protein extracts isolated from two parasite species. Induction of ABT IL-1β and TNFα2 by PAMPs and protein extracts from D. katsuwonicola and P. appendiculatus, as well as during natural infection with two parasites, suggests these cytokines play an important role in inflammation, being engaged in controlling parasite infections, in contrast to ABT TNFα1. Cellular innate response to the digenean D. katsuwonicola showed rather chronic character, resulting with parasite encapsulation in connective tissue. Mast cells, eosinophils, goblet cells, and occasional rodlet cells found at the site of infection, along with the induction of TNFα2, suggest the presence of a moderate inflammatory reaction that fails to seriously endanger digenean existence. In contrast, copepod P. appendiculatus, attached to the gill epithelium by clamping, caused direct tissue disruption with undergoing necrotic or apoptotic processes, and extensive proliferation of rodlet and goblet cells. Differential expression patterns of target cytokines in tissue surrounding two parasites and in vitro PBL model suggest that quality and quantity of tuna immune response is conditioned by parasite adaptive mechanisms and pathogenicity.

Sensors of Infection: Viral Nucleic Acid PRRs in Fish

Viruses produce nucleic acids during their replication, either during genomic replication or transcription. These nucleic acids are present in the cytoplasm or endosome of an infected cell, or in the extracellular space to be sensed by neighboring cells during lytic infections. Cells have mechanisms of sensing virus-generated nucleic acids; these nucleic acids act as flags to the cell, indicating an infection requiring defense mechanisms. The viral nucleic acids are called pathogen-associated molecular patterns (PAMPs) and the sensors that bind them are called pattern recognition receptors (PRRs). This review article focuses on the most recent findings regarding nucleic acids PRRs in fish, including: Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), cytoplasmic DNA sensors (CDSs) and class A scavenger receptors (SR-As). It also discusses what is currently known of the downstream signaling molecules for each PRR family and the resulting antiviral response, either type I interferons (IFNs) or pro-inflammatory cytokine production. The review highlights what is known but also defines what still requires elucidation in this economically important animal. Understanding innate immune systems to virus infections will aid in the development of better antiviral therapies and vaccines for the future.

Effect of dietary arginine on the immune response and gene expression in head kidney and spleen following infection of Jian carp with Aeromonas hydrophila

This study was conducted to test the hypothesis that elevated dietary arginine enhances immunity of juvenile Jian carp (Cyprinus carpio var. Jian). Fish were fed graded levels of dietary arginine for 9 weeks. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila. Head kidney and spleen weights, as well as erythrocyte and leukocyte counts were significantly influenced by dietary arginine levels. A similar trend was also observed for hemagglutination titre, serum lysozyme activity, IgM concentration, C3 and C4 content. The highest survival rates following A. hydrophila infection were obtained in fish fed the diets containing arginine at 16.1-21.9 g/kg diet. Phagocytic activity of leukocytes was significantly enhanced by dietary arginine supplementation. In contrast, acid phosphatase activity significantly decreased with dietary arginine levels. Dietary arginine levels did not have a significant effect on the total iron-binding capacity. Gene expression of TNF-α and TGF-β in head kidney significantly increased with dietary arginine levels up to 21.9 g/kg diet, and decreased thereafter. Fish fed the basal diet exhibited the highest IL-10 mRNA expression level. Gene expression of IL-1β and TOR increased with dietary arginine addition, reaching a plateau at 18.5 and 21.9 g arginine/kg diet, respectively. In spleen, higher IL-1β and TNF-α gene expressions were obtained in fish fed the diets containing 24.5 g arginine/kg diet than in fish fed the other dietary treatments. TGF-β mRNA expression levels were significantly lower in fish fed the diets containing ≤21.9 g arginine/kg diet. IL-10 and TOR mRNA expression levels were lower in fish fed 16.1 g arginine/kg diet, while 4E-BP mRNA expression levels increased with dietary arginine levels up to 12.7 g/kg diet and decreased thereafter. Our results indicate that arginine has beneficial effects on regulating mRNA expression of inflammatory cytokines, as well as TOR and 4E-BP and improving humoral and cellular immunity, therefore enhancing disease resistance of fish.

Ultrapure LPS induces inflammatory and antibacterial responses attenuated in vitro by exogenous sera in Atlantic cod and Atlantic salmon

Phagocyte recognition of lipopolysaccharide (LPS) is an early key event for triggering the host innate immune response necessary for clearance of invading bacteria. The ability of fishes to recognise LPS has been questioned as contradictory results have been presented. We show here that monocyte/macrophage cultures from Atlantic cod (Gadus morhua) and Atlantic salmon (Salmo salar) respond with an increased expression of inflammatory and antibacterial genes to both crude and ultrapure Escherichia coli LPS. Crude LPS produces higher induction than the ultrapure LPS type in both species in vitro as well as in vivo in cod injected with LPS. Crude LPS gave, in contrast to ultrapure LPS, an additional weak up-regulation of antiviral genes in salmon macrophages, most likely because of contaminants in the LPS preparation. Increased levels of chicken (c)-type lysozyme transcripts and enzyme activity were measured in salmon macrophages following ultrapure LPS stimulation demonstrating not only increased transcription but also translation. Simultaneous use and even pre-treatment with bovine sera suppressed the LPS-induced expression thereby reflecting the presence of transcription inhibitory components in sera. Together, these findings show that both cod and salmon recognise LPS per se and that the observed induction is highly dependent on the absence of sera.

Characterization of the annual regulation of reproductive and immune parameters on the testis of European sea bass

The European sea bass, Dicentrarchus labrax L., is a seasonal gonochoristic species, the males of which are generally mature during their second year of life. It has been demonstrated that cytokines and immune cells play a key role in the testicular development. This reproductive-immune interaction might be very important in the sea bass since several pathogens are able to colonise the gonad and persist in this tissue, altering further reproductive functions and spreading disease. This study aims to investigate the reproductive cycle of 1-year European sea bass males by analysing cell proliferation and apoptosis and the expression profile of some reproductive and immune-related genes in the testis, as well as the serum sex steroid levels. Our data demonstrate that, in 1-year-old European sea bass males, the testis undergoes the spermatogenesis process and that the reproductive and immune parameters analysed varied during the reproductive cycle. In the testis, the highest proliferative rates were recorded at the spermatogenesis stage, while the highest apoptotic rates were recorded at the spawning stage. We have also analysed, for the first time in European sea bass males, the serum levels of 17β-estradiol (E2) and dihydrotestosterone and the gene expression profile of the enzymes implied in their production, determining that at least E2 might be involved in the regulation of the reproductive cycle. Some immune relevant genes, including cytokines, lymphocyte receptors, and anti-viral and anti-bacterial molecules were detected in the testis of naïve European sea bass specimens, and their expression profile was related to the stages of the reproductive cycle, suggesting an important role for the defence of the reproductive tissues.

Preliminary study on expression of antimicrobial peptides in European sea bass (Dicentrarchus labrax) following in vivo infection with Vibrio anguillarum. A time course experiment

Antimicrobial polypeptides (AMPPs) are humoral components of the vertebrates and invertebrates innate immune system. Their potent broad spectrum antimicrobial activities have drawn the attention of the scientific community to their potential use not only as an alternative to antibiotics but also as functional targets for immunostimulants in order to enhance the host immunity. Fish synthesize a great number of these peptides but in European sea bass, an important fish species in the Mediterranean aquaculture, only a few AMPPs have been studied and these surveys have highlighted their functional role as predictive markers of stressful conditions. Many aspects concerning AMPP mode of action in the host during bacterial infections are still unknown. In this work a 72 h time course experiment, performed on juvenile sea bass intraperitoneally (i.p.) injected with a sub-lethal dose of Vibrio anguillarum, was aimed to investigate the mRNA expression of four specific AMPP genes and interleukin-1β (IL-1β) in skin, gills, spleen, and head kidney. AMPP genes were: dicentracin (DIC), histone-like protein 1 (HLP-1), histone-like protein 2 (HLP-2) and hemoglobin-like protein (Hb-LP). The delta-delta C(T) method in real-time RT-PCR allowed to gain more knowledge about temporal dynamics, preferential sites of expression as well as immunological and physiological role of these molecular markers. DIC was significantly up-regulated mainly in head kidney at 1.5-3 h post-infection (p.i.). HLP-1 showed an extended-time overexpression in gills and a significant up-regulation in spleen. HLP-2 was interestingly overexpressed in gills at 24 h p.i., while Hb-LP showed a significant up-regulation in skin for all the 72 h trial as well as lower but always significant values either in gills or in spleen. Different was the response of IL-1β that showed a dramatic up-regulation in spleen and head kidney at 8 h p.i. whilst in gills it displayed a severe inhibition. During this survey the i.p. stimulus surely conditioned the AMPP expression in skin and gills, especially as regards the DIC that as piscidin-related gene has an important defensive role in the mucosal tissues. However, two unconventional AMPP genes such as HLP-2 and Hb-LP, strictly related to the physiological mechanisms of fish, were less affected in terms of expression by the route of infection, being more evident in peripheral loci. These findings might suggest them as potential markers to be analyzed within plans of health survey in fish farms.

A short history of research on immunity to infectious diseases in fish

This review describes the history of research on immunity to infectious diseases of fish in the period between 1965 and today. Special attention is paid to those studies, which are dealing with the interaction between immune system and invading pathogens in bony fish. Moreover, additional biographic information will be provided of people involved. In the 1960s and 1970s the focus of most studies was on humoral (Ig, B-cell) responses. Thorough studies on specific cellular (T-cell) responses and innate immunity (lectins, lysozyme, interferon, phagocytic cells) became available later. In the period between 1980 and today an overwhelming amount of data on regulation (e.g. cell cooperation, cytokines) and cell surface receptors (e.g. T-cell receptor; MHC) was published. It became also clear, that innate responses were often interacting with the acquired immune responses. Fish turned out to be vertebrates like all others with a sophisticated immune system showing specificity and memory. These basic data on the immune system could be applied in vaccination or in selection of disease resistant fish. Successful vaccines against bacterial diseases became available in the 1970s and 1980s. Effective anti-viral vaccines appeared from the 1980s onwards. There is no doubt, that Fish Immunology has become a flourishing science by the end of the 20th century and has contributed to our understanding of fish diseases as well as the success of aquaculture.

Purification and molecular characterization of IgM in olive barb, Puntius Sarana

In the present article, immunoglobulin (Ig) of Puntius sarana (a vulnerable medium carp species) was purified by affinity chromatography, characterized, and identified as only IgM type with a native molecular weight of 879 kDa having one heavy (88 kDa) and one light (26 kDa) chain. Further, the developed rabbit antisera against IgM was found to be quite specific to P. sarana IgM and used in ELISA to measure the antibody titer in P. sarana at different time periods, against an antigen (hemocyanin) injection with and without adjuvant. The antibody titer was significantly higher in most of the time periods in both groups, however, the adjuvant-treated group showed higher antibody titer at days 43 and 90, compared to non adjuvant-treated group. Further, the partial IgM sequence was amplified and its expression level was checked during ontogenesis. The IgM transcript was detected from unfertilized egg stage to 4 days post fertilization (dpf) and again reappeared at 21 dpf whereas during infection with Aeromonas hydrophila, significantly marked up-regulation of the gene was observed at 12 hr, 24 hr, and 7 days post-infection time periods indicating the role of IgM during early embryonic time period as well as during bacterial pathogenesis.