Metabolomics and microbiome co-analysis reveals altered innate immune responses in Charybdis japonica following Aeromonas hydrophila infection

A comprehensive bioinformatics analysis was conducted to elucidate the innate immune response of Charybdis japonica following exposure to Aeromonas hydrophila. This study integrated metabolomics, 16S rRNA sequencing, and enzymatic activity data to dissect the immune mechanisms activated in response to infection. Infection with A. hydrophila resulted in an increased abundance of beneficial intestinal genera such as Photobacterium spp., Rhodobacter spp., Polaribacter spp., Psychrilyobacter spp., and Mesoflavibacter spp. These probiotics appear to suppress A. hydrophila colonization by competitively dominating the intestinal microbiota. Key metabolic pathways affected included fatty acid biosynthesis, galactose metabolism, and nitrogen metabolism, highlighting their role in the crab's intestinal response. Enzymatic analysis revealed a decrease in activities of hexokinase, phosphofructokinase, and pyruvate kinase, which are essential for energy homeostasis and ATP production necessary for stress responses. Additionally, reductions were observed in the activities of acetyl-CoA carboxylase and fatty acid synthase. Gene expression analysis showed downregulation in Peroxiredoxin 1 (PRDX1), Peroxiredoxin 2 (PRDX2), glutathione-S-transferase (GST), catalase (CAT), and glutathione (GSH), with concurrent increases in malondialdehyde (MDA) levels, indicating severe oxidative stress. This study provides insights into the molecular strategies employed by marine crabs to counteract bacterial invasions in their natural habitat.

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.

Lytic Bacteriophage PZL-Ah152 as Biocontrol Measures Against Lethal Aeromonas hydrophila Without Distorting Gut Microbiota

Phage therapy is an alternative approach to overcome the problem of multidrug resistance in bacteria. In this study, a bacteriophage named PZL-Ah152, which infects Aeromonas hydrophila, was isolated from sewage, and its biological characteristics and genome were studied. The genome contained 54 putative coding sequences and lacked known putative virulence factors, so it could be applied to phage therapy. Therefore, we performed a study to (i) investigate the efficacy of PZL-Ah152 in reducing the abundance of pathogenic A. hydrophila strain 152 in experimentally infected crucian carps, (ii) evaluate the safety of 12 consecutive days of intraperitoneal phage injection in crucian carps, and (iii) determine how bacteriophages impact the normal gut microbiota. The in vivo and in vitro results indicated that the phage could effectively eliminate A. hydrophila. Administering PZL-Ah152 (2 × 10⁹ PFU) could effectively protect the fish (2 × 10⁸ CFU/carp). Furthermore, a 12-day consecutive injection of PZL-Ah152 did not cause significant adverse effects in the main organs of the treated animals. We also found that members of the genus Aeromonas could enter and colonize the gut. The phage PZL-Ah152 reduced the number of colonies of the genus Aeromonas. However, no significant changes were observed in α-diversity and β-diversity parameters, which suggested that the consumed phage had little effect on the gut microbiota. All the results illustrated that PZL-Ah152 could be a new therapeutic method for infections caused by A. hydrophila.

An Antioxidant Supplement Function Exploration: Rescue of Intestinal Structure Injury by Mannan Oligosaccharides after Aeromonas hydrophila Infection in Grass Carp (Ctenopharyngodon idella)

Mannan oligosaccharides (MOS) are a type of functional oligosaccharide which have received increased attention because of their beneficial effects on fish intestinal health. However, intestinal structural integrity is a necessary prerequisite for intestinal health. This study focused on exploring the protective effects of dietary MOS supplementation on the grass carp’s (Ctenopharyngodon idella) intestinal structural integrity (including tight junction (TJ) and adherent junction (AJ)) and its related signalling molecule mechanism. A total of 540 grass carp (215.85 ± 0.30 g) were fed six diets containing graded levels of dietary MOS supplementation (0, 200, 400, 600, 800 and 1000 mg/kg) for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila for 14 days. We used ELISA, spectrophotometry, transmission electron microscope, immunohistochemistry, qRT-PCR and Western blotting to determine the effect of dietary MOS supplementation on intestinal structural integrity and antioxidant capacity. The results revealed that dietary MOS supplementation protected the microvillus of the intestine; reduced serum diamine oxidase and d-lactate levels (p < 0.05); enhanced intestinal total antioxidant capacity (p < 0.01); up-regulated most intestinal TJ and AJ mRNA levels; and decreased GTP-RhoA protein levels (p < 0.01). In addition, we also found several interesting results suggesting that MOS supplementation has no effects on ZO-2 and Claudin-15b. Overall, these findings suggested that dietary MOS supplementation could protect intestinal ultrastructure, reduce intestinal mucosal permeability and maintain intestinal structural integrity via inhibiting MLCK and RhoA/ROCK signalling pathways.

Rainbow trout gastrointestinal mucus, mucin production, mucin glycosylation and response to lipopolysaccharide

Mucus, whereof the highly glycosylated mucins are a major component, protects the epithelial mucosal surfaces. The aim of this study was to characterize the rainbow trout (Oncorhynchus mykiss) gastrointestinal mucus barrier function, mucin production, glycosylation and response to lipopolysaccharide. Both gastric and intestinal mucus was thick and impenetrable to bacteria-sized beads ex vivo. The secreted mucus covering the gastric epithelium predominantly contained sialylated mucins. Plume-like structures emerging from the gastric pits were both sialylated and fucosylated, indicating heterogeneity in gastric mucus secreted by the surface mucus cells and gland secretory cells, whereas intestinal mucus appeared more homogenous. In vivo metabolic mucin labelling revealed regional differences in mucin production and basal to apical transport, while lipopolysaccharide stimulation increased the rate of mucin production and basal to apical transport in both stomach and intestine. Using mass spectrometry, 34 mucin O-glycans were identified, with ∼70% of the relative abundance being sialylated, ∼40% di-sialylated and 20-25% fucosylated. No effects of lipopolysaccharide treatment were apparent regarding O-glycan repertoires, relative abundance of components, size distribution or core structures. Thus, the mucus production and organization differ between epithelial sites but provide a barrier to bacteria in both stomach and intestine. Furthermore, mucin production and basal to apical transport was stimulated by lipopolysaccharide in all regions, suggesting a mechanism to combat infections.

Toll-Like Receptor Evolution: Does Temperature Matter?

Toll-like receptors (TLRs) recognize conserved pathogen-associated molecular patterns (PAMPs) and are an ancient and well-conserved group of pattern recognition receptors (PRRs). The isolation of the Antarctic continent and its unique teleost fish and microbiota prompted the present investigation into Tlr evolution. Gene homologues of tlr members in teleosts from temperate regions were present in the genome of Antarctic Nototheniidae and the non-Antarctic sister lineage Bovichtidae. Overall, in Nototheniidae apart from D. mawsoni, no major tlr gene family expansion or contraction occurred. Instead, lineage and species-specific changes in the ectodomain and LRR of Tlrs occurred, particularly in the Tlr11 superfamily that is well represented in fish. Positive selective pressure and associated sequence modifications in the TLR ectodomain and within the leucine-rich repeats (LRR), important for pathogen recognition, occurred in Tlr5, Tlr8, Tlr13, Tlr21, Tlr22, and Tlr23 presumably associated with the unique Antarctic microbiota. Exposure to lipopolysaccharide (Escherichia coli O111:B4) Gram negative bacteria did not modify tlr gene expression in N. rossii head–kidney or anterior intestine, although increased water temperature (+4°C) had a significant effect.

Identification of IκBα in Japanese eel Anguilla japonica that impairs the IKKα-dependent activation of NF-κB, AP1, and type I IFN signaling pathways

As a member of inhibitory κB family (IκB) family, IκBα is best-characterized and plays a central negative feedback regulator of NF-κB pathway in mammals, but the information about IκBα in the regulation of immune responses is still limited in teleost fishes. In the present study, the full-length cDNA of an IκBα homologue, AjIκBα, was cloned by 5' and 3' SMART RACE from Japanese eel, and its characteristics of expression in response to various PAMPs and A. hydrophila infection were investigated both in vivo and in vitro using quantitative real-time polymerase chain reaction (qRT-PCR). In addition, the subcellular localization of AjIκBα GFP fusion protein and the induction of AjIκBα alone or co-expression with Japanese eel IKKα (AjIKKα) in the activation of NF-κB, type I IFN and AP1 performed using Dual-Glo luciferase assay system were also detected. Sequence comparison analysis revealed that AjIκBα has typical conserved domains, including the N-terminal conserved degradation motif, the ankyrin repeats, and the C-terminal PEST domain. The predicted three-dimensional structure of AjIκBα is similar to that of human IκBα. qRT-PCR analysis revealed a broad expression for AjIκBα in a wide range of tissues, with the highest expression in the spleen, followed by intestine, liver, gills, skin, kidney, and with a lower expression in the heart and muscle. The AjIκBα expressions in the kidney, spleen, and especially in liver were significantly induced following injection with Gram-negative bacterial component LPS, the viral mimic poly I:C and Aeromonas hydrophila infection. In vitro, the AjIκBα transcripts of Japanese eel liver cells were significantly enhanced by the treatment of LPS, poly I:C, or the stimulation of different concentration of Aeromonas hydrophil. Luciferase assays demonstrated that not only could the AjIκBα expression significantly decrease the activation of NF-κB, AP1, and IFNβ-responsive promoters in HEK293 cells and EPC cells, but also robustly inhibited the activity of these three promoters in HEK293 cells or NF-κB and AP1-responsive promoters in EPC cells induced by AjIKKα. Additionally, subcellular localization studies showed that AjIκBα was evenly distributed in the cytoplasm and nucleus both in HEK293 cells and EPC cells under natural state. AjIκBα was found to aggregate into spots in the cytoplasm and nucleus stimulated by LPS or mostly aggregate into nucleus with the treatment of poly I:C in HEK293 cells, whereas the elevated expression of AjIκBα was observed in the cytoplasm of EPC cells upon the stimulation of poly I:C. These results collectively indicated that AjIκBα function as an important negative regulation in innate immunity of host against antibacterial and antiviral infection likely via the inhibition of the activation of NF-κB, AP1, and type I IFN signaling pathways.

Pro- and anti-inflammatory responses of common carp Cyprinus carpio head kidney leukocytes to E.coli LPS as modified by different dietary plant oils

Dietary lipids could modify fatty acid (FA) composition in fish tissues. Long chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic acid (ARA), eicosapentaneoic acid (EPA) and docosahexaenoic acid (DHA) are able to modulate the immune status in fish through an inflammatory process but their availability may be limited when fish are exclusively fed plant oils. This study was conducted to evaluate how to maximise the utilisation of dietary plant oil for an efficient inflammatory response in common carp head kidney leukocytes (HKLs) exposed to a gram-negative bacterial endotoxin, Escherichia coli lipopolysaccharides (LPS). HKLs were isolated from fish fed cod liver oil (CLO), linseed oil (LO), sesame oil (SO) a blend of SO and LO (SLO, v:v 1:1), and these plant oil diets supplemented with DHA (SO + DHA, SOD) or ARA (LO + ARA, LOA) for 6 weeks. Cells were then exposed to LPS at a dose of 10 μg/mL for 4 and 24 h. Peroxidase activity, total Ig, and NO levels were measured in the culture medium, while cells were used for expression analyses of candidate genes in pattern recognition (tlr-4), eicosanoid metabolism (pge2, 5-lox), pro-inflammatory (il-1, il-6, il-8, tnf-α, nf-kb, inos, cxc), anti-inflammatory (il-10, nf-kbi, tgf-β1) responses, and cytoprotective (gpx-1, prdx-3) processes. Results showed that LPS induced significantly inflammatory responses, evidenced by a high level of almost all the targeted humoral immune parameters and/or gene expression. Expression of inflammatory cytokines and other inflammatory mediators was upregulated after 4 h-LPS exposure and reverted to basal levels after 24 h. HKLs from fish fed SLO, LOA, or SOD diet exhibited a more efficient regulation of acute inflammatory processes than those fed CLO diet. The results indicate that the immune competence of fish fed plant oil mixture was comparable to the one of fish fed fish oil diet. Moreover, the supplementation of ARA or DHA induced similar immunomodulation in common carp.

Molecular and functional characterization of a mitochondrial glutathione reductase homolog from redlip mullet (Liza haematocheila): Disclosing its antioxidant properties in the fish immune response mechanism

Glutathione reductase (GSHR) is a biologically important enzyme involved in the conversion of oxidized glutathione (GSSG) into its reduced form, reduced glutathione (GSH), with the catalytic activity of NADPH. Most animals and aquatic organisms, including fish, possess high levels of this enzyme system to neutralize oxidative stress in cells. The current study was conducted to broaden our knowledge of GSHR in fish by identifying a mitochondrial isoform of this enzyme (LhGSHRm) in redlip mullet, Liza haematocheila, and clarifying its structure and function. The complete open reading frame of LhGSHRm consists of 1527 base pairs, encoding 508 amino acids, with a predicted molecular weight of 55.43 kDa. Multiple sequence alignment revealed the conservation of important amino acids in this fish. Phylogenetic analysis demonstrated the closest evolutionary relationship between LhGSHRm and other fish GSHRm counterparts. In tissue distribution analysis, the highest mRNA expression of LhGSHRm was observed in the gill tissue under normal physiological conditions. Following pathogenic challenges, the LhGSHRm transcription level was upregulated in a time-dependent manner in the gill and liver tissues, which may modulate the immune reaction against pathogens. rLhGSHRm showed considerable glutathione reductase activity in an enzyme assay. Further, the biological activity of rLhGSHRm in balancing cellular oxidative stress was observed in both disk diffusion and DPPH assays. Collectively, these results support that LhGSHRm has profound effects on modulating the immune reaction in fish to sustain precise redox homeostasis.

Postbiotics Applications as Infectious Disease Control Agent in Aquaculture

Aquaculture is developing so fast that infectious disease outbreak happens regularly. Antibiotic treatment results in development of antibiotic resistance pathogens, thus cause urgent action in searching of other alternative treatment method. Postbiotic was one of the explored strategies among various proposed alternatives. Due to its benefits in agriculture industry, it may be useful in aquaculture industry. Although many reviews were reported on other alternative strategies, the review on postbiotic in aquaculture is limited. This mini review provides an overview of different postbiotics as aquaculture disease control agents. Peptides and exopolysaccharides have antimicrobial properties against bacterial pathogens. Then, short chain fatty acids have both antimicrobial activities against bacterial pathogens and immunostimulating effects to aquatic organism. Vitamins, peptidoglycan and lipopolysaccharide are reported as immunostimulants. Finally, cell surface proteins and teichoic acid can act as vaccine.

Spirulina maxima Derived Pectin Nanoparticles Enhance the Immunomodulation, Stress Tolerance, and Wound Healing in Zebrafish

In this study, Spirulina maxima derived pectin nanoparticles (SmPNPs) were synthesized and multiple biological effects were investigated using in vitro and in vivo models. SmPNPs were not toxic to Raw 264.7 cells and zebrafish embryos up to 1 mg/mL and 200 µg/mL, respectively. SmPNPs upregulated Il 10, Cat, Sod 2, Def 1, Def 2, and Muc 1 in Raw 264.7 cells and tlr2, tlr4b, tlr5b, il1β, tnfα, cxcl8a, cxcl18b, ccl34a.4, ccl34b.4, muc5.1, muc5.2, muc5.3, hamp, cstd, hsp70, cat, and sod1 in the larvae and adult zebrafish, suggesting immunomodulatory activity. Exposure of larvae to SmPNPs followed by challenge with pathogenic bacterium Aeromonas hydrophila resulted a two-fold reduction of reactive oxygen species, indicating reduced oxidative stress compared to that in the control group. The cumulative percent survival of larvae exposed to SmPNPs (50 µg/mL) and adults fed diet supplemented with SmPNPs (4%) was 53.3% and 76.7%, respectively. Topical application of SmPNPs on adult zebrafish showed a higher wound healing percentage (48.9%) compared to that in the vehicle treated group (38.8%). Upregulated wound healing markers (tgfβ1, timp2b, mmp9, tnfα, il1β,ccl34a.4, and ccl34b.4), enhanced wound closure, and restored pigmentation indicated wound healing properties of SmPNPs. Overall, results uncover the multiple bioactivities of SmPNPs, which could be a promising biocompatible candidate for broad range of aquatic and human therapies.

Potentilla alba Extracts Affect the Viability and Proliferation of Non-Cancerous and Cancerous Colon Human Epithelial Cells

The aim of this study was to determine the anti-tumor activity of extracts isolated from Potentilla alba L. on human colon cancer cells of the HT-29 line and on non-cancer colon epithelial cells of the CCD 841 CoTr line. The research methods we used to determine the cytotoxic and proliferative properties were 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and neutral red (NR) assays, the ability to produce nitric oxide, the Griess method, and the biochemical properties like 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) methods indicating reduction activity of tested samples. In order to obtain a phytochemical profile of the different extracts an analytical method based on liquid chromatography-photodiode array detection-electrospray ionization ion-trap time-of-flight mass spectrometry (LC-PDA-ESI-MS/TOF) was applied. Finally, the effects of the extracts on the morphology and cell counts were assessed by May–Grünwald–Giemsa staining. After a comprehensive analysis of all the experiments, the extracts were found to demonstrate cytotoxic properties, they stimulated the division of non-cancer cells, and they were able to scavenge free radicals. In the NR method, the cell viability dropped to approximately 80% compared to the control. In the MTT assay, tumor cell proliferation decreased to 9.5% compared to the control. Therefore, we concluded that this plant has medical potential.

Characterization of the immune roles of cathepsin L in turbot (Scophthalmus maximus L.) mucosal immunity

Cathepsin L (CTSL) is one of the crucial enzymes in cathepsin family, which has been widely known for its involvement in the innate immunity. However, it still remains poorly understood how CTSL modulates the immune system of teleosts. In this study, we captured three cathepsin L genes (SmCTSL, SmCTSL.1 and SmCTSL1) from turbot (Scophthalmus maximus). The coding sequences of SmCTSL, SmCTSL.1 and SmCTSL1 are 1,026 bp, 1,005 bp and 1,017 bp in length and encode 341, 334 and 338 amino acids, respectively. In details, transcripts of CTSL genes share same domains as other CTSL genes, one signal peptide, one propeptide and one papain family cysteine protease domain. Protein interaction network analysis indicated that turbot CTSL genes may play important roles in apoptotic signaling and involve in innate immune response. Evidence from subcellular localization demonstrated that the three Cathepsin L proteins were ubiquitous in nucleus and cytoplasm. The cathepsin L genes were widely expressed in all the tested tissues with the highest expression level of SmCTSL in spleen, and SmCTSL.1 and SmCTSL1 in intestine. Following Vibrio anguillarum, Edwardsiella tarda and Streptococcus iniae challenge, these cathepsin L genes were significantly regulated in mucosal tissues in all the challenges, especially significant down-regulation occurred rapidly in intestine in all the three challenges. In addition, the three cathepsin L genes showed strong binding ability to all the examined microbial ligands (LPS, PGN and LTA). Further studies should be used to analyze the specific function of these three cathepsin L genes. By then, we can use their function to maintain the integrity of the mucosal barrier, thereby promoting the disease resistance line and family selection in turbot.

Advances in salmonid fish immunology: A review of methods and techniques for lymphoid tissue and peripheral blood leucocyte isolation and application

Evaluating studies over the past almost 40 years, this review outlines the current knowledge and research gaps in the use of isolated leucocytes in salmonid immunology understanding. This contribution focuses on the techniques used to isolate salmonid immune cells and popular immunological assays. The paper also analyses the use of leucocytes to demonstrate immunomodulation following dietary manipulation, exposure to physical and chemical stressors, effects of pathogens and parasites, vaccine design and application strategies assessment. We also present findings on development of fish immune cell lines and their potential uses in aquaculture immunology. The review recovered 114 studies, where discontinuous density gradient centrifugation (DDGC) with Percoll density gradient was the most popular leucocyte isolation method. Fish head kidney (HK) and peripheral blood (PB) were the main sources of leucocytes, from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Phagocytosis and respiratory burst were the most popular immunological assays. Studies used isolated leucocytes to demonstrate that dietary manipulations enhance fish immunity, while chemical and physical stressors suppress immunity. In addition, parasites, and microbial pathogens depress fish innate immunity and induce pro-inflammatory cytokine gene transcripts production, while vaccines enhance immunity. This review found 10 developed salmonid cell lines, mainly from S. salar and O. mykiss HK tissue, which require fish euthanisation to isolate. In the face of high costs involved with density gradient reagents, the application of hypotonic lysis in conjunction with mico-volume blood methods can potentially reduce research costs, time, and using nonlethal and ethically flexible approaches. Since the targeted literature review for this study retrieved no metabolomics study of leucocytes, indicates that this approach, together with traditional technics and novel flow cytometry could help open new opportunities for in vitro studies in aquaculture immunology and vaccinology.

In vitro immune response of chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells stimulated by bacterial lipopolysaccharide

We investigated cellular functional and targeted immune cytokine responses of farmed Chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells (PBMCs) in vitro to LPS from Escherichia coli (E. coli) serotypes O111: B4 and O55: B5, and a phorbol ester phorbol 12-myristate 13-acetate (PMA). Bacterial LPS and PMA significantly (p < 0.05) induced reactive oxygen species (ROS) production in O. tshawytscha PBMCs, and enhanced by interferon (IFN)-inducible cytokine production. Cellular phagocytosis was significantly enhanced with PMA and E. coli serotype O111: B4 LPS after 1 and 2 h respectively. At the molecular level, LPS and PMA significantly (p < 0.05) upregulated pro-inflammatory cytokine gene transcripts for IFNγ, TNF-α, and anti-inflammatory IL-10, 24 h post-stimulation. This response is postulated to be mediated via the MyD88 and TRIF pathways in TLR4, or synergistic TLR1 and TLR2 receptors. This is the first report of LPS induced immune related in vitro responses in farmed O. tshawytscha PBMCs.

Measuring the Asian seabass (Lates calcarifer) neutrophil respiratory burst activity by the dihydrorhodamine-123 reduction flow cytometry assay in whole blood

The neutrophil oxidative respiratory burst response is a key component of the innate immune system responsible for killing microbial pathogens. Since fish rely on the innate immune system for health, monitoring the respiratory burst activity may be an effective means of gauging fish health status. Here we report that the respiratory burst of Asian seabass neutrophils can be measured in whole blood by the dihydrorhodamine (DHR)-123 reduction assay and flow cytometry. Neutrophils responded to phorbol myristate acetate (PMA) in a concentration dependent manner with significant respiratory burst activity at 100-1000 nM. Other known neutrophil agonists, such as bacterial lipopolysaccharide, tumor necrosis factor, the tripeptide f-met-leu-phe and zymosan, did not induce a significant DHR reduction. Thus, the findings enable us to propose that the DHR-123 flow cytometry whole blood assay, incorporating PMA as a stimulator, would not only facilitate future studies into fish blood neutrophil research but provides a simple, rapid and reliable assay for gauging fish natural immunity status and health.

Bacteriophage-based cocktail modulates selected immunological parameters and post-challenge survival of rainbow trout (Oncorhynchus mykiss)

Recently, a rapid increase in the resistance of pathogenic bacteria to antibiotics and chemotherapeutics admitted for use in aquaculture has been observed. This happens especially often in intensive breeding. The use of drugs in closed circuits is problematic because it can damage biological filters. Therefore, in recent years, there has been a growing interest in natural methods of combating pathogens. These include bacteriophages. The aim of the study was to determine the safety of the new BAFADOR^® bacteriophage-based preparation, its effect on selected immunological parameters and the effectiveness of prophylactic and therapeutic use after experimental infections with pathogenic bacteria Aeromonas hydrophila and Pseudomonas fluorescens. The use of BAFADOR^® increased the activity of lysozyme, total protein level and immunoglobulin level. The level of ceruloplasmin in the rainbow trout serum remained unchanged regardless of the route of administration of the preparation. Potential killing activity and metabolic activity of spleen phagocytes and proliferation of pronephros lymphocytes were higher compared to the control group. Both therapeutic and prophylactic application of the preparation after mixed experimental infection of A. hydrophila and P. fluorescens limited the mortality of rainbow trout.

Dietary chitosan-selenium nanoparticle (CTS-SeNP) enhance immunity and disease resistance in zebrafish

Selenium (Se) is an essential micronutrient for human and animals. It plays an important role in antioxidative stress, selenoenzymes regulation and immunomodulation. In this study, two common immunostimulants chitosan (CTS) and Se were used to synthesize nanoparticles (CTS-SeNP). Immunomodulation of CTS-SeNP were explored in wild-type zebrafish (Danio rerio). Dietary supplementation of CTS-SeNP enhanced lysozyme activity, phagocytic respiratory burst as well as splenocytes proliferation stimulated by LPS and ConA. CTS-SeNP showed immunomodulation effect from 5 to 20 μg/g but the best outcome was observed at 10 μg/g. Immunomodulation effect were rapidly induced after 3-9d and can sustain to 60. The zebrafish fed with 10 μg/g CTS-SeNP also showed 26.7% higher survival rate than the control after intraperitoneal injection of common bacterium Aeromonas hydrophila. Our results suggested that CTS-SeNP is an effective immunostimulant to fish and has potential application in aquaculture.

Influence of bacteriophages cocktail on European eel (Anguilla anguilla) immunity and survival after experimental challenge

Inland fishery belongs to those branches of animal production that use very large amounts of chemotherapeutics, in particular antibiotics. The accumulation of chemotherapeutic agents in bottom sediments is a direct threat to the aquatic environment and directly affects the condition and health of the fish. Finding a preparation that could be used both prophylactically to increase the resistance of fish and therapeutically in case of infection with pathogenic bacteria, without side effects for fish and aquatic environment could be a great solution to this problem. Our aim was to determine influence of BAFADOR^® the new bacteriophage-based preparation on European eel immunity and survival after experimental challenge. Application of BAFADOR^® increased total protein level, immunoglobulin level, lysozyme activity and ceruloplasmin level in European eel serum. Potential killing activity and metabolic activity of spleen phagocytes as well as pronephros lymphocyte proliferation of was higher compared to control. The preparation also reduced mortality after experimental infections with the pathogenic bacteria Aeromonas hydrophila and Pseudomonas fluorescens. Our results showed that preparation BAFADOR^® is well tolerated by the fish organism causing stimulation of cellular and humoral immunity parameters and reduces the mortality of the European eel after experimental challenge.

The protective efficacy of four iron-related recombinant proteins and their single-walled carbon nanotube encapsulated counterparts against Aeromonas hydrophila infection in zebrafish

Iron-related proteins play important roles in iron homeostasis, and they may be potential vaccine candidates against pathogenic Aeromonas hydrophila. In addition, the encapsulation of antigens in single-walled carbon nanotubes (SWCNTs) has recently been shown to effectively stimulate the host immune response. To investigate the immune response of zebrafish to iron-related proteins and SWCNT-encapsulated proteins, we overexpressed and purified four iron-related recombinant proteins (P55870, A0KGK5, A0KPP0, and A0KIY3) from A. hydrophila. We then vaccinated zebrafish with these proteins and their SWCNT-encapsulated counterparts via both intraperitoneal injection and bath immunization. The target proteins evoked an immune response in zebrafish after intraperitoneal injection, and SWCNT-encapsulation significantly increased the immune response after bath immunization. When challenged with virulent A. hydrophila, zebrafish administered 5 μg intraperitoneal injections of SWCNT-P55870, A0KGK5, A0KPP0, or A0KIY3 had remarkably high relative percent survivals (RPSs) (50%, 55.6%, 66.7%, and 94.44% respectively). The RPSs of zebrafish vaccinated via immunization bath with 40 mg/L SWCNT-encapsulated counterparts were also high (52.94%, 55.56%, 61.11%, and 86.11%, respectively). These results indicated that zebrafish vaccinated with P55870, A0KGK5, SWCNT-P55870, and SWCNT-A0KGK5 were partially protected, while A0KPP0 and A0KIY3 were promising vaccine candidates against pathogenic A. hydrophila infection.

Molecular characterization of kappa class glutathione S-transferase from the disk abalone (Haliotis discus discus) and changes in expression following immune and stress challenges

Glutathione S-transferase (GST; EC 2.5.1.18) isoenzymes represent a complex group of proteins that are involved in phase II detoxification in several organisms. In this study, GST kappa (GSTκ) from the disk abalone (Haliotis discus discus; AbGSTκ) was characterized at both the transcriptional and functional levels to determine its potential capacity to perform as a detoxification agent under conditions of different stress. The predicted AbGSTκ protein consists of 227 amino acids, with a predicted molecular weight of 25.6 kDa and a theoretical isoelectric point (pI) of 7.78. In silico analysis reveals that AbGSTκ is a disulfide bond formation protein A (DsbA), consisting of a thioredoxin domain, GSH binding sites (G-sites), and a catalytic residue. In contrast, no hydrophobic ligand binding site (H-site), or signal peptides, were detected. AbGSTκ showed the highest sequence identity with the orthologue from pufferfish (Takifugu obscurus) (60.0%). In a phylogenetic tree, AbGSTκ clustered closely together with other fish GSTκs, and was evolutionarily distanced from other cytosolic GSTs. The predicted three-dimensional structure clearly demonstrates that the dimer adopts a butterfly-like shape. A tissue distribution analysis revealed that GSTκ was highly expressed in the digestive tract, suggesting it has detoxification ability. Depending on the tissue and time, AbGSTκ showed different expression patterns, and levels of expression, following challenge of the abalone with immune stimulants. Enzyme kinetics of the purified recombinant proteins demonstrated its conjugating ability using 1-Chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH) as substrates, and suggested it has a low affinity for both substrates. The optimum temperature and pH for the rAbGSTκ GSH: CDNB conjugating activity were found to be 35 °C and pH 8, respectively indicating that the abalone is well adapted to a wide range of environmental conditions. Cibacron blue (100 μM) was capable of completely inhibiting rAbGSTκ (100%) with an IC₅₀ (half maximal inhibitory concentration) of 0.05 μM. A disk diffusion assay revealed that rAbGSTκ could significantly protect cells from H₂O₂, CdCl_2, and ZnCl₂. Altogether, this current study suggests that AbGSTκ is involved in detoxification and immunological host defense mechanisms and allows abalones to overcome stresses in order for them to have an increased chance of survival.

Molecular characterization and functional analysis of four teleostean K+ channels in macrophages of sea perch (Lateolabrax japonicas)

Potassium ion channels are one of the most diversely and widely distributed channels, which are involved in all kinds of physiological functions in both excitable and non-excitable cells. The expression of voltage-gated potassium ion (Kv) channels is highly variable according to the state of macrophages activation. Macrophages have an important function in innate immunity against intruding pathogens. They produce a variety of inflammatory and immunoactive molecules that modulate imflammatory responses. Here we show that blockade of K⁺ channels by non-selective Kv channel inhibitor tetraethylammonium chloride (TEA), and 4-aminopyridine (4-AP) inhibited proinflammatory cytokines expression, cell proliferation, and reactive oxygen species (ROS) production in LPS-stimulated macrophages of Sea perch (Lateolabrax japonicas). Then we isolated four Kv channels genes (spKv1.1, spKv1.2, spKv1.5 and spKv3.1) in LPS-activated fish macrophages. These channels genes were up-regulated after LPS stimulation except spKv3.1, which remained unchanged during the test. The results of this study indicate that Kv channels could be required for modulating the immune function of fish macrophages.

EMA and EFSA Joint Scientific Opinion on measures to reduce the need to use antimicrobial agents in animal husbandry in the European Union, and the resulting impacts on food safety (RONAFA)

EFSA and EMA have jointly reviewed measures taken in the EU to reduce the need for and use of antimicrobials in food-producing animals, and the resultant impacts on antimicrobial resistance (AMR). Reduction strategies have been implemented successfully in some Member States. Such strategies include national reduction targets, benchmarking of antimicrobial use, controls on prescribing and restrictions on use of specific critically important antimicrobials, together with improvements to animal husbandry and disease prevention and control measures. Due to the multiplicity of factors contributing to AMR, the impact of any single measure is difficult to quantify, although there is evidence of an association between reduction in antimicrobial use and reduced AMR. To minimise antimicrobial use, a multifaceted integrated approach should be implemented, adapted to local circumstances. Recommended options (non-prioritised) include: development of national strategies; harmonised systems for monitoring antimicrobial use and AMR development; establishing national targets for antimicrobial use reduction; use of on-farm health plans; increasing the responsibility of veterinarians for antimicrobial prescribing; training, education and raising public awareness; increasing the availability of rapid and reliable diagnostics; improving husbandry and management procedures for disease prevention and control; rethinking livestock production systems to reduce inherent disease risk. A limited number of studies provide robust evidence of alternatives to antimicrobials that positively influence health parameters. Possible alternatives include probiotics and prebiotics, competitive exclusion, bacteriophages, immunomodulators, organic acids and teat sealants. Development of a legislative framework that permits the use of specific products as alternatives should be considered. Further research to evaluate the potential of alternative farming systems on reducing AMR is also recommended. Animals suffering from bacterial infections should only be treated with antimicrobials based on veterinary diagnosis and prescription. Options should be reviewed to phase out most preventive use of antimicrobials and to reduce and refine metaphylaxis by applying recognised alternative measures.

In vitro modulation of Drimys winteri bark extract and the active compound polygodial on Salmo salar immune genes after exposure to Saprolegnia parasitica

The rapid development of the aquaculture industry has global concerns with health management and control strategies to prevent and/or treat diseases and increase sustainability standards. Saprolegniosis is a disease caused by Saprolegnia parasitica, and is characterized by promoting an immunosuppression in the host. This study evaluated in vitro the extract and one active compound (polygodial) of Drimys winteri, a Chilean medicinal tree as a potential early immunostimulatory aid in Saprolegniosis control. Atlantic salmon (Salmo salar) head kidney cells (ASK-1) were incubated with both extract and pure polygodial before exposure to S. parasitica mycelium, and the expression of the immune-related genes interleukin 1β (IL-1β), interferon α (IFNα), and major histocompatibility complex II (MHCII) was evaluated. Both evidenced immunomodulatory capacities by increasing gene expressions. This immunomodulation related to a mitigatory action counteracting the immunosuppressing effects of S. parasitica. Despite that most immune-related genes were up-regulated, the down-regulation of MHCII, characteristic of S. parasitica infection, was lessened by pre-incubation with the compounds. This study provides the first insight on the potential of D. winteri bark extract as a possible immunomodulatory and defensive strategy against this oomycete infection in fish.

Immunohistochemical study of inducible nitric oxide synthase and tumour necrosis factor alpha response in turbot (Scophthalmus maximus) experimentally infected with Aeromonas salmonicida subsp. salmonicida

Aeromonas salmonicida subsp. salmonicida represents one of the major threats in aquaculture, especially in salmonid fish and turbot farming. In order to fight bacterial infections, fish have an immune system composed by innate and specific cellular and humoral elements analogous to those present in mammals. However, innate immunity plays a primordial role against bacterial infections in teleost fish. Among these non-specific mechanisms, the production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) pathway and the tumour necrosis factor-alpha (TNFα) produced by mononuclear phagocytes, are two of the main immune effectors to eliminate bacterial pathogens. In this study, the distribution and kinetic of iNOS and TNFα-producing cells of kidney and spleen of turbot experimentally inoculated with A. salmonicida was assessed by immunohistochemistry. In control and challenged fish, individual iNOS(+) and TNFα(+) cells, showing a similar pattern of distribution, were detected. In challenged fish, the number of immunoreactive cells was significantly increased in the evaluated organs, as well as the melanomacrophage centres showed variable positivity for both antigens. These results indicate that A. salmonicida induced an immune response in challenged turbot, which involved the increase of the activity of iNOS and TNFα in the leukocytic population from kidney and spleen.

Pinocembrin attenuates lipopolysaccharide-induced inflammatory responses in Labeo rohita macrophages via the suppression of the NF-κB signalling pathway

Pinocembrin is a flavonoid that has been reported to exhibit various pharmacological and biological activities including antimicrobial, antioxidant, and anti-inflammatory. To explore the anti-inflammatory activity of pinocembrin in a fish cell line, we investigated its ability to regulate the inflammatory mediators elevated by lipopolysaccharide (LPS) in Labeo rohita head-kidney (HK) macrophages. HK macrophages of L. rohita were treated with LPS (1 μg mL(-1)) in the presence or absence of pinocembrin. We examined the inhibitory effect of pinocembrin on LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production. The inhibitory effect of pinocembrin on nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) was investigated by RT-PCR and western blot. The effect of pinocembrin on pro-inflammatory cytokines (tumour necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β)) and anti-inflammatory cytokine IL-10 was investigated by ELISA and RT-PCR. The phosphorylation of three mitogen activated protein kinases (MAPKs) ERK, JNK, and p38 was analysed by western blot. Pinocembrin inhibited LPS-induced productions of NO and PGE2, and also markedly inhibited TNF-α, IL-1β, iNOS, and COX-2 production in a concentration-dependent manner. In addition, TNF-α and IL-1β mRNA expression levels decreased significantly, while IL-10 mRNA expression increased (P < 0.05) with pinocembrin pre-treatment. RT-PCR and western blot analysis showed that pinocembrin decreased both the mRNA and protein expression levels of LPS-induced iNOS and COX-2 in HK macrophages. Pinocembrin suppressed the phosphorylation of MAPK in LPS-stimulated HK macrophages. Further, pinocembrin significantly inhibited LPS-induced NF-κB transcriptional activity via the attenuation of IκBα degradation. Taken together, pinocembrin reduced the levels of pro-inflammatory mediators, such as iNOS, COX-2, TNF-α, and IL-1β, by inhibiting NF-κB activation via the suppression of ERK and p38 phosphorylation, and by attenuating the degradation of IκBα. These results suggest that pinocembrin is a potential novel candidate for the treatment of inflammatory conditions in L. rohita macrophages.

TLR21's agonists in combination with Aeromonas antigens synergistically up-regulate functional TLR21 and cytokine gene expression in yellowtail leucocytes

The purpose of this study was to characterize the TLR21 gene from yellowtail (Seriola lalandi) and its functional activity using TLR agonist stimulation and Aeromonas antigens. The TLR21 nucleotide sequence from yellowtail was obtained using the whole-genome shotgun sequencing method and bioinformatics tools. Basal TLR21 gene expression was analyzed in several tissues. Subsequently, the gene expression of TLR21 and cytokines IL-1β and TNF-α was evaluated in TLR agonist (CpG-ODN2006, LPS, and Poly I:C) exposing head kidney leucocytes, which were then subjected to Aeromonas antigen stimulation. The yellowtail full-length cDNA sequence of SlTLR21 was 3615 bp (980 aa) showing a high degree of similarity with the counterparts of other fish species and sharing the common structural architecture of the TLR family, including LRR domains, one C-terminal LRR region, and a TIR domain. Gene expression studies revealed the constitutive expression of TLR21 mRNA in all the analyzed tissues; the highest levels were observed in spleen and head kidney where they play an important role in the fish immune system. Transcripts of TLR21 and the downstream IL-1β and TNF-α cytokine genes were most strongly up-regulated after exposure to the TLR agonists following Aeromonas antigen stimulation, suggesting they are involved in immune response. The results indicated that TLR agonists, in combination with Aeromonas antigens in head kidney leucocytes, synergistically enhance TLR21 and cytokines in yellowtail.

Role of Bacillus subtilis VSG4-derived biosurfactant in mediating immune responses in Labeo rohita

This study aimed to isolate biosurfactant from CO2-sequestering Bacillus subtilis VSG4 and to evaluate its immunostimulatory effect in Labeo rohita fingerlings. Fish were injected intraperitoneally (i.p.) with 0.1 mL of phosphate-buffered saline (PBS) containing the water-soluble fraction of purified biosurfactant at 50 (S50), 100 (S100), 200 (S200), or 300 (S300) μg mL(-1). Fish injected with PBS served as controls. Various immunological parameters, including immune-related gene expression, were measured at 14, 21, and 28 days post administration (dpa). At 28 dpa, the fish were challenged with Aeromonas hydrophila and mortality was recorded up to 14 days. Among the immune parameters tested, lysozyme levels (36.32 ± 1.79 U mL(-1)), alternative complement pathway activity (76.26 ± 2.18 U mL(-1)), phagocytic activity (32.18 ± 0.67%), and serum bactericidal activity (73.2 ± 4.7%) were significantly higher (P < 0.05) in the S200 group at 21 dpa than in the controls. Respiratory burst activity (0.386 ± 0.008 OD630nm) was the highest in the S200 group at 28 dpa. Of the immune-related genes examined, pro-inflammatory cytokines (TNF-α and IL-1β) were significantly down-regulated in the S200 and S300 groups. Expression of anti-inflammatory cytokines (IL-10 and TGF-β) as well as IKB-α was higher (P < 0.05) in the S100‒S300 groups at 21 dpa. The expression of NF-κB p65, IKK-β, MAPKp38, and Myd88 was down-regulated in the treated groups when compared to the controls. Fish in the S200 group exhibited the highest post-challenge relative survival rate (67.88%). Collectively, these results suggest that secondary metabolite (biosurfactant) isolated from B. subtilis VSG4 at 200 μg mL(-1) can positively influence immune responses, enhance disease resistance, and stimulate immune-related gene expression in L. rohita.

Aflatoxin B1 degradation by liquid cultures and lysates of three bacterial strains

Aflatoxin contamination remains a daunting issue to address in food safety. In spite of the efforts geared towards prevention and elimination of this toxin, it still persists in agricultural commodities. This has necessitated the search for other measures such as microbial degradation to combat this hazard. In this study, we investigated the biodegradation of aflatoxin B1 (AFB1), using lysates of three bacterial strains (Pseudomonas anguilliseptica VGF1, Pseudomonas fluorescens and Staphylococcus sp. VGF2) isolated from a gold mine aquifer. The bacterial cells were intermittently lysed in the presence and absence of protease inhibitors to obtain protease free lysates, subsequently incubated with AFB1 for 3, 6, 12, 24, and 48h to investigate whether any possible AFB1 degradation occurred using high performance liquid chromatography (HPLC) for detection. Results obtained revealed that after 6h of incubation, protease inhibited lysates of Staphylococcus sp. VGF2 demonstrated the highest degradation capacity of 100%, whereas P. anguilliseptica VGF1 and P. fluorescens lysates degraded AFB1 by 66.5 and 63%, respectively. After further incubation to 12h, no residual AFB1 was detected for all the lysates. Lower degrading ability was however observed for liquid cultures and uninhibited lysates. Data on cytotoxicity studies against human lymphocytes showed that the degraded products were less toxic than the parent AFB1. From this study, it can thus be deduced that the mechanism of degradation by these bacterial lysates is enzymatic. This study shows the efficacy of crude bacterial lysates for detoxifying AFB1 indicating potential for application in the food and feed industry.

Protective effects of leucine against lipopolysaccharide-induced inflammatory response in Labeo rohita fingerlings

The present study investigated the protective effects of leucine against lipopolysaccharide (LPS)-induced inflammatory responses in Labeo rohita (rohu) in vivo and in vitro. Primary hepatocytes, isolated from the hepatopancreas, were exposed to different concentrations of LPS for 24 h to induce an inflammatory response, and the protective effects of leucine against LPS-induced inflammation were studied. Finally, we investigated the efficiency of dietary leucine supplementation in attenuating an immune challenge induced by LPS in vivo. Exposure of cells to 10-25 μg mL(-1) of LPS for 24 h resulted in a significant production of nitric oxide and release of lactate dehydrogenase to the medium, whereas cell viability and protein content were reduced (p < 0.05). LPS exposure (10 μg mL(-1)) increased mRNA levels of the pro-inflammatory cytokines TNF-α, IL-1β and IL-8 in vitro (p < 0.05). However, pretreatment with leucine prevented the LPS-induced upregulation of TNF-α, IL-1β and IL-8 mRNAs by downregulating TLR4, MyD88, NF-κBp65, and MAPKp38 mRNA expression. Interestingly, mRNA expression of the anti-inflammatory cytokine, IL-10, which was increased by LPS treatment, was further enhanced (p < 0.05) by leucine pretreatment. The enhanced expression of IL-10 might inhibit the production of other pro-inflammatory cytokines. It was found that leucine pretreatment attenuated the excessive activation of LPS-induced TLR4-MyD88 signaling as manifested by lower level of TLR4, MyD88, MAPKp38, NF-κBp65 and increased level of IκB-α protein in leucine pre-treatment group. In vivo experiments demonstrated that leucine pre-supplementation could protect fish against LPS-induced inflammation through an attenuation of TLR4-MyD88 signaling pathway. Taken together, we propose that leucine pre-supplementation decreases LPS-induced immune damage in rohu by enhancing the expression of IL-10 and by regulating the TLR4-MyD88 signaling pathways.

Heat-killed whole-cell products of the probiotic Pseudomonas aeruginosa VSG2 strain affect in vitro cytokine expression in head kidney macrophages of Labeo rohita

Present study was undertaken to investigate the efficiency of heat-killed whole-cell products (HKWCPs) of probiotic Pseudomonas aeruginosa VSG2 strain in stimulating the cytokine responses in the head kidney (HK) macrophages of Labeo rohita. The HK macrophages were incubated with HKWCPs or lipopolysaccharide (LPS), and the responses of cytokine genes, namely interleukin-10 (IL-10), IL-1β, IL-p35, IL-12p40, tumour necrosis factor-α (TNF-α), nuclear factor kappa B (NF-κB), cyclooxygenase-2 (COX-2), interferon-alpha (IFN-α), and interferon-gamma (IFN-γ) were assessed by quantitative real-time PCR (qRT-PCR) at 2, 8, 16, 24, 48, 72 h post-stimulation (hps). Among proinflammatory cytokines, significantly higher expression of IL-1β and TNF-α was observed at 8-24 hps, and 2-16 hps with HKWCPs, respectively, as compared to controls. However, COX-2 and NF-κB displayed strong expression (P < 0.05) at 2-8 hps, and 8, 16 and 72 hps with HKWCPs, respectively. Antiviral cytokines IFN-α and IFN-γ displayed strong expression (P < 0.05) at 8-24 hps, and 2, 24 and 48 hps with HKWCPs, respectively. Expressions of cell-mediated immune factor genes (IL-12p35 and IL-12p40) were also significantly upregulated at various time points, except IL-12p40 at 72 hps, in HK macrophages stimulated with HKWCPs. Expression of the anti-inflammatory cytokine IL-10 was upregulated (P < 0.05) at 2-24 hps HKWCPs, compared to controls. Enhanced cellular (phagocytic activity and superoxide anion production) and humoral (lysozyme) immune parameters of treated HK macrophages confirmed the induction of inflammatory response. Thus, our results indicated that HKWCPs of probiotic P. aeruginosa VSG2 had greater potential for stimulating the in vitro expression of cytokines in fish and that these HKWCPs may be used as vaccine adjuvants in aquaculture.

Cathepsin L of the sea cucumber Apostichopus japonicus-molecular characterization and transcriptional response to Vibrio splendidus infection

Cathepsin L, a lysosomal endopeptidase, has been noted for its involvement in the innate immune response in invertebrates. Here, the cathepsin L cDNA of the sea cucumber Apostichopus japonicus (AjCatL) is identified from an EST library and then cloned by the rapid amplification of the cDNA ends (RACE) PCR. The full-length cDNA is 1678 bp long containing an open reading frame (ORF) of 1002 bp, an 80 bp 5' UTR and a 599 bp 3' UTR. The cDNA encodes 333 amino acid residues with a predicted molecular mass of 37.07 kDa and a theoretical isoelectric point (pI) of 5.01. The full-length AjCatL contains three active sites of eukaryotic thiol (cysteine) protease at positions 133-144, 278-288 and 295-314. Analysis of the predicted tertiary structure of prepro-CatL (17-333 aa) and mature-CatL (116-333 aa) reveals that the propeptide region (17-115 aa) blocks access to the substrate-binding cleft. Phylogenetic analysis shows that the AjCatL is clustered together with two other CatLs from Strongylocentrotus purpuratus. The enzymatic activity of AjCatL was verified using a substrate hydrolyzing assay with recombinant mAjCatL. Further analysis of real time-PCR demonstrates that the expression of AjCatL mRNA is significantly up-regulated in the coelomocytes in cases of infection with the common bacterial pathogen, Vibrio splendidus. This suggests that the AjCatL is likely to be involved in the immune response.

Effects of intracellular products of Bacillus subtilis VSG1 and Lactobacillus plantarum VSG3 on cytokine responses in the head kidney macrophages of Labeo rohita

The efficiency of intracellular products (ICPs) of the probiotics Bacillus subtilis VSG1 and Lactobacillus plantarum VSG3 in stimulating cytokine responses in the head kidney (HK) macrophages of Labeo rohita was investigated. The HK macrophages were incubated with ICPs and lipopolysaccharide (LPS), and the responses of cytokine genes, namely interleukin-10 (IL-10), IL-1β, IL-12p35, IL-12p40, IL-18, tumour necrosis factor-α (TNF-α), nuclear factor kappa B (NF-κB), cyclo-oxygenase-2 (COX-2), interferon-1 (IFN-1), and IFN-γ were assessed by quantitative real-time PCR (qRT-PCR) at 2, 6, 12, 24, and 48 h post-stimulation (hps). Among the proinflammatory cytokines, a strong increase in the gene expression of IL-1β and TNF-α was displayed mainly at 2-6 hps with ICPs, as compared to that of the positive control (LPS) or the negative control (PBS) (P < 0.05). However, COX-2 and NF-κB showed higher expression at 2 and 24 hps, and 6-24 hps with ICPs, respectively. Antiviral cytokines IFN-1 and IFN-γ displayed strong expressions (P < 0.05) at 6-12 hps, and 12-24 hps with ICPs, respectively. Upregulation of the anti-inflammatory cytokine, IL-10, was recorded at 6-24 hps with ICPs, as compared to that controls. Expressions of cell-mediated immune factor genes (IL-12p35, IL-12p40, and IL-18) were also significantly upregulated at different time points, except 48 hps, in HK macrophages stimulated with ICPs. Furthermore, enhanced cellular (phagocytic activity and nitroblue tetrazolium assay) and humoral (lysozyme) immune parameters in stimulated cells confirmed the induction of the inflammatory response. Therefore, the results of this in vitro study indicate that the ICPs of B. subtilis VSG1 or L. plantarum VSG3 have great potential for stimulating the cytokine responses in fish, and are thereby potential immunostimulants to fish. Further studies could be conducted to explore its suitability as an adjuvant vaccine in aquaculture.

Probiotics, immunostimulants, plant products and oral vaccines, and their role as feed supplements in the control of bacterial fish diseases

There is a rapidly increasing literature pointing to the success of probiotics, immunostimulants, plant products and oral vaccines in immunomodulation, namely stimulation of the innate, cellular and/or humoral immune response, and the control of bacterial fish diseases. Probiotics are regarded as live micro-organisms administered orally and leading to health benefits. However, in contrast with the use in terrestrial animals, a diverse range of micro-organisms have been evaluated in aquaculture with the mode of action often reflecting immunomodulation. Moreover, the need for living cells has been questioned. Also, key subcellular components, including lipopolysaccharides, have been attributed to the beneficial effect in fish. Here, there is a link with immunostimulants, which may also be administered orally. Furthermore, numerous plant products have been reported to have health benefits, namely protection against disease for which stimulation of some immune parameters has been reported. Oral vaccines confer protection against some diseases, although the mode of action is usually linked to humoral rather than the innate and cellular immune responses. This review explores the relationship between probiotics, immunostimulants, plant products and oral vaccines.

The in vitro immunomodulatory effect of extracellular products (ECPs) of Vagococcus fluvialis L21 on European sea bass (Dicentrarchus labrax) leucocytes

The immune associated genes, interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin 10 (IL-10), tumor necrosis factor-α (TNF-α), ciclo-oxigenase-2 (COX-2), and Mx gene were studied by real-time PCR in head-kidney leucocytes of sea bass after incubation with the extracellular products (ECPs) of the probiotic strain Vagococcus fluvialis L21 and polyinosinic:polycytidylic acid (POLY I:C), at different times (T1.5, T6, T12, T24, T48 and T72). In general, we can observe how pro-inflammatory cytokines IL-1β, TNF-α, IL-6 and COX-2 studied displayed a strong peak after stimulation with 1.5 h of ECPs of V. fluvialis L21, significant differences (P < 0.05) exist with other periods and with the POLY I: C at the same time. Similarly to the case of IL-10 also produced a statistically significant (P < 0.05) peak of expression on leukocytes that were stimulated with the ECPs of V. fluvialis L21. In the case of Mx gene expression, we note that in almost all sampling times there is an up-regulation of the Mx gene in leucocytes incubated with ECPs and POLY I:C compared to the control and Mx expression was higher in leucocytes that were stimulated with the ECPs of V. fluvialis for all times, except in T24. With these results we can consider that the ECPs of V. fluvialis L21 have a great power of stimulating the in vitro expression of immune-related genes and may even be useful as adjuvants for vaccine in aquaculture.

Effects of aluminium and bacterial lipopolysaccharide on oxidative stress and immune parameters in roach, Rutilus rutilus L

Aluminium is used in diverse anthropogenic processes at the origin of pollution events in aquatic ecosystems. In the Champagne region (France), high concentrations of aluminium (Al) are detected due to vine-growing practices. In fish, little is known about the possible immune-related effects at relevant environmental concentrations. The present study analyzes the simultaneous effects of aluminium and bacterial lipopolysaccharide (LPS), alone and in combination, on toxicological biomarkers in the freshwater fish species Rutilus rutilus. For this purpose, roach treated or not with LPS were exposed to environmental concentrations of aluminium (100 μg/L) under laboratory-controlled conditions for 2, 7, 14 and 21 days. After each exposure time, we assessed hepatic lipoperoxidation, catalase activity, glutathione reductase activity and total glutathione content. We also analyzed cellular components related to the LPS-induced inflammatory response in possible target tissues, i.e. head kidney and spleen. Our results revealed a significant prooxidant effect in the liver cells and head kidney leukocytes of roach exposed to 100 μg of Al/L for 2 days. In liver, we observed more lipoperoxidation products and lower endogenous antioxidant activity levels such as glutathione reductase activity and total glutathione content. These prooxidant effects were associated with a higher oxidative burst in head kidney leukocytes, and they were all the more important in fish stimulated by LPS injection. These findings demonstrate that environmental concentrations of Al induce oxidative and immunotoxic effects in fish and are associated to an immunomodulatory process related to the inflammatory response.

Can immunostimulants efficiently replace antibiotic in striped catfish (Pangasianodon hypophthalmus) against bacterial infection by Edwardsiella ictaluri?

The present study was performed to determine the efficacy of lipopolysaccharide (LPS) and levamisole on immune response and disease resistance in striped catfish and to compare their respective efficiency with the one of an antibiotic treatment after infection of fish by the bacteria Edwardsiella ictaluri. Fish were divided into 3 groups and each group was injected with LPS (3 mg/kg fish), levamisole (5 mg/kg fish) or phosphate buffer saline as control. At day 21st post immunostimulant injection, fish were bled for assaying immunological variables and then challenged with E. ictaluri. Three days after bacterial infection, an antibiotic treatment was applied into fish subgroups and mortality was compared daily between antibiotic treated and untreated fish until 2 weeks post-challenge. LPS and levamisole significantly enhanced non-specific immune responses such as respiratory burst, lysozyme and complement activity in fish compared with control (p < 0.05). Respiratory burst and complement activity significantly increased in levamisole groups when compared with LPS groups while lysozyme activity did not differ significantly between immunostimulant treatments. Total immunoglobulins significantly increased in levamisole treatment compared with control. After challenge test, accumulated mortality was reduced significantly in both non-antibiotic and antibiotic subgroups of LPS and levamisole compared with control. Moreover, no differences of mortality were observed between fish treated with levamisole or LPS without antibiotics and control fish treated with antibiotics. These results support the possible replacement of antibiotics in striped catfish farming by immunostimulants such as levamisole and LPS.

Application of bacterial lipopolysaccharide to improve survival of the black tiger shrimp after Vibrio harveyi exposure

This study investigates an effect of bacterial lipopolysaccharide (LPS) as feed supplement to improve immunity of the black tiger shrimp (Penaeus monodon). LPS was coated to commercial feed pellets and given to the shrimp once or twice a day for 10 days before an exposure with shrimp pathogenic bacterium Vibrio harveyi. The growth rates, percent weight gains, total hemocyte and granulocyte counts and survival rates of shrimp between the LPS-coated pellet fed groups and a control group where shrimp fed with commercial feed pellets were compared. After 10 days of the feeding trials, growth rates were not significantly different in all groups, suggesting no toxicity from LPS supplement. To determine beneficial effect of LPS diets, each group was subsequently exposed to V. harveyi by immersion method and the survival rates were recorded for seven days after the immersion. Regardless of the dosages of LPS, the shrimp groups fed with LPS-coated pellets showed higher survival rates than the control group. There was no significant difference in survival rates between the two LPS dosages groups. In addition to survival under pathogen challenge, we also determine effect of LPS on immune-related genes after 10-day feeding trial. Gene expression analysis in the P. monodon intestines revealed that antilipopolysaccharide factor isoform 3 (ALF3), C-type lectin, and mucine-like peritrophin (mucin-like PM) were expressed significantly higher in a group fed with LPS supplemental diet once or twice a day than in a control group. The transcript levels of C-type lectin and mucin-like PM had increased significantly when LPS was given once a day, while significant induction of ALF3 transcripts was observed when shrimp were fed with LPS twice a day. The up-regulation of the immune gene levels in intestines and higher resistance to V. harveyi of the shrimp fed with LPS provide the evidence for potential application of LPS as an immunostimulant in P. monodon farming.

Effects of dietary inulin, Bacillus subtilis and microalgae on intestinal gene expression in gilthead seabream (Sparus aurata L.)

The present work describes effects of dietary inulin, two microalgae (Tetraselmis chuii and Phaeodactylum tricornutum) and Bacillus subtilis (solely or combined with inulin or microalgae) on the expression of different genes in the intestine of the gilthead seabream (Sparus aurata L.) following four weeks of a feeding trial. Selected genes were grouped into five categories: genes involved in inflammation (genes encoding proinflammatory proteins), genes related to the cytoskeleton, genes encoding proteins of junction complexes, genes implicated in digestion processes and genes related to transport proteins. Regarding proinflammatory genes, interleukin-8 (IL-8) expression showed a significant increase in the fish fed all the assayed diets, except the B. subtilis + inulin diet, whereas the expression of caspase-1 (CASP-1) was also increased by the B. subtilis and B. subtilis + T. chuii diets. Cyclooxygenase-2 (COX-2) gene expression only increased in fish fed the B. subtilis diet. Among cytoskeletal and junctional genes, only β-actin and occludin were significantly affected by the assayed diets. β-actin expression was up-regulated by the inulin-containing diets (inulin and B. subtilis + inulin diets), whereas occludin expression increased in the fish fed all the assayed diets, except the P. tricornutum diet. Finally, the expression of transport protein genes demonstrated that the inulin diet and all the experimental diets containing B. subtilis significantly increased transferrin expression, whereas digestive enzymes were not affected by the experimental diets. In conclusion, our results demonstrated that inulin, B. subtilis and microalgae can modulate intestinal gene expression in the gilthead seabream. To our knowledge, this is the first study of the effects of some food additives on the intestinal expression of different genes in this species. More studies are needed to understand the role of these genes in maintaining the integrity and functionality of the intestine.

Histological alterations and microbial ecology of the intestine in gilthead seabream (Sparus aurata L.) fed dietary probiotics and microalgae

The effects on histology and microbial ecology in gilthead seabream (Sparus aurata) intestine caused by dietary probiotic and microalgae were studied. Fish were fed non-supplemented (C, control) or supplemented diets with Tetraselmis chuii, Phaeodactylum tricornutum and Bacillus subtilis single or combined (diets T, P, B, BT and BP) for 4 weeks. Curiously, fish fed the experimental diets showed similar morphological alterations when studied by light and electron microscopy and significant signs of intestinal damage were detected. No effect of microalgae or B. subtilis on the intestinal absorptive area was observed, whereas the number of goblet cells and IELs were significantly lower in fish fed the T, P, B and BT diets and T, BT and BP diets, respectively. Interestingly, only the diets containing B. subtilis resulted in a significant reduction of microvilli height. Alterations such as wide intercellular spaces and large vacuoles in enterocytes were observed in fish fed T, B, BT, BT and P in lesser degrees. These observations demonstrate that fish fed experimental diets presented different signs of oedema and inflammation that could compromise their body homeostasis. Moreover, the experimental diets cause important alterations in the intestinal microbiota by a significant decrease in bacterial diversity, as demonstrated by the fall in specific richness, Shannon and range-weighted richness indices. To our knowledge, this is the first in vivo study regarding the implications of the use of probiotics in combination with immunostimulants on fish intestinal morphology and microbiota. More morphofunctional studies are needed in order to correlate the nutritional and immune aspects of fish gut.

Behavioural fever boosts the inflammatory response in rainbow trout Oncorhynchus mykiss

Behavioural fever, manifested as an increased preferred temperature, was shown in rainbow trout Oncorhynchus mykiss following an injection of bacterial lipopolysaccharide. Simulated behavioural fever, through a 2·5° C water temperature rise following bacterial lipopolysaccharide injection, enhanced the expression of the cytokine interleukin-1β, in comparison with an untreated group held at the initial temperature. The present findings show that an important mediator in the immune response can be boosted through behavioural fever in fishes.

Bacterial composition and activity determines host gene-expression responses in gnotobiotic Atlantic cod (Gadus morhua) larvae

In this study the effects of different live versus dead bacteria on the survival and gene-expression patterns in Atlantic cod (Gadus morhua) larvae were examined. Seventeen different gnotobiotic conditions were tested in a 5-day experiment, and the effects of these conditions on the expression of selected genes involved in immune response, xenobiotic breakdown and nutrition (C3, Gpx, Cyp1a1 and Fdps) were investigated. For some of the conditions where dead bacteria were added, we observed significantly higher survival compared to the axenic control. Microbial specificity of host-responses was observed for all four genes, for both live and dead bacteria, although expression of Gpx and Fdps was more influenced by active bacteria. Live bacteria generally resulted in higher transcript levels of all the genes investigated, indicating that these host-responses are partly dependent on microbial activity, and not just due to interactions with bacteria as particles. The observed microbial specificity toward dead bacteria highlights the need to take into account the role of bacterial components when investigating host-microbe relationships.

Antimicrobial mechanisms of fish leukocytes

Early activation and coordination of innate defenses are critical for effective responses against infiltrating pathogens. Rapid engagement of immune cells provides a critical first line of defense soon after pathogen infiltration. Activation leads to a well-orchestrated set of events that sees the induction and regulation of intracellular and extracellular antimicrobial defenses. An array of regulatory mediators, highly toxic soluble molecules, degradative enzymes and antimicrobial peptides provides maximal protection against a wide range of pathogens while limiting endogenous damage to host tissues. In this review we highlight recent advances in our understanding of innate cellular antimicrobial responses of teleost fish and discuss their implications to cell survival, immunomodulation and death. The evolutionary conservation of these responses is a testament to their effectiveness against pathogen infiltration and their commitment to effective maintenance of host homeostasis. Importantly, recent developments in teleost fish systems have identified novel host defense strategies that may be unique to this lower vertebrate group or may point to previously unknown innate mechanisms that also play a significant role in higher vertebrate host immunity.

Transcriptomic responses to functional feeds in Atlantic salmon (Salmo salar)

Functional feeds are diets that have positive effects on both health and growth promoting performance of the animals ingesting them, by supplying additional compounds above and beyond the basic nutritional requirements for animal growth alone. The most common additives used in aquaculture diets are probiotics, prebiotics, immunostimulants, vitamins and nucleotides. Inclusion of these components to fish diets can increase feed conversion efficiency and growth, as well as having positive effects on the fish immune system. This review discusses the results from previous studies on fish nutrition and includes a novel genomic approach, using microarray analysis, to elucidate nutritional responses in Atlantic salmon (Salmo salar) fed a newly developed functional feed health premix diet. The transcriptome analysis demonstrated that compared to the standard diet feeding with the functional feed had significant effects on biological processes in the liver. This resulted in a reduction of the expression of genes related to protein turnover, reduced circulating plasma proteins and a down regulation of genes involved in the immune response. These results suggest that the functional feed may infer a decrease in whole body metabolic demands, suppressing both protein turnover and whole body oxygen demand, as well as down regulating several genes involved in the innate immune system. Together these changes appear to result in less energy wastage in fish and an enhanced growth and performance.