Comparative transcriptional analysis reveals distinct expression patterns of channel catfish genes after the first infection and re-infection with Aeromonas hydrophila

Innate immune and chronic heat stress responses in sturgeons: Advances and insights from studies on Russian sturgeons

Chronic stress deteriorates the immune function of fish, thereby increasing their vulnerability to infections. However, the molecular and cellular mechanisms underlying stress-mediated immunosuppression and infection susceptibility in fish remain largely unknown. Understanding these mechanisms will contribute to improving fish welfare and their farm production. Herein, we review the challenges of sturgeon aquaculture in subtropical countries, where current climate change has giving rise to significant temperature increments during summer. This leads to the exposure of fish to stressful conditions during these months. Chronic heat stress deserves attention considering the rapid warming rate of the planet. It is already affecting wild fish populations, with disastrous consequences for sturgeons, which are one of the most endangered fish species in the world. In this context, we discuss the most recent advances through the studies on the effects of chronic heat stress on the innate immune components of sturgeons. To this end, we summarise the findings of studies focusing on the aquaculture of Russian sturgeons and observations made on other Acipenser species. Special attention is given to acute-phase proteins, as they might be valuable biomarkers of heat stress and infection, with applicability in monitoring the fish health status in farms.

CcGSDMEa functions the pore-formation in cytomembrane and the regulation on the secretion of IL-lβ in common carp (Cyprinus carpio haematopterus)

GSDME is the only direct executor of caspase-dependent pyroptosis in both canonical and non-canonical inflammasomes known to date in fish, and plays an important role in anti-bacterial infection and inflammatory response. In order to determine the regulation of GSDMEa on antibacterial infection in innate immune response, the CcGSDMEa gene in common carp (Cyprinus carpio haematopterus) was first identified and characterized, and then its function related to immune defense was investigated. Our results showed that the expressions of CcGSDMEa at the mRNA and protein levels were both significantly increased after Aeromonas hydrophila intraperitoneal infection at the early stage than that in the control group. We found that CcGSDMEa could be cleaved by inflammatory caspase (CcCaspase-1b) and apoptotic caspases (CcCaspase-3a/b and CcCaspase-7a/b). Interestingly, only the CcGSDMEa-NT (1-252 aa) displayed bactericidal activity to Escherichia coli and could punch holes in the membrane of HEK293T cells, whereas CcGSDMEa-FL (1-532 aa) and CcGSDMEa-CT (257-532 aa) showed no above activity and pore-forming ability. Overexpression of CcGSDMEa increased the secretion of CcIL-1β and the release of LDH, and could reduce the A. hydrophila burdens in fish. On the contrary, knockdown of CcGSDMEa reduced the secretion of CcIL-1β and the release of LDH, and could increase the A. hydrophila burdens in fish. Taken together, the elevated expression of CcGSDMEa was a positive immune response to A. hydrophila challenge in fish. CcGSDMEa could perform the pore-formation in cell membrane and the regulation on the secretion of IL-lβ, and further regulate the bacterial clearance in vivo. These results suggested that CcGSDMEa played an important role in immune defense against A. hydrophila and could provide a new insight into understanding the immune mechanism to resist pathogen invasion in teleost.

Different response of Acipenser gueldenstaedtii CRP/SAP and SAA to bacterial challenge and chronic thermal stress sheds light on the innate immune system of sturgeons

Sturgeons are chondrostean fish critically endangered due to anthropogenic loss and degradation of natural habitat and overfishing for meat and caviar production. Consequently, sturgeon aquaculture has extensively developed lately, being Russian sturgeon (Acipenser gueldenstaedtii) the second most important species reared for caviar production. However, Russian sturgeon aquaculture in subtropical countries, such as Uruguay, confronts difficulties because fish have to endure excessive summertime warm temperatures, which weaken their innate defences facilitating opportunistic infections. To address this problem, we look for identifying putative acute phase proteins (APPs), which might be robust serum biomarkers of both infection and chronic thermal stress, applied to monitoring Russian sturgeon health status in farms. We focused on the C-Reactive Protein/Serum Amyloid P (CRP/SAP) pentraxin since the pentraxin family includes well-known APPs, better characterised in mammals than fish. We identified A.gueldenstaedtii CRP/SAP (AgCRP/SAP), as a member of the universal CRP/SAP pentraxin sub-family, and studied AgCRP/SAP involvement in sturgeon response to bacterial challenge and chronic thermal stress, in comparison with A. gueldenstaedtii Serum Amyloid A (AgSAA), a previously described positive APP. Results showed that AgCRP/SAP is a constitutive serum component that remained constant upon Aeromonas hydrophila challenge and chronic thermal stress. Contrastingly, serum AgSAA was subjected to regulation by bacterial and thermal stress challenges, showing a 50-fold increase and 3-fold decline in serum levels, respectively. Overall, results highlight the potential value of AgSAA, but not of AgCRP/SAP, as a biomarker of bacterial infection and the need to continue searching for robust chronic thermal stress biomarkers in sturgeons.

Aeromonas hydrophila infection induces Toll-like receptor 2 (tlr2) and associated downstream signaling in Indian catfish, Clarias magur (Hamilton, 1822)

Motile Aeromonas septicaemia (MAS), caused by Aeromonas hydrophila, is one of the most significant bacterial disease responsible for mortality in Indian catfish, Clarias magur, a potential aquaculture species in the Indian subcontinent. In fish, innate immunity elicited by pathogen recognition receptors (PRRs) plays an important role in providing protection against bacterial infection. Information on PRRs including Toll-like receptors (tlrs) and their response to bacterial pathogens remains unexplored in magur. Toll-like receptor 2 (tlr2), a phylogenetically conserved germ-line encoded PRR recognizes specific microbial structure and trigger MyD88-dependent signaling pathway to induce release of various cytokines responsible for innate immune response. In the present study, tlr2 gene of magur was characterized and downstream signaling was studied following challenge with A. hydrophila. The full-length cDNA of magur tlr2 (mtlr2) comprised of 3,066 bp with a single open reading frame of 2,373 bp encoding 790 amino acids having a theoretical pI value of 6.11 and molecular weight of 90 kDa. Structurally, it comprised of signal peptide (1–42aa), one leucine-rich repeat region (LRR) at N-terminal (LRR1-NT: 50–73 aa) and C-terminal (LRR-CT: 588–608 aa), twenty LRRs in between, one trans-membrane (Tm) domain (609–631aa) followed by cytoplasmic TIR domain (670–783aa). Phylogenetically, mtlr2 is closely related to pangasius and channel catfish. Highest basal expression of mtlr2, myd88 and il-1β in spleen, nf-kb in anterior kidney was observed. Lowest basal expression of mtlr2 in skin and myd88, nf-kb and il-1β in muscle was detected. Significant up-regulation of mtlr2 and downstream expression occurred at 3, 8, 24 h post infection to A. hydrophila in important immune organs such as liver, spleen, intestine and kidney. These findings highlight the vital role of tlr2 in eliciting innate immune defence against A. hydrophila infection.

Molecular structure, expression, and function analysis of BAFF gene in Chinese sucker, Myxocyprinus asiaticus

B cell activating factor (BAFF), belonging to the tumor necrosis factor superfamily (TNFSF), is a critical cytokine for B cell survival and immunoglobulin secretion. Here, the BAFF gene of Chinese sucker (Myxocyprinus asiaticus) (MaBAFF) was cloned using RT-PCR and RACE (rapid amplification of cDNA end) techniques. The open reading frame (ORF) of MaBAFF encodes a 272-amino acid protein containing a transmembrane domain, a TNF family signature, and a putative furin protease cleavage site as seen in BAFFs from other species. Tissue expression profiles of MaBAFF determined by absolute and relative quantification of real-time quantitative PCR (qPCR) showed that MaBAFF is widely distributed in various tissues, with the highest expression in spleen. MaBAFF can be detected during fertilized egg period by RT-PCR. Upon induction by A. hydrophila, the expression of MaBAFF was up-regulated in spleen from 48 to 72 h, and the expression of BAFF and IgM all reached a peak at 48 h in head kidney. The soluble BAFF gene (MasBAFF) had been cloned into pET30a. SDS-PAGE and Western blotting analysis confirmed that the His-MasBAFF was efficiently expressed in Escherichia coli Rosset (DE3). CCK-8 assay indicated that the MasBAFF recombinant protein (200 ng/ml) could prolong the survival of peripheral blood leukocytes. Based on ELISA screening and Western blotting, monoclonal antibody 1-F2A3 against recombinant MasBAFF was selected and used for immunohistochemistry, which showed that BAFF-positive cells were detected in spleen and head kidney. Our results raise the possibility that MaBAFF may be useful to enhance immune efficacy in Chinese sucker disease defense.

Serum amyloid A is a positive acute phase protein in Russian sturgeon challenged with Aeromonas hydrophila

The immune system of sturgeons, one of the most ancient and economically valuable fish worldwide, is poorly understood. The lack of molecular tools and data about infection biomarkers hinders the possibility to monitor sturgeon health during farming and detect infection outbreaks. To tackle this issue, we mined publicly available transcriptomic datasets and identified putative positive acute-phase proteins (APPs) of Russian sturgeons that could be induced by a bacterial infection and monitored using non-invasive methods. Teleost literature compelled us to focus on five promising candidates: hepcidin, a warm acclimation associated hemopexin, intelectin, serum amyloid A protein (SAA) and serotransferrin. Among them, SAA was the most upregulated protein at the mRNA level in the liver of sturgeons challenged with heat-inactivated or live Aeromonas hydrophila. To assess whether this upregulation yielded increasing SAA levels in circulation, we developed an in-house ELISA to quantify SAA levels in sturgeon serum. Circulating SAA rose upon bacterial challenge and positively correlated with hepatic saa expression. This is the first time serum SAA has been quantified in an Actinopterygii fish. Since APPs vary across different fish species, our work sheds light on sturgeon acute-phase response, revealing that SAA is a positive APP with potential value as infection biomarker.

Dose effects of a DNA vaccine encoding immobilization antigen on immune response of channel catfish against Ichthyophthirius multifiliis

Channel catfish (Ictalurus punctatus) vaccinated with pcDNA3.1-IAg52b plasmid DNA vaccine encoding immobilization antigen genes of Ichthyophthirius multifiliis (Ich) produced anti-Ich antibodies and were partially protected (20% survival) in a previous study. Here we evaluated whether a higher dose or two doses of pcDNA3.1-IAg52b vaccine could provide better protection for catfish against Ich. Fish were distributed into 6 groups and vaccinated using following schemes: 1.10 μg pcDNA3.1-IAg52b fish^-1, 2.20 μg pcDNA3.1-IAg52b fish^-1, 3. two doses of 10 μg pcDNA3.1-IAg52b fish^-1 with 7 days between doses, 4.20 μg pcDNA3.1 fish^-1 (mock-vaccinated control), 5.15,000 live theronts fish^-1 (positive control), and 6. non-vaccinated and non-challenge control. Parasite infection levels, serum anti-Ich antibody levels, fish mortality and immune-related gene expression were determined during the trial. Fish vaccinated with a single dose of 20 μg pcDNA3.1-IAg52b fish^-1 or two doses of 10 μg fish^-1 had higher anti-Ich antibody levels than fish receiving a single dose of 10 μg fish^-1. Survival was significantly higher in fish receiving 20 μg vaccine fish^-1 (35.6%) or 2 doses of 10 μg fish^-1 (48.9%) than fish injected with a single dose of 10 μg fish^-1 (15.6%) or mock-vaccinated control (0%). Fish vaccinated at the dose 20 μg fish^-1 had higher expression of vaccine DNA in muscle than fish vaccinated with 10 μg fish^-1. Fish vaccinated with the DNA vaccine showed higher up-regulation than mock-vaccinated control in the expression of IgM, CD4, MHC I and TcR-α genes during most of time points after vaccination. Further studies are needed to improve efficacy of DNA vaccines by using multiple antigens in the DNA vaccines.

Characterization of the cathepsin D in Procambarus clarkii and its biological role in innate immune responses

Cathepsin D belongs to aspartic protease family, produced in the rough endoplasmic reticulum, and then transported to lysosomes, where it participates in various physiological processes. Despite its importance, only a few reports available on the functional role of cathepsin D in crustaceans. Herein, we cloned a cDNA fragment of cathepsin D from the hepatopancreas of the red swamp crayfish, Procambarus clarkii (Pc-cathepsin D) for the first time. It included 1158 base pairs open reading frame, encoding a protein of 385 amino acids. Multiple alignment analysis confirmed the presence of aspartic proteinase active sites and N glycosylation sites. Pc-cathepsin D mRNA expression was high in the gills followed by gut, heart, hepatopancreas of P. clarkii. At different time points post-infection with lipopolysaccharides, peptidoglycan, or polyinosinic polycytidylic acid, Pc-cathepsin D mRNA expression significantly enhanced compared with the control group. Knockdown of the Pc-cathepsin D by double-stranded RNA, strikingly, changed the expression of all the tested P. clarkii immune-associated genes, including Pc-Toll, Pc-lectin, Pc-cactus, Pc-anti-lipopolysaccharide factor, Pc-phospholipase, and Pc-sptzale. Altogether, these results suggest that Pc-cathepsin D is needed to confer innate immunity against microbial pathogens by modulating the expression of crucial transcripts that encode immune-associated genes.

Immune response of channel catfish (Ictalurus punctatus) against Ichthyophthirius multifiliis post vaccination using DNA vaccines encoding immobilization antigens

The channel catfish (Ictalurus punctatus) immune response against Ichthyophthirius multifiliis (Ich) after vaccination using plasmid DNA vaccines pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, encoding Ich immobilization antigen genes was studied. Parasite infection level, serum anti-Ich antibodies level, fish mortality after theront challenge, and immune-related gene expression were measured. After in vitro transfection of walking catfish gill cells (G1b) with both pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, antigens IAG52A and IAG52B were detected. During the vaccination trial, 76-fold increase in the Iag52b gene expression was observed in the vaccinated fish group h4 post vaccination. Administration of DNA vaccines by IM injection induced significant gene up-regulation in the head kidney, including immunoglobulin M (IgM), cluster of differentiation 4 (CD4), major histocompatibility I (MHC I), and T cell receptor α (TcR-α) from h4 to d5 post immunization. Fish vaccinated with DNA vaccines or theronts showed increased gene expression of the cytokine interferon (IFN-γ), complement component 3 (C3), and toll-like receptor-1 (TLR-1). Anti-Ich antibodies were detected in fish received pcDNA3.1-IAg52a, pcDNA3.1-IAg52b and the combination of both vaccines d10 post vaccination. Fish vaccinated with pcDNA3.1-IAg52b showed mild parasite infection level, partial survival (20%) and longer mean day to death (MDD) after theront challenge. By contrast, a heavy parasite load, 0% survival and short MDD were observed in the sham vaccinated control fish that received pcDNA3.1 (plasmid without genes encoding Ich immobilization antigen). Further research is needed to improve DNA vaccines for Ich that can induce strong protective immunity in fish. Suggested studies include improved transfection efficiency, use of appropriate adjuvants and including additional parasite antigen genes in the plasmid.

Multiple subtypes of TLR22 molecule from Schizothorax prenanti present the functional diversity in ligand recognition and signal activation

Evolutionary development has increased the diversity of genotypes and the complexity of gene functions in fish. TLR22 has been identified as a teleost-specific gene, but its functions are tremendously different among different fish species. Whether the functional diversity relates to the difference of genotypes remains poorly understand. In this study, we cloned and identified three TLR22 molecules from Schizothorax prenanti (S. prenanti), named as spTLR22-1, spTLR22-2 and spTLR22-3. The full-length coding regions of spTLR22s are 2841 bp, 2805 bp and 2868 bp and coding 946 aa, 934 aa and 955 aa, respectively. All spTLR22s are composed of multiple leucine-rich repeat (LRR) domains, a transmembrane structure and a Toll/IL-1 receptor (TIR) region. The phylogenetic analysis showed that three spTLR22s were close to Cyprinus carpio TLR22-1, TLR22-2 and TLR22-3, respectively. Among the spTLR22s, they presented not close relationship but remained to belong to TLR22 subfamily. All spTLR22s were ubiquitously expressed in all tested tissues, but the expression levels of spTLR22s were dominant in immune-related tissues, such as gill and spleen. The expression levels of spTLR22-1 and spTLR22-3 were significantly increased after treatment with bacteria, LPS and Poly(I:C). However, spTLR22-2 seems like no response to these treatments. The luciferase reporter assay demonstrated that all spTLR22s could activate NF-κB signaling pathway, but only spTLR22-1 and spTLR22-2 could activate IFN-β signaling pathway. Interestingly, in the ligand recognition analysis, spTLR22-1 and spTLR22-3 but not spTLR22-2 had the recognized potential to Poly(I:C), and all spTLR22s could not recognize LPS. Both spTLR22-1 and spTLR22-3 significantly up-regulated the expression of anti-viral-related genes (Mx, IFN and ISG15) and down-regulated the expression of anti-inflammatory factor IL-10 after the overexpression in carp EPC cell line, but spTLR22-2 failed to impact the expression of these genes. Moreover, we found that all spTLR22s localized to the intracellular region. Taken together, our results reveal that spTLR22-1 and spTLR22-3 but not spTLR22-2 may be involved into the anti-viral immune response via IFN-β signaling pathway, and all spTLR22s can activate NF-κB signaling pathway but only spTLR22-1 and spTLR22-3 response to the stimulation of bacteria and LPS.

GWAS Analysis Indicated Importance of NF-κB Signaling Pathway in Host Resistance Against Motile Aeromonas Septicemia Disease in Catfish

Motile Aeromonas septicemia (MAS) disease caused by a bacterial pathogen, Aeromonas hydrophila, is an emerging but severe disease of catfish. Genetic enhancement of disease resistance is considered to be effective to control the disease. To provide an insight into the genomic basis of MAS disease resistance, in this study, we conducted a genome-wide association study (GWAS) to identify quantitative trait loci (QTL). A total of 1820 interspecific backcross catfish of 7 families were challenged with A. hydrophila, and 382 phenotypic extremes were selected for genotyping with the catfish 690 K SNP arrays. Three QTL on linkage group (LG) 2, 26 and 29 were identified to be significantly associated with MAS resistance. Within these regions, a total of 24 genes had known functions in immunity, 10 of which were involved in NF-κB signaling pathway, suggesting the importance of NF-κB signaling pathway in MAS resistance. In addition, three suggestively significant QTL were identified on LG 11, 17, and 20. The limited numbers of QTL involved in MAS resistance suggests that marker-assisted selection may be a viable approach for catfish breeding.

Teleost-specific TLR25 identified from Schizothorax prenanti may recognize bacterial/viral components and activate NF-κB and type I IFNs signaling pathways

TLR25 is a new member of TLR1 family that is only identified in teleosts, but its function in immune response is still unclear. In current study, the coding sequence (CDS) of TLR25 was cloned from Schizothorax prenanti (named spTLR25), and spTLR25 is 2454 bp in length and coding a protein of 817 aa. The spTLR25 contains a signal peptide, twenty leucine-rich repeat (LRR) domains, a LRR C-terminal (LRRCT) motif, a transmembrane region and a Toll/IL-1 receptor (TIR) domain. Phylogenetic analysis indicates that spTLR25 has the closest relationship with Cyprinus carpio (C. carpio) TLR25-2. The 3D structure of spTLR25 exhibits 5 α-helices and 3 β-sheets in the TIR domain, and 8 α-helices and 6 β-sheets in the LRR domains. The spTLR25 is mainly expressed in immune-related tissues and peripheral blood leukocytes (PBL). Furthermore, the expression levels of spTLR25 were upregulated in spleen, head kidney and liver while S. prenanti was challenged with LPS or Aeromonas hydrophila (Ah), and the upregulation was also detected in head kidney leukocytes (HKL) after LPS and Poly (I:C) stimulation. The luciferase reporter assay demonstrated that NF-κB and type I IFNs signaling pathways can be activated by spTLR25, and this process may involve in the cascade amplification of TLR25-MyD88 signaling. In addition, the co-localization analysis showed that spTLR25 localizes to intracellular region. Taken together, our results reveal that teleost-specific TLR25 may be a multifunctional receptor for recognizing both LPS and Poly (I:C) and may activate NF-κB and type I IFNs signaling pathways.

Post-translational protein deimination in cod (Gadus morhua L.) ontogeny novel roles in tissue remodelling and mucosal immune defences?

Peptidylarginine deiminases (PADs) are calcium dependent enzymes with physiological and pathophysiological roles conserved throughout phylogeny. PADs promote post-translational deimination of protein arginine to citrulline, altering the structure and function of target proteins. Deiminated proteins were detected in the early developmental stages of cod from 11 days post fertilisation to 70 days post hatching. Deiminated proteins were present in mucosal surfaces and in liver, pancreas, spleen, gut, muscle, brain and eye during early cod larval development. Deiminated protein targets identified in skin mucosa included nuclear histones; cytoskeletal proteins such as tubulin and beta-actin; metabolic and immune related proteins such as galectin, mannan-binding lectin, toll-like receptor, kininogen, Beta2-microglobulin, aldehyde dehydrogenase, bloodthirsty and preproapolipoprotein A-I. Deiminated histone H3, a marker for anti-pathogenic neutrophil extracellular traps, was particularly elevated in mucosal tissues in immunostimulated cod larvae. PAD-mediated protein deimination may facilitate protein moonlighting, allowing the same protein to exhibit a range of biological functions, in tissue remodelling and mucosal immune defences in teleost ontogeny.

Effect of Dietary Acidolysis-Oxidized Konjac Glucomannan Supplementation on Serum Immune Parameters and Intestinal Immune-Related Gene Expression of Schizothorax prenanti

The present study was conducted to investigate the effects of dietary acidolysis-oxidized konjac glucomannan (A-OKGM) (0%, 0.4%, 0.8%, and 1.6%) supplementation on the immunity and expression of immune-related genes in Schizothorax prenanti. After feeding for eight weeks, the serum and guts were used for measurement of biochemical parameters, and immune-related gene expression in the gut were also analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). C-reactive protein and IgM levels were significantly higher in the A-OKGM fed groups than in the control group, regardless of the dosage. The 0.4% and 1.6% A-OKGM groups showed significant up-regulation of tumor necrosis factor α (TNFα) in the anterior gut. The 0.8% and 1.6% A-OKGM groups also showed significantly enhanced TNFα expression in the mid- and distal guts. Interleukin-1β (IL-1β) expression in the anterior gut of fish fed with 0.4% and 1.6% A-OKGM diets was significantly enhanced. The 0.8% and 1.6% A-OKGM diets resulted in significantly increased the expression of IL-1β in the distal gut. Similarly, the interleukin-6 (IL-6) messenger RNA (mRNA) levels in the 0.4% and 1.6% diet groups were significantly higher in the anterior gut. The 0.8% and 1.6% A-OKGM diet groups showed significant induction of IL-6 gene expression in the distal gut. A-OKGM modified from KGM can act as an immunostimulant to enhance the immunity of S. prenanti.

Expression of immune genes in skin of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

The objective of this study was to evaluate differential expression of innate and adaptive immune genes, including immunoglobulin, immune cell receptor, cytokine, inflammatory protein, toll-like receptors (TLR) and recombination-activating gene (RAG) in skin from channel catfish, Ictalurus punctatus after immunization with live theronts of Ichthyophthirius multifiliis (Ich) by intraperitoneal injection. The immunized catfish showed significantly higher survival rate (95%) than those of mock-immunized control fish (0% survival) after the theront challenge. The gene expression of innate immune system, such as cytokines (IL-1β type a, IL-1β type b, IFN-γ, TGF1-β and TNF-α) and inflammatory proteins (NF-kB and iNOS 2), showed significant upregulation at day 1 (D1) post-immunization. Expression of TLR genes exhibited a rapid increase from hour 4 (h4) to D10 post-immunization. Genes of the adaptive response, such as the cell receptor MHC I, CD8⁺ , CD4⁺ and TCR-α, showed upregulation at D1, D6 and D10. The TCR-β expression increased rapidly at h4 and remained upregulated until D10. Immunoglobulin IgM upregulation was detected from h4 until D2 while IgD expression was increased from D1 until D10. Rapid upregulation of innate and adaptive immune genes in skin of catfish following live theront vaccination was demonstrated in this study ultimately resulting in significant protection against Ich infection.

Transcriptome differences between enrofloxacin-resistant and enrofloxacin-susceptible strains of Aeromonas hydrophila

Enrofloxacin is the most commonly used antibiotic to control diseases in aquatic animals caused by A. hydrophila. This study conducted de novo transcriptome sequencing and compared the global transcriptomes of enrofloxacin-resistant and enrofloxacin-susceptible strains. We got a total of 4,714 unigenes were assembled. Of these, 4,122 were annotated. A total of 3,280 unigenes were assigned to GO, 3,388 unigenes were classified into Cluster of Orthologous Groups of proteins (COG) using BLAST and BLAST2GO software, and 2,568 were mapped onto pathways using the Kyoto Encyclopedia of Gene and Genomes Pathway database. Furthermore, 218 unigenes were deemed to be DEGs. After enrofloxacin treatment, 135 genes were upregulated and 83 genes were downregulated. The GO terms biological process (126 genes) and metabolic process (136 genes) were the most enriched, and the terms for protein folding, response to stress, and SOS response were also significantly enriched.

This study identified enrofloxacin treatment affects multiple biological functions of A. hydrophila. Enrofloxacin resistance in A. hydrophila is closely related to the reduction of intracellular drug accumulation caused by ABC transporters and increased expression of topoisomerase IV.

Expression analysis of nine Toll-like receptors in yellow catfish (Pelteobagrus fulvidraco) responding to Aeromonas hydrophila challenge

Toll-like receptors (TLRs) are important components of pattern recognition receptors (PRRs), which play significant roles in innate immunity to defense against pathogen invasion. Many TLRs have been found in teleosts, but there are no reports about cloning and expression of TLR genes in yellow catfish (Pelteobagrus fulvidraco). In this study, we analyzed the sequence characters and the relative mRNA expression levels of nine TLRs (TLR1, TLR2, TLR3, TLR4-1, TLR5, TLR7, TLR8-2, TLR9 and TLR22) in different tissues of yellow catfish. The results showed that all nine TLR genes are highly expressed in head kidney, trunk kidney, spleen and liver, all of which are related to host immunity. Subsequently we used Aeromonas hydrophila as a stimulating agent to detect the expression profiles of these nine TLRs in the liver, spleen, trunk kidney and head kidney of yellow catfish at different time points after injection with killed Aeromonas hydrophila. All nine TLRs responded to A. hydrophila challenge with tissue-specific patterns in different immune tissues. The kinetics of up- or down-regulation of these nine TLRs exhibited a similar trend, rising to an elevated level at first and then falling to the basal level, but the peak value differed at different time points in different tissues. The expression levels of the TLR3, TLR4-1, TLR9 and TLR22 genes were significantly up-regulated after bacterial challenge in the liver, spleen, head kidney and trunk kidney. The relatively high expression of TLR genes in the immune tissues in response to the A. hydrophila challenge indicated that TLRs may play important roles in the innate immune response against gram-negative bacteria in yellow catfish.

Transcriptome profiling of spleen provides insights into the antiviral mechanism in Schizothorax prenanti after poly (I: C) challenge

Schizothorax prenanti (S. prenanti) is an important economical cold-water fish species in southwestern China, but it is susceptible to various pathogens infection. In order to clearly elucidate the antiviral mechanism, in this study, we have analyzed the transcriptome of S. prenanti spleen after challenge with the virus mimic, poly (I:C) (pIC), using next generation sequencing technology (RNA-seq). A total of 313 differential expressed genes (DEGs) in spleen at 12 h were obtained after pIC treatment, including 268 significantly up-regulated unigenes (fold change > 2) and 45 significantly down-regulated unigenes (fold change > 2). Through the immune-related DEGs (IRDs) screening, 47 IRDs were used to establish heat map, which intuitively showed a significantly difference after pIC treatment. To validate the RNA-seq data and observe gene expression, the expression levels of 14 IRDs were detected by qPCR after pIC treatment at 0, 4, 8, 12, and 24 h. The results indicated that the qPCR data presented a positive line correlation with RNA-seq data, and the 14 IRDs were responsive to pIC stimulation except IL-1β. Thus, based on the RNA-seq and qPCR data, we inferred that MDA5- and Jak-mediated signaling pathways may involve in the antiviral signaling transduction, and induce type I IFNs and ISGs to block virus invasion, respectively. Unfortunately, TLR3 and TLR22, as receptors of virus dsRNA, were no significantly expressed in this study. Nonetheless, our study still provides useful mRNA sequences of antiviral immunity for further immunological research, and facilitates improving disease restriction in S. prenanti.

Effects of dietary oxidized konjac glucomannan sulfates (OKGMS) and acidolysis-oxidized konjac glucomannan (A-OKGM) on the immunity and expression of immune-related genes of Schizothorax prenanti

In the present study, konjac glucomannan (KGM) was degraded by H2O2, and then used trisulfonated sodium amine and HCl, individually, to obtain two kinds of derivatives: oxidized konjac glucomannan sulfates (OKGMS) and acidolysis-oxidized konjac glucomannan (A-OKGM). The effects of two OKGM modified products on the immune parameters and expressions of toll-like receptor 22 (TLR22), myeloid differentiation factor 88 (MyD88) and interferon regulatory factors 7 (IRF7) genes in Schizothorax prenanti were determined. The alternative haemolytic complement (ACH50) activity was found to be significantly increased by the OKGMS diets. The immunoglobulin M (IgM) level was significantly enhanced by the OKGMS diets. The lysozyme activity was significantly increased by both OKGMS and A-OKGM diets. The superoxide dismutase (T-SOD) activity in fish fed with all doses of OKGMS diets was significantly higher than that in fish fed with basal diet. The glutathione peroxidase (GSH-PX) activity in fish fed with 0.8% and 1.6% A-OKGM diets was significantly higher than control group. The malondialdehyde (MDA) level was significantly decreased by both OKGMS and A-OKGM diets. The 0.8% A-OKGM diet significantly up-regulated TLR22 gene expression in the head kidney and spleen. TLR22 gene expression was significantly promoted by all OKGMS diets in the mesonephros and liver. The MyD88 mRNA level in 1.6% A-OKGM group significantly increased in the head kidney. The low dose of OKGMS significantly induced the MyD88 gene expression in the mesonephros, gut and liver, while 0.8% A-OKGM group also showed a significantly enhanced MyD88 mRNA expression in the gut. High dose of OKGMS significantly increased the IRF7 mRNA expression in the mesonephros and spleen. Fish fed with low dose of A-OKGM showed significantly higher expression of IRF7 in the gut and liver. Present study suggested that OKGMS and A-OKGM can act as immunostimulant to improve the immune indexes and up-regulate the immune-related gene expressions.

Protective immunity of grass carp immunized with DNA vaccine against Aeromonas hydrophila by using carbon nanotubes as a carrier molecule

To reduce the economic losses caused by diseases in aquaculture industry, more efficient and economic prophylactic measures should be urgently investigated. In this research, the effects of a novel functionalized single-walled carbon nanotubes (SWCNTs) applied as a delivery vehicle for DNA vaccine administration in juvenile grass carp against Aeromonas hydrophila were studied. Our results showed that SWCNTs loaded with DNA vaccine induced a better protection to juvenile grass carp against A. hydrophila. Moreover, SWCNTs conjugated with DNA vaccine provided significantly protective immunity compared with free DNA vaccine. Thereby, SWCNTs may be considered as a potential efficient DNA vaccine carrier to enhance the immunological activity.

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.

Molecular immune response of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

The parasite Ichthyophthirius multifiliis (Ich) has been reported in various freshwater fishes worldwide and results in severe losses to both food and aquarium fish production. The fish surviving natural infections or immunized with live theronts develop strong specific and non-specific immune responses. Little is known about how these immune genes are induced or how they interact and lead to specific immunity against Ichthyophthirius multifiliis in channel catfish Ictalurus punctatus. This study evaluated the differential expression of immune-related genes, including immunoglobulin, immune cell receptor, cytokine, complement factor and toll-like receptors in head kidney from channel catfish at different time points after immunization with live theronts of I. multifiliis. The immunized fish showed significantly higher anti-Ich antibody expressed as immobilization titer and ELISA titer than those of control fish. The vast majority of immunized fish (95%) survived theront challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hour (h4) to 2 days (d2) post immunization. Expression of immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) showed up-regulation from h4 to d6 post immunization, indicating that different immune cells were actively involved in cellular immune response. Cytokine gene expression (IL-1βa, IL-1βb, IFN-γ and TNF-α) increased rapidly at h4 post immunization and were at an up-regulated level until d2 compared to the bovine serum albumin control. Expression of complement factor and toll-like receptor genes exhibited a rapid increase from h4 to d2 post immunization. Results of this study demonstrated differential expression of genes involved in the specific or non-specific immune response post immunization and that the vaccination against Ich resulted in protection against infection by I. multifiliis.

Immune responses to Aeromonas hydrophila infection in Schizothorax prenanti fed with oxidized konjac glucomannan and its acidolysis products

The objective of the present study was to determine the effect of dietary oxidized konjac glucomannan (OKGM) and its acidolysis products (L-OKGM) on the immune parameters and the gene expression profile of some inflammatory-related cytokines from Schizothorax prenanti during the early stages of injection with Aeromonas hydrophila. Fish were orally administered with seven different diets containing 0 g kg(-1) (control diet), 8.0, 16.0 and 32.0 g kg(-1) OKGM and L-OKGM diets for 60 days prior to injection. After 60 days, the control and the treated fish were intraperitoneally injected with 0.2 ml PBS or 2 × 10(7) cfu/ml bacteria per fish and sampled at time 6 h post-injection. The results showed that the serum lysozyme activity and complement C3 level of fish fed 8.0 g kg(-1) L-OKGM was significantly increased after bacterial infection. Moreover, the injection with A. hydrophila generally up-regulated the expression of all measured genes when compared to their corresponding controls. When compared with the control group, the expression of TLR22, TNF-α and IL-1β was significantly increased in fish fed OKGM and L-OKGM diet after bacterial injection. Furthermore, the L-OKGM diet showed higher activity to trigger the immune response against bacteria, especially the low dosage L-OKGM diet. The results suggested that both of OKGM and L-OKGM are promising feed additive for S. prenanti in aquaculture.

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.

The effects of dietary oxidized konjac glucomannan and its acidolysis products on the immune response, expression of immune related genes and disease resistance of Schizothorax prenanti

In the present study, KGM was degraded by H2O2 and HCl to obtain two products with different molecular weights: oxidized konjac glucomannan (OKGM, 4.7 × 10(5) Da) and low-molecular-weight oxidized konjac glucomannan (L-OKGM, 9.2 × 10(3) Da). The effects of the two OKGM products on IL-1β, TNF-α, and TLR22 gene expression, and immune parameters and the resistance to Aeromonas hydrophila of Schizothorax prenanti were determined. The results showed that the lysozyme activity was significantly enhanced by the L-OKGM diets. The SOD activity was significantly increased by both OKGM and L-OKGM diets. The MDA level of fish fed the OKGM and L-OKGM diets was significantly lower than the control group. IL-1β mRNA level in the spleen significantly increased in all L-OKGM fed groups. The 8.0 g kg(-1) L-OKGM diet also significantly up-regulated IL-1β gene expression in the head kidney. In the gut, IL-1β mRNA levels were significantly higher in fish fed with the 8.0 g kg(-1) OKGM and 16.0 g kg(-1) L-OKGM diets. The TNF-α mRNA level of L-OKGM group significantly increased in the spleen, head kidney and gut. High dosing of OKGM significantly up-regulated TNF-α transcription in the head kidney, while only the 8.0 g kg(-1) OKGM group showed significantly higher TNF-α mRNA expression in the mesonephros. Fish fed the L-OKGM diets showed significantly higher expression of TLR22 in the spleen, head kidney and mesonephros. After the injection of A. hydrophila, the 8.0 g kg(-1) L-OKGM group showed a significantly higher survival rate than did the control group. Present study suggests that OKGM and L-OKGM can up-regulate immune-related gene expression and enhance disease resistance in S. prenanti, and L-OKGM exhibits higher immunomodulatory activity.

Identification and characterization of a cathepsin D homologue from lampreys (Lampetra japonica)

Cathepsin D (EC 3.4.23.5) is a lysosomal aspartic proteinase of the pepsin superfamily which participates in various digestive processes within the cell. In the present study, the full length cDNA of a novel cathepsin D homologue was cloned from the buccal glands of lampreys (Lampetra japonica) for the first time, including a 124-bp 5' terminal untranslated region (5'-UTR), a 1194-bp open reading frame encoding 397 amino acids, and a 472-bp 3'-UTR. Lamprey cathepsin D is composed of a signal peptide (Met 1-Ala 20), a propeptide domain (Leu 21-Ala 48) and a mature domain (Glu 76-Val 397), and has a conserved bilobal structure. Cathepsin D was widely distributed in the buccal glands, immune bodies, hearts, intestines, kidneys, livers, and gills of lampreys. After challenging with Escherichia coli or Staphylococcus aureus, the expression level of lamprey cathepsin D in the buccal gland was 8.5-fold or 6.5-fold higher than that in the PBS group. In addition, lamprey cathepsin D stimulated with Escherichia coli was also up-regulated in the hearts, kidneys, and intestines. As for the Staphylococcus aureus challenged group, the expression level of lamprey cathepsin D was found increased in the intestines. The above results revealed that lamprey cathepsin D may play key roles in immune response to exogenous pathogen and could serve as a potential antibacterial agent in the near future. In addition, lamprey cathepsin D was subcloned into pcDNA 3.1 vector and expressed in the human embryonic kidney 293 cells. The recombinant lamprey cathepsin D could degrade hemoglobin, fibrinogen, and serum albumin which are the major components in the blood, suggested that lamprey cathepsin D may also act as a digestive enzyme during the adaptation to a blood-feeding lifestyle.

Rock bream (Oplegnathus fasciatus) IL-12p40: identification, expression, and effect on bacterial infection

IL-12p40, also called IL-12β, is a subunit of the proinflammatory cytokines interleukin (IL)-12 and IL-23. In teleost, IL-12p40 homologues have been identified in several species, however, the biological function of fish IL-12p40 is essentially unknown. In this work, we reported the identification and analysis of an IL-12p40, OfIL-12p40, from rock bream (Oplegnathus fasciatus). OfIL-12p40 is composed of 361 amino acids and possesses a conserved IL-12p40 domain and a WSxWS signature motif characteristic of known IL-12p40. Constitutive expression of OfIL-12p40 occurred in multiple tissues and was highest in kidney. Experimental infection with bacterial pathogen upregulated the expression of OfIL-12p40 in kidney and spleen in a time-dependent manner. Purified recombinant OfIL-12p40 (rOfIL-12p40) stimulated the respiratory burst activity of peripheral blood leukocytes in a dose-dependent manner. rOfIL-12p40 also enhanced the resistance of rock bream against bacterial infection and upregulated the expression of innate immune genes in kidney. Taken together, these results indicate that OfIL-12p40 possesses cytokine-like property and plays a role in immune defense against bacterial infection.