Molecular mechanism of the NOS/NOX regulation of antibacterial activity in Eriocheir sinensis

To elucidate the role of nitric oxide synthase (NOS), which produces the free radical nitric oxide (NO), and nicotinamide adenine dinucleotide phosphate oxidase (NOX), which produces the superoxide anion (O2-), in the innate immunity of Eriocheir sinensis, the full lengths of the NOS and NOX genes were cloned via rapid amplification of the cDNA ends and then expressed in the prokaryotic form to obtain the recombinant proteins, NOS-HIS and NOX-HIS. Through bacterial binding and stimulation experiments, the molecular mechanisms of NOS and NOX in the innate immunity of E. sinensis were explored. Based on the results, NOS and NOX were 5900 bp and 4504 bp long, respectively, and were evolutionarily conserved. Quantitative real-time PCR revealed that NOS and NOX were expressed in all studied tissues, and both were expressed in the highest amounts in hemocytes. NOS-HIS and NOX-HIS could bind to bacteria with different binding powers; their binding ability to gram-positive bacteria was higher than that of binding to gram-negative bacteria. After stimulation with Aeromonas hydrophila, NOS expression was significantly up-regulated at 3, 6, and 48 h, and NOX expression was significantly down-regulated at 3, 12, 24, and 48 h. After bacterial stimulation, the NOS enzyme activity in the serum of E. sinensis was also significantly up-regulated at 6 and 48 h, and the NOX enzyme activity was significantly down-regulated at 12 and 48 h, aligning with the gene expression trend. Moreover, the related free radical molecules, NO, O2-, and H2O2, tended to decrease after bacterial stimulation. Overall, the gene expression and enzyme activity of NOS and NOX had been changed respectively, and the contents of a series of free radical molecules (NO, O2- and H2O2) were induced in E. sinensis after bacterial stimulation, which then exert antibacterial immunity.

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

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

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

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

Identification and characterization of a Reeler domain containing protein in Procambarus clarkii provides new insights into antibacterial immunity in crustacean

Crayfish, as an invertebrate, relies only on the innate immune system to resist external pathogens. In this study, a molecule containing a single Reeler domain was identified from red swamp crayfish Procambarus clarkii (named as PcReeler). Tissue distribution analysis showed that PcReeler was highly expressed in gills and its expression was induced by bacterial stimulation. Inhibiting the expression of PcReeler by RNA interference led to a significant increase in the bacterial abundance in the gills of crayfish, and a significant increase in the crayfish mortality. Silencing of PcReeler influenced the stability of the microbiota in the gills revealed by 16S rDNA high-throughput sequencing. Recombinant PcReeler showed the ability to bind microbial polysaccharide and bacteria and to inhibit the formation of bacterial biofilms. These results provided direct evidence for the involvement of PcReeler in the antibacterial immune mechanism of P. clarkii.

Two novel teleost calreticulins PoCrt-1/2, with bacterial binding and agglutination activity, are involved in antibacterial immunity

Calreticulin (Crt), a conserved lectin-like pleiotropic protein, plays crucial roles in mammalian immune response. In fish, the immunological function of Crt is limited investigated. Herein, we studied the antibacterial immunity of two type of Crt homologues (i.e. PoCrt-1 and PoCrt-2) in Japanese flounder (Paralichthys olivaceus). PoCrt-1 and PoCrt-2 are composed of 419 and 427 amino acid residues respectively, with 69.09% overall sequence identities with each other. Both PoCrt-1 and PoCrt-2 contain a signal peptide and three functional domains i.e. N-, P- and C-domains. Both PoCrt-1 and PoCrt-2 were constitutively expressed at various tissues with highest expression level in liver, and obviously regulated by Edwardsiella tarda and Vibrio harveyi. Furthermore, recombinant PoCrt-1 and PoCrt-2 (rPoCrt-1 and rPoCrt-2) could bind to different Gram-negative bacteria with highest binding index with E. tarda. At same time, in vitro rPoCrt-1 and rPoCrt-2 could agglutinate E. tarda, V. harveyi, and Vibrio anguillarum, and inhibit the bacterial growth. Similarly, in vivo rPoCrt-1 and rPoCrt-2 could significantly suppress the dissemination of E. tarda. Overall, these observations add new insights into the antibacterial immunity of Crt in P. olivaceus.

Effects of the tumor necrosis factor on hemocyte proliferation and bacterial infection in Chinese mitten crab (Eriocheir sinensis)

Tumor necrosis factor (TNF) is an important cytokine that can regulate a variety of cellular responses by binding tumor necrosis factor receptor (TNFR). We studied whether the TNF of Eriocheir sinensis can regulate hemocyte proliferation. The results showed that the EsTNF and EsTNFR were constitutively expressed in all tested tissues, including the heart, hepatopancreas, muscles, gills, stomachs, intestines, and hemocytes. We found that low levels of EsTNF and EsTNFR transcripts were present in hemocytes. The gene expression levels were significantly increased in the hemocytes after being stimulated by Staphylococcus aureus or Vibrio parahaemolyticus. We also found some genes related to cell proliferation were expressed at a higher level in pulsing rTNF-stimulated hemocytes compared with the control group. We also knocked down the EsTNFR gene with RNAi technology. The results showed that the expression level of these genes related to cell proliferation was significantly down-regulated compared with the control group when the TNF does not bind TNFR. We used Edu technology to repeat the above experiments and the results were similar. Compared with the control group, the hemocytes stimulated by rTNF showed more significant proliferation, and the proliferation rate was significantly down-regulated after knocking down the EsTNFR gene. Therefore, we indicate that TNF binding TNFR can affect the proliferation of E. sinensis hemocytes, which might be manifested by affecting the expression of some proliferation-related genes.

Duox and Jak/Stat signalling influence disease tolerance in Drosophila during Pseudomonas entomophila infection

Disease tolerance describes an infected host's ability to maintain health independently of the ability to clear microbe loads. The Jak/Stat pathway plays a pivotal role in humoral innate immunity by detecting tissue damage and triggering cellular renewal, making it a candidate tolerance mechanism. Here, we find that in Drosophila melanogaster infected with Pseudomonas entomophila disrupting ROS-producing dual oxidase (duox) or the negative regulator of Jak/Stat Socs36E, render male flies less tolerant. Another negative regulator of Jak/Stat, G9a - which has previously been associated with variable tolerance of viral infections - did not affect the rate of mortality with increasing microbe loads compared to flies with functional G9a, suggesting it does not affect tolerance of bacterial infection as in viral infection. Our findings highlight that ROS production and Jak/Stat signalling influence the ability of flies to tolerate bacterial infection sex-specifically and may therefore contribute to sexually dimorphic infection outcomes in Drosophila.

Thymosin beta-4 participate in antibacterial immunity and wound healing in black tiger shrimp, Penaeus monodon

Thymosin beta-4 (Tβ4) is a ubiquitous protein with multiple and diverse intracellular and extracellular functions in vertebrates, which play fundamental roles in innate immune against pathogens and wound healing. In this study, the full-length cDNA of Tβ4 was cloned from Penaeus monodon (designated as PmTβ4), using the technology of rapid amplification of cDNA ends (RACE). The cDNA of PmTβ4 was 1361 bp with an open reading frame (ORF) of 501 bp, which encoding a polypeptide of 166 amino acid. The Quantitative Real-time PCR (qRT-PCR) analysis results showed that PmTβ4 was ubiquitously expressed in all the tested shrimp tissues, with the highest expression level was detected in the hemolymph, while the lowest expression level in the muscle. The expression level of PmTβ4 was significantly up-regulated in hepatopancreas after challenged by Vibrio parahaemolyticus, Vibrio harveyi and Staphylococcus aureus. In vitro antimicrobial test showed that the recombinant protein of PmTβ4 (rPmTβ4) had broad-spectrum of antimicrobial activity, which could inhibit both the growth of gram-negative bacteria and gram-positive bacteria, including Vibrio vulnificus, V. parahaemolyticus, Streptococcus agalactiae, S. aureus and Aeromonas hydrophila. Moreover, rPmTβ4 had a certain binding ability to different bacteria, and this binding ability exhibits a strong dose-dependent effect. In vivo, PmTβ4 could facilitate external bacterial clearance in shrimp, and have beneficial to shrimp survival post V. parahaemolyticus infection. Furthermore, wound-healing assay was carried out to study the role of PmTβ4 in the process of wound healing. The results showed that the PmTβ4 expression was significantly up-regulated by injury treatment, and exerted positive effects to promote wound healing. In addition, PmTβ4 can significantly increase the expression level of superoxide dismutase (SOD) and Catalase (CAT) after injury treatment in shrimp, which would involve in scavenging reactive oxygen species (ROS) caused by the wound. In conclusion, these results indicated that PmTβ4 may play important roles in antibacterial immunity and wound healing in Penaeus monodon.

CpG ODN 1668 as TLR9 agonist mediates humpback grouper (Cromileptes altivelis) antibacterial immune responses

Cromileptes altivelis (humpback grouper) is the main farmed species in the southern coastal area of China owing to its important economic value. Toll-like receptor 9 (TLR9) belongs to the toll-like receptor (TLR) family and functions as a pattern recognition receptor, recognising unmethylated oligodeoxynucleotides containing the CpG motif (CpG ODNs) in bacterial and viral genomes, thereby activating host immune response. In this study, the C. altivelis TLR9 (CaTLR9) ligand CpG ODN 1668 was screened and found to significantly enhance the antibacterial immunity of humpback grouper in vivo and head kidney lymphocytes (HKLs) in vitro. In addition, CpG ODN 1668 also promoted the cell proliferation and immune gene expression of HKLs and strengthened the phagocytosis activity of head kidney macrophages. However, when the CaTLR9 expression was knocked down in the humpback group, the expression levels of TLR9, myeloid differentiation factor 88 (Myd88), tumour necrosis factor-α (TNF-α), interferon γ (IFN-γ), interleukin-1β (IL-1β), IL-6, and IL-8 were significantly reduced, and the antibacterial immune effects induced by CpG ODN 1668 were mostly abolished. Therefore, CpG ODN 1668 induced antibacterial immune responses in a CaTLR9-dependent pathway. These results enhance the knowledge of the antibacterial immunity of fish TLR signalling pathways and have important implications for exploring natural antibacterial molecules in fish.

Caspar negatively regulates anti-bacterial immunity by controlling the nuclear translocation of Relish in Chinese mitten crab (Eriocheir sinensis)

Caspar, a homolog of the Fas-associated factor 1 (FAF1) family, contains an N-terminal ubiquitin interaction domain, a ubiquitin-like self-association domain, and a C-terminal ubiquitin regulatory domain. Caspar has been reported to be involved in the antibacterial immunity of Drosophila, which is unclear whether it is involved in the antibacterial immune process of crustaceans. In this article, we identified a Caspar gene in Eriocheir sinensis and named it EsCaspar. EsCaspar positively respond to bacterial stimulation and downregulate the expression of certain associated antimicrobial peptides by inhibiting the nuclear translocation of EsRelish. Thus, EsCaspar might be a suppressor of the immune deficiency (IMD) pathway that prevents over-activation of the immune system. Indeed, excess EsCaspar protein in crabs reduced resistance to bacterial infection. In conclusion, EsCaspar is a suppressor of the IMD pathway in crabs that plays a negative regulatory role in antimicrobial immunity.

CpG ODN 2102 promotes antibacterial immune responses and enhances vaccine-induced protection in golden pompano (Trachinotusovatus)

CpG oligodeoxynucleotides (ODNs) are oligodeoxynucleotides containing CpG motifs and can be recognized by toll-like receptor 9 (TLR9), activating the host's immune responses. In this study, ten different CpG ODNs were designed and synthesized to study the antibacterial immune responses of CpG ODNs in golden pompano (Trachinotus ovatus). Results showed that CpG ODN 2102 significantly improved the immunity of golden pompano against bacteria. Besides, CpG ODN 2102 promoted the proliferation of head kidney lymphocytes and activated the head kidney macrophages. When TLR9-specific small interfering RNA (siRNA) was used to interfere with TLR9 expression, the immune responses were decreased. Moreover, the expression levels of myeloid differentiation primary response 88 (Myd88), p65, tumor necrosis factor receptor-associated factor 6 (TRAF6), and tumor necrosis factor-alpha (TNF-α) in the TLR9-knockdown golden pompano kidney (GPK) cells were significantly reduced. The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) promoter activity of the TLR9-knockdown GPK cells was also significantly reduced. In vivo, the antibacterial immune effects induced by CpG ODN 2102 in golden pompano were mostly abolished when TLR9 expression was knocked down. These results suggested that TLR9 was involved in the immune responses induced by CpG ODN 2102. CpG ODN 2102 also enhanced the protective effect of the Vibrio harveyi vaccine pCTssJ, where the survival rate of golden pompano was significantly improved by 20%. In addition, CpG ODN 2102 enhanced the messenger RNA (mRNA) expression levels of TLR9, Myxovirus resistance (Mx), interferon γ (IFN-γ), TNF-α, interleukin (IL)-1β, IL-8, major histocompatibility complex class (MHC) Iα, MHC IIα, Immunoglobulin D (IgD), and IgM. Therefore, TLR9 was involved in the antibacterial immune responses induced by CpG ODN 2102 and CpG ODN 2102 possessed adjuvant immune effects. These results enlarged our knowledge of the antibacterial immunity of fish TLRs signaling pathway and had important implications for exploring natural antibacterial molecules in fish and developing new vaccine adjuvants.

A soluble TLR5 is involved in PBLs activation and antibacterial immunity via TLR5M-MyD88-signaling pathway in tongue sole Cynoglossus semilaevis

In higher vertebrates, there is only a membranal TLR5 (TLR5M), which is crucial for host defense against microbes via MyD88 signaling pathway. In teleost, both TLR5M and soluble TLR5 (TLR5S) are identified, whereas the antibacterial mechanism of TLR5S is largely unknown. In this study, we studied the immune antibacterial mechanism of Cynoglossus semilaevis TLR5S homologue (named CsTLR5S). CsTLR5S, a 71.1 kDa protein, consists of 649 amino acid residues and shares 41.7 %-57.8 % overall sequence identities with teleost TLR5S homologues. CsTLR5S contains a single extracellular domain (ECD) composed of 12 leucine-rich repeats. CsTLR5S expression was constitutively identified and upregulated by bacterial infection in tissues. In vitro recombinant CsTLR5S (rCsTLR5S) could interact with bacteria and tongue sole rTLR5M (rCsTLR5M). Furthermore, rCsTLR5S could bind to the membranal CsTLR5M of peripheral blood leukocytes (PBLs), which led to enhancing the activity and the antibacterial role of PBLs via Myd88-NF-κB pathway. In vivo rCsTLR5S could activate the Myd88-NF-κB pathway, facilitate the release of proinflammatory cytokines, and enhance the host antibacterial response against Vibrio harveyi. Moreover, the knockdown of CsTLR5M or the Myd88 inhibitor could significantly suppress the antibacterial effect of rCsTLR5S. Collectively, our findings added important insights into the TLR5S immune antibacterial property in a TLR5M-MyD88-dependent manner.

TroTNFSF6, a tumor necrosis factor ligand superfamily member, promotes antibacterial immune response of golden pompano, Trachinotus ovatus

Tumor necrosis factor ligand superfamily member 6 (TNFSF6), also known as FasL/CD95L, is essential for maintaining the body's immune homeostasis. However, the current reports on TNFSF6 in fish are relatively scarce. In the present study, we conducted functional analyses of a TNFSF6 (TroTNFSF6) from the teleost fish golden pompano (Trachinotus ovatus). TroTNFSF6 is composed of 228 amino acids and has a low similarity with other species (9.65%-58.79%). TroTNFSF6 was expressed in the 11 tissues tested and was significantly up-regulated after Edwardsiella tarda infection. In vivo, overexpression of TroTNFSF6 effectively stimulated the AKP and ACP activities, and reduced bacterial infection in fish tissues. Correspondingly, knockdown of TroTNFSF6 expression resulted in increasing bacterial dissemination and colonization in fish tissues. In vitro, recombinant TroTNFSF6 protein promoted the proliferation of T. ovatus head kidney lymphocytes (HKLs), and promoted the apoptosis of murine liver cancer cells (Hepa1-6). The results indicated that TroTNFSF6 plays an important role in the T. ovatus antibacterial immunity. These observations will facilitate the future in-depth study of teleost TNFSF6.

Bactericidal permeability-increasing protein/LPS-binding protein (BPI/LBP) enhances resistance of golden pompano Trachinotus ovatus against bacterial infection

Antimicrobial peptides are crucial components of innate immunity against microbial invasions. As a kind of antimicrobial peptides, bactericidal permeability-increasing protein (BPI)/lipopolysaccharide-binding protein (LBP) play vital roles in defending the host against gram-negative bacteria. In the current study, a novel BPI/LBP from Trachinotus ovatus (TroBPI/LBP) was characterized. The full length of TroBPI/LBP cDNA sequence is 1434 bp, which contained 477 amino acids. Multiple amino acid alignments of TroBPI/LBP shows 34.07%-84.49% identity with other fish BPI/LBP. Similar to other BPI/LBP, TroBPI/LBP also possesses an N-terminal signal peptide, a BPI/LBP/CETP N-terminal domain, and a BPI/LBP/CETP C-terminal domain. In vitro, the recombinant protein of TroBPI/LBP showed effective bacterial depression activity and binding activity to gram-negative bacteria. In vivo, TroBPI/LBP was constitutively expressed in tested tissues, and the highest expression level was in liver. Following Vibrio alginolyticus stimulation, the mRNA expression of TroBPI/LBP was significantly upregulated in immune-related tissues, and peaked at 12 h post-infection, which confirmed that TroBPI/LBP was highly sensitive to V. alginolyticus stimuli. Furthermore, functional analyses showed that the overexpression of TroBPI/LBP could enhance the ability of fish to against V. alginolyticus infection, and the knockdown of TroBPI/LBP significantly diminished bacterial clearance capacity post-infection. Therefore, these results suggest that TroBPI/LBP may play an important role in host defense against bacterial infection.

A new SVWC protein functions as a pattern recognition protein in antibacterial responses in Chinese mitten crab (Eriocheirsinensis)

Because invertebrates lack acquired immunity, they rely primarily on the innate immune system to defend themselves against viral and bacterial infections. SVWC, also called Vago, is a class of small-molecule proteins characterized by a single von Willebrand factor C-domain and appears to be restricted to arthropods. It has been reported that SVWC is involved in antiviral immunity in invertebrates, but whether it is involved in antimicrobial immunity and the mechanism of its involvement in antimicrobial immunity remains unclear. In this study, we identified a novel SVWC gene in Eriocheir sinensis and named it EsSVWC. EsSVWC was found to respond positively to bacterial stimulation and to regulate the expression of related antimicrobial peptides (AMPs). The EsSVWC protein recognized and bound to a variety of pathogen-associated molecular patterns (PAMPs) but did not exhibit direct bactericidal effects. Thus, the EsSVWC protein in crabs helps resist bacterial infection and improve survival rates. In summary, EsSVWC may regulate the innate immune system of crabs in response to microbial invasion in an indirect manner.

Antibacterial responses and functional characterization of the interferon gamma inducible lysosomal thiol reductase (GILT) protein in Chinese mitten crab (Eriocheir sinensis)

The inducible reductase of interferon gamma (IFN- γ), IFN-γ-induced lysosomal thiol reductase (GILT) is important in antiviral immunity, but its mechanism in invertebrate antimicrobial immunity is unclear. We determined that GILT protein was involved in the antibacterial immunity of Chinese mitten crab (Eriocheir sinensis). GILT protein was highly expressed in crab hemocytes and was significantly upregulated 6 h after bacterial stimulation. Recombinant E. sinensis GILT (rEsGILT) contained a CXXS active site that catalyzed disulfide bond reduction. Vibrio parahaemolyticus and Staphylococcus aureus were bound through interaction with peptidoglycan and lipopolysaccharide, respectively, and bacterial agglutination and clearance in the crabs was markedly promoted. Nevertheless, EsGILT exhibited no direct antibacterial or bactericidal activity. EsGILT also promoted crab hemocyte phagocytosis and played an anti-bacterial role, and inhibited hemocyte apoptosis. In summary, EsGILT promoted bacterial agglutination, clearance, and phagocytosis by recognizing and agglutinating pathogenic microorganisms and reduced the apoptosis level, indirectly participating in antibacterial reactions.

Effect of polystyrene nanoplastics on cell apoptosis, glucose metabolism, and antibacterial immunity of Eriocheir sinensis

The adverse effects of plastic waste and nanoplastics on the water environment have become a focus of global attention in recent years. In the present study, using adult Chinese mitten crabs (Eriocheir sinensis) as an animal model, the bioaccumulation and the in vivo and in vitro toxicity of polystyrene nanoplastics (PS NPs), alone or in combination with the bacteria, were investigated. This study aimed to investigate the effects of PS NPs on apoptosis and glucose metabolism in Chinese mitten crabs, and whether PS NPs could synergistically affect the antibacterial immunity of crabs. We observed that NPs were endocytosed by hemocytes, which are immune cells in crustaceans and are involved in innate immunity. The RNA sequencing data showed that after hemocytes endocytosed NPs, apoptosis and glucose metabolism-related gene expression was significantly induced, resulting in abnormal cell apoptosis and a glucose metabolism disorder. In addition, exposure to NPs resulted in changes in the antimicrobial immunity of crabs, including changes in antimicrobial peptide expression, survival, and bacterial clearance. In summary, NPs could be endocytosed by crab hemocytes, which adversely affected the cell apoptosis, glucose metabolism, and antibacterial immunity of Eriocheir sinensis. This study revealed the effects of NPs on crab immunity and lays the foundation for further exploration of the synergistic effect of NPs and bacteria.

TNFR2 is a regulatory target of pol-miR-194a and promotes the antibacterial immunity of Japanese flounder Paralichthys olivaceus

MicroRNAs (miRNAs) are regulatory RNAs that modulate target gene expression after transcription. Pol-miR-194a had been reported to be a miRNA of Japanese flounder (Paralichthys olivaceus) involved in Edwardsiella tarda infection. Here, we identified tumor necrosis factor receptor 2 (TNFR2) as a target gene of pol-miR-194a. Pol-miR-194a markedly repressed the protein expression of flounder TNFR2 (PoTNFR2) via specific interaction with the 3'UTR of PoTNFR2. PoTNFR2 responded to E. tarda infection in a manner that was opposite to that of pol-miR-194a and inhibited E. tarda invasion by activating the NF-κB pathway. Consistently, dysregulation of PoTNFR2 had a significant impact on E. tarda dissemination in flounder tissues. Together, these results add new insights into the regulation mechanism and immune function of fish TNFR2 and pol-miR-194a.

Zinc-doped ferric oxyhydroxide nano-layer enhances the bactericidal activity and osseointegration of a magnesium alloy through augmenting the formation of neutrophil extracellular traps

Implant-associated infections (IAI) and osseointegration disorders are the most common complications in orthopedics. Studies have shown that neutrophils surrounding implants play a vital role in regulating these complications. Although magnesium (Mg) and its alloys are considered promising biodegradable bone implants, their role in neutrophil-mediated antibacteria has not yet been examined. Considering the rapid corrosion of Mg, it is necessary to develop methods to inhibit its corrosion. To solve these issues, a zinc-doped ferric oxyhydroxide nano-layer modified plasma electrolytic oxidation (PEO)-coated Mg alloy (PEO-FeZn) was developed in this study, and its antibacterial, immune anti-infective, and osteogenic ability were systematically evaluated. The results showed that PEO-FeZn nano-layer enhanced the corrosion resistance, biocompatibility, bactericidal activity, and osteoblastic differentiation activity of the Mg alloy. Moreover, PEO-FeZn nano-layer inhibited immune evasion-related gene expression and contributed to the formation of neutrophil extracellular traps (NETs) by activating the extracellular release of DNA fibers and granule proteins, and thereby suppressing bacterial invasion and promoting osseointegration in vivo in Staphylococcus aureus (S. aureus)-infected rat femurs. Overall, the findings of this study could serve as a reference for the fabrication of highly biocompatible and corrosion resistant Mg alloys to address the challenges of IAI and osseointegration disorders. STATEMENT OF SIGNIFICANCE: The widely used metallic biomaterials usually come with the risk of IAI. As the first responder around the biomaterials, neutrophils could form NETs to defense against microorganism and promote tissue remodeling. Therefore, biomaterials addressing antibacterial and neutrophils-modulatory strategies are highly necessary in reducing IAI. To solve these issues, we grew PEO-FeZn nano-layers in situ on Mg alloy using a simple and green technique. The nano-layer not only enhanced the corrosion resistance and biocompatibility of Mg alloy, but also elevated the antibacterial and osteogenesis capability. Moreover, nano-layer contributed to NETs formation, thereby suppressing bacterial invasion and even promoting osseointegration in S.aureus-infected femurs. Accordingly, this functionalized multilayer coating with antibacterial immunity represents a novel therapeutic strategy for IAI and weak osseointegration.

Cathepsin C (CTSC) contributes to the antibacterial immunity in golden pompano (Trachinotus ovatus)

Cathepsins, as a class of protein hydrolases, are widely found in the lysosomes of many tissues and play an essential role in various physiological activities. Cathepsin C (CTSC), a lysosomal cysteine protease, is an essential component of the lysosomal hydrolase family. In this study, we identified a CTSC from Trachinotus ovatus (TroCTSC) and analyzed its function. TroCTSC contained an ORF of 1368 bp and encoded 455 amino acids, which included three conserved catalytically active sites (Cys²⁵¹, His³⁹⁷, and Asn⁴¹⁹). It shares high homology (69.47%-90.77%) with the other known CTSC sequences of teleosts, which was most closely related to Seriola dumerili. TroCTSC was most abundant in the muscle, liver, and head kidney. After Vibrio harveyi infection, the expression levels of TroCTSC in liver, spleen, and head kidney were significantly up-regulated. TroCTSC was found in the cytoplasm with some of which were co-located with the lysosome. After V. harveyi stimulation, TroCTSC was translocated to nucleus in golden pompano snout (GPS) cells. In vitro, results revealed that the optimal hydrolase activity of the recombinant protein, rTroCTSC, was at 40 °C and pH 5.5. The activity of rTroCTSC was promoted by Zn²⁺ and Ca²⁺ but inhibited by Fe²⁺ and Cu²⁺. However, three mutant proteins, rTroCTSC-C251A, rTroCTSC-H397A, rTroCTSC-N419A, were dramatically reduced the proteolytic activity. Furthermore, in vivo results showed that overexpression of TroCTSC could significantly enhance body's ability to resist V. harveyi and promote the expression of proinflammatory cytokines, including interleukin 1-beta (IL-1β), IL-6, IL-8, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α). In contrast, the interference of TroCTSC expression induced a significant increase in the number of bacteria after V. harveyi infection. Our results suggested that TroCTSC was an essential effector of the innate immune system and played a pivotal role in antibacterial immunity.

The role of ficolin as a pattern recognition receptor in antibacterial immunity in Eriocheir sinensis

Ficolin, a member of the fibrinogen-related proteins family (FREPs), functions as a pattern recognition receptor (PRR) in vertebrates and in invertebrates as a novel lectin. In this study, we discovered the Ficolin homolog of Chinese mitten crab (Eriocheir sinensis), which we named EsFicolin. The obtained sequence showed that it has a highly conserved C-terminal fibrinogen-related domain (FReD) and a coiled-coil structure for trimer formation. EsFicolin was up-regulated in hemocytes after being stimulated by bacteria. Recombinant EsFicolin protein binds to gram-negative and gram-positive bacteria and agglutinates bacteria through pathogen-associated molecular patterns. In-depth study found that recombinant EsFicolin could effectively remove bacteria and showed direct antibacterial activity. EsFicolin could also promote the phagocytosis of hemocytes to enhance bacterial clearance. These findings suggest that EsFicolin plays an important role in the crab antibacterial immune response.

Macrophage migration inhibitory factor (MIF) of golden pompano (Trachinotus ovatus) is involved in the antibacterial immune response

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine with a unique structure involved in immune regulation and inflammation. In the present study, we identified a MIF from Trachinotus ovatus (golden pompano) and analyzed its function. TroMIF shares high homology (58.26%-94.78%) with the other known MIF sequences of vertebrates. TroMIF is most closely related to large yellow croaker (Larimichthys crocea). The expression of TroMIF was most abundant in the liver and head kidney, and was significantly up-regulated after Edwardsiella tarda infection. The subcellular localization of TroMIF was mostly distributed in the cytoplasm. In vitro results revealed that the recombinant protein rTroMIF could inhibit the migration of head kidney lymphocytes (HKLs) and macrophages (HKMs) and enhance the phagocytic activity of HKMs. As a pro-inflammatory cytokine, rTroMIF could increase the expression levels of some pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1β), IL-6, IL-8, and interferon-gamma (IFN-γ) and decrease the expression of IL-10. The rTroMIF was proved to have enzymatic redox activity in vitro. Furthermore, overexpression of TroMIF in the head kidney cell line of golden pompano could significantly enhance its ability to resist E. tarda infection from 1 h to 4 h. The knockdown of TroMIF expression induced a significant increase in the number of bacteria after E. tarda infection at 1, 2, and 4 hpi. Our results suggest that TroMIF is an essential effector of the innate immune system and plays a pivotal role in antibacterial immunity.

Membrane orthologs of TLR5 of tongue sole Cynoglossus semilaevis: Expression patterns, signaling pathway and antibacterial property

Mammalian toll-like receptor 5 (TLR5) is crucial for recognizing bacterial flagellin and initiating the inflammatory signaling cascades via myeloid differentiation factor 88 (MyD88) signaling pathway, which plays vital roles in innate immune against pathogenic bacteria. Herein, we reported the signaling pathway and antibacterial property of tongue sole (Cynoglossus semilaevis) membrane forms of TLR5 (i.e. CsTLR5M1and CsTLR5M2). CsTLR5M1/M2 contain 936 and 885 amino acid residues respectively. CsTLR5M1 shares 86.7% overall sequence identities with CsTLR5M2. CsTLR5M1/M2 possess the same extracellular domain (ECD) and transmembrane domain (TMD), but the different toll-interleukin-1 receptor (TIR) domain. CsTLR5M1/M2 expression occurred constitutively in multiple tissues and regulated by bacterial stimulation. Recombinant CsTLR5M1/M2 (rCsTLR5M) could bind to flagellin and Gram-negative/positive bacteria, which could suppress bacterial growth. Stimulation of the CsTLR5M pathway by flagellin resulted in increased expression of MyD88-dependent signaling molecules and inflammatory cytokines. Blocking rCsTLR5M by antibody markedly reduced the phagocytosis and ROS production of peripheral blood leukocytes (PBLs), which in turn in vivo promoted the dissemination of bacteria. Overall, these observations add new insights into the signaling pathway and immune function of teleost TLR5M.

Regulatory role of BTLA and HVEM checkpoint inhibitors in T cell activation in a perciform fish Larimichthys crocea

The BTLA and HVEM are two well-characterized immune checkpoint inhibitors in humans and other mammalian species. However, the occurrence and functionality of these two molecules in non-mammalian species remain poorly understood. In the present study, we identified the BTLA and HVEM homologs from large yellow croaker (Larimichthys crocea), an economically important marine species of the perciform fish family. The Larimichthys crocea BTLA and HVEM (LcBTLA and LcHVEM) share conserved structural features to their mammalian counterparts, and they were expressed in various tissues and cells examined at different transcriptional levels, with particular abundance in immune-relevant tissues and splenic leukocytes. Immunofluorescence staining and flow cytometry analysis showed that LcHVEM and LcBTLA proteins were distributed on MHC-II⁺ APCs and CD4-2⁺ T cells, and a strong interaction between LcBTLA and LcHVEM was detected in splenic leukocytes in the mixed lymphocyte reaction (MLR). By blockade assays using anti-LcBTLA and anti-LcHVEM Abs as well as recombinant soluble LcBTLA and LcHVEM proteins in different combinations, it was found that LcBTLA-LcHVEM interactions play an important inhibitory role in the activation of alloreactive T cells using MLR as a model, and APC-initiated antigen-specific CD4-2⁺ T cells in response to A. hydrophila (A. h) stimulation. These observations highlight the extensive functional roles of LcBTLA and LcHVEM immune-checkpoint inhibitors in allogeneic T cell reactions, and CD4-2⁺ T cell-mediated adaptive immune responses in Larimichthys crocea. Thus, the BTLA-HVEM checkpoint may represent an ancient coinhibitory pathway, which was originated in fish and was conserved from fish to mammals throughout the vertebrate evolution.

CsIL-11, a teleost interleukin-11, is involved in promoting phagocytosis and antibacterial immune defense

Interleukin (IL)-11 is a multifunctional cytokine belonging to the IL-6 family, which plays essential roles in immune response. However, much less is known about the immunological functions of IL-11 in teleost. In this study, we investigated the immune properties of a teleost IL-11 homologue (CsIL-11) from tongue sole Cynoglossus semilaevis. CsIL-11 possesses four conserved α-helices and conserved CsIL-11 receptor binding residues L86 and R187, and shares 23.3%-80.1% identities with other IL-11 homologues. CsIL-11 expression was constitutive in tissues, with most abundant in blood and least abundant in spleen, and upregulated by bacterial challenge in blood, spleen, and head kidney. Recombinant CsIL-11 (rCsIL-11) in the native form of monomer, could bind to peripheral blood leukocytes (PBLs) membrane and enhance the activation and phagocytosis of PBLs. When administered in vivo, rCsIL-11 could markedly promote the host to defend against microbial infection. Overall, our findings show that CsIL-11 plays a pivotal role in regulating PBLs phagocytosis and antibacterial immunity.

Molecular and functional characterization of mitochondrial manganese superoxide dismutase from Macrobrachium rosenbergii during bacterial infection

Superoxide dismutases (SODs) are the main antioxidant enzymes involved in alleviating oxidative stress. Although mitochondrial manganese SOD (mMnSOD) has been reported to be correlated with the immune response in crustaceans, its biological properties and role in the immune response remain unclear. Here, we cloned the Macrobrachium rosenbergii mMnSOD (MrmMnSOD), analyzed its activity and expression pattern under Staphylococcus aureus and Vibrio parahaemolyticus infection, and further explored its possible mechanism during antibacterial immune response. The results showed that both enzyme activity and the expression of MrmMnSOD were significantly up-regulated by bacterial infection. MrmMnSOD knockdown made the prawn susceptible to Vibrio infection, which increased the mortality rate and the number of bacteria in haemocytes. The bacterial agglutination assay confirmed that MrmMnSOD decreases bacterial abundance via agglutination. Overall, this work identified antibacterial function of MrmMnSOD in the immune response. In addition to contributing to immunological theory, these findings aid disease prevention and control in crustacean aquaculture.

Calreticulin functions in antimicrobial immunity of obscure puffer Takifugu obscurus

Calreticulin (Crt) is a highly conserved and multi-functional protein with lectin-like properties and important immunological activities. In this study, a Crt homolog, namely, ToCrt, was cloned and characterized from the obscure puffer Takifugu obscurus with an open reading frame of 1278 bp encoding a putative protein of 425 amino acids. The deduced amino acid sequence of ToCrt consisted of three conserved structural domains: N-domain, P-domain, and C-terminal domain. In the phylogenetic tree, ToCrt formed a separate cluster with three Crts from other pufferfish species (Takifugu rubripes, Takifugu flavidus, and Takifugu bimaculatus). The mRNA transcript of ToCrt was ubiquitously expressed in all the examined tissues in a decreasing order: liver, spleen, kidney, gills, intestine, and heart. After Vibrio harveyi, Edwardsiella tarda, and Aeromonas hydrophila stimulations, the levels of ToCrt mRNA in the kidney and spleen were significantly upregulated compared with that in the control group. The recombinant calreticulin domain of ToCrt (rToCrt) could bind three Gram-negative bacteria (V. harveyi, E. tarda, and A. hydrophila) and polysaccharides from bacterial cell walls such as lipopolysaccharide and peptidoglycan. Meanwhile, rToCrt could agglutinate different kinds of microorganisms and exhibit antimicrobial activity. These results suggested that T. obscurus ToCrt could serve as an antimicrobial effector in the host immune response against invading microorganisms.

Functional characterization of cathepsin B and its role in the antimicrobial immune responses in golden pompano (Trachinotus ovatus)

Cathepsin B (CTSB) is one of the typical representatives of cysteine protease family. It has the activity of both exopeptidase and endopeptidase. It plays an important role in antigen presentation, degradation, apoptosis, inflammatory response and physiological process of many diseases. In this study, CTSB of Trachinotus ovatus (TroCTSB) was cloned, and its structure and function were analyzed. The results showed that the coding region of TroCTSB was 993 bp, encoding 330 amino acid residues. The homology analysis showed that the amino acid sequence of TroCTSB was similar to that in other teleosts and mammals (68.69%-88.48%). Under normal physiological conditions, TroCTSB was widely distributed in various tissues with the highest expression level in stomach, followed by liver, and the lowest expression level in blood. The optimal pH and temperature of purified recombinant protein rTroCTSB were 5.5 and 40 °C, respectively. The toxicity test of metal ions showed that Fe²⁺, Cu²⁺, Ca²⁺ and Zn²⁺ could all inhibit the activity of TroCTSB, with Zn²⁺ ranking the first. In addition, after Edwardsiella tarda infection, the expression of TroCTSB was significantly up-regulated in liver, spleen and head kidney. The overexpression of TroCTSB significantly inhibited the infection of E. tarda in golden pompano tissues, and the knockdown of TroCTSB remarkably promoted the reproduction of E. tarda in golden pompano tissues in vivo. This study suggests that TroCTSB was involved in the antibacterial immune response of T. ovatus, and provided a reference for further research in elucidating the resistance mechanism of TroCTSB.

Escherichia coli induced ferroptosis in red blood cells of grass carp (Ctenopharyngodon idella)

The red blood cells (RBCs) of fish make up around 95% of the total peripheral blood cells, and the long-held paradigm is that RBCs are mainly responsible for transporting oxygen. Previous studies have showed that the RBCs can be involved in the immune response against bacterial infection; however, this mechanism remains enigmatic. Here, we explored the structure of grass carp RBCs (GcRBCs). The results showed that the GcRBCs released a pseudopodia-like structure when grown in a 24-well plate, and the transmission electron microscopy (TEM) result showed that GcRBCs contained some organelle-like structures. To further verify the organelle-like structures might be the mitochondria and lysosome which similar to other immune cells, a fluorescent labeling assay was used to verify it. To decipher the antibacterial immunity of GcRBCs, transcriptomic profiling of grass carp RBCs after the incubation with E. coli was analyzed. The results showed that there were 4099 differently expressed genes (DEGs) of GcRBCs upon E. coli incubation, including 2041 up-regulated and 2058 down-regulated genes. In addition, to validate our transcriptomic data, we checked the expression of several cytokines, such as CCL4, CCL20, IL4, IL12 and IFN-α, and the results showed that all the selected gens were significantly up-regulated after E. coli incubation. Furthermore, E. coli incubation induced hemoglobin oxidation and increased the heme in GcRBCs, which further activated the expression of heme oxygenase 1 (HO-1), autophagy related genes 5 (ATG5), and ferritin. In contrast, E. coli incubation inhibited the expression of Ferroportin-1 (FPN1), which increased intracellular iron levels, induced Fenton reaction to release reactive oxygen species (ROS), and activated the ferroptosis signaling pathway in GcRBCs. Herein, we demonstrate that E. coli can induce teleost RBCs cell death through an iron-mediated ferroptosis pathway, which sheds new light on the interaction between bacteria and teleost RBCs.

A novel SNW/SKIP domain-containing protein, Bx42, is involved in the antibacterial responses of Macrobrachium nipponense

Bx42, the homologue of SNW1 in mammals, is involved in pre-mRNA splicing and transcriptional regulation. However, the presence and function of Bx42 have remained poorly understood in invertebrates until now. In the current study, a novel SNW domain-containing protein (MnBx42) from Macrobrachium nipponense was identified, and its potential role in the immune response was investigated. The full-length MnBx42 was 7467 bp with an open reading frame of 1653 bp, encoding 550 amino acids. Real-time PCR analysis suggested that MnBx42 was predominantly expressed in the intestine, gills and hepatopancreas, and immunofluorescence assays indicated that it was located in the nucleus. Its expression level was significantly decreased in M. nipponense post-challenge with white spot syndrome virus (WSSV) as well as Aeromonas hydrophila and Staphylococcus aureus, implying its participation in the innate immune response. The knockdown of MnBx42 in vivo notably increased the susceptibility of the prawns to bacterial infection, markedly increased the bacterial load in the gills, and significantly attenuated the phagocytic activity of haemocytes. Dual-luciferase reporter assays illustrated that MnBx42 could activate the NF-κB pathway. Consistent with this, when MnBx42 was silenced in vivo, the expression levels of antimicrobial peptides (AMPs), including ALF2, ALF3, ALF4, ALF5, Cru1 and Cru2, and NF-κB signalling genes, including dorsal, relish, TAK1, TAB1, Ikkβ, and Ikkε, were significantly reduced. Taken together, these findings may provide new insights about Bx42 in crustaceans and pave the way for a better understanding of the crustacean innate immune system.

Molecular characterization and antibacterial immunity functional analysis of liver-expressed antimicrobial peptide 2 (LEAP-2) gene in golden pompano (Trachinotus ovatus)

Liver-expressed antimicrobial peptide-2 (LEAP-2) is a member of the antimicrobial peptides family. Research has demonstrated that LEAP-2 contains a number of cations and plays a key role in the innate immune system of organism. In this study, we cloned and identified TroLEAP-2, from the golden pompano (Trachinotus ovatus), and analyzed its functions in vivo and in vitro. Results showed that TroLEAP-2 contains a 321 bp open reading frame (ORF) that encodes 106 putative amino acids with a molecular weight of 11.65 kDa. The mature TroLEAP-2 peptide possesses four conserved cysteine residues, which can form a core structure with two disulfide bonds between the cysteine residues in the relative 1-3 (Cys 77 and Cys 88) and 2-4 (Cys 83 and Cys 93) positions. It has a high amino acid sequence similarity (38.68%-83.02%) with the liver-expressed antimicrobial peptide -2 of other teleosts. Phylogenetic analysis showed that TroLEAP-2 clustered with the LEAP-2 of Paralichthys olivaceus and Miichthy milluy. TroLEAP-2 was most abundantly expressed in the liver, spleen, and kidney, and was significantly upregulated during Edwardsiella tarda and Streptococcus agalactiae infection. Purified recombinant TroLEAP-2 (rTroLEAP-2) could significantly inhibit the in vitro growth of E. tarda and S. agalactiae. Overexpression of TroLEAP-2 in vivo was shown to significantly reduce E. tarda and S. agalactiae colonization of tissues, whereas its knockdown resulted in an increase of bacteria in fish tissues. We also saw that TroLEAP-2 overexpression significantly improved macrophage activation in vivo. Moreover, TroLEAP-2 can induce the expression of nonspecific immune-related genes. These results showed that it might play a significant role in the innate immune system of golden pompano. In conclusion, our results indicate that TroLEAP-2 plays an important role in antibacterial immunity and provides a new avenue for protection against pathogenic infections in golden pompano.

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

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

First identification and characterization of a triple WAP domain containing protein in Procambarus clarkii provides new insights into the classification and evolution of WAP proteins in crustacean

Whey acidic protein domain (WAPD) is a usual motif in crustaceans, and is found mainly in the immune-related proteins. In the present study, a protein containing three tandem WAPDs was identified in red swamp crayfish Procambarus clarkii and designated as PcTWD. This is the first report of a protein of such domain architecture in crustaceans. Introducing the WAPDs of PcTWD into phylogenetic analysis led to the classification of crustacean WAP proteins into classical crustins and proteins containing solely WAPDs. PcTWD was widely expressed in multiple tissues, including hemocytes, gills, hepatopancreas, heart, stomach and intestine. Its expression could be significantly induced by Staphylococcus aureus or Aeromonas hydrophila challenge. Knockdown PcTWD expression by RNAi suppressed host resistance against A. hydrophila, while exogenous recombinant PcTWD could enhance the host immunity. The three WAPDs showed a labor division. The first two domains were responsible for the protease inhibitory activity, and the third domain contributed to the antimicrobial activity. Thus PcTWD was found as an important protein in crayfish antibacterial immunity.

A β-defensin gene of Trachinotus ovatus might be involved in the antimicrobial and antiviral immune response

Defensins are a group of small cationic and cysteine-rich peptides that are important components of the innate immune system. However, studies on defensins in teleosts are very limited, particularly studies on defensin functions through in vivo assays. In this study, we cloned and identified one β-defensin (TroBD) the golden pompano, Trachinotus ovatus, and analyzed the functions of TroBD in both in vivo and in vitro assays. TroBD is composed of 63 amino acids and shares high sequence identities (27.27-98.41%) with known β-defensins of other teleosts. The protein has a signature motif of six conserved cysteine residues within the mature peptide. The expression of TroBD was most abundant in the head kidney and spleen and was significantly upregulated following infection by Vibrio harveyi and viral nervous necrosis virus (VNNV). Purified recombinant TroBD (rTroBD) inhibited the growth of V. harveyi, and its antimicrobial activity was influenced by salt concentration. TroBD was found to have a chemotactic effect on macrophages in vitro. The results of an in vivo study demonstrated that TroBD overexpression/knockdown in T. ovatus significantly reduced/increased bacterial colonization or viral copy numbers in tissues. Taken together, these results indicate that TroBD plays a significant role in both antibacterial and antiviral immunity and provide new avenues for protection against pathogen infection in the aquaculture industry.

Transcriptome analysis of Pacific white shrimp (Litopenaeus vannamei) challenged by Vibrio parahaemolyticus reveals unique immune-related genes

Pacific white shrimp (Litopenaeus vannamei) is an important cultural species worldwide. However, Vibrio spp. infections have caused a great economic loss in Pacific white shrimp culture industry. The immune responses of Pacific white shrimp to the Vibrio spp. is not fully characterized. In this study, the transcriptomic profiles of L. vannamei hemocytes were explored by injecting with or without Vibrio parahaemolyticus. Totally, 42,632 high-quality unigenes were obtained from RNAseq data. Comparative genome analysis showed 2258 differentially expressed genes (DEGs) following the Vibrio challenge, including 1017 up-regulated and 1241 down-regulated genes. Eight DEGs were randomly selected for further validation by quantitative real-time RT-PCR (qRT-PCR) and the results showed that are consistent with the RNA-seq data. Due to the lack of predictable adaptive immunity, shrimps rely on an innate immune system to defend themselves against invading microbes by recognizing and clearing them through humoral and cellular immune responses. Here we focused our studies on the humoral immunity, five genes (SR, MNK, CTL3, GILT, and ALFP) were selected from the transcriptomic data, which were significantly up-regulated by V. parahaemolyticus infection. These genes were widely expressed in six different tissues and were up-regulated by both Gram negative bacteria (V. parahaemolyticus) and Gram positive bacteria (Staphylococcus aureus). To further extend our studies, we knock-down those five genes by dsRNA in L. vannamei and analyzed the functions of specific genes against V. parahaemolyticus and S. aureus by bacterial clearance analysis. We found that the ability of L. vannamei was significantly reduced in bacterial clearance when treated with those specific dsRNA. These results indicate that those five genes play essential roles in antibacterial immunity and have its specific functions against different types of pathogens. The obtained data will shed a new light on the immunity of L. vannamei and pave a new way for fighting against the bacterial infection in Pacific white shrimp.

Thymosin β4 is involved in the antimicrobial immune response of Golden pompano, Trachinotus ovatus

Thymosin beta belongs to the thymosin family, which consists of a series of highly conserved peptides involved in various biological processes. In teleosts, understanding of the immunological functions of thymosin beta is limited, particularly in vivo, which is essentially unknown. In the current study, we cloned and identified thymosin beta 4 from the teleost fish Golden pompano (Trachinotus ovatus), which we have named TroTβ4. We investigated the expression patterns and functions of TroTβ4 in both in vivo and in vitro assays. TroTβ4 is composed of 44 amino acids and shares high sequence identities with known thymosin β4 species in other teleosts, which contains a highly conserved actin-binding motif (LKKTET). The expression of TroTβ4 was most abundant in immune organs, and was significantly up-regulated in response to infection bacterial with one of a number of bacteria (including Edwardsiella tarda, Vibrio harveyi, and Streptococcus agalactiae). Purified recombinant TroTβ4 (rTroTβ4) inhibited the growth of bacteria, as measured using an automatic growth curve analyzer, indicating that TroTβ4 has antimicrobial functions. When administered in vivo, overexpression of TroTβ4 in T. ovatus, bacterial colonization of tissues was significantly reduced. In contrast, when a DNA vector-based siRNA technology was used to knock down TroTβ4 expression, bacterial dissemination and colonization of tissues increased significantly. Taken together, these results provide the first in vivo evidence to indicate that teleost thymosin beta 4 plays a significant role in innate antibacterial immune responses in addition to in vitro bacteriostatic activity. This provides valuable information regarding the biological functions of teleost thymosin beta.