Orange-spotted grouper (Epinephelus coioides) toll-like receptor 22: molecular characterization, expression pattern and pertinent signaling pathways

Positive effects of dietary Clostridium butyricum supplementation on growth performance, antioxidant capacity, immunity and viability against hypoxic stress in largemouth bass

The effects of dietary supplementation of Clostridium butyricum (CB) on growth performance, serum biochemistry, antioxidant activity, mRNA levels of immune-related genes and resistance to hypoxia stress were studied in largemouth bass. Feed with CB0 (control, 0 CFU/kg), CB1 (4.3×108 CFU/kg), CB2 (7.5×108 CFU/kg), CB3 (1.5×109 CFU/kg) and CB4 (3.2×109 CFU/kg) CB for 56 days, and then a 3 h hypoxic stress experiment was performed. The results showed that dietary CB significantly increased the WGR (weight gain rate), SGR (specific growth rate), PDR (protein deposition rate) and ISI (Intestosomatic index) of largemouth bass (P<0.05). Hepatic GH (growth hormone)/IGF-1 (insulin-like growth factor-1) gene expression was significantly upregulated in the CB3 and CB4 groups compared with the CB0 group (P<0.05), while the FC (feed conversion) was significantly decreased (P<0.05). Serum TP (total protein) and GLU (glucose) levels were significantly higher in the CB4 group than in the CB0 group (P<0.05), while the contents of serum AST (aspartate transaminase), ALT (alanine transaminase), AKP (alkline phosphatase) and UN (urea nitrogen) in CB4 were significantly lower than those in CB0 (P<0.05). T-AOC (total antioxidant capacity), SOD (superoxide dismutase), CAT (catalase), POD (peroxidase) and GSH-Px (glutathione peroxidase) activities were significantly higher in CB3 and CB4 groups than in CB0 group (P<0. 05). The liver MDA (malondialdehyde) content of CB1, CB2, CB3 and CB4 groups was significantly higher than that of CB0 group (P<0. 05). The relative expressions of IL-1β (interleukin 1β), TNF-α (tumor necrosis factor α) and TLR22 (toll-like receptor-22) genes in CB2, CB3 and CB4 groups were significantly lower than those in CB0 group (P<0.05). The relative expression of IL-8 (malondialdehyde) and MyD88 (Myeloid differentiation factor 88) genes in the CB4 group was significantly lower than that in the CB0 group (P<0.05). The liver LZM (lysozyme) content of CB2, CB3 and CB4 groups was significantly higher than that of CB0 group (P<0. 05). The relative expression of IL-10 (interleukin 10) and TGF-β (transforming growth factor β) genes in the CB4 group was significantly higher than that in the CB0 group (P<0.05). Under hypoxic stress for 3 h, the CMR of CB0 group was significantly higher than that of CB1, CB2, CB3 and CB4 groups (P<0.05). Dietary CB can improve the growth performance and resistance to hypoxic stress of largemouth bass by regulating the expression of GH/IGF-1 gene and inflammatory factors and inhibiting TLR22/MyD88 signaling pathway.

Molecular Cloning of Toll-like Receptor 2 and 4 (SpTLR2, 4) and Expression of TLR-Related Genes from Schizothorax prenanti after Poly (I:C) Stimulation

Toll-like receptor (TLR) signaling is conserved between fish and mammals, except for TLR4, which is absent in most fish. In the present study, we aimed to evaluate whether TLR4 is expressed in Schizothorax prenanti (SpTLR4). The SpTLR2 and SpTLR4 were cloned and identified, and their tissue distribution was examined. The cDNA encoding SpTLR4 and SpTLR2 complete coding sequences (CDS) were identified and cloned. Additionally, we examined the expression levels of seven SpTLRs (SpTLR2, 3, 4, 18, 22-1, 22-2, and 22-3), as well as SpMyD88 and SpIRF3 in the liver, head kidney, hindgut, and spleen of S. prenanti, after intraperitoneal injection of polyinosinic-polycytidylic acid (poly (I:C)). The SpTLR2 and SpTLR4 shared amino acid sequence identity of 42.15-96.21% and 36.21-93.58%, respectively, with sequences from other vertebrates. SpTLR2 and SpTLR4 were expressed in all S. prenanti tissues examined, particularly in immune-related tissues. Poly (I:C) significantly upregulated most of the genes evaluated in the four immune organs compared with the PBS-control (p < 0.05); expression of these different genes was tissue-specific. Our findings demonstrate that TLR2 and TLR4 are expressed in S. prenanti and that poly (I:C) affects the expression of nine TLR-related genes, which are potentially involved in S. prenanti antiviral immunity or mediating pathological processes with differential kinetics. This will contribute to a better understanding of the roles of these TLR-related genes in antiviral immunity.

Understanding the molecular response of non-mammalian toll-like receptor 22 (TLR22) in amphibious air-breathing catfish, Clarias magur (Hamilton, 1822) to bacterial infection or ligand stimulation through molecular cloning and expression profiling

Toll-like receptor (TLR) 22 is a non-mammalian TLR, which is identified initially as a functional substitute of mammalian TLR3 in recognizing cell surface long dsRNA in teleosts. To understand the pathogen surveillance role played by TLR22 in an air-breathing catfish model the full-length cDNA of TLR22 was identified in Clarias magur and found to be consisted of 3597 nucleotides encoding for 966 amino acids. In the deduced amino acid sequence of C. magur TLR22 (CmTLR22) key signature domains such as one signal peptide, 13 LRRs, one transmembrane domain, one LRR_CT domain and an intracellular TIR domain could be identified. The CmTLR22 formed a separate cluster with other catfish TLR22 genes and situated within the TLR22 cluster in the phylogenetic analysis of teleost TLR groups. The CmTLR22 was constitutively expressed in all the 12 tested tissues of healthy C. magur juveniles with the highest transcript abundance in spleen followed by brain, intestine and head kidney. Following induction with the dsRNA viral analogue, poly (I:C), the level of expression of CmTLR22 was up-regulated in tissues such as kidney, spleen and gills. Whereas, in Aeromonas hydrophila-challenged C. magur, the expression levels of CmTLR22 was found to be up-regulated in gills, kidney and spleen, and down-regulated in liver. The findings of the current study suggest that the specific function of TLR22 is evolutionarily conserved in C. magur and might play a key role in mounting immune response by recognizing Gram-negative fish pathogen such as A. hydrophila and aquatic viruses in air-breathing amphibious catfishes.

Molecular characterization of a teleost-specific toll-like receptor 22 (tlr22) gene from yellow catfish (Pelteobagrus fulvidraco) and its transcriptional change in response to poly I:C and Aeromonas hydrophila stimuli

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that can recognize pathogen-associated molecular patterns (PMPs) and play important roles in the innate immune system in vertebrates. In this study, we identified a teleost-specific tlr22 gene from yellow catfish (Pelteobagrus fulvidraco) and its immune roles in response to different pathogens were also determined. The open reading frame (ORF) of the tlr22 was 2892 bp in length, encoding a protein of 963 amino acids. Multiple protein sequences alignment, secondary and three-dimensional structure analyses revealed that TLR22 is highly conserved among different fish species. Phylogenetic analysis showed that the phylogenetic topology was divided into six families of TLR1, TLR3, TLR4, TLR5, TLR7 and TLR11, and TLR22 subfamily was clustered into TLR11 family. Meanwhile, synteny and gene structure comparisons revealed functional and evolutionary conservation of the tlr22 gene in teleosts. Furthermore, tlr22 gene was shown to be widely expressed in detected tissues except barbel and eye, with highest expression level in liver. The transcription of tlr22 was significantly increased in spleen, kidney, liver and gill tissues at different timepoints after Poly I:C infection, suggesting TLR22 plays critical roles in defensing virus invasion. Similarly, the transcription of tlr22 was also dramatically up-regulated in spleen, kidney and gill tissues with different patterns after Aeromonas hydrophila infection, indicating that TLR22 is also involved in resisting bacteria invasion. Our findings will provide a solid basis for the investigation the immune functions of tlr22 gene in teleosts, as well as provide useful information for disease control and treatment for yellow catfish.

Impacts of tea polyphenols on growth, antioxidant capacity and immunity in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed high-lipid diets

The experiment aimed to investigate the alteration of tea polyphenols (TP) in growth and immunity for hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed high-lipid diets. Six concentrations of TP (0, 0.01, 0.02, 0.04, 0.08, 0.16%, named TP1 (basic diet control), TP2, TP3, TP4, TP5, TP6) were supplied in isonitrogenous (51%) and isolipidic (16.7%) experimental diets. These diets were fed to the juvenile grouper (8.68 ± 0.22 g) for 8 weeks. The results showed that dietary TP significantly increased the weight gain rate and specific growth rate (P < 0.05), compared with the control group. The protein efficiency ratio in TP4 group was significantly higher than that of the control group (P < 0.05). TP supplement in high-lipid diets increased antioxidant capacity in the serum (CAT, GSH-Px, T-AOC) and liver (SOD, CAT, GSH-Px, T-AOC). Additionally, dietary TP decreased oxidative stress (ROS, MDA) and improved immunity (ACP, AKP, LYS, IgM) in the liver. The histology of hepatic tissue indicated that dietary TP alleviated pathological symptoms caused by high-lipid diets. Compared with the control group, appropriate dietary TP significantly up-regulated expression of sod, cat, gsh-px, nrf2, keap1, hsp70, hsp90, myd88, tnfα and down-regulated expression of tlr22, il8, il1β, il10 in the liver (P < 0.05). In the head kidney, expression of myd88, il1β, tnfα and il6 were significantly up-regulated and expression of tlr22 and il10 were significantly down-regulated by dietary TP (P < 0.05). After the challenge of Vibrio harveyi, survival rate in higher doses of TP group (TP4 ∼ TP6) was evidently higher, compared with the control group. In conclusion, TP supplement in high-lipid diets improved antioxidant capacity and enhanced immunity of grouper. We speculate that TP may play the role of an immunostimulant, enhancing immunity and disease resistance by cytokine-medicated immune responses. Based on the second-order regression, 0.092-0.106% tea polyphenols were recommended in juvenile grouper high-lipid diets.

The positive effects of dietary inositol on juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) fed high-lipid diets: Growthperformance, antioxidant capacity and immunity

The objective of the present research was to assess the influence of inositol supplementation on growth performance, histological morphology of liver, immunity and expression of immune-related genes in juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu). Hybrid grouper (initial weight 6.76 ± 0.34 g) were fed isonitrogenous and isolipidic diets (16%) with various inositol levels of 0.17 g/kg (J1, the control group), 0.62 g/kg (J2), 1.03 g/kg (J3), 1.78 g/kg (J4), 3.43 g/kg (J5), 6.59 g/kg (J6), respectively. The growth experiment lasted for 8 weeks. The results indicated that dietary inositol had a significant promoting effect on final mean body weight of the J5 and J6 groups and specific growth rate (SGR) of the J3, J4, J5 and J6 groups (P < 0.05). In the serum, superoxide dismutase (SOD) of the J4 group became significantly active compared with that of the control group (P < 0.05), while aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (AKP) activities in the inositol-treated groups showed distinctly decreased compared with those of the control group (P < 0.05). In the liver, dietary inositol could significantly increase the activities of SOD, catalase (CAT), lysozyme (LYZ) and the contents of total antioxidative capacity (T-AOC) and immunoglobulin M (IgM) (P < 0.05), and distinctly reduce the content of malondialdehyde (MDA) as well as reactive oxygen species (ROS) (P < 0.05). Compared with the control group, the damaged histological morphology of the liver was relieved and even returned to normal after an inositol increase (0.4-3.2 g/kg). In the liver, the remarkable up-regulation of SOD, CAT, glutathione peroxidase (GPX), heat shock protein70 (HSP70) and heat shock protein90 (HSP90) expression levels were stimulated by supply of inositol, while interleukin 6 (IL6), interleukin 8 (IL8) and transforming growth factor β (TGF-β) expression levels were down-regulated by supply of inositol. In head kidney, the mRNA of toll-like receptor 22 (TLR22), myeloid differentiation factor 88 (MyD88) and interleukin 1β (IL1β) expression levels were significantly down-regulated (P < 0.05), which could further lead to remarkable down-regulation of IL6 and tumor necrosis factor α (TNF-α) expression (P < 0.05). These results indicated that high-lipid diets with supply of inositol promoted growth, increased the antioxidant capacity, and suppressed the inflammation of the liver and head kidney by inhibiting the expression of pro-inflammation factors (IL6, IL8, TGF-β and TNF-α). In conclusion, these results indicated that dietary inositol promoted growth, improved antioxidant capacity and immunity of hybrid grouper fed high-lipid diets. Based on SGR, broken-line regression analysis showed that 1.66 g/kg inositol supply was recommended in high-lipid diets of juvenile grouper.

Docosahexaenoic Acid Alleviates Palmitic Acid-Induced Inflammation of Macrophages via TLR22-MAPK-PPARγ/Nrf2 Pathway in Large Yellow Croaker (Larimichthys crocea)

Palmitic acid (PA) is a saturated fatty acid (SFA) that can cause an inflammatory response, while docosahexaenoic acid (DHA) is always used as a nutritional modulator due to its anti-inflammatory properties. However, the potential molecular mechanism is still not completely elucidated in fish. Herein, the PA treatment induced an inflammatory response in macrophages of large yellow croaker (Larimichthys crocea). Meanwhile, the mRNA expression of Toll-like receptor (TLR)-related genes, especially tlr22, and the phosphorylation of the mitogen-activated protein kinase (MAPK) pathway were significantly upregulated by PA. Further investigation found that the PA-induced inflammatory response was suppressed by tlr22 knockdown and MAPK inhibitors. Moreover, the results of the peroxisome proliferator-activated receptor γ (PPARγ) agonist and inhibitor treatment proved that PPARγ was involved in the PA-induced inflammation. PA treatment decreased the protein expression of PPARγ, while tlr22 knockdown and MAPK inhibitors recovered the decreased expression. Besides, the PA-induced activation of Nrf2 was regulated by p38 MAPK. Furthermore, DHA-executed anti-inflammatory effects by regulating the phosphorylation of the MAPK pathway and expressions of PPARγ and Nrf2. Overall, the present study revealed that DHA alleviated PA-induced inflammation in macrophages via the TLR22-MAPK-PPARγ/Nrf2 pathway. These results could advance the understanding of the molecular mechanism of the SFA-induced inflammatory response and provide nutritional mitigative strategies.

TLR22-mediated activation of TNF-α-caspase-1/IL-1β inflammatory axis leads to apoptosis of Aeromonas hydrophila-infected macrophages

Toll-like receptors (TLRs) represent first line of host defence against microbes. Amongst different TLRs, TLR22 is exclusively expressed in non-mammalian vertebrates, including fish. The precise role of TLR22 in fish-immunity remains abstruse. Herein, we used headkidney macrophages (HKM) from Clarias gariepinus and deciphered its role in fish-immunity. Highest tlr22 expression was observed in the immunocompetent organ - headkidney; nonetheless expression in other tissues suggests its possible involvement in non-immune sites also. Aeromonas hydrophila infection up-regulates tlr22 expression in HKM. Our RNAi based study suggested TLR22 restricts intracellular survival of A. hydrophila. Inhibitor and RNAi studies further implicated TLR22 induces pro-inflammatory cytokines TNF-α and IL-1β. We observed heightened caspase-1 activity and our results suggest the role of TLR22 in activating TNF-α/caspase-1/IL-1β cascade leading to caspase-3 mediated apoptosis of A. hydrophila-infected HKM. We conclude, TLR22 plays critical role in immune-surveillance and triggers pro-inflammatory cytokines leading to caspase mediated HKM apoptosis and pathogen clearance.

Mechanisms by Which Fermented Soybean Meal and Soybean Meal Induced Enteritis in Marine Fish Juvenile Pearl Gentian Grouper

Soy meals can cause intestinal inflammation and even injury in animals, especially infants and juvenile individuals. This study investigated the effects of fermented soybean meal (FSBM) on the growth and intestinal homeostasis of juvenile pearl gentian grouper and examined the mechanisms by which FSBM and soybean meal (SBM) induced enteritis in fish, using "3+2" full-length transcriptome sequencing. We randomly assigned 720 female juvenile groupers into three treatment groups: FM control group, 20% FSBM group (FSBM20), and FSBM40 group (n = 4). Three iso-nitrogenous (50% protein) and iso-lipidic (10% lipid) diets were prepared and fed to fish for 10 weeks. The water volume in each barrel was about 1 m3, using natural light and temperature. Results showed that dietary FSBM, at experimental level, significantly affected fish growth and intestinal structure negatively and significantly increased enteritis indices. The degree of intestinal injury and inflammation was determined by the enzyme activities of trypsin and lysozyme, and the contents of IgM, C3, C4, and malondialdehyde, and the expressions of pro-inflammatory genes (IL1β, IL8, IL17, and TNFα) and anti-inflammatory genes (IL4, IL10, and TGFβ1). Full-length transcriptome analysis identified 2,305 and 3,462 differentially expressed genes (DEGs) in SBM40 and FSBM40 groups, respectively. However, only 18.98% (920/5,445) of DEGs had similar expression patterns, indicating that high levels of SBM40 and FSBM40 have different metabolic strategies. KEGG enrichment analysis indicated that among the significant pathways, ~45% were related to immune diseases/systems, infectious diseases, and signal transduction in both SBM and FSBM groups. Based on PacBio SMRT sequencing, nine toll-like receptor (TLR) members, including TLR1, TLR2, TLR3, TLR5, TLR8, TLR9, TLR13, TLR21, and TLR22, were detected in intestinal tissues of pearl gentian grouper. TLR-MyD88-NF-κB signaling pathway played an important role in the development of FSBM- and SBM-induced enteritis in pearl gentian grouper; however, TLR receptors used in SBM and FSBM groups were different. TLR1, TLR8, TLR13, and TLR22 were the main receptors used in FSBM group, while TLR5, TLR8, TLR9, TLR21, and TLR22 were the main receptors used in SBM group. Present study provides valuable theoretical references for further research on soy protein-induced enteritis in fish.

Characterization, expression and function analysis of the TLR3 gene in golden pompano (Trachinotus ovatus)

Toll-like receptors (TLRs)are pattern recognition receptors (PRRs) that are important in invertebrate innate immunity for the recognition and elimination of pathogens. Although they were reported in many fishes, Toll-like receptors subfamily contain a large number of members with different functions that need to research in deep. In the present study, the full-length cDNA of TLR3 from the golden pompano, Trachinotus ovatus, was cloned and characterized. The full length of ToTLR3 cDNA was 3710 bp including an open reading frame of 2760 bp encoding a peptide of 919 amino acids. The derived amino acids sequence comprised of 14 leucine-rich repeats (LRR), capped with LRRCT followed by transmembrane domain and cytoplasmic Toll/IL-1R domain (TIR). Multiple sequence alignment and phylogenetic analysis revealed that ToTLR3 shared the highest similarity to the teleost fish and suggested ToTLR3 is fairly conservative in evolution process. Tissues distribution analysis indicated that ToTLR3 showed a tissue-specific variation with high expression in blood and liver. After the fish were stimulated by poly(I:C), flagellin and LPS, ToTLR3 expression in the liver, intestine, blood, kidney, skin and muscle was significantly upregulated in a time-depended manner, especially in immune related tissues such as liver, blood and kidney. Binding assay revealed the specificity of rToTLR3 for pathogen-associated molecular patterns (PAMPs) and bacteria that included Vibrio harveyi, V. vulnificus, V. anguillarum, Photobacterium damselae, Escherichia coli, Aeromonas hydrophila, Staphylococcus aureus and PolyI:C, LPS, Flagellin, and PGN. In addition, a luciferase reporter assay showed that overexpression ToTLR3 significantly increased NF-κB activity. Collectively, our results suggested that ToTLR3 might play an important role as a pattern recognition receptor (PRR) in the immune response towards pathogen infections, and transmiss the danger signal to downstream signaling pathways.

Full-length transcriptome sequencing combined with RNA-seq analysis revealed the immune response of fat greenling (Hexagrammos otakii) to Vibrio harveyi in early infection

Fat greenling (Hexagrammos otakii) is an important commercial marine fish species cultured in northeast Asia, but its available gene sequences are limited. Vibrio harveyi is a causative agent of vibriosis in fat greenling and also causes severe losses to the aquaculture industry in China. In order to obtain more high-quality transcript information and investigate the early immune response of fat greenling against V. harveyi, the fish were artificially infected with V. harveyi, and five sampling points were set within 48 h. Iso-Seq combined with RNA-Seq were applied in the comprehensive transcriptome analysis of V. harveyi-infected fat greenling. Total 42,225 consensus isoforms were successfully extracted from the result of Iso-Seq, and more than 19,000 ORFs were predicted. In addition, total three modules were identified by WGCNA which significantly positive correlated to the infection time, and the KEGG analysis showed that the immune-related genes in these modules mainly enriched in TLR signaling pathway, NF-κB signaling pathway and Endocytosis. The activation of inflammation and endocytosis was the most significant characteristics of fat greenling immune response during the early infection. Based on the WGCNA, a series of high-degree nodes in the networks were identified as hub genes. The protein structures of cold-inducible RNA-binding protein (CIRBP), poly [ADP-ribose] polymerase 1 (PARP1) and protein arginine N-methyl transferase 1 (PRMT1) were subsequently found to be highly conserved in vertebrate, and the gene expression pattern of CIRBP, PARP1, PRMT1 and a part of TLR/NF-κB pathway-related genes indicated that these proteins might have similar biological functions in regulation of inflammatory response in teleost fish. The results of this study provided the first systematical full-length transcriptome profile of fat greenling and characterized its immune responses in early infection of V. harvey, which will serve as the foundation for further exploring the molecular mechanism of immune defense against bacterial infection in fat greenling.

The effect of partial replacement of fish meal by soy protein concentrate on growth performance, immune responses, gut morphology and intestinal inflammation for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

An 8-week feeding trial was conducted to investigate the effects of partial replacement of fish meal by soy protein concentrate (SPC) on the growth performance, immune responses, intestine morphology and relation gene expression of intestinal inflammation for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) (initial weight 12.5 ± 0.00 g). Eight isonitrogenous and isolipidic diets (48.61% protein and 11.17% lipid) were formulated by replacing 0% (the control), 11%, 22%, 33%, 44%, 55%, 66%, and 77% of fish meal (FM) with SPC, respectively (the eight dietary be named FM, S11, S22, S33, S44, S55, S66, and S77, respectively). With the replacement level increased, the final body weight, weight gain ratio (WGR), specific growth rate (SGR), and survival rate of fish were significantly decreased (P < 0.05) compared with the group FM. By contrast, the feed conversion ratio (FCR) of fish was significantly increased (P < 0.05) when the replacement level up to 44%. Partial FM replacement by SPC (ranging from 11% to 77%) substantially reduced (P < 0.05) the serum total protein, albumin, and total cholesterol contents compared with the group FM. Liver total superoxide dismutase, glutathione peroxidase, catalase activities, and total antioxidant capacity showed the same trend of gradual increase first and then decrease. Their highest values were found in the replacement levels of 55%, 33%, 22%, and 55% and were significantly higher (P < 0.05) than the control group. The lowest malondialdehyde content was observed in group S77 and was significantly lower (P < 0.05) than that of the control group. The complements C3 and C4 contents of fish fed with experimental diets (replacement level ranged from 11% to 66%) were significantly higher (P < 0.05) than the group FM. The liver lysozyme activity of the control group was the lowest and was significantly lower than that of other dietary treatments (P < 0.05). Villus length and muscle thickness in the intestine of fish were significantly lower (P < 0.05) than other groups when the replacement level exceeded 44%. With dietary replacement levels increased, the TLR22, MyD88, p65, pro-inflammatory cytokines (IL-1β, TNF-α, IL-12P40 and INF-γ) and anti-inflammatory cytokines (TGF-β, IL-10, epinecidin, MHCIIβ and hepcidin) mRNA levels in the proximal intestine were significantly up-regulated (P < 0.05). The TLR22, MyD88, p65, pro-inflammatory cytokines (IL-1β, TNF-α, IL-12P40 and INF-γ) and anti-inflammatory cytokines (TGF-β, IL-10, MHCIIβ and hepcidin) mRNA levels in the mid intestine were significantly up-regulated (P < 0.05). The mRNA levels of TLR22, anti-inflammatory cytokines (IL-1β, TNF-α, IL-12P40, INF-γ) and anti-inflammatory cytokines (TGF-β, IL-10, epinecidin, MHCIIβ and hepcidin) in the distal intestine were significantly down-regulated (P < 0.05). The mRNA expression of MyD88 and p65 mRNA were showed a tend increased first and then decreased, and the highest values were observed in group S33 and S55 (P < 0.05), respectively. Based on the present work, the correlation between WGR and FM replacement level with SPC was described using the broken-line model, which estimated the optimum FM replacement to 37.23% for juvenile hybrid grouper dietary.

Thoroughly Remold the Localization and Signaling Pathway of TLR22

TLR22 exists in nearly all the poikilothermic vertebrates and plays a central role in the initiation of innate immunity and activation of adaptive immunity. TLR22 signaling pathway has been characterized in detail in fugu (Takifugu rubripes). Here, we thoroughly remold the localization and signaling pathways of TLR22. We characterized TLR22a and TLR22b in grass carp (Ctenopharyngodon idella), designated as CiTLR22a and CiTLR22b, and explored the ligand(s), adaptor(s), and signaling pathway(s). Results show that both CiTLR22a and CiTLR22b localize to lysosome, acidic compartment. Correspondingly, CiTLR22a and CiTLR22b directly bind and respond to dsRNA analog poly(I:C) at pH 5, but not at pH 7.4, the physiological pH. Moreover, CiTLR22a and CiTLR22b exhibit antagonistic function in signal transmission, wherein CiTLR22a facilitates the protein and phosphorylation levels of IRF7 and enhances the promoter activities of major IFNs and NF-κBs, while CiTLR22b downregulates IRF7 phosphorylation and IRF3 protein level and suppresses the IFN and NF-κB pathways. Further investigations revealed that CiTLR22a restrains grass carp reovirus (GCRV) replication and protects cells from GCRV infection, whereas CiTLR22b plays a negative role in response to GCRV infection. This is the first time to systematically clarify the signaling pathways of two isotype TLR22s; especially, subcellular localization and adaptor are different from previous TLR22 report, which results from technical limitations. The results will serve the antiviral immune mechanisms in poikilothermic vertebrates and evolutionary immunology.

Duplication of toll-like receptor 22 in teleost fishes

The TLRs of teleost fishes have distinct features and are highly diverse, but the duplication characteristics and expression patterns of the tlr22 gene remain unclear. Here, we identified paralogous tlr22 genes in 13 teleost fishes by screening available fish genomic resources and using molecular cloning. We then conducted comprehensive bioinformatics analyses and investigated spatiotemporal differences in the expression patterns of the tlr22 genes in G. eckloni. The results indicated that more than three paralogous tlr22 genes were possessed by some teleost fishes. Of these, tlr22c is specific to some subfamilies of the Cyprinidae (e.g., Barbinae, Cyprininae, Schizothoracinae, and Leuciscinae). Phylogenetic and syntenic analyses showed that the paralogous tlr22 genes originated from two single-gene duplication events. Molecular clock calculations dated the two gene duplication events at 49.5 and 39.3 MYA, which is before the common carp-specific genome duplication event and well after the fish-specific genome duplication. Gene duplication of tlr22 was followed by gene loss or pseudogene events in certain lineages. Spatiotemporal expression differences between the three duplicated tlr22 genes from G. eckloni suggested that these genes diverged functionally after gene duplication.

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.

Immunostimulatory Activities of CpG-Oligodeoxynucleotides in Teleosts: Toll-Like Receptors 9 and 21

Toll-like receptors (TLRs) are pattern-recognition receptors that detect a wide variety of microbial pathogens for the initiation of host defense immunological responses. Thirteen TLRs have been identified in mammals, and teleosts contain 22 mammalian or non-mammalian TLRs. Of these, TLR9 and TLR21 are the cytosine-phosphate-guanosine-oligodeoxynucleotides (CpG-ODNs) recognition TLRs in teleosts. TLR9 is a mammalian TLR expressed in teleost but not in the avian species. TLR21 is a non-mammalian TLR expressed in both teleost and the avian species. Synthetic CpG-ODNs are potent immunostimulants that are being studied for their application against tumors, allergies, and infectious diseases, and as a vaccine adjuvant in humans. The immunostimulatory effects of CpG-ODNs as vaccine adjuvants and their antimicrobial function in domestic animals and teleosts are also being investigated. Most of our current knowledge about the molecular basis for the immunostimulatory activity of CpG-ODNs comes from earlier studies of the interaction between CpG-ODN and TLR9. More recent studies indicate that in addition to TLR9, TLR21 is another receptor for CpG-ODN recognition in teleosts to initiate immune responses. Whether these two receptors have differential functions in mediating the immunostimulatory activity of CpG-ODN in teleost has not been well-studied. Nevertheless, the existence of two recognition TLRs suggests that the molecular basis for the immunostimulatory activity of CpG-ODN in teleosts is different and more complex than in mammals. This article reviews the current knowledge of TLR9 and TLR21 activation by CpG-ODNs. The key points that need to be considered for CpG-ODNs as immunostimulants with maximum effectiveness in activation of immune responses in teleosts are discussed. This includes the structure/activity relationship of CpG-ODN activities for TLR9 and TLR21, the structure/functional relationship of these two TLRs, and differential expression levels and tissue distributions for these two TLRs.

Characterization of the TLR Family in Branchiostoma lanceolatum and Discovery of a Novel TLR22-Like Involved in dsRNA Recognition in Amphioxus

Toll-like receptors (TLRs) are important for raising innate immune responses in both invertebrates and vertebrates. Amphioxus belongs to an ancient chordate lineage which shares key features with vertebrates. The genomic research on TLR genes in Branchiostoma floridae and Branchiostoma belcheri reveals the expansion of TLRs in amphioxus. However, the repertoire of TLRs in Branchiostoma lanceolatum has not been studied and the functionality of amphioxus TLRs has not been reported. We have identified from transcriptomic data 30 new putative TLRs in B. lanceolatum and all of them are transcribed in adult amphioxus. Phylogenetic analysis showed that the repertoire of TLRs consists of both non-vertebrate and vertebrate-like TLRs. It also indicated a lineage-specific expansion in orthologous clusters of the vertebrate TLR11 family. We did not detect any representatives of the vertebrate TLR1, TLR3, TLR4, TLR5 and TLR7 families. To gain insight into these TLRs, we studied in depth a particular TLR highly similar to a B. belcheri gene annotated as bbtTLR1. The phylogenetic analysis of this novel BlTLR showed that it clusters with the vertebrate TLR11 family and it might be more related to TLR13 subfamily according to similar domain architecture. Transient and stable expression in HEK293 cells showed that the BlTLR localizes on the plasma membrane, but it did not respond to the most common mammalian TLR ligands. However, when the ectodomain of BlTLR is fused to the TIR domain of human TLR2, the chimeric protein could indeed induce NF-κB transactivation in response to the viral ligand Poly I:C, also indicating that in amphioxus, specific accessory proteins are needed for downstream activation. Based on the phylogenetic, subcellular localization and functional analysis, we propose that the novel BlTLR might be classified as an antiviral receptor sharing at least partly the functions performed by vertebrate TLR22. TLR22 is thought to be viral teleost-specific TLR but here we demonstrate that teleosts and amphioxus TLR22-like probably shared a common ancestor. Additional functional studies with other lancelet TLR genes will enrich our understanding of the immune response in amphioxus and will provide a unique perspective on the evolution of the immune system.

Molecular characterization of three toll-like receptors (TLR21, TLR22, and TLR25) from a primitive ray-finned fish Dabry's sturgeon (Acipenser dabryanus)

Dabry's sturgeon (Acipenser dabryanus) is a useful model for the study of fish evolution, as it is one of the most primitive actinopterygian species. However, studies of the immune system of this fish are limited. Here, we identified three toll-like receptors (adaTLR21, adaTLR22, and adaTLR25) from Dabry's sturgeon. The three sturgeon TLRs had characteristic TLR features, including a signal peptide, several leucine rich repeat (LRR) domains, a transmembrane domain, and a Toll/interleukin-1 receptor (TIR) domain. Although the predicted amino acid sequences encoded by the sturgeon adaTLR21, adaTLR22, and adaTLR25 had somewhat low levels of sequence identity and similarity with TLRs from other fish species, the three sturgeon TLRs fell in well-supported clades with other teleost TLRs in our neighbor-joining phylogenetic tree. Real-time quantitative PCR showed that the three sturgeon TLRs were ubiquitously expressed in all examined tissues from healthy adult sturgeon, but that their expression patterns varied greatly among the different tissues. The three sturgeon TLRs were also expressed across all embryonic developmental stages that were examined, but their expression levels differed between developmental stages. All three TLRs were upregulated in head-kidney primary leucocytes following lipopolysaccharide (LPS) and polyinosinic: polycytidylic acid (polyI:C) stimulation. To the best of our knowledge, this is the first characterization of these three TLRs in Darby's sturgeon. Our results provide a framework for further studies of TLR ligand specificity and signaling pathways in sturgeon, and increase our understanding of the functional evolution of TLRs in vertebrates.

Identification and functional analysis of grouper (Epinephelus coioides) B-cell linker protein BLNK

B-cell linker protein (BLNK) is an adaptor protein that plays a crucial role in the B cell antigen receptor (BCR) signal pathway. To investigate the function of BLNK in teleost fish, we cloned a BLNK ortholog gene from the orange-spotted grouper (Epinephelus coioides). Homology analysis showed that the grouper BLNK (EcBLNK) had a 34%-77% amino acid identity in comparison to other vertebrates and shared the highest amino acid identity with BLNK from the Asian seabass Lates calcarifer. EcBLNK comprises an N-terminal SAM domain and a C-terminal B-cell linker SH2 domain. Ten tyrosine residues were well conserved between teleost fish and mammals. Tissue distribution analysis showed that EcBLNK was expressed mainly in immune organs and expression was at the highest level in head kidney. Co-localization of EcBLNK and EcCD79a was observed in transfected HEK293T cells. Overexpression of EcBLNK did not activate nuclear factor kappa-light-chain-enhancer of activated B cells. The protein level of EcBLNK in grouper head kidney leukocytes was increased by stimulation with lipopolysaccharide. In groupers infected with Cryptocaryon irritans, EcBLNK was regulated in the infected sites and the systemic organ which suggests that EcBLNK was activated in the immune response to parasite infection.

The effect of intermittent hypoxia under different temperature on the immunomodulation in Streptococcus agalactiae vaccinated Nile tilapia (Oreochromis niloticus)

Dissolved oxygen (DO) and temperature are the potential immunomodulators in fish and play the important roles in regulating immunity. We studied the effect of intermittent hypoxia under different temperature on the immunomodulation in vaccinated Nile tilapia (Oreochromis niloticus). The expression of immune-related genes, enzymatic activities, histology, cumulative mortality, and S. agalactiae clearance were assessed. Study conditions were intermittently hypoxic (4.0 ± 1.0 mg/L DO) at 30 ± 0.5 °C or 35 ± 0.5 °C. Interleukin-1beta (IL-1β), tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) mRNA expression in spleen and head kidney were significantly lower in vaccinated hypoxic fish compared to the vaccinated normoxic fish. Levels of heat shock protein 70 (HSP70) in tissues showed an opposite tendency. Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities were significantly lower in vaccinated hypoxic fish. Malondialdehyde levels were significantly greater under hypoxic conditions. In vitro studies evaluated the effects of intermittent hypoxia at different temperatures on cells of vaccinated O. niloticus. Phagocytic activity of peripheral blood leucocytes (PBLs) and intracellular reactive oxygen species (ROS) production in head kidney cells were significantly decreased by intermittent hypoxia at either 30 °C or 35 °C, while nitric oxide levels in tissues cells increased significantly under hypoxic conditions. These changes were well reflected by the further suppression modulation on S. agalactiae clearance in vaccinated O. niloticus and higher cumulative mortality by intermittent hypoxia. Taken together, intermittent hypoxia at either 30 °C or 35 °C could suppress immunomodulation in vaccinated Nile tilapia.

Molecular characterization and function analysis of grouper (Epinephelus coioides) Bruton's tyrosine kinase BTK

Bruton's tyrosine kinase (BTK) is a Tec-family tyrosine kinase and plays a crucial role in B cell antigen receptor (BCR) signal pathway. Mutations in humans and mice BTK gene results in X-linked agammaglobulinemia (XLA) and X-linked immunodeficiency (XLD), respectively. To study the function of BTK in teleost, we cloned a BTK gene from orange-spotted grouper. Homology analysis showed that the grouper BTK (EcBTK) had a high amino acid identity with other vertebrates (63%-92%) and shared the highest amino acid identity with ballan wrasse Labrus bergylta BTK. EcBTK comprises a Bruton's tyrosine kinase pleckstrin homology (PH) domain, a Tec homology (TH) domain, a Src homology 3 (SH3) domain, a Src homology 2 (SH2) domain and a Protein Kinases, catalytic (PKc) domain. Tissue distribution analysis showed that EcBTK was mainly expressed in immune organs. EcBTK was uniform distributed throughout the cytoplasm of transfected HEK293T cells and overexpression of EcBTK slightly down-regulates NF-κB activity. Ibrutinib treatment can reduce the phosphorylation level of grouper's BTK. In groupers infected with Cryptocaryon irritans, up-regulation of EcBTK were not seen in the early stage of infected skin and gill until days 14-21. The phosphorylation level of grouper BTK was significantly increased in infected skin and gill.

MicroRNA regulation of Toll-like receptor signaling pathways in teleost fish

The innate immune system is the first line defense mechanism that recognizes, responds to, controls or eliminates invading pathogens. Toll-like receptors (TLRs) are a critical family of pattern recognition receptors (PRRs) tightly regulated by complex mechanisms involving many molecules to ensure a beneficial outcome in response to foreign invaders. MicroRNAs (miRNAs), a transcriptional and posttranscriptional regulator family in a wide range of biological processes, have been identified as new molecules related to the regulation of TLR-signaling pathways in immune responses. To date, at least 22 TLR types have been identified in more than a dozen different fish species. However, the functions and underlying mechanisms of miRNAs in the regulation of inflammatory responses related to the TLR-signaling pathway in fish is lacking. In this review, we summarize the regulation of miRNA expression profiles in the presence of TLR ligands or pathogen infections in teleost fish. We focus on the effects of miRNAs in regulating TLR-signaling pathways by targeting multiple molecules, including TLRs themselves, TLR-associated signaling proteins, and TLR-induced cytokines. An understanding of the relationship between the TLR-signaling pathways and miRNAs may provide new insights for drug intervention to manipulate immune responses in fish.

Toll-like receptor (TLR) 22, a non-mammalian TLR in Asian seabass, Lates calcarifer: Characterisation, ontogeny and inductive expression upon exposure with bacteria and ligands

Toll-like receptor (TLR) 22 is a non-mammalian TLR found mostly in teleosts and characterized initially as a cell surface surveillance receptor for detecting extracellular long dsRNA. In the current study, the full-length cDNA sequence consisting of 3312 nucleotides encoding for 960 amino acids in Asian seabass (Lates calcarifer) TLR22 (AsTLR22) was identified. From the putative protein sequence, signature TLR domains such as 18 LRR domains, two transmembrane domains, a single LRR_CT domain and an intracellular TIR domain could be predicted. Phylogenetic analysis showed that AsTLR22 is clustered with other teleost TLR22 and is distinctly different from the other TLR groups. The transcript of AsTLR22 was ubiquitously expressed in all the tissues tested of healthy juveniles with the highest expression in gill followed by hindgut, spleen and skin. The AsTLR22 mRNA transcript was also detected in all the developmental stages as early as unfertilized eggs with higher expression in later stages such as neurula and early embryo. The dsRNA viral analogue, poly (I:C) and Gram-negative bacterium, Vibrio alginolyticus, were found to modulate the AsTLR22 expression in different tissues with the highest expression in kidney and liver. Gram-positive bacterium, Staphylococcus aureus, was also found to regulate the AsTLR22 expression at certain time-points with the highest expression in gill. Similarly, noticeable change in AsTLR22 expression was detected in SISK cell line induced with different ligands such as poly (I:C), LPS and PGN. The findings indicate that AsTLR22 responds in transcript level towards bacteria-borne PAMPs and extracellular dsRNA in the euryhaline teleost Asian seabass. Further, this might act as an important pathogen surveillance receptor during early developmental stages.

Identification and functional characterization of Toll-like receptor 13 from orange-spotted grouper (Epinephelus coioides)

Toll-like receptors (TLRs) are one of the most important innate immune receptors, which recognize various pathogen-associated molecular patterns and activate the downstream immune response. Mouse TLR13 has been found to recognize a highly conserved sequence from bacterial or viral RNA and activate the myeloid differentiation primary response gene 88-dependent signaling response. The function of teleost tlr13 is still not fully understood, especially its relationship with bacterial RNA. In our study, we identified and characterized a tlr13 from Epinephelus coioides (orange-spotted grouper). The full-length cDNA of Eco. tlr13 contained a 2844 bp open reading frame, encoding 947 amino acids. The polypeptide was constitutive of a signal peptide, 13 leucine-rich repeats domains, a C-terminal leucine-rich repeats, a transmembrane domain and a conserved Toll/interleukin (IL)-1 receptor domain, indicating that Eco. Tlr13 exhibited a typical TLR structure. Multiple alignments showed that the Toll/IL-1 receptor domain of Eco. Tlr13 was identical with other homologues, and the phylogenetic tree suggested that Eco. Tlr13 was clustered with other TLR13s and had the closest relationship with predicted Lates calcarifer (sea bass) Tlr13. Subcellular localization analysis revealed that Eco. Tlr13 colocalized with the endoplasmic reticulum and early endosome. Moreover, Eco. tlr13 was broadly observed in all tested tissues with the relatively high expressions in the brain and immune-related tissues. After challenged with 19-mer Staphylococcus aureus 23S ribosomal RNA-derived oligoribonucleotide (ORN Sa19), the expression of Eco. tlr13 was significantly up-regulated in grouper spleen cells. Also, the luciferase assay further revealed that with the overexpression of Eco. Tlr13 in human embryonic kidney 293T cells, ORN Sa19 activated the promoter activity of interferon-β in a dose-dependent pattern. These results indicate that Eco. tlr13 may involve in the recognition of bacterial RNA.

Intracellular TLR22 acts as an inflammation equalizer via suppression of NF-κB and selective activation of MAPK pathway in fish

TLR22, a typical member of the fish-specific TLRs, is a crucial sensor in virally triggered innate immune signalling retained from natural selection. To elucidate the role of the TLR22-specific signalling cascade mechanism, we provide evidence that the double-stranded (ds) RNA-sensor TLR22 positively regulates the ERK pathway and negatively regulates the JNK, p38 MAP kinase and NF-κB pathway. Here, we show that TLR22 restrains NF-κB activation and IFN (interferon) β and AP-1 (activator protein-1) promoter binding (impairing "primary response" genes (TNF and IL-1)), induces "secondary response" genes (IL-12 and IL-6) and mediates the irregular expression of inflammatory genes. Therefore, TLR22 promotes ERK phosphorylation but impairs the JNK and p38 MAP kinases and IκB phosphorylation. Additionally, TLR22 controls the excessive generation of reactive oxygen species (ROS) to avoid damaging the organism. The specific kinetics of TLR22 depends on its distinct cellular localization. We demonstrate that TLR22 is an intracellular receptor localized in the endosome, and the TLR22-TIR domain is the functional structure inducing the signalling cascade post-viral replication in the body. As mentioned above, our data reveal a novel mechanism whereby TLR22-induced positive adjustment and negative regulation evolved independently to avoid harmful and inappropriate inflammatory responses.

Expression and functional characterization of TRIF in orange-spotted grouper (Epinephelus coioides)

Antiviral immune responses are triggered by the innate immune recognition of viral infection. Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-β (TRIF) is an adapter in responding to activation of Toll-like receptors, which provides early clearance of viral pathogens. Our study focuses on the functional characterization of grouper TRIF (EcTRIF) based on the comparison of its sequence and functional evolution from grouper fish to mammals. The results show that the open reading frame of EcTRIF encoded a protein of 580 amino acids. Real-time PCR analysis indicates that EcTRIF was constitutively expressed in all the analyzed tissues in healthy grouper. EcTRIF was significantly induced in spleen post-LPS and poly (I:C) stimulation. Fluorescence microscopy shows that EcTRIF is colocalized with a Golgi apparatus marker, implying its unique subcellular localization in the Golgi apparatus. Luciferase reporter assays confirmed that EcTRIF was able to activate the IFN and NF-κB promoter. Overexpression of EcTRIF in grouper brain cells inhibited the replication of red-spotted grouper nervous necrosis virus (RGNNV). These results indicate that EcTRIF plays an important role in modulating antiviral innate immune responses. Our results have applications in functional studies on TRIF in teleost fish and immune evolution.

Ameliorative effect of vitamin E on hepatic oxidative stress and hypoimmunity induced by high-fat diet in turbot (Scophthalmus maximus)

This study was conducted to examine the effects of vitamin E on growth performance, oxidative stress and non-specific immunity of turbot (Scophthalmus maximus) fed with high-fat diet. Results showed that high-fat diet significantly increased hepatosomatic index, viscerosomatic index, hepatic malondialdehyde level and decreased catalase and superoxide dismutase activities, whereas final weight, specific growth rate and survival rate remained unchanged. Meanwhile, nitro blue tetrazolium positive leucocytes of head kidney, respiratory burst activity in head-kidney macrophage, phagocytic index and serum lysozyme activity were significantly reduced after feeding with high-fat diet. Furthermore, fish fed with high-fat diet promoted higher expression of heat shock protein (hsp70, hsp90), and inhibited expression of complement component 3 (c3) in the liver and tumor necrosis factor-α (tnf-α), interleukine 1β (il-1β), toll like receptor 22 (tlr-22) in the spleen and head-kidney, respectively. However, simultaneous supplementation with 480 mg kg^-1 vitamin E protected turbot against high-fat diet-induced hepatic oxidative stress, hypoimmunity through attenuating lipid peroxidation, renewing antioxidant enzymes activities and nonspecific immune responses, and modulating the expression of stress protein (hsp70, hsp90) and immune-related genes (c3, tnf-α, il-1β, tlr-22). In conclusion, the obtained results indicate the vitamin E as a wildly used functional feed additive contributes potentially to alleviate high-fat diet-induced hepatic oxidative stress and hypoimmunity, maintain the health, and improve the broodstock management for turbot.

Molecular characterization and expression analysis of three TLR genes in yellow catfish (Pelteobagrus fulvidraco): Responses to stimulation of Aeromonas hydrophila and TLR ligands

Toll-like receptors (TLRs) are one of the most extensively researched pattern recognition receptors (PRRs) and play an important role in the innate immune system. In this study, partial cDNA sequences of the Pf_TLR18 and Pf_TLR19 genes and complete cDNA sequence of the Pf_TLR21 gene were cloned from yellow catfish (Pelteobagrus fulvidraco). The open reading frames (ORFs) of the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes were 1956 bp, 2262 bp and 2949 bp in length, encoding 651, 753 and 982 amino acids, respectively. The Pf_TLR18 and Pf_TLR19 consist of leucine-rich repeats (LRRs), a transmembrane domain and a Toll/interleukin-I receptor domain, and the Pf_TLR21 only has LRRs and TIR domain. Homologous identity revealed that the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes have high nucleotide and protein sequence similarity with channel catfish, especially the TIR domains that exhibited the greatest conservation compared to channel catfish. Ontogenetic expression analyses indicated that the mRNA expressions of the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes could be detected from fertilized eggs to 30 day post-hatching and they exhibited different variation trends after hatching. The three TLR genes were expressed in various tissues, but they were mostly highly expressed in the spleen. The mRNA expression levels of the three genes were up-regulated in the spleen, head kidney, trunk kidney, liver and blood after challenge of killed Aeromonas hydrophila. In addition, the expressions of the three TLR genes were induced to up-regulate in isolated peripheral blood lymphocytes of yellow catfish after stimulation with lipopolysaccharides (LPS), peptidoglycan (PGN) and polyinosinic-polycytidylic acid (Poly I:C). Our findings indicate that the three TLR genes may play a potential role in the host defense against pathogenic microbes. These results will provide valuable information to better understand the function of TLR genes in the innate immune system of yellow catfish.

Tlr22 structure and expression characteristic of barbel chub, Squaliobarbus curriculus provides insights into antiviral immunity against infection with grass carp reovirus

Grass carp reovirus (GCRV) is the most virulent agent to Grass carp, Ctenopharyngodon idella, and causes a severe infectious disease called hemorrhagic disease of grass carp. Generally, barbel chub, Squaliobarbus curriculus, a genetically closely related species to grass carp, exhibits significant resistance against GCRV infection compared to grass carp. To investigate whether the Toll-like receptor 22 (tlr22) has got a vital role against the GCRV infection, the full cDNA sequence of tlr22 from barbel chub (Sctlr22) was cloned by RACE-PCR, and the structure and expression feature were studied. The complete cDNA sequence of Sctlr22 has a size of 3504 bp, encoding for 960 amino acid residues. Sctlr22 possesses typical structural features of the tlrs family, including 19 leucine rich repeats (LRRs), a transmembrane (TM) and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis revealed that barbel chub Tlr22 was clustered together with the Tlr22 of grass carp (Citlr22). Structurally, barbel chub Tlr22 have two different structure in LRRs domain and TIR domain with grass carp (Susceptible to GCRV), but was similar to that of Danio rerio and Cyprinus carpio (Resistance to GCRV). Quantitative RT-PCR analysis has shown that Sctlr22 is prominently expressed in immune relevant tissues such as head kidney and spleen. After GCRV infection, Sctlr22 expression level was up-regulated in four tested tissues and the highest expression of Sctlr22 appeared fast and higher than Citlr22. The interferon-β (ifn-β) expression level in CIK cells over-expressing fused cDNA encoding the LRR domain of Sctlr22 to the transmembrane and TIR domain of Citlr22 was significantly higher than that cells overexpressing Citlr22 after GCRV infection. The virus titer was significantly reduced compared to Citlr22 over-expressing cells. These results suggested that Sctlr22 seems to play a vital role in the immune response against GCRV.

Characterization of Toll-like receptor 22 in turbot (Scophthalmus maximus)

Toll-like receptors (TLRs) are essential for activation of the innate immune system in response to invading pathogens. In this paper, expression profiles of the turbot (Scophthalmus maximus) TLR22 gene (tbTLR22) were analyzed with RT-PCR and in situ hybridization. Then its expression patterns simulated with ligands or pathogens were investigated. Streptococcus iniae, Edwardsiella tarda, Hirame rhabdovirus virus (HIRRV), polyinosinic: polycytidylic acid (Poly I:C), peptidoglycan (PGN), or lipopolysaccharides (LPS) was injected to turbot; poly I:C, PGN, or LPS was added into cultured peripheral blood leukocytes (PBL); and then the tbTLR22 in liver, spleen, gill, kidney and cultured PBL was measured using Quantitative PCR. The recombinant protein of tbTLR22 (rp-tbTLR22) and its antibody were produced, then the reactions of antibody to tissues were detected by Western-blotting, and the binding of rp-tbTLR22 to all the stimulants was detected using ELISA. The results showed tbTLR22 expression was significantly up-regulated by PolyI: C, but no significant change in PGN and LPS groups; tbTLR22 significantly increased in liver and spleen after S. iniae infection with the maximum of 3.6 times and 3.3 times; in liver and kidney after E. tarda infection with the maximum of 3.4 times and 4.1 times; and then in gill and kidney after HIRRV infection by 4.8 and 4.1 times. Rp-tbTLR22 antibody could recognize the total protein from liver, kidney, gill and spleen at 40 kDa, 90 kDa and 120 kDa, respectively. The rp-tbTLR22 could bind to three ligands and pathogens in vitro. The expression and reaction data gave a clear recognization model of tbTLR22.

Role of cyclooxygenase-mediated metabolites in lipid metabolism and expression of some immune-related genes in juvenile grass carp (Ctenopharyngodon idellus) fed arachidonic acid

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid (ARA) to prostaglandins, and COX-mediated metabolites play important roles in the regulation of lipid metabolism and immunity in mammals. However, such roles of COX in fish remain largely unknown. In this study, we designed three semi-purified diets, namely ARA-free (control), ARA, and ARA + acetylsalicylic acid (ASA; a COX inhibitor), and used them to feed grass carp (27.65 ± 3.05 g) for 8 weeks. The results showed that dietary ARA significantly increased the amount of ARA in the hepatopancreas, muscle, and kidney (P < 0.05), whereas this increase was reduced by dietary ASA. The hepatopancreatic prostaglandin E₂ content increased in the ARA group, and this increase was inhibited by ASA (P < 0.05). ARA decreased the lipid content in the hepatopancreas, whereas ASA recovered lipid content to a significant level (P < 0.05). ARA significantly decreased the messenger RNA (mRNA) expression levels of fatty acid synthase and stearoyl-CoA desaturase in the hepatopancreas (P < 0.05). However, ASA did not rescue the mRNA expression of these genes (P > 0.05). Interestingly, ARA significantly enhanced the level of peroxisome proliferator-activated receptor α gene expression, and this increase was attenuated by ASA (P < 0.05). Finally, ARA significantly enhanced the mRNA expression of myeloid differentiation factor 88 (MyD88) in the kidney, and ASA attenuated the expression of toll-like receptor 22 and MyD88 (P < 0.05). In conclusion, our findings suggest that COX metabolites play important roles in the inhibition of lipid accumulation in the hepatopancreas of grass carp fed with ARA and that regulation of gene expression promotes lipid catabolism rather than lipogenic activities. Additionally, these eicosanoids might participate in the upregulation of immunity-related genes in the kidney.

Molecular characterization and expression analysis of toll-like receptors 5 and 22 from natural triploid Carassius auratus

Innate immunity, as the most primitive and universal host defense in fish, constitutes an efficient first line of defense to combat invading microbes. Toll-like receptors (TLRs) play essential roles in the innate immunity, and TLR5 and TLR22 are two important TLRs that can recognize flagellin and double stranded RNA (dsRNA), respectively. In this study, we identified and characterized two TLRs genes of Qihe crucian carp (Carassius auratus) (designated as CaTLR5 and CaTLR22). The full-length cDNA sequence of CaTLR5 was cloned with 2972 bp including a 140 bp 5'-terminal untranslated region (UTR), a 183 bp 3'-UTR, and a 2649 bp open reading frame (ORF) encoding a deduced protein with 882 amino acids. The full-length cDNA of CaTLR22 was identified to be 3613 bp, consisting of a 228 bp 5'-UTR, a 547 bp 3'-UTR, and a 2838 bp ORF encoding a predicted protein of 945 amino acids. A typical TLR structure (an extracellular leucine-rich repeat domain, a transmembrane domain, and an intracellular Toll/IL-1 receptor domain) was found in CaTLR5 and CaTLR22. For either CaTLR5 or CaTLR22 gene, the mRNA expression levels varied in the different periods during the early stages of development. It was suggested that expression changes of gene CaTLR5 and CaTLR22 at mRNA levels were involved in developmental regulation in the early stages, and it was postulated that CaTLR5 and CaTLR22 play the important roles in immune defense in the early development stages of fish. Quantitative Real-Time PCR (qRT-PCR) revealed that CaTLR5 and CaTLR22 were constitutively expressed in all eleven tissues examined, although the mRNA expression level varied considerably among the different tissues. Following exposure to polyI:C, flagellin, and Aeromonas hydrophila, CaTLR5 and CaTLR22 were up-regulated in different tissues, and it was suggested that CaTLR5 and CaTLR22 were involved in the immune response of Qihe crucian carp against pathogenic invasions. The present findings will provide the valuable information for understanding the structure, function, expression, and the immune defense process of CaTLR5 and CaTLR22 in Qihe crucian carp, and provide new insights for developing the new strategies of disease control to protect fish against pathogens infection.

Molecular characterization of a fish-specific toll-like receptor 22 (TLR22) gene from common carp (Cyprinus carpio L.): Evolutionary relationship and induced expression upon immune stimulants

In the host innate immune system, various pattern recognition receptors (PRRs) recognize conserved pathogens-associated molecular patterns (PAMPs), and represent an efficient first line of defense against invading pathogens. TLR22 is one of the fish-specific Toll-like receptors (TLRs), identified in a variety of fish species. In this study, we report the cloning and identification of a TLR22 cDNA from the gills of common carp (Cyprinus carpio L.). The full-length CcTLR22 cDNA was 3301 bp long, including a 32 bp 5'-untranslated region (UTR), an open reading frame (ORF) of 2838 bp and a 432 bp 3'-UTR.The CcTLR22 protein was found to comprise a signal peptide, 16 LRR domains, a LRRCT domain in the extracellular region and a TIR domain in the cytoplasmic region, which fits with the characteristic TLR domain architecture. The genomic organization of CcTLR22 was identified, which was encoded by an uninterrupted exon. Sequence alignment and phylogenetic analysis showed that all known teleost TLR22 members were clustered into an independent clade of the TLR22 family, and showed high amino acid identities with other fish TLRs. Real-time PCR assay showed that CcTLR22 mRNA was expressed in almost all tissues examined, while the levels obviously varied among different tissues. When challenged with poly(I:C) (a viral model) or A. hydrophila bacteria, the expression level of CcTLR22 was up-regulated in a variety of common carp tissues. These results indicate that CcTLR22 plays a significant role in systemic as well as mucosal defence after viral or bacterial stimulation or infection.

Characterization and expression of Megalobrama amblycephala toll-like receptor 22 involved in the response to Aeromonas hydrophila

The toll-like receptors (TLR) tlr22 was identified and characterized for the first time in one of the economically most important freshwater fish species in China, Megalobrama amblycephala. The full-length cDNA (4039 bp) of M. amblycephala tlr22 contains an open reading frame of 2706 bp, encoding a 901 amino-acid long polypeptide. The putative polypeptide contains 16 leucine-rich repeat (LRR) motifs, an LRR C-terminal, a transmembrane region and a cytoplasmic toll-interleukin-1 receptor (TIR) domain. Phylogenetic analyses revealed that M. amblycephala Tlr22 shared the closest relationship with a grass carp ortholog. tlr22 was constitutively expressed in nine tissues and during 10 developmental stages studied, albeit with varying expression levels. Along with many pathological changes observed after Aeromonas hydrophila bacterium infection, tlr22 and myd88 mRNA were significantly upregulated in blood, head kidney, spleen and intestine, indicating that tlr22 is involved in the immune response. These results provide an insight into tlr22 regulation mechanisms in the innate immune response to bacterial infection.

Grouper (Epinephelus coioides) BCR signaling pathway was involved in response against Cryptocaryon irritans infection

B cell antigen receptor (BCR) plays a crucial role in B cell development and antibody production. It comprises membrane immunoglobulin non-covalently associated with CD79a/CD79b heterodimer. After B cell activation, initial extracellular signals are transduced by BCR complex and amplified by two protein tyrosine kinases, LYN and SYK, which then trigger various pathways. In the present study, we cloned grouper genes for BCR accessory molecules, EcCD79a (669 bp) and EcCD79b (639 bp), as well as two protein tyrosine kinases, EcLYN (1482 bp) and EcSYK (1854 bp). Homology analysis showed that all four molecules had a relatively high amino acid identity compared with those in other animals. Among them, they all shared the highest identity with Takifugu rubripes (EcCD79a 49%, EcCD79b 52%, EcLYN 82% and EcSYK 77%). The conserved features and important functional residues were analyzed. Together with IgM and IgT, tissue distribution analysis showed that all six molecules were mainly expressed in immune organs, particularly systematic immune organs. In groupers infected with Cryptocaryon irritans, up-regulation of EcCD79a and b, EcIgM and EcIgT were not seen in the early stage skin and gill until 14-21 days. Up-regulation of EcCD79a was seen in head kidney at most time points, while EcCD79a and b were only significantly up-regulated in day 14 spleen. Significant up-regulation of EcIgT were seen in day 21 head kidney and day 1, day14 spleen. Significant up-regulation of EcIgM were seen in day 1 head kidney and 12 h spleen. In addition, two protein kinase genes, EcLYN and EcSYK, were up-regulated in the skin at most time points, which suggested that B cells may be activated at the skin local infection site.

Immunity to nervous necrosis virus infections of orange-spotted grouper (Epinephelus coioides) by vaccination with virus-like particles

Nervous necrosis virus (NNV) is a kind of the betanodaviruses, which can cause viral nervous necrosis (VNN) and massive mortality in larval and juvenile stages of orange-spotted grouper (Epinephelus coioides). Due to the lack of viral genomes, virus-like particles (VLPs) are considered as one of the most promising candidates in vaccine study to control this disease. In this study, a type of VLPs, which was engineered on the basis of orange-spotted grouper nervous necrosis virus (OGNNV), was produced from prokaryotes. They possessed the similar structure and size to the native NNV. In addition, synthetic oligodeoxynucleotide (ODN) containing CpG motif was added in vaccines, and the expression patterns of several genes were analyzed after injecting with VLP and VLP with adjuvant (VA) to assess the regulation effect of vaccine for inducing immune responses. RT-PCR assays showed that six related genes in healthy tissues were ubiquitously expressed in all nine tested tissues. The vaccine alone was able to enhance the expression of genes, including MHCIa, MyD88, TLR3, TLR9 and TLR22 after vaccination, indicating that the vaccine was able to induce immune response in grouper. In liver, spleen and kidney, the gene expressions of VA group were all significantly higher than that of VLP group at 72 h post-stimulation, showing that the fish of VA challenge group obtained the longer-lasting protective immunity and resistance to pathogen challenge than that of VLP group. The data indicated that the efficacy of vaccine could be further enhanced by CpG ODN after vaccination and provided the reference for the development of future viral vaccine in grouper.

Identification and characterization of three TLR1 subfamily members from the orange-spotted grouper, Epinephelus coioides

Toll-like receptors (TLRs), which play important roles in host defense against pathogen infection, are the most intensively studied pattern recognition receptors (PRRs). In this study, we identified three novel TLR1 subfamily members, including TLR1 (EcTLR1b), TLR2 (EcTLR2b) and TLR14 (EcTLR14), from the orange-spotted grouper (Epinephelus coioides). EcTLR1b and EcTLR2b displayed low sequence identity with the previously reported grouper TLR1 (EcTLR1a) and TLR2 (EcTLR2a), respectively. The open reading frames (ORFs) of EcTLR1b, EcTLR2b and EcTLR14 contain 2484 bp, 2394 bp and 2640 bp, which encode the corresponding 827 amino acids (aa), 797 aa and 879 aa, respectively. All three TLRs have leucine-rich repeat (LRR) domains (including an LRR-NT (except for EcTLR1b), several LRR motifs and an LRR-CT), a trans-membrane region and a Toll/interleukin-1 receptor (TIR) domain. The TIR domains of the three TLRs exhibited conserved boxes, namely box1, box2 and box3, and their 3D models were similar to those of human TLR1 or TLR2. Sequence alignment demonstrated that the TIR domains of the three TLRs shared higher sequence identity with those of other species than the full-length receptors. Phylogenetic analysis indicated that EcTLR1s and EcTLR2s are characterized by their differing evolutionary status, whereas EcTLR14 was found to be in the same group as other piscine TLR14/18s. The three TLRs were ubiquitously expressed in seven tested tissues of healthy groupers, although their expression profiles were different. Post Cryptocaryon irritans infection, TLR1s expression was up-regulated in the gills. The expression of TLR2b was mainly increased in the spleen, but decreased in the gills, which was similar to the expression pattern of TLR2a post C. irritans infection. Unlike EcTLR1b and EcTLR2b, however, the grouper TLR14 transcript was substantially induced in both tissues post challenge. These findings may be helpful in understanding the innate immune mechanism of host anti-parasite infection.

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.

Function analysis of fish Tollip gene in response to virus infection

Toll-interacting protein (Tollip) is one of the important regulatory proteins of Toll-like receptor (TLR) signaling pathways. In previous studies, a Tollip sequence of grouper (Epinephelus coioides) was identified and the signal transduction functions of Tollip were studied. However, the response of Tollip to virus infection has not been characterized from grouper. In the present paper, the Tollip homolog (EtTollip) from grouper (Epinephelus tauvina) was cloned and its immune response to Singapore grouper iridovirus (SGIV) was investigated. EtTollip shares significant similarities to other mammalian Tollips, which contain a centrally localized protein kinase C conserved region 2 (C2) domain and a C-terminal CUE domain. After challenging with SGIV, the expression levels of EtTollip were altered in the spleen and head kidney of grouper. EtTollip mainly aggregated in the cytoplasm in a condensed state and was also distributed on the membranes of GS cells. EtTollip significantly inhibited the activities of NF-κB and IFN-β luciferase reporter when transfected into grouper spleen (GS) cells. SGIV can increase the activities of NF-κB and IFN-β luciferase reporter, especially to IFN-β. When transfected EtTollip with EcMyd88, the activity of NF-κB was increased, while transfected EtTollip with EcIRF3, the activity of IFN-β was significantly increased. Over-expressed EtTollip inhibited the transcription of SGIV genes significantly in GS cells, and silencing of EtTollip with siRNA led to increase of SGIV genes loads. Taken together, the results provide new insights in to the importance of Tollip as evolutionarily conserved molecule for grouper innate immunity against virus infection.

Identification and characterization of the TLR18 gene in grass carp (Ctenopharyngodon idella)

Toll-like receptors (TLRs) play a critical role in the innate immune system. Although TLR18 is an important member of this family of receptors in fish, the role of the tlr18 gene in responses to pathogen infection is still unclear. In this study, we identified and characterized the grass carp tlr18 gene (gctlr18) to further clarify the function of TLR18 in teleost fish. Gctlr18 spans over 3600 bp and encodes a polypeptide of 852 amino acids. Analysis of the deduced amino acid sequence showed that gctlr18 encodes structures typical of the TLR family, including a signal peptide, seven leucine-rich repeats (LRRs), a transmembrane region, and a (Toll-interleukin-1 receptor) TIR domain. Quantitative RT-PCR analysis showed that gctlr18 was constitutively expressed in all investigated tissues, with abundant expression in spleen, gill, heart, intestine, kidney and fin and low expression in skin, liver and brain. Following grass carp reovirus-challenge and Aeromonas hydrophila inoculation, gctlr18 transcripts were upregulated significantly in immune-relevant tissues. Stimulation of Ctenopharyngodon idella kidney (CIK) cells with purified flagellin from Salmo typhimurium, lipopolysaccharide and polyinosinic-polycytidylic acid stimulation in vitro resulted in significantly increased gctlr18 expression, reaching a peak followed by restoration of normal levels. Overexpression of gctlr18 reduced A. hydrophila invasion by 83.4%. In CIK cells, gctlr18 induced the expression of proinflammatory cytokines, including il-8, inf-1 and tnf-α. Our results indicate that gctlr18 plays a key role in innate immune responses in teleost fish.

Molecular cloning and comparative responses of Toll-like receptor 22 following ligands stimulation and parasitic infection in yellowtail (Seriola lalandi)

TLR22 is exclusively present in teleosts and amphibians and is expected to play the distinctive role in innate immunity. In this study, we cloned the full-length cDNA sequence of yellowtail (Seriola lalandi) TLR22 (SlTLR22). The complete cDNA sequence of SlTLR22 was 4208 bp and encodes a polypeptide of 961 amino acids. Analysis of the deduced amino acid sequence indicated that SlTLR22 has typical structural features of proteins belonging to the TLR family. These included 17 LRR domains (residues 91-633) and one C-terminal LRR domain (LRR-CT, residues 693-744) in the extracellular region, and a TIR domain (residues 800-943) in the cytoplasmic region. Comparison with homologous proteins showed that the deduced SlTLR22 has the highest sequence identity to turbot TLR22 (76%). Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of SlTLR22 mRNA in all examined tissues with higher levels in the head kidney, intestine, skin and spleen. Further, SlTLR22 expression was significantly up-regulated following TLR ligands injection with lipopolysaccharide (LPS), CpG ODN2006 and polyinosinic: polycytidylic acid (poly I:C) in spleen and liver. Amyloodinium ocellatum infection also induced a high expression of SlTLR22 in spleen, intestine, muscle, skin and gill, with maximum increases ranging from 1000 to 100 fold upon different ligands and organs. Finally, histological examination in gill tissue confirmed infection by the parasite and histopathological lesion was observed also in spleen and skin. These findings suggest a possible role of SlTLR22 in the immune responses to the infections of a broad range of pathogens that include DNA and RNA viruses and parasites.

Cloning and expression analysis of a Toll-like receptor 22 (tlr22) gene from turbot, Scophthalmus maximus

Toll-like receptor 22 (TLR22) exists exclusively in aquatic animals and recognizes double stranded RNA (dsRNA). In the present study, a tlr22 gene and its 5'-flanking sequence were cloned from turbot, Scophthalmus maximus, its immune responsive expression was subsequently studied in vivo. The turbot (sm)tlr22 gene spans over 5.6 kb with a structure of 4 exon-3 intron and encodes 962 amino acids. The deduced protein shows the highest sequence identity (76.7%) to Japanese flounder Tlr22 and possesses a signal peptide sequence, a leucine-rich repeat (LRR) domain composed of 27 LRR motifs, a transmembrane region and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis grouped it with other teleost Tlr22s. The interferon-stimulated response element (ISRE) and signal transducer and activator of transcription (STAT) binding site important for the basal transcriptional activity of TLR3 were predicted in the 5'-flanking sequence of smtlr22 gene. Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of smtlr22 mRNA in all examined tissues with higher levels in the head kidney, kidney and spleen. Further, smtlr22 expression was significantly up-regulated following challenge with polyinosinic: polycytidylic acid (poly I:C), lipopolysaccharide (LPS) or turbot reddish body iridovirus (TRBIV) in the gills, head kidney, spleen and muscle, with maximum increases ranging from 2.56 to 6.24 fold upon different immunostimulants and organs. These findings suggest a possible role of Smtlr22 in the immune responses to the infections of a broad range of pathogens that include DNA and RNA viruses and Gram-negative bacteria.

Hm-MyD88 and Hm-SARM: two key regulators of the neuroimmune system and neural repair in the medicinal leech

Unlike mammals, the CNS of the medicinal leech can regenerate damaged neurites, thus restoring neural functions after lesion. We previously demonstrated that the injured leech nerve cord is able to mount an immune response promoting the regenerative processes. Indeed neurons and microglia express sensing receptors like Hm-TLR1, a leech TLR ortholog, associated with chemokine release in response to a septic challenge or lesion. To gain insights into the TLR signaling pathways involved during these neuroimmune responses, members of the MyD88 family were investigated. In the present study, we report the characterization of Hm-MyD88 and Hm-SARM. The expression of their encoding gene was strongly regulated in leech CNS not only upon immune challenge but also during CNS repair, suggesting their involvement in both processes. This work also showed for the first time that differentiated neurons of the CNS could respond to LPS through a MyD88-dependent signalling pathway, while in mammals, studies describing the direct effect of LPS on neurons and the outcomes of such treatment are scarce and controversial. In the present study, we established that this PAMP induced the relocalization of Hm-MyD88 in isolated neurons.

Grouper (Epinephelus coioides) IL-34/MCSF2 and MCSFR1/MCSFR2 were involved in mononuclear phagocytes activation against Cryptocaryon irritans infection

MCSF and its well-known receptor MCSFR had been well studied in humans, regulating the differentiation, proliferation, and survival of the mononuclear phagocyte system. IL-34, which is an alternative ligand of MCSF receptor, was recently identified as a novel cytokine and functionally overlaps with MCSF. However, the functional study of these receptors and their ligands in fish are largely unknown. In the present study, the cDNA of two potential grouper MCSFR ligands have been cloned, EcIL-34 (657 bp) and EcMCSF2 (804 bp), as well as an additional copy of grouper MCSFR, EcMCSFR2 (3141 bp). Sequence analysis showed that these three molecules had higher identities with other fish counterparts compared to mammals and their conserved structures and important functional residues were also analyzed. Tissue distribution analysis showed that EcIL-34 is dominant in brain, gill and spleen compared to EcMCSF2, which is dominant in head kidney, trunk kidney, skin, heart and muscle. EcMCSFR1 was dominant in the most tissues except head kidney and liver compared to EcMCSFR2. The different tissue distribution patterns of these two grouper MCSF receptors and their two ligands indicate the different mononuclear phagocyte differentiation and activation modes in different tissues. In Cryptocaryon irritans infected grouper, EcIL-34 and EcMCSFR2 were the most strongly up-regulated ligand and receptor in the infected sites, gill and skin. Their up-regulation confirmed the proliferation and activation of phagocytes in C. irritans infected sites, which would improve the antigen presentation and elicit the host local specific immune response. In C. irritans infected grouper head kidney, both ligands EcIL-34 and EcMCSF2 (especially EcMCSF2) were up-regulated, but both receptors EcMCSFR1 and EcMCSFR2 were down-regulated, which indicated that the phagocytes differentiation and proliferation may have occurred in this hemopoietic organ, and after that they migrated to the infected cites. The down-regulation of EcIL-34 and EcMCSF2 and no significant change of EcMCSFR1 and EcMCSFR2 in most time point of grouper spleen showed it was less involved in phagocytes response to C. irritans infection.

Early activation of teleost B cells in response to rhabdovirus infection

To date, the response of teleost B cells to specific pathogens has been only scarcely addressed. In this work, we have demonstrated that viral hemorrhagic septicemia virus (VHSV), a fish rhabdovirus, has the capacity to infect rainbow trout spleen IgM-positive (IgM(+)) cells, although the infection is not productive. Consequently, we have studied the effects of VHSV on IgM(+) cell functionality, comparing these effects to those elicited by a Toll-like receptor 3 (TLR3) ligand, poly(I·C). We found that poly(I·C) and VHSV significantly upregulated TLR3 and type I interferon (IFN) transcription in spleen and blood IgM(+) cells. Further effects included the upregulated transcription of the CK5B chemokine. The significant inhibition of some of these effects in the presence of bafilomycin A1 (BAF), an inhibitor of endosomal acidification, suggests the involvement of an intracellular TLR in these responses. In the case of VHSV, these transcriptional effects were dependent on viral entry into B cells and the initiation of viral transcription. VHSV also provoked the activation of NF-κB and the upregulation of major histocompatibility complex class II (MHC-II) cell surface expression on IgM(+) cells, which, along with the increased transcription of the costimulatory molecules CD80/86 and CD83, pointed to VHSV-induced IgM(+) cell activation toward an antigen-presenting profile. Finally, despite the moderate effects of VHSV on IgM(+) cell proliferation, a consistent effect on IgM(+) cell survival was detected.

IMPORTANCE

Innate immune responses to pathogens established through their recognition by pattern recognition receptors (PRRs) have been traditionally ascribed to innate cells. However, recent evidence in mammals has revealed that innate pathogen recognition by B lymphocytes is a crucial factor in shaping the type of immune response that is mounted. In teleosts, these immediate effects of viral encounter on B lymphocytes have not been addressed to date. In our study, we have demonstrated that VHSV infection provoked immediate transcriptional effects on B cells, at least partially mediated by intracellular PRR signaling. VHSV also activated NF-κB and increased IgM(+) cell survival. Interestingly, VHSV activated B lymphocytes toward an antigen-presenting profile, suggesting an important role of IgM(+) cells in VHSV presentation. Our results provide a first description of the effects provoked by fish rhabdoviruses through their early interaction with teleost B cells.

Toll-like receptor recognition of bacteria in fish: ligand specificity and signal pathways

Pattern recognition receptors (PRRs) recognize the conserved molecular structure of pathogens and trigger the signaling pathways that activate immune cells in response to pathogen infection. Toll-like receptors (TLRs) are the first and best characterized innate immune receptors. To date, at least 20 TLR types (TLR1, 2, 3, 4, 5M, 5S, 7, 8, 9, 13, 14, 18, 19, 20, 21, 22, 23, 24, 25, and 26) have been found in more than a dozen of fish species. However, of the TLRs identified in fish, direct evidence of ligand specificity has only been shown for TLR2, TLR3, TLR5M, TLR5S, TLR9, TLR21, and TLR22. Some studies have suggested that TLR2, TLR5M, TLR5S, TLR9, and TLR21 could specifically recognize PAMPs from bacteria. In addition, other TLRs including TLR1, TLR4, TLR14, TLR18, and TLR25 may also be sensors of bacteria. TLR signaling pathways in fish exhibit some particular features different from that in mammals. In this review, the ligand specificity and signal pathways of TLRs that recognize bacteria in fish are summarized. References for further studies on the specificity for recognizing bacteria using TLRs and the following reactions triggered are discussed. In-depth studies should be continuously performed to identify the ligand specificity of all TLRs in fish, particularly non-mammalian TLRs, and their signaling pathways. The discovery of TLRs and their functions will contribute to the understanding of disease resistance mechanisms in fish and provide new insights for drug intervention to manipulate immune responses.

First evidence of comparative responses of Toll-like receptor 22 (TLR22) to relatively resistant and susceptible Indian farmed carps to Argulus siamensis infection

Toll-like receptor 22 (TLR22) is present in teleost but not in mammals. Among Indian farmed carps, Catla catla is relatively more resistant than Labeo rohita to Argulus siamensis lice infection. TLR22 is believed to be associated with innate immunity against ectoparasite infection. To investigate the TLR22 mediated immunity against argulosis, we have cloned and characterized TLR22 genes of L. rohita (rTLR22) and C. catla (cTLR22). The full-length cDNAs of rTLR22 and cTLR22 contained an open reading frame of 2838 and 2841 nucleotides, respectively; bearing the typical structural features. Phylogenetically rTLR22/cTLR22 was most closely related to Cyprinus carpio (common carp) counterpart, having highest sequence identity of 86.0%. The TIR domain remained highly conserved with 90% identity within freshwater fishes. The sequence information of cDNA and genomic DNA together revealed that the rTLR22/cTLR22 genes are encoded by uninterrupted exons. The co-habitation challenge study with A. siamensis infection confirmed that C. catla is comparatively more resistant than L. rohita. Further, comparative mRNA expression profile in immune relevant tissues also suggested about the participatory role of TLR22 during lice infection. However, TLR22 might not solely be involved in conferring relative resistance among carp species against argulosis.

Molecular characterizations of grass carp (Ctenopharyngodon idella) TBK1 gene and its roles in regulating IFN-I pathway

TANK-binding kinase 1 (TBK1), a kinase at the crossroads of multiple IFN-inducing signaling pathways, plays essential roles in both antiviral and antibacterial innate immunity in mammals. Here, TBK1 gene (10339bp) was identified and characterized from grass carp Ctenopharyngodon idella (CiTBK1). The genomic sequence is shorter than other orthologs in vertebrate, and a promoter region is found in intron 1. mRNA expression of CiTBK1 was widespread in fifteen tissues investigated, and was up-regulated post GCRV challenge in vivo and in vitro, as well as after stimulation of viral/bacterial PAMPs in vitro. CiTBK1 mediates IFN-I signal pathway through over-expression experiment. Post GCRV challenge, CiTBK1 over-expression inhibits viral infection by induction of CiIFN-I and CiMx1 mainly via CiIRF7. In CiTBK1 over-expression cells, mRNA expressions of CiIRF3, CiIRF7 and CiIFN-I were inhibited, whereas CiMx1 was facilitated after poly I:C stimulation, comparing to those in control group. The result indicated that CiMx1 expression mediated by CiTBK1 is in IFN-I independent way after poly I:C stimulation. However, over-expression of CiTBK1 diminishes LPS-induced expressions of CiIRF3 and CiIRF7 but promotes the induction of CiIFN-I and CiMx1 in comparison with the control, which suggests that CiTBK1-triggered IFN-I activation is in IRF3/IRF7-independent manner after LPS stimulation. Notably, over-expression of CiTBK1 negatively regulated PGN-induced IRF3, IRF7, IFN-I and Mx1 immune response. Taken together, CiTBK1 participates in broad antiviral and antibacterial immune responses in different manners, and keeps regulatory balance that prevents harmful effects from excessive activation.