Molecular characterization of an IL-1β gene from ayu, Plecoglossus altivelis

Micro-and nano-plastics induce kidney damage and suppression of innate immune function in zebrafish (Danio rerio) larvae

Aquatic environments serve as critical repositories for pollutants and have significantly accumulated micro- and nanoplastics (MNPs) due to the extensive production and application of plastic products. While the disease resistance and immunity of fish are closely linked to the condition of their aquatic habitats, the specific effects of nanoplastics (NPs) and microplastics (MPs) within these environments on fish immune functions are still not fully understood. The present study utilized zebrafish (Danio rerio) embryos and larvae as model organisms to examine the impacts of polystyrene NPs (100 nm) and MPs (5 μm) on fish immune responses. Our findings reveal that NPs and MPs tend to accumulate on the surfaces of embryos and within the intestines of larvae, triggering oxidative stress and significantly increasing susceptibility to Edwardsiella piscicida infection in zebrafish larvae. Transmission electron microscopy examined that both NPs and MPs inflicted damage to the kidney, an essential immune organ, with NPs predominantly inducing endoplasmic reticulum stress and MPs causing lipid accumulation. Transcriptomic analysis further demonstrated that both NPs and MPs significantly suppress the expression of key innate immune pathways, notably the C-type lectin receptor signaling pathway and the cytosolic DNA-sensing pathway. Within these pathways, the immune factor interleukin-1 beta (il1b) was consistently downregulated in both exposure groups. Furthermore, exposure to E. piscicida resulted in restricted upregulation of il1b mRNA and protein levels, likely contributing to diminished disease resistance in zebrafish larvae exposed to MNPs. Our findings suggest that NPs and MPs similarly impair the innate immune function of zebrafish larvae and weaken their disease resistance, highlighting the significant environmental threat posed by these pollutants.

A computational analysis of the molecular mechanisms underlying the effects of ibuprofen and dibutyl phthalate on gene expression in fish

The impact of emerging pollutants such as ibuprofen and dibutyl phthalate on aquatic species is a growing concern and the need for proper assessment and evaluation of these toxicants is imperative. The objective of this study was to examine the toxicogenomic impacts of ibuprofen and dibutyl phthalate on Clarias gariepinus, a widely distributed African catfish species. Results showed that exposure to the test compounds caused significant changes in gene expression, including upregulation of growth hormone, interleukin, melatonin receptors, 17β-Hydroxysteroid Dehydrogenase, heat shock protein, doublesex, and mab-3 related transcription factor. On the other hand, expression of forkhead Box Protein L2 and cytochrome P450 was downregulated, revealing a potential to induce female to male sex reversal. The binding affinities and hydrophobic interactions of the test compounds with the reference genes were also studied, showing that ibuprofen had the lowest binding energy and the highest affinity for the docked genes. Both compounds revealed a mutual molecular interaction with amino acids residues within the catalytic cavity of the docked genes. These results provide new insights into the toxic effects of ibuprofen and dibutyl phthalate on Clarias gariepinus, contributing to a better understanding of the environmental impact of these pollutants.

Derivation and characterization of new cell line from intestine of turbot (Scophthalmus maximus)

A continuous intestine cell line from turbot (Scophthalmus maximus) designated as SMI was established utilizing the tissue explant technique. Primary SMI cell was cultured at 24 °C in a medium with 20% fetal bovine serum (FBS), then subcultured in 10% FBS after 10 passages. Impacts of medium or temperature on the growth of SMI were examined and the results indicated it grew well in DMEM supplemented with 10% FBS at 24 °C. The SMI cell line was subcultured more than 60 times. Karyotyping, chromosome number, and ribosomal RNA genotyping analysis revealed that SMI had a modal diploid chromosome number of 44 and originated from turbot. After being transfected with pEGFP-N1 and FAM-siRNA, a large number of green fluorescence signals were observed in SMI, indicating that SMI could be used as an ideal platform to explore gene function in vitro. In addition, the expression of epithelium-associated genes such as itga6, itgb4, gja1, claudin1, zo-1, and E-cadherin in SMI suggested the SMI had some characteristics of epidermal cells. The upregulation of immune-associated genes such as TNF-β, NF-κB, and IL-1β in SMI after stimulation with pathogen-associated molecular patterns suggested the SMI might exhibit immune functions similar to the intestinal epithelium in vivo.

Structural and Functional Aspects of the Spleen in Molly Fish Poecilia sphenops (Valenciennes, 1846): Synergistic Interactions of Stem Cells, Neurons, and Immune Cells

In fish, the spleen is the prime secondary lymphoid organ. It has a role in the induction of adaptive immune responses, in addition to its significance in the elimination of immune complexes. This study was conducted on 18 randomly obtained adult molly fish (Poecilia sphenops) of both sexes using histological, immunohistochemical, and ultrastructural studies to highlight the cellular components of the spleen and their potential role in the immune system. The spleen of molly fish was characterized by the presence of well-distinct melanomacrophage centers, and other basic structures present in higher vertebrates including red and white pulps, blood vessels, and ellipsoids. Some mitotic cells could also be identified in the red pulp. Mast cells with characteristic metachromatic granules could be seen among the splenic cells. Rodlet cells were randomly distributed in the spleen and were also observed around the ellipsoids. The white pulp of the spleen expressed APG5. The expressions were well distinct in the melanomacrophages, leukocytes, and macrophages. Myostatin was expressed in leukocytes and epithelial reticular cells. IL-1β showed immunoreactivity in monocytes and macrophages around the ellipsoids. NF-κB and TGF-β were expressed in macrophages and epithelial reticular cells. Nrf2 expression was detected in stem cells and rodlet cells. Sox-9 had a higher expression in epithelial reticular cells and stem cells. The high frequency of immune cells in the spleen confirmed its role in the regulation of both innate and adaptive immunity, cell proliferation, and apoptosis.

An IL-1β homologue induced inflammation and antibacterial immune defense in Siberian sturgeon (Acipenser baeri)

Interleukin-1β is a key pro-inflammatory cytokine functioning in initiation of inflammatory responses against bacterial- and viral-infections. In the present study, a putative IL-1β counterpart was identified from Siberian sturgeon (Acipenser baeri) and designated as AbIL-1β. The Abil-1β cDNA sequence consists of 1130 bp with an open reading frame (ORF) of 585 bp, which encodes a 194 amino acid (aa) protein. Multiple amino acid sequence alignment revealed that a possible mature peptide could start at Leu¹⁸, although no cut site for ICE (IL-1β converting enzyme) enzyme was present in Siberian sturgeon IL-1β. Even if AbIL-1β shares a relative low identity (33.6%) with another sturgeon type II IL-1β gene from Acipenser dabryanus, they still clustered together in phylogenetic tree. Endogenous Abil-1β was highly expressed in brain, blood, head kidney and spleen of healthy Siberian sturgeon, and remarkably up regulated in head kidney, spleen, and liver upon Aeromonas hydrophila (A.h) challenge. Consistently, in vitro stimulation test using heat-killed A.h and LPS significantly increased Abil-1β transcripts of primary spleen cells. To investigate the bactericidal capability of AbIL-1β, recombinant AbIL-1β (rAbIL-1β) was generated by prokaryotes. Pre-injection of rAbIL-1β reduced the bacterial load in sturgeon spleen after A.h infection. Further, rAbIL-1β was served as feed additive and demonstrated to enhance hybrid sturgeon's defense against A.h infection by increased expressional levels of immune-related genes (IL-1β, IL-6, IL-8, IgM and MHCIIβ), elevated activities of serum lysosome, ACH50, and MPO, as well as higher percent survival. In summary, the current results suggested that AbIL-1β functions in immune regulation and could improve sturgeon's resistance to bacterial infection.

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

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

Alteration of the gut microbiome and immune factors of grass carp infected with Aeromonas veronii and screening of an antagonistic bacterial strain (Streptomyces flavotricini)

Aeromonas veronii is a widely distributed novel pathogen that can affect humans and animals, it can cause sepsis in fish with high mortality and serious economic losses to aquaculture. In the study, the gut microbiome of the infected and uninfected grass carp with Aeromonas veronii were analyzed probiotics and pathogenic bacteria by the Miseq high-throughput sequencing, the results showed that the infected fish were significantly higher in Proteobacteria, Firmicutes, Fusobacteria, and the immune factors in liver and kidney were up-regulated by qRT-PCR. In order to effectively inhibit the pathogen, we screened an actinomycete strain and had good antibacterial effect on Aeromonas veronii. The new antagonistic bacteria was named as Streptomyces flavotricini X101, the whole genome sequencing revealed that the metabolic process was most active. After grass carp was inoculated with the minimum inhibitory concentration of 900 μg/mL of the strain's fermentation supernatant, then Aeromonas veronii was injected, we found that the pathological symptoms such as body surface, anus and abdominal congestion were alleviated by H&E staining. Cellular experiments showed that it wasn't toxic to liver cells of grass carp. Overall, this is the first study of changes in intestinal flora, phenotype, and immune factors in grass crap infected with Aeromonas veronii, it had important theoretical significance and application value for immunization and prevention.

Antibacterial synergy between rutin and florfenicol enhances therapeutic spectrum against drug resistant Aeromonas hydrophila

Emergence of antibiotic resistant bacteria has necessitated the drive to explore competent antimicrobial agents or to develop novel formulations to treat infections including Aeromonas hydrophila. The present study investigates the synergistic antibacterial effects of citrus flavonoid rutin and florfenicol (FF) against A. hydrophila in vitro and in vivo. Rutin is extracted and purified from Citrus sinensis peel through preparative HPLC and characterized through TLC, GC-MS and ¹H and ¹³C NMR analyses. Though rutin did not display significant antibacterial activity, it modulated FF activity resulting in four-fold reduction in the MIC value for FF. The anti-biofilm potential of synergistic association of rutin and FF was validated by protein analysis, quantification of exopolysaccharide (EPS) and microscopy studies using sub-MIC doses. Besides antibacterial action, in vivo studies showed that Rutin/FF combination enhanced host immunity by improving blood cell count, anti-protease, and lysozyme activities as well as decreased the oxidative stress and the pathological changes of tilapia Oreochromis niloticus against A. hydrophila infection. No significant DNA damages or clastogenic effects were detected in tilapia challenged with A. hydrophila under Rutin/FF treatment. It is shown that an acute-phase Lipopolysaccharide binding protein (LBP) enhances the innate host defence against bacterial challenge. Semi quantitative RT-PCR and western blot results revealed the significant increase of LBP in the supernatant of tilapia monocytes/macrophages challenged with A. hydrophila upon treatment. The study findings substantiate that the combination of natural molecules with antibiotics may open up possibilities to treat MDR strains.

A Novel Lipopolysaccharide Recognition Mechanism Mediated by Internalization in Teleost Macrophages

Macrophages in teleosts are less sensitive to lipopolysaccharide (LPS) compared to mammals. The functional equivalent of the mammalian LPS surface receptor in teleost macrophages for the pro-inflammatory response is either non-existent or replaced by negative regulation. LPS signaling in teleost macrophages remains unclear. Here, we found a scavenger receptor class B 2a (PaSRB2a) that played a crucial role in LPS signaling in teleost macrophages. The internalization of LPS and subsequent pro-inflammatory responses in macrophages were mediated by PaSRB2a, which is a novel isoform of the mammalian SRB2 gene. LPS internalization by PaSRB2a is dependent on its C-terminal intracellular domain. Following LPS internalization, it interacts with the ayu intracellular receptors nucleotide-binding oligomerization domain protein 1 (PaNOD1) and PaNOD2. Moreover, LPS pre-stimulation with sub-threshold concentrations reduced the effect of secondary LPS treatment on pro-inflammatory responses that were mediated by PaSRB2a. The pro-inflammatory responses in LPS-treated ayu were down-regulated upon PaSRB2a knockdown by lentivirus siRNA delivery. In grass carp and spotted green pufferfish, SRB2a also mediated LPS internalization and pro-inflammatory responses. Our work identifies a novel LPS signaling pathway in teleosts that differs from those in mammals, and contributes to our understanding of the evolution of pathogen recognition in vertebrates.

Molecular characterization of a tissue factor gene from ayu: A pro-inflammatory mediator via regulating monocytes/macrophages

Tissue factor (TF) plays an important role in the host's immune system as the principal initiator of coagulation. However, the precise function of TF in teleosts remains unclear. We determined the cDNA sequence of TF from ayu Plecoglossus altivelis (PaTF). The PaTF transcript was expressed in all tested tissues, and changes in expression were observed in tissues and monocytes/macrophages (MO/MФ) upon infection with Vibrio anguillarum. PaTF was prokaryotically expressed and purified to prepare anti-PaTF antibodies. Western blot analysis revealed that native PaTF was glycosylated in thrombocytes, but not in ayu MO/MФ. Microparticles could transfer PaTF to thrombocytes. PaTF neutralization or knockdown led to anti-inflammatory status in ayu MO/MФ upon V. anguillarum infection. PaTF neutralization reduced the apoptosis of ayu MO/MФ and improve survival rate in V. anguillarum-infected ayu. Our results indicate that PaTF plays a role in ayu immune response against bacterial infection as a pro-inflammatory mediator.

Molecular identification and functional analysis of KLF2 in Plecoglossus altivelis (ayu): It's regulatory role in monocyte/macrophage activation

Monocytes/macrophages (MO/MФ) play an important role in the response to infection in Plecoglossus altivelis (ayu). However, the role of transcription factors in the function of ayu MO/MФ is poorly understood. Here, we cloned the cDNA sequence of the Kruppel-like factor 2 (PaKLF2) gene from ayu. Phylogenetic analysis indicated that PaKLF2 was closest to that of Atlantic salmon (Salmo salar). Real time quantitative PCR (RT-qPCR) revealed that the PaKLF2 mRNA level was highest in the peripheral blood mononuclear cells among all tested tissues. The mRNA expression of PaKLF2 was upregulated in the head kidney, liver, spleen, and brain after Listonella anguillarum infection. Subsequently, PaKLF2 was expressed and purified to prepare anti-PaKLF2 antibodies. After L. anguillarum challenge, the PaKLF2 mRNA and protein levels were significantly upregulated in ayu MO/MФ. Moreover, PaKLF2 knockdown in MO/MФ resulted in the enhancement of cytokine production as well as phagocytotic and bactericidal capability. Therefore, PaKLF2 may modulate the immune response in ayu by suppressing the function of MO/MФ.

Molecular and functional characterization of liver X receptor in ayu, Plecoglossus altivelis: Regulator of inflammation and efferocytosis

Liver X receptors (LXR) are modulators of metabolic processes and inflammation in mammals as nuclear receptors. However, the precise function of LXR in teleosts remains unclear. Here, we characterized a LXR gene (PaLXR) from ayu, Plecoglossus altivelis. The PaLXR transcript was expressed widely in all tissues studied, and changes in expression were observed in tissues and monocytes/macrophages (MO/MΦ) upon infection with the bacterium Edwardsiella ictaluri. PaLXR activation decreased the mRNA expression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-10 upon E. ictaluri infection, while their expression was increased following the knockdown of PaLXR by siRNA. Moreover, E. ictaluri infection induced the apoptosis of ayu neutrophils and PaLXR activation enhanced the internalization of E. ictaluri-infected apoptotic neutrophils by MO/MΦ (efferocytosis), while PaLXR knockdown led to decreased efferocytosis. Furthermore, PaLXR activation inhibited intracellular bacterial survival during efferocytosis, while PaLXR knockdown enhanced survival. In conclusion, our results indicate that PaLXR plays a role in the modulation of innate immune responses in ayu MO/MФ.

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

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

A transmembrane C-type lectin receptor mediates LECT2 effects on head kidney-derived monocytes/macrophages in a teleost, Plecoglossus altivelis

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multifunctional cytokine involved in many diseases in which immune dysfunction is present. Ayu LECT2 (PaLECT2), which interacts with a C-type lectin receptor (PaCLR), was shown to activate ayu head kidney-derived monocytes/macrophages (MO/MΦ) to improve the outcomes of fish upon bacterial infections. However, it is not known if PaCLR mediates PaLECT2 effects on ayu MO/MΦ. In this study, we determined the role of PaCLR in signal transduction of PaLECT2 on ayu MO/MΦ. We expressed the PaCLR ectodomain in Escherichia coli and produced a refolded recombinant protein (rPaCLR) that was then used to produce the anti-PaCLR IgG (anti-PaCLR) for neutralization. Addition of the refolded PaLECT2 mature peptide (rPaLECT2m) to ayu MO/MΦ cultures, increased cytokine expression, induced chemotaxis, and enhanced phagocytosis and bactericidal activity of these cells were observed. When we added anti-PaCLR to block the ectodomain of PaCLR, these effects were significantly inhibited. Based on our previous works and the data presented here, we conclude that PaCLR mediates the immunomodulatory effects of PaLECT2 on ayu MO/MΦ, thus defining a mechanism by which LECT2 protects fish against pathogens.

Molecular Characterization of E-Type Prostanoid Receptor 4 (EP4) from Ayu (Plecoglossus altivelis) and Its Functional Analysis in the Monocytes/Macrophages

Prostaglandin E2 (PGE2) plays an important role in a broad spectrum of physiological and pathological processes by interacting with E-type prostanoid receptors (EPs). EP4 is one of four EP subtypes known to mediate the immune response in mammalian monocytes/macrophages. However, the precise function and characteristics of EP4 in fish remain unclear. In this study, we characterized a novel EP4-like (PaEP4L) gene from ayu, Plecoglossus altivelis. The cDNA sequence of PaEP4L is 2781 nucleotides (nts) in length, encoding a polypeptide of 459 amino acid residues with a calculated molecular weight of 51.17 kDa. Sequence comparison and phylogenetic tree analysis showed that PaEP4L shared 76% amino acid identity with that of the Atlantic salmon (Salmo salar). PaEP4L mRNA was detected by real-time quantitative PCR (QPCR) in all tested tissues and head kidney-derived monocytes/macrophages (MO/MФ). It varied greatly in liver, spleen and MO/MФ upon Vibrio anguillarum infection. Western blot analysis revealed a significant increase of PaEP4L in cell homogenates from ayu MO/MФ upon V. anguillarum infection. Moreover, anti-PaEP4L IgG reversed the down-regulation of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) mRNA expression as well as phagocytosis in ayu MO/MФ caused by PGE2. There were no significant differences in the respiratory burst response between PGE2 treated and untreated cells. We further found that cAMP mediated PGE2/PaEP4L signal in ayu MO/MФ. In conclusion, our results indicate that PaEP4L mediates PGE2 effects on ayu MO/MФ function, revealing that EP4 also plays a role in the modulation of cells of the fish’s innate immune system.

Four pro-inflammatory cytokines of rohu (Labeo rohita) during early developmental stages, their tissue distribution and expression by leucocytes upon in-vitro stimulation

Cytokines are important components of both adaptive and innate immunity, and are required to initiate and regulate immune responses following infection. The ontogeny and tissue specific distribution of four pro-inflammatory cytokines, interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), IL-8 and IL-1β in rohu (Labeo rohita), and their responses by leucocytes from anterior-kidney/head-kidney (HKLs), spleen (SPLs) and peripheral blood (PBLs) following stimulation with concanavalin A (ConA), ConA with phorbol 12-myristate 13-acetate (ConA/PMA) and formalin-killed Aeromonas hydrophila cells (FAH) were studied. In ontogeny study, mRNA levels of IL-6 and IL-1β were evident in unfertilized egg stages of L. rohita whereas IL-8 and TNF-α transcripts were found from 1 to 3 h post-fertilization (hpf) onwards till day 15 post-fertilization, respectively. Basal level of all four cytokines was observed in all twelve tissues (eye, brain, heart, gill, anterior kidney, posterior kidney, spleen, liver, skin, muscle, hindgut and foregut) of L. rohita juveniles. Expression levels of IL-6 and IL-8 were found to be the highest in liver and heart tissues, respectively, while TNF-α transcripts were high in anterior kidney and liver tissues. Transcripts of IL-1β showed high expression in muscle, heart and spleen. Upon in vitro stimulation of leucocytes, there was variable up-regulation of all the four cytokines following different treatments throughout the experimental time period. Induction of cytokines was more pronounced in PBLs stimulated with FAH compared to other stimuli. However, an up-regulated IL-8 expression was evident in all the leucocytes following stimulation with FAH thus indicating IL-8 could be used as an indicator or indirect marker to monitor vaccine status or health status of L. rohita during bacterial infection.

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

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

Identification and functional characterization of the CSF1R gene from grass carp Ctenopharyngodon idellus and its use as a marker of monocytes/macrophages

Colony-stimulating factor 1 receptor (CSF1R) is an important regulator of monocytes/macrophages (MO/MΦ). Although CSF1R gene has been identified and functionally studied in many fish, the precise role of CSF1R in grass carp (Ctenopharyngodon idellus) remains unclear. In this study, we determined the cDNA sequence of CSF1R (CiCSF1R) from a teleost fish, grass carp. Sequence comparison and phylogenetic tree analysis showed that CiCSF1R was most closely related to the CSF1R of zebrafish. The CiCSF1R transcript was mainly expressed in the spleen, head kidney, and head kidney-derived MO/MΦ, and its expression was altered in various tissues upon Aeromonas hydrophila infection. We prepared antibodies for neutralization of CiCSF1R on grass carp MO/MΦ. CiCSF1R neutralization or knockdown led to anti-inflammatory status in MO/MΦ upon A. hydrophila infection. CiCSF1R neutralization or knockdown also decreased the phagocytic activity of MO/MΦ. Flow cytometric analysis showed that more than 85% of grass carp MO/MΦ were CiCSF1R-positive cells. The percentage of CiCSF1R-positive cells in the head kidney of grass carp was above 10%, whereas it was only 5% and 4% in the spleen and liver, respectively. In conclusion, CSF1R is a specific surface marker of grass carp MO/MΦ, and it regulates the functions of MO/MΦ.

Dual-parallel inhibition of IL-10 and TGF-β1 controls LPS-induced inflammatory response via NF-κB signaling in grass carp monocytes/macrophages

In fish, the knowledge on the regulation of inflammatory responses is limited. In the present study, LPS rapidly increased the mRNA levels of grass carp pro-inflammatory factors, including tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), inducible nitric oxides synthase (iNOS) and IL-8 in monocytes/macrophages, indicating the occurrence of innate inflammatory responses in fish as seen in mammals. Intriguingly, the gene expression and protein secretion of grass carp IL-10 (gcIL-10) and TGF-β1 (gcTGF-β1) were induced by LPS in the same cell model, promoting us to clarify their roles in regulating inflammatory response. Results revealed that grass carp IL-10 polyclonal antibody (anti-gcIL-10 pAb) and grass carp TGF-β1 monoclonal antibody (anti-gcTGF-β1 mAb) could amplify the stimulation of LPS on the mRNA levels of tnfα, il1β, inos and il8, suggesting the inhibitory tone of endogenous IL-10 and TGF-β1 in LPS-challenged immune responses. This notion was further supported by the fact that recombinant grass carp IL-10 (rgcIL-10) and recombinant grass carp TGF-β1 (rgcTGF-β1) attenuated LPS-stimulated tnfα, il1β, inos and il8 gene expression in monocytes/macrophages. Further study revealed that rgcIL-10 and rgcTGF-β1 impaired NF-κB activation by blocking LPS-induced grass carp IκBα (gcIκBα) protein degradation in the cells. In addition, the correlation between gcIL-10 and gcTGF-β1 in this regulation was examined by immunoneutralization, unveiling that anti-gcTGF-β1 mAb and anti-gcIL-10 pAb were unable to alter the inhibitory effects of rgcIL-10 and rgcTGF-β1 on pro-inflammatory factors expression in grass carp monocytes/macrophages, respectively. This dual and parallel effect of gcIL-10 and gcTGF-β1 strengthened their importance in controlling inflammatory responses. Taken together, our findings shed a light on the functional role, regulatory mechanism and relationship of fish IL-10 and TGF-β1 in regulating inflammatory response.

Molecular characterization and functional analysis of a novel C-type lectin receptor-like gene from a teleost fish, Plecoglossus altivelis

C-type lectin-like receptors (CLRs) are important pathogen pattern recognition molecules that recognize carbohydrate structures. However, the functions of these receptors in fish keep less known. In this study, we characterized a novel CLR from a teleost fish, Plecoglossus altivelis (ayu), tentatively named PaCD209L. The cDNA of PaCD209L is 1464 nucleotides (nts) in length, encoding a polypeptide of 281 amino acid residues with a calculated molecular weight of 31.5 kDa. Multiple alignment of the deduced amino acid sequences of PaCD209L and other related fish CLRs revealed that the PaCD209L sequence had typical characteristics of fish CLRs, but without Ca(2+)-binding sites. Sequence comparison and phylogenetic tree analysis showed that PaCD209L shared the highest amino acid identity (44%) with rainbow trout (Oncorhynchus mykiss) CD209 aE PaCD209L transcripts were detected in all of the tissues examined, mainly expressed in the brain and heart. Upon Vibrio anguillarum infection, PaCD209L transcripts were upregulated in all tested tissues and in monocytes/macrophages (MO/MΦ). We prepared recombinant PaCD209L (rPaCD209L) by prokaryotic expression and raised antiserum against PaCD209L. Western blot analysis revealed that native PaCD209L was glycosylated, and its protein expression significantly increased in ayu MO/MΦ upon V. anguillarum infection. In addition, rPaCD209L was able to bind Gram-positive and Gram-negative bacteria in the absence of Ca(2+). After PaCD209L was blocked by anti-PaCD209L IgG, the phagocytosis and bacterial killing activity of MO/MΦ significantly decreased. These results suggest that PaCD209L plays an important role in the regulation of MO/MΦ functions in ayu.

LECT2 improves the outcomes in ayu with Vibrio anguillarum infection via monocytes/macrophages

Leukocyte cell-derived chemotaxin 2 (LECT2) is reported to be a cytokine involved in the immune response against pathogenic microorganisms in fish. However, its accurate function in whole fish remains unclear. In this study, we provide the first report on the effect of LECT2 on fish defenses against pathogens in vivo. The administration of recombinant LECT2 improved the survival rate of Vibrio anguillarum infected ayu. The bacterial burden of V. anguillarum infected ayu was decreased in LECT2-treated ayu blood, liver, spleen, and kidney compared with saline control. In bacteria-infected ayu, LECT2 treatment altered the mRNA expression of cytokines, including TNFα, IL-1β, and IL-10, which are all important for the inflammatory response in fish. LECT2 treatment also reduced histological damage in bacteria-infected ayu, and increased peritoneal monocytes/macrophages in both healthy and infected ayu at 12 h post infection. When ayu monocytes/macrophages were depleted by clodronate-liposomes treatment, LECT2 treatment did not increase the survival rate of bacteria-infected fish compared with healthy control fish. Thus our results suggest that LECT2 can modulate host defense in ayu and mediate antibacterial protection against V. anguillarum through monocytes/macrophages.

Molecular characterization of a CXCL8-like protein from ayu and its effect on chemotaxis of neutrophils and monocytes/macrophages

CXCL8, a CXC-type chemokine, plays a crucial role in acute inflammation by recruiting and mediating neutrophils and other cells. In this study, the cDNA and genomic DNA sequence of a CXCL8-like protein (PaCXCL8l) from ayu (Plecoglossus altivelis) was determined. Sequence analysis showed that PaCXCL8l represented the typical structure of animal CXCL8s. Phylogenetic tree analysis indicated that PaCXCL8l was closest to CXCL8 of Atlantic cod (Gadus morhua). Constitutive expression of PaCXCL8l was detected in all tested tissues and monocytes/macrophages, and its expression dramatically increased upon Listonella anguillarum infection. In vitro, recombinant PaCXCL8l exhibited a significant chemotactic effect on neutrophils at 0.1 μg/ml and on monocytes/macrophages at 1.0 μg/ml. In vivo, the numbers of peritoneal neutrophils and monocytes/macrophages were both up-regulated following intraperitoneal administration of recombinant PaCXCL8l. These results suggest that PaCXCL8l is crucially involved in the immune response of ayu by mediating chemotaxis of neutrophils and monocytes/macrophages.

Molecular characterization and functional analysis of two distinct liver-expressed antimicrobial peptide 2 (LEAP-2) genes in large yellow croaker (Larimichthys crocea)

Liver-expressed antimicrobial peptide 2 (LEAP-2) plays a vital role in the host innate immune system. In the present study, two LEAP-2 genes (LcLEAP-2A and LcLEAP-2C) from large yellow croaker (Larimichthys crocea) were cloned, both of which consist of 3 exons and 2 introns. The LcLEAP-2A transcripts were expressed in a wide range of tissues, with the highest mRNA levels found in the liver and intestine, while LcLEAP-2C transcripts showed obvious lower mRNA levels in all tested tissues compared to LcLEAP-2A. Upon infection by Vibrio alginolyticus, LcLEAP-2A transcripts were significantly up-regulated in liver, trunk kidney, spleen, head kidney, and gill, but down-regulated in intestine. In addition, significant up-regulation of LcLEAP-2C transcripts were also detected in all tissues tested, including intestine. The LcLEAP-2A and LcLEAP-2C mature peptides were chemically synthesized and found to exhibit selective antimicrobial activity in vitro against various species of bacteria. LcLEAP-2C, but not LcLEAP-2A, had antimicrobial activity against V. alginolyticus. Moreover, LcLEAP-2C treatment at low concentrations was evaluated and found to improve survival rate in V. alginolyticus-infected large yellow croaker, resulting in a decrease in bacterial load and expression of inflammatory cytokines. These results suggest that LcLEAP-2 isoforms play an important role in innate immunity by killing bacteria and inhibiting early inflammatory response in large yellow croaker.

A novel lipopolysaccharide-binding protein (LBP) gene from sweetfish Plecoglossus altivelis: molecular characterization and its role in the immune response of monocytes/macrophages

Lipopolysaccharide-binding protein (LBP) belongs to the lipid transfer/LBP (LT-LBP) family, and plays a crucial role in the recognition of bacterial components that modulate cellular signals in phagocytic cells. Although several LBPs have been identified in teleosts, the effects of LBP homologs on teleost phagocytic cells are still obscure. Here, we report the cloning a novel full-length cDNA sequence of LBP-like protein (paLBP) gene from sweetfish, Plecoglossus altivelis. The paLBP cDNA encoded a 464 aa polypeptide, which was closest to that of rainbow smelt (Osmerus mordax). paLBP mRNA was detected mainly in the spleen, liver, and head kidney and levels dramatically increased in various tissues after Listonella anguillarum infection. In contrast to mammalian studies, paLBP mRNA could also be detected in sweetfish monocytes/macrophages. Recombinant paLBP showed LPS-binding activity and Western blot results revealed a significant increase of paLBP in the supernatant of sweetfish monocytes/macrophages challenged with L. anguillarum. Moreover, paLBP neutralization led to up-regulation of IL-1β and TNF-α mRNA as well as respiratory burst activity in sweetfish monocytes/macrophages in response to L. anguillarum or LPS challenge. Therefore, these results suggest that paLBP is an inducible acute-phase protein mediating the immune response of sweetfish monocytes/macrophages upon bacterial challenge.

Passive protective effect of chicken egg yolk immunoglobulins against experimental Vibrio anguillarum infection in ayu (Plecoglossus altivelis)

Oral administration of chicken egg yolk immunoglobulins (IgY) has attracted much attention as a means for controlling infectious diseases caused by microorganisms. This study evaluated the protective effect of IgY against Vibrio anguillarum infection in ayu, Plecoglossus altivelis. IgY was isolated from egg yolks laid by hens initially immunized with formalin-inactivated V. anguillarum. Lower mortality of ayu was observed in groups treated with anti-V. anguillarum IgY (aVIgY), compared with those treated with saline or with nonspecific IgY (nspIgY). All fish in saline-treated groups died within seven days after bacterial inoculation. The bacterial load in blood, liver, and spleen was significantly lower in fish treated with aVIgY than in fish treated with nspIgY. aVIgY treatment significantly reduced tumor necrosis factor-α (PaTNF-α), interleukin-1β (PaIL-1β), transforming growth factor-β (PaTGF-β), and leukocyte cell-derived chemotaxin-2 (PaLECT2) transcript levels in the head kidney, spleen, and liver of ayu challenged by V. anguillarum, compared with nspIgY treatment. The phagocytic activity of macrophages for V. anguillarum in the presence of specific IgY was significantly higher than that seen for nonspecific IgY. These results suggest that passive immunization by oral intubation with pathogen-specific IgY may provide a valuable treatment for V. anguillarum infection in ayu.