The role of gamma interferon in innate immunity in the zebrafish embryo

Interferon- and infectious diseases: Lessons and prospects

Infectious diseases continue to claim many lives. Prevention of morbidity and mortality from these diseases would benefit not just from new medicines and vaccines but also from a better understanding of what constitutes protective immunity. Among the major immune signals that mobilize host defense against infection is interferon-γ (IFN-γ), a protein secreted by lymphocytes. Forty years ago, IFN-γ was identified as a macrophage-activating factor, and, in recent years, there has been a resurgent interest in IFN-γ biology and its role in human defense. Here we assess the current understanding of IFN-γ, revisit its designation as an "interferon," and weigh its prospects as a therapeutic against globally pervasive microbial pathogens.

Mechanism of Chinese sturgeon IFN-γ inhibition on Mycobacterium marinum (Acipenser sinensis)

IFN-γ plays a crucial role in both innate and adaptive immune responses and is a typical Th1 cytokine that promotes Th1 response and activates macrophages. When macrophages were incubated with IFN-γ, their phagocytosis ratio against Mycobacterium marinum increased significantly, as observed under fluorescence microscopy. The macrophages engulfed a large number of M. marinum. The proliferative ability of macrophages treated with IFN-γ was significantly weaker on the 4th and 7th day after phagocytosis and subsequent re-infection with marine chlamydia (P < 0.001). This suggests that IFN-γ enhances the phagocytosis and killing ability of macrophages against M. marinum. IFN-γ protein also significantly increased the production of reactive oxygen species (H2O2) and nitric oxide (NO) by macrophages. Additionally, the expression levels of toll-like receptor 2 (tlr2) and caspase 8 (casp8) were significantly higher in macrophages after IFN-γ incubation compared to direct infection after 12 h of M. marinum stimulation. Apoptosis was also observed to a higher degree in IFN-γ incubated macrophage. Moreover, mRNA expression of major histocompatibility complex (MHC) molecules produced by macrophages after IFN-γ incubation was significantly higher than direct infection. This indicates that IFN-γ enhances antigen presentation by upregulating MHC expression. It also upregulates tlr2 and casp8 expression through the TLR2 signaling pathway to induce apoptosis in macrophages. The pro-inflammatory cytokine showed an initial increase followed by a decline, suggesting that IFN-γ enhances the immune response of macrophages against M. marinum infection. On the other hand, the anti-inflammatory cytokine showed a delayed increase, significantly reducing the expression of pro-inflammatory cytokines. The expression of both cytokines balanced each other and together regulated the inflammatory reaction against M. marinum infection.

Fenpropathrin disrupted the gills of common carp (Cyprinus carpio L.) through oxidative stress, inflammatory responses, apoptosis, and transcriptional alterations

Fenpropathrin (FEN) is an extensively utilized synthetic pyrethroid insecticide frequently found in aquatic ecosystems. However, the adverse effects and potential mechanisms of FEN on aquatic species are poorly understood. In this work, common carp were treated with FEN at concentrations of 0.45 and 1.35 μg/L FEN for 14 days, after which the tissue structure, physiological alterations, and mRNA transcriptome of the gills were evaluated. Specifically, FEN exposure caused pathological damage to the gills of carp, downregulated the levels of claudin-1, occludin, and zonula occluden-1 (ZO-1), and inhibited Na+-K+-ATPase activity in the gills. In addition, FEN exposure promoted an increase in reactive oxygen species (ROS) levels and significantly upregulated the levels of malondialdehyde (MDA), 8-hydroxy-2 deoxyguanosine (8-OHdG), and protein carbonyl (PC) in the gills. Moreover, the inflammation-related indices (TNF-α, IL-1β, and IFN-γ) and the apoptosis-related parameter caspase-3 were generally increased, especially in the 1.35 μg/L FEN group, and these indices were significantly greater than those in the control group. These findings suggest that FEN exposure can cause oxidative stress, the inflammatory response, and apoptosis in carp gills. Importantly, the results of RNA-seq analysis showed that 0.45 and 1.35 μg/L FEN could significantly interfere with multiple immune and metabolic pathways, including the phagosome, NOD-like receptor (NLR) signalling pathway, Toll-like receptor (TLR) signalling pathway, necroptosis, and arachidonic acid metabolism pathways, indicating that the effects of FEN on the gills of fish are intricate. In summary, our findings confirm the toxic effects of FEN on common carp gills and provide additional comprehensive information for evaluating the toxicity and underlying molecular mechanisms of FEN in aquatic organisms.

A zebrafish model of Ifih1-driven Aicardi-Goutières syndrome reproduces the interferon signature and the exacerbated inflammation of patients

Type I interferonopathies are a heterogenic group of rare diseases associated with an increase in type I interferon (IFN). The main challenge for the study of Type I interferonopathies is the lack of a well-founded animal model to better characterize the phenotype as well as to perform fast and large drug screenings to offer the best treatment options. In this study, we report the development of a transgenic zebrafish model of Type I interferonopathy overexpressing ifih1 carrying the mutation p.Arg742His (Tg(ifih1_mut)), corresponding to the human mutation p.Arg779His. RNA sequence analysis from Tg(ifih1_mut) larvae revealed a systemic inflammation and IFN signature upon a suboptimal poly I:C induction compared with wild-type larvae, confirming the phenotype observed in patients suffering from Type I interferonopathies. More interestingly, the phenotype was manifested in the zebrafish inflammation and Type I IFN reporters nfkb:eGFP and isg15:eGFP, respectively, making this zebrafish model suitable for future high-throughput chemical screening (HTS). Using the unique advantages of the zebrafish model for gene editing, we have generated Tg(ifih1_mut) knocked down for mavs and ikbke, which completely abrogated the Poly I:C induction and activation of the GFP of the reporters. Finally, we used an FDA-approved drug, Baricitinib (Jak1/Jak2 inhibitor), which was able to reduce the inflammation and the ISG expression. Our results demonstrate the potential of this model to further understand AGS pathological mechanisms and to identify novel therapeutic drugs by HTS.

Sphk1 deficiency induces apoptosis and developmental defects and premature death in zebrafish

The sphk1 gene plays a crucial role in cell growth and signal transduction. However, the developmental functions of the sphk1 gene during early vertebrate zebrafish embryo remain not completely understood. In this study, we constructed zebrafish sphk1 mutants through CRISPR/Cas9 to investigate its role in zebrafish embryonic development. Knockout of the sphk1 gene was found to cause abnormal development in zebrafish embryos, such as darkening and atrophy of the head, trunk deformities, pericardial edema, retarded yolk sac development, reduced heart rate, and premature death. The acetylcholinesterase activity was significantly increased after the knockout of sphk1, and some of the neurodevelopmental genes and neurotransmission system-related genes were expressed abnormally. The deletion of sphk1 led to abnormal expression of immune genes, as well as a significant decrease in the number of hematopoietic stem cells and neutrophils. The mRNA levels of cardiac development-related genes were significantly decreased. In addition, cell apoptosis increases in the sphk1 mutants, and the proliferation of head cells decreases. Therefore, our study has shown that the sphk1 is a key gene for zebrafish embryonic survival and regulation of organ development. It deepened our understanding of its physiological function. Our study lays the foundation for investigating the mechanism of the sphk1 gene in early zebrafish embryonic development.

How modular protein nanoparticles may expand the ability of subunit anti-viral vaccines: The spring viremia carp virus (SVCV) case

Spring viremia of carp (SVC) remains as a vaccine orphan disease mostly affecting juvenile specimens. Young fish are especially difficult to vaccinate and oral administration of vaccine combined with food would be the election system to minimise stress and the vaccination costs associated to injection. However, administration of prophylactics with food pellets faces off several drawbacks mainly related with vaccine degradation and weak protection correlates of oral vaccines. Here we present a platform based on recombinant proteins (subunit vaccines) manufactured as highly resistant nanostructured materials, and providing excellent levels of protection against SVC virus in a preliminary i.p injection challenge. The G3 domain of SVCV glycoprotein G was overexpressed in E. coli together with IFNγ and the modular protein was purified from bacterial aggregates (inclusion bodies) as highly organised nanostructured biomaterial (nanopellets, NP). These SVCV-IFN^NP were taken up by zebrafish cells leading to the enhanced expression of different antiviral and IFN markers (e.g vig1, mx, lmp2 or ifngr1 among others) in zebrafish liver cells (ZFL). To monitor if SVCV^NP and SVCV-IFN^NP can be taken up by intestinal epithelia and can induce antiviral response we performed experiments with SVCV^NP and SVCV-IFN^NP in 3 days post fertilization (dpf) zebrafish larvae. Both, SVCV^NP and SVCV-IFN^NP were taken up and accumulated in the intestine without signs of toxicity. The antiviral response in larvae showed a different induction pattern: SVCV-IFN^NP did not induce an antiviral response while SVCV^NP showed a good antiviral induction. Interestingly ZF4, an embryonic derived cell line, showed an antiviral response like ZFL cells, although the lmp2 and ifngr1 (markers of the IFNγ response) were not overexpressed. Experiments with adult zebrafish indicated an excellent level of protection against a SVCV model infection where SVCV-IFN^NP vaccinated fish reached 20% cumulative mortality while control fish reached over 80% cumulative mortality.

Asparagus racemosus improves immune-related parameters in Nile tilapia (Oreochromis niloticus) and mitigates deltamethrin-induced toxicity

Deltamethrin (DM) is one of the most toxic but widely used pyrethroid insecticides. Even though a non-target animal, fish are at high risk as they are deficient in the enzyme system that hydrolyses pyrethroids. Enhancing the immune system is a potential method in preventing fish diseases. The present investigation aims to study the modulations in the immune response-related parameters in Oreochromis niloticus that were exposed to DM, by dietary supplementation of aqueous root extract of Asparagus racemosus (ARE). The experiment compared fish in control, DM (1 μg/L) exposed (added to water), ARE (10 g, 20 g, and 30 g ARE/kg of feed) supplemented, and DM-ARE cotreated groups. After 21 days of experimental period, serological, histopathological, and immune response related-gene and protein analysis were carried out. The DM-ARE cotreated group showed significant increase in weight gain, specific growth rate, and decreased feed conversion ratio compared to the DM exposed group. The ARE cotreatment could significantly revert the alteration induced by DM in lysozyme, respiratory burst, myeloperoxidase, C-reactive protein, glucose, cortisol, total protein, albumin, and triglyceride levels. The liver histopathology showed membrane breakage, severe necrosis, infiltration of inflammatory cells, melano-macrophages, and nuclear atrophy, and the kidney showed tubular necrosis, hematopoietic necrosis, Bowman's capsule edema, and glomerulus degeneration in DM exposed group. In ARE cotreated group, the liver showed regenerative cellular changes and only mild to moderate cellular damages, and the kidney tubules and glomerulus had intact structure. ARE discernibly regulated the expression of immune-related genes and proteins (IgM, TNFα, IFN-γ, IL-1β, and IL-8) in fish. The DM-ARE cotreated groups showed reduced cumulative mortality and higher relative percent survival on experimental challenge with Aeromonas hydrophila compared to the DM group. Thus, ARE possess protective potential against DM-induced toxicity, and can be used as a cost-effective technique in aquafarming.

Microplastics accumulation in gastrointestinal tracts of Mullus barbatus and Merluccius merluccius is associated with increased cytokine production and signaling

There is clear evidence that different marine species can be impacted by microplastic (MP) ingestion accumulating such MPs mainly in the gastrointestinal tract. However, there is still limited knowledge on the consequences of MPs' accumulation in the gut. The present study aims to assess MPs and their potential immunotoxic effects in the digestive tract of two species showing different ecological traits: the red mullet (Mullus barbatus) and the European hake (Merluccius merluccius). Infrared spectroscopy (FTIR-ATR), micro-Raman and electron scanning microscope (SEM) were used to accurately identify the main plastic polymers detected in gut contents. In addition, we investigated the association between MP uptake and intestinal inflammation by evaluating expression and secretion of proinflammatory cytokines. MP abundance ranged from 1 to 20 items/individual in red mullet and from 2 to 15 items/individual in European hake. The majority of ingested MPs were fibers, while the dominant colors were black and blue in both species. Chemical characterization indicated polyethylene and polypropylene as the most common polymer types. Moreover, it was observed that MP abundance was highly positive correlated to cytokines (i.e. interleukin-1β, 10, and interferon) and antioxidant enzyme (i.e. catalase and superoxide dismutase) transcript levels suggesting ROS generation and an infiltration of immune cells in the gut. Our findings provide evidence that the induction of cytokine-dependent signaling pathways is one aspect of the complex mechanism by which MPs affect the gut system in fish.

Human Norovirus-Induced Gene Expression Biomarkers in Zebrafish

ABSTRACT

The challenges associated with development of an animal model system to replicate human norovirus (HuNoV) has hampered the study of the pathogenesis and therapeutic interventions for this virus. In this study, we replicated HuNoV GII.4 and evaluated virus gene expression in infected zebrafish. Three doses of inoculation resulted in successful virus replication. Genes for transmembrane transporters (tfa, cftr, slc26a3, and slc26a6), a heat shock chaperone (hspa8), and immune response cytokines (ifng1 and il1b) were highly expressed in HuNoV-infected zebrafish; however, expression levels of genes were reduced in zebrafish infected with thermally inactivated HuNoV. These results confirm HuNoV replication in juvenile zebrafish and will facilitate the investigation of biomarker gene expression during HuNoV infection.

HIGHLIGHTS

Interferons and interferon receptors in the channel catfish, Ictalurus punctatus

In this work, we describe the complete repertoire of channel catfish, Ictalurus punctatus, IFNs and IFN receptor genes. Based on multiple genomic and transcriptomic resources we identified 16 type I IFN genes, which represent the six type I IFN subgroups previously defined in salmonids (a-f.) No representatives of subgroup h previously only found in percomorphs were identified. An expansion in copy numbers of subgroup d IFN genes was of particular interest, as this has not been reported in other fish species to date. Furthermore, we confirmed the presence of two type II ifn genes encoding orthologs of IFNγ and the teleost-specific IFNγRel. Six homologs of IFN type I receptor genes were found in an array that shows conserved synteny with human chromosome 21. Three homologs of type II IFN receptor genes were also identified. These type I and type II receptor sequences are compatible with the dual type I IFN receptors, and the potentially more complex type II IFN receptors described in teleosts. Our data provide a comprehensive resource for future studies of channel catfish innate antiviral immunity.

Identification and establishment of type IV interferon and the characterization of interferon-υ including its class II cytokine receptors IFN-υR1 and IL-10R2

Interferons (IFNs) are critical soluble factors in the immune system and are composed of three types, (I, II and III) that utilize different receptor complexes IFN-αR1/IFN-αR2, IFN-γR1/IFN-γR2, and IFN-λR1/IL-10R2, respectively. Here we identify IFN-υ from the genomic sequences of vertebrates. The members of class II cytokine receptors, IFN-υR1 and IL-10R2, are identified as the receptor complex of IFN-υ, and are associated with IFN-υ stimulated gene expression and antiviral activity in zebrafish (Danio rerio) and African clawed frog (Xenopus laevis). IFN-υ and IFN-υR1 are separately located at unique and highly conserved loci, being distinct from all other three-type IFNs. IFN-υ and IFN-υR1 are phylogenetically clustered with class II cytokines and class II cytokine receptors, respectively. Therefore, the finding of this IFN ligand-receptor system may be considered as a type IV IFN, in addition to the currently recognized three types of IFNs in vertebrates.

Interferons are critical soluble components of the inflammatory process and are composed of three types with associated receptor complexes. Here the authors identify and characterise the type IV interferon, IFN-υ, and identify its associated receptors, denote functionality during in vivo infection and ascertain its genomic localisation.

Functional analysis and regulation mechanism of interferon gamma in macrophages of large yellow croaker (Larimichthys crocea)

Interferon gamma (IFN-γ) is a widely expressed cytokine that has potent antiviral and immunomodulatory effects. The expression and bioactivity of IFN-γ have been reported in several fish species. However, the molecular mechanism mediated by IFN-γ in fish macrophages has not been completely elucidated. This study used the macrophage cell line to investigate the functional activities and regulation mechanism of large yellow croaker IFN-γ (LcIFN-γ). Herein, the mRNA expression of Lcifn-γ was significantly upregulated in macrophages after LPS and poly(I:C) treatment. Recombinant LcIFN-γ protein (rLcIFN-γ) significantly enhanced the phagocytic ability and respiratory burst activity of macrophages. Meanwhile, rLcIFN-γ induced M1 phenotype polarization of macrophages with the upregulated expressions of pro-inflammatory gene. Moreover, rLcIFN-γ upregulated the IFN-stimulated genes (ISGs) expression and activated JAK (Janus tyrosine kinases)-STAT (signal transducer and activator of transcription) signaling pathway by causing the phosphorylation of JAK1 and STAT1^Tyr701. Furthermore, the promoter activity of IFN-regulatory factor 1 (IRF1) was significantly upregulated by the phosphorylated transcription factor STAT1 through binding to its promoter region. In addition to the classical JAK-STAT pathway, rLcIFN-γ also activated multiple distinct signaling cascades such as mitogen-activated protein kinase (MAPK) and protein kinase B (AKT) pathways. Overall, this study indicated the powerful effects of LcIFN-γ on macrophage activation of large yellow croaker and its molecular mechanism.

The flagellin of Vibrio parahaemolyticus induces the inflammatory response of Tetraodon nigroviridis through TLR5M

Vibrio parahaemolyticus is an important marine pathogen that cause inflammation even death in teleost. It has brought huge economic losses to aquaculture and serious threats to the sustainable development of marine fisheries. Here, we isolated the DNA, RNA, and total flagellin from V. parahaemolyticus, and obtained the primary spleen and head kidney cells (including leukocytes) from Tetraodon nigroviridis. V. parahaemolyticus DNA, RNA, and total flagellin were used to treat the T. nigroviridis primary cells described above. The results show that the nitric oxide (NO) production and respiratory burst response were significantly induced after stimulation with V. parahaemolyticus total flagellin in T. nigroviridis head kidney and spleen cells. And total flagellin could promote the gene expression and protein production of IL-1β in T. nigroviridis leukocytes. T. nigroviridis TLR5M (TnTLR5M) and TLR5S (TnTLR5S) ORF sequences were obtained as the main recognition receptor for flagellin. Real-time fluorescent quantitative PCR (qRT-PCR) was performed to detect the expression of pattern recognition receptor TnTLR5M and TnTLR5S, the important signal molecule of inflammatory system TnMyD88 and TnTRAF6, and inflammatory cytokines TnIL-1β and TnIFN-γ2. The results show that there were a significant upregulation after challenge with V. parahaemolyticus total flagellin. We further demonstrated that the total flagellin of V. parahaemolyticus could activate the luciferase activity of the NF-κB reporter gene mediated by TnTLR5M. Overall, our results suggest that V. parahaemolyticus total flagellin activated the NO production, respiratory burst response, and inflammatory cytokines expressions, such as TnIL-1β and TnIFN-γ2, through the TnTLR5M-NF-κB signaling pathway in T. nigroviridis.

Comparative Analysis of Salmon Cell Lines and Zebrafish Primary Cell Cultures Infection with the Fish Pathogen Piscirickettsia salmonis

Piscirickettsia salmonis is the etiologic agent of piscirickettsiosis, a disease that causes significant losses in the salmon farming industry. In order to unveil the pathogenic mechanisms of P. salmonis, appropriate molecular and cellular studies in multiple cell lines with different origins need to be conducted. Toward that end, we established a cell viability assay that is suitable for high-throughput analysis using the alamarBlue reagent to follow the distinct stages of the bacterial infection cycle. Changes in host cell viability can be easily detected using either an absorbance- or fluorescence-based plate reader. Our method accurately tracked the infection cycle across two different Atlantic salmon-derived cell lines, with macrophage and epithelial cell properties, and zebrafish primary cell cultures. Analyses were also carried out to quantify intracellular bacterial replication in combination with fluorescence microscopy to visualize P. salmonis and cellular structures in fixed cells. In addition, dual gene expression analysis showed that the pro-inflammatory cytokines IL-6, IL-12, and TNFα were upregulated, while the cytokines IL1b and IFNγ were downregulated in the three cell culture types. The expression of the P. salmonis metal uptake and heme acquisition genes, together with the toxin and effector genes ospD3, ymt, pipB2 and pepO, were upregulated at the early and late stages of infection regardless of the cell culture type. On the other hand, Dot/Icm secretion system genes as well as stationary state and nutrient scarcity-related genes were upregulated only at the late stage of P. salmonis intracellular infection. We propose that these genes encoding putative P. salmonis virulence factors and immune-related proteins could be suitable biomarkers of P. salmonis infection. The infection protocol and cell viability assay described here provide a reliable method to compare the molecular and cellular changes induced by P. salmonis in other cell lines and has the potential to be used for high-throughput screenings of novel antimicrobials targeting this important fish intracellular pathogen.

Molecular characterization and expressional analysis of two poly (ADP-ribose) polymerase (PARP) domain-containing Gig2 isoforms in rockfish (Sebastes schlegelii) and their antiviral activity against viral hemorrhagic septicemia virus

Remedies toward sustainable aquaculture rely upon research that unveils the molecular mechanisms behind host immunity and their interactions with pathogens. Antiviral defense is a major innate immune response in fish. The antiviral protein GCHV-induced gene-2 (Gig2), a member of the interferon-stimulated gene (ISG), was identified and characterized from rockfish (Sebastes schlegelii). Gig2 exists in two isoforms, namely, SsGig2-I1 and SsGig2-I2, in rockfish with lengths of 163 and 223 bp, respectively. Bioinformatic analysis indicated the availability of poly (ADP-ribose) polymerase domain in both proteins, and 51.3% identity and 71.3% similarity between both isoforms were observed. The basal expression pattern revealed the highest tissue-specific expression in rockfish gills for both isoforms. The immune challenge experiment disclosed a distinctive and strong expression of each transcript in the presence of poly I:C. Both isoforms are localized in the endoplasmic reticulum. Interferon (IFN) pathway gene analysis revealed no significant upregulation of IFN related genes. Viral hemorrhagic septicemia virus (VHSV) gene expression analysis revealed strong downregulation of viral transcripts after 48 h of infection in the presence of Gig2 isoforms. Collectively, these results indicate the protective role of Gig2 in rockfish against VHSV infection and help broaden our understanding of the innate immunity of fish.

Modulating the Inflammatory Response to Wounds and Cancer Through Infection

The zebrafish (Danio rerio) has recently emerged as an excellent model to study cancer biology and the tumour microenvironment, including the early inflammatory response to both wounding and early cancer growth. Here, we use high-resolution confocal imaging of translucent zebrafish larvae, with novel automated tracking and cell:cell interaction software, to investigate how innate immune cells behave and interact with repairing wounds and early cancer (pre-neoplastic) cells expressing a mutant active human oncogene (HRASG12V). We show that bacterial infections, delivered either systemically or locally, induce a change in the number and behaviour of neutrophils and macrophages recruited to acute wounds and to pre-neoplastic cells, and that infection can modify cellular interactions in ways that lead to a significant delay in wound healing and a reduction in the number of pre-neoplastic cells. Besides offering insights as to how Coley’s toxins and other cancer bacteriotherapies may function to reduce cancer burden, our study also highlights novel software tools that can be easily adapted to investigate cellular behaviours and interactions in other zebrafish models.

Dydrogesterone Affects the Transcription of Genes in Innate Immune and Coagulation Cascade in Zebrafish Embryos

Dydrogesterone (DDG) acts on the reproduction but also affects the functioning of non-reproductive system. So far, the knowledge about other effects of DDG remains limited. Here we investigated the effects of DDG on the transcription of genes in innate immune and coagulation cascade in zebrafish embryos. The zebrafish embryos were exposed to DDG at 49.0, 527 and 5890 ng L^- 1 for 144 hour post fertilization (hpf). The results showed that DDG significantly decreased the transcription of marker genes (e.g. tnfa, il8 and cc-chem) involved in the innate immune response at environmental concentrations. Moreover, DDG also down-regulated the transcription of genes in coagulation cascade (e.g. fga, fgb, fgg and f2). These results indicated that DDG had potential effects on the innate immune and coagulation cascade functions in the early life zebrafish, thus further affecting fish growth and health.

MicroRNA-29b modulates the innate immune response by suppressing IFNγs production in orange-spotted grouper (Epinephelus coioides)

Interferon-γ (IFNγ), a type II interferon, is essential to host resistance against various infections. Unlike other vertebrates, fish have two types of IFNγs, IFNγ1 (also named IFNγ-rel) and IFNγ2. MicroRNAs (miRNAs) regulate multiple biological processes by suppressing mRNA translation or inducing mRNA degradation. Among them, miR-29 can directly target IFNγ and affact innate and adaptive immune responses in mice. There are five members of the miR-29 family in orange-spotted grouper (Epinephelus coioides), which share the same miRNA seed region. However, whether miR-29 directly targets E. coioides IFNγs and regulate IFNγ production is still unknown. In the present study, the negative correlation between miR-29b and both IFNγs in immune tissues of healthy E. coioides and grouper spleen cells (GS cells) stimulated with LPS or poly I:C was demonstrated. Moreover, dual-luciferase reporter assays and western blotting were performed to demonstrate that miR-29b suppressed E. coioides IFNγ production. Studies of NO production in GS cells after miR-29b transfection revealed that miR-29b overexpression affected NO production through the downregulation of IFNγ expression. Taken together, our results suggest that miR-29b may directly target E. coioides IFNγs and modulate IFNγ-mediated innate immune responses by suppressing E. coioides IFNγs production.

Metabolic Regulation of Inflammasome Activity Controls Embryonic Hematopoietic Stem and Progenitor Cell Production

Embryonic hematopoietic stem and progenitor cells (HSPCs) robustly proliferate while maintaining multilineage potential in vivo; however, an incomplete understanding of spatiotemporal cues governing their generation has impeded robust production from human induced pluripotent stem cells (iPSCs) in vitro. Using the zebrafish model, we demonstrate that NLRP3 inflammasome-mediated interleukin-1-beta (IL1β) signaling drives HSPC production in response to metabolic activity. Genetic induction of active IL1β or pharmacologic inflammasome stimulation increased HSPC number as assessed by in situ hybridization for runx1/cmyb and flow cytometry. Loss of inflammasome components, including il1b, reduced CD41⁺ HSPCs and prevented their expansion in response to metabolic cues. Cell ablation studies indicated that macrophages were essential for initial inflammasome stimulation of Il1rl1⁺ HSPCs. Significantly, in human iPSC-derived hemogenic precursors, transient inflammasome stimulation increased multilineage hematopoietic colony-forming units and T cell progenitors. This work establishes the inflammasome as a conserved metabolic sensor that expands HSPC production in vivo and in vitro.

Zebrafish as a Model for Fish Diseases in Aquaculture

The use of zebrafish as a model for human conditions is widely recognized. Within the last couple of decades, the zebrafish has furthermore increasingly been utilized as a model for diseases in aquacultured fish species. The unique tools available in zebrafish present advantages compared to other animal models and unprecedented in vivo imaging and the use of transgenic zebrafish lines have contributed with novel knowledge to this field. In this review, investigations conducted in zebrafish on economically important diseases in aquacultured fish species are included. Studies are summarized on bacterial, viral and parasitic diseases and described in relation to prophylactic approaches, immunology and infection biology. Considerable attention has been assigned to innate and adaptive immunological responses. Finally, advantages and drawbacks of using the zebrafish as a model for aquacultured fish species are discussed.

The zebrafish as a novel model for the in vivo study of Toxoplasma gondii replication and interaction with macrophages

Toxoplasma gondii is an obligate intracellular parasite capable of invading any nucleated cell. Three main clonal lineages (type I, II, III) exist and murine models have driven the understanding of general and strain-specific immune mechanisms underlying Toxoplasma infection. However, murine models are limited for studying parasite-leukocyte interactions in vivo, and discrepancies exist between cellular immune responses observed in mouse versus human cells. Here, we developed a zebrafish infection model to study the innate immune response to Toxoplasma in vivo By infecting the zebrafish hindbrain ventricle, and using high-resolution microscopy techniques coupled with computer vision-driven automated image analysis, we reveal that Toxoplasma invades brain cells and replicates inside a parasitophorous vacuole to which type I and III parasites recruit host cell mitochondria. We also show that type II and III strains maintain a higher infectious burden than type I strains. To understand how parasites are cleared in vivo, we further analyzed Toxoplasma-macrophage interactions using time-lapse microscopy and three-dimensional correlative light and electron microscopy (3D CLEM). Time-lapse microscopy revealed that macrophages are recruited to the infection site and play a key role in Toxoplasma control. High-resolution 3D CLEM revealed parasitophorous vacuole breakage in brain cells and macrophages in vivo, suggesting that cell-intrinsic mechanisms may be used to destroy the intracellular niche of tachyzoites. Together, our results demonstrate in vivo control of Toxoplasma by macrophages, and highlight the possibility that zebrafish may be further exploited as a novel model system for discoveries within the field of parasite immunity.This article has an associated First Person interview with the first author of the paper.

Prokaryotic ribosomal RNA stimulates zebrafish embryonic innate immune system

Objectives

Cell-culture studies reported that prokaryotic RNA molecules among the various microbe-associated molecular patterns (MAMPs) were uniquely present in live bacteria and were categorized as viability-associated MAMPs. They also reported that specific nucleotide modifications are instrumental in the discrimination between self and nonself RNAs. The aim of this study was to characterize the in vivo immune induction potential of prokaryotic and eukaryotic ribosomal RNAs (rRNAs) using zebrafish embryos as novel whole animal model system. Additionally, we aimed to test the possible role of rRNA modifications in immune recognition.

Results

We used three immune markers to evaluate the induction potential of prokaryotic rRNA derived from Escherichia coli and eukaryotic rRNAs from chicken (nonself) and zebrafish (self). Lipopolysaccharide (LPS) of Pseudomonas aeruginosa served as a positive control. E. coli rRNA had an induction potential equivalent to that of LPS. The zebrafish innate immune system could discriminate between self and nonself rRNAs. Between the nonself rRNAs, E. coli rRNA was more immunogenic than chicken rRNA. The in vitro transcript of zebrafish 18S rRNA gene without the nucleotide modifications was not recognized by its own immune system. Our data suggested that prokaryotic rRNA is immunostimulatory in vivo and could be useful as an adjuvant.

Effects of norfloxacin nicotinate on the early life stage of zebrafish (Danio rerio): Developmental toxicity, oxidative stress and immunotoxicity

Norfloxacin nicotinate (NOR-N), an adduct of norfloxacin (NOR) and nicotinic acid, has been widely used for replacing NOR in animal husbandry and fishery industry. Nowadays, increasing evidences showed that NOR could pose toxic effects on fish and other aquatic organisms, but as its adduct, whether NOR-N could cause adverse effects on aquatic organisms is still unclear. To evaluate the toxic effects of NOR-N on the early life stage of zebrafish, we determined the changes in embryonic development (hatching rate, body length, malformation rate and mortality), antioxidant enzyme (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (Gpx)) activities, malondialdehyde (MDA) content and gene expression levels related to antioxidant enzymes (Cu/Zn-sod, Mn-sod, CAT and Gpx) and innate immune system (tumor necrosis factor α (TNFα), interferon (IFN), Interleukin-1 beta (IL-1β), IL-8, CXCL-clc, CC-chemokine, lysozyme (Lzy) and complement factors (C3)) after embryonic exposure to NOR-N till 96 hpf. The results showed that NOR-N exposure could decreased the hatching rate and body length, and increased abnormality and mortality as concentration-dependent during embryonic development process. NOR-N induced oxidative stress in zebrafish larvae through increasing the contents of MDA and the activities of SOD, CAT and Gpx, as well as the mRNA levels of genes related to these antioxidant enzymes. Moreover, the expression of TNFα, IFN, IL-1β, IL-8, CXCL-clc, CC-chemokine, Lzy and C3 genes were significantly up-regulated after exposure to high concentration (5 and/or 25 mg/L) of NOR-N till 96 hpf, indicating that the innate immune system in zebrafish larvae was disturbed by NOR-N. Overall, our results suggested that NOR-N caused development toxicity, oxidative stress and immunotoxicity on the early life stage of zebrafish. Thus, widespread application of NOR-N might pose potential ecotoxicological risk on aquatic ecosystems.

Short-term developmental toxicity and potential mechanisms of the herbicide metamifop to zebrafish (Danio rerio) embryos

Metamifop is a novel aryloxyphenoxy propionate (AOPP) herbicide that is widely applied in paddy fields, which will inevitably enter aquatic environments and pose a risk to aquatic organisms. However, the potential threat and toxicological mechanisms of metamifop in aquatic organisms are poorly understood. In this study, zebrafish embryos were used to investigate the potential developmental toxicity and mechanisms of metamifop. The results showed that metamifop exhibited high acute toxicity to zebrafish, with 96 h-LC₅₀ values of 0.648 and 0.216 mg/L to embryos and larvae of 72 h post-hatching (hph), respectively. Decreased body lengths, heartbeat number, and hatching rates, and increased malformation rates of embryos were observed after 96 h of exposure to 0.38 mg/L or higher concentration of metamifop. Furthermore, oxidative stress was caused in embryos, with increased contents of reactive oxygen species (ROS) and malondialdehyde (MDA), and altered activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Metamifop exposure clearly triggered cell apoptosis in embryos, result in the increase of Caspase-3 and Caspase-9 activities and up-regulation of apoptosis-related genes (bax, p53, apaf1, caspase-3, and caspase-9). Additionally, the transcriptions of innate immune-related genes (il-8, il-1b, and ifn) were increased in the groups treated with 0.25 and 0.5 mg/L of metamifop. These results indicate that metamifop induced developmental toxicity in zebrafish, and the potential toxicological mechanisms were related to oxidative stress, cell apoptosis, and the innate immune responses in embryos.

Teleost cytotoxic T cells

Cell-mediated cytotoxicity is one of the major mechanisms by which vertebrates control intracellular pathogens. Two cell types are the main players in this immune response, natural killer (NK) cells and cytotoxic T lymphocytes (CTL). While NK cells recognize altered target cells in a relatively unspecific manner CTLs use their T cell receptor to identify pathogen-specific peptides that are presented by major histocompatibility (MHC) class I molecules on the surface of infected cells. However, several other signals are needed to regulate cell-mediated cytotoxicity involving a complex network of cytokine- and ligand-receptor interactions. Since the first description of MHC class I molecules in teleosts during the early 90s of the last century a remarkable amount of information on teleost immune responses has been published. The corresponding studies describe teleost cells and molecules that are involved in CTL responses of higher vertebrates. These studies are backed by functional investigations on the killing activity of CTLs in a few teleost species. The present knowledge on teleost CTLs still leaves considerable room for further investigations on the mechanisms by which CTLs act. Nevertheless the information on teleost CTLs and their regulation might already be useful for the control of fish diseases by designing efficient vaccines against such diseases where CTL responses are known to be decisive for the elimination of the corresponding pathogen. This review summarizes the present knowledge on CTL regulation and functions in teleosts. In a special chapter, the role of CTLs in vaccination is discussed.

Receptor complex and signalling pathway of the two type II IFNs, IFN-γ and IFN-γrel in mandarin fish or the so-called Chinese perch Siniperca chuatsi

IFN-γ, as the sole member of mammalian type II IFN, is a multifunctional cytokine which exerts its effects through two distinct IFN-γ receptors, IFNGR1 and IFNGR2. However, in teleost fish, another IFN-γ homologous gene, namely IFN-γ related gene (IFN-γrel), has been identified. Although IFN-γ and IFN-γrel genes have been described in some fish species, many important aspects remain poorly understood in relation with their signalling and function. In the present study, IFN-γ and IFN-γrel, as well as their receptors, cytokine receptor family B (CRFB) 17, CRFB13, two of which are homologous to IFNGR1 in mammals, and CRFB6, homolomous to IFNGR2, have been characterized in mandarin fish, Siniperca chuatsi. It was revealed that the two type IFN members exhibit antiviral activity, and IFN-γ transduces downstream signalling through CRFB13 and CRFB6, while IFN-γrel interacts with CRFB17 to activate downstream signalling. Moreover, IFN-γ and IFN-γrel have been shown to exert antiviral biological activity in a STAT1-dependent manner. Intracellular domain analysis of CRFB17 and CRFB13 demonstrated that the Y386 tyrosine residue of CRFB13 is required for the activation of the IFN-γ-mediated biologic response, and the Y324 and Y370 residues in CRFB17 are required to activate IFN-γrel signalling.

Insights into teleost interferon-gamma biology: An update

Interferon-gamma (IFN-ϒ) is probably one of the most relevant cytokines orchestrating the immune response in vertebrates. Although the activities mediated by this molecule are well known in mammals, several aspects of the IFN-ϒ system in teleosts remain a riddle to scientists. Numerous studies support a potentially similar role of the fish IFN-ϒ signalling pathway in some well-described immunological processes induced by this cytokine in mammals. Nevertheless, the existence in some teleost species of duplicated ifng genes and an additional gene derived from ifng known as interferon-γ-related (ifngrel), among other things, raises new interesting questions about the mode of action of these various molecules in fish. Moreover, certain IFN-ϒ-mediated activities recently observed in mammals are still fully unknown in fish. Another attractive but mainly unexplored curious property of IFN-ϒ in vertebrates is its potential dual role depending on the type of pathogen. In addition, some aspects mediated by this molecule could favour the resolution of a bacterial infection but be harmful in the context of a viral disease, and vice versa. This review collects old and new aspects of IFN-ϒ research in teleosts and discusses new questions and pathways of investigation based on recent discoveries in mammals.

Chronic Toxic Effects of Flutolanil on the Liver of Zebrafish ( Danio rerio)

Flutolanil is a broad-spectrum amide fungicide that is widely used to prevent fungal pathogens in agriculture. However, its usage may have a potential environmental impact on organisms. So far, few literatures have investigated the chronic toxicity of flutolanil at concentrations relevant to environmental conditions in the nontarget aquatic organisms. This study was aimed at evaluating whether the long-term exposure of flutolanil affects oxidative stress, immune response, and apoptosis in the liver of zebrafish ( Danio rerio). The results showed that the activity of catalase (CAT) was significantly decreased in the liver in all flutolanil-treated groups. Interestingly, the malondialdehyde (MDA) contents were remarkably increased following the flutolanil exposure. Deoxyribonucleic acid (DNA) damage was increased with a concentration-dependent manner. The transcription level of genes involved in apoptosis and the immune system were significantly altered following flutolanil chronic exposure in zebrafish liver. Furthermore, the caspase-3 enzyme activity was significantly increased. Taken together, this study demonstrated that the resulting effects on oxidative stress, immune toxicity, and apoptosis may be responsible for the pathological alterations in zebrafish liver after flutolanil exposure at concentrations relevant to environmental conditions, advancing the knowledge of pesticide environmental risk assessment.

Effects of different concentrations of Microcystis aeruginosa on the intestinal microbiota and immunity of zebrafish (Danio rerio)

Microcystis aeruginosa is a primary species of toxin-producing cyanobacteria. This study explored the effects of short-term exposure (96 h) to M. aeruginosa on the intestinal microflora variation and immune function of zebrafish. After exposure to different cell concentrations of M. aeruginosa, marked histological variation was observed in the intestine, such as goblet cells proliferation and intestinal desquamation. In addition high-concentration M. aeruginosa treatment (initial concentration: 1.59 × 10⁵ cells mL^-1) induced a significant increase in cytokine levels compared with other groups. Low-concentration M. aeruginosa treatment (initial concentration: 0.88 × 10⁵ cells mL^-1) promoted the transcription of inflammatory genes, while high-concentration treatment restrained the transcription of these genes. Moreover, M. aeruginosa exposure also changed the intestinal microbial diversity. At the phylum level, bacteria belonging to Proteobacteria were the most abundant in all groups, and Gammaproteobacteria were the dominant bacteria with major changes. Pathogenic microorganisms such as Shewanella, Plesiomonas, Halomonas, Pseudomonas, and Lactobacillus increased greatly after treatment with different cell concentrations of M. aeruginosa. This study indicates that M. aeruginosa induces an increase in zebrafish goblet cells and enhances the inflammatory response, which may produce detrimental effects in zebrafish, resulting in a greater proportion of pathogenic bacteria and intestinal injury. The results of this study will help improve the understanding of the effects of M. aeruginosa on the intestines of aquatic organisms.

Dual Transcriptomics of Host-Pathogen Interaction of Cystic Fibrosis Isolate Pseudomonas aeruginosa PASS1 With Zebrafish

Pseudomonas aeruginosa is a significant cause of mortality in patients with cystic fibrosis (CF). To explore the interaction of the CF isolate P. aeruginosa PASS1 with the innate immune response, we have used Danio rerio (zebrafish) as an infection model. Confocal laser scanning microscopy (CLSM) enabled visualization of direct interactions between zebrafish macrophages and P. aeruginosa PASS1. Dual RNA-sequencing of host-pathogen was undertaken to profile RNA expression simultaneously in the pathogen and the host during P. aeruginosa infection. Following establishment of infection in zebrafish embryos with PASS1, 3 days post infection (dpi), there were 6739 genes found to be significantly differentially expressed in zebrafish and 176 genes in PASS1. A range of virulence genes were upregulated in PASS1, including genes encoding pyoverdine biosynthesis, flagellin, non-hemolytic phospholipase C, proteases, superoxide dismutase and fimbrial subunits. Additionally, iron and phosphate acquisition genes were upregulated in PASS1 cells in the zebrafish. Transcriptional changes in the host immune response genes highlighted phagocytosis as a key response mechanism to PASS1 infection. Transcriptional regulators of neutrophil and macrophage phagocytosis were upregulated alongside transcriptional regulators governing response to tissue injury, infection, and inflammation. The zebrafish host showed significant downregulation of the ribosomal RNAs and other genes involved in translation, suggesting that protein translation in the host is affected by PASS1 infection.

Molecular characterization and function analysis of three RIG-I-like receptor signaling pathway genes (MDA5, LGP2 and MAVS) in Oreochromis niloticus

The recognition of microbial pathogens, which is mediated by pattern recognition receptors (PRRs), is critical to the initiation of innate immune responses. In the present study, we isolated the full-length cDNA and genomic DNA sequences of the MDA5, LGP2 and MAVS genes in Nile tilapia, termed OnMDA5, OnLGP2 and OnMAVS. The OnMDA5 gene encodes 974 amino acids and contains two caspase-associated recruitment domains (CARDs), a DExDc domain (DExD/H box-containing domain), a HELICc (helicase superfamily C-terminal) domain and a C-terminal regulatory domain (RD). The OnLGP2 gene encodes 679 amino acids and contains a DExDc, a HELICc and an RD. The OnMAVS gene encodes 556 amino acids and contains a CARD, a proline-rich domain, a transmembrane helix domain and a putative TRAF2-binding motif (269PVQDT273). Phylogenetic analyses showed that all three genes from Nile tilapia were clustered together with their counterparts from other teleost fishes. Real-time PCR analyses showed that all three genes were constitutively expressed in all examined tissues in Nile tilapia. OnMDA5 presented the highest expression level in the blood and the lowest expression level in the liver, while OnMAVS presented the highest expression level in the kidney. The highest expression level of OnLGP2 was detected in the liver. An examination of the expression patterns of these RIG-I-like receptors (RLRs) during embryonic development showed that the highest expression levels of OnMDA5 occurred at 2 days postfertilization (dpf), and the expression significantly decreased from 3 to 8 dpf. The expression levels of OnLGP2 significantly increased from 4 to 8 dpf. The expression levels of OnMAVS mRNA were stable from 2 to 8 dpf. Upon stimulation by intraperitoneal injection of Streptococcus agalactiae, the expression levels of OnMDA5 were first downregulated and then upregulated in the blood, gill and spleen. In the intestine and kidney, the expression of OnMDA5 was first upregulated, then downregulated, and then upregulated again. The expression of OnLGP2 was upregulated in the kidney and intestine, and the expression of OnMAVS was upregulated in the spleen. Overexpression of OnMAVS increased NF-κB activation in 293 T cells (p < 0.05), and after cotransfection with OnMDA5, the OnMAVS-dependent NF-κB activation was slightly increased (p > 0.05), after cotransfection with OnLGP2, the OnMAVS-dependent NF-κB activation was significantly decreased (p < 0.05). These findings suggest that, although the deduced protein structure of OnMDA5 is evolutionarily conserved with the structures of other RLR members, its signal transduction function is markedly different. The results also suggest that OnLGP2 has a negative regulatory effect on the OnMAVS gene. OnMDA5 and OnMAVS were uniformly distributed throughout the cytoplasm in 293 T cells, whereas OnLGP2 was distributed throughout the cytoplasm and nucleus. These results are helpful for clarifying the innate immune response against bacterial infection in Nile tilapia.

Synthesis and antiviral activity of a new coumarin derivative against spring viraemia of carp virus

Coumarin as a lead structure have received a considerable attention in the last three decades for the discovery of antiviral agents. Our previous study indicated that imidazole coumarins possessed antiviral activities against SVCV. Based on the structure-activity relationship in that study, a new imidazole coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), was designed, synthesized and its anti-SVCV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC₅₀), we found that BBC (IC₅₀ = 0.56 mg/L) possessed a higher antiviral activity than those imidazole coumarins in our previous study. Besides, BBC can significantly inhibit cell death and reduce cellular morphological damage induced by SVCV. Our further data indicated that intraperitoneal injection of BBC increased the survival rate of zebrafish by 17.5%, decreased viral titer in fish body and inhibited SVCV glycoprotein expression in kidney and spleen. In uninfected zebrafish, the expression levels of ifnγ, ifnφ1, ifnφ2 and rig1 genes were up-regulated after BBC treatment, which indicated that BBC could activate interferon response. In addition, data of the antioxidant enzymes activities and results of the antioxidant enzymes-related genes expressions suggested BBC could reduce SVCV-induced oxidative damage in infected zebrafish. Altogether, BBC is expected to be a therapeutic agent against SVCV infection in the field of aquaculture.

Comparison of polymeric immunoglobulin receptor between fish and mammals

Polymeric immunoglobulin receptor (pIgR) functions in transporting polymeric immunoglobulin across epithelial cells into external secretion in animals. During animal evolution, fish was situated at a transition point on the phylogenetic spectrum between species possessing only innate immunity (i.e., invertebrates) and species depending heavily on adaptive immunity (i.e., mammals). Previous studies reported that fish and mammals significantly differ in pIgR. This review summarized the differences in pIgR structure, function, and transcriptional regulation between fish and mammals. A model of the transcriptional regulation of the pIgR gene was suggested. In this model, microbes could activate Toll-like receptor, trigger the cascade reactions in the signaling pathway, and then activate transcription factors that regulate pIgR expression through combining with the pIgR promoter. This review provides some suggestions for further studies on the function and regulatory mechanism of pIgR in fish and other animals.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

Developmental toxicity and potential mechanisms of pyraoxystrobin to zebrafish (Danio rerio)

As a newly developed, highly efficient strobilurin fungicide, pyraoxystrobin has been reported to be highly toxic to some aquatic organisms. However, the toxicity of pyraoxystrobin to different life stages of fish and the potential underlying mechanisms are still unknown. Hence, in the present study, the acute toxicity of pyraoxystrobin to different life stages of zebrafish (embryo, larva, and adult) was assessed. The developmental toxicity of pyraoxystrobin to zebrafish embryos and its effects on gene transcription in the embryo were also investigated. The results showed that the 96-h LC₅₀ values of pyraoxystrobin to embryos [2h post-fertilization (hpf)], 12h post-hatching (hph) larvae (84 hpf), 72 hph larvae (144 hpf), and adult zebrafish were 4.099, 1.069, 3.236, and 5.970µg/L, respectively. This suggests that pyraoxystrobin has very high toxicity to different life stages of zebrafish, while the newly hatched larvae constitute the most sensitive period of zebrafish to pyraoxystrobin. Decreased heart rate, hatching inhibition, growth regression, and morphological deformities were observed in zebrafish embryos after acute exposure to different concentrations of pyraoxystrobin. The rate of malformation increased in a time- and concentration-dependent manner in embryos, and the most pronounced abnormality was pericardial edema and yolk sac edema. Pyraoxystrobin (2 and 4μg/L) significantly altered the mRNA levels of genes related to mitochondrial respiratory chain and ATP synthesis (NDI, uqcrc, and ATPo6), oxidative stress (Mn-Sod, Cat, and Gpx), apoptosis (p53, Bcl2, Bax, and Cas3), and immune system (TNFα, IFN, and IL-1b) in zebrafish embryos. This result indicates that the alteration of these genes is a potential mechanism underlying the toxic effects of pyraoxystrobin on zebrafish.

Polystyrene microplastics induce microbiota dysbiosis and inflammation in the gut of adult zebrafish

Microplastic (MP) are environmental pollutants and have the potential to cause varying degrees of aquatic toxicity. In this study, the effects on gut microbiota of adult male zebrafish exposed for 14 days to 100 and 1000 μg/L of two sizes of polystyrene MP were evaluated. Both 0.5 and 50 μm-diameter spherical polystyrene MP increased the volume of mucus in the gut at a concentration of 1000 μg/L (about 1.456 × 10¹⁰ particles/L for 0.5 μm and 1.456 × 10⁴ particles/L for 50 μm). At the phylum level, the abundance of Bacteroidetes and Proteobacteria decreased significantly and the abundance of Firmicutes increased significantly in the gut after 14-day exposure to 1000 μg/L of both sizes of polystyrene MP. In addition, high throughput sequencing of the 16S rRNA gene V3-V4 region revealed a significant change in the richness and diversity of microbiota in the gut of polystyrene MP-exposed zebrafish. A more in depth analysis, at the genus level, revealed that a total of 29 gut microbes identified by operational taxonomic unit (OTU) analysis were significantly changed in both 0.5 and 50 μm-diameter polystyrene MP-treated groups. Moreover, it was observed that 0.5 μm polystyrene MP not only increased mRNA levels of IL1α, IL1β and IFN but also their protein levels in the gut, indicating that inflammation occurred after polystyrene MP exposure. Our findings suggest that polystyrene MP could induce microbiota dysbiosis and inflammation in the gut of adult zebrafish.

6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), a novel perfluorooctane sulfonate alternative, induced developmental toxicity in zebrafish embryos

6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) is a major component of Forafac^®1157, a novel perfluorooctane sulfonate (PFOS) alternative used globally in aqueous film forming foams (AFFFs). Although 6:2 FTAB has been recently detected in the aquatic environment, its toxic effects on aquatic organisms remain unclear. Here, zebrafish embryos were exposed to various concentrations of 6:2 FTAB (0, 5, 10, 20, 40, 60, 80, and 100 mg/L) from 6 to 120 h post-fertilization (hpf) to investigate its developmental toxicity and possible mechanism of action. Results showed that exposure to 40 mg/L or higher concentrations of 6:2 FTAB significantly decreased the survival percentage and increased the malformation percentage. The median lethal concentration (LC₅₀) at 120 hpf was 43.73 ± 3.24 mg/L, and the corresponding benchmark dose lower limit (BMDL) of lethal effect was 33.79 mg/L. These values were both higher than those for PFOS, supporting the notion that 6:2 FTAB is less toxic than PFOS to zebrafish embryos. The most common developmental defect in 6:2 FTAB-treated embryos was rough-edged skin/fins. TUNEL assay showed that 6:2 FTAB exposure induced cell apoptosis in the tail region compared with that of the control, which might explain the rough-edged skin/fins. The increased transcriptional levels of p53, bax, and apaf1 and the increased activities of caspase-3, -8, and -9 provided further evidence of 6:2 FTAB-induced apoptosis. We also analyzed the effects of 6:2 FTAB on oxidative stress and the immune system. Results showed that reactive oxygen species and malondialdehyde accumulated in concentration-dependent manners after exposure to 6:2 FTAB, and antioxidant enzyme activities (catalase and glutathione peroxidase) also changed. Exposure to 6:2 FTAB also altered the transcriptional levels of ccl1, il-1β, il-8, tnfα, ifn, and cxcl-c1c, which play important roles in the innate immune system. Collectively, our data suggest that 6:2 FTAB exposure can induce cell apoptosis, oxidative stress, and immunotoxicity, thus highlighting the developmental toxicity of 6:2 FTAB in zebrafish embryos.

Molecular characterisation, ontogeny and expression analysis of melanoma differentiation-associated factor 5 (MDA5) from Asian seabass, Lates calcarifer

MDA5 is the pivotal member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) and is reported to play a crucial role in type I IFN-mediated responses against pathogen-associated molecular patterns (PAMPs), especially nucleic acids. In this study, we have identified and cloned the full-length cDNA sequence of MDA5, which comprises 3398 nucleotides and encodes for a putative protein of 978 AA length, in Asian seabass, Lates calcarifer. From the putative amino acid sequence of AsMDA5, four different conserved domains could be predicted: two N-terminal CARD domains, a DExDc domain, a HELICc domain and a C-terminal RIG-1_C-RD domain. The mRNA transcript of AsMDA5 could be detected in all the 11 tissues tested in healthy animals with the highest expression in heart followed by gill and skin. The ontogenetic expression profile showed constitutive expression in developmental stages starting from unfertilized eggs, which implies the possibility of maternally acquired immunity of RLRs in offspring. The viral analogue poly I:C could modulate the AsMDA5 expression both in vivo and in vitro. In all the tissues, AsMDA5 expression was found to be highly regulated following injection with poly I:C with the highest expression observed in kidney. The expression level of AsMDA5 was found to be modulated at different time-points following challenge with Gram-negative bacterium, Vibrio alginolyticus, and Gram-positive bacterium, Staphylococcus aureus. Similarly, noticeable change in AsMDA5 expression was detected in SISK cell line induced with either LPS or PGN. The observations made in this study suggest that in euryhaline marine teleosts like Asian seabass, MDA5 gene serves as one of the pivotal receptor for the detection of viral and bacterial PAMP, and might play an important antimicrobial role during early embryonic development.

Two Distinct Interferon-γ in the Orange-Spotted Grouper (Epinephelus coioides): Molecular Cloning, Functional Characterization, and Regulation in Toll-Like Receptor Pathway by Induction of miR-146a

Interferon gamma (IFNγ) is a Th1 cytokine that is critical for innate and adaptive immunity. Toll-like receptors (TLRs) signaling pathways are critical in early host defense against invading pathogens. miR-146a has been reported to participate in the regulation of host immunity. The known mechanisms of integrations between the IFNγ and TLR signaling pathways are incompletely understood, especially in teleosts. In this study, orange-spotted grouper (Epinephelus coioides) IFNγ1 and IFNγ2, their biological activities, especially their involvements in TLR pathway, were explored. We identified and cloned two IFNγ genes of E. coioides, namely EcIFNγ1 and EcIFNγ2. The produced recombinant E. coioides IFNγ1 (rEcIFNγ1) and IFNγ2 (rEcIFNγ2) proteins showed functions, which are similar to those of other bony fishes, such as enhancing nitric oxide responses and respiratory burst response. rEcIFNγ2 could regulate TLR pathway by enhancing the promoter activity of miR-146a upstream sequence and thus increasing the expression level of miR-146a, which possibly targets TNF receptor-associated factor 6 (TRAF6), a key adapter molecule in TLR signaling pathway. Taken together, these findings unravel a novel regulatory mechanism of anti-inflammatory response by IFNγ2, which could mediate TLR pathway through IFNγ2-miR-146a-TRAF6 negative regulation loop. It is suggested that IFNγ2 may provide a promising therapeutic, which may help to fine tune the immune response.

Cloning and expression of Malabar grouper (Epinephelus malabaricus) ADAR1 gene in response to immune stimulants and nervous necrosis virus

ADARs are RNA editing catalysts that bind double-stranded RNA and convert adenosine to inosine, a process that can lead to destabilization of dsRNA structures and suppression of mRNA translation. In mammals, ADAR1 genes are involved in various cellular pathways, including interferon (IFN)-mediated response. However, the function of fish ADAR1 remains unclear. We report here the cloning of ADAR1 in Malabar grouper (Epinephelus malabaricus) (MgADAR1) and its response to various immune stimulants. The MgADAR1 cDNA is 5371-bp long, consisting of an open reading frame encoding a putative protein of 1381 amino acids, a 235-nt 5'-terminal untranslated region (UTR), and a 990-nt 3'-UTR. The deduced amino acid sequence exhibits signature features of a chitin synthesis regulation domain, two Z-DNA-binding domains (Z alpha), three dsRNA binding motifs (DSRM) and one tRNA-specific and dsRNA adenosine deaminase domain (ADEAMc). MgADAR1 mRNA expressed ubiquitously in tissues of healthy Malabar grouper, with elevated levels in the brain, gills and eyes. In response to poly (I: C), the MgADAR1 mRNA level was significantly up-regulated in the brain and spleen, but not head kidney. Upon nervous necrosis virus (NNV) infection the level of MgADAR1 increased in the brain, whereas Mx increased in the brain, spleen and head kidney. Induction of MgADAR1 by poly (I: C) and NNV was also observed in vitro. Additionally, the expression of MgADAR1 was upregulated by recombinant grouper IFN in grouper cells. These data indicate an intricate interplay between ADAR1 and NNV infection in grouper as MgADAR1 might be regulated in a tissue-specific manner.

Functional activities of interferon gamma in large yellow croaker Larimichthys crocea

Interferon gamma (IFN-γ) is a T helper cell type 1 (Th1) cytokine that plays important roles in almost all phases of immune and inflammatory responses. Although IFN-γ gene in large yellow croaker Larimichthys crocea has been reported, little is known about its bioactivity. In this study, large yellow croaker IFN-γ (LycIFN-γ) gene was found to be constitutively expressed in all tissues tested, with the highest levels in blood and heart. Based on stimulation with polyinosinic-polycytidylic acid [poly (I:C)] or inactivated trivalent bacterial vaccine, LycIFN-γ mRNA was significantly increased in spleen and head kidney tissues. LycIFN-γ transcripts were also detected in head kidney granulocytes, primary head kidney macrophages (PKM), head kidney leukocytes, and large yellow croaker head kidney cell line (LYCK), and were significantly up-regulated by poly(I:C) or lipopolysaccharide (LPS) in head kidney leukocytes. Recombinant LycIFN-γ protein (rLycIFN-γ) produced in Escherichia coli could enhance respiratory burst responses in PKM. Furthermore, rLycIFN-γ not only induced the expression of iNOS gene and release of NO, but also up-regulated the expression of proinflammatory cytokines TNF-α and IL-1β in PKM. These findings therefore indicated that LycIFN-γ has a role in mediating inflammatory response. In addition, rLycIFN-γ could significantly up-regulate expression of IFN-γ receptor CRFB13, signal transduction factor STAT1, transcription factors IRF1 and T-bet, and Th1-related cytokines IFN-γ and IL-2 in head kidney leukocytes, suggesting that LycIFN-γ may have the potential to promote Th1 immune response in large yellow croaker. Taken together, our results show that LycIFN-γ may be involved in inflammatory response and promote Th1 immune response as its mammalian counterpart.

Molecular characterization and expression analysis of interferon-gamma in black seabream Acanthopagrus schlegelii

Interferon gamma (IFN-γ) is a major component in immunological signaling and plays a key role in resisting viral infection. In this study, we identified and characterized an IFN-γ gene (AsIFN-γ) in the marine fish black seabream (Acanthopagrus schlegelii). We cloned AsIFN-γ genomic sequence, which comprises four exons, three introns and an upstream promoter including several conserved regulatory elements. The complete cDNA of AsIFN-γ was 816 bp in length and encoded a putative 194 amino acids (aa) protein with a 22 aa signal peptide, six α-helices and one nuclear localization signal (NLS). Multiple alignment showed that AsIFN-γ protein shared 31-60% identity with IFN-γ of other fish but low identity with fish IFN-γrel and IFN-γ of other vertebrates. AsIFN-γ was constitutively expressed in all examined tissues with the highest expression level in immune organs, such as spleen, gill and kidney. In black seabream infected by red spotted nervous necrosis virus (RGNNV), the expression of AsIFN-γ was significantly up-regulated in most tissues, and RGNNV infection in vitro also induced significant up-regulation of AsIFN-γ, indicating that AsIFN-γ was involved in immune response to RGNNV infection. Overexpression of AsIFN-γ in cultured Acanthopagrus schlegelii brain (AsB) cells rapidly and transiently stimulated the expression of JAK-STAT signaling pathway related genes including STAT1, STAT2 and IRF9, as well as the downstream antiviral genes MX1 and ISG15. Furthermore, overexpression of AsIFN-γ was able to significantly inhibit RGNNV replication and virus production in AsB cells. In summary, we identified a conserved IFN-γ gene of black seabream, and demonstrated the rapid and strong antiviral activities of AsIFN-γ against RGNNV in black seabream.

Differential gene expression following TLR stimulation in rag1-/- mutant zebrafish tissues and morphological descriptions of lymphocyte-like cell populations

In the absence of lymphocytes, rag1-/- mutant zebrafish develop protective immunity to bacteria. In mammals, induction of protection by innate immunity can be mediated by macrophages or natural killer (NK) cells. To elucidate potential responsive cell populations, we morphologically characterized lymphocyte-like cells (LLCs) from liver, spleen and kidney hematopoietic tissues. In fish, these cells include NK cells and Non-specific cytotoxic cells (NCCs). We also evaluated the transcriptional expression response of select genes that are important indicators of NK and macrophage activation after exposure to specific TLR ligands. The LLC cell populations could be discriminated by size and further discriminated by the presence of cytoplasmic granules. Expression levels of mx, tnfα, ifnγ, t-bet and nitr9 demonstrated dynamic changes in response to intra-coelomically administered β glucan (a TLR2/6 ligand), Poly I:C (a TLR3 ligand) and resiquimod (R848) (a TLR7/8 ligand). Following TLR 2/6 stimulation, there was a greater than 100 fold increase in ifnγ in liver, kidney and spleen and moderate increases in tnfα in liver and kidney. TLR3 stimulation caused broad up regulation of mx, down-regulation of tnfα in kidney and spleen tissues and up regulation of nitr9 in the kidney. Following TLR 7/8 stimulation, there was a greater than 100 fold increase in ifnγ in liver and kidney and t-bet in liver. Our gene expression findings suggest that LLCs and macrophages are stimulated following β glucan exposure. Poly I:C causes type I interferon response and mild induction of LLC in the kidney and R-848 exposure causes the strongest LLC stimulation. Overall, the strongest NK like gene expression occurred in the liver. These differential effects of TLR ligands in rag1-/- mutant zebrafish shows strong NK cell-like gene expression responses, especially in the liver, and provides tools to evaluate the basis for protective immunity mediated by the innate immune cells of fish.

Mycobacterial Acid Tolerance Enables Phagolysosomal Survival and Establishment of Tuberculous Infection In Vivo

The blockade of phagolysosomal fusion is considered a critical mycobacterial strategy to survive in macrophages. However, viable mycobacteria have been observed in phagolysosomes during infection of cultured macrophages, and mycobacteria have the virulence determinant MarP, which confers acid resistance in vitro. Here we show in mice and zebrafish that innate macrophages overcome mycobacterial lysosomal avoidance strategies to rapidly deliver a substantial proportion of infecting bacteria to phagolysosomes. Exploiting the optical transparency of the zebrafish, we tracked the fates of individual mycobacteria delivered to phagosomes versus phagolysosomes and discovered that bacteria survive and grow in phagolysosomes, though growth is slower. MarP is required specifically for phagolysosomal survival, making it an important determinant for the establishment of mycobacterial infection in their hosts. Our work suggests that if pathogenic mycobacteria fail to prevent lysosomal trafficking, they tolerate the resulting acidic environment of the phagolysosome to establish infection.

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In vivo, newly infecting mycobacteria are rapidly trafficked to lysosomes within macrophages

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The mycobacterial acid tolerance determinant MarP enables lysosomal survival and growth

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Phagolysosomal mycobacteria can successfully establish infection, which is MarP dependent

Identification, ontogeny and expression analysis of a novel laboratory of genetics and physiology 2 (LGP2) transcript in Asian seabass, Lates calcarifer

LGP2 (laboratory of genetics and physiology 2) is an important member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), which plays a significant role in antiviral innate immunity. In this study, we have cloned the full-length cDNA sequence of LGP2 from Asian seabass, Lates calcarifer (AsLGP2). The complete AsLGP2 cDNA sequence consisted of 2586 nucleotides encoding a putative protein of 681 amino acids with a molecular mass of 77.6 kDa. From the AsLGP2 protein, four different conserved domains were predicted: a DExDc (DEAD/DEAH box helicase domain), a bacterial type III restriction enzyme domain (RES III), a HELICc (Helicase superfamily c-terminal domain and a RIG-I_C-RD (RIG-I C-terminal regulatory domain). The transcript of AsLGP2 could be detected in all the 11 tissues tested in healthy animals with high expression noticed in tissues facing external environment such as gill, hindgut and skin. The ontogenic expression profile of AsLGP2 implies a possible maternal transfer of this gene as it has been detected in all early embryonic developmental stages along with unfertilized eggs. Viral analogue, poly I:C, injection resulted in rapid up-regulated expression in different tissues with the highest modulation of expression observed in kidney followed by liver and gill. A rapid response of AsLGP2 expression was also observed in the different tissues of Vibrio alginolyticus-injected L. calcarifer, while significant change in expression was noticed following Staphylococcus aureus infection. Similarly, exposure to different pathogen-mimicking microbial analogues such as poly I:C, LPS and PGN resulted in enhanced expression of AsLGP2 in SISK cell-line. Taking together, these observations suggest that AsLGP2 can act as both antiviral and antibacterial cytosolic receptor and may play a significant role in embryonic and larval development in marine euryhaline teleosts like Asian seabass.

Pathogen-dependent role of turbot (Scophthalmus maximus) interferon-gamma

Interferon-gamma has been typically described as a pro-inflammatory cytokine playing an important role in the resolution of both viral and bacterial diseases. Nevertheless, some anti-inflammatory functions are also attributed to this molecule. In this work we have characterized for the first time the turbot (Scophthalmus maximus) interferon-gamma gene (ifng) and its expression pattern under basal conditions, after type I IFNs administration, and viral and bacterial infection. The intramuscular injection of an expression plasmid encoding turbot Ifng (pMCV1.4-ifng) was not able to affect the transcription of numerous immune genes directly related to the activity of IFN-gamma, with the exception of macrophage-colony stimulating factor (csf1). It was also unable to reduce the mortality caused by a Viral Hemorrhagic Septicemia Virus (VHSV) or Aeromonas salmonicida challenge. Interestingly, at 24 h post-infection, turbot previously inoculated with pMCV1.4-ifng and infected with VHSV showed an increase in the expression of pro-inflammatory cytokines and type I IFNs compared to those fish not receiving expression plasmid, indicating a synergic effect of Ifng and VHSV. On the other hand, some macrophage markers, such as the macrophage receptor with collagenous structure (marco), were down-regulated by Ifng during the viral infection. Ifng had the opposite effect in those turbot infected with the bacteria, showing a reduction in the transcription of pro-inflammatory and type I IFNs genes, and an increase in the expression of genes related to the activity of macrophages.

Identification and characterization of a constitutively expressed Ctenopharyngodon idella ADAR1 splicing isoform (CiADAR1a)

As one member of ADAR family, ADAR1 (adenosine deaminase acting on RNA 1) can convert adenosine to inosine within dsRNA. There are many ADAR1 splicing isoforms in mammals, including an interferon (IFN) inducible ∼150 kD protein (ADAR1-p150) and a constitutively expressed ∼110 kD protein (ADAR1-p110). The structural diversity of ADAR1 splicing isoforms may reflect their multiple functions. ADAR1 splicing isoforms were also found in fish. In our previous study, we have cloned and identified two different grass carp ADAR1 splicing isoforms, i.e. CiADAR1 and CiADAR1-like, both of them are IFN-inducible proteins. In this paper, we identified a novel CiADAR1 splicing isoform gene (named CiADAR1a). CiADAR1a gene contains 15 exons and 14 introns. Its full-length cDNA is comprised of a 5' UTR (359 bp), a 3' UTR (229 bp) and a 2952 bp ORF encoding a polypeptide of 983 amino acids with one Z-DNA binding domain, three dsRNA binding motifs and a highly conserved hydrolytic deamination domain. CiADAR1a was constitutively expressed in Ctenopharyngodon idella kidney (CIK) cells regardless of Poly I:C stimulation by Western blot assay. In normal condition, CiADAR1a was found to be present mainly in the nucleus. After treatment with Poly I:C, it gradually shifted to cytoplasm. To further investigate the mechanism of transcriptional regulation of CiADAR1a, we cloned and identified its promoter sequence. The transcriptional start site of CiADAR1a is mapped within the truncated exon 2. CiADAR1a promoter is 1303 bp in length containing 4 IRF-Es. In the present study, we constructed pcDNA3.1 eukaryotic expression vectors with IRF1 and IRF3 and co-transfected them with pGL3-CiADAR1a promoter into CIK cells. The results showed that neither the over-expression of IRF1 or IRF3 nor Poly I:C stimulation significantly impacted CiADAR1a promoter activity in CIK cells. Together, according to the molecular and expression characteristics, subcellular localization and transcriptional regulatory mechanism, we deduced that CiADAR1a shared a high degree of homology with mammalian ADAR1-p110.

Analysis of interferon gamma protein expression in zebrafish (Danio rerio)

IFN-γ is a major effector cytokine, produced to induce type I immune responses. It has been cloned in several fish species including zebrafish, however to date few studies have looked at IFN-γ protein expression and bioactivity in fish. Hence, the current study focused on developing a monoclonal antibody (moAb) against zfIFN-γ. We show that the zfIFN-γ moAb specifically recognises E. coli produced recombinant IFN-γ protein and zfIFN-γ produced in transfected HEK293 cells, by Western blot analysis. Next we analysed the production of the native protein following expression induced by PHA stimulation of leukocytes in vitro or antigen re-stimulation in vivo. We show the IFN-γ protein is produced as a dimer, and that a good correlation exists between transcript expression levels and protein levels.

Evolution of Cytokine Receptor Signaling

Cytokines represent essential mediators of cell–cell communication with particularly important roles within the immune system. These secreted factors are produced in response to developmental and/or environmental cues and act via cognate cytokine receptors on target cells, stimulating specific intracellular signaling pathways to facilitate appropriate cellular responses. This review describes the evolution of cytokine receptor signaling, focusing on the class I and class II receptor families and the downstream JAK–STAT pathway along with its key negative regulators. Individual components generated over a long evolutionary time frame coalesced to form an archetypal signaling pathway in bilateria that was expanded extensively during early vertebrate evolution to establish a substantial “core” signaling network, which has subsequently undergone limited diversification within discrete lineages. The evolution of cytokine receptor signaling parallels that of the immune system, particularly the emergence of adaptive immunity, which has likely been a major evolutionary driver.