Molecular characterization and expression analysis of the putative interleukin 6 receptor (IL-6Rα and glycoprotein-130) in rainbow trout (Oncorhynchus mykiss): Salmonid IL-6Rα possesses a polymorphic N-terminal Ig domain with variable numbers of two repeats

The IL-12 family cytokines in fish: Molecular structure, expression profile and function

Interleukin (IL)-12 family cytokines including IL-12, IL-23, IL-27, IL-35 and IL-39 are heterodimeric cytokines composed of two subunits, an α-chain (entitled p35, p19 and p28) and a β-chain (namely p40 and Epstein-Barr virus-induced gene 3, EBI3). Unlike in mammals, specific whole genome duplication events in fish may generate more paralogues of these subunits as the components of IL-12 family cytokines. Although all subunit genes of IL-12 family have been isolated and identified in various fish species, some important issues on fish IL-12 family are needed to be addressed compared to the extensive study in mammals: Whether the expansion of these subunit genes results in the generation of multiple isoforms of the family cytokines; Whether the related receptor genes have similar complex repertoire corresponding to their ligands; How about the expression kinetics of these subunit paralogues particularly under the circumstance of pathogen infection and immune stimulation; How about the functional properties of IL-12 family in fish. In the past ten years, these concerns have received increasing attentions to establish the biological significance of this family cytokines in fish immunity. In this review, we summarized the current understanding of IL-12 family with a special focus on the molecular structures, inducible expression profiles and functions of IL-12 family members in fish.

Dietary Supplementation of Bacillus sp. PM8313 with β-glucan Modulates the Intestinal Microbiota of Red Sea Bream (Pagrus major) to Increase Growth, Immunity, and Disease Resistance

A 56-day feeding trial was conducted to determine the effect of dietary supplementation with Bacillus sp. isolated from the intestines of red sea bream on the growth performance, immunity, and gut microbiome composition of red sea bream. Three diets (a control diet and two treatments) were formulated without Bacillus sp. PM8313 or β-glucan (control, CD), 1 × 108 CFU g-1 PM8313 (BSD), and 1 × 108 CFU g-1 PM8313 + 0.1% β-glucan (BGSD). At the end of the experiment, the weight, specific growth rate, feed conversion ratio, and protein efficiency ratio of the fish in the BSD and BGSD diet groups were significantly improved than those of the control group (P < 0.05). Additionally, amylase and trypsin activities were significantly higher (P < 0.05) in both groups compared to the control. Superoxide dismutase and lysozyme activity, which are serum non-specific immune responses, only increased in the BGSD group. The two treatment groups exhibited a marked difference in the intestinal microbiota composition compared to the control group. Furthermore, the treatment groups exhibited an upregulation of IL-6 and NF-κb, coupled with high survival rates when challenged with Edwardsiella tarda. Therefore, dietary supplementation with PM8313 improved the growth performance, digestive enzyme activity, non-specific immunity, and pathogen resistance of red sea bream, in addition to affecting the composition of its intestinal microflora.

Construction of a Joint Prediction Model for the Occurrence of Ischemic Stroke and Acute Myocardial Infarction Based on Bioinformatic Analysis

Ischemic stroke (IS) has imposed significant threat to both middle-aged and elderly people worldwide. Acute myocardial infarction (AMI) is a rare but serious complication following IS, which can further increase patient disability and mortality rates. With the development of intravenous thrombolysis and endovascular treatment, the prognosis of IS has been greatly improved. However, the pathogenesis of IS complicated with AMI is still unclear. To fill this gap, this work uses bioinformatic analysis, where IS and AMI datasets were combined for differential gene analysis, and then, a ROC prediction model for target gene analysis was constructed. It is found that OSM gene has the highest prediction accuracy (AUC = 0.793), followed by IL6ST, IL6, JAK1, IL6R, and JAK2 genes. Joint prediction model showed higher accuracy in predicting the outcome of control and case (AUC = 0.918). The etiology of ischemic stroke and acute myocardial infarction is complicated. Their cooccurring pathological mechanisms and the conversion between the two diseases could not be explained by a single gene. Therefore, the joint prediction model in this work can provide a better prediction accuracy for research purpose.

The Dynamic Immune Response of Yellow Catfish (Pelteobagrus fulvidraco) Infected With Edwardsiella ictaluri Presenting the Inflammation Process

Edwardsiella ictaluri is a highly destructive pathogen in cultured yellow catfish, thus it was very necessary to study the immune response of yellow catfish against bacterial infection. In this study, RNA-Seq technology was used to study the immune response in two distinct tissues of yellow catfish at eight different time points (h) after E. ictaluri infection. The number of differentially expressed genes (DEGs) in the spleen and liver was low at 3 h and 6 h post-infection, respectively. Afterwards, the most number of DEGs in the spleen was detected at 72 h, while the number of DEGs in the liver maintained a high level from 24 h to 120 h. The GO and KEGG enrichment analyses of DEGs at different time points uncovered that cytokines were continuously transcribed at 6 h to 120 h; whereas the liver is the main organ that secretes the components of the complement system, and metabolic regulation was activated from 12 h to 120 h. Moreover, an overview of the inflammation response of yellow catfish was exhibited including pattern-recognition receptors, inflammatory cytokines, chemokines, complements, and inflammation-related signal pathways. The similar expression tendency of nine genes by qRT-PCR validated the accuracy of transcriptome analyses. The different transcriptomic profiles obtained from the spleen and liver will help to better understand the dynamic immune response of fish against bacterial infection, and will provide basic information for establishing effective measures to prevent and control diseases in fish.

Molecular and functional characterization of IL-6 receptor (IL-6R) and glycoprotein 130 (gp130) in Nile tilapia (Oreochromis niloticus)

Interleukin 6 (IL-6) is a pleiotropic cytokine that exerts its biological functions through interaction with its receptor system consisting of a ligand-specific IL-6 receptor (IL-6R) and a common signal-transducing receptor (gp130). In this study, OnIL-6R and Ongp130 genes from Nile tilapia (Oreochromis niloticus) were identified, and their roles in bacterial or viral infection and in regulation of inflammatory response involved in IL-6 were investigated. The open reading frames (ORFs) of OnIL-6R and Ongp130 are 2019 bp and 2679 bp, encoding 672 and 892 amino acids, respectively. Domain analysis of the deduced amino acid sequences of OnIL-6R and Ongp130 showed that both of them contained a conserved Ig-like domain, FNIII domains, and a WSXWS motif. The transcripts of OnIL-6R and Ongp130 were widely expressed in all examined tissues. Following in vivo challenges with Streptococcus agalactia, Poly I: C and lipopolysaccharide (LPS), the mRNAs of OnIL-6R and Ongp130 were notably induced in liver, head kidney and spleen. The transcriptional up-regulations of OnIL-6R and Ongp130 were also detected in Nile tilapia monocytes/macrophages and lymphocytes after in vitro stimulations with S. agalactiae, Poly I: C and LPS. Besides, increasing mRNA levels of the inflammation-related cytokines (IL-1β, TNF-α, IL-6, IL-10, and MIF) induced by recombinant OnIL-6 could be further enhanced by co-treatment with recombinant soluble OnIL-6R in lymphocytes. Furthermore, recombinant soluble Ongp130 suppressed the induction of expression of these cytokines in lymphocytes when co-stimulated with (r)OnIL-6 and (r)sOnIL-6R. Taken together, these results indicated that OnIL-6R and Ongp130 were likely involved in the resistance to bacterial or viral infection in Nile tilapia. Moreover, soluble OnIL-6R and soluble Ongp130 have an agonistic effect or antagonistic effect in the inflammation response involved in OnIL-6.

Transcriptomic analysis of the impacts of ethinylestradiol (EE2) and its consequences for proliferative kidney disease outcome in rainbow trout (Oncorhynchus mykiss)

Freshwater fish are threatened by the cumulative impact of multiple stressors. The purpose of this study was to unravel the molecular and organism level reactions of rainbow trout, Oncorhynchus mykiss, to the combined impact of two such stressors that occur in the natural habitat of salmonids. Fish were infected with either the myxozoan parasite, Tetracapsuloides bryosalmonae, which causes proliferative kidney disease (PKD), or exposed to ethinylestradiol (EE2) an estrogenic endocrine disrupting compound, or to a combination of both (PKD × EE2). PKD is a slow progressive chronic disease here we focused on a later time point (130-day post-infection (d.p.i.)) when parasite intensity in the fish kidney has already started to decrease. At 130 d.p.i., RNA-seq technology was applied to the posterior kidney, the main target organ for parasite development. This resulted with 280 (PKD), 14 (EE2) and 444 (PKD × EE2) differentially expressed genes (DEGs) observed in the experimental groups. In fish exposed to the combination of stressors (PKD × EE2), a number of pathways were regulated that were neither observed in the single stressor groups. Parasite infection, alone and in combination with EE2, only resulted in a low intensity immune response that negatively correlated with an upregulation of genes involved in a variety of metabolic and inflammation resolution processes. This could indicate a trade-off whereby the host increases investment in recovery/resolution processes over immune responses at a later stage of disease. When PKD infection took place under simultaneous exposure to EE2 (PKD × EE2), parasite intensity decreased and pathological alterations in the posterior kidney were reduced in comparison to the PKD only condition. These findings suggest that EE2 modulated these response profiles in PKD infected fish, attenuating the disease impact on the fish.

Molecular characterization of grass carp interleukin-6 receptor and the agonistic activity of its soluble form in head kidney leucocytes

Interleukin (IL)-6 receptor (IL-6R) can specifically bind to IL-6 and the complex subsequently recruits a transmembrane signal transducer, gp130, to trigger the intracellular signal transduction. IL-6R exists in two forms, a transmembrane IL-6R and a soluble IL-6R (sIL-6R), leading to different signal transduction mechanisms as classic signaling and trans-signaling, respectively. There is now a general consensus that these two modes of signal transduction can mediate anti-inflammatory and pro-inflammatory activities of IL-6. The study on Il-6r is limited although Il-6 has been well studied in teleost. In the present study, a cDNA encoding grass carp Il-6r (gcIl-6r) was isolated. An in-silico analysis showed that gcIl-6r shared the same functional domains and conserved gene synteny at its loci with mouse homologue, and its amino acid sequence was conserved in fish species. A tissue distribution assay demonstrated that gcil6r mRNA was expressed with high levels in immune tissues including spleen and head kidney, and its expression was induced by LPS and Poly I:C in grass carp head kidney leucocytes (HKLs). An in vitro binding assay showed that recombinant soluble gcIl-6r (rgcsIl-6r) could specifically bind to recombinant gcIl-6 (rgcIl-6) protein. Moreover, rgcIl-6 stimulated suppressor of cytokine signaling 3 (socs3)'s mRNA expression in grass carp HKLs and it combined with rgcsIl-6r increased socs3 mRNA expression in CIK cells with gp130 but without Il-6r expression. In HKLs, rgcIl-6 stimulated the mRNA levels of both pro-inflammatory (tnfa and il1b) and anti-inflammatory (il10) cytokines, and rgcsIl-6r could augment these stimulatory effects of gcIl-6. Taken these data together, gcsIl-6r can mediate the immuno-regulatory functions of gcIl-6 and has an agonistic property in these actions of Il-6 in grass carp.

Phylotranscriptomics suggests the jawed vertebrate ancestor could generate diverse helper and regulatory T cell subsets

BACKGROUND

The cartilaginous fishes diverged from other jawed vertebrates ~ 450 million years ago (mya). Despite this key evolutionary position, the only high-quality cartilaginous fish genome available is for the elephant shark (Callorhinchus milii), a chimaera whose ancestors split from the elasmobranch lineage ~ 420 mya. Initial analysis of this resource led to proposals that key components of the cartilaginous fish adaptive immune system, most notably their array of T cell subsets, was primitive compared to mammals. This proposal is at odds with the robust, antigen-specific antibody responses reported in elasmobranchs following immunization. To explore this discrepancy, we generated a multi-tissue transcriptome for small-spotted catshark (Scyliorhinus canicula), a tractable elasmobranch model for functional studies. We searched this, and other newly available sequence datasets, for CD4+ T cell subset-defining genes, aiming to confirm the presence or absence of each subset in cartilaginous fishes.

RESULTS

We generated a new transcriptome based on a normalised, multi-tissue RNA pool, aiming to maximise representation of tissue-specific and lowly expressed genes. We utilized multiple transcriptomic datasets and assembly variants in phylogenetic reconstructions to unambiguously identify several T cell subset-specific molecules in cartilaginous fishes for the first time, including interleukins, interleukin receptors, and key transcription factors. Our results reveal the inability of standard phylogenetic reconstruction approaches to capture the site-specific evolutionary processes of fast-evolving immune genes but show that site-heterogeneous mixture models can adequately do so.

CONCLUSIONS

Our analyses reveal that cartilaginous fishes are capable of producing a range of CD4+ T cell subsets comparable to that of mammals. Further, that the key molecules required for the differentiation and functioning of these subsets existed in the jawed vertebrate ancestor. Additionally, we highlight the importance of considering phylogenetic diversity and, where possible, utilizing multiple datasets for individual species, to accurately infer gene presence or absence at higher taxonomic levels.

First in-depth analysis of the novel Th2-type cytokines in salmonid fish reveals distinct patterns of expression and modulation but overlapping bioactivities

IL-4 and IL-13 are closely related canonical type-2 cytokines in mammals and have overlapping bioactivities via shared receptors. They are frequently activated together as part of the same immune response and are the signature cytokines produced by T-helper (Th)2 cells and type-2 innate lymphoid cells (ILC2), mediating immunity against extracellular pathogens. Little is known about the origin of type-2 responses, and whether they were an essential component of the early adaptive immune system that gave a fitness advantage by limiting collateral damage caused by metazoan parasites. Two evolutionary related type-2 cytokines, IL-4/13A and IL-4/13B, have been identified recently in several teleost fish that likely arose by duplication of an ancestral IL-4/13 gene as a consequence of a whole genome duplication event that occurred at the base of this lineage. However, studies of their comparative expression levels are largely missing and bioactivity analysis has been limited to IL-4/13A in zebrafish. Through interrogation of the recently released salmonid genomes, species in which an additional whole genome duplication event has occurred, four genomic IL-4/13 loci have been identified leading to the cloning of three active genes, IL-4/13A, IL-4/13B1 and IL-4/13B2, in both rainbow trout and Atlantic salmon. Comparative expression analysis by real-time PCR in rainbow trout revealed that the IL-4/13A expression is broad and high constitutively but less responsive to pathogen-associated molecular patterns (PAMPs) and pathogen challenge. In contrast, the expression of IL-4/13B1 and IL-4/13B2 is low constitutively but is highly induced by viral haemorrhagic septicaemia virus (VHSH) infection and during proliferative kidney disease (PKD) in vivo, and by formalin-killed bacteria, PAMPs, the T cell mitogen PHA, and the T-cell cytokines IL-2 and IL-21 in vitro. Moreover, bioactive recombinant cytokines of both IL-4/13A and B were produced and found to have shared but also distinct bioactivities. Both cytokines rapidly induce the gene expression of antimicrobial peptides and acute phase proteins, providing an effector mechanism of fish type-2 cytokines in immunity. They are anti-inflammatory via up-regulation of IL-10 and down-regulation of IL-1β and IFN-γ. They modulate the expression of cellular markers of T cells, macrophages and B cells, the receptors of IFN-γ, the IL-6 cytokine family and their own potential receptors, suggesting multiple target cells and important roles of fish type-2 cytokines in the piscine cytokine network. Furthermore both cytokines increased the number of IgM secreting B cells but had no effects on the proliferation of IgM⁺ B cells in vitro. Taken as a whole, fish IL-4/13A may provide a basal level of type-2 immunity whilst IL-4/13B, when activated, provides an enhanced type-2 immunity, which may have an important role in specific cell-mediated immunity. To our knowledge this is the first in-depth analysis of the expression, modulation and bioactivities of type-2 cytokines in the same fish species, and in any early vertebrate. It contributes to a broader understanding of the evolution of type-2 immunity in vertebrates, and establishes a framework for further studies and manipulation of type-2 cytokines in fish.

Hypothermal stress induced differential expression profiles of the immune response gene, warm-temperature-acclimation associated 65-kDa protein (Wap65), in the liver of fresh water and seawater milkfish, Chanos chanos

The milkfish (Chanos chanos), an important aquaculture species, is intolerant to cold environments. Temperature fluctuations in the environment affect the physiological response, behavior, and survival rate of the fish. The warm-temperature-acclimation associated 65-kDa protein (Wap65) of teleosts was identified after heat shock treatment and has two isoforms. Both the isoforms were involved in the induction of immune responses in fish. They showed high degree of sequence conservation with the mammalian hemopexin and had high affinity for heme, which helped in the neutralization of free-heme and its transport to the liver. In this study, we isolated and characterized the two isoforms of wap65 genes (Ccwap65-1 and Ccwap65-2) from the liver of milkfish. The Ccwap65-1 and Ccwap65-2 are mainly expressed in livers of milkfish. In hypothermal treatment, the expression levels of Ccwap65-2 in the livers of SW and FW milkfish were up-regulated after exposure to low temperature (18 °C) for 12 h and 96 h compared to those in the normal temperature (28 °C) group, respectively. After intraperitoneal injection of lipopolysaccharide (LPS), the expression of Ccwap65-2 was elevated in both SW and FW milkfish, whereas that of Ccwap65-1 was not affected in both the groups. Thus, Ccwap65-2 expressed in the milkfish liver under hypothermal stress was identified as a novel immune biomarker. In addition, according to the transcriptome database, up-regulation of the other immune-response genes indicated increased pathogen infection status under hypothermal stress. Acute increase in the expression of hepatic Ccwap65-2 in response to pathogen infection might lead to better cold tolerance of SW milkfish compared to that of the FW individuals upon cold challenge.

Acquired immunity and vaccination against infectious pancreatic necrosis virus of salmon

Acquired immunity plays an important role in the protection of salmonids vaccinated against infectious pancreatic necrosis virus (IPNV) infections. In recent years, vaccine research has taken a functional approach to find the correlates of protective immunity against IPNV infections. Accumulating evidence suggests that the humoral response, specifically IgM is a correlate of vaccine protection against IPNV infections. The role of IgT on the other hand, especially at the sites of virus entry into the host is yet to be established. The kinetics of CD4+ and CD8+ T-cell gene expression have also been shown to correlate with protection in salmonids, suggesting that other arms of the adaptive immune response e.g. cytotoxic T cell responses and Th1 may also be important. Overall, the mechanisms of vaccine protection observed in salmonids are comparable to those seen in other vertebrates suggesting that the immunological basis of vaccine protection has been conserved across vertebrate taxa.

The cytokine networks of adaptive immunity in fish

Cytokines, produced at the site of entry of a pathogen, drive inflammatory signals that regulate the capacity of resident and newly arrived phagocytes to destroy the invading pathogen. They also regulate antigen presenting cells (APCs), and their migration to lymph nodes to initiate the adaptive immune response. When naive CD4+ T cells recognize a foreign antigen-derived peptide presented in the context of major histocompatibility complex class II on APCs, they undergo massive proliferation and differentiation into at least four different T-helper (Th) cell subsets (Th1, Th2, Th17, and induced T-regulatory (iTreg) cells in mammals. Each cell subset expresses a unique set of signature cytokines. The profile and magnitude of cytokines produced in response to invasion of a foreign organism or to other danger signals by activated CD4+ T cells themselves, and/or other cell types during the course of differentiation, define to a large extent whether subsequent immune responses will have beneficial or detrimental effects to the host. The major players of the cytokine network of adaptive immunity in fish are described in this review with a focus on the salmonid cytokine network. We highlight the molecular, and increasing cellular, evidence for the existence of T-helper cells in fish. Whether these cells will match exactly to the mammalian paradigm remains to be seen, but the early evidence suggests that there will be many similarities to known subsets. Alternative or additional Th populations may also exist in fish, perhaps influenced by the types of pathogen encountered by a particular species and/or fish group. These Th cells are crucial for eliciting disease resistance post-vaccination, and hopefully will help resolve some of the difficulties in producing efficacious vaccines to certain fish diseases.

Transcriptional regulation of the gilthead seabream (Sparus aurata) interleukin-6 gene promoter

Interleukin-6 (IL-6) has been identified and characterized from several fish species and its mRNA expression is induced by pathogen-associated molecular patterns (PAMPs) and cytokines in immune cells and tissues. However, the transcriptional regulation of the IL-6 gene in fish is not well understood. In the present study, we have cloned and sequenced a 1028 bp 5'-flanking DNA region from the IL-6 gene in seabream (Sparus aurata). Sequence analysis of the seabream IL-6 promoter (sbIL-6P) evidenced the presence of a conserved TATA motif and conserved response elements for NF-κB, C/EBPβ (NF-IL6), AP-1 and GRE, similar to other vertebrate IL-6 promoters. Functional characterization of sbIL-6P was performed by cloning sbIL-6P into a luciferase expression vector and by transfecting it into L6 muscle cells, a mammalian cell line shown previously to express IL-6 in response to pro-inflammatory stimuli. We show here that the activity of sbIL-6P was significantly induced by pro-inflammatory cytokines such as tumor necrosis factor alpha (TNFα), IL-6 and IL-2, as well as by lipopolysaccharide (LPS), but significantly repressed by dexamethasone. In addition, the stimulatory effects of TNFα on sbIL-6P activity appeared to be mediated by the NF-κB, p38 MAPK and JNK signaling pathways. Deletion analyses of sbIL-6P suggested that activation of sbIL-6P by TNFα and IL-6 required the presence of binding motifs present in the proximal promoter (-171 to -84) whereas activation by IL-2 required binding motifs present in the distal promoter (-1024 to -864). The results from this study indicate, for the first time in fish, that pro-inflammatory cytokines, LPS and glucocorticoids can regulate the activity of the IL-6 gene at a transcriptional level and identify important regions in its response to cytokines.

Teleost IL-6 promotes antibody production through STAT3 signaling via IL-6R and gp130

Teleost IL-6 is upregulated after antigen stimulation; therefore, we hypothesized that fish IL-6 contributes to antibody production during immune responses against infections. To verify this hypothesis, we first cloned IL-6R and gp130 in fugu (Takifugu rubripes) in the present study. The membrane and soluble forms of IL-6R were identified by the identification of cDNA clones of IL-6R homologues. Three STAT3-docking sites were found in the intracellular region of fugu gp130. Expression analysis showed that fugu IL-6R and gp130 were expressed in mIgM(+) B cells, suggesting that fugu B cells are stimulated by IL-6. Recombinant fugu IL-6 (rfIL-6) increased the gene expression of secretory antibodies by mIgM(+) B cells in vitro. The rfIL-6 and soluble form of rfIL-6R activated STAT3 phosphorylation in the B cells and a cultured cell line transfected with fugu gp130. These results indicate that fugu IL-6 enhances antibody production in the B-cell lineage via gp130 and STAT3 signaling.