Cloning and characterization of the rainbow trout (Oncorhynchus mykiss) type II interleukin-1 receptor cDNA

Re-identification and characterization of grass carp Ctenopharyngodon idella TLR20

Toll-like receptors (TLRs) play a crucial role in the recognition of microbial-associated molecular patterns in the innate immune system. Fish TLRs have undergone significant gene expansion to adapt to complex aquatic environments. Among them, TLR20 from the TLR11 family actively responds to viral and bacterial invasions. Previous studies have reported two TLR20s in grass carp (Ctenopharyngodon idella), and in this study, we revised this conclusion. Based on the latest grass carp genome, we identified a new TLR20 member. These three TLR20s are arranged in tandem on chromosome 9, indicating that they are generated by gene duplication events. They were renamed CiTLR20.1 to CiTLR20.3 based on their chromosomal positions. The CiTLR20s in C. idella exhibit higher similarities with those in Danio rerio, Cyprinus carpio, and Megalobrama amblycephala, and lower similarities with those in other distantly related fish species. Selective pressure analysis revealed low conservation and negative evolution of TLR20s during evolution. The 3D structures of the three TLR20s showed significant differences, reflecting functional variations and different downstream adaptor molecule recruitment. Transcriptome data revealed tissue distribution differences of TLR20s, with TLR20.1 showing relatively low expression levels in all the tissues, while TLR20.2 and TLR20.3 showed higher expression in the head kidney, spleen, and gill. Additionally, TLR20.2 and TLR20.3 actively responded to GCRV-II infection, with higher upregulation of TLR20.2 in response to Aeromonas hydrophila challenge. In conclusion, this study corrected the number of grass carp TLR20 members and analyzed TLR20 from an evolutionary and structural perspective, exploring its role in antiviral and antibacterial defense. This study provides reference for future research on fish TLR20.

Cloning of Toll-like Receptor 3 Gene from Schizothorax prenanti (SpTLR3), and Expressions of Seven SpTLRs and SpMyD88 after Lipopolysaccharide Induction

Toll-like receptor 3 (SpTLR3) from Schizothorax prenanti (S. prenanti) was cloned and identified, and the tissue distribution of the SpTLR3 gene was examined in this study. Moreover, the relative mRNA expression levels of myeloid differentiation factor 88 gene (SpMyD88) and seven TLR genes (SpTLR2, SpTLR3, SpTLR4, SpTLR18, SpTLR22-1, SpTLR22-2 and SpTLR22-3) from S. prenanti after lipopolysaccharide (LPS) challenge were analyzed through quantitative real-time polymerase chain reaction (qRT-PCR). The full length of SpTLR3 gene is 3097 bp, and complete coding sequence (CDS) is 2715 bp, which encodes 904 amino acids. The SpTLR3 amino acid sequence shared 43.94−100% identity with TLR3 sequences from other vertebrates; SpTLR3 was expressed in all eight tissues examined; and the highest level appeared in the liver, which was significantly higher than in all other tissues (p < 0.05), followed by the levels in the heart and muscles. LPS significantly up-regulated all eight genes in the S. prenanti tissues at 12 or 24 h (p < 0.05). Compared with the PBS control group, no significant transcripts changes were found in SpTLR2 or SpTLR3 at 12 h after LPS induction, but they were significantly up-regulated at 24 h (p < 0.001). The most abundant transcripts were found in the head kidney SpTLR22 genes after 24 h LPS induction, with high to low levels, which were SpTLR22-1 (564-fold), SpTLR22-3 (508-fold) and SpTLR22-2 (351-fold). Among these eight genes, the expression level of SpTLR4 was the least up-regulated. Overall, SpTLR4 in the head kidney was involved in the antibacterial immune response earlier, and the level was increased at 12 h with extreme significance after LPS stimulation (p < 0.001), while the other seven genes were the most significantly up-regulated at 24 h post injection. Taken together, the results suggest that SpMyD88, SpTLR2, SpTLR3, SpTLR4, SpTLR18, SpTLR22-1, SpTLR22-2 and SpTLR22-3 participate in an innate immune response stimulated by LPS, and the response intensity of the genes was organ-specific, with differing kinetics. Our findings will contribute to a more complete understanding of the roles of these TLR genes in antibacterial immunity.

Raptor/mTORC1 Acts as a Modulatory Center to Regulate Anti-bacterial Immune Response in Rockfish

The mammalian target of rapamycin (mTOR) is an evolutionarily highly conserved atypical serine/threonine protein kinase, which regulates cell growth, proliferation, apoptosis, autophagy, and metabolism. As a regulatory protein, Raptor is awfully important for the stability and function of mTOR complex 1 (mTORC1). However, the studies about how Raptor/mTORC1 participates in and regulates immune response in lower vertebrates are still limited. In this study, we investigated the regulation of immune response by the Raptor/mTORC1 signaling pathway in rockfish Sebastes schlegelii. Sebastes schlegelii Raptor (Ss-Raptor) is a highly conserved protein during the evolution, in both primary and tertiary structure. Ss-Raptor mRNA was widely distributed in various tissues of rockfish and has a relative higher expression in spleen and blood. After infected by Micrococcus luteus or Listonella anguillarum, mRNA expression of Ss-Raptor rapidly increased within 48 h. Once Raptor/mTORC1 signaling was blocked by rapamycin, expression of the pro-inflammatory cytokines IL-1β and IL-8 was severely impaired, suggesting potential regulatory role of Raptor/mTORC1 signaling in the innate immune response of rockfish. In addition, Raptor/mTORC1 pathway participated in lymphocyte activation of rockfish through promoting 4EBP1 and S6 phosphorylation. Inhibition of Raptor/mTORC1 signaling crippled the lymphocyte expansion during primary adaptive immune response, manifesting by the decrease of lymphoid organ weight and lymphocyte numbers. More importantly, inhibition of Raptor/mTORC1 signaling impaired the lymphocyte mediated cytotoxic response, and made the fish more vulnerable to the bacterial infection. Together, our results suggested that Raptor and its tightly regulated mTORC1 signaling acts as modulatory center to regulate both innate and lymphocyte-mediated adaptive immune response during bacterial infection. This research has shed new light on regulatory mechanism of teleost immune response, and provide helpful evidences to understand the evolution of immune system.

Advances in salmonid fish immunology: A review of methods and techniques for lymphoid tissue and peripheral blood leucocyte isolation and application

Evaluating studies over the past almost 40 years, this review outlines the current knowledge and research gaps in the use of isolated leucocytes in salmonid immunology understanding. This contribution focuses on the techniques used to isolate salmonid immune cells and popular immunological assays. The paper also analyses the use of leucocytes to demonstrate immunomodulation following dietary manipulation, exposure to physical and chemical stressors, effects of pathogens and parasites, vaccine design and application strategies assessment. We also present findings on development of fish immune cell lines and their potential uses in aquaculture immunology. The review recovered 114 studies, where discontinuous density gradient centrifugation (DDGC) with Percoll density gradient was the most popular leucocyte isolation method. Fish head kidney (HK) and peripheral blood (PB) were the main sources of leucocytes, from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Phagocytosis and respiratory burst were the most popular immunological assays. Studies used isolated leucocytes to demonstrate that dietary manipulations enhance fish immunity, while chemical and physical stressors suppress immunity. In addition, parasites, and microbial pathogens depress fish innate immunity and induce pro-inflammatory cytokine gene transcripts production, while vaccines enhance immunity. This review found 10 developed salmonid cell lines, mainly from S. salar and O. mykiss HK tissue, which require fish euthanisation to isolate. In the face of high costs involved with density gradient reagents, the application of hypotonic lysis in conjunction with mico-volume blood methods can potentially reduce research costs, time, and using nonlethal and ethically flexible approaches. Since the targeted literature review for this study retrieved no metabolomics study of leucocytes, indicates that this approach, together with traditional technics and novel flow cytometry could help open new opportunities for in vitro studies in aquaculture immunology and vaccinology.

In vitro immune response of chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells stimulated by bacterial lipopolysaccharide

We investigated cellular functional and targeted immune cytokine responses of farmed Chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells (PBMCs) in vitro to LPS from Escherichia coli (E. coli) serotypes O111: B4 and O55: B5, and a phorbol ester phorbol 12-myristate 13-acetate (PMA). Bacterial LPS and PMA significantly (p < 0.05) induced reactive oxygen species (ROS) production in O. tshawytscha PBMCs, and enhanced by interferon (IFN)-inducible cytokine production. Cellular phagocytosis was significantly enhanced with PMA and E. coli serotype O111: B4 LPS after 1 and 2 h respectively. At the molecular level, LPS and PMA significantly (p < 0.05) upregulated pro-inflammatory cytokine gene transcripts for IFNγ, TNF-α, and anti-inflammatory IL-10, 24 h post-stimulation. This response is postulated to be mediated via the MyD88 and TRIF pathways in TLR4, or synergistic TLR1 and TLR2 receptors. This is the first report of LPS induced immune related in vitro responses in farmed O. tshawytscha PBMCs.

Phylogeny and expression modulation of interleukin 1 receptors in grass carp (Ctenopharyngodon idella)

The interleukin (IL) -1 family members play an important role in regulating inflammatory responses and their functions are mediated by a group of receptors consisting of immunoglobulin and Toll/IL-1 receptor (TIR) domains. In humans, 10 IL-1Rs are found. In this study, 5 IL-1 receptors including IL-1R3/IL-1RAcP, IL-1R8/SIGIRR, IL-1R9a/IL-1RAcPL1a, IL-1R9b/IL-1RAcPL1b and IL-1R10/IL-1RAcPL2 were identified in grass carp (Ctenopharyngodon idella). Phylogenetic analysis reveals that the IL-1R9a/IL-1RAcPL1a and IL-1R9b/IL-1RAcPL1b share significantly high sequence similarity and are believed to have been duplicated from the same gene prior to the radiation of teleosts. Further, these two receptors closely relate to the IL-1R10/IL-1RAcPL2, suggesting that they may have evolved from a common ancestor. The IL-1R3/IL-1RAcP, IL-1R9a/IL-1RAcPL1a, IL-1R9b/IL-1RAcPL1b and IL-1R10/IL-1RAcPL2 are highly expressed in the brain. Stimulation of primary spleen leucocytes by LPS and intraperitoneal injection of fish with poly (I:C) or bacterial infection results in significant increases of IL-1R3/IL-1RAcP expression. Interestingly, the IL-1R8/SIGIRR and IL-1R10/IL-1RAcPL2 showed similar expression patterns.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.

Immunohistochemical characterization of Toll-like receptor 2 in gut epithelial cells and macrophages of goldfish Carassius auratus fed with a high-cholesterol diet

Toll-like receptors (TLRs) are a group of pattern recognition molecules that play a crucial role in innate immunity. The structural conservation of the archaic TLR system suggests that the regulation of the immune response might be similar in fish and mammals. Several TLRs (TLR-1, -2, and -4) are expressed by activated macrophages, "foam cells" in human atherosclerotic lesions. To date, 20 different TLRs were identified in more than a dozen different fish species. In this study we found that feeding goldfish, Carrassius auratus, a high-cholesterol diet (HCD) resulted macrophage foam cell formation in the intestinal tissues. The expression of TLR2 has been found in foam cells and in the cytoplasm of enterocytes, however the staining was more intense at the apical surface of polarized intestinal epithelial cells and in the lamina propria. In the intestinal epithelial cells and in the lamina propria cells of the control fish the TLR2 was expressed at low levels. The intestinal epithelium is directly involved in the mucosal immune response through its expression of proinflammatory genes, release of inflammatory cytokines, and recruitment of inflammatory cells.

Proinflammatory cytokine and cytokine receptor gene expression kinetics following challenge with Flavobacterium psychrophilum in resistant and susceptible lines of rainbow trout (Oncorhynchus mykiss)

Flavobacterium psychrophilum (Fp) is the causative agent of bacterial cold water disease (BCWD) which causes appreciable economic losses in rainbow trout aquaculture. We previously reported development of a genetic line, designated ARS-Fp-R that exhibits higher survival relative to a susceptible line, designated ARS-Fp-S, following either laboratory or natural on-farm challenge. The objectives of this study were to determine the temporal kinetics of gene expression between experimentally-challenged ARS-Fp-R and ARS-Fp-S fish and the correlation between gene expression and pathogen load. We developed a GeXP multiplex RT-PCR assay to simultaneously examine expression of immune-relevant genes, concentrating on tumor necrosis factor and interleukin-1 ligand/receptor systems and acute phase response genes. Spleen tissue was sampled at 6 h, 24 h, 48 h and 144 h post-challenge and pathogen load quantified by qPCR. Transcript abundance of cytokine genes tnfa1, tnfa2, tnfa3, il1b1, il1b2, il11a; acute phase response genes saa and drtp1; and putative cytokine receptors il1r1-like-b, il1r2, tnfrsf1a, tnfrsf9, tnfrsf1a-like-b increased following challenge while the transcript abundance of il1r-like-1 and tnfrsf1a-like-a decreased compared to PBS-injected line-matched control fish. Principal component analysis identified transcript levels of genes il1r-like-1 and tnfrsf1a-like-a as exhibiting differential expression between genetic lines. In summary, Fp i.p. injection challenge elicited a proinflammatory cytokine gene expression response in the spleen, with ARS-Fp-R line fish exhibiting modestly higher basal expression levels of several putative cytokine receptors. This study furthers the understanding of the immune response following Fp challenge and differences in gene expression associated with selective breeding for disease resistance.

Molecular characterization and expression analysis of toll-like receptor 2 in response to bacteria in silvery pomfret intestinal epithelial cells

Toll-like receptor 2 (TLR2) has been shown to play a crucial role in the host defense of pathogenic microbes in innate immunity. In this study, the full-length cDNA of TLR2 in silvery pomfret (Pampus argenteus) was cloned by homology cloning and the rapid amplification of cDNA ends (RACE) technique. The complete cDNA sequence of TLR2 was 2932 bp, containing an open reading frame (ORF) of 2469 bp encoding 822 amino acids. A multiple alignment analysis of the silvery pomfret TLR2 protein-coding sequence with other known TLR2 sequences from Oplegnathus fasciatus, Epinephelus coioides, Larimichthys crocea, Miichthys miiuy, Oreochromis niloticus, Paralichthys olivaceus, Trematomus bernacchii, Sparus aurata, and Chionodraco hamatus exhibited a high degree of homology of 78.83%, 75.91%, 74.21%, 74.94%, 71.95%, 72.57%, 73.68%, 75%, and 72.52 respectively, between these fish. Analysis of the TLR2 domain structures indicated that TLR2 from the silvery pomfret has the typical structural features of proteins that belong to the TLR family, including one transmembrane domain, eleven leucine-rich repeats (LRRs), and one Toll/IL-1 receptor homology domain (TIR). In vitro immunostimulation experiments revealed that Lactobacillus plantarum and Clostridium butyricum induce high levels of TLR2 mRNA and protein expression, but they induce only moderate levels of IL-8 and TNF-α production compared to Vibrio anguillarum. This suggests that TLR2 might play a vital role in the L. plantarum and C. butyricum-mediated immune response. In contrast, V. anguillarum significantly increased the secretion of IL-8 and TNF-α and induced cell apoptosis and necrosis. Due to the lower expression of TLR2 and higher levels of IL-8 and TNF-α induced by V. anguillarum, we hypothesize that a V. anguillarum infection is independent of the TLR2-induced production of pro-inflammatory cytokines. These results indicate that TLR2 may be involved in molecular interactions between the host and commensal bacteria, that exist in the silvery pomfret intestinal tract.

Characterization of Toll-like receptor gene expression in goldfish (Carassius auratus) during Dactylogyrus intermedius infection

Toll-like receptors (TLRs), the first and best understood innate immune receptors, play a notable role in the innate immune system by sensing pathogenic agents and initiating appropriate immune responses. However, studies about the roles of fish TLRs in response to the infection of the ectoparasitic monogenean Dactylogyrus intermedius have been surprisingly vacant. In the present study, cDNA fragments of five members of TLRs family in goldfish (Carassius auratus) were cloned and the expression patterns of nine TLRs in five tissues at different time points during D. intermedius infection were subsequently investigated. We found that the expressions of TLR4, TLR5, TLR20 and TLR22 were significantly elevated after infection at some time points, of which the transcription of TLR5 was progressively increased nearly in all tissues, whereas the mRNA levels of other TLRs (TLR2, 3, 7, 9 and 21) were down-regulated or showed no significant change compared with the control at most time points. Additionally, this paper was also conducted to explore the expression of above TLRs after re-infected with D. intermedius. The results showed a significant upregulation of TLR4, TLR5 and TLR22 in all tested tissues at these two time points, especially the levels of TLR4 and TLR22 expression, were even higher comparing with the first infection. Besides, tissue-specific expression analysis revealed that spleen featured the highest expressions of almost all the TLR-encoding genes among detected tissues. The informations obtained here could be helpful towards understanding the functions of TLRs in response to parasitic infection in goldfish and provide new insights for the development of preventive and therapeutic approaches against D. intermedius infection.

The Function of Fish Cytokines

What is known about the biological activity of fish cytokines is reviewed. Most of the functional studies performed to date have been in teleost fish, and have focused on the induced effects of cytokine recombinant proteins, or have used loss- and gain-of-function experiments in zebrafish. Such studies begin to tell us about the role of these molecules in the regulation of fish immune responses and whether they are similar or divergent to the well-characterised functions of mammalian cytokines. This knowledge will aid our ability to determine and modulate the pathways leading to protective immunity, to improve fish health in aquaculture.

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

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

Characterization of Toll-like receptor gene expression and the pathogen agonist response in the antarctic bullhead notothen Notothenia coriiceps

Notothenia coriiceps, a typical Antarctic notothenioid teleost, has evolved to adapt to the extreme Antarctic marine environment. We previously reported an extensive analysis of the Antarctic notothenioid transcriptome. In this study, we focused on a key component of the innate immune system, the Toll-like receptors (TLRs). We cloned the full-length sequence of 12 TLRs of N. coriiceps. The N. coriiceps transcriptome for TLR homologue (ncTLR) genes encode a typical TLR structure, with multiple extracellular leucine-rich regions and an intracellular Toll/IL-1 receptor (TIR) domain. Using phylogenetic analysis, we established that all of the cloned ncTLR genes could be classified into the same orthologous clade with other teleost TLRs. ncTLRs were widely expressed in various organs, with the highest expression levels observed in immune-related tissues, such as the skin, spleen, and kidney. A subset of the ncTLR genes was expressed at higher levels in fish exposed to pathogen-mimicking agonists, heat-killed Escherichia coli, and polyinosinic-polycytidylic acid (poly(I:C)). However, the mechanism involved in the upregulation of TLR expression following pathogen exposure in fish is currently unknown. Further research is required to elucidate these mechanisms and to thereby increase our understanding of vertebrate immune system evolution.

A short history of research on immunity to infectious diseases in fish

This review describes the history of research on immunity to infectious diseases of fish in the period between 1965 and today. Special attention is paid to those studies, which are dealing with the interaction between immune system and invading pathogens in bony fish. Moreover, additional biographic information will be provided of people involved. In the 1960s and 1970s the focus of most studies was on humoral (Ig, B-cell) responses. Thorough studies on specific cellular (T-cell) responses and innate immunity (lectins, lysozyme, interferon, phagocytic cells) became available later. In the period between 1980 and today an overwhelming amount of data on regulation (e.g. cell cooperation, cytokines) and cell surface receptors (e.g. T-cell receptor; MHC) was published. It became also clear, that innate responses were often interacting with the acquired immune responses. Fish turned out to be vertebrates like all others with a sophisticated immune system showing specificity and memory. These basic data on the immune system could be applied in vaccination or in selection of disease resistant fish. Successful vaccines against bacterial diseases became available in the 1970s and 1980s. Effective anti-viral vaccines appeared from the 1980s onwards. There is no doubt, that Fish Immunology has become a flourishing science by the end of the 20th century and has contributed to our understanding of fish diseases as well as the success of aquaculture.

Molecular and functional characterization of IL-1 receptor type 2 in grass carp: a potent inhibitor of IL-1β signaling in head kidney leukocytes

IL-1 receptor type 2 (IL-1R2) is known as one of natural IL-1β singling inhibitors in mammals. However, the functional role of IL-1R2 in fish remains largely unknown. In this study, grass carp (Ctenopharyngodon idellus) IL-1R2 (gcIL-1R2) was identified and functionally characterized. Similar to its fish homologs, the deduced protein of gcIL-1R2 possessed two Ig-like domains in its extracellular region but lacked an intracellular signaling domain. The involvement of gcIL-1R2 in immune response was demonstrated by investigating its expression profiles in head kidney and head kidney leukocytes (HKLs) following in vivo bacterial infection and in vitro LPS treatment, respectively. Moreover, recombinant grass carp IL-1β (rgcIL-1β) was able to stimulate gcIL-1R2 mRNA expression with a rapid kinetics. This stimulation was possibly dependent on p38, JNK, p42/44 and NF-κB pathways in grass carp HKLs, revealing a new regulatory point of IL-1β signaling at receptor level in fish. Furthermore, recombinant protein of the gcIL-1R2 extracellular region (rgcIL-1R2) was demonstrated to interact with rgcIL-1β by using ELISA, elucidating the binding specificity of gcIL-1R2. Importantly, the stimulatory effect of rgcIL-1β on its own mRNA expression was blocked by rgcIL-1R2 in a dose-dependent manner in grass carp HKLs, providing the evidence for a functional role of IL-1R2 in IL-1β signaling in teleost. These findings suggested that teleost IL-1R2 may serve as a local naturally occurring inhibitor involving in IL-1β signaling as seen in mammals.

Soluble interleukin-1 receptor, a potential negative regulator of orange-spotted grouper Epinephelus coioides interleukin-1 system

In this study, the cDNA sequence encoding interleukin-1 (Il-1) receptor-like protein of orange-spotted grouper Epinephelus coioides was obtained. The newly identified sequence was named soluble type I Il-1 receptor (sIl-1rI) owing to its structural composition, which had two Ig-like domains, lack of transmembrane region and the Toll/interleukin-1 receptor (TIR) domain, similar to the brown rat Rattus norvegicus soluble Il-1rI. In addition, sequence comparison and phylogenetic analysis indicated that E. coioides sequence had a closer relationship with Il-1rI than Il-1rII. Real-time PCR revealed that sil-1rI mRNA expression presented a process of decrease, restoration and increase in Cryptocaryon irritans-infected E. coioides. The negative correlation between Il-1β and sil-1rI mRNA in C. irritans-infected head-kidney implied the potential negative regulatory role of sil-1rI in E. coioides Il-1 system. The leucocytes incubated with lipopolysaccharide or polyriboinosinic polyribocytidylic acid exhibited different expression profiles of sil-1rI. Recombinant Il-1β (rIl-1β) protein was capable of inducing sil-1rI mRNA under the concentration of 100 ng ml(-1) , suggesting that high dosage or excess Il-1β would stimulate the expression of sil-1rI to maintain the homoeostasis of E. coioides Il-1 system. For the first time, the role of teleost Il-1rI in parasite infection has been identified, and soluble Il-1r was found in fish.

Advances in research of fish immune-relevant genes: a comparative overview of innate and adaptive immunity in teleosts

Fish is considered to be an important model in comparative immunology studies because it is a representative population of lower vertebrates serving as an essential link to early vertebrate evolution. Fish immune-relevant genes have received considerable attention due to its role in improving understanding of both fish immunology and the evolution of immune systems. In this review, we discuss the current understanding of teleost immune-relevant genes for both innate and adaptive immunity, including pattern recognition receptors, antimicrobial peptides, complement molecules, lectins, interferons and signaling factors, inflammatory cytokines, chemokines, adaptive immunity relevant cytokines and negative regulators, major histocompatibility complexes, immunoglobulins, and costimulatory molecules. The implications of these factors on the evolutionary history of immune systems were discussed and a perspective outline of innate and adaptive immunity of teleost fish was described. This review may provide clues on the evolution of the essential defense system in vertebrates.

The innate immune-related genes in catfish

Catfish is one of the most important aquaculture species in America (as well as in Asia and Africa). In recent years, the production of catfish has suffered massive financial losses due to pathogen spread and breakouts. Innate immunity plays a crucial role in increasing resistance to pathogenic organisms and has generated increasing interest in the past few years. This review summarizes the current understanding of innate immune-related genes in catfish, including pattern recognition receptors, antimicrobial peptides, complements, lectins, cytokines, transferrin and gene expression profiling using microarrays and next generation sequencing technologies. This review will benefit the understanding of innate immune system in catfish and further efforts in studying the innate immune-related genes in fish.

Cloning of the IL-1β3 gene and IL-1β4 pseudogene in salmonids uncovers a second type of IL-1β gene in teleost fish

To date two closely related interleukin-1β genes (IL-1β1 and IL-β2) have been found in salmonids. The cloning of trout and salmon IL-1β3, and a salmon IL-1β4 pseudogene reveals that two types of IL-1β genes exist in teleost species. Type I teleost IL-1β genes, including salmonid IL-1β3, share a similar 6 coding exon structure as in tetrapods. Type II teleost IL-1β genes, e.g. salmonid IL-1β1-2, lack one or two coding exons at their 5'-end, and share higher identities within this subgroup than within the type I subgroup. Both types of IL-1β genes have been found in species of Salmoniformes, Perciformes and Beloniformes, suggesting the divergence occurred early in teleost evolution. Trout IL-1β3 is highly expressed in ovary suggesting a role in reproduction. A relatively high constitutive expression in gills, spleen and kidney and the up-regulation by PAMPs, proinflammatory cytokines and viral infection suggests IL-1β3 also has a role in inflammation and host defence.

Description of an Atlantic salmon (Salmo salar L.) type II interleukin-1 receptor cDNA and analysis of interleukin-1 receptor expression in amoebic gill disease-affected fish

Previously, we showed that IL-1β transcription is induced in the gills of amoebic gill disease (AGD)-affected fish in an AGD lesion-restricted fashion. However, in this environment, there is very little evidence of inflammation on histopathological or transcriptional levels and we hypothesised that aberrant signalling may occur. As a first step in investigating this issue, we cloned and sequenced the Atlantic salmon IL-1 receptor type II (IL-1RII) mRNA, and then examined the expression of both the IL-1RI (IL-1 receptor-like protein) and II during Neoparamoeba perurans infection. In gill lesions from AGD-affected fish, a step-wise temporal increase in the relative expression of IL-1β coincided with a significant reduction in IL-1RI, whereas the IL-1RII mRNA remained unchanged. Down-regulation of IL-1RI could explain the paucity of inflammation in affected tissue, although simultaneous up-regulation of IL-1β-inducible transcripts indicated that this is not due to a complete blockage of the IL-1RI pathway. Rather, it appears that IL-1RI transcription is reduced and this rate limits the effects of chronic IL-1β over-expression.

Discovery of the DIGIRR gene from teleost fish: a novel Toll-IL-1 receptor family member serving as a negative regulator of IL-1 signaling

Toll-IL-1R (TIR) family members play crucial roles in a variety of defense, inflammatory, injury, and stress responses. Although they have been widely investigated in mammals, little is known about TIRs in ancient vertebrates. In this study, we report a novel double Ig IL-1R related molecule (DIGIRR) from three model fish (Tetraodon nigroviridis, Gasterosteus aculeatus, and Takifugu rubripes), adding a previously unknown homolog to the TIR family. This DIGIRR molecule contains two Ig-like domains in the extracellular region, one Arg-Tyr-mutated TIR domain in the intracellular region, and a unique subcellular distribution within the Golgi apparatus. These characteristics distinguish DIGIRR from other known family members. In vitro injection of DIGIRR into zebrafish embryos dramatically inhibited LPS-induced and IL-1β-induced NF-κB activation. Moreover, in vivo knockdown of DIGIRR by small interfering RNA significantly promoted the expression of IL-1β-stimulated proinflammatory cytokines (IL-6 and IL-1β) in DIGIRR-silenced liver and kidney tissues and in leukocytes. These results strongly suggest that DIGIRR is an important negative regulator of LPS-mediated and IL-1β-mediated signaling pathways and inflammatory responses. The Arg-Tyr-mutated site disrupted the signal transduction ability of DIGIRR TIR. Evolutionally, we propose a hypothesis that DIGIRR and single Ig IL-1R related molecule (SIGIRR) might originate from a common ancient IL-1R-like molecule that lost one (in DIGIRR) or two (in SIGIRR) extracellular Ig-like domains and intracellular Ser and Arg-Tyr amino acids. DIGIRR might be an evolutionary "transitional molecule" between IL-1R and SIGIRR, representing a shift from a potent receptor to a negative regulator. These results help define the evolutionary history of TIR family members and their associated signaling pathways and mechanisms.

Association between Yersinia ruckeri infection, cytokine expression and survival in rainbow trout (Oncorhynchus mykiss)

The immune response against bacterial pathogens has been widely studied in teleosts and it is evident that survival chances differ significantly within a host population. Identification of indicators for susceptibility and responsiveness will improve our understanding of this host-pathogen interaction. The present work shows that the transcripts of cytokine genes in blood cells sampled three days post-infection was significantly higher in fish which obtained a high bacteriemia and died at later time points when compared to both non-infected control fish and infected fish that survived the infection. Rainbow trout were infected by bath challenge in a bacterial suspension (LD(60) dose, 1.8 × 10(9) CFU/ml Yersiniaruckeri for 1 h) and subsequently transferred to individual aquaria for 30 days of observation. Blood samples were analyzed for presence of Y. ruckeri both by culture and quantitative RT real-time PCR (qRT-PCR) and transcript levels of 28 genes encoding molecules which are important in the immune response. The transcript levels of a number of central cytokines, chemokines and cytokine receptors (IL-1β, IL-6, IL-8, IL-10, TNF-α, IL-receptor II) were significantly increased in infected fish that died later. In addition, a significantly higher amount of Y. ruckeri was found in the blood of the fish that died when compared to survivors. The study indicates that highly susceptible trout obtain an early heavy septicemia infection, which elicits a high up-regulation of the transcript of pro-inflammatory cytokines. Thus, less susceptible fish are protected by other factors and contract merely a weak non-lethal infection eliciting no or a weak cytokine response.

Stress-related hormones modulate cytokine expression in the head kidney of gilthead seabream (Sparus aurata)

Neuro-endocrine and immune systems closely interact in fish, and their regulation is crucial for the maintenance of good health of cultured fish. We have used the seabream head kidney to study whether stress-related hormones can modulate the immune response. For this purpose, the effects of adrenaline, adrenocorticotropic hormone (ACTH) and cortisol on the expression of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) and the anti-inflammatory cytokine TGF-beta1 were determined by means of quantitative real-time PCR on isolated head kidney cells. ACTH (150 ng mL(-1)) caused an acute increase of TNF-alpha and IL-6 mRNA levels as well as an inhibition of IL-1beta expression. The expression of the anti-inflammatory cytokine TGF-beta1 was also increased, although in a lower extent. Adrenaline (1 muM) early effects were only clear inhibiting IL-1beta expression but not TNF-alpha, IL-6 or TGF-beta1 mRNA levels, while a longer exposure to the hormone inhibited all cytokines. Moreover, cortisol (50 and 100 ng mL(-1)) reduced the expression of all cytokines in a dose-dependent manner. Bacterial lipopolysaccharide (LPS) stimulated IL-1beta expression and inhibited that of the anti-inflammatory TGF-beta1, although it was ineffective on TNF-alpha and IL-6. In addition, adrenaline and cortisol decreased the LPS-stimulated IL-1beta expression, further demonstrating their previously reported anti-inflammatory effects. The combination of ACTH and LPS, on the other hand, did not affect LPS-stimulated IL-1beta expression but was effective increasing TNF-alpha expression. Taking all these results in consideration, we conclude that the expression of pro- and anti-inflammatory cytokines in the seabream head kidney is highly influenced by stress-related hormones, thus indicating an important role for the endocrine system in the modulation of the immune response in teleost fish.

The innate immune response of finfish--a review of current knowledge

The decline in the fisheries of traditional marine species has been an incentive for the diversification of today's aquaculture sector into the intensive rearing of many finfish species. The increasing interest in commercial farming of different finfish species is expected to result in similar environmental and husbandry-related problems as have been experienced in the development of the salmonid farming industry. An understanding of the biology of the fish species being cultured, in particular the immune response is important for improved husbandry and health management of the species. The innate immune system of fish has generated increasing interest in recent years and is now thought to be of key importance in primary defence and in driving adaptive immunity. This review focuses on key components (cellular and humoral) of the innate immune responses of different fish species of commercial importance.

The type II interleukin-1 receptor (IL-1RII) of the bony fish gilthead seabream Sparus aurata is strongly induced after infection and tightly regulated at transcriptional and post-transcriptional levels

Interleukin-1beta (IL-1beta) is the prototypic pro-inflammatory cytokine. All the biological effects of IL-1beta are mediated through interaction with type 1 IL-1 receptor (IL-1RI), whereas another receptor, called type 2 IL-1R (IL-1RII), lacks an intracellular signalling domain and acts as a decoy receptor that down-regulates responses to IL-1beta. Although both receptors are present in bony fish, their expression and biological role in the regulation of IL-1beta activity in non-mammalian vertebrates remain to be established. In this study, a homologue of mammalian IL-1RII was isolated and characterized in the gilthead seabream (Sparus aurata). The seabream IL-1RII harboured two Ig-like domains in its extracellular region and a short cytoplasmic tail lacking a signalling domain. The seabream IL-1RII cDNA showed an unexpectedly long 3'UTR compared with that from other species and contained three ATTTA instability motifs, which seem to be responsible for its relatively short half-life (less than 2h). The expression of seabream IL-1RII was dramatically up-regulated after infection with Vibrio anguillarum in all the immune tissues examined and was even more strongly induced than the IL-1beta gene in the head kidney, spleen and liver. Strikingly, the mRNA levels of IL-1RII were 15-fold higher than those of IL-1beta in the liver, suggesting a role for this organ in the neutralization of IL-1beta leaking into the systemic circulation from the sites of inflammation. In vitro, bacterial DNA and flagellin increased the mRNA levels of IL-1RII in macrophages, while only flagellin was able to weakly induce its expression in acidophilic granulocytes. Finally, the seabream IL-1RII was localized in the plasma membrane when expressed in HEK293 cells and was able to bind IL-1beta.

The interleukin-1 receptor family

The cytokines IL-1 and IL-18 are key molecules both in the innate and in the adaptive immune response. Their activity is mediated by specific receptors present on the membrane of target cells. It has become apparent that these receptors are members of a larger family of related receptors, most of which are apparently involved in the mechanisms of host defense. Thus, the large Toll/IL-1R (TIR) superfamily encompasses the Ig domain family (IL-1 receptors, IL-18 receptors, and IL-1R-like receptors), the leucine-rich domain family [the Toll-like receptors (TLR) and similar receptors], and a series of TIR domain-containing intracellular adapter molecules. The TIR superfamily is defined by a common intracellular TIR domain, involved in the initiation of signaling. A group of TIR domain-containing adapters (MyD88, TIRAP, TRIF, and TRAM) are differentially recruited to the Toll/IL-1 receptors, contributing to the specificity of signaling. Recent studies have also begun to unravel the mechanisms of negative regulation of the Toll/IL-1 receptors. The orphan receptor TIR8/SIGIRR, a member of TIR superfamily, while unable to initiate signaling, can negatively modulate the TIR-mediated responses. Other negative regulators of the Toll/IL-1R family include T1/ST2, some soluble forms of TLR, and MyD88s. The coordinated positive and negative regulation of the TIR activation ensures the appropriate modulation of the innate and inflammatory responses and avoids the risk of pathological derangement. This chapter will consider in detail the characteristics and functional role of the Ig domain receptor subfamily in the regulation of host defense and their possible role in pathology.

Biological activity of sea bass (Dicentrarchus labrax L.) recombinant interleukin-1beta

Biological activities of a putative mature sea bass interleukin-1beta peptide, produced as a recombinant protein (rIL-1beta) in Escherichia coli, have been investigated. The rIL-1beta contains a 6-histidine tag at the N-terminus, and protein purification has been achieved through this tag by affinity chromatography. Biological activities have been investigated both at the cellular and gene expression levels. In in vitro assays sea bass rIL-1beta induced the proliferation of murine D10.G4.1 cells and increased yeast phagocytosis by sea bass head kidney leukocytes. The purified cytokine was also tested in a lymphocyte-activation factor assay, where it induced the proliferation of sea bass thymocytes. Finally, in an in vivo assay, rIL-1beta administered intraperitoneally increased expression levels of the IL-1beta gene and activated macrophages to produce a cyclooxygenase 2 homologue (COX-2) gene in the head kidney.

Comparison of select innate immune mechanisms of fish and mammals

The study of innate immunity has become increasingly popular since the discovery of homologs of many of the innate immune system components and pathways in lower organisms including invertebrates. As fish occupy a key position in the evolution of the innate and adaptive immune responses, there has been a great deal of interest regarding similarities and differences between their defense mechanisms and those of higher vertebrates. This review focuses on describing select mechanisms of the innate immune responses of fish and the implications for evolution of immunity in higher vertebrates.

Analysis of genes isolated from lipopolysaccharide-stimulated rainbow trout (Oncorhynchus mykiss) macrophages

A primary cell culture system was used to obtain differentiated rainbow trout (Oncorhynchus mykiss) macrophages that were stimulated with Escherichia coli lipopolysaccharide (LPS-10 microg/ml) for 12 h in vitro. Messenger RNA from the LPS-stimulated cells was used to create two cDNA libraries from which a total of 1048 sequences were analyzed. A large number of cDNAs were obtained that could be related to immune function including structural proteins, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors, lectins and immunoglobulins, cytokines and chemokines, cell surface antigens, signal transduction proteins, antimicrobial peptides, and enzymes involved in eicosanoid synthesis. Selected genes that were analyzed by RT-PCR and real time PCR and found to be upregulated by LPS, included vascular cell adhesion molecule, the CCAAT/enhancer binding protein beta, the inhibitor of NF-kB alpha, CD209, a major histocompatibility class II-invariant chain protein, cyclin L1, acute phase serum amyloid A, and prostaglandin endoperoxide synthase 2.

Effects of lipopolysaccharide treatment on feeding of goldfish: role of appetite-regulating peptides

The gram-negative bacteria-derived endotoxin lipopolysaccharide (LPS) is known to play an important role in immune and neurological manifestations during bacterial infections. In mammals, peripheral or brain administration of LPS induces anorexia and is thought to exert its effects through activation of pro-inflammatory cytokines. In this study, we investigated the effects of peripheral (intraperitoneal, IP) and central (intracerebroventricular, ICV) injections of LPS on food intake of goldfish. Fish treated IP with 10, 25, 50, 100 or 250 ng/g LPS or ICV with 1, 10 and 100 ng/g LPS showed a significant dose-dependent decrease in food intake, compared to the saline-treated fish. We also examined the brain mRNA expression of several hypothalamic appetite-related neuropeptides in response to the administration of LPS. IP injections of LPS (100 ng/g) induced a decrease in NPY expression and an increase in CCK, CRF and CART expression. These results indicate that LPS is a potent anorexigenic factor in goldfish and that this endotoxin induces a reduction in appetite, at least in part, by influencing gene expression of appetite-related neuropeptides.

Cloning and characterisation of a putative ST2L homologue from Atlantic salmon (Salmo salar)

The ST2L receptor is a member of the interleukin-1 (IL-1) receptor family and has previously been cloned from human, mouse, rat and chicken. This orphan receptor has no known physiological role but has been implicated in T helper cell type 2 effector function. We describe in this report the cloning and characterisation of a cDNA encoding a homologue of ST2L in Atlantic salmon (Salmo salar). The salmon ST2L cDNA is 2364bp in length and has an open reading frame encoding a polypeptide of 582 amino acids. Similar to other members of the IL-1 receptor (IL-1R) family, the predicted protein has a potential signal peptide, extracellular immunoglobulin-like domains, a short transmembrane region and a characteristic cytoplasmic Toll-IL-1R domain. The predicted protein shows 33% identity and 44% similarity to the chicken ST2L homologue. Phylogenetic analyses cluster the putative salmon ST2L with the chicken and the mammalian ST2L homologues, away from the other members of the IL-1R family. Salmon ST2L is constitutively expressed in brain, white and red blood cells, head kidney, liver, gills and muscle, with highest level of expression in spleen. In vivo stimulation of salmon with lipopolysaccaride does not appear to have a significant effect on expression of the ST2L homologue.

Characterisation, expression and promoter analysis of an interleukin 10 homologue in the puffer fish, Fugu rubripes

Using computer-based tools, an interleukin (IL) 10 homologue has been identified from the puffer fish ( Fugu rubripes) genome database. This is the first report on the existence of an IL-10 homologue in a non-mammalian vertebrate species. The Fugu IL-10 gene is located within a 2790-bp fragment including 549 bp of coding sequence which translates into an 183-amino-acid protein. It is predicted to contain five exons and four introns, sharing the same organization with the mammalian IL-10 genes. The size of the introns in the Fugu IL-10 gene is much smaller compared to mammalian IL-10 genes, whilst the size of the exons is similar. The deduced protein sequence shares 44-50% homology with the mammalian IL-10 sequences, 39-42% with the viral IL-10 sequences and 37-42% with other members of the IL-10 family, IL-20 and IL-22. Southern blot analysis indicates that a single copy of the IL-10 gene is present in the Fugu genome. A very low level of constitutive expression was detected in tissues of healthy fish including liver, kidney, gut and spinal cord, whilst no expression was detectable in spleen, gill, brain, gonad and eye. Analysis of the transcription regulation elements in the promoter region revealed that trans elements are located in the region between 1 bp and 721 bp, cis elements between 934 bp and 1114 bp and a tumour necrosis factor alpha responsive transcription element was located 92 bp upstream of the TATA box.

Gyrodactylus derjavini infection elicits IL-1beta expression in rainbow trout skin

Specific gene expression of the pro-inflammatory cytokine IL-1beta and the type II IL-1beta receptor (IL-1RII, 'decoy receptor') was studied in skin of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) fry during infection with the ectoparasitic monogenean Gyrodactylus derjavini Mikailov, 1975. Cytokine expression was studied in both primary and secondary infections using a semi-quantitative RT-PCR technique. Generally, low levels of specific IL-1beta1, IL-1beta2 and IL-1RII gene transcription were found in uninfected hosts. In contrast, a clear induction of both IL-1beta isoforms could be observed during the initial phases of primary G. derjavini infections. A less obvious induction of IL-1beta expression was seen in secondary infections imposed just after recovery from the priming infection. However, challenge infections given one-month post full recovery of the primary infections did not elicit transcription levels above those seen in skin samples from uninfected hosts. Despite this, hosts carrying a secondary infection elicited a stronger response toward G. derjavini thus expelling parasites quicker than their nai;ve counterparts. When induced, indications of a more tight regulation of the IL-1beta1 isoform compared to IL-1beta2 could be observed. Increased expression of IL-1RII was seen later during the course of a primary infection and could be involved in the observed down regulation of IL-1, especially the beta1 isoform. The current study represents the first example of cytokine expression in fish induced by an ectoparasitic infection and indicates the importance of localised mucosal immune reactions in responses of fish towards gyrodactylids.

Evolution of interleukin-1beta

All jawed vertebrates possess a complex immune system, which is capable of anticipatory and innate immune responses. Jawless vertebrates possess an equally complex immune system but with no evidence of an anticipatory immune response. From these findings it has been speculated that the initiation and regulation of the immune system within vertebrates will be equally complex, although very little has been done to look at the evolution of cytokine genes, despite well-known biological activities within vertebrates. In recent years, cytokines, which have been well characterised within mammals, have begun to be cloned and sequenced within non-mammalian vertebrates, with the number of cytokine sequences available from primitive vertebrates growing rapidly. The identification of cytokines, which are mammalian homologues, will give a better insight into where immune system communicators arose and may also reveal molecules, which are unique to certain organisms. Work has focussed on interleukin-1 (IL-1), a major mediator of inflammation which initiates and/or increases a wide variety of non-structural, function associated genes that are characteristically expressed during inflammation. Other than mammalian IL-1beta sequences there are now full cDNA sequences and genomic organisations available from bird, amphibian, bony fish and cartilaginous fish, with many of these genes having been obtained using an homology cloning approach. This review considers how the IL-1beta gene has changed through vertebrate evolution and whether its role and regulation are conserved within selected non-mammalian vertebrates.

Neuroendocrine-immune interactions in fish: a role for interleukin-1

Bi-directional communication between the hypothalamus-pituitary-adrenal (HPA)-axis and the sympathetic nervous system with the immune system is crucial to ensure homeostasis. Shared use of ligands and especially receptors forms a key component of this bi-directional interaction. Glucocorticoids (GC), the major end products of the HPA-axis differentially modulate immune function. Cytokines, especially interleukin-1 (IL-1), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), ensure immune signalling to the neuroendocrine system. In addition, hormones from leukocyte origin such as corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and beta-endorphin, as well as centrally synthesised and secreted cytokines, contribute to the communication network. In teleost fish cortisol is the major product of the hypothalamus-pituitary-interrenal (HPI)-axis which is the teleost equivalent of the HPA-axis. Moderate and substantial increases in cortisol during stressful circumstances negatively affect B-lymphocytes, whereas rescue of neutrophilic granulocytes may support innate immunity. Recent elucidation of lower vertebrate cytokine sequences has facilitated research into neuroendocrine-immune interactions in teleosts and the first evidence for a significant function of interleukin-1 in the bi-directional communication is discussed.

Cloning of a Salmo salar interleukin-1 receptor-like cDNA

The interleukin-1 receptor/toll-like receptor (IL-1R/TLR) superfamily, defined by a cytosolic Toll/IL-1R (TIR) signalling domain, participates in host responses to injury and infection. We describe in this study the cloning of a cDNA encoding a Salmo salar interleukin-1 receptor-like protein (SalIL-1RLP). SalIL-1RLP comprises a potential signal peptide, three extracellular immunoglobulin domains, a short transmembrane region and an intracellular region that contains the TIR domain. The predicted amino acid sequence of SalIL-1RLP displays 43-44% similarities and 31% identities to chicken and human IL-1RI sequences. Within the intracellular region, SalIL-1RLP displays highest similarity (59%) and identity (46%) to the chicken IL-1RI sequence. Two different 5' distal UTRs were identified among six salmon IL-1RLP clones. The six clones, however, displayed identical 5' proximal UTRs, coding regions and 3' UTRs. SalIL-1RLP expression is induced in liver, head kidney, spleen and gills upon injection of salmon with bacterial lipopolysaccharide. Sequence comparisons, protein domain structures, expression patterns and phylogenetic analyses indicate that SalIL-1RLP is most closely related to type I interleukin-1 receptors and interleukin-1 receptor related proteins.

Cloning of a novel rainbow trout (Oncorhynchus mykiss) CC chemokine with a fractalkine-like stalk and a TNF decoy receptor using cDNA fragments containing AU-rich elements

An activation-specific cDNA library was made from phytohaemagglutinin (PHA)-activated haematopoietic cells of the rainbow trout (Oncorhynchus mykiss) using the technique of suppression subtractive hybridization. Several immune system genes were identified, including an interleukin (IL)1 receptor related protein and two invariant chain-like proteins. Many clones showed no similarity by BLAST search, but had AU-rich elements. These fragments were labelled and used for hybridization with a PHA-activated head kidney cDNA library. Several immune system genes were isolated by this technique, including a tumour necrosis factor (TNF) decoy receptor and a novel chemokine, designated trout chemokine 2. The TNF receptor is 285 amino acids in length and is 32-36% identical to a brook trout and human homologue. The CC chemokine is 44% identical at the amino acid level to a carp CC chemokine and approximately 20% identical to several mammalian CC chemokines. However, it has a 91 amino acid stalk-like structure at its COOH end, which is similar to the glycosylated stalk of fractalkine, a mammalian CX(3)C chemokine. In summary, AU-rich fragments obtained from an activation-specific library proved useful as hybridization probes for isolating trout immune system genes.

Molecular cloning of an IL-8-like CXC chemokine and tissue factor in rainbow trout (Oncorhynchus mykiss) by use of suppression subtractive hybridization

Suppression subtractive hybridization (SSH) was performed to construct a Rainbow trout cDNA library enriched in sequences up-regulated in head kidney leukocytes after lipopolysaccharide (LPS) and tumour necrosis factor alpha (TNFalpha) stimulation. Random sequencing of fifty clones allowed the identification of a Rainbow trout interleukin 8 (IL-8)-related CXC chemokine, as well as the Rainbow trout tissue factor (TF) precursor. Expression of both the IL-8-like chemokine and TF is induced after LPS and TNFalpha stimulation, indicating that they are associated with inflammatory responses in fish, as has been suggested in mammals. These results confirm the potential of SSH to identify cytokines and immuno-regulatory genes in fish.