Teleostean IL11b exhibits complementing function to IL11a and expansive involvement in antibacterial and antiviral responses

Toxic effects and transcriptome analysis of the early life stages of Larimichthys crocea exposed to the bloom-forming dinoflagellate Alexandrium tamarense

This study investigated the effects of the bloom-forming dinoflagellate Alexandrium tamarense and its potentially associated paralytic shellfish toxins on the early life stages of Larimichthys crocea (large yellow croaker) by integrating physiological effects with transcriptomic analysis to explore the molecular mechanisms underlying these harmful impacts. The results showed that 48-h acute exposure to A. tamarense culture and cell-free filtrate significantly reduced the heart rate in embryos and increased mortality rates in both embryos and larvae. Transcriptome sequencing of the filtrate-exposed group identified 130 differentially expressed genes in the embryo group and 884 in the juvenile group. Further analysis revealed that algal exposure triggered the activation of innate immunity in embryos, as evidenced by the significant upregulation of immune-related cytokines such as CCL20, IL11, and ILRA10. These genes were enriched in the cytokine-cytokine receptor interaction pathway and may induce immune responses through their respective downstream pathways. Additionally, the downregulation of the RNA polymerase and ribosome pathways suggests that protein synthesis was affected during the embryo stress response induced by A. tamarense. In juveniles, genes related to cardiac function, particularly those associated with myocardial contraction and calcium ion regulation, were downregulated after exposure to algal filtrate, further suggesting that A. tamarense, possibly through paralytic shellfish toxins, inhibits the heart function of L. crocea. The findings of this study elucidate the toxicological mechanisms of A. tamarense on the early life stages of L. crocea, providing scientific evidence for the impact of harmful algal blooms on marine life health and offering valuable insights for management strategies in aquaculture.

Contribution of interleukins in the regulation of teleost fish immunity: A review from the perspective of regulating macrophages

Interleukins (ILs) are potent secreted regulators of a wide range of cell types and cellular activities, particularly in the immune system. They are able to participate in intercellular communication in homeostasis and disease, thereby exerting immune functions. Macrophages serve as the innate immune cells of vertebrates and play a pivotal role in defending against and eliminating external pathogens. In mammals, the immune response mounted by macrophages is intricately linked to ILs. Given the fact that teleost fish have evolved an innate immune system that closely resembles those of mammals, particularly in terms of the functionality of macrophages, raises the intriguing possibility that the regulatory function of ILs in macrophage-mediated immunity might be evolutionarily conserved across both mammal and teleost fish lineages. Consequently, from the perspective of interleukin regulation of macrophages, this review outlines the relationship between ILs and macrophages in teleost fish, and elucidates the regulatory role of ILs of immune cell function in teleost fish, thereby contributing to our understanding of the key role of these cytokines in the prevention and control of aquaculture diseases.

Roles of IL-11 in the regulation of bone metabolism

Bone metabolism is the basis for maintaining the normal physiological state of bone, and imbalance of bone metabolism can lead to a series of metabolic bone diseases. As a member of the IL-6 family, IL-11 acts primarily through the classical signaling pathway IL-11/Receptors, IL-11 (IL-11R)/Glycoprotein 130 (gp130). The regulatory role of IL-11 in bone metabolism has been found earlier, but mainly focuses on the effects on osteogenesis and osteoclasis. In recent years, more studies have focused on IL-11's roles and related mechanisms in different bone metabolism activities. IL-11 regulates osteoblasts, osteoclasts, BM stromal cells, adipose tissue-derived mesenchymal stem cells, and chondrocytes. It's involved in bone homeostasis, including osteogenesis, osteolysis, bone marrow (BM) hematopoiesis, BM adipogenesis, and bone metastasis. This review exams IL-11's role in pathology and bone tissue, the cytokines and pathways that regulate IL-11 expression, and the feedback regulations of these pathways.

Identification and functional characterization of Interleukin-11 in goldfish (Carassius auratus L.)

Interleukin-11 (IL-11) is a versatile cytokine that modulates cellular differentiation and proliferation in various cell types and tissues. In this study, IL-11 gene from goldfish (Carassius auratus L.) has been identified and characterized. Goldfish IL-11 (gfIL-11) has an open reading frame (ORF) that spans 591 base pairs (bp). The ORF encodes a precursor protein consisting of 196 amino acids (aa), which includes a 26 aa signal peptide and a conserved domain belonging to the IL-11 superfamily. Based on phylogenetic analysis, gfIL-11 was found to be closely related to other IL-11 homologues identified in various fish species. The gfIL-11 transcript exhibited varied expression levels across all the analyzed tissues, with the highest expression observed in the gill and spleen. Treatment of goldfish head kidney leukocytes (HKLs) with LPS and live Aeromonas hydrophila, increased gfIL-11 mRNA expression level. Recombinant gfIL-11 protein (rgIL-11) induced a dose-dependent production of TNF-α and IFNγ from goldfish HKLs. Furthermore, the administration of rgIL-11 to goldfish HKLs triggered an increase in the expression of various transcription factors such as MafB, cJun, GATA2, and Egr1, which play a vital role in the differentiation of myeloid precursors into macrophages and monocytes. Our findings provide evidence that IL-11 is a crucial cytokine that promotes cell proliferation, immune response, and differentiation across various hematopoietic lineages and stages of goldfish.

CsIL-11, a teleost interleukin-11, is involved in promoting phagocytosis and antibacterial immune defense

Interleukin (IL)-11 is a multifunctional cytokine belonging to the IL-6 family, which plays essential roles in immune response. However, much less is known about the immunological functions of IL-11 in teleost. In this study, we investigated the immune properties of a teleost IL-11 homologue (CsIL-11) from tongue sole Cynoglossus semilaevis. CsIL-11 possesses four conserved α-helices and conserved CsIL-11 receptor binding residues L86 and R187, and shares 23.3%-80.1% identities with other IL-11 homologues. CsIL-11 expression was constitutive in tissues, with most abundant in blood and least abundant in spleen, and upregulated by bacterial challenge in blood, spleen, and head kidney. Recombinant CsIL-11 (rCsIL-11) in the native form of monomer, could bind to peripheral blood leukocytes (PBLs) membrane and enhance the activation and phagocytosis of PBLs. When administered in vivo, rCsIL-11 could markedly promote the host to defend against microbial infection. Overall, our findings show that CsIL-11 plays a pivotal role in regulating PBLs phagocytosis and antibacterial immunity.

Molecular and immunological characterizations of interleukin-11 in large yellow croaker (Larimichthys crocea)

Interleukin (IL)-11 is a multifunctional cytokine that exerts a series of important immunomodulatory effects and exists in many tissues and cells. A 1106-bp nucleotide sequence representing the complete cDNA of IL-11 was obtained from large yellow croaker (Larimichthys crocea), containing an open reading frame (ORF) of 603 bp encoding for 200 amino acids (aa). The predicted LcIL-11 protein included a 12aa signal peptide and a conserved IL-11 domain. The polypeptide sequence identities between LcIL-11 and its counterparts in mammals and other fish are from 84% to 92% with known fish IL-11a and 22%-27% with fish IL-11b. LcIL-11 mRNA existed in most tissues with the most predominant expression in the gill. After immune challenge, the expression levels of LcIL-11 were induced largely in vivo and in vitro, with the peak-value of 32 times as much as the control in the liver at 24 h after Vibrio parahaemolyticus injection (p < 0.05) and the greatest value of 13.9 times as much as the control in LCK cells at 12 h after poly I:C stimulation (p < 0.05). Furthermore, the overexpression vector pcDNA3.1-LcIL-11 was constructed and transfected to LCK cells. Our results showed that the transcriptional expression levels of tumor necrosis factor (TNF)-α and myxovirus resistant protein (Mx) significantly up-regulated in LCK cells after LcIL-11 overexpression (p < 0.05). However, no significant changes of IL-1β, janus kinase (JAK)2 and signal transducers and activators of transcription (STAT)5 was detected. Our finding indicated that LcIL-11 might enhance TNF-α and antiviral protein Mx expression in large yellow croaker.

Identification, expression profiling and functional characterization of interleukin 11a ortholog from redlip mullet Liza haematocheila: Insight into its roles in the inflammation and apoptosis regulation

Interleukin 11 (IL-11) is a secretory cytokine with pleotropic properties, including anti-inflammatory and anti-apoptotic functions. This study aimed to functionally characterize a teleostean IL-11a ortholog from redlip mullet (LhIL-11a) through bioinformatic analysis, transcriptional expression profiling and protein function assays. The deduced LhIL-11a protein sequence is 200 amino acids long, with a predicted molecular weight of 23.168 kDa. Multiple sequence alignment indicates that LhIL-11a has a typical four-bundle architecture of α-helixes as observed in other IL-11s. The identity-similarity matrix show a higher identity between LhIL-11a and other fish IL-11a sequences. Phylogenetic analysis demonstrated that LhIL-11a falls within a clade including other fish counterparts. In the tissue distribution analysis, the highest constitutive expression of LhIL-11a mRNA was observed in the mullet gastrointestinal tract and brain tissues. Following the challenges with LPS, poly I:C and Lactococcus garvie, the transcription levels of LhIL-11a were significantly upregulated in both PBCs and liver. In the biological functional assay, recombinant LhIL-11a protein showed strong activities of suppressing pro-inflammatory cytokines and apoptotic gene expression in mullet kidney cells and reducing LPS stimulated NO production in murine macrophage cells. Overall, the findings in this study provide the experimental clues to understanding the functional roles of fish IL-11a in inflammation and apoptosis regulation during host defense against invading microbial pathogens.

Comparative analysis of the expression patterns of IL-1β, IL-11, and IL-34 in golden pompano (Trachinotus ovatus) following different pathogens challenge

Interleukins (ILs) are a subgroup of cytokines, which are molecules involved in the intercellular regulation of the immune system. These cytokines have been extensively studied in mammalian models, but systematic analyses of fish are limited. In the current study, 3 IL genes from golden pompano (Trachinotus ovatus) were characterized. The IL-1β protein contains IL-1 family signature motif, and four long helices (αA - αD) in IL-11 and IL-34, which were well conserved. All 3 ILs clustered phylogenetically with their respective IL relatives in mammalian and other teleost species. Under normal physiological conditions, the expression of IL-1β, IL-11, and IL-34 were detected at varied levels in the 11 tissues examined. Most of the 3 ILs examined were highly expressed in liver, spleen, kidney, gill, or skin. Following pathogenic bacterial, viral, or parasitic challenge, IL-1β, IL-11, and IL-34 exhibited distinctly different expression profiles in a time-, tissue-, and pathogen-dependent manner. In general, IL-1β was expressed at higher levels following challenge with all pathogens examined than was observed for IL-11 and IL-34. Furthermore, Streptococcus agalactiae and Cryptocaryon irritans caused higher levels of IL-1β and IL-11 expression than Vibrio harveyi and viral nervous necrosis virus (VNNV). The increased expression of IL-34 caused by VNNV and C. irritans were higher than that caused by V. harveyi and S. agalactiae. These results suggest that these 3 ILs in T. ovatus may play different effect pathogen type specific responses.

Biofloc technology (BFT): An alternative aquaculture system for prevention of Cyprinid herpesvirus 2 infection in gibel carp (Carassius auratus gibelio)

Gibel carp (Carassius auratus gibelio), a major aquaculture species in China, has emerged in a seriously epizootic disease caused by Cyprinid herpesvirus 2 (CyHV-2). There are no effective methods to prevent or control this serious disease. Biofloc technology (BFT) can improve water quality, reduce pathogens introduction, enhance cultured species immunity and disease resistance. In this study, a 30-day experiment was conducted to investigate the effect of BFT on innate immune response and disease resistance of gibel carp against CyHV-2 infection. Gibel carp was cultured at different total suspended solid (TSS) concentrations of 10, 300, 600, 800 and 1000 mg L^-1, which were named as groups BF0, BF300, BF600, BF800 and BF1000. Results showed that fish in groups BF600/800 had significantly higher weight gain (WG) and specific growth rate (SGR) than them in control group (BF0). The transcriptional levels of seven immune-related genes in BF300/600/800 groups, including myeloid-specific- peroxidase (MPO), keratin 8 (KRT 8), dual specificity phosphatase 1 (DUSP 1), interleukin-11 (IL-11), intelectin (ITLN), purine nucleoside phosphorylase 5α (PNP 5α) and c-type lysozyme (c-lys), were up-regulated significantly compared to BF0 group. Furthermore, cumulative mortality of gibel carp in BF600 group after being challenged with CyHV-2 reduced significantly. In vivo viral replication in kidney demonstrated that CyHV-2 load at 168 h post injection in BF600 group was significantly higher than that in BF0 group. In conclusion, BFT could improve growth, immune response and disease resistance of gibel carp, and the effect was related with TSS concentration. The optimal TSS concentration of 600-800 mg L^-1 was recommended in the present study.

Comparative study of the adjuvant potential of four Th0 cytokines of flounder (Paralichthys olivaceus) on an E. tarda subunit vaccine

Cytokines have the potential as adjuvants for the application of vaccines in mammals. However, the adjuvant potential of teleost cytokines was limited. In the present work, the adjuvant effects of four recombinant cytokines including IL-1β, IL-8, TNF-α and G-CSF on E. tarda subunit vaccine rOmpV were comparatively investigated in flounder (Paralichthys olivaceus). Compared with control, the levels of specific serum antibodies and IgM + B lymphocytes were significantly enhanced by rIL-1β, rIL-8 and rG-CSF, whereas rIL-1β and rIL-8 induced significantly higher levels than rG-CSF. All four cytokines enhanced the expression of genes involved in humoral and/or cellular immunities, whereas rIL-1β and rIL-8 induced highest levels of genes involved in humoral immunities and cellular immunities, respectively. Compared to the relative percent survivals (RPS) of control group (40%) and rOmpV plus rG-CSF group (54%), rOmpV plus rIL-1β or rIL-8 produced higher RPS of 75% and 68%, respectively. Our results indicated that rIL-1β and rIL-8 are promising adjuvants for subunit vaccines against E. tarda.

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.

Distinct herpesvirus resistances and immune responses of three gynogenetic clones of gibel carp revealed by comprehensive transcriptomes

Background

Gibel carp is an important aquaculture species in China, and a herpesvirus, called as Carassius auratus herpesvirus (CaHV), has hampered the aquaculture development. Diverse gynogenetic clones of gibel carp have been identified or created, and some of them have been used as aquaculture varieties, but their resistances to herpesvirus and the underlying mechanism remain unknown.

Results

To reveal their susceptibility differences, we firstly performed herpesvirus challenge experiments in three gynogenetic clones of gibel carp, including the leading variety clone A⁺, candidate variety clone F and wild clone H. Three clones showed distinct resistances to CaHV. Moreover, 8772, 8679 and 10,982 differentially expressed unigenes (DEUs) were identified from comparative transcriptomes between diseased individuals and control individuals of clone A⁺, F and H, respectively. Comprehensive analysis of the shared DEUs in all three clones displayed common defense pathways to the herpesvirus infection, activating IFN system and suppressing complements. KEGG pathway analysis of specifically changed DEUs in respective clones revealed distinct immune responses to the herpesvirus infection. The DEU numbers identified from clone H in KEGG immune-related pathways, such as “chemokine signaling pathway”, “Toll-like receptor signaling pathway” and others, were remarkably much more than those from clone A⁺ and F. Several IFN-related genes, including Mx1, viperin, PKR and others, showed higher increases in the resistant clone H than that in the others. IFNphi3, IFI44-like and Gig2 displayed the highest expression in clone F and IRF1 uniquely increased in susceptible clone A⁺. In contrast to strong immune defense in resistant clone H, susceptible clone A⁺ showed remarkable up-regulation of genes related to apoptosis or death, indicating that clone A⁺ failed to resist virus offensive and evidently induced apoptosis or death.

Conclusions

Our study is the first attempt to screen distinct resistances and immune responses of three gynogenetic gibel carp clones to herpesvirus infection by comprehensive transcriptomes. These differential DEUs, immune-related pathways and IFN system genes identified from susceptible and resistant clones will be beneficial to marker-assisted selection (MAS) breeding or molecular module-based resistance breeding in gibel carp.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3945-6) contains supplementary material, which is available to authorized users.

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.

Protective immunity in gibel carp, Carassius gibelio of the truncated proteins of cyprinid herpesvirus 2 expressed in Pichia pastoris

Cyprinid herpesvirus 2 (CyHV-2) infection is a newly emerged infectious disease of farmed gibel carp (Carassius gibelio) in China and causes huge economic losses to the aquaculture industry. In this study, the three membrane proteins encoded by genes ORF25, ORF25C, and ORF25D of CyHV-2 were truncated and expressed in yeast, Pichia pastoris. Screening of the recombinant yeasts was done by detecting the truncated proteins using Western blot. Through immunogold labeling, it was shown that proteins binding the colloidal gold were presented on the surface of cells. In the experiment of inhibition of virus binding by the recombinant truncated proteins, the TCID50 of the tORF25 group (10(4.1)/ml) was lower than that of tORF25C (10(4.6)/ml) or tORF25D groups (10(5)/ml). These results suggested that the proteins may be involved in attachment of the virus to the cell surface. Healthy gibel carp were immunized with 20 μg of tORF25, tORF25C, and tORF25D proteins, and the control group received PBS. Interleukin 11 (IL-11) expression in the spleens of the immunized fish peaked at day 4 and the complement component C3 (C3) genes were significantly up-regulated at day 7 post-immunization. Specific antibodies were measured in the three immunized groups and the titer detected in the tORF25 group reached 327, that was significantly higher than the tORF25C (247) or tORF25D (228) groups. When the immunized fish were challenged with live CyHV-2 by intraperitoneal injection the relative percent survival (RPS) of the tORF25, tORF25C, and tORF25D immunized groups was 75%, 63%, and 54%, respectively. The feasibility of the P. pastoris yeast expression system for the production of the recombinant truncated proteins and their apparent bioactivity suggests that tORF25, tORF25C, and tORF25D are potential candidate vaccines against Cyprinid herpesvirus 2 infection in gibel carp.

De novo assembly, characterization and functional annotation of Senegalese sole (Solea senegalensis) and common sole (Solea solea) transcriptomes: integration in a database and design of a microarray

Background

Senegalese sole (Solea senegalensis) and common sole (S. solea) are two economically and evolutionary important flatfish species both in fisheries and aquaculture. Although some genomic resources and tools were recently described in these species, further sequencing efforts are required to establish a complete transcriptome, and to identify new molecular markers. Moreover, the comparative analysis of transcriptomes will be useful to understand flatfish evolution.

Results

A comprehensive characterization of the transcriptome for each species was carried out using a large set of Illumina data (more than 1,800 millions reads for each sole species) and 454 reads (more than 5 millions reads only in S. senegalensis), providing coverages ranging from 1,384x to 2,543x. After a de novo assembly, 45,063 and 38,402 different transcripts were obtained, comprising 18,738 and 22,683 full-length cDNAs in S. senegalensis and S. solea, respectively. A reference transcriptome with the longest unique transcripts and putative non-redundant new transcripts was established for each species. A subset of 11,953 reference transcripts was qualified as highly reliable orthologs (>97% identity) between both species. A small subset of putative species-specific, lineage-specific and flatfish-specific transcripts were also identified. Furthermore, transcriptome data permitted the identification of single nucleotide polymorphisms and simple-sequence repeats confirmed by FISH to be used in further genetic and expression studies. Moreover, evidences on the retention of crystallins crybb1, crybb1-like and crybb3 in the two species of soles are also presented. Transcriptome information was applied to the design of a microarray tool in S. senegalensis that was successfully tested and validated by qPCR. Finally, transcriptomic data were hosted and structured at SoleaDB.

Conclusions

Transcriptomes and molecular markers identified in this study represent a valuable source for future genomic studies in these economically important species. Orthology analysis provided new clues regarding sole genome evolution indicating a divergent evolution of crystallins in flatfish. The design of a microarray and establishment of a reference transcriptome will be useful for large-scale gene expression studies. Moreover, the integration of transcriptomic data in the SoleaDB will facilitate the management of genomic information in these important species.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-952) contains supplementary material, which is available to authorized users.

Transcriptome analysis of epithelioma papulosum cyprini cells after SVCV infection

BACKGROUND

Spring viraemia of carp virus (SVCV) has been identified as the causative agent of spring viraemia of carp (SVC) and it has caused significant losses in the cultured common carp (Cyprinus carpio) industry. The molecular mechanisms that underlie the pathogenesis of the disease remain poorly understood. In this study, deep RNA sequencing was used to analyse the transcriptome and gene expression profile of EPC cells at progressive times after SVCV infection. This study addressed the complexity of virus-cell interactions and added knowledge that may help to understand SVCV.

RESULTS

A total of 33,849,764 clean data from 36,000,000 sequence reads, with a mean read length 100 bp, were obtained. These raw data were assembled into 88,772 contigs. Of these contigs, 19,642 and 25,966 had significant hits to the NR and Uniprot databases where they matched 17,642 and 13,351 unique protein accessions, respectively. At 24 h post SVCV infection (1.0 MOI), a total of 623 genes were differentially expressed in EPC cells compared to non-infected cells, including 288 up-regulated genes and 335 down-regulated genes. These regulated genes were primarily involved in pathways of apoptosis, oxidative stress and the interferon system, all of which may be involved in viral pathogenesis. In addition, 8 differentially expressed genes (DEGs) were validated by quantitative PCR.

CONCLUSIONS

Our findings demonstrate previously unrecognised changes in gene transcription that are associated with SVCV infection in vitro, and many potential cascades identified in the study clearly warrant further experimental investigation. Our data provide new clues to the mechanism of viral susceptibility in EPC cells.

Different expression profiles of Interleukin 11 (IL-11), Intelectin (ITLN) and Purine nucleoside phosphorylase 5a (PNP 5a) in crucian carp (Carassius auratus gibelio) in response to Cyprinid herpesvirus 2 and Aeromonas hydrophila

Interleukin 11 (IL-11), Intelectin (ITLN) and Purine nucleoside phosphorylase 5a (PNP5a) play important roles in innate immunity. In a previous study to identify differentially expressed immune-related genes, suppression subtractive hybridization (SSH) assay was used to characterize differentially expressed genes in crucian carp (Carassius auratus gibelio) infected with Cyprinid herpesvirus 2 (CyHV-2) in which IL-11, ITLN and PNP5a were identified to be the three most significantly up-regulated genes (Xu et al., Archives of Virology, 2014, http://dx.doi.org/10.1007/s00705-014-2011-9). In this study, the complete open reading frames (ORF) of IL-11, ITLN and PNP5a genes were cloned and sequenced. The full-length cDNAs of the three genes contained an ORF of 597, 945 and 882 bp, encoding a polypeptide of 198, 314 and 293 amino acids, respectively. Phylogenetic analysis indicated that the three genes shared high homology to other bony fish species including Zebrafish. Interestingly, the ITLN gene of crucian carp lacked a 10 aa peptide that was found in the C-terminal of other fish species. A real-time RT-PCR assay was developed to quantitatively examine their tissue distribution. We found that IL-11, ITLN and PNP5a were expressed at low levels in all of the tissues examined. To monitor the response of these genes to CyHV- 2 or Aeromonas hydrophila (A. hydrophila) infection, we determined the expression level of IL-11, ITLN and PNP5a at different time points after infection in kidney. Significant up-regulation of IL-11, ITLN and PNP5a was only observed 72 h post-CyHV-2 injection (P < 0.01), whereas significant up-regulation was observed as early as 6 h after infection with A. hydrophila (P < 0.01). Our results demonstrated that host innate immune response to CyHV-2, at least in which IL-11, ITLN and PNP5a were involved, was slow in comparison to that induced by A. hydrophila. It suggested that CyHV-2 might suppress host innate response during early infection. The lack of a C-terminal peptide of crucian carp ITLN gene implied a possible functional difference of this gene during evolution, which merit further investigation.

The interleukins of fish

Interleukins are a subgroup of cytokines, molecules involved in the intercellular regulation of the immune system. The term interleukin was first coined in 1979 to refer to molecules that signal between different leucocyte types, although not exclusively restricted to leucocyte communication. Whilst it is now known that interleukins are produced by a wide variety of cell types, nevertheless many are synthesised by CD4(+) T helper cells, macrophages/monocytes and endothelial cells. The nomenclature is relatively straightforward, with interleukin 1 the first discovered and interleukin 2 the second, etc. However, whilst 35 interleukins are currently described in mammals, several are in fact terms referring to subfamilies of more molecules, as with the IL-1 family where 11 members (IL-1F1-IL-1F11) are present, and the IL-17 family where 6 members (IL-17A-IL-17F) are present. So the total is much higher and splice variants and allelic variation increase this diversity further. This review will focus on what is known about interleukins in fish, and will refer to the major subfamilies rather than try to work through 35 descriptions in a row. It is clear that many direct homologues of molecules known in mammals are present in fish, but that not all are present and some novel interleukins exist that may have arisen from fish specific gene duplication events.

Characterisation and expression analysis of the Atlantic halibut (Hippoglossus hippoglossus L.) cytokines: IL-1β, IL-6, IL-11, IL-12β and IFNγ

Genes encoding the five Atlantic halibut (Hippoglossus hippoglossus L.) cytokines; interleukin (IL)-1β, IL-6, IL-11b, IL-12βc, and interferon (IFN) γ, were cloned and characterised at a molecular level. The genomic organisation of the halibut cytokine genes was similar to that seen in mammals and/or other fish species. Several mRNA instability motifs were found within the 3′-untranslated region (UTR) of all cytokine cDNA sequences. The putative cytokine protein sequences showed a low sequence identity with the corresponding homologues in mammals, avian and other fish species. Nevertheless, important structural features were presumably conserved such as the presence, or absence in the case of IL-1β, of a signal peptide, secondary structure and family signature motifs. The relative expression pattern of the cytokine genes was analyzed in several halibut organs, revealing a constitutive expression in both lymphoid and non-lymphoid organs. Interestingly, the gills showed a relatively high expression of IL-1β, IL-12βc and IFNγ. The real time RT-PCR data also showed that the mRNA level of IL-1β, IL-6, IL-12βc and IFNγ was high in the thymus, while IL-11b was relatively highly expressed in the posterior kidney and posterior gut. Moreover, the halibut brain showed a relatively high level of IL-6 transcripts. Anterior kidney leucocytes in vitro stimulated with imiquimod showed a significant increase in mRNA level of the five halibut cytokine genes. The sequence and characterisation data presented here will be useful for further investigation of both innate and adaptive immune responses in halibut, and be helpful in the design of vaccines for the control of various infectious diseases.