Sequencing of a second interleukin-10 gene in rainbow trout Oncorhynchus mykiss and comparative investigation of the expression and modulation of the paralogues in vitro and in vivo

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.

Molecular features and expression kinetics of interleukin-10 gene from the marine teleost, Snubnose pompano (Trachinotus blochii)

BACKGROUND

Interleukin 10 (IL-10) is uniquely positioned in the immune regulation of teleosts. Modifying the IL-10 pathway changes the teleost's disease susceptibility; however, there is no data on its post-transcriptional regulation. Trachinotus blochii is a high-value mariculture species.

METHODS

The full-length tbil-10 gene was generated through the Rapid Amplification of cDNA Ends-PCR. After the detailed sequence analysis, the identified features were compared with other IL-10 sequences. The gene expressions in healthy and challenged (Vibrio harveyi) fish were studied.

RESULTS

The sequence analysis showed an open reading frame of 564 bp and a 3' UTR (untranslated region) of 217 bp. The phylogram revealed an evolutionary distinction between marine and freshwater teleost IL-10. The shorter 3' UTR, additional conserved cysteines capable of forming stable disulphide bonds, and lesser mRNA instability moieties suggest the better structural stability of teleost IL-10 than tetrapods. Results identified 60 miRNA-mRNA duplexes that can regulate IL-10 3' UTR. Nine identified miRNAs are involved in immune response and seven are expressed in macrophages. The gills showed the highest gene expression in healthy fish. The study discovered two IL-10 mRNA transcripts that differed in 5' UTR lengths and thermodynamic ensemble's free energy. There was an increased expression of both tbil-10-mRNA transcripts from 2 to 48 h post-challenge which peaked at 24 h after the challenge, with higher expression of short mRNA transcript.

CONCLUSIONS

The results gave insights into the structural, functional, post-transcriptional regulatory mechanisms, and expression characteristics of the IL-10 gene in T. blochii.

Effects of stress conditions on plasma parameters and gene expression in the skin mucus of farmed rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the physiological response of rainbow trout (Oncorhynchus mykiss) before slaughtering in the last phase of farming analyzing skin mucus and plasma. Two groups of rainbow trout were considered: Group UN ("unstressed"), represented by fish randomly captured from raceways, in the last phase of a standard fattening cycle; Group S ("stressed"), collected at the end of the pre-slaughtering tank, soon after slaughtering. The fish skin mucus was swabbed from head to tail using a sterile plastic spatula and the blood was collected through an endocardial puncture. qRT-PCR was used to study the gene expression in skin mucus. The mRNA expression levels of the IL-6 and IgD genes were higher in the S than in the Group UN. The plasma analysis showed an only a decrease in the glucose plasma levels in the Group S when compared to the Group UN. The present results indicated that the procedures adopted after slaughtering only affected changes in plasma glucose and skin mucus activity in rainbow trout suggesting that management protocol was compatible with non-stressful farming conditions.

Effects of artificial photoperiods on antigen-dependent immune responses in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the effects of the artificial photoperiods that mimic summer (16L:8D) and winter (8L:16D) solstices, equinoxes (12L:12D), and the artificial 24-h light regimen (24L:0D) on the leukocyte populations and the T helper and regulatory type responses on rainbow trout (Oncorhynchus mykiss). Using flow cytometry analysis, we found that photoperiod induces changes in head kidney leukocyte subsets. The lymphoid subset increased in the 16L:8D summer solstice regime. The analysis using antibodies against B and T cells showed the increase of CD4-1⁺ T lymphocytes and other unidentified lymphoid cells, with no changes in the B cells. To investigate the modulatory influence of the photoperiod on the fish T cell response, we quantified in the head kidney the transcript levels of genes involved in the Th1 type response (t-bet, ifn-ƴ, il-12p35, il-12p40c), Th2 type response (gata3, il-4/13a), Th17 response (ror-ƴt, il-17a/f), T regulatory response (foxp3α, il-10a, tgf-β1), and the T cell growth factor il-2. The results showed that the seasonal photoperiod alone has a limited influence on the expression of these genes, as the only difference was observed in il-14/13a and il-10a transcripts of fish kept on the 16L:8D regimen. In addition, the 24L:0D treatment used in aquaculture produces a reduction of il-14/13a and il-17a/f. We also evaluated the effect of photoperiod in the presence of an antigenic stimulus. Thus, in fish immunized with the recombinant viral protein 1 (rVP1) of infectious pancreatic necrosis virus (IPNV), the photoperiod had a striking influence on the type of adaptive immune response. Each photoperiod fosters a unique immune signature of antigenic response. A classical type 1 response is observed in fish subjected to the 16D:8L photoperiod. In contrast, fish in the 12L:12D photoperiod showed only the upregulation of il-12p40c. Furthermore, none of the cytokines were increased in fish maintained on the artificial 24L:0D regimen, and a decrease in the master transcription factors (t-bet, ror-ƴt, and foxp3α) was observed. Thus, fish on the 12L:12D and 24L:0D photoperiod appear hyporesponsive regarding the T cell response. Altogether, this study showed that photoperiods modify the magnitude and quality of the T-helper response in rainbow trout and thus impact essential mechanisms for the generation of immune memory and protection against microorganisms.

Novel insights into the cytokine network of rainbow trout Oncorhynchus mykiss using cell lines and primary leukocyte populations

Cytokines are small proteins that regulate innate and adaptive immune responses and are released by both immune and non-immune cell types. In the current study, the constitutive and induced gene expression profiles of a suite of proinflammatory and regulatory cytokines was examined comparatively in eight rainbow trout (Oncorhynchus mykiss) cell lines, in order to establish the cytokine repertoires of these different cell types, especially the understudied non-immune cells. They included three epithelial cell lines (RTgut, RTgill, and RTL), one endothelial cell line (RTH), one fibroblast cell line (RTG-2), two stromal cell lines (TSS and TPS-2) and one monocyte/macrophage-like cell line (RTS-11). Three types of primary leukocytes (derived from blood, spleen and head kidney) of trout were also included in the analysis, to allow comparison to the repertoires expressed in T cells, as a major source of cytokines in immune responses. The major findings are: 1) IL-2A, IL-2B, IL-4/13B1, IL-4/13B2, IL-10b, P40B1, P28B, IL-17A/F1b, TNF-α3, TNF-α4, IFNγ1, CCL20L2b and CCL20L3a are expressed mainly in leukocytes but IL-17 N, IL-17D, IL-20 and CCL20L1b2 are not expressed in these cells. Hence future studies in these cell lines will help establish their function in fish; 2) Some of the cytokines were differentially expressed in the cell lines, revealing the potential role of these cell types in aspects of trout mucosal and inflammatory immune responses, 3) Similar cell types grouped together in the cell cluster analysis, including the leukocyte cluster, stromal cell cluster, and epithelial and endothelial cell cluster. Taken together, this investigation of these trout cell lines forms a good database for studying the function of cytokines not expressed in isolated leukocytes or that are preferentially expressed in the cell lines. Furthermore, the cytokine expression analysis undertaken confirmed the phenotypic relationship of these cell types at the molecular level.

Interleukin-2 family cytokines: An overview of genes, expression, signaling and functional roles in teleost

The interleukin-2 (IL-2) family cytokines include IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21, which share γ chain (γc) subunit in receptors. The IL-2 family cytokines have unique biological effects that regulate differentiation, survival and activation of multiple lymphocyte lineages. Deficiency of IL-2 family signaling pathway in mammals prevents CD4⁺ T cells from developing effector functions and CD8⁺ T cells from developing immunological memory. In the present review, we addressed available information from teleost IL-2 family cytokines and discussed implications in teleost immunity. Also, we described and discussed their expression profiles, receptors, signaling transductions and functions. In teleost, IL-2 family has 5 members (IL-2, IL-4/13, IL-7, IL-15, IL-21) without IL-9, and their receptors share a common γc subunit and include other 6 subunits (IL-2Rβ1/2, IL-4Rα1/2, IL-13Rα1/2, IL-7Rα, IL-15Rα, and IL-21Rα1/2). Some paralogues have changes in domain structure and show differential expression, modulation, functions. IL-2 family cytokines constitutively express in many immune associated tissues and are largely induced after pathogenic microbial stimulation. In general, there are relatively conserved functions in the IL-2 family throughout vertebrates, and many of the key IL-2 family members are important in lymphocyte proliferation and differentiation, development, inflammation from fishes to mammals. This review will give an update on the effective information of teleost IL-2 family cytokines. Thus, it will provide a source of reference for other researchers/readers and inspire further interest.

IL-10 Negatively Controls the Primary T Cell Response of Tilapia by Triggering the JAK1/STAT3/SOCS3 Axis That Suppresses NF-κB and MAPK/ERK Signaling

The braking mechanisms to protect the host from tissue damage and inflammatory disease caused by an overexuberant immune response are common in many T cell subsets. However, the negative regulation of T cell responses and detailed mechanisms are not well understood in early vertebrates. In the current study, using a Nile tilapia (Oreochromis niloticus) model, we investigated the suppression of T cell immunity by IL-10. Tilapia encodes an evolutionarily conserved IL-10, whose expression in lymphocytes is markedly induced during the primary adaptive immune response against Aeromonas hydrophila infection. Activated T cells of tilapia produce IL-10, which in turn inhibits proinflammatory cytokine expression and suppresses PHA-induced T cell activation. Moreover, administration of IL-10 impairs the proliferation of tilapia T cells, reduces their potential to differentiate into Th subsets, and cripples the cytotoxic function, rendering the animals more vulnerable to pathogen attack. After binding to its receptor IL-10Ra, IL-10 activates the JAK1/STAT3 axis by phosphorylation and enhances the expression of the suppressor of cytokine signaling 3 (SOCS3), which in turn attenuates the activation of the NF-κB and MAPK/ERK signaling pathways, thus suppressing the T cell response of tilapia. Our findings elucidate a negative regulatory mechanism of T cell immunity in a fish species and support the notion that the braking mechanism of T cells executed through IL-10 existed prior to the divergence of the tetrapod lineage from teleosts. Therefore, this study, to our knowledge, provides a novel perspective on the evolution of the adaptive immune system.

Effects of white mustard (Sinapis alba) oil on growth performance, immune response, blood parameters, digestive and antioxidant enzyme activities in rainbow trout (Oncorhynchusmykiss)

A study was conducted to evaluate the effects of dietary supplementation of white mustard (Sinapis alba) oil (WMO) on growth performance, immune responses, digestive and antioxidant enzyme activities in juvenile rainbow trout (Oncorhynchus mykiss). For this purpose, fish (initial weight: 25.77 ± 0.13 g) were divided into four experimental groups in triplicate and fed ad libitum twice a day with diets containing WMO at 0 (control), 0.5, 1, and 1.5% of diet for 9 weeks. Three fish from each tank (n:9 per treatment) were sampled on 21st, 42nd, and 63rd days for further analyses. At the end of the feeding period, fish were challenged with Aeromonas hydrophila and Yersinia ruckeri in two separate experimental setups. Results showed that final weight, weight gain, and specific growth rate were significantly increased in all experimental groups compared to the control. Feed conversion ratio was similar among treatments. Respiratory burst and potential killing activity decreased in all experimental groups compared to the control (P < 0.05). Lysozyme and myeloperoxidase activities were elevated in all experimental groups at the end of the experiment compared to the control (P < 0.05). Cytokine gene expressions in the head kidney and intestine were elevated in all experimental groups compared to that of the control in general (P < 0.05). Hematological responses of the experimental fish groups were similar to that of the control (P > 0.05). Pepsin and trypsin levels decreased in all experimental groups (P < 0.05). In terms of antioxidant enzyme activities, significant improvement in liver superoxide dismutase, catalase, and glutathione s-transferase activities in all treatment groups were determined (P < 0.05). In addition, a significant decline in liver lipid peroxidation levels was recorded in all treated groups at all sampling times compared to the control (P < 0.05). At the end of this feeding trial, no significant differences (P > 0.05) were observed in survival against A. hydrophila among experimental groups compared to the control (P > 0.05). However, increased survival against Y. ruckeri was determined in experimental fish groups (P < 0.05). This study suggests that white mustard oil had a favorable effect on the overall health and growth of rainbow trout.

Oral administration of Sargassum polycystum extracts stimulates immune response and increases survival against Aeromonas hydrophila infection in Oncorhynchus mykiss

This study investigated the immunomodulatory effects of Sargassum polycystum extract administration in rainbow trout (Oncorhynchus mykiss). S. polycystum methanolic extract was administered orally using feeding needles to individual rainbow trout at the dose of 0 (control), 1 (S1), 3 (S3) and 5 (S5) mg/100 μl/per fish twice a day for 7 days. On 1st, 5th, 3rd and 7th day, blood and tissues were collected from the fish and changes in humoral immune responses and immune-related gene expressions were determined. The result of oxidative radical production showed no difference during early stage of the experiment and was lately decreased (P < 0.05). Lysozyme activity increased on 3rd and 7th day of the study in S5 fish group and on 5th day in S3 group compared to control (P < 0.05). Myeloperoxidase activity had an increased level on the 1st and 3rd day in S1, S5 and S5 fish groups, respectively. IL-1β gene was significantly up-regulated in kidney and intestine in all experimental groups (except on the 1st day, in the intestine of S5 fish group) compared to control (P < 0.05). IL-8 gene expression was elevated on 1st and 3rd day in kidney of all experimental fish groups. IL-6 transcript enhanced in a dose-dependent manner on 3rd and 7th day. IL-10 and IL-12 genes were also up-regulated. Survival in all treated fish groups challenged with Aeromonas hydrophila was significantly increased compared to that of control. The highest survival rate was recorded in S5 fish group (83.65%) followed by S3 fish group (82.62%). Our results suggest that S. polycystum aqueous methanolic extract is an effective immunostimulant and provide protection against A. hydrophila infection in rainbow trout at a dose of 3-10 mg/20 g body weight/day.

Montanide™ ISA 763A VG and ISA 761 VG induce different immune pathway responses in rainbow trout (Oncorhynchus mykiss) when used as adjuvant for an Aeromonas salmonicida bacterin

Adjuvants are the helper substances that increase vaccine efficacy by enhancing the potency and longevity of specific immune responses to antigens. Most existing fish vaccines are presented in the form of oil-based emulsions delivered by intraperitoneal injection. The characterization of their mode of action is a valuable aid to future vaccine development, particularly for the potential identification and stimulation of specific immunological pathways related to the desired protective response. This study characterized the expression of selected immune-related genes in the peritoneal cavity, head kidney and spleen following the administration of two adjuvanted-bacterial vaccines thought to induce humoral (Montanide™ ISA 763A VG) or humoral and cell mediated (Montanide™ ISA 761 VG) immune responses, to determine if differences in responsiveness are readily apparent. The most informative site was the spleen, where Montanide™ ISA 763A VG + bacterin gave rise to upregulation of genes driving T-cell/lymphoid responses, namely IL-2, IL-15 and IL-21. This combined with upregulation of IFNγ1 and IFNγ2, IL-4/13B2, p35A1 and p40 (B1 and C) indicated that the induction of Th1 and possibly Th2 immunity was occurring in fish vaccinated with this adjuvant. Perhaps the most intriguing finding was the lack of a detectable Th1 response in fish given Montanide™ ISA 761 VG + bacterin, suggesting some other arm of the immune system is activated to give protection. Whatever the reason for the different responses detected, it is clear from the present study that the adjuvant used has a major impact on the responses elicited. Since these differences are readily detectable it allows, in principle, their use to help select the most appropriate adjuvants for inclusion into fish vaccines, where the type of response elicited may need to be tailored to a particular pathogen to confer protection.

Processed Animal Proteins from Insect and Poultry By-Products in a Fish Meal-Free Diet for Rainbow Trout: Impact on Intestinal Microbiota and Inflammatory Markers

Sustainability of aquaculture is tied to the origin of feed ingredients. In search of sustainable fish meal-free formulations for rainbow trout, we evaluated the effect of Hermetia illucens meal (H) and poultry by-product meal (P), singly (10, 30, and 60% of either H or P) or in combination (10% H + 50% P, H10P50), as partial replacement of vegetable protein (VM) on gut microbiota (GM), inflammatory, and immune biomarkers. Fish fed the mixture H10P50 had the best growth performance. H, P, and especially the combination H10P50 partially restored α-diversity that was negatively affected by VM. Diets did not differ in the Firmicutes:Proteobacteria ratio, although the relative abundance of Gammaproteobacteria was reduced in H and was higher in P and in the fishmeal control. H had higher relative abundance of chitin-degrading Actinomyces and Bacillus, Dorea, and Enterococcus. Actinomyces was also higher in H feed, suggesting feed-chain microbiome transmission. P increased the relative abundance of protein degraders Paeniclostridium and Bacteroidales. IL-1β, IL-10, TGF-β, COX-2, and TCR-β gene expression in the midgut and head kidney and plasma lipopolysaccharide (LPS) revealed that the diets did not compromise the gut barrier function or induce inflammation. H, P, and H10P50 therefore appear valid protein sources in fishmeal-free aquafeeds.

pH-Controlled Release of Antigens Using Mesoporous Silica Nanoparticles Delivery System for Developing a Fish Oral Vaccine

The development of effective vaccines and delivery systems in aquaculture is a long-term challenge for controlling emerging and reemerging infections. Cost-efficient and advanced nanoparticle vaccines are of tremendous applicability in prevention of infectious diseases of fish. In this study, dihydrolipoamide dehydrogenase (DLDH) antigens of Vibrio alginolyticus were loaded into mesoporous silica nanoparticles (MSN) to compose the vaccine delivery system. Hydroxypropyl methylcellulose phthalate (HP55) was coated to provide protection of immunogen. The morphology, loading capacity, acid-base triggered release were characterized and the toxicity of nanoparticle vaccine was determined in vitro. Further, the vaccine immune effects were evaluated in large yellow croaker via oral administration. In vitro studies confirmed that the antigen could be stable in enzymes-rich artificial gastric fluid and released under artificial intestinal fluid environment. In vitro cytotoxicity assessment demonstrated the vaccines within 120 μg/ml have good biocompatibility for large yellow croaker kidney cells. Our data confirmed that the nanoparticle vaccine in vivo could elicit innate and adaptive immune response, and provide good protection against Vibrio alginolyticus challenge. The MSN delivery system prepared may be a potential candidate carrier for fish vaccine via oral administration feeding. Further, we provide theoretical basis for developing convenient, high-performance, and cost-efficient vaccine against infectious diseases in aquaculture.

Age-Related Differences in Molecular Profiles for Immune Checkpoint Blockade Therapy

Immune checkpoint blockade (ICB) therapies have significantly improved the prognosis and shown considerable promise for cancer therapy; however, differences in ICB treatment efficacy between the elderly and young are unknown. We analyzed the studies enrolled in the meta-analysis using the deft approach, and found no difference in efficacy except melanoma patients receiving anti–PD-1 therapy. Similarly, higher treatment response rate and more favorable prognosis were observed in elderly patients in some cancer types (e.g., melanoma) with data from published ICB treatment clinical trials. In addition, we comprehensively compared immunotherapy-related molecular profiles between elderly and young patients from public trials and The Cancer Genome Atlas (TCGA), and validated these findings in several independent datasets. We discovered a divergent age-biased immune profiling, including the properties of tumors (e.g., tumor mutation load) and immune features (e.g., immune cells), in a pancancer setting across 27 cancer types. We believe that ICB treatment efficacy might vary depending on specific cancer types and be determined by both the tumor internal features and external immune microenvironment. Considering the high mutational properties in elderly patients in many cancer types, modulating immune function could be beneficial to immunotherapy in the elderly, which requires further investigation.

Effective isolation of GALT cells: Insights into the intestine immune response of rainbow trout (Oncorhynchus mykiss) to different bacterin vaccine preparations

The teleost gut is a multifunction complex structure that plays a pivotal immunological role in homeostasis and the maintenance of health, in addition to digestion of food and/or nutrient absorption. In vitro examination of the intestine leucocyte repertoire has the potential to aid our understanding of gut immune competence and allows a rapid screen of host-microorganism interactions in different immunological contexts. To explore this possibility, in the present study we investigated the response of isolated gut leucocytes to 4 bacterins of Aeromonas salmonicida, prepared from different strains, combinations and strains grown in different environments, in comparison to a Yersinia ruckeri bacterin for which a commercial/effective oral booster vaccine has been developed. To aid this study we also optimized further our method of GALT cell isolation from rainbow trout, so as to avoid mechanical clearance of the intestine contents. This drastically increased the cell yield from ~12 × 10⁶ to ~210 × 10⁶/fish with no change in the percent cell viability over time or presence of transcripts typical of the key leucocyte types needed for the study of immune modulation (i.e. T- and B-cells, dendritic cells and macrophages). A wide array of immune transcripts were modulated by the bacterins, demonstrating the diversity of GALT cell responses to bacterial stimulation. Indeed, the GALT leucocyte responses were sensitive enough to distinguish the different bacterial species, strains and membrane proteins, as seen by distinct kinetics of immune gene expression. However, the response of the GALT cells was often relatively slow and of a low magnitude compared to those of PBL. These results enhance our knowledge of the gut biocapacity and help validate the use of this model for screening of oral vaccine candidates.

Regulation of Il-10 gene expression by Il-6 via Stat3 in grass carp head kidney leucocytes

Interleukin (IL)-10 is a critical anti-inflammatory and late cytokine being produced after the proinflammatory mediators while IL-6 is a promptly synthesized cytokine in response to inflammation in mammals. This chronological expression of interleukin (Il)-6 and Il-10 was also found in grass carp head kidney leucocytes (HKLs) treated by heat-killed Aeromonas hydrophila, supporting the possible interplay between grass carp (gc)Il-6 and gcIl-10 in HKLs. Our further findings were in agreement with this hypothesis that recombinant gcIl-6 (rgcIl-6) promptly and transiently increased gcil10 mRNA levels in grass carp HKLs. Moreover, rgcIl-6 enhanced its own mRNA level and this self-enhancement of gcil6 mRNA level could be partially blocked by rgcIl-10. These results collectively suggest that gcIl-10 production stimulated by gcIl-6 may provide a negative feedback to gcIl-6 production. Interestingly, rgcIl-6 significantly decreased gcil10 mRNA levels in grass carp HKLs after the treatment for 12 and 24 h in contrast to its enhancement of gcil10 levels after the treatment for 3 h. Involvement of Stat3 but not MEK, p38 MAPK or JNK pathway in the increase of gcil10 mRNA levels by rgcIl-6 was revealed by using the signaling pathway inhibitors. This was supported by the fact that rgcIl-6 stimulated Stat3 phosphorylation in grass carp HKLs. Furthermore, rgcIl-6 had no effect on the stability of gcil10 mRNA after the treatment for 3 to 36 h while it increased gcil10 promoter activity after the treatment for 24 h. Taken these data together, gcIl-6 can stimulate Il-10 production at early stage but subsequently inhibit il10 mRNA expression in grass carp HKLs, shedding light on the dynamic regulation of il10 mRNA expression by Il-6 in fish immune cells.

Distinct response of immune gene expression in peripheral blood leucocytes modulated by bacterin vaccine candidates in rainbow trout Oncorhynchus mykiss: A potential in vitro screening and batch testing system for vaccine development in aquaculture

Fish aquaculture is the world's fastest growing food production industry and infectious diseases are a major limiting factor. Vaccination is the most appropriate method for controlling infectious diseases and a key reason for the success of salmonid cultivation and has reduced the use of antibiotics. The development of fish vaccines requires the use of a great number of experimental animals that are challenged with virulent pathogens. In vitro cell culture systems have the potential to replace in vivo pathogen exposure for initial screening and testing of novel vaccine candidates/preparations, and for batch potency and safety tests. PBL contain major immune cells that enable the detection of both innate and adaptive immune responses in vitro. Fish PBL can be easily prepared using a hypotonic method and is the only way to obtain large numbers of immune cells non-lethally. Distinct gene expression profiles of innate and adaptive immunity have been observed between bacterins prepared from different bacterial species, as well as from different strains or culturing conditions of the same bacterial species. Distinct immune pathways are activated by pathogens or vaccines in vivo that can be detected in PBL in vitro. Immune gene expression in PBL after stimulation with vaccine candidates may shed light on the immune pathways involved that lead to vaccine-mediated protection. This study suggests that PBL are a suitable platform for initial screening of vaccine candidates, for evaluation of vaccine-induced immune responses, and a cheap alternative for potency testing to reduce animal use in aquaculture vaccine development.

Therapeutic effects of beard lichen, Usnea barbata extract against Lactococcus garvieae infection in rainbow trout (Oncorhynchus mykiss)

In this study, therapeutic effects of aqueous methanolic extracts of beard lichen (Usnea barbata) against Lactococcus garvieae (ATCC 43921) in rainbow trout (Onchorhynchus mykiss) were investigated. Six different experimental groups [0 mg/100 μL (Control), 4 mg/100 μL, 8 mg/100 μL, 12 mg/100 μL, 6 mg/100 μL florfenicol (positive control), 6 mg/100 μL erythromycin (positive control)] were set up to determine effects of lichen extract on immune responses and survival rate. In the study, superoxide radical production was increased in fish treated with 12 mg beard lichen extract, florfenicol and erythromycin compared to that of control (P < 0.05). Lysozyme activity was generally decreased (P < 0.05) or no differences were observed in all experimental groups compared to that of control (P > 0.05). Myeloperoxidase was significantly increased in all antibiotic treated groups. No differences were observed in liver histology of experimental groups compared to control. Cytokine gene expressions were elevated in all experimental groups compared to that of control (P < 0.05), except IL-1β expression at 10th day sampling time. Other immune related genes (IL-8, TGF- β, IL-12 Beta, TNFα1, IL-10, COX-2, IL-6, TLR5, C3, IGM, MHC-II, iNOS, IgT, IFN1, IFN2, IFN reg) were also elevated in all experimental groups compared to that of control group. The survival rates obtained in 4 mg beard lichen treated group, 8 mg beard lichen treated group and erythromycin treated group were 73.08, 65.38 and 80.77% respectively. Our results suggest that beard lichen methanolic extract could be an effective therapeutic agent to be used against L. garvieae infection in rainbow trout at the dose of 4 mg/17.41 ± 0.3 g body weight/day.

Dissecting the immune pathways stimulated following injection vaccination of rainbow trout (Oncorhynchus mykiss) against enteric redmouth disease (ERM)

Enteric redmouth disease (ERM or yersiniosis) is one of the most important diseases of salmonids and leads to significant economic losses. It is caused by the Gram-negative bacterium Yersinia ruckeri but can be controlled by bacterin vaccination. The first commercial ERM vaccine was licenced in 1976 and is one of the most significant and successful health practices within the aquaculture industry. Although ERM vaccination provides complete protection, knowledge of the host immune response to the vaccine and the molecular mechanisms that underpin the protection elicited is limited. In this report, we analysed the expression in spleen and gills of a large set of genes encoding for cytokines, acute phase proteins (APPs) and antimicrobial peptides (AMPs) in response to ERM vaccination in rainbow trout, Oncorhynchus mykiss. Many immune genes in teleost fish are known to have multiple paralogues that can show differential responses to ERM vaccination, highlighting the necessity to determine whether all of the genes present react in a similar manner. ERM vaccination immediately activated a balanced inflammatory response with correlated expression of both pro- and anti-inflammatory cytokines (eg IL-1β1-2, TNF-α1-3, IL-6, IL-8 and IL-10A etc.) in the spleen. The increase of pro-inflammatory cytokines may explain the systemic upregulation of APPs (eg serum amyloid A protein and serum amyloid protein P) and AMPs (eg cathelicidins and hepcidin) seen in both spleen and gills. We also observed an upregulation of all the α-chains but only one β-chain (p40B2) of the IL-12 family cytokines, that suggests specific IL-12 and IL-23 isoforms with distinct functions might be produced in the spleen of vaccinated fish. Notably the expression of Th1 cytokines (IFN-γ1-2) and a Th17 cytokine (IL-17A/F1a) was also up-regulated and correlated with enhanced expression of the IL-12 family α-chains, and the majority of pro- and anti-inflammatory cytokines, APPs and AMPs. These expression profiles may suggest that ERM vaccination activates host innate immunity and expression of specific IL-12 and IL-23 isoforms leading to a Th1 and Th17 biased immune response. A late induction of Th2 cytokines (IL-4/13B1-2) was also observed, that may have a homeostatic role and/or involvement in antibody production. This study has increased our understanding of the host immune response to ERM vaccination and the adaptive pathways involved. The early responses of a set of genes established in this study may provide essential information and function as biomarkers in future vaccine development in aquaculture.

Studies on the Use of Flagellin as an Immunostimulant and Vaccine Adjuvant in Fish Aquaculture

Immunostimulants and vaccines are important for controlling infectious diseases in fish aquaculture. In this study we assess the potential of flagellin to be used for such purposes in rainbow trout (Oncorhynchus mykiss). A recombinant flagellin from the salmonid pathogen Yersinia ruckeri (YRF) has been produced previously by us and shown to be a potent activator of inflammatory cytokines, acute phase proteins and antimicrobial peptides in vitro. Here we show that YRF is the most potent inflammatory activator of three bacterial PAMPs (LPS, peptidoglycan and flagellin) tested. The host response to flagellin was next studied in vivo. The YRF modulated gene expression was examined in two systemic (spleen and liver) and two mucosa-associated (gills and skin) tissues. YRF injection initiated a transient systemic inflammatory response with key pro-inflammatory cytokines (IL-1β, TNFα, IL-6, and IL-11 etc.) and chemokines (CXCL_F4 and CXCL-8) induced rapidly (by 6 h) but subsiding quickly (by 24 h) in multiple tissues. Consequently, a variety of anti-microbial pathways were activated systemically with heightened expression of acute phase proteins, antimicrobial peptides and complement genes in multiple tissues, which was sustained to 24 h in the liver and mucosal tissues. The Th17 cytokine IL-17A/F1 was also induced in the spleen and liver, and Th2 cytokine IL-4/13 was induced in the liver. However, the anti-inflammatory IL-10 and the Th1 cytokine IFNγ were refractory. A secreted form of TLR5 (TLR5s) was induced by flagellin in all tissues examined whilst the membrane form was refractory, suggesting that TLR5s may function as a negative feedback regulator. Trout liver appeared to be an important organ responding to flagellin stimulation, with marked induction of IL-11, IL-23P19, IL-17C1, SAA, and cathelicidin-2. YRF induced a strong antibody response. These antibodies reacted against the middle domain of YRF and were able to decrease YRF bioactivity. Intact YRF was necessary for its bioactivity, as deletion of the N-terminal, C terminal or middle domain of YRF led to functional loss. This study suggests that flagellin could be a potent immunostimulant and vaccine adjuvant for fish aquaculture.

CD4: a vital player in the teleost fish immune system

CD4 is a nonpolymorphic transmembrane glycoprotein molecule that is expressed on the surface of T-helper cells and plays an essential role in the immune response. It functions as a coreceptor with the T-cell receptor by binding to major histocompatibility complex class II on the surface of dendritic cells that present antigens. CD4+ T cells hold a key position in coordinating the immune system through production of several cytokines after activation and differentiation. The CD4+ T helper subtypes (T-helper 1, T-helper 2, T-helper 17, T-helper 9, and regulatory-T cells) perform different immune functions subsequent to their differentiation from the naive T cells. Different types of CD4+ T cells require different cytokines such as drivers and effectors, as well as master transcription factors for their activation. Fish cells that express CD4-related genes are activated in the presence of a pathogen and release cytokines against the pathogen. This review highlights the types of CD4+ T cells in fish and describes their direct role in cell-mediated and humoral immunity for protection against the intracellular bacterial as well as viral infections in fish.

Interleukin (IL)-2 Is a Key Regulator of T Helper 1 and T Helper 2 Cytokine Expression in Fish: Functional Characterization of Two Divergent IL2 Paralogs in Salmonids

Mammalian interleukin (IL)-2 is a cytokine centrally involved in the differentiation and survival of CD4+ T helper subsets and CD4+ T regulatory cells and in activation of cytotoxic effector lymphocytes. In bony fish, IL2 orthologs have been identified with an additional divergent IL2-Like gene on the same locus present in several fish species. We report here two divergent IL2 paralogs, IL2A and IL2B, in salmonids that originated from the whole genome duplication event in this fish lineage. The salmonid IL2 paralogs differ not only in sequence but also in exon sizes. The IL-2 isoforms that are encoded have disparate pI values and may have evolved to preferentially bind specific IL-2 receptors. Rainbow trout IL2 paralogs are highly expressed in thymus, spleen, gills, kidney and intestine, important tissues/organs in fish T cell development and function. Their expression in peripheral blood leukocytes (PBL) is low constitutively but can be upregulated by the mixed leukocyte reaction, by the T cell mitogen phytohemagglutinin and by signal mimics of T cell activation (phorbol 12-myristate 13-acetate and calcium ionophore). Both trout IL-2 isoforms promoted PBL proliferation and sustained high-level expression of CD4 and CD8, suggesting that trout IL-2 isoforms are T cell growth/survival factors mainly expressed by activated T cells. The recombinant proteins for these two trout IL2 paralogs have been produced in E. coli and possess shared but also distinct bioactivities. IL-2A, but not IL-2B, induced IL12P35A1 and CXCR1 expression in PBL. IL-2B had a stronger effect on upregulation of the T helper 1 (Th1) cytokine interferon-γ (IFNγ) and could sustain CD8α and CD8β expression levels. Nevertheless, both cytokines upregulated key Th1 (IFNγ1, IFNγ2, TNFα2 and IL12) and T helper 2 (Th2) cytokines (IL4/13B1 and IL4/13B2), cytokine and chemokine receptors and the antimicrobial peptide cathelicidin-1 but had limited effects on T helper 17 cytokines and TGFβ1 in PBL. They could also enhance PBL phagocytosis. These results suggest, for the first time in fish, that IL-2 isoforms may have an important role in regulating Th1 and Th2 cell development, and innate and adaptive host defenses in fish, and shed light on lineage-specific expansion, evolution, and functional diversification of IL2 in vertebrates.

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.

Rainbow trout (Oncorhynchus mykiss) adipose tissue undergoes major changes in immune gene expression following bacterial infection or stimulation with pro-inflammatory molecules

In mammals, visceral adipose is increasingly seen as playing an important role in immune function with numerous pro-inflammatory, anti-inflammatory and immune-modulating proteins and peptides being identified in adipocytes. Adipose is also now known as a tissue that has an important role in the regulation of peritoneal immune responses. Despite this, only lately has consideration been given to visceral adipose as an important immune tissue in fish, especially in the context of intraperitoneal vaccination. The present study demonstrates that fish visceral adipose is capable of expressing a large range of immune molecules in response to stimulation with a live bacterium (A. salmonicida), a bacterial PAMP (Y. ruckeri flagellin), and the pro-inflammatory cytokines IL-1β, TNF-α3 and IFN-γ. Following infection and stimulation with flagellin and IL-1β a large upregulation of pro-inflammatory and antimicrobial molecules was seen, with a high degree of overlap. TNF-α treatment affected relatively few genes and the effects were more modest. IFN-γ had the smallest impact on adipose but IFN-γ inducible genes showed some of the largest effects. Overall, it is clear that adipose tissue should be considered an active immune site in fish, capable of participating in and influencing immune responses.

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

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

Molecular characterization and expression of interleukin-10 and interleukin-22 in golden pompano (Trachinotus ovatus) in response to Streptococcus agalactiae stimulus

In the present study, members of the interleukin (IL)-10 family of cytokines, including IL-10 (TOIL-10) and IL-22 (TOIL-22) of golden pompano (Trachinotus ovatus), were cloned for the first time, and their expression patterns and 3D structures analyzed. The full-length cDNA sequences of TOIL-10 and TOIL-22 contained open reading frames of 564 and 567 bp, respectively. TOIL-10 and TOIL-22 shared higher homology (78%-89%) with the corresponding genes from various fish relative to other species (25%-34%) and contained the IL-10 family signature and four cysteine residues that are well conserved in other vertebrate IL-10 members. Phylogenetic tree analysis of our sequences alongside other IL-10 family proteins revealed that TOIL-10 and TOIL-22 cluster together with other teleost IL-10 and IL-22 molecules. Expression of TOIL-10 and TOIL-22 genes was ubiquitous in all tissues examined. The TOIL-10 gene was also highly expressed in skin, heart, gill, spleen, kidney, brain and liver, and lower levels were detected in intestine and muscle. High expression of the TOIL-22 gene was observed in gill, intestine, kidney, spleen, with the lowest levels in liver. TOIL-10 and TOIL-22 were rapidly activated after SAΔphoB immunization and significantly increased to peak levels at 12 h and 4 d in golden pompano kidney and spleen respectively following challenge. Expression in the brain reached peak levels at 4 d and 3 d respectively after post-immunization. Our results collectively indicate that TOIL-10 and TOIL-22 participate in the host immune response to bacterial infection. Moreover, TOIL-22 plays a potentially important role in mucosal immunity.

Carp Il10a and Il10b exert identical biological activities in vitro, but are differentially regulated in vivo

We recently reported on the functional characterization of carp Il10. We showed that carp Il10 is able to downregulate proinflammatory activities by carp phagocytes and promote B cell proliferation, differentiation and antibody production as well as proliferation of memory T cells. Taking advantage of the recent annotation of the carp genome, we completed the sequence of a second il10 paralogue, named il10b, the presence of which was expected owing to the recent (8 million years ago) fourth round of whole genome duplication that occurred in common carp. In the present study we closely compared the two Il10 paralogues and show that Il10a and Il10b have almost identical gene structure, synteny, protein sequence as well as bioactivity on phagocytes. Although the two il10 paralogues show a large overlap in tissue expression, il10b has a low constitutive expression and is highly upregulated upon infection, whereas il10a is higher expressed under basal conditions but its gene expression remains constant during viral and parasitic infections. This differential regulation is most likely due to the observed differences in their promoter regions. Altogether our results demonstrate that gene duplication in carp, although recent, led to sub-functionalization and expression divergence rather than functional redundancy of the Il10 paralogues, yet with very similar protein sequences.

Piscirickettsia salmonis Imbalances the Innate Immune Response to Succeed in a Productive Infection in a Salmonid Cell Line Model

Piscirickettsia salmonis is a facultative intracellular bacterium that causes the disease called "salmon rickettsial syndrome". Attempts to control this disease have been unsuccessful, because existing vaccines have not achieved the expected effectiveness and the antibiotics used fail to completely eradicate the pathogen. This is in part the product of lack of scientific information that still lacks on the mechanisms used by this bacterium to overcome infected-cell responses and survive to induce a productive infection in macrophages. For that, this work was focused in determining if P. salmonis is able to modify the expression and the imbalance of IL-12 and IL-10 using an in vitro model. Additionally, we also evaluated the role the antimicrobial peptide hepcidin had in the control of this pathogen in infected cells. Therefore, the expression of IL-10 and IL-12 was evaluated at earlier stages of infection in the RTS11 cell line derived from Oncorhynchus mykiss macrophages. Simultaneously, the hepcidin expression and location was analyzed in the macrophages infected with the pathogen. Our results suggest that IL-10 is clearly induced at early stages of infection with values peaking at 36 hours post infection. Furthermore, infective P. salmonis downregulates the expression of antimicrobial peptide hepcidin and vesicles containing this peptide were unable to merge with the infective bacteria. Our results suggest that P. salmonis is able to manipulate the behavior of host cytokines and likely might constitute a virulence mechanism that promotes intracellular bacterial replication in leukocytes cells lines of trout and salmon. This mechanism involves the generation of an optimum environment for the microorganism and the downregulation of antimicrobial effectors like hepcidin.

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.

Re-examination of the rainbow trout (Oncorhynchus mykiss) immune response to flagellin: Yersinia ruckeri flagellin is a potent activator of acute phase proteins, anti-microbial peptides and pro-inflammatory cytokines in vitro

Flagellin is the principal component of bacterial flagellum and a major target of the host immune system. To provide new insights into the role of flagellin in fish immune responses to flagellated microorganisms, a recombinant flagellin from Yersinia ruckeri (rYRF) was produced and its bioactivity investigated in the trout macrophage cell line RTS-11 and head kidney cells. rYRF is a potent activator of pro-inflammatory cytokines, acute phase proteins, antimicrobial peptides and subunits of the IL-12 cytokine family. This and the synergy seen with IFN-γ to enhance further expression of specific IL-12 and TNF-α isoforms may suggest that flagellin could be a useful immune stimulant or adjuvant for use in aquaculture. Gene paralogues were often differentially modulated, highlighting the need to study all of the paralogues of immune genes in fish to gain a full understanding of the effects of PAMPs or other stimulants, and the potential immune responses elicited.

Sequence and Expression Analysis of Interferon Regulatory Factor 10 (IRF10) in Three Diverse Teleost Fish Reveals Its Role in Antiviral Defense

BACKGROUND

Interferon regulatory factor (IRF) 10 was first found in birds and is present in the genome of other tetrapods (but not humans and mice), as well as in teleost fish. The functional role of IRF10 in vertebrate immunity is relatively unknown compared to IRF1-9. The target of this research was to clone and characterize the IRF10 genes in three economically important fish species that will facilitate future evaluation of this molecule in fish innate and adaptive immunity.

MOLECULAR CHARACTERIZATION OF IRF10 IN THREE FISH SPECIES

In the present study, a single IRF10 gene was cloned in grass carp Ctenopharyngodon idella and Asian swamp eel Monopterus albus, and two, named IRF10a and IRF10b, in rainbow trout Oncorhynchus mykiss. The fish IRF10 molecules share highest identities to other vertebrate IRF10s, and have a well conserved DNA binding domain, IRF-associated domain, and an 8 exon/7 intron structure with conserved intron phase. The presence of an upstream ATG or open reading frame (ORF) in the 5'-untranslated region of different fish IRF10 cDNA sequences suggests potential regulation at the translational level, and this has been verified by in vitro transcription/translation experiments of the trout IRF10a cDNA, but would still need to be validated in fish cells.

EXPRESSION ANALYSIS OF IRF10 IN VIVO AND IN VITRO

Both trout IRF10 paralogues are highly expressed in thymus, blood and spleen but are relatively low in head kidney and caudal kidney. Trout IRF10b expression is significantly higher than IRF10a in integumentary tissues i.e. gills, scales, skin, intestine, adipose fin and tail fins, suggesting that IRF10b may be more important in mucosal immunity. The expression of both trout IRF10 paralogues is up-regulated by recombinant IFN-γ. The expression of the IRF10 genes is highly induced by Poly I:C in vitro and in vivo, and by viral infection, but is less responsive to peptidoglycan and bacterial infection, suggesting an important role of fish IRF10 in antiviral defense.

Innate and adaptive immune responses in migrating spring-run adult chinook salmon, Oncorhynchus tshawytscha

Adult Chinook salmon (Oncorhynchus tshawytscha) migrate from salt water to freshwater streams to spawn. Immune responses in migrating adult salmon are thought to diminish in the run up to spawning, though the exact mechanisms for diminished immune responses remain unknown. Here we examine both adaptive and innate immune responses as well as pathogen burdens in migrating adult Chinook salmon in the Upper Willamette River basin. Messenger RNA transcripts encoding antibody heavy chain molecules slightly diminish as a function of time, but are still present even after fish have successfully spawned. In contrast, the innate anti-bacterial effector proteins present in fish plasma rapidly decrease as spawning approaches. Fish also were examined for the presence and severity of eight different pathogens in different organs. While pathogen burden tended to increase during the migration, no specific pathogen signature was associated with diminished immune responses. Transcript levels of the immunosuppressive cytokines IL-10 and TGF beta were measured and did not change during the migration. These results suggest that loss of immune functions in adult migrating salmon are not due to pathogen infection or cytokine-mediated immune suppression, but is rather part of the life history of Chinook salmon likely induced by diminished energy reserves or hormonal changes which accompany spawning.

Cloning of interleukin-10 from African clawed frog (Xenopus tropicalis), with the Finding of IL-19/20 homologue in the IL-10 locus

Interleukin-10 (IL-10) is a pleiotropic cytokine that plays an important role in immune system. In the present study, the IL-10 gene of African clawed frog (Xenopus tropicalis) was first cloned, and its expression pattern and 3D structure were also analyzed. The frog IL-10 mRNA encoded 172 amino acids which possessed several conserved features found in IL-10s from other species, including five-exon/four-intron genomic structure, conserved four cysteine residues, IL-10 family motif, and six α-helices. Real-time PCR showed that frog IL-10 mRNA was ubiquitous expressed in all examined tissues, highly in some immune related tissues including kidney, spleen, and intestine and lowly in heart, stomach, and liver. The frog IL-10 mRNA was upregulated at 24 h after LPS stimulation, indicating that it plays a part in the host immune response to bacterial infection. Another IL, termed as IL-20, was identified from the frog IL-10 locus, which might be the homologue of mammalian IL-19/20 according to the analysis results of the phylogenetic tree and the sequence identities.

Molecular characterisation of four class 2 cytokine receptor family members in rainbow trout, Oncorhynchus mykiss

The interleukin (IL)-10 cytokine family includes IL-10, IL-19, IL-20, IL-22, IL-24, IL-26 and the lambda/type III interferons. They are highly pleiotropic and mediate a variety of activities, including immune suppression and antibacterial immunity. To exert their functions they signal through a heterodimeric receptor composed of a subunit with a long intracellular domain (R1 type receptors; IL-10R1, IL-20R1 or IL-22R1) and a subunit with a short intracellular domain (R2 type receptors; IL-10R2 or IL-20R2). In this study we report the identification of three R1 type receptors (named IL-10R1/CRFB7, IL-20R1a/CRFB8a and IL-20R1b/CRFB8b) and one R2 type receptor (named IL-10R2/CRFB4) in rainbow trout. The nomenclature of the receptors was supported by homology analysis, conserved motifs and phylogenetic tree analysis, confirming they belong to the piscine class 2 cytokine receptor family. For instance, they all displayed the presence of characteristic features, such as conserved fibronectin type-III domains. Expression analysis in tissues collected from healthy fish revealed different patterns of expression for each receptor, suggesting their potential involvement in different types of immune responses. When studying the modulation of the genes in cell lines and primary cultures, a greater effect was observed in the cell lines, where the expression of most receptors was affected by incubation with microbial mimics (LPS and PolyI:C) or the pro-inflammatory cytokine rIFN-γ. In addition, expression of the four receptors was modulated by viral infection, suggesting a potential involvement of such receptors and their ligands in antiviral defence.

Acquired immunity and vaccination against infectious pancreatic necrosis virus of salmon

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

The cytokine networks of adaptive immunity in fish

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

Two types of TNF-α exist in teleost fish: phylogeny, expression, and bioactivity analysis of type-II TNF-α3 in rainbow trout Oncorhynchus mykiss

TNF-α is a cytokine involved in systemic inflammation and regulation of immune cells. It is produced chiefly by activated macrophages as a membrane or secreted form. In rainbow trout, two TNF-α molecules were described previously. In this article, we report a third TNF-α (TNF-α3) that has only low identities to known trout molecules. Phylogenetic tree and synteny analyses of trout and other fish species suggest that two types (named I and II) of TNF-α exist in teleost fish. The fish type-II TNF-α has a short stalk that may impact on its enzymatic release or restrict it to a membrane-bound form. The constitutive expression of trout TNF-α3 was generally lower than the other two genes in tissues and cell lines, with the exception of the macrophage RTS-11 cell line, in which expression was higher. Expression of all three TNF-α isoforms could be modulated by crude LPS, peptidoglycan, polyinosinic:polycytidylic acid, and rIFN-γ in cell lines and primary macrophages, as well as by bacterial and viral infections. TNF-α3 is the most responsive gene at early time points post-LPS stimulation and can be highly induced by the T cell-stimulant PHA, suggesting it is a particularly important TNF-α isoform. rTNF-α3 produced in CHO cells was bioactive in different cell lines and primary macrophages. In the latter, it induced the expression of proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-17C, and TNF-αs), negative regulators (SOCS1-3, TGF-β1b), antimicrobial peptides (cathelicidin-1 and hepcidin), and the macrophage growth factor IL-34, verifying its key role in the inflammatory cytokine network and macrophage biology of fish.

Red mark syndrome in rainbow trout Oncorhynchus mykiss: investigation of immune responses in lesions using histology, immunohistochemistry and analysis of immune gene expression

Red mark syndrome (RMS) is an economically significant disease which affects farmed rainbow trout in the United Kingdom, in the US and in mainland Europe. From the pattern of incidence, it appears to be transmissable, although no causative agent has yet been identified. RMS presents as a severe lymphocytic infiltration centred on the dermis and an alternative, host-focused approach was taken to understand the disease through investigating immune responses occurring in the lesion. Lesion and non-lesion skin at different stages of lesion development were examined using histochemistry and immunohistochemistry on paraffin sections. Expression of immune-related genes was compared between lesion and non-lesion skin. Investigation of early stage lesions suggested that the initial immune response is targeted at the region of the scale pocket, with lymphocyte infiltration and anti-tumour necrosis factor (TNF)-α staining of the stratum spongiosum, and increased numbers of major histocompatibility complex (MHC) II-positive cells immediately adjacent to the scale pocket. Gene expression analysis suggested a counterbalancing T helper (Th)1 and T regulatory (Treg) - type response is occurring in the lesion, with repression of Th2 and Th17-type responses.

Inflammatory response of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) larvae against Ichthyophthirius multifiliis

At hatching, the immune system of the rainbow trout larva is not fully developed. The larva emerges from the egg and is exposed to the aquatic freshwater environment containing pathogenic organisms. At this early stage, protection from disease causing organisms is thought to depend on innate immune mechanisms. Here, we studied the ability of young post-hatch rainbow trout larvae to respond immunologically to an infection with Ichthyophthirius multifiliis and also report on the localization of 5 different immune relevant molecules in the tissue of infected and uninfected larvae. Quantitative RT-PCR (qPCR) was used to analyze the genetic regulation of IL-1β, IL-8, IL-6, TNF-α, iNOS, SAA, cathelicidin-2, hepcidin, IL-10, IL-22, IgM and IgT. Also, a panel of 5 monoclonal antibodies was used to investigate the presence and localization of the proteins CD8, SAA, MHCII, IgM and IgT. At 10 days (84 degree days) post-hatching, larvae were infected with I. multifiliis and sampled for qPCR at 3, 6, 12, 24, 48 and 72 h post-infection (p.i.). At 72 h p.i. samples were taken for antibody staining. The first of the examined genes to be up-regulated was IL-1β. Subsequently, IL-8 and cathelicidin-2 were up-regulated and later TNF-α, hepcidin, IL-6, iNOS and SAA. Immunohistochemical staining showed presence of CD8 and MHCII in the thymus of both infected and non-infected larvae. Staining of MHCII and SAA was seen at sites of parasite localization and weak staining of SAA was seen in the liver of infected larvae. Staining of IgT was seen at site of infection in the gills which may be one of the earliest adaptive factors seen. No positive staining was seen for IgM. The study illustrates that rainbow trout larvae as young as 10 days (84 degree days) post-hatch are able to regulate important immune relevant cytokines, chemokines and acute phase proteins in response to infection with a skin parasitizing protozoan parasite.

Identification and molecular characterization of the interleukin-10 receptor 1 of the zebrafish (Danio rerio) and the goldfish (Carassius auratus L.)

This is the first report of the identification and molecular characterization of an interleukin-10 receptor 1 in bony fish. By gene synteny analysis, we identified the zebrafish interleukin-10 receptor 1 (IL10R1) and using this IL10R1 sequence, we cloned the goldfish IL10R1 cDNA transcript. The identified fish IL10R1 protein sequences had a putative JAK1 binding site, only one of the two STAT3 binding sites, that are present in all other vertebrates IL10R1 proteins as well as C-terminal serine rich areas, believed to be responsible for the anti-inflammatory properties of IL10R1. Phylogenetically, the fish IL10R1 proteins grouped independently of the amphibian, avian and mammalian IL10R1s. Quantitative gene expression analysis of the IL10R1 of zebrafish and goldfish revealed highest mRNA levels in the spleen tissues. High mRNA levels were also observed in the zebrafish muscle in contrast to low mRNA levels in the muscle of the goldfish. Moderate IL10R1 mRNA levels were seen in most other tissues examined and lowest gene expression was in the liver of both fish species. Goldfish monocytes stimulated with a recombinant goldfish interleukin-10 (rgIL-10) or with heat killed fish pathogens, Aeromonas salmonicida or Trypanosoma carassii, exhibited significantly reduced mRNA levels of the IL10R1. Furthermore, we produced a recombinant form of the goldfish IL10R1 (rgIL10R1) and using in vitro binding studies, demonstrated that the dimerized rgIL-10 specifically interacted with rgIL10R1. Our results suggest that interleukin-10 system has been highly conserved throughout evolution.