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

Megalobrama amblycephala IL-22 attenuates Aeromonas hydrophila induced inflammation, apoptosis and tissue injury by regulating the ROS/NLRP3 inflammasome axis

Mammalian interleukin-22 (IL-22) attenuates organismal injury by inhibiting reactive oxygen species (ROS) and impeding the NLRP3 inflammasome activation. However, the role of fish IL-22 in this process remains unclear. We characterized MaIL-22, an IL-22 homolog in blunt snout bream (Megalobrama amblycephala). Despite its low sequence identity, it shares conserved structures and close evolutionary relationships with other teleost IL-22s. Furthermore, Aeromonas hydrophila (A. hydrophila) infection leads to tissue injury in M. amblycephala immune organs and concomitantly altered Mail-22 mRNA expression, suggesting that MaIL-22 was involved in the antimicrobial immune response. To explore MaIL-22's biological functions, we produced recombinant MaIL-22 (rMaIL-22) protein and demonstrated it significantly enhanced the survival of M. amblycephala post-A. hydrophila infection. To unravel its protective mechanisms, we explored the ROS/NLRP3 inflammasome axis and its downstream signaling responses. The results showed that rMaIL-22 treatment significantly elevated antioxidant enzyme (T-SOD, CAT and GSH-PX) activities to inhibit MDA activity and scavenge ROS in visceral tissues. Meanwhile, rMaIL-22 impeded the activation of NLRP3 inflammasome by suppressing NLRP3 protein and mRNA expression. This indicated that rMaIL-22 contributed to inhibit A. hydrophila-induced activation of the ROS/NLRP3 inflammasome axis. Consistent with these findings, rMaIL-22 treatment attenuated the expression of proinflammatory cytokines (il-1β, tnf-α and il-6) and proapoptotic genes (caspase-3 and caspase-8) while promoting antiapoptotic genes (bcl-2b and mcl-1a) expression, ultimately mitigating tissue injury in visceral tissues. In conclusion, our research underscores MaIL-22's key role in microbial immune regulation, offering insights for developing IL-22-targeted therapies and breeding programs.

Identification, functional characterization and immune response profiles of interleukin-10 in Nibea albiflora

Interleukin-10 (IL-10) is an immunosuppressive cytokine, which plays a vital role in regulating inflammation for inhibiting the generation and function of pro-inflammatory cytokines in vivo or in vitro. In the present study, the full length cDNA of IL-10 was characterized from Nibea albiflora (named as NaIL-10) of 1238 base pairs (bp), containing a 5'-UTR (untranslated region) of 350 bp, a 3'-UTR of 333 bp and an open reading frame (ORF) of 555 bp (Fig. 1A) to encode 184 amino acid residues with a signal peptide at the N-terminus. The sequence analysis showed that NaIL-10 possessed the typical IL-10 family symbolic motif and conversed cysteine residues, similar to its teleost orthologues. Real-time PCR indicated that NaIL-10 had wide distribution in different healthy tissues, with a relatively high expression in immune-related tissues (head kidney, spleen, kidney, liver and gill). Significantly, up-regulations of NaIL-10 after infection against Vibrio parahaemolyticus, Vibrio alginolyticus and Poly I:C were also observed. Subcellular localization manifested that NaIL-10 mainly distributed in the cytoplasm unevenly and aggregately, and there was also a small amount on the cell membrane, indicating that NaIL-10 was secreted to the extracellular space as the known IL-10 homologous molecules. It could co-locate with IL-10 Rα on the membrane of HEK293T cells for their potential interaction, and GST pull-down and Co-IP studies certified the specific and direct interaction between NaIL-10 and NaIL-10 Rα, confirming that an IL-10 ligand-receptor system existed in N.albiflora. The expression of pro-inflammatory cytokines, including TNF-α, IL-6, IL-1β, were dramatically inhibited in LPS-stimulated RAW264.7 macrophages pre-incubated with recombinant NaIL-10 protein, demonstrating its anti-inflammatory roles. Taken together, the results demonstrated the existence of IL-10 ligand-receptor system in N.albiflora for the first time, and indicated the suppressive function of NaIL-10 on pro-inflammatory cytokine expression in inflammatory response, which would be conducive to better comprehending the role of IL-10 in the immunomodulatory mechanisms of teleost.

Padina Minor Extract Confers Resistance against Candida Albicans Infection: Evaluation in a Zebrafish Model

Padina minor is a seaweed rich in polysaccharides often used in food, feed, fertilizers, and antibacterial drugs. This study is the first to evaluate the effect of feeding zebrafish with Padina minor extract on preventing and treating C. albicans infections. This study evaluated the growth, survival, and disease resistance effects of P. minor extract on zebrafish. The fish were divided into four groups: three groups treated with 1%, 5%, or 10% P. minor extract and one untreated group (c, control). Subsequently, we analyzed how the extract affected the immune function of zebrafish infected with C. albicans. Based on the lethal concentration (LC50) calculated in the first stage, 1% was used as the effective therapeutic concentration. The results showed that the growth rate of the 1% feed group was the best, and no significant difference in survival rates between the four groups was observed. Feeding with 1% P. minor extract downregulated the expression of key inflammatory genes like tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and IL-10, effectively preventing and treating C. albicans infections in zebrafish. This study is a preliminary evaluation of the therapeutic efficacy of P. minor extracts against C. albicans.

Spring Viremia of Carp Virus Infection Induces Carp IL-10 Expression, Both In Vitro and In Vivo

Interleukin-10 (IL-10) is a pleiotropic cytokine with both immune enhancement and immunosuppression activities, but the main role is immunosuppression and anti-inflammatory ability. In order to use the immunosuppressive function of IL-10, many viruses, such as SARS-CoV-2, hepatitis B virus and EB virus, can evade the host's immune surveillance and clearance by increasing the expression of host IL-10. However, it has not been reported whether the aquatic animal infection virus can upregulate the expression of host IL-10 and the mechanisms are still unknown. Spring viremia of carp (SVC) is a fatal viral disease for many fish species and is caused by spring viremia of carp virus (SVCV). This disease has caused significant economic losses in the aquaculture industry worldwide. In this study, the expression of carp IL-10 with or without infection of SVCV in epithelioma papulosum cyprinid (EPC) cells, carp head kidney (cHK) primary cells and common carp tissues were analyzed using RT-PCR and ELISA. The results show that SVCV infection induced carp IL-10 mRNA and protein expression, both in vitro and in vivo. However, the upregulation of carp IL-10 by SVCV was hindered by specific inhibitors of the JAK inhibitor (CP-690550), STAT3 inhibitor (STA-21), NF-κB inhibitor (BAY11-7082) and p38 MAPK (mitogen-activated protein kinase) inhibitor (SB202190), but not JNK inhibitor (SP600125). Furthermore, the results demonstrated that JAK1, JAK2, JAK3, TYK2 and STAT5 played important roles in carp IL-10 production induced by SVCV infection. Taken together, SVCV infection significantly induced carp IL-10 expression and the upregulation trigged in JAK-STAT, NF-κB and p38MAPK pathways. To our knowledge, this is the first time that a fish infection virus upregulated the host IL-10 expression through the JAK-STAT, NF-κB and p38MAPK pathways. Altogether, fish viruses may have a similar mechanism as human or other mammalian viruses to escape host immune surveillance and clearance.

Cytokine networks that suppress fish cellular immunity

Immunosuppressive cytokines are a class of cytokines produced by immune cells and certain non-immune cells that have a suppressive effect on immune function. Currently known immunosuppressive cytokines include interleukin (IL)-10, transforming growth factor beta (TGF-β), IL-35, and IL-37. Although latest sequencing technologies have facilitated the identification of immunosuppressive cytokines in fish, IL-10 and TGF-β were the most well-known ones that have been widely studied and received continuous attention. Fish IL-10 and TGF-β have been identified as anti-inflammatory and immunosuppressive factors, acting on both innate and adaptive immune systems. However, unlike mammals, teleost fish underwent a third or fourth whole-genome duplication event, which significantly expanded the gene family associated with the cytokine signaling pathway, making the function and mechanism of these molecules need further investigation. In this review, we summarize the advances of studies on fish immunosuppressive cytokines IL-10 and TGF-β since their identification, mainly focusing on production, signaling transduction, and effects on the immunological function. This review aims to expand the understanding of the immunosuppressive cytokine network in fish.

Molecular Characterization and Expression Analysis of IL-10 and IL-6 in Channel Catfish (Ictalurus punctatus)

IL-10 and IL-6 play important roles in protecting against inflammation and clearing pathogens from the body. In this study, homologous compounds of IL-10 and IL-6 were identified in channel catfish, and their immune responses were analyzed. The CDS sequences of IL-10 and IL-6 were 549 bp and 642 bp, respectively, and showed the highest homology with Ameiurus melas. In addition, the expression of the IL-10 and IL-6 genes was ubiquitous in 10 tissues examined. IL-10 is highly expressed in the liver and slightly expressed in the gill. The high expression of the IL-6 gene was observed in the spleen, heart, and gonad, with the lowest levels in the liver. LPS, Poly(I:C), PHA, and PMA showed a highly significant increase in IL-10 and IL-6 expression 48 h after CCK stimulation (p < 0.01). Otherwise, Yersinia ruckeri, Streptococcus iniae, channel catfish virus, and deltamethrin induced IL-10 and IL-6 expression, varying in intensity between different organs. Our results suggest that IL-10 and IL-6 are involved in the immune response of the host against the pathogen.

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.

Interleukin (IL)-22 in common carp (Cyprinus carpio L.): Immune modulation, antibacterial defense, and activation of the JAK-STAT signaling pathway

Interleukin (IL)-22 is an IL-10 family cytokine secreted by CD4⁺ T cells and plays an important role in regulating inflammation and infection elimination. IL-22 homologues have been reported in the teleost, but the functions of IL-22 are still unclear. In this study, we identified two duplicated IL-22 genes in common carp (Cyprinus carpio L.), termed Cc_IL-22A and Cc_IL-22B. Sequence analysis showed that Cc_IL-22A and Cc_IL-22B had four conserved cysteine residues, which could form two intra-chain disulfide bridges. The Cc_IL-22A and Cc_IL-22B were constitutively expressed in various tissues, with the highest expression in the gill. The mRNA expression levels of Cc_IL-22A and Cc_IL-22B were significantly up-regulated in the gill, intestine, head kidney, and spleen of common carp challenged with Aeromonas. hydrophila. In vivo study showed that the expression levels of pro-inflammatory cytokines were significantly up-regulated in the head kidney and spleen when Cc_IL-22A or Cc_IL-22B were over-expressed. Furthermore, the over-expression of Cc_IL-22A and Cc_IL-22B indicated a protective effect on tissues, with only lymphocytic infiltration observed in comparison to the control and pcN3 groups, without obvious change in tissue morphology. Similar stimulatory effects of rIL-22A and rIL-22B were observed in vitro. When HKLs were stimulated with rIL-22A or rIL-22B, the expression levels of critical signaling molecules in the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathway were significantly induced, including JAK1, JAK3, STAT1, and STAT3, as well as pro-inflammatory cytokines (IL-1β and TNF-α). Together, these results suggest that Cc_IL-22A and Cc_IL-22B may regulate inflammatory responses through the JAK-STAT signaling pathway and have a significant impact on the immune defense of common carp against bacterial infection. Therefore, our study provides a new perspective on the functions of Cc_IL-22A and Cc_IL-22B in the immune defense mechanism of fish.

Toxicological impacts of nanopolystyrene on zebrafish oocyte with insight into the mechanism of action: An expression-based analysis

Many studies have investigated the negative impacts of microplastics on teleost fishes with very little or no evidence of their mechanism of action. This scenario entreats us to investigate the toxicities of nanopolystyrene in zebrafish oocyte with emphasis on the mechanism of action. In the present study, the cellular levels of mRNA transcripts of different genetic markers (such as: sod, gpx, nrf2, inos, ucp2, and atp6 (redox-sensitive markers); nfkβ, tnfα, il-10, ikβ, gdf9, and bmp15 (immune markers); gadd45, rad51, p53 and bcl2 (DNA damage and apoptotic)) have been quantified by real-time PCR after 6 h of incubation of isolated oocyte with different doses of nanopolystyrene viz. P0 (control i.e. no polystyrene in culture medium), P1 (100 ng/ml), and P2 (400 ng/ml). Results showed that both the treatment concentrations of nanopolystyrene induce oxidative stress with % DPPH = 30.75, 31.61, and 32.43% for P0, P1, and P2, respectively. Increase in oxidative stress in oocytes with increasing doses of nanopolystyrene was also observed in TBARS assay with MDA content 0.12 and 0.21 μM for P1 and P2, respectively as compaired to the control 0.08 μM. This increased oxidative stress can regulate the expression pattern (upregulation/downregulation) of selected genes leading to different toxic effects like - oxidative stress, immunotoxicity, and apoptosis in oocytes, which suggests the impairment of reproductive functions by nanopolystyrene.

Tongue sole (Cynoglossus semilaevis) interleukin 10 receptors are involved in the immune response against bacterial infection

Interleukin (IL)-10, an immune-regulatory cytokine, exerts various biological functions through interaction with IL-10 receptors. In teleost, very limited functional studies on IL-10 receptors have been documented. In this study, we reported the expression patterns of IL-10 receptor 1 (CsIL-10R1) and receptor 2 (CsIL-10R2) of tongue sole (Cynoglossus semilaevis) and examined their biological properties. The expression of CsIL-10R1 and CsIL-10R2 occurred in multiple tissues and were regulated by bacterial challenge. In vitro binding studies showed that recombinant extracellular region of CsIL-10R1 (rCsIL-10R1ex) rather than rCsIL-10R2ex could bind with rCsIL-10. Cellular study showed that both CsIL-10R1 and CsIL-10R2 were expressed on peripheral blood leukocytes (PBLs), and blockade of CsIL-10R1 or CsIL-10R2 by antibody could reduce inhibitory effect of CsIL-10 on ROS production of PBLs. When injected in vivo, anti-rCsIL-10R1 or anti-rCsIL-10R2 antibody dramatically promoted the expression of proinflammatory cytokines and suppressed bacterial dissemination in tongue sole tissues. Consistently, the overexpression of CsIL-10R1 or CsIL-10R2 significantly enhanced bacterial dissemination, and the overexpression of CsIL-10R1M bearing STAT3 site mutation reduced bacterial dissemination. Overall, these results demonstrate for the first time teleost IL-10 receptors play a negative role in antibacterial immunity and add insight into the function of CsIL-10 receptors.

Characterization of IL-22 Bioactivity and IL-22-Positive Cells in Grass Carp Ctenopharyngodon idella

Interleukin (IL)-22 plays an important role in regulating inflammation and clearance of infectious pathogens. IL-22 homologs have been discovered in fish, but the functions and sources of IL-22 have not been fully characterized. In this study, an IL-22 homolog was identified in grass carp and its bioactivities were investigated. The grass carp IL-22 was constitutively expressed in tissues, with the highest expression detected in the gills and hindgut. It was upregulated in the spleen after infection with Flavobacterium columnare and grass carp reovirus and in the primary head kidney and spleen leukocytes stimulated with LPS and IL-34. Conversely, it was downregulated by Th2 cytokines such as IL-4/13B and IL-10. The recombinant IL-22 produced in bacteria showed a stimulatory effect on the expression of inflammatory cytokines and STAT3 in the primary head kidney leukocytes and CIK cells. Moreover, the IL-22-positive cells were found to be induced in the hindgut and head kidney 24 h after infection by F. columnare. Our data suggest that IL-22 plays an important role in regulating mucosal and systemic immunity against bacterial and viral infection.

Zebrafish IL-4-like Cytokines and IL-10 Suppress Inflammation but Only IL-10 Is Essential for Gill Homeostasis

Mucosal surfaces such as fish gills interface between the organism and the external environment and as such are major sites of foreign Ag encounter. In the gills, the balance between inflammatory responses to waterborne pathogens and regulatory responses toward commensal microbes is critical for effective barrier function and overall fish health. In mammals, IL-4 and IL-13 in concert with IL-10 are essential for balancing immune responses to pathogens and suppressing inflammation. Although considerable progress has been made in the field of fish immunology in recent years, whether the fish counterparts of these key mammalian cytokines perform similar roles is still an open question. In this study, we have generated IL-4/13A and IL-4/13B mutant zebrafish (Danio rerio) and, together with an existing IL-10 mutant line, characterized the consequences of loss of function of these cytokines. We demonstrate that IL-4/13A and IL-4/13B are required for the maintenance of a Th2-like phenotype in the gills and the suppression of type 1 immune responses. As in mammals, IL-10 appears to have a more striking anti-inflammatory function than IL-4-like cytokines and is essential for gill homeostasis. Thus, both IL-4/13 and IL-10 paralogs in zebrafish exhibit aspects of conserved function with their mammalian counterparts.

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.

Induction of IL-22 protein and IL-22-producing cells in rainbow trout Oncorhynchus mykiss

IL-22 is a critical cytokine which is involved in modulating tissue responses during inflammation, and is produced mainly by T cells and innate leucocytes. In mammals, IL-22 is a key component in mucosal defences, tissue repair, epithelial cell survival and proliferation. In teleosts, IL-22 has been cloned and studied in several species, and the transcript is highly expressed in mucosal tissues and induced by pathogen associated molecular patterns (PAMPs), suggesting IL-22 also functions as an important component of the innate immune response in fish. To investigate these immune responses further, we have validated and characterised two monoclonal antibodies (mAbs) which were raised against two different peptide immunogens of salmonid IL-22. Our results show that both mAbs specifically react to their own peptide immunogens and recombinant IL-22, and are able to detect the induction of native protein expression after stimulation. In flow cytometry, an increase in IL-22 positive cells was detected after stimulation in vitro with cytokines and PAMPs and in vivo after bacterial challenge. The immunohistochemistry results showed that IL-22 is highly upregulated in the gills after challenge, both in cells within the gill filaments and in the interbranchial lymphoid tissue. Such results suggest IL-22 may have a role in triggering local antimicrobial defences in fish that may facilitate efficient microbial clearance. Hence monitoring IL-22 producing cells/protein secretion may provide an alternative mean to assess the effectiveness of mucosal vaccines.

Tongue sole (Cynoglossus semilaevis) interleukin 10 plays a negative role in the immune response against bacterial infection

Interleukin-10 (IL-10) is a pleiotropic cytokine and plays a crucial role in immunity. In the current study, we examined the expression patterns and biological functions of tongue sole Cynoglossus semilaevis IL-10 (CsIL-10). CsIL-10 is composed of 186 amino acid residues and shares 46.3%-71.7% identities with other teleost IL-10. Csil-10 expression occurred in multiple tissues and was regulated by bacterial infection. Recombinant CsIL-10 (rCsIL-10) in the form of a dimer bound to a wide range of bacterial species but did not affect bacterial growth. rCsIL-10 could interact with peripheral blood leukocytes (PBL) and significantly reduce the phagocytic activity, ROS production, and apoptosis of PBL. When injected in vivo, rCsIL-10 significantly suppressed the expression of proinflammatory cytokines and promoted bacterial dissemination in tongue sole tissues. Consistently, knockdown of Csil-10 significantly inhibited bacterial infection in tongue sole. Taken together, these results indicate that CsIL-10 plays a negative regulatory role in the immune response against bacterial infection.

Characterization and initial functional analysis of cathepsin K in turbot (Scophthalmus maximus L.)

Cathepsins are the best-known group of proteases in lysosomes, playing a significant role in immune responses. Cathepsin K (CTSK) is abundantly and selectively expressed in osteoclasts, dendritic cells and monocyte-derived macrophages, where it is involved in ECM degradation and bone remodeling. A growing body of evidences have indicated the vital roles of cathepsin K in innate immune responses. Here, one CTSK gene was captured in turbot (SmCTSK) with a 993 bp open reading frame (ORF). The genomic structure analysis showed that SmCTSK had 7 exons similar to other vertebrate species. The syntenic analysis revealed that CTSK had the same neighboring genes across all the selected species, which suggested the synteny encompassing CTSK region was conserved during vertebrate evolution. Subsequently, SmCTSK was widely expressed in all the examined tissues, with the highest expression level in spleen and the lowest expression level in liver. In addition, SmCTSK was significantly down-regulated in intestine following Gram-negative bacteria Vibrio anguillarum immersion challenge, but up-regulated in three tissues (gill, skin and intestine) following Gram-positive bacteria Streptococcus iniae immersion challenge. Finally, the rSmCTSK showed strong binding ability to all the examined microbial ligands. Taken together, our results suggested SmCTSK played vital roles in fish innate immune responses against infection. However, the knowledge of SmCTSK is still limited in teleost species, further studies should be carried out to better characterize its comprehensive roles in teleost mucosal immunity.

Functional characterization of IL-10 and its receptor subunits in a perciform fish, the mandarin fish, Siniperca chuatsi

Interleukin (IL)-10 is an immune-regulatory cytokine with multiple functions. In the current study, IL-10 and its two receptors, IL-10R1 and IL-10R2 were identified in mandarin fish, Siniperca chuatsi. The inhibitory effect of mandarin fish IL-10 was investigated on pro-inflammatory cytokine expression and the ligand-receptor relationship. This IL-10 possesses conserved cysteine residues, predicted α-helices and a typical IL-10 family signature motif, similar to its mammalian orthologue, and IL-10R1 harbours predicted JAK1 and STAT3 binding sites in the intracellular region. The fish IL-10 and IL-10R1 exhibit high expression levels in several immune-related organs/tissues, such as spleen, trunk kidney and head kidney, and IL-10R2 possesses a constitutive expression pattern. The expression of IL-10 shows significant increase in spleen from infectious spleen and kidney necrosis virus (ISKNV) infected mandarin fish, where the two receptors also exhibit different levels of induced expression. Mandarin fish IL-10 also exhibits significant response to the stimulation of LPS, PHA and PMA, with the two receptors exhibiting an interesting decrease in expression following the treatment of PMA. The pro-inflammatory cytokines, IL-6, IL-1β, IL-8, TNF-α, show diminished up-regulation in LPS-stimulated splenocytes pre-incubated with IL-10, indicating the anti-inflammatory roles of mandarin fish IL-10. In EPC cells transfected with different combinations of receptors, IL-10 can enhance the expression of suppressor of cytokine signalling 3 (SOCS3) only when IL-10R1 and IL-10R2 are both expressed, suggesting the participation of the two receptors in signal transduction of mandarin fish IL-10. Similar results are observed with the usage of chimeric receptors, IL-10R1/CRFB1 and IL-10R2/CRFB5. Overall, mandarin fish IL-10 shares conserved ligand-receptor system and the prototypical inhibitory activities on pro-inflammatory cytokine expression with mammalian IL-10, implying the evolutionary conservation of this cytokine.

Molecular Cloning and Expression Analysis of Interleukin-8 and -10 in Yellow Catfish and in Response to Bacterial Pathogen Infection

The yellow catfish (Pelteobagrus fulvidraco) is an important economic freshwater aquaculture species in Asia. However, little is known about its immune response to bacterial pathogen infection. Here, two cytokines, the proinflammatory cytokine interleukin-8 (IL-8) and the anti-inflammatory cytokine interleukin-10 (IL-10), were identified and characterized in the yellow catfish for the first time. We found that the full length of the IL-8 cDNA was 784 bp and contained an open reading frame (ORF) of 336 bp, while the IL-10 gene was 973 bp in length with a 549 bp of ORF. In addition, both the IL-8 and the IL-10 had similar tissue-specific expression patterns. They were more abundant in the spleen and lowest expressed in the liver. Furthermore, IL-10 but not IL-8 was significantly upregulated in the intestine of yellow catfish by feed supplementation of Clostridium butyricum (CB). More importantly, the expression levels of intestinal IL-10 and IL-8 were up- and downregulated by pathogen Aeromonas punctata stimuli with the presence of CB, respectively. Collectively, these results suggest that IL-10 and IL-8 mediate important roles in the immunity of yellow catfish, and feed supplementation of CB may able to reduce the intestinal inflammation caused by bacteria infections through regulating the expression of IL-10 and IL-8.

Genome and Phylogenetic Analysis of Genes Involved in the Immune System of Solea senegalensis - Potential Applications in Aquaculture

Global aquaculture production continues to increase rapidly. One of the most important species of marine fish currently cultivated in Southern Europe is Solea senegalensis, reaching more than 300 Tn in 2017. In the present work, 14 Bacterial Artificial Chromosome (BAC) clones containing candidate genes involved in the immune system (b2m, il10, tlr3, tap1, tnfα, tlr8, trim25, lysg, irf5, hmgb2, calr, trim16, and mx), were examined and compared with other species using multicolor Fluorescence in situ Hybridization (mFISH), massive sequencing and bioinformatic analysis to determine the genomic surroundings and syntenic chromosomal conservation of the genomic region contained in each BAC clone. The mFISH showed that the groups of genes hmgb2-trim25-irf5-b2m; tlr3-lysg; tnfα-tap1, and il10-mx-trim16 were co-localized on the same chromosomes. Synteny results suggested that the studied BACs are placed in a smaller number of chromosomes in S. senegalensis that in other species. Phylogenetic analyses suggested that the evolutionary rate of immune system genes studied is similar among the taxa studied, given that the clustering obtained was in accordance with the accepted phylogenetic relationships among these species. This study contributes to a better understanding of the structure and function of the immune system of the Senegalese sole, which is essential for the development of new technologies and products to improve fish health and productivity.

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.

Molecular characterization and expression analysis of big-belly seahorse (Hippocampus abdominalis) interleukin-10 and analysis of its potent anti-inflammatory properties in LPS-induced murine macrophage RAW 264.7 cells

Interleukin-10 (IL-10) is a pleiotropic cytokine involved in the regulation of innate and adaptive immunity. In this study, IL-10 from big-belly seahorse (Hippocampus abdominalis) (HaIL-10) was characterized based on its molecular and functional aspects. The coding sequence of HaIL-10 is 570 bp in length and encodes a 189-amino acid residue protein (calculated molecular weight, 21.89 kDa). The deduced amino acid sequence comprises a typical signal peptide and a mature peptide domain sequence carrying four conserved Cys residues and two additional Cys residues specific to fish. Phylogenetic analysis indicated an evolutionary relationship between HaIL-10 and its counterparts in other vertebrates, with close clustering to the fish-specific homologs. Recombinant HaIL-10 (rHaIL-10) significantly reduced nitric oxide (NO) production by lipopolysaccharide (LPS)-induced murine macrophage RAW 264.7 cells in a concentration-dependent manner but had no effect on cell viability, suggestive of its involvement in immune response. The protein expressions of iNOS and COX-2 were significantly reduced by rHaIL-10 in LPS-induced murine macrophages RAW 264.7 cells. HaIL-10 mRNA expression was observed in all analyzed tissues, with the maximum expression being noted in the kidney and ovary. However, transcriptional levels of HaIL-10 were significantly higher in the blood, gill, and intestine upon in vivo induction with LPS, polyinosinic:polycytidylic acid [poly (I:C)], and Streptococcus iniae. To summarize, our findings help in the improved understanding of the biological functions of HaIL-10 and modulation of HaIL-10 mRNA expression in response to immune stress.

Molecular characterization and expression analysis of IL-22 and its two receptors genes in yellow catfish (Pelteobagrus filvidraco) in response to Edwardsiella ictaluri challenge

Interleukin (IL)-22, as a member of the interleukin (IL)-10 family, is an important mediator between the immune cells and epithelial tissues during infection and inflammation. This study reported the characterization and mRNA expression patterns of Pf_IL-22 gene and its cell surface-associated receptors Pf_IL-22RA1 and soluble Pf_IL-22RA2 genes in yellow catfish (Pelteobagrus filvidraco). The open reading frames (ORFs) of the Pf_IL-22, Pf_IL-22RA1 and Pf_IL-22RA2 genes were 546 bp, 1740 bp and 690 bp in length, encoding 181, 579 and 229 amino acids, respectively. Alignments of the deduced amino acid sequences present that the Pf_IL-22 has a conserved IL-10 family signature motif, and the Pf_IL-22RA1 and Pf_IL-22RA2 have two conserved fibronectin type-III domains. Quantitative real-time PCR (qPCR) analyses showed that the Pf_IL-22 and Pf_IL-22RA1 mRNAs were highly expressed in mucosal tissues such as the fin, gill, intestine, skin mucus and stomach, and were weakly expressed in the kidney, liver and head kidney of adult yellow catfish, indicating that the Pf_IL-22 transcripts may be mainly produced by mucosal immune cells/tissues in healthy yellow catfish. The mRNA expression levels of the Pf_IL-22RA2 gene were high in the muscle and liver, and were relatively low in the spleen and kidney. The mRNA expression levels of the Pf_IL-22 and its two receptor genes were significantly up-regulated in both mucosal tissues (gill, hindgut, and skin mucus) and systemic immune tissues (spleen, head kidney and blood) after Edwardsiella ictaluri challenge. These results indicated that the Pf_IL-22 and its two receptors genes might play an important role in the innate immune defense against bacterial invasion.

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.

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.

Transcriptome signatures in common carp spleen in response to Aeromonas hydrophila infection

The common carp is an important aquaculture species that is worldwide distributed. Nowadays, intensive rearing in aquaculture increases the susceptibility of fish to various pathogens such as Aeromonas hydrophila, which has caused severe damage to carp production. However, systematic analysis on the host response of common carp against A. hydrophila is less studied. In order to better understand the common carp immune response process against bacteria at the global gene expression level, we examined transcriptional profiles of the common carp spleen at three timepoints following experimental infection with A. hydrophila. A total of 545 million 125-bp paired end reads were generated, and all trimmed clean reads were mapped onto the common carp whole genome sequence. Comparison of the transcriptomes between the treatment and control group fish revealed 2900 unigenes with significantly differential expression, including 732, 936, 928 genes up-regulated, and 248, 475, 700 genes down-regulated at 4 h, 12 h, 24 h post infection respectively. The captured significantly differentially expressed genes are mainly involved in the pathways including junction/adhesion, pathogen recognition, cell surface receptor signaling, and immune system process/defense response. Our study will provide fundamental information on molecular mechanism underlying the immune response of teleost against bacterial infection and might suggest strategies for selection of resistant strains of common carp in aquaculture.

Identification, Molecular Cloning of IL-1β and Its Expression Profile during Nocardia seriolae Infection in Largemouth Bass, Micropterus salmoides

In the present study, IL-1β cDNA was identified and analyzed from largemouth bass (Micropterus salmoides). Full length IL-1β mRNA was obtained using Rapid Amplification of cDNA Ends (RACE), which contains 78 bp 3'-UTR, a 455 bp 5'-UTR, and an open reading frame (ORF) of 702 bp coding for 233 amino acid residues. The molecular weight and theoretical isoelectric point of largemouth bass IL-1β protein was predicted to be 26.7 kDa and 6.08 respectively. A largemouth bass IL-1β phylogenetic analysis showed a close relation to the IL-1βs of striped trumpeter (Latris lineata), Chinese perch (Siniperca chuatsi), and Japanese sea bass (Lateolabrax japonicus). Peptidoglycan upregulated IL-1β in the spleen and head kidney, while lipopolysaccharide upregulated detectable levels of IL-1β in the spleen only. Largemouth bass, challenged with Nocardia seriolae (1.0 × 10⁶ cfu/mL), showed a significant increase in IL-1β at 3 and 5 days post infection (dpi) in the spleen, while in the head kidney significant expression was found at 2 and 3 dpi, peaking at 3 dpi. Furthermore, tumor necrosis factor α (TNF-α) showed significantly higher expression in the spleen at 3 and 5 dpi, and in the head kidney at 1 and 3 dpi, with expression decreasing at 5 dpi in both tissues.

Structural and Functional Characterization of Recombinant Interleukin-10 from Indian Major Carp Labeo rohita

Interleukin-10, an important regulator of both the innate and adaptive immune systems, is a multifunctional major cytokine. Though it is one of the major cytokines, IL-10 from the Indian major carp, Labeo rohita, has not yet been characterized. In the present study, we report large scale production and purification of biologically active recombinant IL-10 of L. rohita (rLrIL-10) using a heterologous expression system and its biophysical and functional characterization. High yield (~70 mg/L) of soluble rLrIL-10 was obtained at shake flask level. The rLrIL-10 was found to exist as a dimer. Far-UV CD spectroscopy showed presence of predominantly alpha helices. The tertiary structure of the purified rLrIL-10 was verified by fluorescence spectroscopy. Two-dimensional gel analysis revealed the presence of six isoforms of the rLrIL-10. The rLrIL-10 was biologically active and its administration significantly reduced serum proinflammatory cytokines, namely, interleukin 1β, TNFα, and IL-8, and augmented the NKEF transcript levels in spleen of L. rohita. Anti-inflammatory role of the rLrIL-10 was further established by inhibition of phagocytosis using NBT reduction assay in vitro. The data indicate that the dimeric alpha helical structure and function of IL-10 of L. rohita as a key regulator of anti-inflammatory response have remained conserved during evolution.

Importance of prebiotics in aquaculture as immunostimulants. Effects on immune system of Sparus aurata and Dicentrarchus labrax

Infectious diseases in fish represent a major problem for the aquaculture field as they produce extensive damages and loss. Over the last few years, with increased development of the aquaculture industry, different methods have been used to contrast these pathologies. Common interest has led to the use of components (as additives in diets) that could contrast diseases without causing any negative impact on the environment. These components are represented by prebiotics, probiotics, and plant extracts. In this review, the effects of prebiotics are described. Prebiotics are indigestible fibres fermented by gut enzymes and commensal bacteria, whose beneficial effects are due to the by-products generated from fermentation. The influence of pre-biotics on the immune system of fish is called immunosaccharides. Mannanoligosaccharides (MOS), Fructooligosaccharides (FOS) and Inulin act at different levels in the innate immune response. For example, through phagocytosis, lysozyme activity, and the complement system activity, an increase in fish growth and an amelioration of their health status is brought about. In this review, the use of prebiotics in aquaculture, such as immunostimulants, has been highlighted: particularly in two teleost fish species, Sparus aurata and Dicentrarchus labrax. The results demonstrate that the road is still long and further studies are required, but the use of prebiotics, individually or coupled together, can open the doors to pioneering a new model of alternative components to antimicrobial agents.

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.

Carp Il10 Has Anti-Inflammatory Activities on Phagocytes, Promotes Proliferation of Memory T Cells, and Regulates B Cell Differentiation and Antibody Secretion

In the current study, we investigated the effects of carp Il10 on phagocytes and lymphocytes. Carp Il10 shares several prototypical inhibitory activities on phagocytes with mammalian IL-10, including deactivation of neutrophils and macrophages, as shown by inhibition of oxygen and nitrogen radical production, as well as reduced expression of proinflammatory genes and mhc genes involved in Ag presentation. Similar to mammalian IL-10, carp Il10 acts through a signaling pathway involving phosphorylation of Stat3, ultimately leading to the early upregulation of socs3 expression. To our knowledge, this is the first study of the effects of Il10 on lymphocytes in fish. Although Il10 did not affect survival and proliferation of T cells from naive animals, it greatly promoted survival and proliferation of T cells in cultures from immunized animals, but only when used in combination with the immunizing Ag. Preliminary gene expression analysis suggests that, under these circumstances, carp Il10 stimulates a subset of CD8+ memory T cells while downregulating CD4+ memory Th1 and Th2 responses. In addition to the regulatory effect on T cells, carp Il10 stimulates proliferation, differentiation, and Ab secretion by IgM+ B cells. Overall, carp Il10 shares several prototypical activities with mammalian IL-10, including downregulation of the inflammatory response of phagocytes, stimulation of proliferation of subsets of memory T lymphocytes, and proliferation, differentiation, and Ab secretion by IgM+ B lymphocytes. To our knowledge, this is the first comprehensive analysis of biological activities of fish Il10 on both phagocytes and lymphocytes showing functional conservation of several properties of Il10.

Effect of hydrogen peroxide and/or Flavobacterium psychrophilum on the gills of rainbow trout, Oncorhynchus mykiss (Walbaum)

The immune response and morphological changes in the gills of rainbow trout fry after immersion in hydrogen peroxide (H2O2), Flavobacterium psychrophilum or combined exposure were examined. The gills were sampled 4, 48, 125 and 192 h after exposure, and the regulation of expression of the following genes was investigated using qPCR: IgT, IgM, CD8, CD4, MHC I, MHC II, IL-4/13A, TcR-β, IL-10, IL-1β, IL-17, SAA and FoxP3. Bacteria were not observed in haematoxylin-and-eosin-stained gill tissue, but the presence of F. psychrophilum 16S rRNA was detected using qPCR. The 16S rRNA levels were correlated with gene expression. Although pretreatment with H2O2 before immersion in F. psychrophilum did not significantly alter the amount of bacteria found in the gill, the immune response was influenced: exposure to F. psychrophilum resulted in a negative correlation with expression of IL-17c1, MHC I and MHC II, while pretreatment with H2O2 resulted in a positive correlation with IL-4/13A and IgM. Exposure to either H2O2 or F. psychrophilum influenced the regulation of gene expression and damaged tissue. Exposure to both combined altered the immune response to infection and postponed healing of gill tissue.

Transciptome analysis of the gill and swimbladder of Takifugu rubripes by RNA-Seq

The fish gill, as one of the mucosal barriers, plays an important role in mucosal immune response. The fish swimbladder functions for regulating buoyancy. The fish swimbladder has long been postulated as a homologous organ of the tetrapod lung, but the molecular evidence is scarce. In order to provide new information that is complementary to gill immune genes, initiate new research directions concerning the genetic basis of the gill immune response and understand the molecular function of swimbladder as well as its relationship with lungs, transcriptome analysis of the fugu Takifugu rubripes gill and swimbladder was carried out by RNA-Seq. Approximately 55,061,524 and 44,736,850 raw sequence reads from gill and swimbladder were generated, respectively. Gene ontology (GO) and KEGG pathway analysis revealed diverse biological functions and processes. Transcriptome comparison between gill and swimbladder resulted in 3,790 differentially expressed genes, of which 1,520 were up-regulated in the swimbladder while 2,270 were down-regulated. In addition, 406 up regulated isoforms and 296 down regulated isoforms were observed in swimbladder in comparison to gill. By the gene enrichment analysis, the three immune-related pathways and 32 immune-related genes in gill were identified. In swimbladder, five pathways including 43 swimbladder-enriched genes were identified. This work should set the foundation for studying immune-related genes for the mucosal immunity and provide genomic resources to study the relatedness of the fish swimbladder and mammalian lung.

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.

Cloning and characterization of bottlenose dolphin (Tursiops truncatus) interleukin-10

The function of cytokines in cetaceans has so far only been determined for the proinflammatory cytokines. In this study, we cloned bottlenose dolphin (Tursiops truncatus) interleukin-10 (IL-10) cDNA from concanavalin A (Con A)-stimulated peripheral blood mononuclear cells (PBMC), and investigated the mRNA expression levels in various tissues and the bioactivity of recombinant dolphin (rd) IL-10. The gene encodes a polypeptide of 178 amino acids which encompasses the mature protein sequence of 158 amino acids. Quantitative expression analysis of dolphin IL-10 revealed that the highest mRNA levels are found in the spleen. To assess its function, rdIL-10 was produced in human embryonic kidney 293 cells and its bioactivity was demonstrated through IL-10-induced inhibition of proinflammatory cytokine mRNA expression IFN-γ, TNF-α, and IL-2 of Con A-stimulated PBMC. These results indicated that the structure and function of bottlenose dolphin IL-10 is similar to that of other animals. This is the first report of the characterization of an anti-inflammatory cytokine in cetaceans.

Trout oral VP2 DNA vaccination mimics transcriptional responses occurring after infection with infectious pancreatic necrosis virus (IPNV)

Time-course and organ transcriptional response profiles in rainbow trout Oncorhynchus mykiss were studied after oral DNA-vaccination with the VP2 gene of the infectious pancreatic necrosis virus (IPNV) encapsulated in alginates. The profiles were also compared with those obtained after infection with IPNV. A group of immune-related genes (stat1, ifn1, ifng, mx1, mx3, il8, il10, il11, il12b, tnf2, mhc1uda, igm and igt) previously selected from microarray analysis of successful oral vaccination of rainbow trout, were used for the RTqPCR analysis. The results showed that oral VP2-vaccination qualitatively mimicked both the time-course and organ (head kidney, spleen, intestine, pyloric ceca, and thymus) transcriptional profiles obtained after IPNV-infection. Highest transcriptional differential expression levels after oral vaccination were obtained in thymus, suggesting those might be important for subsequent protection against IPNV challenges. However, transcriptional differential expression levels of most of the genes mentioned above were lower in VP2-vaccinated than in IPNV-infected trout, except for ifn1 which were similar. Together all the results suggest that the oral-alginate VP2-vaccination procedure immunizes trout against IPNV in a similar way as IPNV-infection does while there is still room for additional improvements in the oral vaccination procedure. Some of the genes described here could be used as markers to further optimize the oral immunization method.

Approaches towards DNA vaccination against a skin ciliate parasite in fish

Rainbow trout (Oncorhynchus mykiss) were immunized with plasmid DNA vaccine constructs encoding selected antigens from the parasite Ichthyophthirius multifiliis. Two immobilization antigens (I-ags) and one cysteine protease were tested as genetic vaccine antigen candidates. Antigenicity was evaluated by immunostaining of transfected fish cells using I-ag specific mono- and polyclonal antibodies. I. multifiliis specific antibody production, regulation of immune-relevant genes and/or protection in terms of parasite burden or mortality was measured to evaluate the induced immune response in vaccinated fish. Apart from intramuscular injection, needle free injection and gene gun delivery were tested as alternative administration techniques. For the I-ags the complement protein fragment C3d and the termini of the viral haemorrhagic septicaemia virus glyco(G)protein (VHSV G) were tested as opsonisation and cellular localisation mediators, respectively, while the full length viral G protein was tested as molecular adjuvant. Expression of I-ags in transfected fish cells was demonstrated for several constructs and by immunohistochemistry it was possible to detect expression of a secreted form of the Iag52B in the muscle cells of injected fish. Up-regulations of mRNA coding for IgM, MHC I, MHC II and TCR β, respectively, were observed in muscle tissue at the injection site in selected trials. In the spleen up-regulations were found for IFN-γ and IL-10. The highest up-regulations were seen following co-administration of I-ag and cysteine protease plasmid constructs. This correlated with a slight elevation of an I. multifiliis specific antibody response. However, in spite of detectable antigen expression and immune reactions, none of the tested vaccination strategies provided significant protection. This might suggest an insufficiency of DNA vaccination alone to trigger protective mechanisms against I. multifiliis or that other or additional parasite antigens are required for such a vaccine to be successful.

Genomic structure, molecular characterization and functional analysis of Pekin duck interleukin-10

Here we describe the cloning and expression of Pekin duck IL-10 (duIL-10) and a six exon-5 intron structure of an IL-10 gene. Two transcripts encoding duIL-10 with an alternatively spliced 3'UTR, and a transcript lacking exon 5 with a novel coding sequence for its C-terminus (duIL-10ΔE5) were isolated from splenocytes. The duIL-10 protein has an amino acid identity of 79% and 47% with chicken and human IL-10, respectively. The duck IL-10 gene shares a similar structure of the respective exons 1-5 with the IL-10 genes of other vertebrates but has an alternative exon. The duIL-10 3D structure by homology modeling was similar to that of the human IL-10 monomer, whereas the predicted duIL-10ΔE5 protein lacks helix F. DuIL-10 and duIL-10ΔE5 transcripts were most abundant in primary and secondary immune organs and lung. Recombinant duIL-10 suppressed duck IL-2 transcripts in mitogen-activated PBMCs. Our observation suggests evolutionary conservation of structure and function of the duIL-10 protein but the roles of the novel IL-10 splice variants in the regulation of duck immune responses and evolution of vertebrate immunity remain to be elucidated.

Atlantic salmon reovirus infection causes a CD8 T cell myocarditis in Atlantic salmon (Salmo salar L.)

Heart and skeletal inflammation (HSMI) of farmed Atlantic salmon (Salmo salar L.) is a disease characterized by a chronic myocarditis involving the epicardium and the compact and spongious part of the heart ventricle. Chronic myositis of the red skeletal muscle is also a typical finding of HSMI. Piscine reovirus (PRV) has been detected by real-time PCR from farmed and wild salmon with and without typical changes of HSMI and thus the causal relationship between presence of virus and the disease has not been fully determined. In this study we show that the Atlantic salmon reovirus (ASRV), identical to PRV, can be passaged in GF-1 cells and experimental challenge of naïve Atlantic salmon with cell culture passaged reovirus results in cardiac and skeletal muscle pathology typical of HSMI with onset of pathology from 6 weeks, peaking by 9 weeks post challenge. ASRV replicates in heart tissue and the peak level of virus replication coincides with peak of heart lesions. We further demonstrate mRNA transcript assessment and in situ characterization that challenged fish develop a CD8+ T cell myocarditis.

Essential role of IL-4 and IL-4Rα interaction in adaptive immunity of zebrafish: insight into the origin of Th2-like regulatory mechanism in ancient vertebrates

The roles of IL-4 and IL-4Rα in Th2-mediated immunity have been well characterized in humans and other mammals. In contrast, few reports have been documented in ancient vertebrates. Several putative IL-4- and IL-4Rα-like molecules were identified recently from a few fish species, providing preliminary insight into the occurrence of Th2-type immunity in teleosts. However, functional determination still is required to address this hypothesis. To this end, these two molecules were characterized functionally in zebrafish (Danio rerio). Besides the identification of a full-length IL-4Rα molecule and an isoform lacking most of the cytoplasmic region as predicted previously, two novel alternatively spliced soluble variants with the extracellular domain only also were identified. Zebrafish IL-4Rα (DrIL-4Rα) shared overall conserved structural features of the IL-4Rα family. Immunofluorescence staining showed that DrIL-4Rα distributed on B cells. In vitro binding assays demonstrated that zebrafish IL-4 (DrIL-4) can bind specifically to DrIL-4Rα. In vivo administration of DrIL-4 significantly upregulated B cell proliferation and Ab production. These DrIL-4-elicited immune responses were downregulated by the administration of zebrafish soluble IL-4Rα or by DrIL-4Rα blockade using anti-DrIL-4Rα Abs. In addition, Th2-related cytokines or transcription factors were upregulated by DrIL-4. The DrIL-4-DrIL-4Rα interaction promoted CD40 expression on B cells and enhanced the CD154-CD40 costimulatory response, both of which are crucial for the initiation of Th2-type immunity. To our knowledge, this is the first report showing that a possible Th2-mediated regulatory mechanism may have appeared before the divergence of teleosts and mammals. These results add greater insight into the evolutionary history of adaptive immunity.

IPNV modulation of pro and anti-inflammatory cytokine expression in Atlantic salmon might help the establishment of infection and persistence

IPNV is the agent of a well-characterized acute disease that produces a systemic infection and high mortality in farmed fish species and persistent infection in surviving fish after outbreaks. Because modulation of the host expression of pro and anti-inflammatory cytokines can help establish persistence, in this study, we examined the expression of IL-1β, IL-8, IFNα1 and IL-10 during acute and persistent IPNV infection of Atlantic salmon. Results showed that IPNV infection induces an increase of the IFNα1 and IL-10 mRNA levels in the spleen and head kidney (HK) of fish after acute experimental infection. Levels of the pro-inflammatory cytokines IL-1β and IL-8 did not rise in the spleen although an increase of IL-1β, but not of IL-8, was observed in head kidney. In carrier asymptomatic salmon, cytokine gene expression of IFNα1 in the spleen and IL-10 in head kidney were also significantly higher than expression in non-carrier fish. Interestingly, a decrease of IL-8 expression was also observed. IPNV infection of SHK-1, which is a macrophage-like cell line of salmon, also induced an increase of expression of the anti-inflammatory cytokine IL-10 with no effects on the expression of IL-1β and IL-8. The effects are induced by an unknown mechanism during viral infection because poly I:C and the viral genomic dsRNA showed the opposite effects on cytokine expression in SHK-1 cells. In summary, IPNV always induces up-regulation of the anti-inflammatory cytokine IL-10 in Atlantic salmon. As this is accompanied by a lack of induction of the pro-inflammatory cytokines IL-1β and IL-8, the anti-inflammatory milieu may explain the high frequency, prevalence and persistence of IPNV in salmon. Effects might be part of the viral mechanisms of immune evasion.

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.

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.

The alloherpesviral counterparts of interleukin 10 in European eel and common carp

Viral interleukin 10 (IL-10) like open reading frames have been identified in several pox- and herpesviruses, including the fish herpesviruses Anguillid herpesvirus 1 (AngHV-1) and Cyprinid herpesvirus 3 (CyHV-3). European eel (Anguilla anguilla) IL-10 was sequenced, in order to compare European eel and common carp (Cyprinus carpio) IL-10 with their alloherpesviral counterparts. Homology between the virus and host IL-10 amino acid sequences is low, which is confirmed by phylogenetic analysis. However, the three dimensional structures of the fish and alloherpesviral IL-10 proteins as predicted by modeling are highly similar to human IL-10. Closely related AngHV-1 and CyHV-3 are expected to have obtained their viral IL-10 genes independently in the course of coexistence with their respective hosts. The presence and structural conservation of these alloherpesviral IL-10 genes suggest that they might play an important role in the evolution of pathogenesis.

Heterogeneity of macrophage activation in fish

In this review, we focus on four different activation states of fish macrophages. In vitro, stimulation with microbial ligands induces the development of innate activated macrophages whereas classically activated macrophages can be induced by stimulation with LPS in combination with (recombinant) IFNγ. Both types of macrophages show elevated phagocytic activity, expression of pro-inflammatory cytokine genes and radical production. Alternatively activated macrophages require the cytokines IL-4/IL-13 for induction of, among others, arginase activity. Until in vitro studies identify the effects of putative IL-4 and IL-13 homologues on fish macrophages, arginase enzyme activity remains the most reliable marker for the presence of alternatively activated macrophages in fish. The best evidence for the existence of regulatory macrophages, associated with the presence of IL-10, comes from in vivo studies, for example during parasitic infections of carp. Altogether, differentially activated macrophages in fish largely resemble the phenotypes of mammalian macrophages. However, the presence of fish-specific ligand recognition by TLRs and of duplicated genes coding for proteins with particular activities, poses additional challenges for the characterization of phenotype-specific gene signatures and cell surface markers.

Fish T cells: recent advances through genomics

This brief review is intended to provide a concise overview of the current literature concerning T cells, advances in identifying distinct T cell functional subsets, and in distinguishing effector cells from memory cells. We compare and contrast a wealth of recent progress made in T cell immunology of teleost, elasmobranch, and agnathan fish, to knowledge derived from mammalian T cell studies. From genome studies, fish clearly have most components associated with T cell function and we can speculate on the presence of putative T cell subsets, and the ability to detect their differentiation to form memory cells. Some recombinant proteins for T cell associated cytokines and antibodies for T cell surface receptors have been generated that will facilitate studying the functional roles of teleost T cells during immune responses. Although there is still a long way to go, major advances have occurred in recent years for investigating T cell responses, thus phenotypic and functional characterization is on the near horizon.

Multiple tissue transcriptomic responses toPiscirickettsia salmonisin Atlantic salmon (Salmo salar)

The bacterium Piscirickettsia salmonis is the etiological agent of salmonid rickettsial septicemia (SRS), a severe disease that causes major economic losses to the Atlantic salmon aquaculture industry every year. Little is known about the infective strategy of P. salmonis, which is able to infect, survive within, and replicate inside salmonid macrophages as an intracellular parasite. Similarly there is little knowledge concerning the fish host's response to invasion by this pathogen. We have examined the transcriptional response of postsmolt Atlantic salmon ( Salmo salar) to P. salmonis at 48 h following infection in three tissues, liver, head kidney, and muscle, using an Atlantic salmon oligonucleotide microarray (Salar_2, Agilent 4x44K). The infection led to a large alteration of transcriptional activity in all the tissues studied. In infected salmon 886, 207, and 153 transcripts were differentially expressed in liver, head kidney, and muscle, respectively. Assessment of enrichment for particular biological pathways by gene ontology analysis showed an upregulation of genes involved in oxidative and inflammatory responses in infected fish, indicative of the activation of the innate immune response. The downregulation of genes involved in the adaptive immune response, G protein signaling pathway, and apoptotic process in infected fish may be reflective of mechanisms used by P. salmonis to survive, replicate, and escape host defenses. There was also evidence of differential responses between studied tissues, with protein metabolism being decreased in muscle of infected fish and with a concomitant increase being shown in liver.