Molecular characterization of the nonspecific cytotoxic cell receptor (NCCRP-1) demonstrates gilthead seabream NCC heterogeneity

Bioinformatic and gene expression analysis of the somatostatin/cortistatin gene family in the gilthead seabream (Sparus aurata)

Somatostatin (SST) and cortistatin (CST) are neuromodulators with distinct expression patterns and functions. While SST and CST have been extensively studied in mammalian central nervous system (CNS) and immune system, their roles in teleost fish remain poorly explored due to evolutionary emergence of multiple SST paralogous genes. This study aimed to identify SST isoforms in gilthead seabream (Sparus aurata) and assess their transcriptional levels. Phylogeny and synteny analyses reclassified the six SST genes and proteins as SST1, SST3, SST3-like, SST4, SST5, and SST6. The protein sequences showed high conservation, except for an additional region upstream of the SST3-like protein's leader region. Evolutionary differences were mainly due to specific amino acid residue changes in the mature peptide. Genetic analyses revealed constitutive expression of five genes (sst1, sst3, sst5, sst4 and sst6) in all studied organs, except for sst3 in the heart, liver, and blood. The highest expression of sst1, sst3, sst4 and sst6 genes occurred in the brain's forebrain, while sst5 was most expressed in the heart. However, sst4 exhibited very low basal expression across all analysed tissues. In vitro, λ-carrageenan and cantharidin upregulated sst6 transcription in head kidney leucocytes (HKLs), indicating a potential anti-inflammatory role similar to mammalian CST. Additionally, sst5 expression was downregulated during the innate cell-mediated cytotoxic response, suggesting a regulatory role. These findings provide insights into the SST/CST gene family in gilthead seabream, necessitating gene and protein reclassification, and underscore their significant neuroendocrine and immune system functions, relevant for teleost research.

Novel C-type lectin mediated non-specific cytotoxic cells killing activity through NCCRP-1 in nile tilapia (Oreochromis niloticus)

Non-specific cytotoxic cells (NCCs) are vital immune cells involved in teleost's non-specific immunity. As a receptor molecule on the NCCs' surface, the non-specific cytotoxic cell receptor protein 1 (NCCRP-1) is known to play a crucial role in mediating their activity. Nevertheless, there have been limited studies on the signal molecule that transmits signals via NCCRP-1. In this study, a yeast two-hybrid (Y2H) library of tilapia liver and head kidney was constructed and subsequently screened with the bait vector NCCRP-1 of Oreochromis niloticus (On-NCCRP-1) to obtain a C-type lectin (On-CTL) with an interacting protein sequence. Consequently, the full-length sequence of On-CTL was cloned and analyzed. The expression analysis revealed that On-CTL is highly expressed in the liver and is widely distributed in other tissues. Furthermore, On-CTL expression was significantly up-regulated in the brain, intestine, and head kidney following a challenge with Streptococcus agalactiae. A point-to-point Y2H method was also used to confirm the binding between On-NCCRP-1 and On-CTL. The recombinant On-CTL (rOn-CTL) protein was purified. In vitro experiments demonstrated that rOn-CTL can up-regulate the expression of killer effector molecules in NCCs via its interaction with On-NCCRP-1. Moreover, activation of NCCs by rOn-CTL resulted in a remarkable enhancement in their ability to eliminate fathead minnow cells, indicating that rOn-CTL effectively modulates the killing activity of NCCs through the NCC receptor molecule On-NCCRP-1. These findings significantly contribute to our comprehension of the regulatory mechanisms governing NCC activity, paving the way for future research in this field.

Molecular characteristics and functional analysis of non-specific cytotoxic cell receptor (NCCRP1) in golden pompano (Trachinotus ovatus)

Non-specific cytotoxic cells (NCCs) are cytotoxic cell population found in innate immune system of teleost, playing crucial role in immune defense. Non-specific cytotoxic cell receptor protein 1 (NCCRP1) is responsible for recognizing target cells and activating NCCs. That said, since the studies regarding NCCs' role in fish during pathogen infection are few, it is necessary to conduct more comprehensive studies. In this study, we identified NCCRP1 from Trachinotus ovatus (ToNCCRP1). The open reading frame of ToNCCRP1 was found to be 702 bp, encoding a protein of 233 amino acids. Additionally, ToNCCRP1 contained a conserved F-box-associated domain and exhibited more than 61 % similarity to NCCRP1 in other fish species. Quantitative real-time PCR analysis showed that ToNCCRP1 mRNA was generally expressed in all tissues, with the highest level expressed in the liver. Furthermore, the expression of ToNCCRP1 was significantly upregulated following infection with Streptococcus iniae. In vitro experiments demonstrated that recombinant ToNCCRP1 possessed bacterial agglutination and binding capabilities, suggesting its antibacterial function. Additionally, we investigated the immune response of head kidney leukocytes (HKLs) to ToNCCRP1. The challenge experiments revealed that ToNCCRP1 played a role in the immune response by influencing the inflammatory response, regulating signaling pathways and apoptosis in HKLs. These findings suggest that NCCRP1 is involved in the immune defense against pathogenic infections in golden pompano, providing insights into the immune mechanisms of teleost.

Transcriptomic and targeted immune transcript analyses confirm localized skin immune responses in Atlantic salmon towards the salmon louse

Atlantic salmon (Salmo salar) are highly susceptible to infestations with the ectoparasite Lepeophtheirus salmonis, the salmon louse. Infestations elicit an immune response in the fish, but the response does not lead to parasite clearance, nor does it protect against subsequent infestations. It is, however, not known why the immune response is not adequate, possibly because the local response directly underneath the louse has been poorly evaluated. The present study describes the transcriptomic response by RNA sequencing of skin at the site of copepodid attachment. Analysing differentially expressed genes, 2864 were higher and 1357 were lower expressed at the louse attachment site compared to uninfested sites in the louse infested fish, while gene expression at uninfested sites were similar to uninfested control fish. The transcriptional patterns of selected immune genes were further detailed in three skin compartments/types: Whole skin, scales only and fin tissue. The elevation of pro-inflammatory cytokines and immune cell marker transcripts observed in whole skin and scale samples were not induced in fin, and a higher cytokine transcript level in scale samples suggest it can be used as a nonlethal sampling method to enhance selective breeding trials. Furthermore, the immune response was followed in both skin and anterior kidney as the infestation developed. Here, newly moulted preadult 1 stage lice induced a higher immune response than chalimi and adult lice. Overall, infestation with salmon louse induce a modest but early immune response with an elevation of mainly innate immune transcripts, with the response primarily localized to the site of attachment.

Expression changes of non-specific cytotoxic cell receptor (NCCRP1) and proliferation and migration of NCCs post-Nocardia seriolae infection in Northern Snakehead

Non-specific cytotoxic cells (NCCs) are essential to the cytotoxic cell-mediated immune response in teleost. The fish non-specific cytotoxic cell receptor protein 1 (NCCRP1) plays an important role as a membrane protein in the recognition of target cells and the activation of NCC. However, the roles of fish NCCs during pathogen infection require comprehensive studies. In this study, the coding sequence of northern snakehead (Channa argus) nccrp1 (Canccrp1) was cloned. Canccrp1 contains an open reading frame of 690 bp, encoding a peptide of 229 amino acids with a conserved F-box-associated domain (FBA) and proline-rich motifs (PRMs). Transcriptional expression analysis revealed that the constitutive expression of Canccrp1 was higher in the immune-related organs, such as liver, kidneys, and spleen. Moreover, mRNA and protein expression of Canccrp1 gradually increased in the spleen at 1-6 days post infection (dpi) with Nocardia seriolae, in addition to reaching peak expression in both the kidneys and liver at 2 dpi. A polyclonal antibody prepared against recombinant CaNCCRP1 effectively labeled NCCs in peripheral blood and different tissues. Then, immunofluorescence (IF) staining showed that the number of NCCs was significantly increased and showed a scattered distribution in the early stages of N. seriolae infection (2 and 4 dpi) before the forming of granulomas. At the late stages of N. seriolae infection (6 dpi), more NCCs migrated to preexisting granulomas, showing significant coaccumulation with N. seriolae. All these results clearly indicate the expression changes of CaNCCRP1, and the number and localization changes of NCCs post-N. seriolae infection, implying potential roles for fish NCCs in the antimicrobial infection process in fish.

Massive gene expansion of hepcidin, a host defense peptide, in gilthead seabream (Sparus aurata)

Host defense peptides (HDP) are among the most ancient immune molecules in animals and clearly reflect an ancestral evolutionary history involving pathogen-host interactions. Hepcidins are a very widespread family of HDPs among vertebrates and are especially diverse in teleosts. We have investigated the identification of new hepcidins in gilthead seabream (Sparus aurata), a fish farmed in the Mediterranean. Targeted gene predictions supported with expressed sequence tags (ESTs) derived from Hidden Markov Models were used to find the hamp genes in the seabream genome. The results revealed a massively clustered hamp duplication on chromosome 17. In fact, the seabream genome contains the largest number of hepcidin copies described in any vertebrate. The evolutionary history of hepcidins in seabream, and vertebrates generally, clearly indicates high adaptation in teleosts and novel subgroups within hepcidin type II. Furthermore, basal hepcidin gene expression analysis indicates specific-tissue expression profiles, while the presence and distribution of transcription factor binding sites (TFBS) in hamp promoters as well as their transcription profile upon bacterial challenge indicates different immune roles depending on the type of hepcidin and tissue. This massive duplication of HDP genes in a bony fish could point to a far more specific and adaptive innate immune system than assumed in the classic concept of immunity in mammals. Hence, a new world of knowledge regarding hepcidins in fish and vertebrates is being initiated.

Salmon louse rhabdoviruses: Impact on louse development and transcription of selected Atlantic salmon immune genes

Recently, it has been shown that the salmon louse (Lepeophtheirus salmonis) is commonly infected by one or two vertically transmitted Lepeophtheirus salmonis rhabdoviruses (LsRVs). As shown in the present study, the viruses have limited effect on louse survival, developmental rate and fecundity. Since the LsRVs were confirmed to be present in the louse salivary glands, the salmon cutaneous immune response towards LsRV positive and negative lice was analyzed. In general, L. salmonis increased the expression of IL1β, IL8 and IL4/13A at the attachment site, in addition to the non-specific cytotoxic cell receptor protein 1 (NCCRP-1). Interestingly, LsRV free lice induced a higher skin expression of IL1β, IL8, and NCCRP-1 than the LsRV infected lice. The inflammatory response is important for louse clearance, and the present results suggest that the LsRVs can be beneficial for the louse by dampening inflammation. Further research is, however; needed to ascertain whether this is a direct modulatory effect of secreted virions, or if virus replication is altering the level of louse salivary gland proteins.

Dietary administration of the probiotic Shewanella putrefaciens Pdp11 promotes transcriptional changes of genes involved in growth and immunity in Solea senegalensis larvae

Senegalese sole (Solea senegalensis) has been proposed as a high-potential species for aquaculture diversification in Southern Europe. It has been demonstrated that a proper feeding regimen during the first life stages influences larval growth and survival, as well as fry and juvenile quality. The bacterial strain Shewanella putrefaciens Pdp11 (SpPdp11) has shown very good probiotic properties in Senegalese sole, but information is scarce about its effect in the earliest stages of sole development. Thus, the aim of this study was to investigate the effect of SpPdp11, bioencapsulated in live diet, administered during metamorphosis (10-21 dph) or from the first exogenous feeding of Senegalese sole (2-21 dph). To evaluate the persistence of the probiotic effect, we sampled sole specimens from metamorphosis until the end of weaning (from 23 to 73 dph). This study demonstrated that probiotic administration from the first exogenous feeding produced beneficial effects on Senegalese sole larval development, given that specimens fed this diet exhibited higher and less dispersed weight, as well as increases in both total protein concentration and alkaline phosphatase activity, and in non-specific immune response. Moreover, real-time PCR documented changes in the expression of a set of genes involved in central metabolic functions including genes related to growth, genes coding for proteases (including several digestive enzymes), and genes implicated in the response to stress and in immunity. Overall, these results support the application of SpPdp11 in the first life stages of S. senegalensis as an effective tool with the clear potential to benefit sole aquaculture.

Characterization of the gilthead seabream (Sparus aurata L.) immune response under a natural lymphocystis disease virus outbreak

Lymphocystis or lymphocystis disease virus (LCDV) is distributed worldwide and affects many fresh and marine water fish species. LCDV is commonly found in aquaria fish species but also in farmed fish species, among them the gilthead seabream (Sparus aurata L.). The immune status of gilthead seabream (S. aurata) specimens under a natural outbreak of LCDV was studied. The replication of the virus was demonstrated in infected fish, but not in control fish. The results showed decreased total serum IgM levels and increased innate cellular immune response (peroxidase and respiratory burst activities) of head kidney leucocytes in LCDV-infected fish, compared to the values obtained in uninfected specimens. In addition, transcription of antiviral genes (ifn and irf3) was down-regulated in the skin of LCDV-positive fish as well as genes involved in cellular immunity (csf1r, mhc2a, tcra and ighm) that were down-regulated in skin and head kidney of infected fish. By contrast, the transcription of nccrp1 was up-regulated in head kidney after LCDV infection. These present results show that head kidney leucocytes are activated to encounter the virus at the sites of replication.

Differential proteome profile of skin mucus of gilthead seabream (Sparus aurata) after probiotic intake and/or overcrowding stress

Gilthead seabream (Sparus aurata L.) is the major cultured fish species in the Mediterranean area. High density stocking causes stress and increases the impact of diseases leading to economic losses. Probiotics could represent a solution to prevent diseases through several mechanisms such as improving the immune status and/or mucosal microbiota or competing with pathogens. The probiotic Shewanella putrefaciens, also known as Pdp11, was firstly isolated from the skin of healthy gilthead seabream. Our study focuses on the skin mucus proteome after dietary probiotic Pdp11 intake in fish maintained under normal or overcrowding conditions. 2-DE of skin mucus followed by LC-MS/MS analysis was done for each experimental group and differentially expressed proteins were identified. The results showed differentially expressed proteins especially involved in immune processes, such as lysozyme, complement C3, natural killer cell enhancing factor and nonspecific cytotoxic cell receptor protein 1, whose transcript profiles were studied by qPCR. A consistency between lysozyme protein levels in the mucus and lysozyme mRNA levels in skin was found. Further research is necessary to unravel the implications of skin mucosal immunity on fish welfare and disease.

BIOLOGICAL SIGNIFICANCE

The present work reveals the proteomic changes, which are taking place in the skin mucus of stressed and non-stressed gilthead seabream after Pdp11 probiotic intake. The study contributes to improving the knowledge on skin mucosal immunology of this relevant farmed fish species. Furthermore, the paper shows for the first time how a suitable proteomic methodology, in this case 2-DE followed by LC-MS/MS is useful to perform a comparative study with a non-invasive technique of skin mucus of gilthead seabream.

Investigating the potential immune role of fish NCAMs: Molecular cloning and expression analysis in mandarin fish

The immune role of NCAMs has been revealed in mammals, yet there is no such report in fish. Hence, we analyzed the molecular characterizations and immune-associated expression patterns of NCAMs in mandarin fish. Three NCAM members, named mfNCAM1a, mfNCAM1b and mfNCAM2, were identified. Among the cDNA sequences of mfNCAMs, AU-rich elements in the 3' UTRs of mfNCAM1b and mfNCAM2 as well as VASE sequences in the fourth Ig-like domain-encoding regions of mfNCAM1a and mfNCAM1b were discovered. Moreover, the syntenic analysis suggested that the duplication of NCAM1 is fish-specific. At mRNA and protein levels, the expression analyses revealed that mfNCAMs existed in both systemic and mucosal immune tissues, and located within lymphoid cells. Upon stimulated either by LPS or poly I:C, the expression level of mfNCAM1a was significantly up-regulated in head kidney, spleen, liver, and gut, whereas mfNCAM1b only in head kidney and liver, and mfNCAM2 only in liver. Additionally, the cells coexpressed mfNCAM1 and mfNCCRP-1 might imply the equivalents to mammalian NK cells. Our finding firstly demonstrates the member-specific immune-related tissue expression pattern and immune activity for fish NCAMs. Current data indicate that mfNCAM2 has little immune activity, while the immune activity of mfNCAM1a exists in more tissues than mfNCAM1b, and mfNCAM1a may tend to respond more actively to viral while mfNCAM1b to bacterial stimulants. Additionally, NCAM1b should be a fish-specific member with unique immune function, judging from its different expression pattern, immune activity as well as phylogenetic relationship to mfNCAM1a.

Molecular cloning of NCCRP-1 gene from orange-spotted grouper (Epinephelus coioides) and characterization of NCCRP-1(+) cells post Cryptocaryon irritans infection

Nonspecific cytotoxic cells (NCCs) are an important cytotoxic cell population in the innate teleost immune system. The receptor designated "NCC receptor protein 1" (NCCRP-1) has been reported to be involved in the recognition and activation of NCCs. In this study, the full-length cDNA of Epinephelus coioides NCCRP-1 (ecnccrp-1) was cloned. The open reading frame (ORF) of ecnccrp-1 is 699 bp, encoding a 232 amino acid protein that includes proline-rich motifs at the N-terminus and is related to the F-box associated family. Although a bioinformatics analysis showed that EcNCCRP-1 had no signal peptide or transmembrane helices, a polyclonal antibody directed against recombinant EcNCCRP-1 efficiently labeled a membrane protein in the head kidney, detected with Western blot analysis, which indicated that the protein localized to the cell surface. RT-PCR showed that the constitutive expression of ecnccrp-1 was higher in the lymphoid organs, such as the trunk kidney, spleen, head kidney, and thymus, and lower in brain, heart, fat, liver, muscle, and skin. After infection with Cryptocaryon irritans, the transcription of ecnccrp-1 was analyzed at the infected sites (skin and gills) and in the systemic immune organs (head kidney and spleen). At the infected sites, especially the skin, ecnccrp-1 expression was upregulated at 6h post infection, reaching peak expression on day 3 post the primary infection. However, the expression patterns differed in the systemic immune organs. In the spleen, ecnccrp-1 was gradually increased in the early infection period and decreased sharply on day 3 post the primary infection, whereas in the head kidney, the transcription of ecnccrp-1 was depressed during almost the whole course of infection. An immunohistochemical analysis showed that EcNCCRP-1(+) cells accumulated at the sites of infection with C. irritans. These results suggested that NCCs were involved in the process of C. irritans infection in E. coioides.

Endosulfan decreases cytotoxic activity of nonspecific cytotoxic cells and expression of granzyme gene in Oreochromis niloticus

The effect of the organochlorinated insecticide endosulfan, on the cytotoxic activity of Nile tilapia nonspecific cytotoxic cells (NCC) was assessed. Juvenile Nile tilapia were exposed to endosulfan (7 ppb) for 96 h and splenic NCC were isolated. Flow cytometric phenotyping of NCC was based on the detection of the NCC specific membrane signaling protein NCCRP-1 by using the monoclonal antibody Mab 5C6; granzyme expression was evaluated by quantitative RT-PCR. The cytotoxic activity of sorted NCC on HL-60 tumoral cells was assessed using propidium iodide (PI) staining of DNA in HL-60 nuclei, indicating dead cells. Nile tilapia splenic NCC had the ability to kill HL-60 tumoral cells, however, the exposure to endosulfan significantly reduced, by a 65%, their cytotoxic activity when using the effector:target ratio of 40:1. Additionally, the exposure to endosulfan tended to increase the expression of NCCRP-1, which is involved in NCC antigen recognition and signaling. Moreover, it decreased the expression of the granzyme gene in exposed group as compared with non-exposed group; however significant differences between groups were not detected. In summary, the acute exposure of Nile tilapia to sublethal concentration of endosulfan induces alteration in function of NCC: significant decrease of cytotoxic activity and a tendency to lower granzyme expression, severe enough to compromise the immunity of this species.

Modulation of leukocytic populations of gilthead sea bream (Sparus aurata) by the intestinal parasite Enteromyxum leei (Myxozoa: Myxosporea)

The cellular mucosal and systemic effectors of gilthead sea bream (GSB) (Sparus aurata) involved in the acute immune response to the intestinal parasite Enteromyxum leei were studied in fish experimentally infected by the anal route. In the intestinal inflammatory infiltrates and in lymphohaematopoietic organs (head kidney and spleen) of parasitized fish, the number of plasma cells, B cells (IgM immunoreactive) and mast cells (histamine immunoreactive) were significantly higher, whereas the number of acidophilic granulocytes (G7 immunoreactive) decreased, compared with non-parasitized and unexposed fish. These differences were stronger at the posterior intestine, the main target of the parasite, and no differences were found in the thymus. In non-parasitized GSB, the percentage of splenic surface occupied by melanomacrophage centres was significantly higher. These results suggest that the cellular response of GSB to E. leei includes proliferation of leukocytes in lymphohaematopoietic organs and recruitment into intestines via blood circulation involving elements of innate and adaptive immunity. Acidophilic granulocytes and mast cells presented opposite patterns of response to the parasite infection, with an overall depletion of the former and an increased amount of the latter. Some differences between both cell types were also detected in regard to their granule density and cell morphology.

Nodavirus infection induces a great innate cell-mediated cytotoxic activity in resistant, gilthead seabream, and susceptible, European sea bass, teleost fish

Viral nervous necrosis (VNN) virus produces great mortalities in fish having susceptible and reservoir species between the most important marine aquaculture species. Cell-mediated cytotoxicity (CMC) is considered, towards the interferon (IFN), the most important mechanism of the immune response to fight against viral infections but it has been very scarcely evaluated. We aimed to evaluate the effects of VNNV infection in the reservoir gilthead seabream (Sparus aurata) and susceptible European sea bass (Dicentrarchus labrax). Firstly, after experimental infection we found mortalities in the sea bass (55%) but no in the seabream. Moreover, VNN virus replicates in the brain of both species as it was reflected by the high up-regulation of the Mx gene expression. Interestingly, the head-kidney leucocyte cell-mediated cytotoxic activity was significantly increased in both species reaching highest activity at 7 days: 3.65- and 2.7-fold increase in seabream and sea bass, respectively. This is supported by the significant up-regulation of the non-specific cytotoxic cell receptor (NCCRP-1) in the two fish species. By contrast, phagocytosis was unaffected in both species. The respiratory burst was increased in seabream 7 days post-infection whilst in sea bass this activity was significantly decreased at days 7 and 15. Our results demonstrate the significance of the CMC activity in both gilthead seabream and European sea bass against nodavirus infections but further studies are still needed to understand the role of cytotoxic cells in the antiviral immune response and the mechanisms involved in either reservoir or susceptible fish species.

Characterization of non-specific cytotoxic cell receptor protein 1: a new member of the lectin-type subfamily of F-box proteins

Our previous microarray study showed that the non-specific cytotoxic cell receptor protein 1 (Nccrp1) transcript is significantly upregulated in the gastric mucosa of carbonic anhydrase IX (CA IX)-deficient (Car9^−/−) mice. In this paper, we aimed to characterize human NCCRP1 and to elucidate its relationship to CA IX. Recombinant NCCRP1 protein was expressed in Escherichia coli, and a novel polyclonal antiserum was raised against the purified full-length protein. Immunocytochemistry showed that NCCRP1 is expressed intracellularly, even though it has previously been described as a transmembrane protein. Using bioinformatic analyses, we identified orthologs of NCCRP1 in 35 vertebrate genomes, and up to five paralogs per genome. These paralogs are FBXO genes whose protein products are components of the E3 ubiquitin ligase complexes. NCCRP1 proteins have no signal peptides or transmembrane domains. NCCRP1 has mainly been studied in fish and was thought to be responsible for the cytolytic function of nonspecific cytotoxic cells (NCCs). Our analyses showed that in humans, NCCRP1 mRNA is expressed in tissues containing squamous epithelium, whereas it shows a more ubiquitous tissue expression pattern in mice. Neither human nor mouse NCCRP1 expression is specific to immune tissues. Silencing CA9 using siRNAs did not affect NCCRP1 levels, indicating that its expression is not directly regulated by CA9. Interestingly, silencing NCCRP1 caused a statistically significant decrease in the growth of HeLa cells. These studies provide ample evidence that the current name, “non-specific cytotoxic cell receptor protein 1,” is not appropriate. We therefore propose that the gene name be changed to FBXO50.

Immune response of gilthead seabream (Sparus aurata) following experimental infection with Aeromonas hydrophila

The Gram-negative bacteria Aeromonas hydrophila is a heterogeneous organism that causes the disease known as motile aeromonad septicaemia, which is responsible for serious economic loss in seabream culture due to bacterial infections. However, the immune mechanisms involved in this disease in fish are still poorly understood. For the purpose of this study, gilthead seabream (Sparus aurata L.) specimens received a double intraperitoneal injection of bacterial inoculums: a primary infection with 1 × 10(7) cell ml(-1) A. hydrophila, followed by a secondary infection with 1 × 10(8) cell ml(-1) fourteen days later. Changes in cellular innate immune parameters - phagocytosis, respiratory burst activity and peroxidase leucocyte content - were evaluated 24 and 48 h after each injection. Simultaneously, the expression levels of nine immune-relevant genes (TLR, NCCRP-1, HEP, TCR, IgM, MHC-IIα, IL-1β, C3 and CSF-1R) were measured in the head-kidney, spleen, intestine and liver, by using q-PCR. Generally, the results showed a significant decrease in cellular immune responses during the primary infection and a significant enhanced during the second infection, principally in respiratory burst and peroxidase activity, thus indicating a recovery of the immune system against this bacterial pathogen. Finally, transcript levels of immune genes were down-regulated during the first infection, except for the IL-1β gene. In contrast, mRNA expression levels during the re-infection were significantly up-regulated. The results seem to suggest a relatively fast elimination of the bacteria and recovery of fish during the secondary infection.

Oral delivery of live yeast Debaryomyces hansenii modulates the main innate immune parameters and the expression of immune-relevant genes in the gilthead seabream (Sparus aurata L.)

Microorganisms isolated from fish can be used as prophylactic tools for aquaculture in the form of probiotic preparations. The purpose of this study was to evaluate the effects of dietary administration of the live yeast Debaryomyces hansenii CBS 8339 on the gilthead seabream (Sparus aurata L.) innate immune responses. Seabream were fed control or D. hansenii-supplemented diets (10(6) colony forming units, CFU g(-1)) for 4 weeks. Humoral (seric alternative complement and peroxidase activities), and cellular (peroxidase, phagocytic, respiratory burst and cytotoxic activities) innate immune parameters and antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) were measured from serum, head-kidney leucocytes and liver, respectively, after 2 and 4 weeks of feeding. Expression levels of immune-associated genes, Hep, IgM, TCR-beta, NCCRP-1, MHC-II alpha, CSF-1R, C3, TNF-alpha and IL-1 beta, were also evaluated by real-time PCR in head-kidney, liver and intestine. Humoral immune parameters were not significantly affected by the dietary supplementation of yeast at any time of the experiment. On the other hand, D. hansenii administration significantly enhanced leucocyte peroxidase and respiratory burst activity at week 4. Phagocytic and cytotoxic activities had significantly increased by week 2 of feeding yeast but unchanged by week 4. A significant increase in liver SOD activity was observed at week 2 of feeding with the supplemented diet; however CAT activity was not affected by the dietary yeast supplement at any time of the experiment. Finally, the yeast supplemented diet down-regulated the expression of most seabream genes, except C3, in liver and intestine and up-regulated all of them in the head-kidney. These results strongly support the idea that live yeast Debaryomyces hansenii strain CBS 8339 can stimulate the innate immune parameters in seabream, especially at cellular level.

Cell-mediated immune responses in rainbow trout after DNA immunization against the viral hemorrhagic septicemia virus

To identify viral proteins that induce cell-mediated cytotoxicity (CMC) against viral hemorrhagic septicemia virus (VHSV)-infected cells, rainbow trout were immunized with DNA vectors encoding the glycoprotein G or the nucleocapsid protein N of VHSV. The G protein was a more potent trigger of cytotoxic cells than the N protein. Peripheral blood leukocytes (PBL) isolated from trout immunized against the G protein killed both VHSV-infected MHC class I matched (RTG-2) and VHSV-infected xenogeneic (EPC) target cells, suggesting the involvement of both cytotoxic T lymphocytes (CTL) and NK cells, respectively. In contrast, PBL from trout that were immunized against the N protein only killed VHSV-infected RTG-2 cells, indicating that this protein only elicits a CTL response. Further, a significant killing capacity of these PBL was only observed during summer months. PBL from fish that were immunized against the VHSV G protein significantly killed VHSV-infected but not infectious hematopoietic necrosis virus (IHNV)-infected targets indicating antigen specificity. Thus, this is the first report on cytotoxic immune responses after DNA vaccination in fish. Furthermore, cells isolated from the inflamed site of DNA injection were stained and transferred to isogeneic DNA-vaccinated recipients. Most of the stained donor leukocytes accumulated at the recipients' DNA injection site showing, for the first time, leukocyte homing in fish. Transferred donor leukocytes mainly migrated to the homologous vaccine injection site rather than to injection sites of heterologous vaccines, suggesting the antigen specificity of homing. By demonstrating CMC responses to distinct viral proteins and homing in rainbow trout, these results substantially contribute to the understanding of the teleost immune system.

The gene structure and expression of the non-specific cytotoxic cell receptor protein (NCCRP-1) in Atlantic cod (Gadus morhua L.)

The non-specific cell receptor protein (NCCRP-1) serves an important function in target cell recognition and activation of non-specific cytotoxic cells in teleosts. Atlantic cod NCCRP-1 was identified in a suppression-subtractive cDNA library and NCCRP-1 from Atlantic salmon, rainbow trout, Japanese medaka and fathead minnow was found deposited in the GenBank as EST sequences. The predicted amino acid sequences of these receptors contain the characteristic functional domains representing NCCRP-1, and phylogenetic analyses support the identification of five NCCRP-1 orthologues. Cod NCCRP-1 is shorter and has a different intron/exon organization from the common carp and channel catfish counterparts, but shows high extent of conservation in NCCRP-1 signature motives. Quantitative real-time PCR analyses showed that the gene expression of cod NCCRP-1 was higher in the lymphoid organs, head kidney (90-fold) and spleen (30-fold), compared to the organ with lowest expression. NCCRP-1 gene expression was not induced by in vitro treatment of head kidney cells with polyinosinic polycytidylic acid (poly I:C) or lipopolysaccharide (LPS), or by in vivo injections with poly I:C or formalin killed Vibrio anguillarum. These results show that the cod NCCRP-1 gene is differentially expressed in organs, and that gene expression is not induced by the tested treatments.

Cloning, distribution and up-regulation of the teleost fish MHC class II alpha suggests a role for granulocytes as antigen-presenting cells

The major histocompatibility complex (MHC) class II alpha chain gene of the teleost fish gilthead seabream (Sparus aurata), Spau-DAA, has been characterized. We cloned, sequenced and studied its polymorphism, before evaluating its expression in resting seabream leucocytes, tissues and tumor cells as well as in primed leucocytes. A complete allele was obtained by overlapping sequence fragments obtained by RT-PCR. The full-length Spau-DAA*101 comprises 1840 bp with a 5'-UTR region of 84 bp, an ORF of 729 bp and a 3'-UTR of 1027 bp. The putative protein of 242 residues shows homology with known MHC class II alpha genes, varying from 71 to 28% in other fish and humans, respectively. The protein sequence showed all the important features: leader peptide, alpha1, alpha2 and CP/TM/CYT regions, conserved cysteines and N-glycosylation site. The phylogenetic tree shows that it is included in the cluster containing the Percomorpha subclass and far from the human and shark genes. It is polymorphic, as seen when we sequenced the complete ORF of 11 alleles showing most of the amino acidic changes in the alpha1 domain, where the peptide-binding region (PBR) is found. Spau-DAA mRNA expression was mainly found in peritoneal exudate leucocytes, head-kidney, spleen, thymus and gill. Minor expression was detected in gut, brain, liver and PBLs. RT-PCR expression studies in isolated leucocyte subpopulations revealed, for the first time in the literature, that acidophilic granulocytes show high MHC class II gene expression. Apart from these granulocytes lymphocytes also express the Spau-DAA gene, although other cell types may also do the same. Finally, incubation of head-kidney leucocytes with yeast cells or pathogenic bacteria up-regulates Spau-DAA gene expression whilst incubation with ConA, ConA+LPS or PHA does not. The possible involvement of the seabream MHC class II alpha gene in the fish defence and antigen presentation are discussed.