Mucosal immunoglobulins and B cells of teleost fish

A Review of the Immunological Mechanisms Following Mucosal Vaccination of Finfish

Mucosal organs are principle portals of entry for microbial invasion and as such developing protective vaccines against these pathogens can serve as a first line of defense against infections. In general, all mucosal organs in finfish are covered by a layer of mucus whose main function is not only to prevent pathogen attachment by being continuously secreted and sloughing-off but it serves as a vehicle for antimicrobial compounds, complement, and immunoglobulins that degrade, opsonize, and neutralize invading pathogens on mucosal surfaces. In addition, all mucosal organs in finfish possess antigen-presenting cells (APCs) that activate cells of the adaptive immune system to generate long-lasting protective immune responses. The functional activities of APCs are orchestrated by a vast array of proinflammatory cytokines and chemokines found in all mucosal organs. The adaptive immune system in mucosal organs is made of humoral immune responses that are able to neutralize invading pathogens as well as cellular-mediated immune responses whose kinetics are comparable to those induced by parenteral vaccines. In general, finfish mucosal immune system has the capacity to serve as the first-line defense mechanism against microbial invasion as well as being responsive to vaccination.

CsBAFF, a Teleost B Cell Activating Factor, Promotes Pathogen-Induced Innate Immunity and Vaccine-Induced Adaptive Immunity

B cell activating factor (BAFF) is a member of the tumor necrosis factor family that is known to play an important role in B cell activation, proliferation, and differentiation in mammals. However, studies of BAFF in teleosts are very limited and its function, in particular that under in vivo conditions, is essentially unknown. In this study, we conducted in vivo as well as in vitro functional analyses of a BAFF homologue (CsBAFF) from the teleost fish tongue sole (Cynoglossus semilaevis). CsBAFF is composed of 261 residues and shares moderate sequence identities with known BAFFs of other teleosts. CsBAFF expression was most abundant in immune organs and was upregulated during bacterial infection. Purified recombinant CsBAFF (rCsBAFF) bound to tongue sole lymphocytes and promoted cellular proliferation and survival. The results of an in vivo study showed that CsBAFF overexpression in tongue sole significantly enhanced macrophage activation and reduced bacterial infection in fish tissues, whereas knockdown of CsBAFF expression resulted in increased bacterial dissemination and colonization in fish tissues. Furthermore, vaccination studies showed that CsBAFF enhanced the immunoprotection of a DNA vaccine and augmented the production of specific serum antibodies. Taken together, these results provide the first in vivo evidence to indicate that teleost BAFF is an immunostimulator that significantly contributes to the innate antibacterial immune response and vaccine-induced adaptive immune response.

The Mucosal Immune System of Teleost Fish

Teleost fish possess an adaptive immune system associated with each of their mucosal body surfaces. Evidence obtained from mucosal vaccination and mucosal infection studies reveal that adaptive immune responses take place at the different mucosal surfaces of teleost. The main mucosa-associated lymphoid tissues (MALT) of teleosts are the gut-associated lymphoid tissue (GALT), skin-associated lymphoid tissue (SALT), the gill-associated lymphoid tissue (GIALT) and the recently discovered nasopharynx-associated lymphoid tissue (NALT). Teleost MALT includes diffuse B cells and T cells with specific phenotypes different from their systemic counterparts that have co-evolved to defend the microbe-rich mucosal environment. Both B and T cells respond to mucosal infection or vaccination. Specific antibody responses can be measured in the gills, gut and skin mucosal secretions of teleost fish following mucosal infection or vaccination. Rainbow trout studies have shown that IgT antibodies and IgT(+) B cells are the predominant B cell subset in all MALT and respond in a compartmentalized manner to mucosal infection. Our current knowledge on adaptive immunity in teleosts is limited compared to the mammalian literature. New research tools and in vivo models are currently being developed in order to help reveal the great intricacy of teleost mucosal adaptive immunity and help improve mucosal vaccination protocols for use in aquaculture.

An oral DNA vaccine against infectious haematopoietic necrosis virus (IHNV) encapsulated in alginate microspheres induces dose-dependent immune responses and significant protection in rainbow trout (Oncorrhynchus mykiss)

Administered by intramuscular injection, a DNA vaccine (pIRF1A-G) containing the promoter regions upstream of the rainbow trout interferon regulatory factor 1A gene (IRF1A) driven the expression of the infectious hematopoietic necrosis virus (IHNV) glycoprotein (G) elicited protective immune responses in rainbow trout (Oncorhynchus mykiss). However, less laborious and cost-effective routes of DNA vaccine delivery are required to vaccinate large numbers of susceptible farmed fish. In this study, the pIRF1A-G vaccine was encapsulated into alginate microspheres and orally administered to rainbow trout. At 1, 3, 5, and 7 d post-vaccination, IHNV G transcripts were detected by quantitative real-time PCR in gills, spleen, kidney and intestinal tissues of vaccinated fish. This result suggested that the encapsulation of pIRF1A-G in alginate microparticles protected the DNA vaccine from degradation in the fish stomach and ensured vaccine early delivery to the hindgut, vaccine passage through the intestinal mucosa and its distribution thought internal and external organs of vaccinated fish. We also observed that the oral route required approximately 20-fold more plasmid DNA than the injection route to induce the expression of significant levels of IHNV G transcripts in kidney and spleen of vaccinated fish. Despite this limitation, increased IFN-1, TLR-7 and IgM gene expression was detected by qRT-PCR in kidney of vaccinated fish when a 10 μg dose of the oral pIRF1A-G vaccine was administered. In contrast, significant Mx-1, Vig-1, Vig-2, TLR-3 and TLR-8 gene expression was only detected when higher doses of pIRF1A-G (50 and 100 μg) were orally administered. The pIRF1A-G vaccine also induced the expression of several markers of the adaptive immune response (CD4, CD8, IgM and IgT) in kidney and spleen of immunized fish in a dose-dependent manner. When vaccinated fish were challenged by immersion with live IHNV, evidence of a dose-response effect of the oral vaccine could also be observed. Although the protective effects of the oral pIRF1A-G vaccine after a challenge with IHNV were partial, significant differences in cumulative percent mortalities among the orally vaccinated fish and the unvaccinated or empty-plasmid vaccinated fish were observed. Similar levels of protection were obtained after the intramuscular administration of 5 μg of pIRF1A-G or after the oral administration of a high dose of pIRF1A-G vaccine (100 μg); with 70 and 56 relative percent survival values, respectively. When fish were vaccinated with alginate microspheres containing high doses of the pIRF1A-G vaccine (50 or 100 μg), a significant increase in the production of anti-IHNV antibodies was detected in serum samples of the vaccinated fish compared with that in unvaccinated fish. At 10 days post-challenge, IHNV N gene expression was nearly undetectable in kidney and spleen of orally vaccinated fish which suggested that the vaccine effectively reduced the amount of virus in tissues of vaccinated fish that survived the challenge. In conclusion, our results demonstrated a significant increase in fish immune responses and resistance to an IHNV infection after the oral administration of increasing concentrations of a DNA vaccine against IHNV encapsulated into alginate microspheres.

Topographical Mapping of the Rainbow Trout (Oncorhynchus mykiss) Microbiome Reveals a Diverse Bacterial Community with Antifungal Properties in the Skin

The mucosal surfaces of wild and farmed aquatic vertebrates face the threat of many aquatic pathogens, including fungi. These surfaces are colonized by diverse symbiotic bacterial communities that may contribute to fight infection. Whereas the gut microbiome of teleosts has been extensively studied using pyrosequencing, this tool has rarely been employed to study the compositions of the bacterial communities present on other teleost mucosal surfaces. Here we provide a topographical map of the mucosal microbiome of an aquatic vertebrate, the rainbow trout (Oncorhynchus mykiss). Using 16S rRNA pyrosequencing, we revealed novel bacterial diversity at each of the five body sites sampled and showed that body site is a strong predictor of community composition. The skin exhibited the highest diversity, followed by the olfactory organ, gills, and gut. Flectobacillus was highly represented within skin and gill communities. Principal coordinate analysis and plots revealed clustering of external sites apart from internal sites. A highly diverse community was present within the epithelium, as demonstrated by confocal microscopy and pyrosequencing. Using in vitro assays, we demonstrated that two Arthrobacter sp. skin isolates, a Psychrobacter sp. strain, and a combined skin aerobic bacterial sample inhibit the growth of Saprolegnia australis and Mucor hiemalis, two important aquatic fungal pathogens. These results underscore the importance of symbiotic bacterial communities of fish and their potential role for the control of aquatic fungal diseases.

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.

Mucosal Immunity and B Cells in Teleosts: Effect of Vaccination and Stress

Fish are subjected to several insults from the environment, which may endanger animal survival. Mucosal surfaces are the first line of defense against these threats, acting as a physical barrier to protect the animal but also functioning as an active immune tissue. Thus, four mucosal-associated lymphoid tissues (MALTs), which lead the immune responses in gut, skin, gills, and nose, have been described in fish. Humoral and cellular immunity, as well as their regulation and the factors that influence the response in these mucosal lymphoid tissues, are still not well known in most fish species. Mucosal B-lymphocytes and immunoglobulins (Igs) are key players in the immune response that takes place in those MALTs. The existence of IgT as a mucosal specialized Ig gives us the opportunity of measuring specific responses after infection or vaccination, a fact that was not possible until recently in most fish species. The vaccination process is influenced by several factors, being stress one of the main stimuli determining the success of the vaccine. Thus, one of the major goals in a vaccination process is to avoid possible situations of stress, which might interfere with fish immune performance. However, interaction between immune and neuroendocrine systems at mucosal tissues is still unknown. In this review, we will summarize the latest findings about B-lymphocytes and Igs in mucosal immunity and the effect of stress and vaccination on B-cell response at mucosal sites. It is important to point out that a limited number of studies have been published regarding stress in mucosa and very few about the influence of stress over mucosal B-lymphocytes.

Evolution of B cell immunity

Two types of adaptive immune strategies are known to have evolved in vertebrates: the VLR-based system, which is present in jawless organisms and is mediated by VLRA and VLRB lymphocytes, and the BCR/TCR-based system, which is present in jawed species and is provided by B and T cell receptors expressed on B and T cells, respectively. Here we summarize features of B cells and their predecessors in the different animal phyla, focusing the review on B cells from jawed vertebrates. We point out the critical role of nonclassical species and comparative immunology studies in the understanding of B cell immunity. Because nonclassical models include species relevant to veterinary medicine, basic science research performed in these animals contributes to the knowledge required for the development of more efficacious vaccines against emerging pathogens.

A Review of Intra- and Extracellular Antigen Delivery Systems for Virus Vaccines of Finfish

Vaccine efficacy in aquaculture has for a long time depended on evaluating relative percent survival and antibody responses after vaccination. However, current advances in vaccine immunology show that the route in which antigens are delivered into cells is deterministic of the type of adaptive immune response evoked by vaccination. Antigens delivered by the intracellular route induce MHC-I restricted CD8+ responses while antigens presented through the extracellular route activate MHC-II restricted CD4+ responses implying that the route of antigen delivery is a conduit to induction of B- or T-cell immune responses. In finfish, different antigen delivery systems have been explored that include live, DNA, inactivated whole virus, fusion protein, virus-like particles, and subunit vaccines although mechanisms linking these delivery systems to protective immunity have not been studied in detail. Hence, in this review we provide a synopsis of different strategies used to administer viral antigens via the intra- or extracellular compartments. Further, we highlight the differences in immune responses induced by antigens processed by the endogenous route compared to exogenously processed antigens. Overall, we anticipate that the synopsis put together in this review will shed insights into limitations and successes of the current vaccination strategies used in finfish vaccinology.

Systemic and mucosal immune response of rainbow trout to immunization with an attenuated Flavobacterium psychrophilum vaccine strain by different routes

Teleosts possess three immunoglobulin (Ig) heavy chain isotypes viz., IgM, IgT and IgD and all three isotypes are reported in rainbow trout. The expression of these Ig isotypes in response to different immunization routes was investigated and results provide a better understanding of the role these Igs in different tissues. Rainbow trout (Oncorhynchus mykiss) were immunized with an attenuated Flavobacterium psychrophilum strain, 259-93-B.17 grown under iron limiting conditions, by intraperitoneal, anal intubation and immersion routes. Serum, gill mucus, skin mucus and intestinal mucus samples were collected at 0, 3, 7, 14, 28, 42 and 56 days post immunization by sacrificing four fish from each treatment group and the unimmunized control group, and the IgM levels were estimated by an enzyme linked immunosorbent assay (ELISA). In addition, blood, gill, skin and intestinal tissue samples were collected for Ig gene expression studies. The secretory IgM, IgD and IgT gene expression levels in these tissues were estimated by reverse transcription quantitative real time PCR (RT-qPCR). Levels of IgM in serum, gill and skin mucus increased significantly by 28 days after immunization in the intraperitoneally immunized group, while no significant increase in IgM level was observed in fish groups immunized by other routes. Secretory IgD and IgT expression levels were significantly upregulated in gills of fish immunized by the immersion route. Similarly, secretory IgT and IgD were upregulated in intestines of fish immunized by anal intubation route. The results confirm mucosal association of IgT and suggest that IgD may also be specialized in mucosal immunity and contribute to immediate protection to the fish at mucosal surfaces.

Early steps in the European eel (Anguilla anguilla)-Vibrio vulnificus interaction in the gills: role of the RtxA13 toxin

Vibrio vulnificus is an aquatic gram-negative bacterium that causes a systemic disease in eels called warm-water vibriosis. Natural disease occurs via water born infection; bacteria attach to the gills (the main portal of entry) and spread to the internal organs through the bloodstream, provoking host death by haemorrhagic septicaemia. V. vulnificus produces a toxin called RtxA13 that hypothetically interferes with the eel immune system facilitating bacterial invasion and subsequent death by septic shock. The aim of this work was to study the early steps of warm-water vibriosis by analysing the expression of three marker mRNA transcripts related to pathogen recognition (tlr2 and tlr5) and inflammation (il-8) in the gills of eels infected by immersion with either the pathogen or a mutant deficient in rtxA13. Results indicate a differential response that is linked to the rtx toxin in the expression levels of the three measured mRNA transcripts. The results suggest that eels are able to distinguish innocuous from harmful microorganisms by the local action of their toxins rather than by surface antigens. Finally, the cells that express these transcripts in the gills are migratory cells primarily located in the second lamellae that re-locate during infection suggesting the activation of a specific immune response to pathogen invasion in the gill.

Comparative genomic of the BAFF and BAFF-like genes and immune response to bacteria of miiuy croaker (Miichthys miiuy)

As a member of the tumor necrosis factor (TNF) family, B cell activating factor (BAFF), also known as TNF ligand superfamily member 13B (TNF13B), playing a critical role in enhancing immune responses. BAFF is a central cytokine for B-cell survival, proliferation, maturation and immunoglobulin secretion. In the present study, we describe the identification of the miiuy croaker BAFF (designed MmBAFF) and BAFF-like (designed MmBAFF-like) genes. The cDNA of MmBAFF contains an open reading frame (ORF) of 795 nucleotides that are translated into a predicted 264 amino acids. The ORF of MmBAFF-like consists of 705 bases encoding 234 amino acids. Amino acid sequence comparison indicated that MmBAFF and MmBAFF-like possessed the TNF signatures, a predicted transmembrane domain, three conserved cysteine residues and a putative furin protease cleavage site, which were the typical characteristics of TNF gene in mammals and birds. The predicted three-dimensional (3D) structure of the MmBAFF and MmBAFF-like monomer analyzed by comparative protein modeling revealed that they were very similar to human counterpart. Comparative genomic analysis revealed that the locations of MmBAFF and MmBAFF-like genes are conserved among the bony fish. Phylogenetic analysis shows the MmBAFF is most closely related to other teleost BAFFs with the highest similarity to Epinephelus awoara. And BAFF-like cluster get together first to BAFF cluster than three closely related TNF superfamily (TNFSF) members. Real-time quantitative PCR analysis shows the MmBAFF and MmBAFF-like transcripts are expressed in a wide range of tissues with the highest expression in skin and lymphoid tissue spleen. Upon induction by Vibrio anguillarum, their expressions are significantly upregulated in liver, spleen and kidney as compared to phosphate-buffered saline injected control fish. The association of increased BAFF expression after bacterial infection suggests that it plays a potentially important role in immune system of fish.

Evaluation of dual nasal delivery of infectious hematopoietic necrosis virus and enteric red mouth vaccines in rainbow trout (Oncorhynchus mykiss)

Farmed fish are susceptible to different infectious disease agents including viruses and bacteria. Thus, multivalent vaccines or vaccination programs against two or more pathogens are valuable tools in aquaculture. Recently, nasal vaccines have been shown to be very effective in rainbow trout. The current study investigates, for the first time, the use of the nasal route in dual vaccination trials against two important aquatic diseases, infectious hematopoietic necrosis virus (IHN) and enteric red mouth (ERM) disease. Rainbow trout received live attenuated IHN virus (IHNV) vaccine and the ERM bacterin using four different vaccine delivery methods and were challenged with virulent IHNV or Yersinia ruckeri 7 (100 deg day) and 28 (400 deg day) days post-vaccination. The highest survival rates against IHNV at day 7 were obtained by nasal vaccination either when IHNV and ERM were delivered separately into each nare or when they were premixed and delivered to both nasal rosettes (group D). Protection at 28 days against IHNV was similar in all four vaccinated groups. Early protection against ERM was highest in fish that received each vaccine in separate nares (group B), whereas protection at 28 days was highest in the i.p. vaccinated group (group E), followed by the nasally vaccinated group (group B). Survival results were supported by histological observations of the left and right olfactory organ which showed strong immune responses one day (14 deg days) after vaccination in group B vaccinated fish. These data indicate that dual vaccination against two different pathogens via the nasal route is a very effective vaccination strategy for use in aquaculture, particularly when each nare is used separately during delivery. Further long-term studies should evaluate the contribution of adaptive immunity to the protection levels observed.

Effects of single and repeated infections with Neoparamoeba perurans on antibody levels and immune gene expression in Atlantic salmon (Salmo salar)

Amoebic gill disease (AGD) is the main health problem for the salmon industry in Tasmania, Australia and is now reported in most salmon producing countries. Antibody and gene expression responses to the pathogen, Neoparamoeba perurans, have been studied independently following primary exposure; however, the effects of sequential reinfection, which can often occur during net-pen culture of salmon, remain unclear. The association between the transcription of immunoglobulin (Ig) and their systemic and mucosal antibody levels in regards to AGD is unknown. Herein, we assessed the antibody responses as well as Ig transcription in the gills of Atlantic salmon infected only once and also sequentially with N. perurans. After four successive AGD challenges, no significant differences in plasma or skin mucus levels of IgM were observed between AGD-naïve and challenged fish. However, IgM gene expression in gill lesions of AGD-affected fish increased up to 31 d after infection, while no changes in IgT, TCR and CD8 transcription were observed. Changes at IgM transcription level did not match the lack of antibody response in mucus, which is possibly explained by weak correlations existing between protein and mRNA abundances in cells and tissues. In the second experiment, which investigated Ig responses to AGD at the transcriptional as well as antibody production level in salmon after a single infection, the levels of serum or skin mucus IgM antibody were not affected and no changes in the IgM or IgT transcription were induced.

Effects of transportation stress and addition of salt to transport water on the skin mucosal homeostasis of rainbow trout (Oncorhynchus mykiss)

Transportation of live fish is a common practice among aquaculture facilities. Many studies have previously reported how transport elicits physiological stress responses and increases disease susceptibility in farmed fish. The aim of this work is to investigate the changes that the skin of rainbow trout (Oncorhynchus mykiss) experiences due to stress. Since NaCl is commonly added to transport water as a stress mitigator, the effects of salt addition on the skin mucosa and skin-associated bacteria were also examined. Three experimental groups (Control, post-transport no salt (PTNS) and post-transport with salt (PTS)) were analyzed in a 5-hour transport acute stress model. Results indicate that the skin mucosa and the skin-associated bacteria are affected by transport stress. Total numbers of culturable skin-associated bacteria increased by ~10-fold and ~50-fold in the PTS and PTNS groups, respectively. Compared to controls, MUC2 expression was increased by 5-fold and 2-fold in the PTNS and PTS groups, respectively. Claudin-7, 8d and 12 expression levels were higher in both PTNS and PTS groups whereas antimicrobial peptide gene expression was lower than controls. Expression of the anti-inflammatory cytokine TGF-β but not IL-1β, IL-6 and TNF-α was up-regulated 2-3 fold in both the PTS and PTNS groups. The addition of salt diminished some of the physiological responses measured including the numbers of skin-associated bacteria. The responses recorded here appeared to be efficient at controlling bacterial translocation since stress did not lead to significant presence of bacteria in the liver or spleen of rainbow trout. When examining the ability of skin mucus to inhibit or promote growth of the bacterial pathogen Vibrio anguillarum, the skin mucus of PTS trout was more efficient at inhibiting V. anguillarum growth (20% inhibition) compared to control or PTNS mucus (11-12% inhibition). Our data clearly indicate the skin and skin microbiota of rainbow trout undergo important physiological responses during stress. The reduction in the magnitude of the skin responses recorded when salt was added to the transport water explains a new mechanism by which salt is an effective stress mitigator in some fish species. Aquaculture specialists will benefit from the present study by taking into consideration the importance of skin health during live transport.

Unique Features of Fish Immune Repertoires: Particularities of Adaptive Immunity Within the Largest Group of Vertebrates

Fishes (i.e., teleost fishes) are the largest group of vertebrates. Although their immune system is based on the fundamental receptors, pathways, and cell types found in all groups of vertebrates, fishes show a diversity of particular features that challenge some classical concepts of immunology. In this chapter, we discuss the particularities of fish immune repertoires from a comparative perspective. We examine how allelic exclusion can be achieved when multiple Ig loci are present, how isotypic diversity and functional specificity impact clonal complexity, how loss of the MHC class II molecules affects the cooperation between T and B cells, and how deep sequencing technologies bring new insights about somatic hypermutation in the absence of germinal centers. The unique coexistence of two distinct B-cell lineages respectively specialized in systemic and mucosal responses is also discussed. Finally, we try to show that the diverse adaptations of immune repertoires in teleosts can help in understanding how somatic adaptive mechanisms of immunity evolved in parallel in different lineages across vertebrates.

T cell transcripts and T cell activities in the gills of the teleost fish sea bass (Dicentrarchus labrax)

The gills of fish are a mucosal tissue that contains T cells involved in the recognition of non-self and pathogens, and in this work we describe some features of gill-associated T cells of European sea bass, a marine model species. A whole transcriptome was obtained by deep sequencing of RNA from unstimulated gills that has been analyzed for the presence of T cell-related transcripts. Of the putative expressed sequences identified in the transcriptome, around 30 were related to main functions related to T cells including Th1/Th2/Th17/Treg cell subpopulations, thus suggesting their possible presence in the branchial epithelium. The number of T cells in the gills of sea bass, measured with the specific T cell mAb DLT15 range from 10% to 20%, and IHC analysis shows their abundance and distribution in the epithelium. Leukocytes from gills are able to proliferate in the presence of lectins ConA and PHA, as measured by flow cytometry using CFSE fluorescence incorporation, and during proliferation the number of T cells counted by immunofluorescence increased. In lectin-proliferating cells the expression of T cell-related genes TRβ, TRγ, CD4, CD8α, CD45 and IL-10 increased dramatically. Our data represent a first analysis on T cell genes and on basic T cell activities of fish gills, and suggest the presence of functionally active subpopulations of T lymphocytes in this tissue.

Changes in the interbranchial lymphoid tissue of Atlantic salmon (Salmo salar) affected by amoebic gill disease

The interbranchial lymphoid tissue (ILT) was recently described in the gills of salmonids. This study examined changes in the ILT during a parasitic infection in marine environment, using amoebic gill disease (AGD) as a model. Atlantic salmon (Salmo salar) experimentally infected with Neoparamoeba perurans were sampled at 0, 3, 7, 14 and 28 days post challenge. Transversal sections of three areas of the gills (dorsal, medial and ventral) were histologically assessed for morphological and cellular changes. AGD induced morphological changes and a cellular response in the ILT of affected fish. These changes included a significant increase in the ILT surface area in fish 28 days after AGD challenge, compared to control fish at the same time point. The length of the ILT increased significantly 28 days post exposure in the dorsal area of the gill arch in the fish affected by AGD. The lymphocyte density of the ILT increased after AGD challenge, peaking at 7 days post exposure; however, by 28 days post exposure, a reduction of lymphocyte density to values close to pre-infection levels was observed. PCNA immunostaining revealed that epithelial hyperplasia was the most likely factor contributing to the ILT enlargement in the affected fish.

Immune parameters in the intestine of wild and reared unvaccinated and vaccinated Atlantic salmon (Salmo salar L.)

Forming a barrier to the outside world, the gut mucosa faces the challenge of absorbing nutrients and fluids while initiating immune reactions towards potential pathogens. As a continuation to our previous publication focusing on the regional intestinal morphology in wild caught post smolt and spawning Atlantic salmon, we here investigate selected immune parameters and compare wild, reared unvaccinated and vaccinated post smolts. We observed highest transcript levels for most immune-related genes in vaccinated post smolts followed by reared unvaccinated and finally wild post smolts, indicating that farming conditions like commercial feed and vaccination might contribute to a more alerted immune system in the gut. In all groups, higher levels of immune transcripts were observed in the second segment of mid-intestine and in the posterior segment. In the life stages and conditions investigated here, we found no indication of a previously suggested population of intestinal T cells expressing MHC class II nor RAG1 expression.

Nasal immunity is an ancient arm of the mucosal immune system of vertebrates

The mucosal surfaces of all vertebrates have been exposed to similar evolutionary pressures for millions of years. In terrestrial vertebrates such as birds and mammals, the nasopharynx-associated lymphoid tissue (NALT) represents a first line of immune defence. Here we propose that NALT is an ancient arm of the mucosal immune system not restricted to terrestrial vertebrates. We find that NALT is present in rainbow trout and that it resembles other teleost mucosa-associated lymphoid tissues. Trout NALT consists of diffuse lymphoid cells and lacks tonsils and adenoids. The predominant B-cell subset found in trout NALT are IgT(+) B cells, similar to skin and gut. The trout olfactory organ is colonized by abundant symbiotic bacteria, which are coated by trout secretory immunoglobulin. Trout NALT is capable of mounting strong anti-viral immune responses following nasal delivery of a live attenuated viral vaccine. Our results open up a new tool for the control of aquatic infectious diseases via nasal vaccination.

Immune gene expressions in grouper larvae (Epinephelus coioides) induced by bath and oral vaccinations with inactivated betanodavirus

Nervous necrosis virus (NNV) has caused mass mortality in many mariculture fish species. Bath vaccination of inactivated NNV and oral immunization of recombinant NNV coat protein are reported to protect grouper larvae against NNV infection. However, the information of immune gene expression in grouper larvae (Epinephelus coioides) after bath and oral immunizations is still limited. In this study, grouper larvae were respectively bath- and orally immunized with binary ethylenimine (BEI)-inactivated NNV, and the expression levels of immune genes were analyzed. Significant gene expressions of IL-1β, Mx, MHC-I, MHC-II, CD8α, IgM and IgT were observed in bath- and orally immunized fish 1-4 weeks post immunization (wpi). Particularly, the up-regulation of IL-1β and Mx gene expression lasted for 4 weeks. The IgT gene expression in gill was only induced by bath immunization, while that in gut was only stimulated by oral immunization. Both immunizations elicited MHC-I and CD8α gene expression relative to cellular immunity. Furthermore, NNV RNA genome, which was detected in inactivated NNV, could induce Mx gene expression in grouper brain (GB) cells, indicating that NNV RNA genome could be recognized by pathogen-recognition receptors (PRRs). In summary, bath and oral vaccinations with BEI-inactivated NNV triggered the gene expression of not only humoral immunity but also cellular immunity.

Mucosal addressin cell adhesion molecule-1 of rhesus macaques: molecular cloning, expression, and alteration after viral infection

BACKGROUND

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1), a member of the immunoglobulin superfamily, is essential for gut-specific homing of leukocytes; however, it has not been well characterized in rhesus macaques.

AIMS

To obtain the complete nucleotide sequence of rhesus macaque MAdCAM-1 cDNA and determine its distribution in gut-associated lymphoid tissues (GALT) and its alteration in duodenal mucosa after simian/human immunodeficiency virus (SHIV) infection.

METHODS

MAdCAM-1 cDNA was cloned from the colon mucosa of a rhesus macaque by 3'- and 5'-RACE. The distribution and abundance of MAdCAM-1 mRNA in the GALT were examined by nested and real-time RT-PCR. The alterations of MAdCAM-1 mRNA levels in SHIV-infected duodenal mucosa were determined by real-time RT-PCR.

RESULTS

The nucleotide sequence of rhesus macaque MAdCAM-1 cDNA (1,503 bp nucleotides) including the 5'- and 3'-untranslated regions was obtained. The coding region (1,086 bp) showed 87.56% and the Ig-like domain 1, 2 and TM + cytoplasmic domains showed >93% nucleotide sequence identity to that of humans. Like humans, rhesus macaques lacked MAdCAM-1 IgA1-like domain, which could be a common feature for all primates appeared later during vertebrate evolution. Two species of MAdCAM-1 mRNA were detected and high-level transcripts were observed primarily in the GALT. The full-length MAdCAM-1 expressed in vitro could bind to human α4β7. MAdCAM-1 mRNA levels were statistically significantly reduced in SHIV-infected duodenal mucosa.

CONCLUSIONS

These data provided a basis for using rhesus macaques in pathological and therapeutic studies on leukocyte homing related diseases such as inflammatory bowel disease and HIV/AIDS.

Molecular cloning, functional identification and expressional analyses of FasL in Tilapia, Oreochromis niloticus

FasL is the most extensively studied apoptosis ligand. In 2000, tilapia FasL was identified using anti-human FasL monoclonal antibody by Evans's research group. Recently, a tilapia FasL-like protein of smaller molecule weight was predicted in Genbank (XM_003445156.2). Based on several clues drawn from previous studies, we cast doubt on the authenticity of the formerly identified tilapia FasL. Conversely, using reverse transcription polymerase chain reaction (RT-PCR), the existence of the predicted FasL-like was verified at the mRNA level (The Genbank accession number of the FasL mRNA sequence we cloned is KM008610). Through multiple alignments, this FasL-like protein was found to be highly similar to the FasL of the Japanese flounder. Moreover, we artificially expressed the functional region of the predicted protein and later confirmed its apoptosis-inducing activity using a methyl thiazolyl tetrazolium (MTT) assay, Annexin-V/Propidium iodide (PI) double staining, and DNA fragment detection. Supported by these evidences, we suggest that the predicted protein is the authentic tilapia FasL. To advance this research further, tilapia FasL mRNA and its protein across different tissues were quantified. High expression levels were identified in the tilapia immune system and sites where active cell turnover conservatively occurs. In this regard, FasL may assume an active role in the immune system and cell homeostasis maintenance in tilapia, similar to that shown in other species. In addition, because the distribution pattern of FasL mRNA did not synchronize with that of the protein, post-transcriptional expression regulation is suggested. Such regulation may be dominated by potential adenylate- and uridylate-rich elements (AREs) featuring AUUUA repeats found in the 3' untranslated region (UTR) of tilapia FasL mRNA.

Functional analysis of an orange-spotted grouper (Epinephelus coioides) interferon gene and characterisation of its expression in response to nodavirus infection

We cloned and sequenced 2C I-IFN, a two-cysteine containing type I interferon (I-IFN) gene, in orange-spotted grouper (Epinephelus coioides). The cDNA has 769 base pairs, the protein has 172 amino acids, and the predicted signal peptide has 18 amino acids with two cysteines. This gene is similar to I-FNs from sea bass and other teleosts. 2C I-IFN has 5 exons and 4 introns, also similar to other teleost I-IFNs. Immunohistochemical (IHC) analysis indicated that expression is predominantly membrane-localized in healthy grouper, but has a zonal distribution in nodavirus-infected grouper. Grouper infected with nodavirus had elevated levels of 2C I-IFN at 72 h and Mx at days 6-7. Recombinant 2C I-IFN activated grouper Mx, leading to upregulated antiviral activity. The grouper Mx promoter was highly induced after treatment with recombinant 2C I-IFN. The present results suggest that expression of grouper 2C I-IFN may participate in the immunologic barrier function against nodavirus.

Fish Immunology. The modification and manipulation of the innate immune system: Brazilian studies

The understanding of fish immune system structure and function is essential for the development of new technologies and products to improve productivity. This is the first review on immune system of fish with Brazilian studies. Aquaculture in Brazil has shown massive growth in recent years due to methods of culture intensification. However, these procedures led to disease outbreaks, as well as the chemotherapy and the misuse of antibiotics. A viable alternative to avoid the use of chemicals and prevent economic losses is the administration of immunostimulants and prebiotcs, which act by increasing the innate immune system. In Brazil there is a lack of studies on fish immune system, except by some groups that have studied the effects of the immunostimulants administration in various species.

Investigation of immunoglobulins in skin of the Antarctic teleost Trematomus bernacchii

The presence and production of IgM in the skin of the Antarctic teleost Trematomus bernacchii were investigated in this study. Immunoglobulins purified from cutaneous mucus and analysed by SDS-PAGE run under non-reducing and reducing conditions, were composed of heavy and light chains of 78 kDa and 25 kDa respectively, with a relative molecular mass of 830 kDa indicating that mucus IgM are tetramers as the serum IgM. Mature transcripts encoding the constant domains of both the secretory and membrane-bound Igμ chain were seen in T. bernacchii skin using a PCR strategy and the expression of the secretory Igμ chain in the skin was compared with that in other tissues by Real-time PCR. Cytological investigations revealed the presence of either immunoglobulins or their transcripts in occasional lymphocytes distributed close to the basal membrane. IgM once produced here, enters the filament-containing cells and is released into the mucus when these cells degenerate and detach from the epidermis. Our findings indicate that a cutaneous defence mechanism, functioning as anatomical and physiological barrier under subzero conditions, is present in this Antarctic species as an important component of the immune system.

Mucosal immunity and probiotics in fish

Teleost mucosal immunity has become the subject of unprecedented research studies in recent years because of its diversity and defining characteristics. Its immune repertoire is governed by the mucosa-associated lymphoid tissues (MALT) which are divided into gut-associated lymphoid tissues (GALT), skin-associated lymphoid tissues (SALT), and gill-associated lymphoid tissues (GIALT). The direct contact with its immediate environment makes the mucosal surfaces of fish susceptible to a wide variety of pathogens. The inherent immunocompetent cells and factors in the mucosal surfaces together with the commensal microbiota have pivotal role against pathogens. Immunomodulation is a popular prophylactic strategy in teleost and probiotics possess this beneficial feature. Most of the studies on the immunomodulatory properties of probiotics in fish mainly discussed their impacts on systemic immunity. In contrast, few of these studies discussed the immunomodulatory features of probiotics in mucosal surfaces and are concentrated on the influences in the gut. Significant attention should be devoted in understanding the relationship of mucosal immunity and probiotics as the present knowledge is limited and are mostly based on extrapolations of studies in humans and terrestrial vertebrates. In the course of the advancement of mucosal immunity and probiotics, new perspectives in probiotics research, e.g., probiogenomics have emerged. This review affirms the relevance of probiotics in the mucosal immunity of fish by revisiting and bridging the current knowledge on teleost mucosal immunity, mucosal microbiota and immunomodulation of mucosal surfaces by probiotics. Expanding the knowledge of immunomodulatory properties of probiotics especially on mucosal immunity is essential in advancing the use of probiotics as a sustainable and viable strategy for successful fish husbandry.

Transcriptional response of immune genes in gills and the interbranchial lymphoid tissue of Atlantic salmon challenged with infectious salmon anaemia virus

Previously, it has been assumed that fish lack organized mucosa-associated lymphoid structures. Recently, an interbranchial lymphoid tissue (ILT) was described in salmonid gills at a site with substantial exposure to antigen. In this study, immune responses were examined in gills, mid-kidney and the laser-dissected ILT of Atlantic salmon (Salmo salar L.) infected with infectious salmon anaemia virus (ISAV). A strong innate response was observed in gills and mid-kidney and even in the laser-dissected ILT, despite the fact that no virus could be traced in this tissue. A small delayed increase in IgT transcripts, exclusively in the ILT, could indicate that this tissue has a role as a secondary lymphoid organ with clonal expansion of IgT expressing B-cells. Compared to the other examined tissues, gills displayed the earliest replication of the virus, further supporting this tissue as the main entry route for infection with ISAV.

Transcriptome profiling reveals insight into distinct immune responses to Aeromonas salmonicida in gill of two rainbow trout strains

The fish gills represent a crucial organ for the communication with the aquatic environment. Transcriptional changes in gills of two hatchery rainbow trout strains in response to injection with the potent pathogen Aeromonas salmonicida were detected by global gene expression profiling using a 4×44K oligonucleotide microarray. Emphasis was placed on "day 3 postinfection" representing a decisive time point for the resolution of inflammation. The comparison of features and pathways differentially regulated in branchial tissues revealed that the local breeding strain BORN and imported American rainbow trout apply common and specific immune strategies. In gills of infected BORN trout, we observed a dynamic regulation of genes controlling NF-κB pathways and the induction of factors promoting the development of myeloid cells, whereas an increased expression of lysozyme and immunoglobulin genes was obvious in gills of infected import trout. In order to prove the relevance of the array-predicted candidates as well as well-known immune genes for gill immunity, a subsequent in vitro experiment was conducted. Altogether, we uncovered dynamic but moderate changes in the expression of a broad range of immune-relevant features implying the gill's involvement in pathogen defense strategies.

Development of an Ussuri catfish Pseudobagrus ussuriensis skin cell line displaying differential cytopathic effects to three aquatic animal viruses

An Ussuri catfish Pseudobagrus ussuriensis skin (UCS) cell line was developed and subcultured for more than 60 passages. UCS cells consisted of mostly epithelial-like cells and multiplied well in TC199 medium supplemented with 10% fetal bovine serum at 25°C. Chromosome analysis revealed that most UCS cells had a normal diploid karyotype with 2n=52. UCS cells showed differential cytopathic effects (CPEs) after inoculation of spring viremia of carp virus (SVCV, a negative-strand RNA virus), grass carp reovirus (GCRV, a multi-segmented double-stranded RNA virus) and Rana grylio virus (RGV, a large double-stranded DNA virus), and were indicative of high sensitivities to these three aquatic animal viruses by a virus titration study. The CPE caused by SVCV appeared as rounded and granular cells, grape-like clusters and small lytic plaques. Characteristic CPE containing plaque-like syncytia was induced by GCRV. RGV-infected cells produced typical CPE characterized by cells shrinkage and aggregation, formation of clear plaques and cell sheet detachment. Furthermore, significant fluorescent signals were observed after UCS cells were transfected with green fluorescent protein reporter plasmids, and the development of CPE induced by a recombinant RGV, ΔTK-RGV, in UCS cells was illustrated using a combination of light and fluorescence microscopy. The data from this study suggested that UCS cell line can potentially serve as a useful tool for the comparison study of different aquatic animal viruses and the isolation of some newly emerging viruses in Ussuri catfish farming.

Oral and anal vaccination confers full protection against enteric redmouth disease (ERM) in rainbow trout

The effect of oral vaccines against bacterial fish diseases has been a topic for debate for decades. Recently both M-like cells and dendritic cells have been discovered in the intestine of rainbow trout. It is therefore likely that antigens reaching the intestine can be taken up and thereby induce immunity in orally vaccinated fish. The objective of this project was to investigate whether oral and anal vaccination of rainbow trout induces protection against an experimental waterborne infection with the pathogenic enterobacteria Yersinia ruckeri O1 biotype 1 the causative agent of enteric redmouth disease (ERM). Rainbow trout were orally vaccinated with AquaVac ERM Oral (MERCK Animal Health) or an experimental vaccine bacterin of Y. ruckeri O1. Both vaccines were tested with and without a booster vaccination four months post the primary vaccination. Furthermore, two groups of positive controls were included, one group receiving the experimental oral vaccine in a 50 times higher dose, and the other group receiving a single dose administered anally in order to bypass the stomach. Each group was bath challenged with 6.3 × 10(8) CFU/ml Y. ruckeri, six months post the primary vaccination. The challenge induced significant mortality in all the infected groups except for the groups vaccinated anally with a single dose or orally with the high dose of bacterin. Both of these groups had 100% survival. These results show that a low dose of Y. ruckeri bacterin induces full protection when the bacterin is administered anally. Oral vaccination also induces full protection, however, at a dose 50 times higher than if the fish were to be vaccinated anally. This indicates that much of the orally fed antigen is digested in the stomach before it reaches the second segment of the intestine where it can be taken up as immunogenic antigens and presented to lymphocytes.

Antiviral functions of CD8(+) cytotoxic T cells in teleost fish

Cytotoxic T-cells (CTLs) play a pivotal role in eliminating viruses in mammalian adaptive immune system. Many recent studies on T-cell immunity of fish have suggested that teleost CTLs are also important for antiviral immunity. Cellular functional studies using clonal ginbuan crucian carp and rainbow trout have provided in vivo and in vitro evidence that in many respects, virus-specific CTLs of fish have functions similar to those of mammalian CTLs. In addition, mRNA expression profiles of CTL-related molecules, such as CD8, TCR and MHC class I, have shown that in a wide range of fish species, CTLs are involved in antiviral adaptive immunity. These findings are a basis to formulate possible vaccination strategies to trigger effective antiviral CTL responses in teleost fish. This review describes recent advances in our understanding of antiviral CTL functions in teleost fish and discusses vaccination strategies for efficiently inducing CTL activities.

Immunity to Ichthyophthirius infections in fish: a synopsis

Ichthyophthirius multifiliis is a ciliated protozoan parasite that infects freshwater fish. It has been the subject of both applied and basic research for over 100years, which can be attributed to its world-wide distribution and its significant economic impact on both food and aquarium fish production. I. multifiliis serves as a model for studies in fish on innate and acquired immunity, as well as on mucosal immunity. Although an obligate parasite, I. multifiliis is relatively easily passaged from infected to naïve fish in laboratory aquaria, and is easily observed and manipulated under laboratory conditions. It parasitizes the epithelia of the skin and gills, which facilitates in vivo experimentation and quantification of challenge. This review provides a description of both mucosal and systemic innate and adaptive immune responses to parasite infection, a synopsis of host-parasite immunobiology, vaccine research, and suggested areas for future research to address critical remaining questions. Studies in carp and rainbow trout have shown that extensive tissue damage occurs when the parasite invades the epithelia of the skin and gills and substantial focal and systemic inflammatory responses are elicited by the innate immune response. The adaptive immune response is initiated when phagocytic cells are activated by antigens released by the parasite. It is not known whether activated T and B cells proliferate locally in the skin and gills following infection or migrate to these sites from the spleen or anterior kidney. I. multifiliis infection elicits both mucosal and systemic antibody production. Fish that survive I. multifiliis infection acquire protective immunity. Memory B cells provide long-term humoral memory. This suggests that protective vaccines are theoretically possible, and substantial efforts have been made toward developing vaccines in various fish species. Exposure of fish to controlled surface infections or by intracoelomic injection of live theronts provides protection. Vaccination with purified immobilization antigens, which are GPI-anchored membrane proteins, also provides protection under laboratory conditions and immobilization antigens are currently the most promising candidates for subunit vaccines against I. multifiliis.

Innate immune responses of salmonid fish to viral infections

Viruses are the most serious pathogenic threat to the production of the main aquacultured salmonid species the rainbow trout Oncorhynchus mykiss and the Atlantic salmon Salmo salar. The viral diseases Infectious Pancreatic Necrosis (IPN), Pancreatic Disease (PD), Infectious Haemorrhagic Necrosis (IHN), Viral Haemorrhagic Septicaemia (VHS), and Infectious Salmon Anaemia (ISA) cause massive economic losses to the global salmonid aquaculture industry every year. To date, no solution exists to treat livestock affected by a viral disease and only a small number of efficient vaccines are available to prevent infection. As a consequence, understanding the host immune response against viruses in these fish species is critical to develop prophylactic and preventive control measures. The innate immune response represents an important part of the host defence mechanism preventing viral replication after infection. It is a fast acting response designed to inhibit virus propagation immediately within the host, allowing for the adaptive specific immunity to develop. It has cellular and humoral components which act in synergy. This review will cover inflammation responses, the cell types involved, apoptosis, antimicrobial peptides. Particular attention will be given to the type I interferon system as the major player in the innate antiviral defence mechanism of salmonids. Viral evasion strategies will also be discussed.

Immunity to amoeba

Amoebic infections in fish are most likely underestimated and sometimes overlooked due to the challenges associated with their diagnosis. Amoebic diseases reported in fish affect either gills or internal organs or may be systemic. Host response ranges from hyperplastic response in gill infections to inflammation (including granuloma formation) in internal organs. This review focuses on the immune response of Atlantic salmon to Neoparamoeba perurans, the causative agent of Amoebic Gill Disease (AGD).

Biology and mucosal immunity to myxozoans

Myxozoans are among the most abundant parasites in nature. Their life cycles involve two hosts: an invertebrate, usually an annelid, and a vertebrate, usually a fish. They affect fish species in their natural habitats but also constitute a menace for fish aquaculture. Using different strategies they are able to parasitize and cause damage in multiple organs, including mucosal tissues, which they use also as portals of entry. In fish, the main mucosal sites include the intestine, skin and gills. Recently the finding of a specific mucosal immunoglobulin in teleost (IgT), analogous to mammalian IgA, and the capacity of fish to develop a specific mucosal immune response against different pathogens, has highlighted the importance of studying immune responses at mucosal sites. In this review, we describe the major biological characteristics of myxozoan parasites and present the data available regarding immune responses for species that infect mucosal sites. As models for mucosal immunity we review the responses to Enteromyxum spp. and Ceratomyxa shasta, both of which parasitize the intestine. The immune response at the skin and gills is also described, as these mucosal tissues are used by myxozoans as attaching surfaces and portal of entry, and some species also parasitize these sites. Finally, the development of immunoprophylactic strategies is discussed.

Interleukin gene expression is strongly modulated at the local level in a fish-parasite model

The goal of this work was to identify interleukin (IL)-related genes in the gilthead sea bream (GSB) (Sparus aurata L.) and how they are modulated by the parasite Enteromyxum leei, a myxozoan that causes severe enteritis with a strong inflammatory response. A Blast-X search of our transcriptomic GSB database (www.nutrigroup-iats.org/seabreamdb) identified 16 new sequences encompassing seven ILs (IL-7, IL-8, IL-10, IL-12β, IL-15, IL-18, and IL-34), the interleukin enhancer-binding factor 2 (ILF2), and eight IL receptors (IL-R); IL-R1, IL-6RA, IL-6RB, IL-8RA, IL-10RA, IL-10RB, IL-18R1, and IL-22R. Except for ILF2, their expression, plus that of IL-1β, IL-1R2, IL-6, and TNF-α (from public repositories), were analysed by 96-well PCR array of samples of blood, spleen, head kidney, and intestine of GSB that were anally intubated with E. leei (recipient group, RCPT). Only the expression profile of the intestine of RCPT fish showed significant difference as compared to samples from PBS-inoculated fish. At 17 days post intubation (dpi), the expression of key pro-inflammatory ILs, such as IL-8, IL-8R, IL-12β, and TNFα was significantly up-regulated, whereas at 64 dpi, anti-inflammatory IL expression (IL-6, IL-6RB, IL-7, IL-10, IL-10RA, and IL-15) was predominant. These results indicate a modification of the IL expression at late times post infection, probably to protect the fish intestine from the parasite and damage inflicted by an excessive inflammatory response. Furthermore, the response is mainly mediated at the local level as no significant changes were detected in blood, spleen and head kidney.

Substitution of dietary fish oil with plant oils is associated with shortened mid intestinal folds in Atlantic salmon (Salmo salar)

Background

Fish meal and fish oil are increasingly replaced by ingredients from terrestrial sources in the feeds for farmed salmonids due to expanding production and reduced availability of marine feed raw material. Fish oil that is rich in n-3 polyunsaturated fatty acids is considered beneficial to human health in general and to prevent intestinal inflammation and carcinogenesis in particular. In contrast, n-6 fatty acids that are present in many vegetable oils have been associated with increased risk of colitis and colon cancer in rodents and humans, as well as lowered transcription levels of certain stress and antioxidant-related genes in Atlantic salmon.

The aim of the present study was to investigate the intestinal health in Atlantic salmon fed with different vegetable oils as partial substitutes of fish oil in the diet. A feed trial lasting for 28 weeks included one reference diet containing fish oil as the sole lipid source and three diets where 80% of the fish oil was replaced by a plant oil blend with either olive oil, rapeseed oil or soybean oil as the main lipid source. These plant oils have intermediate or low n-3/n-6-ratios compared to fish oil having a high n-3/n-6-ratio. The protein and carbohydrate fractions were identical in all the feeds.

Results

Morphometric measurements showed significantly shorter folds in the mid intestine in all groups fed vegetable oils compared to the group fed fish oil. In the distal intestine, the complex folds were significantly shorter in the fish fed soybean oil compared to the fish fed rapeseed oil. Histological and immunohistochemical examination did not show clear difference in the degree of inflammation or proliferation of epithelial cells related to dietary groups, which was further confirmed by real-time RT-PCR which revealed only moderate alterations in the mRNA transcript levels of selected immune-related genes.

Conclusions

Shortened intestinal folds might be associated with reduced intestinal surface and impaired nutrient absorption and growth, but our results suggest that partial substitution of dietary fish oil with vegetable oils does not have any major negative impact on the intestinal health of Atlantic salmon.

Expressed IgH μ and τ transcripts share diversity segment in ranched Thunnus orientalis

It is now appreciated that in addition to the immunoglobulin (Ig)M and D isotypes fish also make the mucosal IgT. In this study we sequenced the full length of Ig τ as well as μ in the commercially important Thunnus orientalis (Pacific bluefin tuna), the first molecular analysis of these two Ig isotypes in a member of the order Perciformes. Tuna IgM and IgT are each composed of four constant (CH) domains. We cloned and sequenced 48 different variable (VH) domain gene rearrangements of tuna immunoglobulins and grouped the VH gene sequences to four VH gene segment families based on 70% nucleotide identity. Three VH gene families were used by both IgM and IgT but one group was only found to be used by IgM. Most interestingly, both μ and τ clones appear to use the same diversity (DH) segment, unlike what has been described in other species, although they have dedicated IgT and IgM joining (JH) gene segments. We complemented this repertoire study with phylogenetic and tissue expression analysis. In addition to supporting the development of humoral vaccines in this important aquaculture species, these data suggest that the DH-JH recombination rather than the VH-DH recombination may be instructive for IgT versus IgM/D bearing lymphocyte lineages in some fish.

iTRAQ analysis of gill proteins from the zebrafish (Danio rerio) infected with Aeromonas hydrophila

The gills are large mucosal surfaces and very important portals for pathogen entry in fish. The aim of this study was to determine the gill immune response at the protein levels, the differential proteomes of the zebrafish gill response to Aeromonas hydrophila infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1338 proteins were identified and classified into the categories primarily related to cellular process (15.36%), metabolic process (11.95%) and biological regulation (8.29%). Of these, 82 differentially expressed proteins were reliably quantified by iTRAQ analysis, 57 proteins were upregulated and 25 proteins were downregulated upon bacterial infection. Gene ontology (GO) enrichment analysis showed that approximately 33 (8.8%) of the differential proteins in gills were involved in the stress and immune responses. Several upregulated proteins were observed such as complement component 5, serpin peptidase inhibitor clade A member 7, annexin A3a, histone H4, glyceraldehyde 3-phosphate dehydrogenase, creatine kinase, and peroxiredoxin. These protein expression changes were further validated at the transcript level using microarray analysis. Moreover, complement and coagulation cascades, pathogenic Escherichia coli infection and phagosome were the significant pathways identified by KEGG enrichment analysis. This is first report on proteome of fish gills against A. hydrophila infection, which contribute to understanding the defense mechanisms of the gills in fish.

Staphylococcus warneri, a resident skin commensal of rainbow trout (Oncorhynchus mykiss) with pathobiont characteristics

Commensal microorganisms live in association with the mucosal surfaces of all vertebrates. The skin of teleost fish is known to harbor commensals. In this study we report for the first time the presence of an intracellular Gram positive bacteria, Staphylococcus warneri that resides in the skin epidermis of rainbow trout (Oncorhynchus mykiss). S. warneri was isolated from healthy hatchery trout skin epithelial cells. In situ hybridization confirmed the intracellular nature of the bacterium. Skin explants exposed in vitro to S. warneri or the extracellular pathogen Vibrio anguillarum show that S. warneri is able to induce an anti-inflammatory cytokine status via TGF-β1b compared to the pro-inflammatory responses (IL-1β, IL-6 and TNF-∝) elicited by V. anguillarum. In vivo experiments showed that S. warneri is not pathogenic to rainbow trout when injected intraperitoneally at high concentrations. However, S. warneri is able to stimulate V. anguillarum growth and biofilm formation on rainbow trout scales. Our results demonstrate that rainbow trout skin commensals such as S. warneri have the potential to become indirect pathobionts by enhancing growth and biofilm formation of pathogens such as V. anguillarum. These results show that fish farming practices (i.e. handling and other manipulations) can alter the skin microbiota and compromise the skin health of rainbow trout.