Side effects in sea bass (Dicentrarchus labrax L.) due to intraperitoneal vaccination against vibriosis and pasteurellosis

Biocompatibility of intraperitoneally implanted TEMPO-oxidized cellulose nanofiber hydrogels for antigen delivery in Atlantic salmon (Salmo salar L.) vaccines

Disease outbreaks are a major impediment to aquaculture production, and vaccines are integral for disease management. Vaccines can be expensive, vary in effectiveness, and come with adjuvant-induced adverse effects, causing fish welfare issues and negative economic impacts. Three-dimensional biopolymer hydrogels are an appealing new technology for vaccine delivery in aquaculture, with the potential for controlled release of multiple immunomodulators and antigens simultaneously, action as local depots, and tunable surface properties. This research examined the intraperitoneal implantation of a cross-linked TEMPO cellulose nanofiber (TOCNF) hydrogel formulated with a Vibrio anguillarum bacterin in Atlantic salmon with macroscopic and microscopic monitoring to 600-degree days post-implantation. Results demonstrated a modified passive integrated transponder tagging (PITT) device allowed for implantation of the hydrogel. However, the Atlantic salmon implanted with TOCNF hydrogels exhibited a significant foreign body response (FBR) compared to sham-injected negative controls. The FBR was characterized by gross and microscopic external and visceral proliferative lesions, granulomas, adhesions, and fibrosis surrounding the hydrogel using Speilberg scoring of the peritoneum and histopathology of the body wall and coelom. Acutely, gross monitoring displayed rapid coagulation of blood in response to the implantation wound with development of fibrinous adhesions surrounding the hydrogel by 72 h post-implantation consistent with early stage FBR. While these results were undesirable for aquaculture vaccines, this work informs on the innate immune response to an implanted biopolymer hydrogel in Atlantic salmon and directs future research using cellulose nanomaterial formulations in Atlantic salmon for a new generation of aquaculture vaccine technology.

Immune response of European sea bass (Dicentrarchus labrax L.) against combination of antigens from three different pathogens

Three of the most important diseases of Mediterranean intensive European sea bass farming are, viral nervous necrosis (VNN) caused by the red grouper nervous necrosis virus (RGNNV) genotype of b-nodavirus, photobacteriosis caused by Photobacterium damselae subsp. piscicida (Phdp) and vibriosis caused mainly by the O1 serotype of Vibrio anguillarum (VaO1). Prevention against these diseases is performed through vaccination with a monovalent vaccine against the viral disease and, usually, with bivalent vaccines against the bacterial diseases. However, it is very difficult to program two vaccinations during the same season for the same fish stock and producers are forced to either vaccinate for the viral or the bacterial diseases or to perform double vaccination with both vaccines, without any prior knowledge on any interactions that may occur due to the plethora of antigens (Ag) injected. Ideally, therefore, a trivalent vaccine should be developed against all three diseases. The objective of this work was to analyse the immune response of sea bass against combinations of Ags from all three pathogens, namely viral particles, Phdp whole cells (WC), lipopolysaccharide (LPS), capsular polysaccharide (CPS) and extracellular products (ECPs) and VaO1 WC and ECPs in respect to the identification of any phenomena of immunodominance/immunosuppression between Ags with a view to select candidate Ags for inclusion in a trivalent vaccine formulation. Eight triplicate groups of fish were immunized with different combinations of the aforementioned Ags and another triplicate group served as negative control. Blood serum was isolated at various time-points post-immunization for the measurement of specific antibodies against each Ag and, in addition, leucocytes were isolated at day 29 post-immunization for analysis of various cellular activities. Results indicated that best levels of specific a-NNV virus antibodies (Abs) were produced when VaO1 ECPs were not included in the Ag combinations, in contrast to the leucocytes proliferation assay where best stimulation against NNV Ags was measured when VaO1 ECPs were present in Ag combinations. VaO1 ECPs apparently is a strong immunogen for both humoral and cellular responses but suppresses immunological reactions against the other Ags.VaO1 WC, Phdp LPS and ECPs raised good humoral immune responses in the groups with best responses against VNN Ags, but only VaO1 WC and Phdp ECPs provided good stimulation of leucocytes, with Phdp WC and CPS effecting either similar stimulation with untrained leucocytes (control groups) or down-stimulation. Results are discussed with a view to select Ags from all three pathogens for inclusion in trivalent vaccine against all three pathogens.

Short-Term Immune Responses of Gilthead Seabream (Sparus aurata) Juveniles against Photobacterium damselae subsp. piscicida

Photobacteriosis is a septicaemic bacterial disease affecting several marine species around the globe, resulting in significant economic losses. Although many studies have been performed related to the pathogen virulence and resistance factors, information regarding the host defence mechanisms activated once an infection takes place is still scarce. The present study was designed to understand innate immune responses of farmed juvenile gilthead seabream (Sparus aurata) after Photobacterium damselae subsp. piscicida (Phdp) infection. Therefore, two groups of seabream juveniles were intraperitoneally injected with 100 µL of PBS (placebo) or 100 µL of exponentially growing Phdp (1 × 10⁶ CFU/mL; infected). The blood, plasma, liver, and head kidney of six fish from each treatment were sampled immediately before infection and 3, 6, 9, 24 and 48 h after infection for the broad screening of fish immune and oxidative stress responses. Infected animals presented marked anaemia, neutrophilia and monocytosis, conditions that are correlated with an increased expression of genes related to inflammation and phagocytic activity. Similar studies with different fish species and bacteria can be useful for the definition of health biomarkers that might help fish farmers to prevent the occurrence of such diseases.

Long-Term Protection and Serologic Response of European Sea Bass Vaccinated with a Betanodavirus Virus-Like Particle Produced in Pichia pastoris

Viral Nervous Necrosis (VNN) causes high mortality and reduced growth in farmed European sea bass (Dicentrarchus labrax) in the Mediterranean. In the current studies, we tested a novel Pichia-produced virus-like particle (VLP) vaccine against VNN in European sea bass, caused by the betanodavirus “Red-Spotted Grouper Nervous Necrosis Virus” (RGNNV). European sea bass were immunized with a VLP-based vaccine formulated with different concentrations of antigen and with or without adjuvant. Antibody response was evaluated by ELISA and serum neutralization. The efficacy of these VLP-vaccine formulations was evaluated by an intramuscular challenge with RGNNV at different time points (1, 2 and 10 months post-vaccination) and both dead and surviving fish were sampled to evaluate the level of viable virus in the brain. The VLP-based vaccines induced an effective protective immunity against experimental infection at 2 months post-vaccination, and even to some degree at 10 months post-vaccination. Furthermore, the vaccine formulations triggered a dose-dependent response in neutralizing antibodies. Serologic response and clinical efficacy, measured as relative percent survival (RPS), seem to be correlated with the administered dose, although for the individual fish, a high titer of neutralizing antibodies prior to challenge was not always enough to protect against disease. The efficacy of the VLP vaccine could not be improved by formulation with a water-in-oil (W/O) adjuvant. The developed RGNNV-VLPs show a promising effect as a vaccine candidate, even without adjuvant, to protect sea bass against disease caused by RGNNV. However, detection of virus in vaccinated survivors means that it cannot be ruled out that survivors can transmit the virus.

Simultaneous Administration of <i>Boesenbergia pandurata</i> Extract and Vaccination to Stimulate Immune Response in Tilapia, <i>Oreochromis niloticus</i>

BACKGROUND AND OBJECTIVE

The use of adjuvants or immunostimulants is often necessary to increase vaccine efficacy, in this study we evaluated the improvement of the immune response in tilapia treated by either oral and immersion administration with vaccine and Boesenbergia pandurata extract (BPE).

MATERIALS AND METHODS

The initial concentration of BPE and the cell density of vaccine were 900 mg L-1 and 104 CFU mL-1 for oral administration while 106 CFU mL-1 for immersion, respectively. The extract and vaccine were mixed homogeneously in a ratio of 1:1. Further, the mixture was supplemented to feed at 1 mL g-1 feed. Tilapia with average initial body weight of 15 g were fed containing vaccine and BPE 3 times a day. The other group of fish was immersed with vaccine and BPE for 20 min. After 7th (d7), 14th (d14) and21th (d21) days of treatment, a challenge test was conducted by intramuscularly injection of 0.1 mL of Aeromonas hydrophila and Pseudomonas fluorescens mixture (1:1) at a density of 105 CFU mL-1. Antibody levels, total white blood cell (WBC) and phagocytic activity (PA) were evaluated to determine the immune improvement of the fish. Furthermore, relative percent survival (RPS) and the survival rate (SR) were evaluated at week 2 and 4 after challenge test.

RESULT

Results indicated that the all parameters of tilapia immune system were increased (p<0.05) after 2-4 weeks of both administration methods. Meanwhile, the efficacy of the vaccine has increased by combining BPE treatment using immersion method better than oral method. The RPS of vaccination plus extract by immersion was 83-100% and by oral administration was 83-87%.

CONCLUSION

The present results implied that B. pandurata extract boost the efficacy of the Pseudomonas sp. vaccine by increasing the immune system and diseases resistance in tilapia.

Intramuscular vaccination of Atlantic lumpfish (Cyclopterus lumpus L.) induces inflammatory reactions and local immunoglobulin M production at the vaccine administration site

Atlantic lumpfish were vaccinated by intramuscular (im) or intraperitoneal (ip) injection with a multivalent oil-based vaccine, while control fish were injected with phosphate-buffered saline. Four lumpfish per group were sampled for skin/muscle and head kidney tissue at 0, 2, 7, 21 and 42 days post-immunization (dpi) for histopathology and immunohistochemistry (IHC). Gene expressions of secretory IgM, membrane-bound IgM, IgD, TCRα, CD3ε and MHC class IIβ were studied in tissues by using qPCR. Im. vaccinated fish showed vaccine-induced inflammation with formation of granulomas and increasing number of eosinophilic granulocyte-like cells over time. On IHC sections, we observed diffuse intercellular staining of secretory IgM at the injection site at 2 dpi, while IgM + cells appeared in small numbers at 21 and 42 dpi. Skin/muscle samples from im. vaccinated fish demonstrated an increase in gene expression of IgM mRNA (secretory and membrane-bound) at 21 and 42 dpi and small changes for other genes. Our results indicated that im. vaccination of lumpfish induced local IgM production at the vaccine injection site, with no apparent proliferation of IgM + cells. Eosinophilic granulocyte-like cells appeared shortly after im. injection and increased in numbers as the inflammation progressed.

Vaccines and immune protection of principal Mediterranean marine fish species

This review describes and summarizes the knowledge on established and experimental vaccines developed against viral and bacterial pathologies affecting the most important farmed marine finfish species present in the Mediterranean area, namely European seabass Dicentrarchus labrax, sea bream Sparus aurata, turbot Psetta maxima and meagre Argyrosomus regius. The diseases that have been recorded in seabass, sea bream and meagre are caused by bacteria Vibrio anguillarum, Photobacterium damselae, Tenacibaculum maritimum as well as by viruses such as Viral Encephalopathy and Retinopathy/Viral Nervous Necrosis and Lymphocystic disease. The main pathologies of turbot are instead bacteriosis provoked by Tenacibaculum maritimum, Aeromonas sp. and Vibrio anguillarum, and virosis by viral hemorrhagic septicaemia virus. Some vaccines have been optimized and are now regularly available for the majority of the above-mentioned pathogens. A measurable immune protection has been conferred principally against Vibrio anguillarum, Photobacterium damselae sub. piscicida and VER/VNN.

Generation and functional evaluation of a DNA vaccine co-expressing Vibrio anguillarum VAA protein and flounder interleukin-2

In our previous study, a DNA plasmid encoding the VAA gene of Vibrio anguillarum was constructed and demonstrated to confer moderated protection against V. anguillarum challenge. Here, a bicistronic DNA vaccine (pVAA-IRES-IL2), co-expressing the VAA gene of V. anguillarum and Interleukin-2 (IL2) gene of flounder, was constructed to increase the protective efficacy of VAA DNA vaccine. The potential of pVAA-IRES-IL2 to express both VAA and IL2 in transfected HINAE cell lines was confirmed by immunofluorescence assay. Further, the variation of sIgM⁺, CD4-1⁺, CD4-2⁺ lymphocytes and production of VAA-specific antibodies in flounder, which was intramuscularly immunized with three DNA plasmids (pIRES, pVAA-IRES, pVAA-IRES-IL2), were investigated, respectively. The bacterial burden and relative percentage survival (RPS) of flounder exposed to V. anguillarum infection were both analyzed to evaluate the efficacy of bicistronic DNA plasmid. Our results revealed that the percentages of sIgM⁺, CD4-1⁺, CD4-2⁺ lymphocytes and antibodies specific to VAA were remarkably increased in pVAA-IRES or pVAA-IRES-IL2 immunized fish. Moreover, the co-expression of IL2 enhanced the immune response in response to VAA DNA vaccination, as shown by the higher percentages of sIgM⁺, CD4-1⁺, CD4-2⁺ lymphocytes and production of specific antibody. Importantly, the RPS in pVAA-IRES-IL2 and pVAA-IRES groups reached 64.1% and 51.3%, respectively, when compared with the 97.5% cumulative mortality in pIRES group. Furthermore, the number of V. anguillarum in liver, spleen and kidney of pVAA-IRES or pVAA-IRES-IL2 immunized flounder after V. anguillarum challenge was significantly reduced, as compared to that in pIRES group. These suggest that the bicistronic DNA vaccine can be an effective immunization strategy in inducing immune response against V. anguillarum infection and IL2 has the potential as the adjuvant for VAA DNA vaccine.

Efficacy of chitosan oligosaccharide as aquatic adjuvant administrated with a formalin-inactivated Vibrio anguillarum vaccine

Vaccine is one of the efficient candidates to prevent fish disease through activating host immune response in aquaculture. Actually, several vaccines are often administered with adjuvants to increase immunostimulation, especially for some water-based formalin-killed vaccines. However, side effects are inevitable after vaccination of some adjuvants. Therefore, exploration for effective and harmless aquatic adjuvants is urgently needed. In this study, immunoprotection of a formalin-inactivated Vibrio anguillarum vaccine applied with chitosan oligosaccharide (COS) was analyzed. High levels of protection were achieved in zebrafish and turbot vaccinated with inactivated vaccine and COS (RPS of 89.0 ± 4.5% and 80.0 ± 6.9%) compared with fish vaccinated with inactivated vaccine alone (RPS of 47.8 ± 6.6% and 64.7 ± 5.8%) at 4 week post vaccination. Moreover, high antibody reaction and cross-protection against Vibrio alginolyticus and Vibrio harveyi were observed of turbot vaccinated with inactivated vaccine and COS. In conclusion, COS can enhance immunoprotection of a formalin-inactivated V. anguillarum vaccine, significantly activate humoral immune response of host, and be benefit for inhibition against pathogens. Therefore, COS would be a potential adjuvant for aquatic vaccine design in the future.

Particle size and traffic of phagocytes between the turbot peritoneal cavity and lymphoid organs

New adjuvants based on microparticles are being developed for use in fish vaccines. The size of the microparticles may affect the immune response generated, as the adjuvant can either be retained at the site of injection or transported to lymphoid organs. The objectives of this study were to evaluate the maximum size of particles that can be exported out of the cavity, to determine the phagocytosis kinetics and to establish the routes whereby particle-containing cells move from the peritoneal cavity after injection. Fish were injected intraperitoneally with fluorescent cyclodextrins or with fluorescent particles of different size (0.1-10 μm). Phagocytes containing beads of size 4 μm or larger did not reach lymphoid organs, although some were able to cross the peritoneal mesothelium. The number of free peritoneal neutrophils and macrophage-like cells containing beads peaked at 6 and 24 h respectively, and the numbers then decreased quickly, indicating migration of cells to the peritoneum or other body areas. Migration of cells containing beads mainly occurs through the visceral peritoneum. These cells were found on the latero-ventral surfaces of the peritoneal folds that connect the visceral organs. Except for some vascularised areas, the surfaces of liver, stomach and intestine were devoid of particle-containing cells. Some cells containing beads were also found attached to the parietal peritoneum, although in lower numbers than in the visceral peritoneum. Such cells were also found in high numbers in the spleen and kidney 6 h post injection. Because cells containing phagocytosed material quickly become attached to the peritoneum or migrate to lymphoid organs, the immune response generated by a vaccine or by an inflammatory stimulus should probably be evaluated in attached cells as well as in free peritoneal cells.

Dietary tryptophan and methionine as modulators of European seabass (Dicentrarchus labrax) immune status and inflammatory response

Amino acids regulate key metabolic pathways important to immune responses and their nutritional supply may increase synthesis of immune-related proteins. The present study aimed to evaluate the effects of dietary supplementation of tryptophan and methionine on European seabass (Dicentrarchus labrax) cellular and humoral status. The immunomodulatory effects of tryptophan and methionine during an inflammatory insult was also evaluated after intraperitoneal injection with inactivated Photobacterium damselae subsp. piscicida (Phdp). A practical isonitrogenous (45% crude protein) and isolipidic (16% crude fat) diets was formulated to include fish meal and a blend of plant feedstuffs as protein sources and fish oil as the main lipid source (CRL diet). Two other diets were formulated similar to the control but including L-tryptophan or L-methionine at ×2 the requirement level (diets TRP and MET, respectively). European seabass weighing 275 g were fed the experimental diets for a period of 15 days before being sampled (trial 1). Then, fish were subjected to a peritoneal inflammation by intraperitoneally injecting UV killed Phdp (10(6) colony forming units ml(-1)) and sampled following 4 and 24 h post-injection (trial 2). Fish injected with a saline solution served as control. The haematological profile, peripheral cell dynamics and several plasma immune parameters were determined in trials 1 and 2, whereas cell migration to the inflammatory focus was also determined in trial 2. MET positively affected European seabass immune status by improving the peripheral leucocyte response, complement activity and bactericidal capacity, a stronger cellular recruitment to the inflammatory focus, and higher plasma peroxidase and bactericidal activities. TRP also seemed to improve immunostimulation, as there was a trend to augment both cell-mediated immunity and humoral capacity. However, TRP failed to improve an inflammatory response, verified by a decrease in blood phagocyte numbers and lack of immune cells recruitment. In summary, it is confirmed that MET has a pronounced influence on the innate immune response to inflammation, which is more evident than TRP, and raises its potential to incorporate in functional feeds to be used in prophylactic strategies against predictable unfavourable events.

Flagellin from Marinobacter algicola and Vibrio vulnificus activates the innate immune response of gilthead seabream

Adjuvants have emerged as the best tools to enhance the efficacy of vaccination. However, the traditional adjuvants used in aquaculture may cause adverse alterations in fish making necessary the development of new adjuvants able to stimulate the immune system and offer strong protection against infectious pathogens with minimal undesirable effects. In this respect, flagellin seems an attractive candidate due to its ability to strongly stimulate the immune response of fish. In the present study, we have evaluated the ability of recombinant flagellin from Marinobacter algicola (MA) and Vibrio vulnificus (Vvul), a non-pathogenic and a pathogenic bacteria, respectively, to stimulate the innate immune system of gilthead seabream (Sparus aurata L.) and compare the effect with that of the classical flagellin from Salmonella enterica serovar Typhimurium (Salmonella Typhimurium, STF). Intraperitoneal injection of MA and Vvul resulted in a strong inflammatory response characterized by increased reactive oxygen species production and the infiltration of acidophilic granulocytes at the injection site. Interestingly, however, only flagellin from MA consistently induced the expression of the gene encoding pro-inflammatory interleukin-1β. These effects were further confirmed in vitro, where a dose-dependent activation of macrophages and acidophilic granulocytes by MA and Vvul flagellins was observed. In contrast, STF flagellin was found to be less potent in both in vivo and in vitro experiments. Our results suggest the potential use of MA and Vvul flagellins as immunostimulants and adjuvants for fish vaccination.

Complement C5a acts as molecular adjuvant in fish by enhancing antibody response to soluble antigen

C5a, the most potent anaphylatoxin generated during complement activation, has important pro-inflammatory actions and has also been shown to enhance antigen-specific antibody response in mammals, thereby acting as a molecular adjuvant. In rainbow trout, C5a has been shown to have a chemoattractant ability and its receptor has also been found on potential APCs. In this study, we tested the possible role of trout C5a as a molecular adjuvant. We demonstrated the presence of native C5a in trout serum using the antibody generated by recombinant trout C5a, and then we generated recombinant infectious hematopoietic necrosis virus glycoprotein (G), and a G-C5a fusion protein to test the adjuvant activity of trout C5a. Recombinant G-C5a displayed a potent chemoattractant activity in contrast to G alone, indicating that the C5a portion of the fusion protein was functional. Thereafter, G-C5a, partially emulsified in a small quantity of IFA, was injected into one group of trout, while the other group of trout was inoculated with the same dose of recombinant G. At four to sixteen weeks post-injection, the serum IgM antibody levels of the fish injected with recombinant G-C5a were obviously higher than those injected with G protein alone. Thus, these results suggest, for the first time, that C5a acts as molecular adjuvant in teleost fish by enhancing antibody response to a soluble antigen.

Inflammatory responses and side effects generated by several adjuvant-containing vaccines in turbot

Several of the adjuvants used in fish vaccines cause adhesions in internal organs when they are injected intraperitoneally. We describe the damage caused by vaccines containing different adjuvants in the turbot Scophthalmus maximus and show that internal adhesions can be greatly reduced by injecting the fish in a specific way. Injection of fish with the needle directed towards the anterior part of the peritoneal cavity induced formation of a single cell-vaccine mass (CVM) that became attached to the parietal peritoneum. However, injection of the fish with the needle pointing in the opposite direction generated many small CVM that became attached to the visceral and parietal peritoneum and in some cases caused internal adhesions. We describe the structural and cellular changes in the adjuvant-induced CVMs. The CVMs mainly comprised neutrophils and macrophages, although most of the former underwent apoptosis, which was particularly evident from day 3 post-injection. The apoptotic cells were phagocytosed by macrophages, which were the dominant cell type from the first days onwards. All of the vaccines induced angiogenesis in the area of contact between the CVM and the mesothelium. Vaccines containing oil-based adjuvants or microspheres induced the formation of granulomas in the CVM; however, no granulomas were observed in the CVM induced by vaccines containing aluminium hydroxide or Matrix-Q(®) as adjuvants. All of the vaccines induced strong migration of cells to the peritoneal cavity. Although some of these cells remained unattached in the peritoneal cavity, most of them formed part of the CVM. We also observed migration of the cells from the peritoneal cavity to lymphoid organs, indicating bidirectional traffic of cells between the inflamed areas and these organs.

Identification and characterization of Cynoglossus semilaevis microRNA response to Vibrio anguillarum infection through high-throughput sequencing

MicroRNAs (miRNA) play key regulatory roles in diverse biological processes. Cynoglossus semilaevis is an important commercial mariculture fish species in China. To identify miRNAs and investigate immune-related miRNAs of C. semilaevis, we performed high-throughput sequencing on three small RNA libraries prepared from C. semilaevis immune tissues (liver, head kidney, spleen, and intestine). One library was prepared under normal conditions (control, CG); two were prepared during Vibrio anguillarum infection, where vibriosis symptoms were obvious and non-obvious (HOSG and NOSG, respectively). We obtained 11,216,875, 12,313,404, and 11,398,695 clean reads per library, respectively. Bioinformatic analysis identified 452 miRNAs, including 24 putative novel miRNAs. We analyzed differentially expressed miRNAs between two libraries using pairwise comparison. For NOSG-CG, there was significant differential expression of 175 (38.72%) miRNAs. There was significant differential expression of 215 (47.57%) miRNAs between HOSG and CG. Compared with CG, The HOSG-NOSG comparison revealed significantly different expression of 122 (26.99%) miRNAs respectively. Real-time quantitative PCR (RT-qPCR) experiments were performed for 10 miRNAs of the three samples, and agreement was found between the sequencing and RT-qPCR data. For miRNAs that were significantly differentially expressed, functional annotation of target genes by Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that a set of miRNAs that were expressed highly abundantly and significantly differentially were might involved in immune system development and immune response. To our understanding, this is the first report of comprehensive identification of C. semilaevis miRNAs being differentially regulated in immune tissues (liver, head kidney, spleen, and intestine) in normal conditions relating to V. anguillarum infection. Many miRNAs were differentially regulated upon pathogen exposure. This work provides an opportunity for further understanding of the molecular mechanisms of miRNA regulation in C. semilaevis host-pathogen interactions.

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.

Status and future perspectives of vaccines for industrialised fin-fish farming

Fin fish farming is developing from extensive to intensive high industrial scale production. Production of fish in high-density growth conditions requires effective vaccines in order to control persistent and emerging diseases. Vaccines can also have significant positive impact on the reduced usage of antibiotics. This was demonstrated when vaccines were introduced in Norway for Atlantic salmon (Salmo salar) in the late eighties and early nineties, resulting in a rapid decline of antibiotics consumption. The present review will focus on current vaccine applications for farmed industrialized fish species such as Atlantic salmon, coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), ayu (Plecoglossus altivelis), cod (Gadus morhua), sea bass (Dicentrarchus labrax), gilt-head sea bream (Sparus aurata), yellowtail (Seriola quinqueradiata), great amberjack (Seriola dumerili), barramundi (Lates calcarifer), japanese flounder (Paralichythys olivaceus), turbot (Scophthalmus maximus), red sea bream (Pagrus major), rock bream (Oplegnathus fasciatus), seven band grouper (Epinephelus septemfasciatus), striped catfish (Pangasianodon hypophthalmus), channel catfish (Ictalurus punctatus) and tilapia (Oreochromis niloticus). This paper will review the current use of licensed vaccines in fin fish farming and describe vaccine administration regimes including immersion, oral and injection vaccination. Future trends for inactivated-, live attenuated - and DNA - vaccines will also be discussed.

Adjuvants and immunostimulants in fish vaccines: current knowledge and future perspectives

Vaccination is the most adequate method to control infectious diseases that threaten the aquaculture industry worldwide. Unfortunately, vaccines are usually not able to confer protection on their own; especially those vaccines based on recombinant antigens or inactivated pathogens. Therefore, the use of adjuvants or immunostimulants is often necessary to increase the vaccine efficacy. Traditional adjuvants such as mineral oils are routinely used in different commercial bacterial vaccines available for fish; however, important side effects may occur with this type of adjuvants. A search for alternative molecules or certain combinations of them as adjuvants is desirable in order to increase animal welfare without reducing protection levels. Especially, combinations that may target specific cell responses and thus a specific pathogen, with no or minor side effects, should be explored. Despite this, the oil adjuvants currently used are quite friendlier with respect to side effects compared with the oil adjuvants previously used. The great lack of fish antiviral vaccines also evidences the importance of identifying optimal combinations of a vaccination strategy with the use of a targeting adjuvant, especially for the promising fish antiviral DNA vaccines. In this review, we summarise previous studies performed with both traditional adjuvants as well as the most promising new generation adjuvants such as ligands for Toll receptors or different cytokines, focussing mostly on their protective efficacies, and also on what is known concerning their effects on the fish immune system when delivered in vivo.

Recombinant TNFα as oral vaccine adjuvant protects European sea bass against vibriosis: insights into the role of the CCL25/CCR9 axis

Vibrio anguillarum is the main causative agent of vibriosis in cultured sea bass. Unfortunately, available vaccines against this disease do not achieve the desired protection. In this study, to accomplish uptake, processing, and presentation of luminal antigens, a commercial sea bass oral vaccine against V. anguillarum was improved with the addition of recombinant fish-self tumor necrosis factor α (rTNFα), as adjuvant. To explore mechanisms, systemic and local responses were analyzed through serum specific IgM titers, gene expression, lymphocytes spatial distribution in the gut, and in vitro functional assays. We found along the trial, over expressed transcripts of genes encoding cytokines and antimicrobial molecules at the gut of rTNFα supplied group. Orally immunized fish with vaccine alone confer protection against V. anguillarum challenge throughout a short time period. In contrast, adjuvant-treated group significantly extended the response. In both cases, achieved protection was independent of serum IgM. Yet, IgT transcripts were found to increase in the gut of rTNFα-treated fish. More importantly, fish treated with rTNFα showed a dramatic change of their T lymphocytes distribution and localization in gut mucosal tissue, suggesting specific antigen recognition and further intraepithelial T lymphocytes (IEL) activation. To determine the mechanism behind IEL infiltration, we characterized the constitutive and activated pattern of chemokines in sea bass hematopoietic tissues, identifying for the first time in fish gut, an intimate relation between the chemokine ligand/receptor CCL25/CCR9. Ex-vivo, chemotaxis analyses confirmed these findings. Together, our results demonstrate that improved oral vaccines targeting key cytokines may provide a means to selectively modulate fish immune defence.

Effect of orally administered azadirachtin on non-specific immune parameters of goldfish Carassius auratus (Linn. 1758) and resistance against Aeromonas hydrophila

Modulation of the immune responses using active bio-ingredients as a possible prophylaxis measure has been novel prospect for aquaculture. The present study evaluated the effects of azadirachtin EC 25% on non-specific immune responses in goldfish Carassius auratus and resistance against pathogenic bacteria Aeromonas hydrophila. The experimental trial for effects of azadirachtin on immuno-haematoloical parameters in goldfish was conducted by feeding the various levels of azadirachtin as control T(0) (without azadirachtin), T(1) (0.1%), T(2) (0.2%), T(3) (0.4%), T(4) (0.8%) and T(5) (1.6%) for a period of 28 days. Fishes were challenged with A. hydrophila 28 days post feeding and relative percentage survival (%) was recorded over 14 days post infection. Immuno-haematoloical (total erythrocyte count, total leukocyte count, haemoglobin, packed cell volume, NBT activity, phagocytic activity, serum lysozyme activity, myeloperoxidase activity, total immunoglobulin) and serum biochemical parameters (serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT) and blood glucose) of fishes were examined at 14 and 28 days of feedings. Fish fed with azadirachtin, showed significantly (p < 0.05) enhanced TEC, TLC, Total Ig, total protein, NBT activity, serum lysozyme activity and myeloperoxidase level in different treatment groups in comparison with control group. Similarly, SGOT, SGPT and blood glucose level were found to be significantly (p < 0.05) high but PCV and Hb did not differ significantly (p > 0.05) in the treatment groups compared to control groups. Azadirachtin at the concentration of 4 g kg(-1) showed significantly (p < 0.05) higher relative percentage survival (42.60%) when compared with the control against A. hydrophila infection. This study indicated that azadirachtin EC 25% (4 g kg(-1)) showed higher NBT activity, serum lysozyme, protein profiles, leukocyte counts and resistance against A. hydrophila infection and thus, can be used as a potential immunostimulant in aquaculture.

Azadirachta indica (neem) leaf dietary effects on the immunity response and disease resistance of Asian seabass, Lates calcarifer challenged with Vibrio harveyi

The present study was aimed to address the possible evaluation of Azadirachta indica (neem) leaf-supplemented diets on innate immune response in Asian seabass, Lates calcarifer fingerlings against Vibrio harveyi infection. Fish were fed for two weeks diets containing six graded levels of neem leaf at 0 g, 1 g, 2 g, 3 g, 4 g and 5 g per kg feed. Fish fed neem leaf-supplemented diet displayed significant differences (p < 0.05) in weight gain, specific growth rate (SGR) and feed conversion ratio (FCR) compared to the control group fed without neem leaf-supplemented diet. Various innate immune parameters were examined pre-challenge and post-challenge. Fish was injected intraperitoneally with a lethal dose of V. harveyi containing 10(8) cells mL(-1). Supplementation of neem leaf diet significantly increased phagocytic activity, superoxide anion production, serum lysozyme, serum bactericidal activity, serum anti-protease activity throughout the experimental period when compared with the control group. Dietary doses of neem leaf diet significantly influenced the immune parameters, haematological parameters and blood biochemical indices of treated fish. The results suggested that fish fed neem leaf-supplemented diet improved the immune system and increased survival rate in L. calcarifer fingerlings against V. harveyi infection.

Effects on mortality and stress response in European sea bass, Dicentrarchus labrax (L.), fed mannan oligosaccharides (MOS) after Vibrio anguillarum exposure

The effects of dietary mannan oligosaccharides (MOS; 4 g kg(-1) ; Bio-Mos, Alltech Inc, USA) in diets for European sea bass, Dicentrarchus labrax (L.), juveniles in relation to disease and stress resistance, combining intestinal infection with Vibrio anguillarum and stress challenge by confinement, were assessed in this study. After 8 weeks of MOS supplementation, fish were exposed to a pathogen challenge test against V. anguillarum by direct gut inoculation combined with a confinement stressor panel. Cumulative mortality of fish fed MOS caused by anally inoculated V. anguillarum decreased from 66% to 12.5% and from 54.1% to 25% in infected and infected + stressed fish, respectively, compared to fish fed control diet. Results for European sea bass revealed a positive effect of MOS dietary inclusion on disease resistance, in terms of cumulative mortality, against gut inoculated V. anguillarum, as well as reduced effects of stress on microbiota diversity. Both of these findings, together with the enhanced innate immune response and the higher gut mucus production and density of eosinophil granulocytes in gut mucosa obtained in previous studies after MOS supplementation (Torrecillas et al. 2007, 2011a,b) suggest that general reinforcement of the innate immune system, and particularly of the intestinal barrier efficiency, is the main defence mechanism of European sea bass fed MOS against pathogenic microorganisms.

A sequential study of incomplete Freund's adjuvant-induced peritonitis in Atlantic cod

Development of diagnostic and prophylactic methodologies is dependent on knowledge of the host's defence system and reaction to different vaccine adjuvants. Here we present a sequential morphological study of peritonitis and inflammatory cell processing of incomplete Freund's adjuvant (IFA) in intraperitoneally injected Atlantic cod. The peritoneal tissue responses were characterised using necropsy, histology and electron microscopy. An extensive inflammatory response as characterised by leukocyte morphology and contents of enzymes, presence of apoptotic cells and IFN-γ-expressing cells was observed. Three days post injection, IFA droplets were surrounded by different types of inflammatory cells and two different patterns could be discerned. The first was characterised by flattened and concentrically arranged interdigitating cells connected by desmosomes and with macrophage-like cells (MLCs) predominant in the periphery. The second type possessed four stratified layers with an inner layer containing many apoptotic MLCs; a second layer containing flattened and shrunken cells and outer layers comprising moderately flattened cells and an outermost layer of mononuclear cells expressing IFN-γ. Oil was detected both inside and outside MLCs. The two types of processes, of which the second was clearly stratified, were similar to those observed in other teleosts, indicating a variety of reaction modes or alternatively sequential process development. The numerous dead MLCs contributed to inflammation.

A variant of the interleukin-1beta gene in European sea bass, Dicentrarchus labrax L., is associated with increased resistance against Vibrio anguillarum

Vibriosis caused by the pathogenic bacterium Vibrio (Listonella) anguillarum leads to serious losses in European sea bass, Dicentrarchus labrax. Because of its pleiotropic activity in controlling immune and inflammatory responses against various pathogens, interleukin-1beta (IL-1beta) is an attractive candidate for resistance to bacterial vibriosis. Four polymorphisms c.76 + 52C>T, c.76 + 157A>G, c.76 + 215A>and c76 + 310A>G of IL1B were genotyped in progeny of four families of wild sea bass captured in geographically distinct regions of the Black Sea and Sea of Azov and challenged with V. anguillarum. In the transmission disequilibrium test, the TGGG haplotype of IL1B showed significant overtransmission from parents to surviving progeny, thereby suggesting an association with higher resistance to V. anguillarum infection (Odds Ratio 0.38, P < 10(-7)). Using a luciferase reporter assay, we found a 1.4-fold increase in transcription activity of the protective IL1B TGGG variant compared to the susceptible CAAA variant of IL1B. The higher transcriptional activity of IL1B TGGG may arise from the functional effects of c.76 + 157A>G and c.76 + 215A>G polymorphisms disrupting potential binding sites for glucocorticoid receptor and YY1, both are negative transcription regulators.

Immunological control of fish diseases

All metazoans possess innate immune defence system whereas parameters of the adaptive immune system make their first appearance in the gnathostomata, the jawed vertebrates. Fish are therefore the first animal phyla to possess both an innate and adaptive immune system making them very interesting as regards developmental studies of the immune system. The massive increase in aquaculture in recent decades has also put greater emphasis on studies of the fish immune system and defence against diseases commonly associated with intensive fish rearing. Some of the main components of the innate and adaptive immune system of fish are described. The innate parameters are at the forefront of immune defence in fish and are a crucial factor in disease resistance. The adaptive response of fish is commonly delayed but is essential for lasting immunity and a key factor in successful vaccination. Some of the inherent and external factors that can manipulate the immune system of fish are discussed, the main fish diseases are listed and the pathogenicity and host defence discussed. The main prophylactic measures are covered, including vaccination, probiotics and immunostimulation. A key element in the immunological control of fish diseases is the great variation in disease susceptibility and immune defence of different fish species, a reflection of the extended time the present day teleosts have been separated in evolution. Future research will probably make use of molecular and proteomic tools both to study important elements in immune defence and prophylactic measures and to assist with breeding programmes for disease resistance.

Scuticociliatosis and its recent prophylactic measures in aquaculture with special reference to South Korea Taxonomy, diversity and diagnosis of scuticociliatosis: Part I Control strategies of scuticociliatosis: Part II

Scuticociliatosis caused by about 20 species belonging to the Phylum Ciliophora has been recognized as an emerging problem inflicting significant economic loss in aquaculture industry in the world. Among these Philasterides dicentrarchi, Miamiensis avidus, and Uronema marinum are the three species responsible for scuticociliatosis in olive flounder farms of South Korea. Some of the parasites living or scavenger ciliates also have become parasites of aquaculture fish. The major clinico-pathological manifestations of scuticociliatosis infected fishes are anemia, weight loss, dark coloration, enteritis, excessive body mucus, yellowish intestinal mucus, loss of scales, hemorrhagic and/or bleached spots on the skin, and dermal necrotic lesions that finally destroy tissues lead to high mortalities. Affected fish exhibit organ-specific pathological changes in the brain, eyes, muscle, gills, liver, kidney, intestine, and stomach that lead to severe mortality. At present, farmers in South Korea manage scuticociliatosis by using therapeutic measures, such as application of antibiotics like oxytetracycline, gentamycine, tetracycline, amoxycililin, and cefazolin and chemicals, such as formalin, hydrogen peroxide, malachite green, and jenoclean at a concentration of 350 +/- 150 ppm. However till date, no systematic scientific study has been conducted under field condition on the efficacy of these management measures. Under laboratory condition the ciliate can be effectively controlled with the antibiotics and chemicals while on the host, but on entering the host no systemic chemotherapeutic treatment has been yet proven effective. Furthermore the indiscriminate uses of harmful chemicals in aquaculture are increasingly becoming a cause of concern. Recently formalin and malachite green, the most widely used chemicals have been banned in food fish production by FDA as not consumer friendly and being carcinogenic respectively. Vaccines and immunostimulants can induce good immune response and protect against scuticociliatosis as it has been proved in the case of freshwater Ich. Now a days a number of probiotics and herbal formulations are in use against freshwater bacterial and fungal diseases, while, little information is available regarding the different prophylactic measures against marine scuticociliatosis. This review attempts to provide information on the various prophylaxic measures practiced against scuticociliatosis with special reference to olive flounder farms in South Korea.

Vaccination of turbot, Psetta maxima (L.), against the protozoan parasite Philasterides dicentrarchi: effects on antibody production and protection

The efficacy of a vaccine against the fish pathogen Philasterides dicentrarchi was evaluated in turbot by measuring the production of specific antibodies and duration of protection. Four groups of turbot were vaccinated twice, on days 0 and 30, with phosphate-buffered saline, mineral oil adjuvant, antigen or antigen plus adjuvant. Specific serum antibodies were determined on day 0 and 1 month after the first and the second vaccinations. Protection was evaluated 1 month after the first vaccination and 1 and 5 months after the second vaccination. Serum antibody titres, measured by enzyme-linked immunosorbent assay, and protection, assessed by challenges, increased significantly 1 month after the second vaccination in the group injected with antigen plus adjuvant and the protection lasted for at least a further 5 months in this group. The relative protection was 77% and 66% 1 and 5 months after the second vaccination, respectively. Administration of antigen or adjuvant separately had no effect on antibody response or protection. The results indicate that emulsion containing antigen plus adjuvant induced durable protection against P. dicentrarchi after the administration of the two vaccinations, and that this preparation can be used as a vaccine against the pathogen.