Immune response of flounder (Paralichthys olivaceus) was associated with the concentration of inactivated Edwardsiella tarda and immersion time

Teleost Muc2 and Muc5ac: Key guardians of mucosal immunity in flounder (Paralichthys olivaceus)

Mucins secreted by mucous cells constitute a core part of the defense line against the invasion of pathogens. However, mucins' structure and immunological functions remain largely unknown in teleost fish. In this study, two typical mucins, Muc2 and Muc5ac of flounder (Paralichthys olivaceus), were cloned and their physicochemical properties, structure and conservation were analyzed. Notably, specific antibodies against flounder Muc2 and Muc5ac were developed. It was verified at the gene and protein level that Muc2 was expressed in the hindgut and gills but not in the skin, while Muc5ac was expressed in the skin and gills but not in the hindgut. After flounders were immunized by immersion with inactivated Edwardsiella tarda, Muc2 and Muc5ac were significantly upregulated at both the gene expression and protein levels, and Muc2+/Muc5ac+ mucous cells proliferated and increased secretion of Muc2 and Muc5ac. Moreover, Muc2 and Muc5ac exerted retention and clearance effects on E. tarda in a short period (within 1 dpi). These results revealed the characterization of fish mucins Muc2 and Muc5ac at the protein level and clarified the role of mucins as key guardians to maintain the mucus barrier, which advanced our understanding of teleost mucosal barrier.

The role of aroA and ppk1 in Aeromonas veronii pathogenicity and the efficacy evaluation of mutant strain AV-ΔaroA/ppk1 as a live attenuated vaccine

Aeromonas veronii is an opportunistic pathogen that poses great threat to aquaculture and human health, so there is an urgent need for green and efficient methods to deal with its infection. In this study, single and double gene deletion strains (AV-ΔaroA, AV-Δppk1 and AV-ΔaroA/ppk1) that can be stably inherited were constructed. Pathogenicity test showed that the toxicity of AV-ΔaroA and AV-ΔaroA/ppk1 was significantly lower compared to wild-type A. veronii. Biological characterization analysis revealed that the decrease in pathogenicity might be due to the declined growth, motility, biofilm formation abilities and the expression of virulence-related genes in mutants. Subsequently, we evaluated the efficacy of AV-ΔaroA/ppk1 as a live attenuated vaccine (LAV). Safety assessment experiments showed that AV-ΔaroA/ppk1 injected at a concentration of 3 × 107 CFU/mL was safe for C. carassius. The relative percentage survival of AV-ΔaroA/ppk1 was 67.85 %, significantly higher than that of the inactivated A. veronii, which had an RPS of 54.84 %. This improved protective effect was mainly attributed to the increased levels of A. veronii specific IgM antibody, enhanced alkaline phosphatase, lysozyme and superoxide dismutase activities, as well as higher expression levels of several immune related genes. Together, these findings deepen our understanding of the functional roles of aroA and ppk1 in A. veronii pathogenicity, provide a good candidate of LAV for A. veronii.

Systemic and mucosal immune responses in red tilapia (Oreochromis sp.) following immersion vaccination with a chitosan polymer-based nanovaccine against Aeromonas veronii

A mucoadhesive chitosan polymer-based nanoplatform has been increasingly recognized as an effective mucosal vaccine delivery system for fish. The present study aimed to investigate the effectiveness of immersion vaccination with a chitosan polymer-based nanovaccine to elicit an immune response in serum and mucus of red tilapia and evaluate its protective efficacy after immersion challenge with a heterogenous strain of Aeromonas veronii UDRT09. Six hundred red tilapia (22 ± 1.8 g) were randomly allocated into four experimental groups: control, empty-polymeric nanoparticle (PC), formalin-killed vaccine (FKV), and chitosan polymer-based nanovaccine (CS-NV) in triplicate. The specific IgM antibody levels and their bactericidal activity were assessed in serum and mucus for 28 days after immersion vaccination and followed by immersion challenge with A. veronii. The immersion vaccine was found to be safe for red tilapia, with no mortalities occurring during the vaccination procedure. The specific IgM antibody levels and bactericidal activity against A. veronii in both serum and mucus were significantly higher in red tilapia vaccinated with CS-NV compared to the FKV and control groups at all time points. Furthermore, the serum lysozyme activity, ACH50, and total Ig levels demonstrated a significant elevation in the groups vaccinated with CS-NV compared to the FKV and control groups. Importantly, the Relative Percentage Survival (RPS) value of the CS-NV group (71 %) was significantly higher than that of the FKV (15.12 %) and PC (2.33 %) groups, respectively. This indicates that the chitosan polymer-based nanovaccine platform is an effective delivery system for the immersion vaccination of tilapia.

Antimicrobial Protein LECT2-b Helps Maintain Gut Microbiota Homeostasis via Selectively Targeting Certain Pathogenic Bacteria

Antimicrobial peptides/proteins (AMPs) constitute a critical component of gut immunity in animals, protecting the gut from pathogenic bacteria. However, the interactions between AMPs and gut microbiota remain elusive. In this study, we show that leukocyte-derived chemotaxin-2 (LECT2)-b, a recently discovered AMP, helps maintain gut homeostasis in grass carp (Ctenopharyngodon idella), one of the major farmed fish species globally, by directly regulating the gut microbiota. Knockdown of LECT2-b resulted in dysregulation of the gut microbiota. Specifically, LECT2-b deficiency led to the dominance of Proteobacteria, consisting of proinflammatory bacterial species, over Firmicutes, which includes anti-inflammatory bacteria. In addition, the opportunistic pathogenic bacteria genus Aeromonas became the dominant genus replacing the probiotic bacteria Lactobacillus and Bacillus. Further analysis revealed that this effect was due to the direct and selective inhibition of certain pathogenic bacterial species by LECT2-b. Moreover, LECT2-b knockdown promoted biofilm formation by gut microbiota, resulting in tissue damage and inflammation. Importantly, LECT2-b treatment alleviated the negative effects induced by LECT2-b knockdown. These findings highlight the crucial role of LECT2-b in maintaining the gut microbiota homeostasis and mucosal health. Overall, our study provides important data for understanding the roles of AMPs in the regulation of gut homeostasis in animals.

Investigation of the effects of cup plant (Silphium perfoliatum L.) on the growth, immunity, gut microbiota and disease resistance of Penaeus vannamei

To investigate the effects of adding different concentrations of cup plant (Silphium perfoliatum L.) to the feed on the growth performance, hepatopancreas and intestinal microstructure, gene expression, enzyme activity, as well as intestinal microorganisms and resistance to Vibrio parahaemolyticus E1 and White spot syndrome virus (WSSV) infection of the shrimp, cup plant was added to the basal feed at 1%, 3%, 5% and 7% respectively, and fed the shrimp for 6 weeks. It was found that the addition of different concentrations of cup plant could significantly improve the specific growth rate and survival rate of shrimp, reduce the feed conversion rate, and improve the resistance to V. parahaemolyticus E1 and WSSV in shrimp, with the best effect of 5% addition. The tissue sections observations showed that the addition of cup plant significantly improved the hepatopancreas and intestinal tissues of shrimp, especially in alleviating the tissue damage caused by V. parahaemolyticus E1 and WSSV infection, but too high an addition (7%) could also cause side effects on the shrimp intestinal tract. Meantime, the addition of cup plant can also increase the activity of immunodigestive-related enzymes in the hepatopancreas and intestinal tissues of shrimp, and can significantly induce the up-regulation of immune-related genes expression, and it is positively correlated with the amount of addition in a certain range. In addition, it was found that the addition of cup plant has a significant regulating effect on the intestinal flora of shrimp, which can significantly promote the growth of beneficial bacteria such as Haloferula sp., Algoriphagus sp. and Coccinimonas sp., and inhibit pathogenic bacteria Vibrio sp., such as the number of Vibrionaceae_Vibrio and Pseudoalteromonadaceae_Vibrio in the experimental group were significantly reduced, and the lowest level in the 5% addition group. In summary, the study shows that cup plant can promote the growth of shrimp, improve the resistance of shrimp to disease, and is a potential green environmental feed additive that can replace antibiotics.

Identification and characterization of immunoglobulin tau (IgT) in Asian Seabass (Lates calcarifer) and mucosal immune response to nervous necrosis virus

Mucosal immunity plays a critical role in the protection of teleost fish against infection, but mucosal immunoglobulin of important aquaculture species unique to Southeast Asia remained greatly understudied. In this study, the sequence of immunoglobulin T (IgT) from Asian sea bass (ASB) is described for the first time. IgT of ASB possesses the characteristic structure of immunoglobulin with a variable heavy chain and four CH4 domains. The CH2-CH4 domains and full-length IgT were expressed and CH2-CH4 specific antibody was validated against full-length IgT expressed in Sf9 III cells. Subsequent use of the anti-CH2-CH4 antibody in immunofluorescence staining confirmed the presence of IgT-positive cells in the ASB gill and intestine. The constitutive expression of ASB IgT was characterized in different tissues and in response to red-spotted grouper nervous necrosis virus (RGNNV) infection. The highest basal expression of secretory IgT (sIgT) was observed in the mucosal and lymphoid tissues such as the gills, intestine and head kidney. Following NNV infection, IgT expression was upregulated in the head kidney and mucosal tissues. Moreover, a significant increase in localized IgT was found in gills and intestines of infected fish on day 14 post-infection. Interestingly, a significant increase in NNV-specific IgT secretion was only observed in the gills of the infected group. Our results suggest that ASB IgT may play an important role in the adaptive mucosal immune responses against viral infection and could potentially be adapted as a tool for the evaluation of prospective mucosal vaccines and adjuvants for the species.

Current status and development prospects of aquatic vaccines

Diseases are a significant impediment to aquaculture's sustainable and healthy growth. The aquaculture industry is suffering significant financial losses as a result of the worsening water quality and increasing frequency of aquatic disease outbreaks caused by the expansion of aquaculture. Drug control, immunoprophylaxis, ecologically integrated control, etc. are the principal control strategies for fish infections. For a long time, the prevention and control of aquatic diseases have mainly relied on the use of various antibiotics and chemical drugs. However, long-term use of chemical inputs not only increases pathogenic bacteria resistance but also damages the fish and aquaculture environments, resulting in drug residues in aquatic products, severely impeding the development of the aquaculture industry. The development and use of aquatic vaccines are the safest and most effective ways to prevent aquatic animal diseases and preserve the health and sustainability of aquaculture. To give references for the development and implementation of aquatic vaccines, this study reviews the development history, types, inoculation techniques, mechanisms of action, development prospects, and challenges encountered with aquatic vaccines.

Splenic protection network revealed by transcriptome analysis in inactivated vaccine-immunized flounder (Paralichthys olivaceus) against Edwardsiella tarda infection

The protective immune response produced by fish after vaccination is crucial for vaccine effectiveness. Our previous studies have shown inactivated vaccine against Edwardsiella tarda can induce immune response in flounder (Paralichthys olivaceus). To elucidate the protective immune response at the genetic level, in this study, flounder was immunized with inactivated E. tarda for 5 weeks, and then they were challenged with E. tarda. The spleen was dissected at 7th day post immunization, 1st and 7th day post challenge, respectively. Transcriptome analysis showed that average of 46 million clean reads were obtained per library, while percentage of clean reads being mapped to reference genome was more than 89% in all cases, which suggested good quality of samples. As for differentially expressed genes (DEGs) identification in inactivated E. tarda groups, at 7th day post immunization, 1422 DEGs were identified and significantly enriched in innate immune-related pathways, such as Phagosome, Cell adhesion molecules and NF-kappa B signaling pathway; At 1st post challenge day, 1210 DEGs were identified and enriched to Antigen processing and presentation and Cell adhesion molecules, indicating that the pathogen was rapidly recognized and delivered; At 7th post challenge day, 1929 DEGs were identified, belonged to Toll-like receptor signaling pathway, Antigen processing and presentation, Th1 and Th2 cell differentiation and Th17 cell differentiation. Compared to 7th post immunization day, 73 immune-associated DEGs were identified at 1st post challenge day. Protein-protein interaction networks analysis revealed 11 hub genes (TLR7, TLR3, CXCR4, IFIH1, TLR8 etc), associated with recognition of pathogens and activation of innate immunity; while for 7th post challenge day, 141 immune-associated DEGs were identified. 30 hub genes (IL6, STAT1, HSP90A.1, TLR7, IL12β etc) were associated with stimulation of lymphocyte differentiation and activation of cellular immunity. Ten immune-related genes were randomly selected for RT-qPCR validation at each time point. In conclusion, data revealed protection of flounder against E. tarda infection by inactivated vaccine is mediated via immediate recognition of pathogen and subsequently activation of cellular immunity. Results give new aspect for vaccine protection cascades, is good references for vaccine evaluation.

Enhancement of growth, survival, immunity and disease resistance in Litopenaeus vannamei, by the probiotic, Lactobacillus plantarum Ep-M17

Green ecological prevention and control technology is a hot spot for aquatic disease research in recent years, and lactic acid bacteria is an important type of probiotic widely used in aquaculture. In this study, a strain of Lactobacillus plantarum Ep-M17 was isolated from the intestine of healthy grouper, which showed good antibacterial activity in vitro. To investigate the application prospects of Ep-M17 as a probiotic, we added it to the diet and fed Litopenaeus vannamei, and then detected its influence on the growth performance, survival rate, disease resistance, intestinal tissue structure, gene transcription, and the flora in the gut of shrimp. The results showed that feeding Ep-M17 increased the specific growth rate, reduced the feed conversion rate, improved the survival rate, and achieved a 76.9% relative protection rate after Vibrio parahaemolyticus E1 infection in shrimp. Histological examination displayed that Ep-M17-fed shrimp had a thick intestinal villi layer, which enhanced the protection against pathogen damage. It was also found that Ep-M17 significantly increased the activity levels of immune and digestion-related enzymes SOD, CAT, TRY, AKP, LIP, and AMS in the gut of shrimp, especially after V. parahaemolyticus E1 infection, these enzymes increased significantly higher than that of control. Transcriptome analysis revealed that Ep-M17 activated significantly differential expression of genes in immune, nutritional, metabolic, and Signal Transduction-related pathways in the gut of shrimp. In addition, Ep-M17 enriched the bacterial diversity of the shrimp gut, with a significant increase in many low-abundance bacterial species, a significant decrease in the number of pathogenic bacteria like Vibrio, and a significant increase in the number of beneficial bacteria. The above results evaluated that Ep-M17 as a potential probiotic can promote the growth and improve the disease resistance of shrimp by regulating the nutritional immune response and flora of the intestine.

Optimization of immunization procedure for SWCNTs-based subunit vaccine with mannose modification against spring viraemia of carp virus in common carp

Immersion vaccination of single-walled carbon nanotubes loaded with mannose-modified glycoprotein (SWCNTs-MG) vaccine has been proved to be effective in preventing spring viraemia of carp virus (SVCV). Immunization procedure has immense consequence on the immune effect of the immersion vaccine. However, immunization procedure optimization for SWCNTs-MG vaccine against SVCV has not been reported. In this study, accordingly, a full-factor experiment was designed to optimize the immunization procedure of SWCNTs-MG vaccine by three aspects of vaccine dose (30 mg/L, 40 mg/L and 50 mg/L), immunization density (8 fish L^-1 , 24 fish L^-1 and 48 fish L^-1 ) and immunization time (6, 12 and 24 hr). Furthermore, we used the immunization group (A1B2C1, 30 mg/L, 24 fish L^-1 and 6 hr) in the previous study as a positive control (PC) to evaluate the immunization effect optimized conditions from the expression of immune-related genes and relative percentage survival (RPS). At 28 days post-vaccination (DPV), common carps were intraperitoneal injected SVCV challenged test indicated that the A1B2C2 group (30 mg/L, 24 fish L^-1 , 12 hr) displayed superiority of protective efficacy compare with other groups and the RPS with 77.9%, which was 15.6% higher than the PC group of RPS with 62.3%. Moreover, the expression of immune-related genes such as IL-10, CD4 and MHC-II was also significantly higher than PC group. The specific experimental flow chart is shown in Figure 1. Conclusively, these results demonstrated that vaccine dose, immunization density and immunization time are 30 mg/L, 24 fish L^-1 and 12 hr, which is the more appropriate immunization programme with juvenile carp for SWCNTs-MG vaccine. This study provides a profitable reference for improving the immune efficiency of aquatic immersion vaccine. [Figure: see text].

Interleukin 1 receptor type I (IL-1RI) is involved in the innate immune response of olive flounder (Paralichthys olivaceus) to resist pathogens

The pleiotropic cytokine IL -1 is involved in important immune responses such as thymocyte proliferation and B cell growth and differentiation. Activation of the IL -1 pathway requires its functional receptor IL -1RI, making IL -1RI the critical point of the IL -1 pathway. In-depth study of IL -1RI will help to understand the immune mechanism involved in IL -1. In this study, we identified the cDNA of the IL -1RI gene of olive flounder (PoIL-1RI). The total length of the PoIL-1RI cDNA is 2490 bp, the open reading frame is 1689 bp long and encodes a protein of 562 amino acids. The protein has three Ig domains and a typical TIR domain, as in other mammals and fish. We found that PoIL-1RI is widely expressed in the tissues studied and shows a significant immune response after stimulation with bacteria and pathogen-associated molecular patterns (PAMPs) both in vitro and in vivo. After PoIL-1RI was overexpressed in olive flounder embryonic cell line (FEC), pro-inflammatory cytokines (IL -1β, IL -6, IL -8, TNF-α) and interferon (IFN-α, IFN-γ) were significantly upregulated. And we found that after overexpressing PoIL-1RI in FEC, the antibacterial ability of FEC was significantly stronger than that of the control group, and we found that overexpression of PoIL-1RI gene significantly increased the activity of NF-κB signaling pathway. These results suggest that PoIL-1RI plays an important role in innate immune response.

Immune adjuvant effects of interferon-gamma (IFN-γ) of flounder (Paralichthys olivaceus) against Edwardsiella tarda

IFN-γ plays a key role in T-cell activation and the establishment of the adaptive immune response, which has a potential as a cytokine adjuvant in the context of vaccination. In this study, we evaluated the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IFN-γ, including pcDNA3.1-IFN-γ (pcIFN-γ) and recombinant IFN-γ (rIFN-γ), and comparatively analyzed the immune responses of flounder to E. tarda subunit vaccine rOmpV. The results showed that vaccination with rOmpV plus pcIFN-γ or rIFN-γ produced a relative percent survival of 57% and 71%, respectively, which were significantly higher than that of the control groups, rOmpV plus pcN3 (36%) or rHis (40%). Compared with the two control groups, vaccination with rOmpV plus pcIFN-γ or rIFN-γ could induce significantly higher levels of specific serum antibodies and sIg + lymphocytes in peripheral blood, spleen and head kidney, and significantly higher upregulated expressions of CD4-1, CD8α, IgM, MHC Ⅰα, MHC Ⅱα, IL-1β and TNF-α were also detected in rOmpV plus pcIFN-γ or rIFN-γ vaccinated fish. In addition, compared with pcIFN-γ, rOmpV co-vaccination with rIFN-γ elicited higher levels of sIg + lymphocytes, specific serum antibodies and several immune-related genes expressions in vaccinated flounder. These results demonstrated that rOmpV co-vaccination with rIFN-γ or pcIFN-γ could both boost the immune responses and evoke highly protective effects against E. tarda, indicating that flounder IFN-γ is a promising adjuvant candidate for fish vaccination via an injection administering route.

New Insights into IgZ as a Maternal Transfer Ig Contributing to the Early Defense of Fish against Pathogen Infection

IgZ or its equivalent IgT is a newly discovered teleost specific Ig class that is highly specialized in mucosal immunity. However, whether this IgZ/IgT class participates in other biological processes remains unclear. In this study, we unexpectedly discovered that IgZ is highly expressed in zebrafish ovary, accumulates in unfertilized eggs, and is transmitted to offspring from eggs to zygotes. Maternally transferred IgZ in zygotes is found at the outer and inner layers of chorion, perivitelline space, periphery of embryo body, and yolk, providing different lines of defense against pathogen infection. A considerable number of IgZ⁺ B cells are found in ovarian connective tissues distributed between eggs. Moreover, pIgR, the transporter of IgZ, is also expressed in the ovary and colocalizes with IgZ in the zona radiata of eggs. Thus, IgZ is possibly secreted by ovarian IgZ⁺ B cells and transported to eggs through association with pIgR in a paracrine manner. Maternal IgZ in zygotes showed a broad bacteriostatic activity to different microbes examined, and this reactivity can be manipulated by orchestrating desired bacteria in water where parent fish live or immunizing the parent fish through vaccination. These observations suggest that maternal IgZ may represent a group of polyclonal Abs, providing protection against various environmental microbes encountered by a parent fish that were potentially high risk to offspring. To our knowledge, our findings provide novel insights into a previously unrecognized functional role of IgZ/IgT Ig in the maternal transfer of immunity in fish, greatly enriching current knowledge about this ancient Ig class.

Differential immune responses of immunoglobulin Z subclass members in antibacterial immunity in a zebrafish model

Immunoglobulin Z (IgZ) or its equivalent immunoglobulin T (IgT) is a newly identified immunoglobulin (Ig) class from teleost fish. This Ig class is characterized by its involvement in mucosa-associated lymphoid tissues (MALTs) for mucosal defence against pathogen infection. Recently, several subclass members of IgZ/IgT, such as IgZ, IgZ2, Igτ1, Igτ2 and Igτ3, have been further identified from zebrafish, common carp and rainbow trout. However, the functional diversity and correlation among these subclasses remain uncertain. Here, we explored the differential immune reactions of the IgZ and IgZ2 subclasses in antibacterial immunity in a zebrafish model. IgZ was extensively distributed in the peripheral serum and skin/gill MALTs and showed a rapid induction upon bacterial infection. IgZ2 was specialized in skin/gill MALTs and showed a strong induction following IgZ production. Correspondingly, the IgZ+ B cells had a wider distribution in the systemic primary/secondary lymphoid tissues and MALTs than the IgZ2+ B cells, which were predominant in MALTs. IgZ and IgZ2 exhibited a complementary effect in antibacterial immunity by possessing differential abilities. That is, IgZ is preferentially involved in bactericidal reaction that is in part C1q-dependent, and IgZ2 participates in neutralization action through bacteria-coating activity. The production of IgZ largely depended on the αβ T/CD4+ T cells, whereas that of IgZ2 did not, suggesting the different dependencies of IgZ and IgZ2 on systemic immunity. Our findings demonstrate that the functional behaviour and mechanism of the IgZ/IgT family are more diverse than previously recognized and thus improve the current knowledge about this ancient Ig class.

Tilapia develop protective immunity including a humoral response following exposure to tilapia lake virus

Tilapia lake virus (TiLV) is an emerging virus associated with high mortality in cultured tilapia. Since the first report of tilapia lake virus, it has been detected in diseased tilapia in sixteen countries around the world. Thus, there is an urgent need to develop an efficacious vaccine to prevent TiLV disease (TiLVD) and reduce its global economic impact. Understanding the role of the adaptive immune response following exposure of tilapia to TiLV is a critical step in the development of such a vaccine. In this study, we challenged red hybrid tilapia by cohabitation or intraperitoneal injection and demonstrated that surviving fish develop a protective immunity. We also demonstrated that tilapia that survived experimental infections possess significant antibodies against the protein encoded by the TiLV segment 4. We then developed a TiLV indirect ELISA to determine the antibody response in tilapia. The ELISA revealed high antibody levels in survivors of experimental challenges and following outbreaks on farms. The ELISA effectively distinguished TiLV-exposed from unexposed tilapia and was used to monitor anti-TiLV antibody kinetics following infection. During the primary infection, tilapia developed an antibody response as early as 7 days post TiLV challenge (dpc), peaked at 15 dpc, showed a gradual decline up until about 42 dpc, but persisted in some fish up until day 110 dpc. Upon re-infection, an increased antibody response occurred within 7-14 days, demonstrating that tilapia that survive TiLV infections develop humoral memory. In conclusion, our results demonstrated that tilapia mount antibody responses against TiLV that supports protective immunity to subsequent TiLV disease. The persistence of anti-TiLV antibodies in survivors following a single exposure suggests a single vaccination might be adequate to protect tilapia during the entire grow-out period. This study provides important information about the immune response of tilapia following exposure to TiLV as a first step in the development of an efficacious vaccine against this emerging and economically important viral disease.

Modelling the effect of vaccination on transmission dynamics of nervous necrosis virus in grouper larvae Epinephelus coioides

Nervous necrosis virus (NNV) infection in susceptible grouper larvae has been reported to cause high mortalities, leading to great economic losses in aquaculture industry. Although the effects of NNV vaccines on grouper have been broadly investigated, vaccination strategies have not been fully established. To this end, we introduced the parsimonious epidemiological models that explored the assessment of key epidemiological parameters and how they changed when vaccinations showed the effects. We showed that the models capture the published cumulative mortality data accurately. We estimated a basic reproduction number R₀  = 2.44 for NNV transmission in grouper larvae without vaccination. To effectively control NNV transmission by vaccination, a model for disease control was also generalized to attain the goals of controlled reproduction number less than 1. Our results indicated that at least 60% of grouper population needed to be immunized for ~75 min. Our data-driven modelling approach that links the transmission dynamics of NNV and vaccination strategies for grouper has the potential to support evidence-based planning and adaptation of integrated control measures. We encourage that the epidemiology-based framework introduced here can be further implemented for establishing effective vaccination and mitigation actions aimed at controlling diseases in fish farming practices.

Current use and management of commercial fish vaccines in Korea

The aquaculture industry in Korea has grown rapidly since the 1960s, and it is a major food source. However, the expansion of aquaculture systems has increased the chances of infectious disease outbreaks, and vaccination plays an important role in commercial fish farming. This is the first comprehensive review of commercial fish vaccines in Korea. It not only provides an overview of commercially available fish vaccines and their associated approval processes and laws, but also some perspectives on research advances regarding fish vaccines in Korea. In Korea, fish vaccines are approved only after their safety and effectiveness have been verified according to the Pharmaceutical Affairs Act, and after approval, each vaccine lot must pass the national evaluation criteria. As of the end of 2019, 29 vaccines were approved for 10 fish pathogens, including both single and combination vaccines containing more than two inactivated pathogens. The approved fish vaccines consist of 2 immersion vaccines, as well as 1 intramuscular and 26 intraperitoneal vaccines, which require syringe injection. All the 29 vaccines are manufactured as formalin-inactivated vaccines; 1 is an adjuvant vaccine and 28 are non-adjuvant vaccines; 25 are bacterial vaccines, 2 are viral vaccines, 1 is a parasite vaccine, and 1 is a parasite and bacterial vaccine. In terms of the target fish species, 27 vaccines are used in the olive flounder (Paralichthys olivaceus), 1 in the starry flounder (Platichthys stellatus), and 1 in the red seabream (Pagrus major), striped beakfish (Oplegnathus fasciatus), and amberjack (Seriola quinqueradiata). This imbalance exists mostly because the olive flounder is the main farmed fish species in Korea. In 2018, 67.71 million vaccine doses were distributed following satisfactory performance in the national evaluation. They were used to vaccinate approximately 80.6% of farmed olive flounders.

Immune responses induced by inactivated vaccine against Aeromonas hydrophila in pacu, Piaractus mesopotamicus

Aeromonas hydrophila is responsible for outbreaks of a severe infectious disease in fish farms around the world and is one of the major causes of economic losses to the neotropical fish farmers. This study assessed the induction of immune responses and protection against A. hydrophila in pacu, Piaractus mesopotamicus, vaccinated through intraperitoneal and immersion route with inactivated virulent strain. Fish were randomly distributed in three vaccinated groups: intraperitoneal (i.p.) route; immersion; and immersion + booster; and control group (unvaccinated). All vaccination protocols used the concentration of 1.7 × 10⁸ CFU mL^-1 of inactivated A. hydrophila., and an oil adjuvant was used for vaccine prepararion for i.p. route vaccination. Blood and skin mucus from 9 fishes per treatment were collected at 14, 28, 42 and 84 days post-vaccination (DPV) for determination of lysozyme concentration in skin mucus, as well as antibodies anti-A. hydrophila in blood serum and skin mucus. Fish were challenged at 84 DPV with homologous and virulent strain of A. hydrophila for evaluation of resistance against bacterial infection. The results demonstrated that vaccination with inactivated A. hydrophila suspension by i.p. or immersion resulted in significant increase of skin mucus lysozyme and specific antibody levels in serum and skin mucus, at 28 and 42 DPV, and this increase in innate and adaptive immunity remained significant in pacu vaccinated through i.p. route up to 84 DPV. Although no significant differences were observed in the survival study, pacu vaccinated through i.p. route presented 31,33% of relative percentage survival (RPS) in LD_50-96h when compared unvaccinated fish challenged at 84 DPV. The results observed in this study indicate that vaccination programs with inactivated A. hydrophila, including booster doses by i.p. or immersion routes, could result in more effective protection in pacu against this bacteriosis, by increasing innate and adaptive mucosal and systemic immune responses.

Development of monoclonal antibodies against serum immunoglobulins from gibel carp (Carassius auratus gibelio) and their applications in serodiagnosis of inapparent infection and evaluation of vaccination strategies

The disease outbreak caused by viral infection and bacterial pathogens has hampered the sustainable development of the gibel carp (Carassius auratus gibelio) industry, lack of monoclonal antibodies against serum immunoglobulin (Ig) of gibel carp has impeded the development of nonfatal immunoassays in detection of pathogen infection and understanding of fish immune response post vaccination. In the present study, serum Ig of gibel carp was purified by a combination of salting-out and DEAE Sepharose Column chromatography. The purified Ig had an apparent molecular weight of 74 kDa and 24 kDa in SDS-PAGE. Three monoclonal antibodies (MAbs) against Ig, designed as 2F4-1G10, 3H3-1E8 and 7H11-1C8, were developed with purified Ig preparations, which were selected on the basis of the indirect enzyme-linked immunosorbent assay (ELISA). Western blotting showed that MAbs 2F4-1G10 and 7H11-1C8 reacted with the heavy chain of IgM, while MAb 3H3-1E8 showed a reaction with the light chain. MAb 7H11-1C8 could react with surface Ig-positive (sIg+) lymphocytes under indirect immunofluorescence assay. Fluorescence-activated cell sorter analysis revealed that the percentage of sIg + lymphocytes were 32.68% in peripheral blood and 12.13% in pronephros. MAb 7H11-1C8 was proven to be effective in detecting the Cyprinid Herpesvirus 2-specific serum Ig, and determining the levels of Aeromonas hydrophila specific Ig in serum and immune organs under different vaccination strategies.

Review on Immersion Vaccines for Fish: An Update 2019

Immersion vaccines are used for a variety of aquacultured fish to protect against infectious diseases caused by bacteria and viruses. During immersion vaccination the antigens are taken up by the skin, gills or gut and processed by the immune system, where the resulting response may lead to protection. The lack of classical secondary responses following repeated immersion vaccination may partly be explained by the limited uptake of antigens by immersion compared to injection. Administration of vaccines depends on the size of the fish. In most cases, immersion vaccination is inferior to injection vaccination with regard to achieved protection. However, injection is problematic in small fish, and fry as small as 0.5 gram may be immersion vaccinated when they are considered adaptively immunocompetent. Inactivated vaccines are, in many cases, weakly immunogenic, resulting in low protection after immersion vaccination. Therefore, during recent years, several studies have focused on different ways to augment the efficacy of these vaccines. Examples are booster vaccination, administration of immunostimulants/adjuvants, pretreatment with low frequency ultrasound, use of live attenuated and DNA vaccines, preincubation in hyperosmotic solutions, percutaneous application of a multiple puncture instrument and application of more suitable inactivation chemicals. Electrostatic coating with positively charged chitosan to obtain mucoadhesive vaccines and a more efficient delivery of inactivated vaccines has also been successful.

Surface display of hirame novirhabdovirus (HIRRV) G protein in Lactococcus lactis and its immune protection in flounder (Paralichthys olivaceus)

Background

Hirame novirhabdovirus (HIRRV) can infect a wide range of marine and freshwater fish, causing huge economic losses to aquaculture industry. Vaccine development, especially oral vaccine, has become an effective and convenient way to control aquatic infectious diseases. HIRRV glycoprotein (G), an immunogenic viral protein is a potential vaccine candidate for prevention of the disease. Here, we aimed to construct a recombinant Lactococcus lactis strain expressing HIRRV-G on the cell surface as an oral vaccine to prevent HIRRV.

Results

Glycoprotein gene of HIRRV was successfully cloned and expressed in L. lactis NZ9000 in a surface-displayed form, yielding Ll:pSLC-G. An approximately 81 kDa recombinant G protein (containing LysM anchoring motif) was confirmed by SDS-PAGE, western blotting and mass spectrometry analysis. The surface-displayed G protein was also verified by immunofluorescence and flow cytometry assays. Furthermore, to evaluate the potential of Ll:pSLC-G as oral vaccine candidate, flounders were continuously fed with commercial diet pellets coated with 1.0 × 10⁹ cfu/g of induced Ll:pSLC-G for 1 week. Four weeks later, booster vaccination was performed with the same procedure. Compared with the controls, Ll:pSLC-G elicited significantly higher levels of specific IgM against HIRRV in flounder gut mucus at the second week and in serum at the fourth week (p < 0.05). Meanwhile, oral immunization with Ll:pSLC-G could provide 60.7% protection against HIRRV infection and a significantly lower virus load was detected than the controls on the third day post-challenge (p < 0.01). Moreover, on the first day post 1-week feeding, approximately 10⁴–10⁵ recombinant L. lactis cells were detected in every gram of foregut, midgut and hindgut of flounder, which were mainly localized at the bottom of gut mucus layer; and on day 21, 10²–10³L. lactis cells could still be recovered.

Conclusions

HIRRV-G protein was successfully expressed on the surface of L. lactis cells, which could trigger mucosal and humoral immune response of flounder and provide considerable immune protection against HIRRV. It suggests that genetically engineered L. lactis expressing G protein can be employed as a promising oral vaccine against HIRRV infection.

Dynamic distribution of formalin-inactivated Edwardsiella tarda in flounder (Paralichthys olivaceus) post intraperitoneal vaccination

In order to investigate the dynamic distribution of antigen in different tissues post vaccination, an absolute real-time quantitative PCR was employed to detect the amount of antigen in flounder (Paralichthys olivaceus) post intraperitoneal (i.p.) injection with three concentrations (10⁷, 10⁸, 10⁹ CFU ml^-1) of formalin-inactivated Edwardsiella tarda bacterin. The results showed that the amount of uptaken antigen quickly increased and then decreased in different tissues. The peak occurred first in the spleen and head kidney at 6-9 h after injection, and in the liver and blood at 9-15 h, then in the gill, intestine and skin at 15-24 h, finally in the muscle at 24-36 h. The amount of antigen was highest in the spleen and head kidney, followed by the blood, liver and gill, and lowest in the intestine, skin and muscle. Among the three concentration groups, the amount of antigen increased with the increasing concentration of the vaccine in the blood, liver, gill, intestine, skin and muscle, except for the spleen and head kidney, in which more antigens were found in the 10⁸ CFU ml^-1 group than that in 10⁹ CFU ml^-1 group. Moreover, IIFA and western blotting was performed to examine the tissue distribution of antigen at 9 h after vaccination with 10⁸ CFU ml^-1 formalin-inactivated E. tarda. The bacteria were mainly observed in the spleen and head kidney, then the liver, gill and blood, and least in the intestine, skin and muscle, which was roughly in accordance with the results of absolute qPCR. Furthermore, the expressions of CD4-1, MHC IIα, CD8α and MHC Iα in different tissues were detected by RT-qPCR, and the expression levels of these genes were highest in the spleen and head kidney, then in the blood, gill, liver, and lowest in the intestine, skin and muscle. All these results provided useful information for dynamic transportation of antigen uptake post vaccination, and also deepened the understanding of immune response to the injection vaccination.

Understanding the roles of surface proteins in regulation of Lactobacillus pentosus HC-2 to immune response and bacterial diversity in midgut of Litopenaeus vannamei

The interactions of microbiota in the intestines play an important role in promoting or maintaining the health of hosts. The present study aim to investigate the effects of the surface proteins of Lactobacillus pentosus HC-2 on the immune response and the bacterial composition of Litopenaeus vannamei, thus, the immune-related genes, surface condition, HC-2 numbers and the bacteria diversity in midgut were explored after shrimp feeding the normal HC-2 and 5 M -  lithium chloride (LiCl) treated HC-2 for four weeks. Obvious improvements in the intestinal surface were observed in R group than the control group and L group. qPCR analysis demonstrated that the selected immune-related genes of lysozyme, proPO, LGBP, PEN-3α, crustin, and lvLec were significantly up-regulated in group R than in group L. Meanwhile, in the challenge test, shrimp in R group received 72% relative percent survival, which was significantly higher than the L group (RPS = 9%). The bacteria composition analysis showed that the abundance of Proteobacteria were significantly higher in group R and L than in group C, and the Bacteroidetes were significantly higher in group C than in group R and L, whereas the numbers of Chloroflexi were significantly higher in group R than in group C and L. The bacterial community difference analysis revealed that the harmful bacteria such as genus of Vibrio, Tenacibaculu and Thalassobius were decreased and the beneficial bacterium as Ruegeria and Lactobacillus were increased in R group, whereas this phenomenon were not found in L group. Taken together, above results indicating that the surface proteins were indispensable for L. pentosus HC-2 adhesion and colonization in shrimp intestines to improve intestine condition, enhance immune response, competitively exclude the pathogens, and promote the beneficial bacteria growth to protect the shrimp from pathogens infection. The findings in this work will help to promote the understanding of the roles of probiotics in shrimp intestines displaying probiotic-function by regulating the intestinal bacteria.

Influence of CD4-1+, CD4-2+ and CD8+ T lymphocytes subpopulations on the immune response of B lymphocytes in flounder (Paralichthys olivaceus) immunized with thymus-dependent or thymus-independent antigen

In order to elucidate the influence of T lymphocytes subpopulations on B lymphocytes immune response, in this paper, CD4-1⁺, CD4-2⁺, CD8⁺ T lymphocytes and B lymphocytes responses to thymus-independent (TI) or thymus-dependent (TD) antigen plus immunosuppressant were investigated in flounder (Paralichthys olivaceus). The results showed that in LPS-immunized group, the percentages of CD4-1⁺, CD4-2⁺, CD8β⁺ T (PCD4-1⁺ T, PCD4-2⁺ T and PCD8β⁺ T) lymphocytes in peripheral blood leucocytes (PBLs) had no significant variations, the percentages of IgM⁺ B (PIgM⁺ B) lymphocytes and LPS-specific antibodies (LA) significantly increased and peaked at 3^rd or 4^th week post-injection; CsA had no inhibition on both T/B lymphocytes and LA; RaPa only suppressed the PIgM⁺ B lymphocytes and LA, and the inhibition maximum (Imax) were about 35% and 20%, respectively. In KLH-immunized group, the PCD4-1⁺, PCD4-2⁺ and PCD8β⁺ T lymphocytes significantly increased and peaked at 3^rd or 5^th day, successively the PIgM⁺ B lymphocytes and KLH-specific antibodies (KA) significantly increased to the peak at 5^th week; the PCD4-1⁺, PCD4-2⁺ T and PIgM⁺ B lymphocytes and LA were inhibited significantly by both CsA and RaPa, and the Imax on them were 13%-33%, 11%-25%, 19%-34%, 22%-26%, respectively, while the PCD8β⁺ T lymphocytes showed no significant suppression. The results indicated that the suppression of PIgM⁺ B lymphocytes in KLH + CsA group was not directly derived from CsA, but due to the suppression of T lymphocytes, especially CD4⁺ T lymphocytes subpopulations. The results showed for the first time that, similar to higher vertebrates, T lymphocytes didn't respond to TI antigen, moreover, T lymphocyte subpopulations had a regulation on the immune response of B lymphocyte for TD antigen in flounder.

Evaluation of bivalent vaccines candidates among VAA, OmpK and OmpR from Vibrio anguillarum in flounder (Paralichthys olivaceus)

Outer membrane protein (Omp) K, OmpR and VAA have been identified with good immunogenicity from Vibrio anguillarum, and their recombinant proteins showed variable relative percent survival (RPS) in previous study. In order to develop effective bivalent vaccine candidates, recombinant (r) VAA + rOmpK (AK), rVAA + rOmpR (AR), rOmpK + rOmpR (KR) among VAA, OmpK and OmpR, or formalin-killed cells (FKC) of V. anguillarum were immunized in flounder, respectively. Results revealed that AK, AR, KR and FKC could induce the proliferation of surface membrane immunoglobulin-positive B lymphocytes or CD3⁺ T lymphocytes in peripheral blood lymphocytes, and significantly enhance the total antibodies, specific antibodies and immune-related gene than those of control group. AK, AR, KR or FKC showed RPS of 74.92%, 78.49%, 82.09% and 56.99%, respectively. These results indicated that three bivalent vaccines AK, AR and KR could induce strong cellular and humoral immunity, and had high protection against V. anguillarum infection in flounders.

Recombinant phosphoglucomutase and CAMP factor as potential subunit vaccine antigens induced high protection against Streptococcus iniae infection in flounder (Paralichthys olivaceus)

AIMS

The aim of this study was to screen vaccine candidates from virulence factors of Streptococcus iniae in flounder model.

METHODS AND RESULTS

The immunogenicity of recombinant phosphoglucomutase (rPGM) and rCAMP factor was confirmed by Western blot. The percentage of surface membrane immunoglobulin-positive (sIg⁺ ) lymphocytes in peripheral blood leucocytes, the specific and total serum IgM and the activity of acid phosphatase (ACP) and peroxidase (POD) in flounder were determined with flow cytometry, ELISA and commercial enzyme activity kits, respectively, after intraperitoneal immunization with rPGM and rCAMP factor. The results showed that rPGM and rCAMP factor could induce significant rise in sIg⁺ lymphocytes, specific serum IgM and activities of ACP and POD. Additionally, the relative percent survival rate of the vaccinated flounder was 64 and 54% in challenge experiment using S. iniae, respectively. These results indicated that rPGM and rCAMP factor could evoke humoural and innate immune response in flounder and provide high-efficiency immunoprotection against S. iniae infection.

CONCLUSIONS

Phosphoglucomutase (PGM) and CAMP factor were promising vaccine candidates against S. iniae in flounder.

SIGNIFICANCE AND IMPACT OF THE STUDY

Phosphoglucomutase and CAMP factor have the potential to be vaccine candidates, which provide important information for us to develop the effective subunit vaccines, especially the multivaccine, against S .iniae in aquaculture.

Development of monoclonal antibodies against IgM of sea bass (Lateolabrax japonicus) and analysis of phagocytosis by mIgM+ lymphocytes

B cells in some fish were recently found to have potent phagocytic activities. Sea bass (Lateolabrax japonicus) as an important economical marine fish species, it could be used as an appropriate model to study the functions of B cells in phagocytosis. In the paper, three positive hybridomas designated as 1E11, 2H4 and 3F3 secreting monoclonal antibodies (MAbs) against sea bass immunoglobulin M (IgM) were produced and used as research tools. Indirect enzyme-linked immunosorbent assay showed that all the three MAbs had a high binding capacity with sea bass serum IgM. Western blotting analysis showed that all the three MAbs were specific for the heavy chain of sea bass IgM. Indirect immunofluorescence assay (IFA) analysis suggested that both MAbs 1E11 and 2H4 could recognize membrane-bound IgM (mIgM) molecule of sea bass. Specificity analysis showed that three MAbs had no cross-reactions with other six teleosts IgMs. Flow cytometric analysis exhibited that the percentages of sea bass mIgM + lymphocytes in peripheral blood, spleen and pronephros were 25.6%, 21.1%, and 17.5%, respectively. Moreover, we found that the mIgM + lymphocytes of sea bass could phagocytose fluorescence microspheres and Lactococcus lactis, but lower phagocytosis rates of L. lactis was observed. These results demonstrated that the MAbs produced in this paper could be used as tools to study secretory IgM and mIgM + lymphocytes of sea bass, and mIgM + lymphocytes might also play an important role in innate immunity of sea bass.

Recombinant Hsp33 and OmpC protein can serve as promising divalent vaccine with protection against Vibrio anguillarum and Edwardsiella tarda in flounder (Paralichthys olivaceus)

Vibrio anguillarum and Edwardsiella tarda are severe aquaculture pathogens shared similar epidemiological characteristics and susceptible to flounder (Paralichthys olivaceus). In our previous studies, recombinant(r) protein heat shock protein 33 (rHsp33) from V. anguillarum and outer membrane protein C (rOmpC) from E. tarda were proved to have protection against V. anguillarum and E. tarda, respectively. In this paper, the cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, and the protection of divalent vaccine candidate (rHsp33 + rOmpC, rHC) against both V. anguillarum and E. tarda were evaluated. RHC, rHsp33, and rOmpC were vaccinated to flounder, respectively, and the percentages of surface immunoglobulin-positive (sIg+) cells in peripheral blood lymphocytes (PBLs), serum IgM, specific antibodies against V. anguillarum or E. tarda, specific antibodies against rHsp33, rOmpC or rHC, the expression of immune-related genes and relative percent survival (RPS) against V. anguillarum or E. tarda were measured. The results showed that: RHC could induced the enhancement of sIg + cells and high levels of specific antibodies against both V. anguillarm and E. tarda; Also a significant increase of specific antibodies against rHsp33, rOmpC or rHC, and up-regulation of gene expression of CD3, CD4-1, CD4-2, CD8α, CD8β and IgM in spleen, head-kidney, and hindgut, RPS of 70 ± 3.45% against V. anguillarum and 60 ± 1.48% against E. tarda, respectively. In addition, rHsp33 induced specific antibodies against E. tarda and rOmpC, and had a RPS of 43.3 ± 3.73% against E. tarda; rOmpC could evoke specific antibodies against V. anguillarum and rHsp33, and had a RPS of 44 ± 1.27% against V. anguillarm; The results demonstrated that there was cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, rHC as a divalent vaccine can induce significant immune response and efficient protection against both E. tarda and V. anguillarum in flounder.

Inhibition of Cyclosporine A or rapamycin on T lymphocyte counts and the influence on the immune responses of B lymphocytes in flounder (Paralichthys olivaceus)

In acquired immunity, T lymphocytes regulate the immune responses of B lymphocytes, including the IgM⁺ B lymphocyte counts and antibody production. In this paper, Cyclosporine A (CsA) and Rapamycin (RaPa) were used, and their inhibition on T lymphocytes and immune responses of B lymphocytes in flounder (Paralichthys olivaceus) were investigated. Flounder was injected with Keyhole Limpet Hemocyanin (KLH), a mixture of KLH and CsA (KLH + CsA), or a mixture of KLH and RaPa (KLH + RaPa). Then, the proportions of T and IgM⁺ B lymphocytes (PT and PB) in peripheral blood leukocytes (PBL) were analysed by flow cytometry (FCM), total antibodies (TA) and KLH specific antibodies (KA) in serum were measured by ELISA, and expression of 9 immune-related genes in the spleen and kidneys were determined using q-PCR. On the other hand, the PBL culture was treated with Concanavalin A (ConA), a mixture of ConA and CsA, and a mixture of ConA and RaPa. Then the PT and PB were measured, and the cell proliferation was examined using the MTT method. The results showed that the PT peaked on the 5^th day in the KLH group, KLH + CsA group and KLH + RaPa group. The maximum inhibition rates (MIR) of CsA and RaPa were 27.44% ± 0.50% and 21.37% ± 2.06%, respectively. The PB peaked at the 5^th week, and the MIR of CsA and RaPa were 44.51% ± 1.36% and 33.3% ± 0.65%, respectively. The KA and TA peaked at the 5^th week. The MIR of CsA and RaPa on TA were 40.31% ± 1.59% and 32.96% ± 2.21%, respectively, and were 27.77% ± 2.02% and 23.41% ± 1.08% for KA, respectively. Nine immune-related genes had significantly lower expression in the KLH + CsA group and KLH + RaPa group compared to the KLH group. The proliferation of the PBL culture was inhibited by CsA or RaPa, and the inhibition rate of CsA and RaPa for PT was 18.14% ± 1.08% and 17.88% ± 1.02%, respectively, and the inhibition rates for PB were 3.03% ± 0.57% and 2.95% ± 0.53%, respectively. The results demonstrated that T lymphocytes counts were inhibited by CsA and RaPa, followed by suppression of IgM⁺ B lymphocytes and antibody production, which suggests that T lymphocytes regulate the immune response of B lymphocytes in flounder.

Development of monoclonal antibodies against IgM of half-smooth tongue sole (Cynoglossus semilaevis) and analysis of phagocytosis of fluorescence microspheres by mIgM+ lymphocytes

In this work, the two positive hybridomas designated as 1B2 and 2G9 secreting monoclonal antibodies (MAbs) against half-smooth tongue sole IgM were produced and then cloned by limited dilution. Western blotting showed that MAbs 1B2 and 2G9 could specifically react with the heavy and light chains of IgM, respectively. The indirect immunofluorescence assay (IFA) showed that green fluorescent signals were detected on the membrane of lymphocytes, which indicated that membrane-bound IgM (mIgM) could be recognized by both MAbs 1B2 and 2G9. Specificity analysis showed that no cross-reactions were detected between IgM of half-smooth tongue sole and other five teleosts IgMs using MAbs 1B2 and 2G9. Flow cytometric analysis (FCA) demonstrated that the percentages of mIgM+ lymphocytes in peripheral blood, spleen and pronephros of health half-smooth tongue sole were 21.1%, 17.6% and 16.1%, respectively. Moreover, the phagocytosis rates of fluorescence microspheres by mIgM+ lymphocytes in isolated leukocytes from peripheral blood, spleen and pronephros of health half-smooth tongue sole were determined to be 4.6 ± 0.5%, 3.6 ± 0.4% and 4.2 ± 0.3% by FCA, respectively, and the proportions of mIgM+ phagocytic lymphocytes in total mIgM+ lymphocytes in the peripheral blood, spleen and pronephros were calculated to be 21.6 ± 1.1%, 20.6 ± 1.8% and 26.0 ± 0.8%, respectively. These results demonstrated that the MAbs produced in this study could specifically recognize the serum IgM and mIgM on B lymphocytes of half-smooth tongue sole. Meanwhile, partial mIgM+ lymphocytes have the phagocytic capacity, which indicates mIgM+ lymphocyte play important role in innate immune response.

Characterization of CD3+ T lymphocytes of Japanese flounder (Paralichthys olivaceus) and its response after immunization with formalin-inactivated Edwardsiella tarda

The CD3 complex is an important cell surface marker of T lymphocytes and essential for T lymphocytes activation in higher vertebrates. In the present work, the CD3ε of Japanese flounder (Paralichthys olivaceus) was recombinantly expressed in E. coli BL21 (DE3) and used as an immunogen to produce mouse anti-rCD3ε polyclonal antibodies, which could specifically recognize a 20 kDa protein in the membrane proteins of peripheral blood lymphocytes (PBL) of Japanese flounder by co-immunoprecipitation assay. Mass spectrometric analysis showed the 20 kDa protein was the native CD3ε of Japanese flounder. Both the flow cytometric analysis and double immunofluorescence assay (DIFA) showed that the CD3⁺ T lymphocytes could be identified specifically by the mouse anti-rCD3ε polyclonal antibodies, which didn't cross-react with the sIgM⁺ lymphocytes. Immunohistochemistry showed that CD3⁺ T lymphocytes could be detected in gill, skin, stomach, intestine, spleen, liver, head-kidney and mid-kidney. Flow cytometric analysis showed the percentages of CD3⁺ T lymphocytes in the PBL, spleen lymphocytes (SL) and head-kidney lymphocytes (HKL) of Japanese flounder increased rapidly after immunization with formalin-inactivated Edwardsiella tarda, and reached their peak levels at 5th day with 12.6%, 9.7% and 8.7%, respectively, and then decreased gradually. These results suggested that CD3⁺ T lymphocytes play important roles in mucosal and cell-mediated immunity, and the results would deepen our understanding on the roles of teleost T lymphocytes in the immune response.

Protective efficacy of six immunogenic recombinant proteins of Vibrio anguillarum and evaluation them as vaccine candidate for flounder (Paralichthys olivaceus)

Vibrio anguillarum is a severe bacterium that causes terminal haemorrhagic septicaemia in freshwater and marine fish. Virulence-associated proteins play an important role in bacterial pathogenicity and could be applied for immunoprophylaxis. In this study, six antigenic proteins from V. anguillarum were selected and the immune protective efficacy of their recombinant proteins was investigated. VirA, CheR, FlaC, OmpK, OmpR and Hsp33 were recombinantly produced and the reactions of recombinant proteins to flounder-anti-V. anguillarum antibodies (fV-ab) were detected, respectively. Then the recombinant proteins were injected to fish, after immunization, the percentages of surface membrane immunoglobulin-positive (sIg+) cell in lymphocytes, total antibodies, antibodies against V. anguillarum, antibodies against recombinant proteins and relative percent survival (RPS) were analyzed, respectively. The results showed that all the recombinant proteins could react to fV-ab, proliferate sIg + cells in lymphocytes and induce production of total antibodies, specific antibodies against V. anguillarum or the recombinant proteins; the RPS of rVirA, rCheR, rFlaC, rOmpK, rOmpR and rHsp33 against V. anguillarum was 70.27%, 27.03%, 16.22%, 62.16%, 45.95% and 81.08%, respectively. The results revealed that rHsp33, rVirA and rOmpK have good protections against V. anguillarum and could be vaccine candidates against V. anguillarum.

The influence of concentration of inactivated Edwardsiella tarda bacterin and immersion time on antigen uptake and expression of immune-related genes in Japanese flounder (Paralichthys olivaceus)

Our previous work has demonstrated that the immune response of Japanese flounder was associated with the concentration of formalin-inactivated Edwardsiella tarda and immersion time. In order to further investigate the influence of immersion vaccine dose and bath time on the antigen uptake, formalin-killed Edwardsiella tarda bacterin was prepared and adjusted to four concentrations (10⁹, 10⁸, 10⁷, 10⁶ cfu ml^-1) for 30, 60 and 90 min immersion in Japanese flounder model, respectively. Absolute quantitative real-time PCR was employed to examine the bacterin uptake in gill, skin, spleen and kidney at 3 and 6 h post vaccination. The results showed that the antigen uptaken in gills and skin were significant higher than spleen and kidney, and the antigen amounts in gill and skin both declined from 3 to 6 h, whereas the antigen amounts in spleen and kidney gradually increased. Significant higher antigen amounts were detected in 10⁹-30, 10⁹-60, 10⁸-60, 10⁸-90 and 10⁸-90 groups than other groups (P < 0.05), especially the 10⁸-60min group displayed the highest antigen uptaken. Meanwhile, the expression profiles of antigen recognization and presentation genes (MHCⅡα, TcRα, CD4-1), immunoglobulins (IgM, IgT), inflammatory cytokines (IL-1β, IL-6), heat shock protein 70 (HSP70) and c-type lysozyme were analyzed using real-time PCR. On the whole, the transcription levels of the eight genes exhibited to be higher in 10⁷-90, 10⁸ and 10⁹ cfu ml^-1 groups than other groups (P < 0.05), especially the 10⁸-60 group displayed the highest up-regulation. These results demonstrated that immersion with formalin-inactivated E. tarda, especially under 10⁸-60 min condition could efficiently enhance the antigen uptake and the expression of immune-related genes, which provided evidences for an enhanced vaccination effects under an optimized combination of vaccine dose and immersion time.

Immunoglobulin Tau Heavy Chain (IgT) in Flounder, Paralichthys olivaceus: Molecular Cloning, Characterization, and Expression Analyses

Immunoglobulin tau (IgT) is a new teleost immunoglobulin isotype, and its potential function in adaptive immunity is not very clear. In the present study, the membrane-bound and secreted IgT (mIgT and sIgT) heavy chain genes were cloned for the first time and characterized in flounder (Paralichthys olivaceus), and found the nucleic acid sequence were exactly same in the Cτ1–Cτ4 constant domains of mIgT and sIgT, but different in variable regions and the C-terminus. The amino acid sequence of mIgT shared higher similarity with Bovichtus diacanthus (51.2%) and Dicentrarchus labrax (45.0%). Amino acid of flounder IgT, IgM, and IgD heavy chain was compared and the highest similarity was found between IgT Cτ1 and IgM Cμ1 (38%). In healthy flounder, the transcript levels of IgT mRNA were the highest in gill, spleen, and liver, and higher in peripheral blood leucocytes, skin, and hindgut. After infection and vaccination with Edwardsiella tarda via intraperitoneal injection and immersion, the qRT-PCR analysis demonstrated that the IgT mRNA level was significantly upregulated in all tested tissues, with similar dynamic tendency that increased firstly and then decreased, and higher in gill, skin, hindgut, liver, and stomach in immersion than in the injection group, but no significant difference existed in spleen and head kidney between immersion and injection groups. These results revealed that IgT responses could be simultaneously induced in both mucosal and systemic tissues after infection/vaccination via injection and immersion route, but IgT might play a more important role in mucosal immunity than in systemic immunity.

Antigen uptake and expression of antigen presentation-related immune genes in flounder (Paralichthys olivaceus) after vaccination with an inactivated Edwardsiella tarda immersion vaccine, following hyperosmotic treatment

Antigen uptake is a critical process for activation of the immune system, and therefore the ability to enhance antigen uptake is a primary consideration in the development of an immersion vaccination of fish. In the present work, flounders (Paralichthys olivaceus) were immersed in three hyperosmotic solutions with 40, 50 and 60‰ salinities, then transferred into seawater of normal salinity (i.e. 30‰) containing formalin-inactivated Edwardsiella tarda for 30 min. The antigen uptake in vaccinated flounder was determined using an absolute quantitative PCR (qPCR). The results showed significantly higher antigen uptake in the tissues of flounders immersed in solutions with 50‰ and 60‰ salinity compared to the control group directly immersed in vaccine (DI) (P < 0.05), and the highest amount of antigen was detected in flounders immersed in the 50‰ salinity solution, whereas there was no significant difference in antigen uptake between the 40‰ salinity group and the DI group (P > 0.05). A rapid and significant increase in antigen uptake was detected in the mucosal-associated tissues including the gill, skin and intestine (P < 0.05) compared with the spleen, kidney and liver. Antigen uptake in the gill and skin both peaked at 30 min post immersion, which was significantly higher than the levels of uptake measured in the other tissues (P < 0.05), and then quickly declined. In contrast, antigen uptake in the spleen, kidney and liver gradually increased 3 h post immersion (hpi). The expression profiles of four antigen presentation-related immune genes (MHC Iα, MHC IIα, CD4-1 and CD8α) were investigated after immersion. These four genes showed a significantly stronger response in the immersed flounders exposed to 50‰ salinity compared with the DI group (P < 0.05). In the mucosal-associated tissues, the expression of MHC Iα and CD8α genes peaked at 24 hpi, while the expression of MHC IIα and CD4-1 genes showed up-regulation in the gill and skin and reached the peak in these tissues at 48 hpi. The expressions of the four genes were also up-regulated in spleen, kidney and liver, but reached peak expression in these tissues at 48-72 hpi. The results demonstrated that hyperosmotic immersion, notably 50‰ salinity significantly enhanced antigen uptake and the expression of selected genes associated with antigen presentation, providing evidence for an enhanced immune activation of the fish's immune response by the hyperosmotic immersion treatment prior to vaccination.