Immune response of turbot (Scophthalmus maximus L.) to a broad spectrum vaccine candidate, recombinant glyceraldehyde-3-phosphate dehydrogenase of Edwardsiella tarda

Comparative transcriptome analysis reveals the immune response of turbot (Scophthalmus maximus) induced by inactivated bivalent vaccine

Vibrio species are important pathogens that affect a wide range of farmed fish. Vaccination is regarded as the most efficacious strategy for fighting bacterial infections. However, the underlying mechanisms remain to be elucidated. In the present study, a comparative transcriptome analysis was performed on the spleens from turbot (Scophthalmus maximus) induced by an inactivated bivalent vaccine (Vibrio anguillarum and Vibrio harveyi, IVVah1) at 4 week and 1 day post further challenge. Strong immune responses were induced by the bivalent vaccine, besides differentially expressed genes (DEGs) associated with adaptive immunity, more innate immunity-related DEGs were detected. At the late stage of vaccination, immune-related molecules associated with pattern recognition receptors, inflammatory factors, complement and coagulation cascade-related components, and antigen processing and presentation were significantly regulated, and some of them were even further up-regulated after the bacterial challenge, indicating the cooperation of multiple immune processes during the vaccine immunization process. In addition to the terms or pathways associated with the immune response, enrichment analysis revealed multiple significantly enriched terms/pathways associated with the response to stimulus/stress, homeostasis, metabolism, and biosynthesis, suggesting that a defensive status was established by the bivalent vaccine. This study furnishes new insights into the internal mechanism of immunity upon a combined vaccine administrating in turbot and lays a foundation for developing highly immunogenic vaccines in teleost.

The moonlighting protein fructose 1,6-bisphosphate aldolase as a potential vaccine candidate against Photobacterium damselae subsp. piscicida in Asian sea bass (Lates calcarifer)

Vaccination is the most effective, safe, and environmentally friendly method to prevent the outbreak of Photobacterium damselae subsp. piscicida (Phdp), a dangerous pathogen in aquaculture worldwide. Here, recombinant proteins of catalase, superoxide dismutase, isocitrate dehydrogenase, fructose 1,6-bisphosphate aldolase (Fba), and a mixture of all four proteins were investigated for their immunoprotective effects against photobacteriosis in Asian sea bass (Lates calcarifer). After immunization, experimental fish showed an increase in specific antibody levels and lysozyme activities, especially the Fba group. After a lethal challenge with Phdp strain AOD105021, the Fba group achieved the highest relative percentage of survival rate (70.21%) and a significantly lower bacterial load in the spleens than other groups 3 days after infection. The results suggest that Fba is a good candidate for subunit vaccine development against photobacteriosis in fish.

Optimized GAPDH-truncated immunogen of Streptococcus equi elicits an enhanced immune response and provides effective protection in a mouse model

Strangles is an acute and frequently diagnosed infectious disease caused by Streptococcus equi subsp. equi. Infection with this pathogen can cause grave losses to the equine industry. The present work investigates glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an important surface-localized virulence factor of S. equi, to determine whether it could be developed into an efficacious and suitable subunit vaccine against strangles. Two different recombinant fragments of S. equi GAPDH, namely, GAPDH-L and GAPDH-S, were constructed and expressed. Further, the antigenicity and immunogenicity of these two recombinant proteins were compared and evaluated in a mouse model. Our results revealed that immune responses were efficiently induced by the proteins in immunized mice. Remarkably, higher survival rates and significantly lower bacterial loads in the lung, liver, kidney, and spleen were observed in the GAPDH-S group compared with the GAPDH-L group after challenge with S. equi. High levels of specific antibodies, elevated antibody titers, and increased proportions of CD8 + T cells further indicated that GAPDH-S elicited better humoral and cellular immune responses than GAPDH-L. Furthermore, the induction of TCR, TLR-2, TLR-3, and TLR-4 significantly increased in the GAPDH-S group compared with those in the GAPDH-L and negative control groups. In summary, our results indicate that the optimized recombinant protein GAPDH-S is a promising candidate construct that may be further developed into a multivalent subunit vaccine for strangles.

Oral administration of microencapsulated egg yolk immunoglobulin (IgY) in turbot (Scophthalmus maximus) to combat against Edwardsiella tarda 2CDM001 infections

Edwardsiellosis, an extremely harmful disease can be caused by Edwardsiella tarda, severely restricts the development of turbot (Scophthalmus maximus) farming worldwide, especially in China. This study aimed to establish an effective and feasible prophylaxis by feeding chitosan-alginate coated egg yolk immunoglobulin (IgY) against E. tarda 2CDM001 infections in the process of turbot farming. Enzyme-linked immunosorbent assays proved that the obtained specific IgY could specifically target E. tarda 2CDM001 and five other E. tarda isolates (1a5p, Hz-s, 1a1s, fs-a1 and 58p8). In-vitro, the bacteriostatic effects of specific IgY showed dose dependencies at concentrations ranging from 1 to 10 mg/mL. Moreover, E. tarda 2CDM001 incubated with 10 mg/mL specific IgY could induce the destruction of cell wall structures and significantly decrease the bacterial surface hydrophobicity (p < 0.05). In this study, turbots were challenged with 10⁷ CFU E. tarda 2CDM001 after seven days of continuous feeding with basal diets containing microencapsulated IgYs. Survival rates of the 5%, 3% and 1% microencapsulated specific IgY groups were 63.3%, 56.7% and 20% on the tenth day post infection, respectively, while the turbots in the positive control and non-specific IgY groups all died within ten days. Oral administration of basal diets containing 5% microencapsulated specific IgY significantly reduced IL-1β, IL-8, TNF-α and C3 transcript levels in the head kidney and spleen of turbots compared with the positive and non-specific IgY groups at 24 h after E. tarda 2CDM001 challenging (p < 0.05). Pathological increase of leukocytes in the specific IgY group was significantly lower than that in the positive control and non-specific IgY groups (p < 0.05), decreasing slowly after 24 h of infection and showing a recovery trend. Erythrocyte counts and hemoglobin concentrations of turbots in positive and non-specific IgY groups showed a marked decrease compared with the negative and specific groups at 96 h after E. tarda 2CDM001 infection (p < 0.05). These results suggest that passive immunity via feeding microencapsulated specific IgY could be used as a valuable preventative in turbot against E. tarda 2CDM001 infections.

Comparative immunohistological study on using capsaicin, piperine, and okadaic acid for the transepithelial passage of the inactivated viral and bacterial vaccines in fish

The practical difficulty of parenteral application of fish vaccines against devastating fish diseases diverted the interest toward oral vaccination. Search for effective methods to enhance the oral uptake of viral and bacterial vaccines is continuing. The current research focus on a new role of mucosal fish vaccine adjuvants inducing the antigen uptake by enhancing vascularity or increasing intestinal permeability. Some inflammatory substances cause reversible pathology to the intestinal epithelium, which could be employed for the transepithelial passage of vaccine particles. The natural inflammatory substances used were capsaicin, piperine, and okadaic acid as 1 mg, 2 mg, and 1 μg/fish, respectively. Two inactivated vaccines were used as antigens to test the effect of these inflammatory substances in two different fish hosts. Tested vaccines were inactivated redspotted grouper nervous necrosis virus vaccine in sevenband grouper (Epinephelus septemfasciatus) and inactivated Edwardsiella tarda vaccine in red sea bream (Pagrus major) fish models. The inflammatory substances and each vaccine were anally intubated to fish. Capsaicin proved to be effectively aiding the transepithelial passage of vaccine particles more than piperine, while okadaic acid had no detectable effect.

Synergistic effect of a combined live Vibrio anguillarum and Edwardsiella piscicida vaccine in turbot

In aquaculture, more than one pathogen usually be isolated from the sick fish, creating an urgent need for developing combined vaccines to control fish disease caused by multiple pathogens simultaneously. In our previous work, two live attenuated vaccines against Vibrio anguillarum and Edwardsiella piscicida were vaccinated in turbot, exhibiting an efficient protection. However, some immunological processes such as antigenic competition, antigenic cross-reaction and antigen induced suppression during combined vaccination are unknown. In this study, we evaluated the effectiveness of the combined live vaccines and explored the immunological processes after vaccination. We found that the combined two live attenuated vaccines for V. anguillarum and E. piscicida induced a stronger immune response without existing antigen competition. Instead, a synergistic effect was observed not only for triggering innate immune response but for stimulation of adaptive immunity. Our study suggested that the two combined live vaccines against V. anguillarum and E. piscicida could be used simultaneously in the future.

Identification of protective protein antigens for vaccination against Streptococcus dysgalactiae in cobia (Rachycentron canadum)

Streptococcus dysgalactiae is considered a causative agent of severe infection and economic loss for the cobia industry in Taiwan. In this study, protective antigens of this pathogenic bacterium were identified and screened in cobia (Rachycentron canadum). Outer surface proteins (OMPs) of this pathogen were extracted using mutanolysin digestion. Immunogenic targets were detected by western blot and then subjected to peptide sequencing using NanoLC-MS/MS. Two surface proteins, namely phosphoenolpyruvate protein phosphotransferase (PtsA) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), showed strong reactions with cobia antisera against S. dysgalactiae. Recombinant proteins were produced in Escherichia coli cells and their protective efficacies were investigated in cobia. Fish immunised with recombinant proteins, rPtsA + ISA (ISA 763 AVG) and rGAPDH + ISA, elicited higher levels of specific antibody responses against the recombinant proteins and had high levels of lysozyme activity. Notably, vaccinated fish were protected from lethal challenge with relative percentage of survival (RPS) values for rPtsA + ISA and rGAPDH + ISA groups being 91.67% and 83.33%, while 0% RPS value was found in both ISA injected and control groups. The results presented in the study demonstrate that the GAPDH and PtsA are promising vaccine candidates for preventing S. dysgalactiae disease in cobia.

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.

Glycolysis-related proteins are broad spectrum vaccine candidates against aquacultural pathogens

Reverse vaccinology (RV) has become a popular method for developing vaccines. Although Edwardsiella tarda is deemed to be an important fish pathogen, so far, no reports have used a genome-based approach to screen vaccine candidates against E. tarda. In the current study, protective antigens of E. tarda were screened using RV. Large-scale cloning, expression and purification of potential candidates were carried out, and their immunoprotective potential was evaluated. A candidate fructose-bisphosphate aldolase (FBA) exhibited broad spectrum protection, as did another glycolysis-related protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which we reported previously, indicating the potential of other glycolysis-related proteins of E. tarda as broad spectrum protective antigens. In total, half (5 out 10) of these proteins showed prominent immunoprotective potential. Therefore, we suggest that glycolysis-related proteins are a class of potential broad spectrum protective antigens and that these proteins should be preferentially selected.

Glyceraldehyde-3-phosphate dehydrogenase acts as an adhesin in Erysipelothrix rhusiopathiae adhesion to porcine endothelial cells and as a receptor in recruitment of host fibronectin and plasminogen

Erysipelothrix rhusiopathiae is the causative agent of animal erysipelas and human erysipeloid. Previous studies suggested glyceraldehyde 3-phosphate dehydrogenase (GAPDH) plays a role in the pathogenesis of E. rhusiopathiae infection. We studied E. rhusiopathiae GAPDH interactions with pig vascular endothelial cells, fibronectin, and plasminogen. Recombinant GAPDH (rGAPDH) was successfully obtained, and it was shown that it plays a role in E. rhusiopathiae adhesion to pig vascular endothelial cells. Moreover, rGAPDH could bind fibronectin and plasminogen in a dose-dependent manner. To our knowledge, this is the first study demonstrating that a moonlighting protein plays a role in pathogenesis of E. rhusiopathiae infections.

Glyceradehyde-3-phosphate dehydrogenase as a suitable vaccine candidate for protection against bacterial and parasitic diseases

The enzyme glyceraldehyde-3-P-dehydrogenase (GAPDH) has been identified as having other properties in addition to its key role in glycolysis. The ability of GAPDH to bind to numerous extracellular matrices, modulation of host-immune responses, a role in virulence and surface location has prompted numerous investigators to postulate that GAPDH may be a good vaccine candidate for protection against numerous pathogens. Although immune responses against GAPDH have been described for many microorganisms, vaccines containing GAPDH have been successfully tested in few cases including those against the trematode-Schistosoma mansoni, the helminth-Enchinococcus multilocularis; the nematode filaria- Litomosoides sigmodontis; fish pathogens such as Aeromonas spp., Vibrio spp., Edwarsiella spp., and Streptococcus iniae; and environmental streptococci, namely, Streptococcus uberis and Streptococcus dysgalactiae. Before GAPDH-based vaccines are considered viable options for protection against numerous pathogens, we need to take into account the homology between the host and pathogen GAPDH proteins to prevent potential autoimmune reactions, thus protective GAPDH epitopes unique to the pathogen protein must be identified.

The secreted fructose 1,6-bisphosphate aldolase as a broad spectrum vaccine candidate against pathogenic bacteria in aquaculture

The development of aquaculture has been hampered by different aquatic pathogens that can cause edwardsiellosis, vibriosis, or other diseases. Therefore, developing a broad spectrum vaccine against different fish diseases is necessary. In this study, fructose 1,6-bisphosphate aldolase (FBA), a conserved enzyme in the glycolytic pathway, was demonstrated to be located in the non-cytoplasmic components of five aquatic pathogenic bacteria and exhibited remarkable protection and cross-protection against these pathogens in turbot and zebrafish. Further analysis revealed that sera sampled from vaccinated turbot had a high level of specific antibody and bactericidal activity against these pathogens. Meanwhile, the increased expressions of immune response-related genes associated with antigen recognition and presentation indicated that the adaptive immune response was effectively aroused. Taken together, our results suggest that FBA can be utilized as a broad-spectrum vaccine against various pathogenic bacteria of aquaculture in the future.

Design and evaluation of a tandemly arranged outer membrane protein U (OmpU) multi-epitope as a potential vaccine antigen against Vibrio mimicus in grass carps (Ctenopharyngodon idella)

Vibrio mimicus (V. mimicus) is an extracellular pathogen that causes ascites disease in aquatic animals. In our previous studies, the outer membrane protein U (OmpU) of V. mimicus has been proven to be a protective antigen, and several mimotopes of the protein were identified. Here, a tandemly arranged multi-epitope peptide (named 6EPIS) was designed with six mimotopes and heterologously expressed. Then, the immunoprotection efficacy of recombinant 6EPIS (r6EPIS) was evaluated in grass carps (Ctenopharyngodon idella) by determining relative percentage survival (RPS), specific immunoglobulin M (IgM) antibody titer, and transcriptional levels of immune-related genes of inoculated grass carps. Fish vaccinated with r6EPIS via intraperitoneal injection exhibited 85.71% RPS over the control, when challenged with V. mimicus. The enzyme-linked immunosorbent assay titer of specific IgM antibodies against r6EPIS reached 1:12,800 on Day 28 post the primary immunization. After 28 days post immunization, the transcriptional level of total IgM mRNA was significantly higher in the r6EPIS-vaccinated fish than in those vaccinated with recombinant OmpU, inactivated bacterin and rHis tag peptide (p<0.05). In addition, the transcription levels of interleukin-1β and tumor necrosis factor-α genes in the spleen and head kidney of r6EPIS-vaccinated fish were significantly increased during the period of immunization and early phase of infection, while the transcription level of interleukin-10 gene was significantly increased from Day 3 to 7 post challenge, compared to the control level. These results show that r6EPIS was highly immunogenic and could elicit strong protective immune responses. It may be an attractive vaccine candidate against V. mimicus infection.