Identification of DLD, by immunoproteomic analysis and evaluation as a potential vaccine antigen against three Vibrio species in Epinephelus coioides

Siglec7 functions as an inhibitory receptor of non-specific cytotoxic cells and can regulate the innate immune responses in a primitive vertebrate (Oreochromis niloticus)

In mammals, siglec7, an integral component of the siglecs, is principally found on the surface of natural killer (NK) cells, macrophages, and monocytes, where it interacts with various pathogens to perform immunological regulatory activities. Nonetheless, the immune defense and mechanism of siglec7 in early vertebrates remain unknown. In this study, we identified siglec7 from Oreochromis niloticus (OnSiglec7) and revealed its immune functions. Specifically, OnSiglec7 was abundantly expressed in immune-related tissues of healthy tilapia and its transcription level was strongly activated after being challenged with A. hydrophila, S. agalactiae, and Poly: IC. Meanwhile, OnSiglec7 protein was purified and analyzed, which could recognize multiple pathogens through binding and agglutinating activity. Moreover, OnSiglec7-positive cells were mainly distributed in non-specific cytotoxic cells (NCC) of tilapia HKLs and showed cell membrane localization. Furthermore, OnSiglec7 blockage affected multiple innate immune responses (inflammation, apoptosis, and pyroptosis process) by regulating the activation of MAPK, NF-κB, TLR, and JAK-STAT pathways. Finally, OnSiglec7 blockage also greatly enhanced the cytotoxic effect of tilapia NCC. Summarily, this study uncovers immune functions and mechanisms of siglec7 in primitive vertebrates, thereby enhancing our understanding of the systemic evolution and ancient functions of other siglecs within the host's innate immune system (to our knowledge).

Field Efficacy of a Feed-Based Inactivated Vaccine against Vibriosis in Cage-Cultured Asian Seabass, Lates calcarifer, in Malaysia

Vibrio spp. are important aquaculture pathogens that cause vibriosis, affecting large numbers of marine fish species. This study determines the field efficacy of a feed-based inactivated vaccine against vibriosis in cage-cultured Asian seabass. A total of 4800 Asian seabass, kept in a field environment, were separated equally into two groups (vaccinated and non-vaccinated) in duplicate. Fish of Group 1 were orally administered the feed-based vaccine on weeks 0 (prime vaccination), 2 (booster), and 6 (second booster) at 4% body weight, while the non-vaccinated fish of Group 2 were fed with a commercial formulated pellet without the vaccine. Fish gut, mucus, and serum were collected, the length and weight of the fish were noted, while the mortality was recorded at 2-week intervals for a period of 16 weeks. The non-specific lysozyme activities were significantly (p < 0.05) higher in the fish of Group 1 than the non-vaccinated fish of Group 2. Similarly, the specific IgM antibody levels in serum and mucus were significantly (p < 0.05) higher in Group 1 than in Group 2, as seen in the second week, with the highest level 8 weeks after primary immunization. At week 16, the growth performance was significantly (p < 0.05) better in Group 1 and showed lower bacterial isolation in the gut than Group 2. Despite the statistical insignificance (p > 0.05), the survival rate was slightly higher in Group 1 (71.3%) than Group 2 (67.7%). This study revealed that feed-based vaccination improves growth performance, stimulates innate and adaptive immune responses, and increases protection of cultured Asian seabass, L. calcarifer, against vibriosis.

Development of Recombinant Dihydrolipoamide Dehydrogenase Subunit Vaccine against Vibrio Infection in Large Yellow Croaker

Large yellow croaker (Larimichthys crocea), an economically important marine fish in China, has suffered from serious vibriosis, which has resulted in great economic losses for the large yellow croaker industry. Vaccination has been considered to be a safe and effective method to prevent and control vibriosis. However, due to the complex diversity and serotypes of the Vibrio genus, the progress of Vibrio vaccine development is still slow. In this study, we prepared recombinant Vibrio dihydrolipoamide dehydrogenase (rDLD) protein and investigated its potential as a candidate to be a subunit vaccine against Vibrio. The lysozyme activity and the rDLD-specific antibody level in sera of large yellow croakers immunized with rDLD were significantly higher than those in the control group, and the transcript levels of proinflammatory cytokines (IL-6, IL-8, IL-1β), MHC IIα/β, CD40, CD8α, IL-4/13A, and IL-4/13B were significantly up-regulated in the spleen and head kidney of large yellow croakers immunized with rDLD, suggesting that rDLD could induce both specific and nonspecific immune responses in this species. In addition, rDLD protein increased the survival rate of large yellow croakers against Vibrio alginolyticus and Vibrio parahaemolyticus, with the relative percent of survival (RPS) being 74.5% and 66.9%, respectively. These results will facilitate the development of a potential subunit vaccine against Vibrio in large yellow croaker aquaculture.

Laboratory and Field Assessments of Oral Vibrio Vaccine Indicate the Potential for Protection against Vibriosis in Cultured Marine Fishes

Vibriosis is one of the most common threats to farmed grouper; thus, substantial efforts are underway to control the disease. This study presents an oral vaccination against multiple Vibrio spp. in a marine fish with double booster immunisation. The Vibrio harveyi strain VH1 vaccine candidate was selected from infected groupers Epinephelus sp. in a local farm and was formalin inactivated and combined with commercial feed at a 10% ratio (v/w). A laboratory vaccination trial was conducted for seventy days. The induction of IgM antibody responses in the serum of Asian seabass Lates calcarifer immunised with the oral Vibrio harveyi strain VH1 was significantly (p < 0.05) increased as early as week one post-primary vaccination. Subsequent administration of the first and second booster for 5 consecutive days, starting on days 14 and 42, respectively, improved the specific antibody level and reached a highly significant (p < 0.05) value at days 35 and 49 before slightly decreasing from day 56 onwards. Antibody titres of the control unvaccinated group remained relatively stable and low throughout the experimental period. At the end of the 70-day vaccination trial, 23 days post final boost, an intraperitoneal challenge with a field strain of Vibrio harveyi, V. alginolyticus, and V. parahaemolyticus was carried out. Our challenge study showed that oral Vibrio harveyi strain VH1 vaccine candidate could induce significant protection, with an RPS of 70–80% against different Vibrio species. Thereafter, a field trial was conducted in a mariculture farm to study the effect of field vaccination using the oral Vibrio harveyi strain VH1 vaccine candidate. A total of 3000 hybrid grouper juveniles were divided into two groups in triplicate. Fish of Group 1 were not vaccinated, while Group 2 were vaccinated with the feed-based vaccine. Vaccinations were carried out on days 0, 14, and 42 via feeding the fish with the vaccine at 4% body weight for 5 consecutive days. At the end of the study period, the fish survival rate was 80% for the vaccinated group, significantly (p < 0.05) higher than the 65% seen in the control unvaccinated group. Furthermore, the vaccinated fish showed significantly (p < 0.05) better growth performances. Therefore, the oral Vibrio vaccine from the inactivated Vibrio harveyi strain VH1 is a potential versatile vaccine candidate that could stimulate good immune responses and confer high protection in both Asian seabass, Lates calcarifer, and farm hybrid grouper Epinephelus fuscoguttatus × Epinephelus lanceolatus.

Mycoplasma synoviae dihydrolipoamide dehydrogenase is an immunogenic fibronectin/plasminogen binding protein and a putative adhesin

Mycoplasma synoviae (M. synoviae) is an important avian pathogen that causes arthritis and airsacculitis in young chickens and turkeys. Infection by M. synoviae results in considerable economic losses to the poultry industry worldwide. Cytoadherence is a crucial stage during mycoplasma infection. Dihydrolipoamide dehydrogenase (PdhD) is a flavin-dependent enzyme that is critical for energy metabolism and redox balance. To date, its role in cytoadherence is poorly understood. In this study, recombinant PdhD from M. synoviae (rMSPdhD) was expressed in the supernatant component of E. coli BL21 and rabbit anti-rMSPdhD serum was prepared. rMSPdhD was shown to be an immunogenic protein by immunoblot assays, while the mycoplasmacidal assay revealed that the rabbit anti-rMSPdhD serum had a high complement-dependent mycoplasmacidal rate (88.5 %). Using a suspension immunofluorescence assay and subcellular localization analysis, MSPdhD was shown to be a surface-localized protein distributed in both the cytoplasm and cell membrane of M. synoviae. The enzymatic activity of rMSPdhD was determined by measuring its ability to reduce lipoamide to dihydrolipoamide and convert NADH to NAD⁺. Using an indirect immunofluorescence assay, rMSPdhD was shown to adhere to DF-1 chicken embryo fibroblast cells. Furthermore, the attachment of M. synoviae to DF-1 cells was significantly inhibited by rabbit anti-rMSPdhD serum. Western blot and ELISA binding assays confirmed that rMSPdhD also bound to fibronectin (Fn) and plasminogen (Plg) in a dose-dependent manner. In conclusion, our data show that MSPdhD is not only a biological enzyme, but also an immunogenic surface-exposed protein that can bind to Fn and Plg as well as adhere to host cells. In addition, we show that rabbit anti-rMSPdhD serum can inhibit the adhesion of M. synoviae to DF-1 cells and has a significant complement-dependent bactericidal activity. Our findings suggest that MSPdhD may be involved in the pathogenesis of M. synoviae.

Omics Strategies in Current Advancements of Infectious Fish Disease Management

Aquaculture is an important industry globally as it remains one of the significant alternatives of animal protein source supplies for humankind. Yet, the progression of this industry is being dampened by the increasing rate of fish mortality, mainly the outbreak of infectious diseases. Consequently, the regress in aquaculture ultimately results in the economy of multiple countries being affected due to the decline of product yields and marketability. By 2025, aquaculture is expected to contribute approximately 57% of fish consumption worldwide. Without a strategic approach to curb infectious diseases, the increasing demands of the aquaculture industry may not be sustainable and hence contributing to the over-fishing of wild fish. Recently, a new holistic approach that utilizes multi-omics platforms including transcriptomics, proteomics, and metabolomics is unraveling the intricate molecular mechanisms of host-pathogen interaction. This approach aims to provide a better understanding of how to improve the resistance of host species. However, no comprehensive review has been published on multi-omics strategies in deciphering fish disease etiology and molecular regulation. Most publications have only covered particular omics and no constructive reviews on various omics findings across fish species, particularly on their immune systems, have been described elsewhere. Our previous publication reviewed the integration of omics application for understanding the mechanism of fish immune response due to microbial infection. Hence, this review provides a thorough compilation of current advancements in omics strategies for fish disease management in the aquaculture industry. The discovery of biomarkers in various fish diseases and their potential advancement to complement the recent progress in combatting fish disease is also discussed in this review.

Identification of novel vaccine candidates in the whole-cell Aeromonas hydrophila biofilm vaccine through reverse vaccinology approach

Biofilm vaccine has been recognised as one of the successful strategy to reduce the Aeromonas hydrophila infection in fish. But, the vaccine contains the protective and non-protective proteins, which may lead to show altered heterologous adaptive immunity response. Moreover, cross protection and effectiveness of previously developed biofilm vaccine was not tested against different geographical A. hydrophila isolates. Therefore, in the present study, whole-cell A. hydrophila biofilm vaccine was evaluated in rohu, vaccinated group showed increased antibody titer and protection against the different geographical A. hydrophila isolates namely KAH₁ and AAH₂ with 78.9% and 84.2% relative percentage survival, respectively. In addition, by using the immune sera of biofilm vaccinated group, a total of six protective proteins were detected using western blot assay. Further, the same proteins were identified by nano LC-MS/MS method, a total of fourteen candidate proteins showing the immunogenic property including highly expressed OMP's tolC, bamA, lamb, AH4AK4_2542, AHGSH82_029580 were identified as potential vaccine candidates. The STRING analysis revealed that, top candidate proteins identified may potentially interact with other intracellular proteins; involved in ribosomal and (tricarboxylic acid) TCA pathway. Importantly, all the selected vaccine candidate proteins contain the B-cell epitope region. Finally, the present study concludes that, whole-cell A. hydrophila biofilm vaccine able to protect the fish against the different geographical A. hydrophila isolates. Further, through reverse vaccinology approach, a total of fourteen proteins were identified as potential vaccine candidates against A. hydrophila pathogen.

pH-Controlled Release of Antigens Using Mesoporous Silica Nanoparticles Delivery System for Developing a Fish Oral Vaccine

The development of effective vaccines and delivery systems in aquaculture is a long-term challenge for controlling emerging and reemerging infections. Cost-efficient and advanced nanoparticle vaccines are of tremendous applicability in prevention of infectious diseases of fish. In this study, dihydrolipoamide dehydrogenase (DLDH) antigens of Vibrio alginolyticus were loaded into mesoporous silica nanoparticles (MSN) to compose the vaccine delivery system. Hydroxypropyl methylcellulose phthalate (HP55) was coated to provide protection of immunogen. The morphology, loading capacity, acid-base triggered release were characterized and the toxicity of nanoparticle vaccine was determined in vitro. Further, the vaccine immune effects were evaluated in large yellow croaker via oral administration. In vitro studies confirmed that the antigen could be stable in enzymes-rich artificial gastric fluid and released under artificial intestinal fluid environment. In vitro cytotoxicity assessment demonstrated the vaccines within 120 μg/ml have good biocompatibility for large yellow croaker kidney cells. Our data confirmed that the nanoparticle vaccine in vivo could elicit innate and adaptive immune response, and provide good protection against Vibrio alginolyticus challenge. The MSN delivery system prepared may be a potential candidate carrier for fish vaccine via oral administration feeding. Further, we provide theoretical basis for developing convenient, high-performance, and cost-efficient vaccine against infectious diseases in aquaculture.

Age-Related Differences in Molecular Profiles for Immune Checkpoint Blockade Therapy

Immune checkpoint blockade (ICB) therapies have significantly improved the prognosis and shown considerable promise for cancer therapy; however, differences in ICB treatment efficacy between the elderly and young are unknown. We analyzed the studies enrolled in the meta-analysis using the deft approach, and found no difference in efficacy except melanoma patients receiving anti–PD-1 therapy. Similarly, higher treatment response rate and more favorable prognosis were observed in elderly patients in some cancer types (e.g., melanoma) with data from published ICB treatment clinical trials. In addition, we comprehensively compared immunotherapy-related molecular profiles between elderly and young patients from public trials and The Cancer Genome Atlas (TCGA), and validated these findings in several independent datasets. We discovered a divergent age-biased immune profiling, including the properties of tumors (e.g., tumor mutation load) and immune features (e.g., immune cells), in a pancancer setting across 27 cancer types. We believe that ICB treatment efficacy might vary depending on specific cancer types and be determined by both the tumor internal features and external immune microenvironment. Considering the high mutational properties in elderly patients in many cancer types, modulating immune function could be beneficial to immunotherapy in the elderly, which requires further investigation.

TLR4 Agonist Combined with Trivalent Protein JointS of Streptococcus suis Provides Immunological Protection in Animals

Streptococcus suis (S. suis) serotype 2 (SS2) is the causative agent of swine streptococcosis and can cause severe diseases in both pigs and humans. Although the traditional inactive vaccine can protect pigs from SS2 infection, novel vaccine candidates are needed to overcome its shortcomings. Three infection-associated proteins in S. suis—muramidase-released protein (MRP), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and DLD, a novel putative dihydrolipoamide dehydrogenase—have been previously identified by immunoproteomic assays. In this study, the effective immune protection of the recombinant trivalent protein GAPDH-MRP-DLD (JointS) against SS2, SS7, and SS9 was determined in zebrafish. To improve the immune efficacy of JointS, monophosphoryl lipid A (MPLA) as a TLR4 agonist adjuvant, which induces a strong innate immune response in the immune cells of mice and pigs, was combined with JointS to immunize the mice. The results showed that immunized mice could induce the production of a high titer of anti-S. suis antibodies; as a result, 100% of mice survived after SS2 infection. Furthermore, JointS provides good protection against virulent SS2 strain infections in piglets. Given the above, there is potential to develop JointS as a novel subunit vaccine for piglets to prevent infection by SS2 and other S. suis serotypes.

Functional characterization of T3SS C-ring component VscQ and evaluation of its mutant as a live attenuated vaccine in zebrafish (Danio rerio) model

Vibrio alginolyticus, a Gram-negative bacterium, has been recognized as an opportunistic pathogen in marine animals as well as humans. Type III secretion system (T3SS) is critical for pathogen virulence and disease development. However, no more information is known about the C-ring component VscQ and its physiological role. In this study, gene vscQ was cloned from V. alginolyticus wild-type strain HY9901 and the mutant strain HY9901ΔvscQ was constructed by the in-frame deletion method. The HY9901ΔvscQ mutant showed an attenuated swarming phenotype and a closely 4.6-fold decrease in the virulence to Danio rerio. However, the HY9901ΔvscQ mutant showed no difference in growth, biofilm formation and ECPase activity. HY9901ΔvscQ reduces the release of LDH, NO and caspase-3 activity of infected FHM cell, which are involved in fish cell apoptosis. Deletion of gene vscQ downregulates the expression level of T3SS-related genes including vscL, vopB, hop, vscO, vscK, vopD, vcrV and vopS and flagellum-related genes (flaA and fliG). And Danio rerio vaccinated via i.m injection with HY9901ΔvscQ induced a relative percent survival (RPS) value of 71% after challenging with the wild-type HY9901. Real-time PCR assays showed that vaccination with HY9901ΔvscQ enhanced the expression of immune-related genes, including TNF-α, TLR5, IL-6R, IgM and c/ebpβ in liver and spleen after vaccination, indicating that it is able to induce humoral and cell-mediated immune response in zebrafish. These results demonstrate that the HY9901ΔvscQ mutant could be used as an effective live vaccine to combat V. alginolyticus infection.

A T3SS Regulator Mutant of Vibrio alginolyticus Affects Antibiotic Susceptibilities and Provides Significant Protection to Danio rerio as a Live Attenuated Vaccine

Vibrio alginolyticus is a major cause of Vibriosis in farmed marine aquatic animals and has caused large economic losses to the Asian aquaculture industry in recent years. Therefore, it is necessary to control V. alginolyticus effectively. The virulence mechanism of V. alginolyticus, the Type III secretion system (T3SS), is closely related to its pathogenicity. In this study, the T3SS gene tyeA was cloned from V. alginolyticus wild-type strain HY9901 and the results showed that the deduced amino acid sequence of V. alginolyticus tyeA shared 75–83% homology with other Vibrio spp. The mutant strain HY9901ΔtyeA was constructed by Overlap-PCR and homologous recombination techniques. The HY9901ΔtyeA mutant exhibited an attenuated swarming phenotype and an ~40-fold reduction in virulence to zebrafish. However, the HY9901ΔtyeA mutant showed no difference in growth, biofilm formation and ECPase activity. Antibiotic susceptibility test was observed that wild and mutant strains were extremely susceptible to Amikacin, Minocycline, Gentamicin, Cefperazone; and resistant to oxacillin, clindamycin, ceftazidime. In contrast wild strains are sensitive to tetracycline, chloramphenicol, kanamycin, doxycycline, while mutant strains are resistant to them. qRT-PCR was employed to analyze the transcription levels of T3SS-related genes, the results showed that compared with HY9901 wild type, ΔtyeA had increased expression of vscL, vscK, vscO, vopS, vopN, vscN, and hop. Following vaccination with the mutant strain, zebrafish had significantly higher survival than controls following infection with the wild-type HY9901 (71.2% relative percent survival; RPS). Analysis of immune gene expression by qPCR showed that vaccination with HY9901ΔtyeA increased the expression of IgM, IL-1β, IL-6, and TNF-α in zebrafish. This study provides evidence of protective efficacy of a live attenuated vaccine targeting the T3SS of V. alginolyticus which may be facilitated by up-regulated pro-inflammatory and immunoglobulin-related genes.

Type F scavenger receptor expressed by endothelial cells (SREC)-II from Epinephelus coioides is a potential pathogen recognition receptor in the immune response to Vibrio parahaemolyticus infection

Scavenger receptors play a central role in defending against infectious diseases in mammals. However, the function of SRECII remains unknown in teleost fish. In this study, type F scavenger receptor expressed by endothelial cells-II (SRECII) cDNA sequence was first identified from Epinephelus coioides, named EcSRECII, which contained an N-terminal signal peptide, eight EGF/EGF-like cysteine-rich motifs and a C-terminal low-complexity region. The gene location maps revealed that EcSRECII has the conservation of synteny among selected species. Subcellular localization showed that EcSRECII was mainly located in the cytoplasm in HEK293T cells and GS cells. In healthy E. coioides, EcSRECII mRNA was highly expressed in spleen, skin, gill, thymus and head kidney. The relative EcSRECII mRNA expression after Vibrio parahaemolyticus infection was significantly up-regulated at 12 h in spleen, head kidney and thymus, but downregulated at 1 d in skin and reduced at 3 d and 1 w in spleen. Furthermore, overexpression of EcSRECII activated NF-κB and IFN-β signaling pathway in vitro. Taken together, these results indicated that EcSRECII could be as the potential pathogen recognition receptor for involving in bacterial infection by regulating innate immunity responses in E. coioides.

Acetylome profiling of Vibrio alginolyticus reveals its role in bacterial virulence

It is well known that lysine acetylation (Kace) modification is a common post-translational modification (PTM) that plays an important role in multiple biological and pathological functions in bacteria. However, few studies have focused on lysine acetylation modification in aquatic pathogens to date. In this study, the acetylome profiling of fish pathogen, Vibrio alginolyticus was investigated by combining affinity enrichment with LC MS/MS. A total of 2883 acetylation modification sites on 1178 proteins in this pathogen were identified. The Kace modification of several selected proteins were further validated by Co-immunocoprecipitation combined with Western blotting. Bioinformatics analysis showed that seven conserved motifs can be enriched among Kace peptides, and many of them were significantly enriched in metabolic processes such as biosynthesis of secondary metabolites, microbial metabolism in diverse environments, and biosynthesis of amino acids, which was similar to data previously published for V. parahaemolyticus. Moreover, we found at least 102 acetylation modified proteins predicted as virulence factors, which indicate the important role of PTM on bacterial virulence. In general, our results provide a promising starting point for further investigations of the biological role of lysine acetylation on bacterial virulence in V. alginolyticus. BIOLOGICAL SIGNIFICANCE: Lysine acetylation (Kace) modification, is well known to play important roles on diverse biological functions in prokaryotic cell, whereas few studies focused on aquatic pathogens to date. In this study, the acetylome profiling of fish pathogen, Vibrio alginolyticus was investigated by combining affinity enrichment with LC MS/MS. A total of 2883 acetylation modification sites on 1178 proteins in this pathogen were identified. The further bioinformatics analysis showed that seven conserved motifs can be enriched among Kace peptides, and many of them were significantly enriched in metabolic processes, which was similar to data previously published for V. parahemolyticus. Moreover, we found at least 102 acetylation modified proteins predicted as virulence factors, which indicate the important role of PTM on bacterial virulence. In general, our results provide a promising starting point for further investigations of the biological role of lysine acetylation on bacterial virulence in V. alginolyticus.

Survival and immune response of white shrimp Litopenaeus vannamei following single and concurrent infections with WSSV and Vibrio parahaemolyticus

The survival and immune responses of Litopenaeus vannamei were evaluated during white spot syndrome virus (WSSV) or Vibrio parahaemolyticus single and concurrent infections. The mortality, WSSV load, activities of 4 immune enzymes: acid phosphatase (ACP), alkaline phosphatase (AKP), peroxidase (POD) and superoxide dismutase (SOD), and the transcription of Evolutionarily Conserved Signaling Intermediate in Toll pathways of L.vannamei (LvECSIT) were quantified at 0, 3, 6, 12, 24, 48, 72 and 96 h post-infection (pi). The results showed: (i) the cumulative mortality of the co-infection group (WSSV and V. Parahaemolyticus 83%) was significantly lower than the WSSV infection group (97%) (P < 0.05) at 96 hpi; (ii) copies of WSSV in the co-infection group were significantly lower than that of the single infection group from 24 to 96 hpi (P < 0.05); (iii) ACP, AKP,POD and SOD activity in the gills of the co-infection group was higher than that of the WSSV group at12, 48 and 96 hpi (P < 0.05).The expression of LvECSIT mRNA in the co-infection group was significantly higher than in the WSSV infection group from 12 to 72 hpi (P < 0.05).The results indicate that proliferation of WSSV is inhibited by V.parahaemolyticus infection. In addition, infection with WSSV alone causes a significant reduction in some immune responses of shrimp than co-infection with WSSV and V.parahaemolyticus occurs at 26 °C. Third, LvECSIT, an essential member of TLR signaling pathway might play a crucial role in shrimp defense against WSSV - Vibrio co-infection.

Comparative Extracellular Proteomics of Aeromonas hydrophila Reveals Iron-Regulated Secreted Proteins as Potential Vaccine Candidates

In our previous study, several iron-related outer membrane proteins in Aeromonas hydrophila, a serious pathogen of farmed fish, conferred high immunoprotectivity to fish, and were proposed as potential vaccine candidates. However, the protective efficacy of these extracellular proteins against A. hydrophila remains largely unknown. Here, we identified secreted proteins that were differentially expressed in A. hydrophila LP-2 in response to iron starvation using an iTRAQ-based quantitative proteomics method. We identified 341 proteins, of which 9 were upregulated in response to iron starvation and 24 were downregulated. Many of the differently expressed proteins were associated with protease activity. We confirmed our proteomics results with Western blotting and qPCR. We constructed three mutants by knocking out three genes encoding differentially expressed proteins (Δorf01830, Δorf01609, and Δorf03641). The physiological characteristics of these mutants were investigated. In all these mutant strains, protease activity decreased, and Δorf01609, and Δorf01830 were less virulent in zebrafish. This indicated that the proteins encoded by these genes may play important roles in bacterial infection. We next evaluated the immune response provoked by the six iron-related recombinant proteins (ORF01609, ORF01830, ORF01839, ORF02943, ORF03355, and ORF03641) in zebrafish as well as the immunization efficacy of these proteins. Immunization with these proteins significantly increased the zebrafish immune response. In addition, the relative percent survival (RPS) of the immunized zebrafish was 50-80% when challenged with three virulent A. hydrophila strains, respectively. Thus, these extracellular secreted proteins might be effective vaccine candidates against A. hydrophila infection in fish.

Divergent immune roles of two fucolectin isoforms in Apostichopus japonicus

The F-type lectin (fucolectin) family represents a new group with innate immunity. In this study, two fucolectin isoforms (designated as AjFTL-1 and AjFTL-2) were identified in sea cucumber (Apostichopus japonicus) through rapid amplification of cDNA ends. Full-length cDNAs of AjFTL-1 and AjFTL-2 measured 2134 and 1286 bp, encoding two secreted proteins comprising 317 and 181 amino acid residues, respectively. The signal peptide, l-fucose binding motif ("HX(26)RXDX(4)R/K") and cation binding sequence motif ("h2DGx") were conserved in AjFTL-1 and AjFTL-2. However, AjFTL-1 contains an additional complement control protein domain. Multiple sequence alignments supported that AjFTL-1 and AjFTL-2 are new members of the F-type lectin family. Tissues distribution analysis indicated that both AjFTL-1 and AjFTL-2 were widely expressed in all tested tissues, featuring differential expression patterns. Vibrio splendidus infection in vivo can significantly upregulate the mRNA transcripts of the two genes, with a larger magnitude observed in AjFTL-1. By contrast, lipopolysaccharide stimulation in vitro can markedly induce the expression level of AjFTL-2 but not that of AjFTL-1. Silencing AjFTL-2 by siRNA can suppress the AjNOS transcript, whereas injection of the recombinant protein of AjFTL-2 can significantly induce AjNOS expression. By contrast, the loss- and gain-of-function of AjFTL-1 caused no effect on the expression of AjNOS. Our present study provides evidence supporting that AjFTL-1 and AjFTL-2 play diverse roles in the innate immune defense of sea cucumbers toward bacterial infection.

Construction of a Vibrio alginolyticus hopPmaJ (hop) mutant and evaluation of its potential as a live attenuated vaccine in orange-spotted grouper (Epinephelus coioides)

Vibrio alginolyticus, a bacterial pathogen in fish and humans, expresses a type III secretion system (T3SS) that is critical for pathogen virulence and disease development. However, little is known about the associated effectors (T3SEs) and their physiological role. In this study, the T3SE gene hopPmaJ (hop) was cloned from V. alginolyticus wild-type strain HY9901 and the mutant strain HY9901Δhop was constructed by the in-frame deletion method. The results showed that the deduced amino acid sequence of V. alginolyticus HopPmaJ shared 78-98% homology with other Vibrio spp. In addition, the HY9901Δhop mutant showed an attenuated swarming phenotype and a 2600-fold decrease in the virulence to grouper. However, the HY9901Δhop mutant showed no difference in morphology, growth, biofilm formation and ECPase activity. Finally, grouper vaccinated via intraperitoneal (IP) injection with HY9901Δhop induced a high antibody titer with a relative percent survival (RPS) value of 84% after challenging with the wild-type HY9901. Real-time PCR assays showed that vaccination with HY9901Δhop enhanced the expression of immune-related genes, including MHC-Iα, MHC-IIα, IgM, and IL-1β after vaccination, indicating that it is able to induce humoral and cell-mediated immune response in grouper. These results demonstrate that the HY9901Δhop mutant could be used as an effective live vaccine to combat V. alginolyticus in grouper.

Marine yeast Yarrowia lipolytica improves the immune responses in Pacific red snapper (Lutjanus peru) leukocytes

The climatic conditions in saltern saline environments allows the growth of microorganisms adapted to these peculiar ambient and could represent a promising source of new bioactive compounds that could have applications on as animal food supplements, including aquaculture. In this study, we evaluated the role of Yarrowia lipolytica N-6 isolate, from a hypersaline natural environment (Guerrero Negro, Baja California Sur, Mexico), as immunostimulant of the non-specific immune response of head-kidney and spleen Pacific red snapper (Lutjanus peru) leukocytes after challenge with Vibrio parahaemolyticus. In this study, the presence of Y. lipolytica reduced considerably the V. parahaemolyticus load in spleen leukocytes. In vitro assays using head-kidney and spleen leukocytes showed that the response to V. parahaemolyticus infection reveled that leukocyte pre-incubated with Y. lipolytica N-6 significantly increased the non-specific immune response such as respiratory burst, phagocytic activity, NO and MPO activities follow by an increase in SOD and CAT activities, and at the same time inhibited leukocyte apoptosis caused by V. parahaemolyticus. Moreover, Y. lipolytica N-6 incubation also regulated the transcription of genes related to immunity (IL-1β) or oxidative stress (MnSOD, icCu/ZnSOD or CAT) in leukocytes. These results strongly support the idea that the extreme yeast Y. lipolytica N-6 isolate can stimulate the non-specific immune parameters and the antioxidant immune mechanism in head-kidney and spleen Pacific red snapper leukocytes and could be used as potential immunostimulant.

Proteogenomic Analysis and Discovery of Immune Antigens in Mycobacterium vaccae

Tuberculosis (TB) is one of the leading causes of death worldwide, especially in developing countries. Neonatal BCG vaccination occurs in various regions, but the level of protection varies in different populations. Recently, Mycobacterium vaccae is found to be an immunomodulating therapeutic agent that could confer a significant level of protection against TB. It is the only vaccine in a phase III trial from WHO to assess its efficacy and safety in preventing TB disease in people with latent TB infection. However, the mechanism of immunotherapy of M. vaccae remains poorly understood. In this study, the full genome of M. vaccae was obtained by next-generation sequencing technology, and a proteogenomic approach was successfully applied to further perform genome annotation using high resolution and high accuracy MS data. A total of 3,387 proteins (22,508 unique peptides) were identified, and 581 proteins annotated as hypothetical proteins in the genome database were confirmed. Furthermore, 38 novel protein products not annotated at the genome level were detected and validated. Additionally, the translational start sites of 445 proteins were confirmed, and 98 proteins were validated through extension of their translational start sites based on N terminus-derived peptides. The physicochemical characteristics of the identified proteins were determined. Thirty-five immunogenic proteins of M. vaccae were identified by immunoproteomic analysis, and 20 of them were selected to be expressed and validated by Western blot for immunoreactivity to serum from patients infected with M. tuberculosis The results revealed that eight of them showed strong specific reactive signals on the immunoblots. Furthermore, cellular immune response was further examined and one protein displayed a higher cellular immune level in pulmonary TB patients. Twelve identified immunogenic proteins have orthologous in H37Rv and BCG. This is the first study to obtain the full genome and annotation of M. vaccae using a proteogenomic approach, and some immunogenic proteins that were validated by immunoproteomic analysis could contribute to the understanding of the mechanism of M. vaccae immunotherapy.

Immunogenicity and efficacy of DNA vaccine encoding antigenic AcfA via addition of the molecular adjuvant Myd88 against Vibrio alginolyticus in Epinephelus coioides

DNA vaccines had been widely used against microbial infection in animals. The use of molecular adjuvants to improve the immunogenicity of DNA vaccines has been increasingly studied in recent years. MyD88 is one of the adapter molecules to activate the signaling cascades and produces inflammatory mediators, and its immunological role and adjuvant potential which had been proved in mammals were rarely reported in fish species. In this study, plasmid pcMyD88 was constructed and the capacity of MyD88 as molecular adjuvant was explored by co-injecting with a DNA vaccine encoding AcfA against Vibrio alginolyticus infection in orange spotted grouper. The results suggested that it needed at least 7 days to transported DNA vaccine pcacfA or molecular adjuvant pcMyD88 from the injected muscle to kidney and spleens and stimulate host's immune system for later protection. The co-injection of pcMyD88 with DNA vaccine pcacfA could increase significantly specific antibody levels and the expression levels of the immune-related genes including MHCIα, MHCIIα, CD4, CD8α, IL-1β and TNFα. Furthermore, pcMyD88 enhanced the immunoprotection of pcacfA against V. alginolyticus infection, with the significantly higher RPS of 83.3% in pcMyD88 + pcacfA group compared with that of pcacfA alone (73.3%) at challenging test of 10 weeks post vaccination. Together, these results clearly demonstrate that MyD88 is an effective adjuvant for the DNA vaccine pcacfA in orange spotted grouper.

Enhancing gilthead seabream immune status and protection against bacterial challenge by means of antigens derived from Vibrio parahaemolyticus

In an attempt to control the proliferation of the pathogenic bacterium Vibrio parahaemolyticus in gilthead seabream (Sparus aurata), the immunostimulant effect of lysate and ToxA from this bacterium was evaluated. Fish were intraperitoneally injected twice (first injection, day 1 of the experiment; second injection, day 7) and sampled after one week (on days 8 and 15). Afterwards, all fish specimens were experimentally infected with V. parahaemolyticus and mortality was recovered for 1 week. Fish injected with lysate, ToxA and phosphate buffer saline (control) showed 100%, 50% and 0% survival, respectively, when challenged with the pathogen. Skin mucus immune parameters and immune-related gene expression in skin and spleen were also evaluated. The results showed that mucus immune parameters were enhanced in the lysate and ToxA groups compared with the values obtained for fish from the control group. Expression of IL-1β, TNF-α, C3 and IgM genes was significantly up-regulated in the lysate and ToxA groups, principally after infection with the bacterium. Interestingly, TLR5 gene expression increased in fish immunized with lysate. The most prominent histological characteristic in gut from infected fish was the presence of a great number of intraepithelial leucocytes as well as inflammation of the submucosa, while severe hydropic degeneration and hemosiderosis were detected in liver from infected fish. Injection of lysate or ToxA had a protective effect against the deleterious consequences of subsequent infection with V. parahaemolyticus in gut and liver. The findings underline the potential of lysate and ToxA as potent preventive antigens against this kind of vibriosis.

LptD is a promising vaccine antigen and potential immunotherapeutic target for protection against Vibrio species infection

Outer membrane proteins (OMPs) are unique to Gram-negative bacteria. Several features, including surface exposure, conservation among strains and ability to induce immune responses, make OMPs attractive targets for using as vaccine antigens and immunotherapeutics. LptD is an essential OMP that mediates the final transport of lipopolysaccharide (LPS) to outer leaflet. The protein in Vibrio parahaemolyticus was identified to have immunogenicity in our previous report. In this study, broad distribution, high conservation and similar surface-epitopes of LptD were found among the major Vibrio species. LptD was further revealed to be associated with immune responses, and it has a strong ability to stimulate antibody response. More importantly, it conferred 100% immune protection against lethal challenge by V. parahaemolyticus in mice when the mice were vaccinated with LptD, and this finding was consistent with the observation of efficient clearance of bacteria in vaccination mice. Strikingly, targeting of bacteria by the LptD antibody caused significant decreases in both the growth and LPS level and an increase in susceptibility to hydrophobic antibiotics. These findings were consistent with those previously obtained in lptD-deletion bacteria. These data demonstrated LptD is a promising vaccine antigens and a potential target for antibody-based therapy to protect against Vibrio infections.

Leukocyte susceptibility and immune response against Vibrio parahaemolyticus in Totoaba macdonaldi

Vibrio parahaemolyticus is a serious pathogen that affects aquaculture. Nonetheless, to the best of our knowledge, no studies have focused on its immunological implications in Totoaba macdonaldi. Thus, the early immune response to V. parahaemolyticus in juveniles of totoaba was studied at 24 h post-infection with an in vivo study. In addition, changes in cellular innate immune parameters - phagocytosis, respiratory burst activity and viability (annexin V/propidium iodide) - were evaluated in vitro in head-kidney, spleen and thymus leukocytes at 6 and 24 h after bacterial stimulation by flow cytometry. Simultaneously, the expression levels of two immune-relevant genes (IL-1β and IL-8) were measured by using real time PCR. During in vivo study, mRNA transcripts of IL-1β were highly expressed in spleen, thymus and intestine and down-regulated in liver after 24 h post-infection. IL-8 gene expression was upregulated in spleen, intestine and liver compared to that of non-infected fish and down-regulated in thymus after 24 h post-infection. Generally, the results showed a significant decrease in cellular immune responses during the infection, principally in phagocytic ability and respiratory burst. The survival or viability of stimulated leukocytes was significantly reduced causing necrosis and apoptosis, indicating a robust killing response by V. parahaemolyticus. Finally the in vitro analysis showed that transcript levels of IL-1β and IL-8 were up-regulated during stimulation with V. parahaemolyticus in head-kidney, spleen and intestine and down-regulated in thymus at any time of the experiment. Although V. parahaemolyticus has been reported to be an important pathogen for many aquatic organisms, to our knowledge this might be the first report of early-immune response in juvenile totoaba and these immune parameters may be reliable indicators and can be useful in the health control of this species.