Differential Antibody Responses to Outer Membrane Proteins Contribute to Differential Immune Protections between Live and Inactivated Vibrio parahemolyticus

Differential polyvalent passive immune protection of egg yolk antibodies (IgY) against live and inactivated Vibrio fluvialis in fish

Egg yolk antibodies (IgY) can be prepared in large quantities and economically, and have potential value as polyvalent passive vaccines (against multiple bacteria) in aquaculture. This study prepared live and inactivated Vibrio fluvialis IgY and immunized Carassius auratus prior to infection with V. fluvialis and Aeromonas hydrophila. The results showed that the two IgY antibodies hold effective passive protective rates against V. fluvialis and A. hydrophila in C. auratus. Further, the serum of C. auratus recognized the two bacteria in vitro, with a decrease in the bacteria content of the kidney. The phagocytic activity of C. auratus plasma was enhanced, with a decrease in the expression of inflammatory and antioxidant factors. Pathological sections showed that the kidney, spleen, and intestinal tissue structures were intact, and apoptosis and DNA damage decreased in kidney cells. Moreover, the immunoprotection conferred by the live V. fluvialis IgY was higher than that of the inactivated IgY. Addition, live V. fluvialis immunity induced IgY antibodies against outer membrane proteins of V. fluvialis were more than inactivated V. fluvialis immunity. Furthermore, heterologous immune bacteria will not cause infection, so V. fluvialis can be used to immunize chickens to obtain a large amount of IgY antibody. These findings suggest that the passive immunization effect of live bacterial IgY antibody on fish is significantly better than that of inactivated bacterial antibody, and the live V. fluvialis IgY hold potential value as polyvalent passive vaccines in aquaculture.

Escherichia coli Activate Extraintestinal Antibody Response and Provide Anti-Infective Immunity

The effects of intestinal microflora on extraintestinal immune response by intestinal cytokines and metabolites have been documented, but whether intestinal microbes stimulate serum antibody generation is unknown. Here, serum antibodies against 69 outer membrane proteins of Escherichia coli, a dominant bacterium in the human intestine, are detected in 141 healthy individuals of varying ages. Antibodies against E. coli outer membrane proteins are determined in all serum samples tested, and frequencies of antibodies to five outer membrane proteins (OmpA, OmpX, TsX, HlpA, and FepA) are close to 100%. Serum antibodies against E. coli outer membrane proteins are further validated by Western blot and bacterial pull-down. Moreover, the present study shows that OstA, HlpA, Tsx, NlpB, OmpC, YfcU, and OmpA provide specific immune protection against pathogenic E. coli, while HlpA and OmpA also exhibit cross-protection against Staphylococcus aureus infection. These finding indicate that intestinal E. coli activate extraintestinal antibody responses and provide anti-infective immunity.

Azithromycin alters Colony Stimulating Factor-1R (CSF-1R) expression and functional output of murine bone marrow-derived macrophages: A novel report

Antibiotic treatment may lead to side effects that require mechanistic explanation. We investigated the effect of azithromycin (AZM) treatment on bone marrow-derived macrophage (Mφ) generation, their functional output, and the subsequent effect on bacterial clearance in a mouse model of S. flexneri infection. To our fascination, AZM increased PU.1, C/EBPβ, CSF-1R/pCSF-1R expressions leading to M2-skewed in vitro BMDM generation. Altered Mφ-functions like- phagocytosis, oxidative stress generation, inflammasome-activation, cytokine release, and phenotype (pro-inflammatory-M1, anti-inflammatory-M2) even in the presence of infection were observed with AZM treatment. AZM increased CD206, egr2, arg1 (M2-marker) expression and activity while reducing CD68, inducible nitric oxide (iNOS) expression, and activity (M1-marker) in Mφs during infection. Pro-inflammatory cytokines (TNF-α, IL-12, IL-1β) were reduced and anti-inflammatory IL-10 release was augmented by AZM-treated-iMφs (aiMφs) along with decreased asc, nlrp3, aim2, nlrp1a, caspase1 expressions, and caspase3 activity signifying that aMφs/aiMφs were primed towards an anti-inflammatory phenotype. Interestingly, CSF-1R blockade increased NO, IL-12, TNF-α, IL-1β, decreased TGF-β release, and CD206 expression in aiMφs. T-cell co-stimulatory molecule cd40, cd86, and cd80 expressions were decreased in ai/aM1-Mφs and co-cultured CD8+, CD4+ T-cells had decreased proliferation, t-bet, IFN-γ, IL-17, IL-2 but increased foxp3, TGF-β, IL-4 which were rescued with CSF-1R blockade. Thus AZM affected Mφ-functions and subsequent T-cell responses independent of its antibacterial actions. This was validated in the balb/c model of S. flexneri infection. We conclude that AZM skewed BMDM generation to anti-inflammatory M2-like via increased CSF-1R expression. This warrants further investigation of AZM-induced altered-Mφ-generation during intracellular infections.

Fructose potentiates the protective efficiency of live Edwardsiella tarda cell vaccine

Vaccination is an effective measure to prevent infection by pathogens. Live vaccines have higher protective efficacy than inactivated vaccines. However, how live vaccines interact with the host from a metabolic perspective is unknown. The present study aimed to explore whether a live Edwardsiella tarda vaccine regulates host metabolism and whether this regulation is related to the protective efficacy of the vaccine. Therefore, a gas chromatography mass spectrometry (GC-MS)-based metabolomics approach was used to investigate the metabolomic profile of mice serum after vaccination with live E. tarda vaccine. Fructose was identified as a key biomarker that contributes to the immune protection induced by the live vaccine. Moreover, co-administration of exogenous fructose and the live vaccine synergistically promoted survival of mice and fish after bacterial challenge. These results indicate that metabolites, especially fructose, can potentiate the live E. tarda vaccine to increase its protective efficiency.

Strategies for Prevention and Control of Vibriosis in Asian Fish Culture

It is estimated that vibriosis account for about half of the economic losses in Asian fish culture. Consequently, the prevention and control of vibriosis is one of the priority research topics in the field of Asian fish culture disease. Relevant measures have been proposed to control some Vibrios that pose a threat to Asian fish culture, but there are currently only a few effective vaccines available to combat these Vibrios. The purpose of our review is to sum up the main prevention methods and the latest control strategies of seven Vibrio species that cause great harm to Asian aquaculture, including Vibrio harveyi, Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio mimicus, Vibrio anguillarum, Vibrio alginolyticus and Vibrio cholerae. Strategies such as antibiotics, probiotics, bacteriophages, antimicrobials from plants and other natural sources, as well as vaccines, are compared and discussed here. We expect this review will provide some new views and recommendations for the future better prevention and control of vibriosis in Asian fish culture.

Taurine promotes Oreochromis niloticus survival against Edwardsiella tarda infection

Edwardsiella tarda represents one of the most important pathogens that infects a variety of hosts including aquatic animals and humans. The outbreak of E. tarda infection is frequently reported in aquaculture that causes huge economic loss. Due to the widespread of antibiotic resistance, available antibiotics to treat bacterial infection are limited. Therefore, enhancing aquatic animals to survive upon E. tarda infection become an urgent issue. In this study, we profiled the metabolomic change of tilapia in-between the dying and survival fish upon E. tarda infection. The dying and survival fish mounts differential metabolic response, from which we identify a key metabolite, taurine, whose abundance is increased in both the survival group and the dying group but is more significant in the survival group. Exogenous taurine increases tilapia survival rate by 37.5% upon E. tarda infection. Further quantitative PCR analysis demonstrate taurine increases the expression of immune genes in liver, spleen and head kidney. Therefore, our study shows a new strategy to enhance fish immune response against bacterial infection.

Synthesis of Escherichia coli OmpA Oral Nanoparticles and Evaluation of Immune Functions against the Major Etiologic Agent of Cow Mastitis

Escherichia coli is a major etiologic agent of cow mastitis, a condition that results in huge economic losses. There is a lack of an oral vaccine for cow mastitis. Previous studies have confirmed that the outer membrane protein A (OmpA) of E. coli is immunogenic and can be used for vaccine design. In the present study, OmpA was encapsulated into nanoparticles (NP-OmpA) for an oral vaccine for cow mastitis. Methods: OmpA was purified with Ni-NTA flow resin and encapsulated with chitosan (CS) to prepare NP-OmpA nanoparticles. The gastrointestinal tract was simulated in vitro (PBS, pH 1.2) to measure the protein release rate. The optimal preparation conditions for NP-OmpA were determined by analyzing the concentrations of OmpA and CS, magnetic mixing speed, mixing time, and the ratio of tripolyphosphate (TPP)/CS (w/w). NP-OmpA safety was assessed by function factors and histopathological examination of livers and kidneys. The immune activity of NP-OmpA was determined using qRT-PCR to assess immune-related gene expression, leukocyte phagocytosis of Staphylococcus aureus, ELISA to evaluate antiserum titer and immune recognition of E. coli, and the organ index. The immune protection function of NP-OmpA was assessed by the protection rate of NP-OmpA to E. coli in mice, qRT-PCR for inflammation-related gene expression, assay kits for antioxidant factors, and visceral injury in the histopathological sections. Results: NP-OmpA nanoparticles had a diameter of about 700 nm, loading efficiency (LE) of 79.27%, and loading capacity (LC) of 20.31%. The release rate of NP-OmpA (0~96 h) was less than 50% in vitro. The optimal preparation conditions for NP-OmpAs were OmpA protein concentration of 2 mg/mL, CS concentration of 5 mg/mL, TPP/CS (w/w) of 1:1, magnetic mixing speed of 150 r/min, and mixing time of 15 min. Histopathological sections and clinical analytes of uric acid (UA), creatinine (Cr), alanine aminotransferase (ALT), aspartate transaminase (AST), catalase (CAT), glutathione (GSH), and malondialdehyde (MDA) showed NP-OmpA did not damage mice livers or kidneys. NP-OmpA could enhance the immune-related gene expression of IFN-γ and HSP70 in the spleen, liver, and kidney and the leukocyte phagocytosis of S. aureus. The antiserum titer (1:3200) was obtained from mice immunized with NP-OmpA, which had an immune recognition effect to E. coli. The immune protection rate of NP-OmpA was 71.43% (p < 0.05) to E. coli. NP-OmpA could down-regulate the inflammation-related gene expression of TNF-a, IL-6, and IL-10 in the spleen, liver, and kidney, and the antioxidant factors MDA and SOD in the liver, and reduce injury in the liver and kidney of mice induced by E. coli. Conclusions: A novel NP-OmpA nanoparticle was encapsulated, and the optimal preparation conditions were determined. The NP-OmpA was safe and had good immune functions. They are expected to induce a response that resists infection with the major etiologic agent (E. coli) of cow mastitis.

Analysis of virulence and immunogenic factors in Aeromonas hydrophila: Towards the development of live vaccines

Aeromonas hydrophila, a bacterium that is widespread in aquatic environments, is responsible for causing haemorrhagic disease in both aquatic and terrestrial species. With the purpose of developing a live vaccine, herein we have investigated nine strains of A. hydrophila (Ah-01 to Ah-09) isolated from diseased fish. A study of virulence factors that contribute to pathogenicity and immunogenicity in the host Cyprinus carpio suggests that the presence of β-hly, act and fla genes contribute to pathogenesis: strains Ah-01, Ah-02 and Ah-03 (β-hly⁺ /act⁺ /fla⁺ genotype) were highly pathogenic to C. carpio, whereas Ah-05 and Ah-06 (β-hly^- /act^- /fla^- genotype) showed weak pathogenicity. Accordingly, Ah-02 and Ah-03 were selected to prepare inactivated vaccines, whereas Ah-05 and Ah-06 were chosen as live vaccines. Ah-06 live vaccine was found to have the best protective efficacy, with a protective rate of about 85%, whereas rates of other vaccines were significantly lower, in the range 37%-59%. In addition, DNA vaccines based on genes altA, aha and omp showed immune protection rates of 25%, 37.5% and 75%, respectively. Our data demonstrate that the β-hly^- /act^- /fla^- /altA⁺ /aha⁺ /omp⁺ genotype has weak pathogenicity and high immunogenicity, and provide a simple and effective way to screen for live A. hydrophila vaccines.

Evaluation of Immunogenicity, Protective Immunity on Aquaculture Pathogenic Vibrio and Fermentation of Vibrio alginolyticus Flagellin FlaC Protein

Background:

Vibrio are the main pathogenic bacteria in aquaculture. The flagellin protein C (FlaC) of Vibrio alginolyticus has good immunogenicity and the prospect of potential application in a vaccine.

Objectives:

We aimed to evaluate the immunogenicity, protective immunity, and prokaryotic expression fermentation of V. alginolyticus FlaC protein for the vaccine in aquaculture.

Material and Methods:

A molecular cloning method was used to construct the expression strain of FlaC protein, and the protein was purified with Ni-affinity chromatography. Polyclonal antiserum was prepared via mice immunized with the FlaC protein. The Western blot and enzyme-linked immunosorbent assay (ELISA) were used to check the specificity and titre of the antiserum. ELISA and pull-down assay detected the interaction between FlaC protein antiserum and Vibrio. The immune protection function of FlaC protein was detected with mice actively immunized with FlaC protein and challenged by V. alginolyticus and V. parahaemolyticus. The optimal expression conditions for FlaC protein were detected using an L₉(3⁴) orthogonal design model.

Results:

The expression strain of FlaC protein was obtained successfully, and purified FlaC protein was prepared using a mice polyclonal antibody. The FlaC protein antiserum held a high specificity, and the titre was 13200. The antiserum directly interacted with V. alginolyticus and V. parahaemolyticus, and the FlaC protein demonstrated a significant immune protection function (50%) against V. alginolyticus infection and some immune protection function (41.66%) against V. parahaemolyticus. The optimal expression conditions for FlaC protein included a strain OD₆₀₀ value of 0.8, final isopropyl-β-d-thiogalactoside (IPTG) concentration of 0.1 mmol/L, an inducing time of 8 hours, and an inducing temperature of 28°C.

Conclusions:

This study showed that the FlaC protein possesses a significant immunogenicity and immune protection effect and obtained the optimal fermentation conditions. It is expected to be a potential vaccine against V. alginolyticus and V. parahaemolyticus.

Identification and innate immunity mechanism of protective immunogens from extracellular proteins of Edwardsiella tarda

One of the most important emerging pathogens in the aquaculture industry is Edwardsiella tarda, and it causes extensive losses in farmed fish globally. The identification of protective immunogens against E. tarda is increasingly valued. We previously investigated 20 recombinant proteins of 38 E. tarda extracellular secretory proteins and identified 10 as protective immunogens in a zebrafish model. Here, we clone 10 of the remaining 18 genes, and the resulting recombinant proteins are used for evaluation of immune protection. ETAE_2147 (FliK), ETAE_0654 (PpdD), and ETAE_3259 (DamX) are identified as protective immunogens. Furthermore, their protection mechanism is explored by the detection of innate immunity genes encoding IL-1b, IL-6, IL-8, C3b, and NF-κB. The three protective immunogens stimulate zebrafish to produce higher and more lasting expression of the five immunity genes than non-protective immunogens during the first 48 h of infection. In addition, these protective immunogens are prone to be regulated by host products, which is helpful for cross-talk between host and pathogen, and thus they become vaccine candidates. These results highlight the way to understand the working mechanisms of protective immunogens.

Innate sensors that regulate vaccine responses

Pattern recognition receptors (PRRs) control elemental functions of antigen presenting cells (APCs) and critically shape adaptive immune responses. Wielding a natural adjuvanticity, live attenuated vaccines elicit exceptionally efficient and durable immunity. Commonly used vaccine adjuvants target individual PRRs or bolster the immunogenicity of vaccines via indirect mechanisms of inflammation. Here, we review the impact of innate sensors on immune responses to live attenuated vaccines and commonly used vaccine adjuvants, with a focus on human vaccine responses. We discuss the unique potential of microbial nucleic acids and their corresponding sensing receptors to mimic live attenuated vaccines and promote protective immunity.

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.

Dead or alive: how the immune system detects microbial viability

Immune detection of microbial viability is increasingly recognized as a potent driver of innate and adaptive immune responses. Here we describe recent mechanistic insights into the process of how the immune system discriminates between viable and non-viable microbial matter. Accumulating evidence suggests a key role for microbial RNA as a widely conserved viability associated PAMP (vita-PAMP) and a molecular signal of increased infectious threat. Toll-like receptor 8 (TLR8) has recently emerged as a critical sensor for viable bacteria, ssRNA viruses, and archaea in human antigen presenting cells (APC). We discuss the role of microbial RNA, and other potential vita-PAMPs in antimicrobial immunity and vaccine responses.