Identification of novel immunogenic proteins in pathogenic Haemophilus parasuis based on genome sequence analysis

Immunogenicity and protection against Glaesserella parasuis serotype 13 infection after vaccination with recombinant protein LolA in mice

Glaesserella parasuis is a pathogen causing Glässer's disease characterized by fibrinous polyserositis, polyarthritis, and meningitis. Owing to the low cross-immunogenicity of different bacterial antigens in commercial vaccines, finding and identifying effective immunoprotective antigens will facilitate the development of novel subunit vaccines. In this study, LolA, identified by bioinformatics approaches, was cloned and successfully expressed as a recombinant protein in Escherichia coli, and its immunogenicity and protection were evaluated in a mouse model. The results showed that the recombinant protein LolA can stimulate mice to produce high levels of IgG antibodies and confer 50% protection against challenge with the highly virulent G. parasuis CY1201 strain (serotype 13). By testing the cytokine levels of interleukin 4 (IL-4), IL-10, and interferon-γ (IFN-γ), it was found that the recombinant protein LolA can induce both Th1 and Th2 immune responses in mice. These results suggest that the recombinant protein LolA has the potential to serve as an alternative antigen for a novel vaccine to prevent G. parasuis infection.

Dosing Regimen of Aditoprim and Sulfamethoxazole Combination for the Glaesserella parasuis Containing Resistance and Virulence Genes

Glaesserella parasuis (G. parasuis) causes Glasser’s disease in pigs and causes high mortality in piglets. The new drug Aditoprim (ADP) alone or combined with Sulfamethoxazole (SMZ) is one of the good choices for treating respiratory infections. The objective of this study was to recommend the optimal dosing regimen for the treatment of G. parasuis infection which contains resistance and virulence genes by ADP/SMZ compound through pharmacokinetics–pharmacodynamics (PK-PD) modeling. The whole genome of the virulent strain G. parasuis H78 was obtained and annotated by whole genome sequencing. The results show that G. parasuis H78 consists of a unilateral circular chromosome with prophages in the genome. The annotation results of G. parasuis H78 showed that the genome contained a large number of virulence-related genes and drug resistance-related genes. The in vitro PD study showed that the antibacterial effect of ADP/SMZ compound against G. parasuis was time-dependent, and AUC/MIC was selected as the PK-PD modeling parameter. The PK study showed that the content of ADP/SMZ compound in pulmonary epithelial lining fluid (PELF) was higher than plasma, and there were no significant differences in ADP and SMZ PK parameters between the healthy and infected group. The dose equation to calculate the optimal dosing regimen of ADP/SMZ compound administration for control of G. parasuis infection was 5/25 mg/kg b.w., intramuscular injection once a day for 3~5 consecutive days. The results of this study provide novel therapeutic options for the treatment of G. parasuis infection to decrease the prevalence and disease burden caused by G. parasuis.

Metal Ion Periplasmic-Binding Protein YfeA of Glaesserella parasuis Induces the Secretion of Pro-Inflammatory Cytokines of Macrophages via MAPK and NF-κB Signaling through TLR2 and TLR4

The YfeA gene, belonging to the well-conserved ABC (ATP-binding cassette) transport system Yfe, encodes the substrate-binding subunit of the iron, zinc, and manganese transport system in bacteria. As a potential vaccine candidate in Glaesserella parasuis, the functional mechanisms of YfeA in the infection process remain obscure. In this study, vaccination with YfeA effectively protected the C56BL6 mouse against the G. parasuis SC1401 challenge. Bioinformatics analysis suggests that YfeA is highly conserved in G. parasuis, and its metal-binding sites have been strictly conserved throughout evolution. Stimulation of RAW 264.7 macrophages with YfeA verified that toll-like receptors (TLR) 2 and 4 participated in the positive transcription and expression of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. The activation of TLR2 and TLR4 utilized the MyD88/MAL and TRIF/TRAM pairs to initiate TLRs signaling. Furthermore, YfeA was shown to stimulate nuclear translocation of NF-κB and activated diverse mitogen-activated protein (MAP) kinase signaling cascades, which are specific to the secretion of particular cytokine(s) in murine macrophages. Separate blocking TLR2, TLR4, MAPK, and RelA (p65) pathways significantly decreased YfeA-induced pro-inflammatory cytokine production. In addition, YfeA-stimulated RAW 264.7 produces the pro-inflammatory hallmark, reactive oxygen species (ROS). In conclusion, our findings indicate that YfeA is a novel pro-inflammatory mediator in G. parasuis and induces TLR2 and TLR4-dependent pro-inflammatory activity in RAW 264.7 macrophages through P38, JNK-MAPK, and NF-κB signaling pathways.

Identification of novel Haemophilus parasuis serovar 5 vaccine candidates using an immunoproteomic approach

Haemophilus parasuis is the aetiological agent of Glässer's disease, which is responsible for cases of fibrinous polyserositis, polyarthritis and meningitis. No vaccine is known that provides cross-protection against all serovars. The identification of novel immunoprotective antigens would undoubtedly contribute to the development of efficient subunit vaccines. In the present study, an immunoproteomic approach was used to analyze secreted proteins of H. parasuis and six proteins with high immunogenicity were identified. Five of them were successfully expressed, and their immunogenicity and protective efficacy were assessed in a mouse challenge model. All five proteins elicited strong humoral antibody and cellular immune responses in mice. They all effectively reduced the growth of H. parasuis in mouse organs and conferred different levels of protection (40-80%) against challenge. IgG subtype analysis revealed that the five proteins induce a bias toward a Th1-type immune response, and a significant increase was observed in the cytokine levels of IL-2, IFN-γ and Th2-specific IL-4 in the culture supernatants of splenocytes isolated from immunized mice. The results suggest that both Th1 and Th2 responses are involved in mediating protection. These data suggest that the five proteins could be potential subunit vaccine candidates for use to prevent H. parasuis infection.

BIOLOGICAL SIGNIFICANCE

Haemophilus parasuis can cause huge financial loss in the swine industry worldwide. There are still no vaccines which can provide cross-protection against all serovars. To address this need, we applied an immunoproteomic approach involving 2-DE, MALDI-TOF/TOF MS and Western-blot to identify the secreted proteins which may be able to provide immunoprotection to this disease. We identified six immunogenic proteins, and the immunogenicity and protective efficacy were validated. This result provides a foundation for developing novel subunit vaccines against Haemophilus parasuis.

Immune response to oligopeptide permease A (OppA) protein in pigs naturally and experimentally infected with Haemophilus parasuis

Haemophilus parasuis is an important swine pathogen that causes Glasser's disease, characterized by pneumonia, polyserositis and meningitis. Protection against H. parasuis infection is associated with the presence of homologous antibodies in serum. However, a H. parasuis antigen that can elicit a protective immune response against all H. parasuis strains has yet to be found. A novel immunogenic and species-specific H. parasuis protein was identified by screening H. parasuis whole cell proteins using swine convalescent sera. One protein of 52kDa was clearly immunodominant and conserved among different H. parasuis strains. This protein was further identified as an oligopeptide permease A (OppA). Because OppA elicited a specific antibody response in pigs that recovered from H. parasuis infection, we investigated its potential role in diagnostics and protective immunity. An ELISA test using recombinant OppA (rOppA) as its coating antigen was further developed and tested. H. parasuis specific antibodies to rOppA were detected in serum from convalescent pigs but not in serum from specific pathogen free (SPF) or conventional pigs. Pigs immunized with rOppA protein had robust serological responses. However, the antibodies were not protective against challenge infection. We conclude that OppA is a universal species-specific H. parasuis immunogen, and a good marker for previous systemic infection with H. parasuis.

Development and antigenic characterization of three recombinant proteins with potential for Glässer's disease prevention

Haemophilus parasuis is the causative agent of Glässer's disease, which causes high morbidity and mortality in piglets, leading to severe economic losses. The lack of a commercial vaccine against a broad spectrum of strains has limited the disease control. H. parasuis outer membrane proteins (OMPs) are potentially essential components for vaccine formulation. In this study, seven putative OMPs were selected from the annotated H. parasuis serovar 5 genome; they were predicted by bioinformatics and annotated as potential virulence-related factors. These proteins were cloned, expressed, and purified as His-tagged proteins. Antigenicity of the candidate proteins was assessed using Western blotting with convalescent sera against H. parasuis serovar 5. The immunogenicity of the seven OMPs was assessed in a guinea pig model. Except VacJ, all the other six recombinant proteins elicited a detectable antibody response. Antisera against four of the selected proteins effectively killed the bacteria in vitro. Three proteins (Omp26, VacJ, and HAPS_0742) were found to confer significant protection against challenge with a lethal dose of H. parasuis in a guinea pig model. The results suggest that these three proteins have a strong potential to be vaccine candidates against Glässer's disease.

Haemophilus parasuis: infection, immunity and enrofloxacin

Haemophilus parasuis is an early colonizer of the porcine upper respiratory tract and is the etiological agent of Glasser’s disease. The factors responsible for H. parasuis colonization and systemic infection are not yet well understood, while prevention and control of Glasser’s disease continues to be challenging. Recent studies on innate immunity to H. parasuis have demonstrated that porcine alveolar macrophages (PAMs) are able to differentially up-regulate several genes related to inflammation and phagocytosis, and several pro-inflammatory cytokines are produced by porcine cells upon exposure to H. parasuis. The susceptibility of H. parasuis strains to phagocytosis by PAMs and the bactericidal effect of complement are influenced by the virulent phenotype of the strains. While non-virulent strains are susceptible to phagocytosis and complement, virulent strains are resistant to both. However, in the presence of specific antibodies against H. parasuis, virulent strains become susceptible to phagocytosis. More information is still needed, though, in order to better understand the host immune responses to H. parasuis. Antimicrobials are commonly used in the swine industry to help treat and control Glasser’s disease. Some of the common antimicrobials have been shown to reduce colonization by H. parasuis, which may have implications for disease dynamics, development of effective immune responses and immunomodulation. Here, we provide the current state of research on innate and adaptive immune responses to H. parasuis and discuss the potential effect of enrofloxacin on the development of a protective immune response against H. parasuis infection.

Concurrent host-pathogen gene expression in the lungs of pigs challenged with Actinobacillus pleuropneumoniae

Background

Actinobacillus pleuropneumoniae causes pleuropneumonia in pigs, a disease which is associated with high morbidity and mortality, as well as impaired animal welfare. To obtain in-depth understanding of this infection, the interplay between virulence factors of the pathogen and defense mechanisms of the porcine host needs to be elucidated. However, research has traditionally focused on either bacteriology or immunology; an unbiased picture of the transcriptional responses can be obtained by investigating both organisms in the same biological sample.

Results

Host and pathogen responses in pigs experimentally infected with A. pleuropneumoniae were analyzed by high-throughput RT-qPCR. This approach allowed concurrent analysis of selected genes encoding proteins known or hypothesized to be important in the acute phase of this infection. The expression of 17 bacterial and 31 porcine genes was quantified in lung samples obtained within the first 48 hours of infection. This provided novel insight into the early time course of bacterial genes involved in synthesis of pathogen-associated molecular patterns (lipopolysaccharide, peptidoglycan, lipoprotein) and genes involved in pattern recognition (TLR4, CD14, MD2, LBP, MYD88) in response to A. pleuropneumoniae. Significant up-regulation of proinflammatory cytokines such as IL1B, IL6, and IL8 was observed, correlating with protein levels, infection status and histopathological findings. Host genes encoding proteins involved in iron metabolism, as well as bacterial genes encoding exotoxins, proteins involved in adhesion, and iron acquisition were found to be differentially expressed according to disease progression. By applying laser capture microdissection, porcine expression of selected genes could be confirmed in the immediate surroundings of the invading pathogen.

Conclusions

Microbial pathogenesis is the product of interactions between host and pathogen. Our results demonstrate the applicability of high-throughput RT-qPCR for the elucidation of dual-organism gene expression analysis during infection. We showed differential expression of 12 bacterial and 24 porcine genes during infection and significant correlation of porcine and bacterial gene expression. This is the first study investigating the concurrent transcriptional response of both bacteria and host at the site of infection during porcine respiratory infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1557-6) contains supplementary material, which is available to authorized users.

Lactobacillus reuteri glyceraldehyde-3-phosphate dehydrogenase functions in adhesion to intestinal epithelial cells

This study was aimed to identify key surface proteins mediating the adhesion of lactobacilli to intestinal epithelial cells. By using Caco-2 and IPEC-J2 cells labeled with sulfo-NHS-biotin in the western blotting, a protein band of an approximately 37 kDa was detected on the surface layer of Lactobacillus reuteri strains ZJ616, ZJ617, ZJ621, and ZJ623 and Lactobacillus rhamnosus GG. Mass spectrometry analysis using the adhesion-related protein from L. reuteri ZJ617 showed that it was 100% homologous to the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of L. reuteri JCM 1112 (GenBank: YP_001841377). The ability of L. reuteri ZJ617 to adhere to epithelial cells decreased significantly by treatment with LiCl or by blocking with an anti-GAPDH antibody, in comparison with the untreated strain (p < 0.05). Immunoelectron microscopic and immunofluorescence analyses confirmed that GAPDH is located on the surface layer of L. reuteri ZJ617. The results indicated that the GAPDH protein of L. reuteri ZJ617 acts as an adhesion component that plays an important role in binding to the intestinal epithelial cells.

The use of genome wide association methods to investigate pathogenicity, population structure and serovar in Haemophilus parasuis

Background

Haemophilus parasuis is the etiologic agent of Glässer’s disease in pigs and causes devastating losses to the farming industry. Whilst some hyper-virulent isolates have been described, the relationship between genetics and disease outcome has been only partially established. In particular, there is weak correlation between serovar and disease phenotype. We sequenced the genomes of 212 isolates of H. parasuis and have used this to describe the pan-genome and to correlate this with clinical and carrier status, as well as with serotype.

Results

Recombination and population structure analyses identified five groups with very high rates of recombination, separated into two clades of H. parasuis with no signs of recombination between them. We used genome-wide association methods including discriminant analysis of principal components (DAPC) and generalised linear modelling (glm) to look for genetic determinants of this population partition, serovar and pathogenicity. We were able to identify genes from the accessory genome that were significantly associated with phenotypes such as potential serovar specific genes including capsule genes, and 48 putative virulence factors that were significantly different between the clinical and non-clinical isolates. We also show that the presence of many previously suggested virulence factors is not an appropriate marker of virulence.

Conclusions

These genes will inform the generation of new molecular diagnostics and vaccines, and refinement of existing typing schemes and show the importance of the accessory genome of a diverse species when investigating the relationship between genotypes and phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1179) contains supplementary material, which is available to authorized users.

Fifteen novel immunoreactive proteins of Chinese virulent Haemophilus parasuis serotype 5 verified by an immunoproteomic assay

Haemophilus parasuis (H. parasuis) is associated with meningitis, polyserositis, polyarthritis and bacterial pneumonia. At present, its prevention and control is difficult because of the lack of suitable subunit vaccines. Nowadays, high-throughput methods, immunoproteomics, are available to screen for more vaccine candidates. A protein extraction method for H. parasuis and two-dimensional electrophoresis (2-DE) were optimized to provide high-resolution profiles covering pH 3 to 10. Twenty immunoreactive spots were excised from gels after strict comparison between 2-DE Western blot membranes and the relevant gels. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and MALDI-TOF-TOF-MS successfully identified 16 different proteins. Fifteen of them were reported as immunoreactive proteins in H. parasuis for the first time. In addition, recombinant HP5-7 (ABC transporter, periplasmic-binding protein) showed immunoreactivity both with hyperimmune rabbit serum and convalescent swine serum. Four recombinants of the 14 successfully expressed genes showed immunoreactivity with hyperimmune rabbit serum.

Serologic profiling of Haemophilus parasuis-vaccinated sows and their litters using a novel oligopeptide permease A enzyme-linked immunosorbent assay reveals unexpected patterns of serological response and maternal antibody transfer

Haemophilus parasuis is an economically important swine pathogen with 15 recognized serovars. An enzyme-linked immunosorbent assay (ELISA) was developed that detects serum antibodies to the oligopeptide permease A (OppA) polypeptide membrane protein present in the reference strains for 13 of the H. parasuis serovars. Using the OppA-ELISA, H. parasuis serologic profiles were assessed on 2 swine farms, with seroconversion defined as an OppA-ELISA sample-to-positive (S/P) ratio ≥0.5. Ten gilts from each farm were vaccinated for H. parasuis using either a live avirulent culture vaccine (farm 1) or an inactivated autogenous vaccine (farm 2). Seroconversion occurred in 100% of farm 1 gilts and 90% of farm 2 gilts, with a mean S/P ratio (MSPR) of 3.36 and 1.43, respectively. The OppA-ELISA MSPRs were determined for 2 piglets, 1 male and 1 female, randomly selected from 10 first-parity (P1), 10 second-parity (P2), and 10 third-parity (P3) litters farrowed by respective vaccinated gilts on each farm. On both farms, postfarrowing MSPRs and rate of seropositivity were highest in P1 versus P2 and P3 dams. Parity 1 piglets had higher MSPRs and rates of seropositivity versus later parities, with the difference being significant (P < 0.05) on farm 2. Polymerase chain reaction analysis of nasal swabs indicated that 100% of farm 1 piglets and 47-84%, depending on parity, of farm 2 piglets were H. parasuis-colonized at weaning. The results indicated that H. parasuis vaccination of gilts will not maintain serologic responses in the OppA-ELISA over their reproductive lifetimes, and that maternally derived antibodies do not prevent H. parasuis colonization of piglets.

Cross-protective efficacy of recombinant transferrin-binding protein A of Haemophilus parasuis in guinea pigs

The causative agent of Glasser's disease in swine is Haemophilus parasuis. Commercial bacterins are widely used for protection of the swine population. However, cross protection is limited because H. parasuis has more than 15 serovars. Transferrin-binding protein A has shown potential as a broad-spectrum vaccine candidate against homologous and heterologous strains. Here we amplified the full-length tbpA gene from an H. parasuis serovar 13 isolate and cloned it into a pET-SUMO expression vector. We then expressed and purified the TbpA protein by Ni affinity chromatography. First, the immunogenicity and protective efficacy of the protein were evaluated in guinea pigs by two subcutaneous immunizations with different doses of Montanide IMS 206 VG adjuvant. The immunized guinea pigs were, respectively, challenged on week 3 after a booster immunization with homologous strain LJ3 (serovar 13) and heterologous strain FX1 (serovar 4), and vaccine-inoculated groups were compared with nonvaccinated controls. All immunized groups showed serum antibody titers higher than those of negative-control groups. Furthermore, the cytokine and chemokine levels were evaluated at the transcriptional level by the real-time PCR analysis of six cytokines and chemokines. Gamma interferon and interleukin-5 in groups immunized with 100 μg were elevated more than 15-fold over those in negative-control groups. The protection rates were 80 and 60% after a challenge with strains LJ3 and FX1, respectively, in the groups vaccinated with 100 μg of recombinant TbpA protein. Subsequently, the data showed that guinea pigs immunized with a single dose (100 μg) were protected at levels of 80, 80, and 60% against LJ3, FX1, and another heterologous strain, SZ (serovar 14), respectively. The results indicate for the first time that TbpA protein cross protects guinea pigs against serovars 13, 4, and 14 of H. parasuis. Taken together, these results suggest that the recombinant TbpA protein is a promising vaccine candidate that needs to be confirmed in a swine population.

Haemophilus influenzae acquires vitronectin via the ubiquitous Protein F to subvert host innate immunity

Acquisition of the complement inhibitor vitronectin (Vn) is important for the respiratory tract pathogen nontypeable Haemophilus influenzae (NTHi) to escape complement-mediated killing. NTHi actively recruits Vn, and we previously showed that this interaction involves Protein E (PE). Here we describe a second Vn-binding protein, a 30 kDa Yersinia YfeA homologue designated as Protein F (PF). An isogenic NTHi 3655Δhpf mutant devoid of PF displayed a reduced binding of Vn, and was consequently more sensitive to killing by human serum compared with the wild type. Surface expression of PF on Escherichia coli conferred binding of Vn that resulted in a serum resistant phenotype. Molecular analyses revealed that the N-terminal of PF (Lys23-Glu48) bound to the C-terminal of Vn (Phe352-Ser374) without disrupting the inhibitory role of Vn on the membrane attack complex. The PF-Vn complex actively delayed C9 deposition on PF-expressing bacteria. Comparative studies of binding affinity and multiple mutants demonstrated that both PE and PF contribute individually to NTHi serum survival. PF was highly conserved and ubiquitously expressed in a series of randomly selected NTHi clinical isolates (n = 18). In conclusion, the multifaceted binding of Vn is beneficial for NTHi survival in serum and may contribute to successful colonization and consequently infection.

Purification and crystallization of the ABC-type transport substrate-binding protein OppA from Thermoanaerobacter tengcongensis

Di- and oligopeptide- binding protein OppAs play important roles in solute and nutrient uptake, sporulation, biofilm formation, cell wall muropeptides recycling, peptide-dependent quorum-sensing responses, adherence to host cells, and a variety of other biological processes. Soluble OppA from Thermoanaerobacter tengcongensis was expressed in Escherichia coli. The protein was found to be >95% pure with SDS-PAGE after a series of purification steps and the purity was further verified by mass spectrometry. The protein was crystallized using the sitting-drop vapour-diffusion method with PEG 400 as the precipitant. Crystal diffraction extended to 2.25 Å. The crystal belonged to space group C222(1), with unit-cell parameters of a=69.395, b=199.572, c=131.673 Å, and α=β=γ=90°.

New insights in cellular immune response in colostrum-deprived pigs after immunization with subunit and commercial vaccines against Glässer's disease

Four groups of colostrum-deprived pigs were immunized with Porcilis Glässer® (PG) or with subunit vaccines developed by us (rTbpA, NPAPT(M) or NPAPT(Cp)) against Glässer's disease, and they were challenged with 3×10(8)CFU of Haemophilus parasuis. A strong reduction in CD3(+)γδTCR(+) cells was seen in non-immunized control and scarcely protected (rTbpA) groups, suggesting that these cells could represent a target of H. parasuis infection. A significant increase in CD172α(+)CD163(+) cells was detected in all groups but PG, while a reduction in SLAIIDR(+) molecules expression was observed after challenge in control animals. Significant increases in CD3ε(+)CD8α(+)CD8β(+) and B cells were detected respectively in control and NPAPT groups, and in scarcely (rTbpA) and well-protected (NPAPT(M) and NPAPT(Cp)) groups. Finally, a greater response in CD4(+)CD8α(-) cells was observed in NPAPT(Cp) compared to NPAPT(M) and PG groups. These results state the potential of NPAPT antigen for developing effective vaccines against Glässer's disease.

Transcriptional portrait of Actinobacillus pleuropneumoniae during acute disease--potential strategies for survival and persistence in the host

Background

Gene expression profiles of bacteria in their natural hosts can provide novel insight into the host-pathogen interactions and molecular determinants of bacterial infections. In the present study, the transcriptional profile of the porcine lung pathogen Actinobacillus pleuropneumoniae was monitored during the acute phase of infection in its natural host.

Methodology/Principal Findings

Bacterial expression profiles of A. pleuropneumoniae isolated from lung lesions of 25 infected pigs were compared in samples taken 6, 12, 24 and 48 hours post experimental challenge. Within 6 hours, focal, fibrino hemorrhagic lesions could be observed in the pig lungs, indicating that A. pleuropneumoniae had managed to establish itself successfully in the host. We identified 237 differentially regulated genes likely to encode functions required by the bacteria for colonization and survival in the host. This group was dominated by genes involved in various aspects of energy metabolism, especially anaerobic respiration and carbohydrate metabolism. Remodeling of the bacterial envelope and modifications of posttranslational processing of proteins also appeared to be of importance during early infection. The results suggested that A. pleuropneumoniae is using various strategies to increase its fitness, such as applying Na+ pumps as an alternative way of gaining energy. Furthermore, the transcriptional data provided potential clues as to how A. pleuropneumoniae is able to circumvent host immune factors and survive within the hostile environment of host macrophages. This persistence within macrophages may be related to urease activity, mobilization of various stress responses and active evasion of the host defenses by cell surface sialylation.

Conclusions/Significance

The data presented here highlight the importance of metabolic adjustments to host conditions as virulence factors of infecting microorganisms and help to provide insight into the mechanisms behind the efficient colonization and persistence of A. pleuropneumoniae during acute disease.

Molecular cloning, sequencing, and expression of the outer membrane protein P2 gene of Haemophilus parasuis

Haemophilus parasuis is the etiological agent of Glässer's disease characterized by fibrinous polyserositis, polyarthritis, and meningitis in young pigs. But it is difficult to develop universal serological diagnostic tools and effective vaccines against this disease because of the serovar diversity of the isolates. In this study, enterobacterial repetitive intergenic consensus-polymerase chain reaction, were performed to investigate the gene profile of 111 isolates of H. parasuis from China. And a specific common gene of H. parasuis was cloned and identified as the outer-membrane protein (OMP) P2 gene. Sequencing results of OMP P2 genes of 22 isolates showed that they had high homology and could be divided into 2 genetic types. Moreover, the OMPP2 protein was expressed in Escherichia coli expressing system. And the purified recombinant protein provided partial protection against H. parasuis infection in mice. It suggested the OMP P2 was an immunogenic protein and had great potential to serve as a vaccine and diagnostic antigen.

Proteomic and immunoproteomic characterization of a DIVA subunit vaccine against Actinobacillus pleuropneumoniae

Background

Protection of pigs by vaccination against Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is hampered by the presence of 15 different serotypes. A DIVA subunit vaccine comprised of detergent-released proteins from A. pleuropneumoniae serotypes 1, 2 and 5 has been developed and shown to protect pigs from clinical symptoms upon homologous and heterologous challenge. This vaccine has not been characterized in-depth so far. Thus we performed i) mass spectrometry in order to identify the exact protein content of the vaccine and ii) cross-serotype 2-D immunoblotting in order to discover cross-reactive antigens. By these approaches we expected to gain results enabling us to argue about the reasons for the efficacy of the analyzed vaccine.

Results

We identified 75 different proteins in the vaccine. Using the PSORTb algorithm these proteins were classified according to their cellular localization. Highly enriched proteins are outer membrane-associated lipoproteins like OmlA and TbpB, integral outer membrane proteins like FrpB, TbpA, OmpA1, OmpA2, HgbA and OmpP2, and secreted Apx toxins. The subunit vaccine also contained large amounts of the ApxIVA toxin so far thought to be expressed only during infection. Applying two-dimensional difference gel electrophoresis (2-D DIGE) we showed different isoforms and variations in expression levels of several proteins among the strains used for vaccine production. For detection of cross-reactive antigens we used detergent released proteins of serotype 7. Sera of pigs vaccinated with the detergent-released proteins of serotypes 1, 2, and 5 detected seven different proteins of serotype 7, and convalescent sera of pigs surviving experimental infection with serotype 7 reacted with 13 different proteins of the detergent-released proteins of A. pleuropneumoniae serotypes 1, 2, and 5.

Conclusions

A detergent extraction-based subunit vaccine of A. pleuropneumoniae was characterized by mass spectrometry. It contained a large variety of immunogenic and virulence associated proteins, among them the ApxIVA toxin. The identification of differences in expression as well as isoform variation between the serotypes implied the importance of combining proteins of different serotypes for vaccine generation. This finding was supported by immunoblotting showing the induction of cross-reactive antibodies against several surface associated proteins in immunized animals.