Major outer membrane protein Omp25 of Brucella suis is involved in inhibition of tumor necrosis factor alpha production during infection of human macrophages

Outer membrane protein 25 of Brucella suppresses TLR-mediated expression of proinflammatory cytokines through degradation of TLRs and adaptor proteins

Toll-like receptors (TLRs) are essential components of innate immunity that serves as the first line of defense against the invaded microorganisms. However, successful infectious pathogens subvert TLR signaling to suppress the activation of innate and adaptive responses. Brucella species are infectious intracellular bacterial pathogens causing the worldwide zoonotic disease, brucellosis, that impacts economic growth of many countries. Brucella species are considered as stealthy bacterial pathogens as they efficiently evade or suppress host innate and adaptive immune responses for their chronic persistence. However, the bacterial effectors and their host targets for modulating the immune responses remain obscure. Brucella encodes various outer membrane proteins (Omps) that facilitate their invasion, intracellular replication, and immunomodulation. Outer membrane protein 25 (Omp25) of Brucella plays an important role in the immune modulation through suppression of proinflammatory cytokines. However, the mechanism and the signaling pathways that are targeted by Omp25 to attenuate the production of proinflammatory cytokines remain obscure. Here, we report that Omp25 and its variants, viz. Omp25b, Omp25c, and Omp25d, suppress production of proinflammatory cytokines that are mediated by various TLRs. Furthermore, we demonstrate that Omp25 and its variants promote enhanced ubiquitination and degradation of TLRs and their adaptor proteins to attenuate the expression of proinflammatory cytokines. Targeting multiple TLRs and adaptor proteins enables Omp25 to effectively suppress the expression of proinflammatory cytokines that are induced by diverse pathogen-associated molecular patterns. This can contribute to the defective adaptive immune response and the chronic persistence of Brucella in the host.

Design of a multi-epitope vaccine against brucellosis fused to IgG-fc by an immunoinformatics approach

Introduction

Brucella, a type of intracellular Gram-negative bacterium, has unique features and acts as a zoonotic pathogen. It can lead to abortion and infertility in animals. Eliminating brucellosis becomes very challenging once it spreads among both humans and animals, putting a heavy burden on livestock and people worldwide. Given the increasing spread of brucellosis, it is crucial to develop improved vaccines for susceptible animals to reduce the disease's impact.

Methods

In this study, we effectively used an immunoinformatics approach with advanced computer software to carefully identify and analyze important antigenic parts of Brucella abortus. Subsequently, we skillfully designed chimeric peptides to enhance the vaccine's strength and effectiveness. We used computer programs to find four important parts of the Brucella bacteria that our immune system recognizes. Then, we carefully looked for eight parts that are recognized by a type of white blood cell called cytotoxic T cells, six parts recognized by T helper cells, and four parts recognized by B cells. We connected these parts together using a special link, creating a strong new vaccine. To make the vaccine even better, we added some extra parts called molecular adjuvants. These included something called human β-defensins 3 (hBD-3) that we found in a database, and another part that helps the immune system called PADRE. We attached these extra parts to the beginning of the vaccine. In a new and clever way, we made the vaccine even stronger by attaching a part from a mouse's immune system to the end of it. This created a new kind of vaccine called MEV-Fc. We used advanced computer methods to study how well the MEV-Fc vaccine interacts with certain receptors in the body (TLR-2 and TLR-4).

Results

In the end, Immunosimulation predictions showed that the MEV-Fc vaccine can make the immune system respond strongly, both in terms of cells and antibodies.

Discussion

In summary, our results provide novel insights for the development of Brucella vaccines. Although further laboratory experiments are required to assess its protective effect.

The outer membrane proteins based seroprevalence strategy for Brucella ovis natural infection in sheep

Introduction

The diagnosis of brucellosis largely relies on tiger red plate agglutination test (RBPT). However, it is difficult to distinguish between natural infection antibody positive and vaccination antibody positive, nevertheless, the identification of specific Brucella species natural infection.

Methods

Here, we analyzed the structure of main outer membrane proteins (OMPs), OMP25 and OMP31 from Brucella ovis (B. ovis) and Brucella melitensis (B. melitensis), which are the main pathogens of sheep brucellosis, and found the OMP25 and OMP31 could be used as the differential antigens for B. ovis and B. melitensis antibody. Then we expressed the OMP25 from B. ovis (OMP25o) and OMP31 from B. melitensis (OMP31m).

Results

They have equally efficiency in antibody detection of vaccinated sheep serum, consistent with the RBPT results. However, through epidemiological investigations, we found some RBPT positive samples were negative by the OMP31m based serum antibody detection, but these samples gave positive results by the OMP25o. We verified these OMP31m negative but OMP25o positive samples by B. ovis and B. melitensis specific primers based PCR detection, and all these samples were B. melitensis negative. However, four out of six samples are B. ovis positive. These results showed that we could use the OMP25o and OMP31m to diagnose sheep brucellosis antibody, especially to discriminate the infection of the B. ovis.

Discussion

Currently, China has not yet approved a vaccine based on B. ovis and B. ovis positive samples should be naturally infected. There should be some implicit transmission of B. ovis in Jilin province. Further epidemiological investigation should be conducted to monitor the B. ovis natural infection.

Bioinformatics analysis of Omp19 and Omp25 proteins for designing multi-epitope vaccines against Brucella

Brucellosis is a zoonotic disease caused by Brucella. There is no effective vaccine against human brucellosis. Omp19 and Omp25 are the outer membrane proteins of Brucella. They are widely expressed and highly conserved in Brucella and have high immunogenicity. Herein, we aim to identify multi-epitope vaccine candidates based on Omp19 and Omp25. We analyzed the physicochemical properties and protein structure of Omp19 and Omp25, and predicted the corresponding B cell and T cell epitopes using bioinformatics analysis. Omp19 and Omp25 were composed of 177 amino acids and 213 amino acids, respectively. They were both stable hydrophilic proteins. The instability indices were 44.8 and 23, respectively. The hydrophilicity was -0.1 and -0.317, respectively. In the secondary structure of Omp19 and Omp25 proteins, the α-helix accounted for 12.43% and 23.94%, the β-sheet was 18.64% and 23.47%, the β-turn was 6.78% and 4.23%, and the random coil was 62.15% and 48.36%. Finally, 5 B cell epitopes, 3 Th-cell epitopes and 5 CTL cell epitopes of Omp19 protein, and 4 B cell epitopes, 3 Th-cell epitopes, and 5 CTL cell epitopes of Omp25 protein were selected as vaccine candidates. In conclusion, we obtained potential B cell and T cell epitopes of the Brucella outer membrane Omp19 and Omp25 proteins. This lays the foundation for the further design of multi-epitope vaccine of Brucella.

A Germin-Like Protein GLP1 of Legumes Mediates Symbiotic Nodulation by Interacting with an Outer Membrane Protein of Rhizobia

Rhizobia can infect legumes and induce the coordinated expression of symbiosis and defense genes for the establishment of mutualistic symbiosis. Numerous studies have elucidated the molecular interactions between rhizobia and host plants, which are associated with Nod factor, exopolysaccharide, and T3SS effector proteins. However, there have been relatively few reports about how the host plant recognizes the outer membrane proteins (OMPs) of rhizobia to mediate symbiotic nodulation. In our previous work, a gene (Mhopa22) encoding an OMP was identified in Mesorhizobium huakuii 7653R, whose homologous genes are widely distributed in Rhizobiales. In this study, a germin-like protein GLP1 interacting with Mhopa22 was identified in Astragalus sinicus. RNA interference of AsGLP1 resulted in a decrease in nodule number, whereas overexpression of AsGLP1 increased the number of nodules in the hairy roots of A. sinicus. Consistent symbiotic phenotypes were identified in Medicago truncatula with MtGLPx (refer to medtr7g111240.1, the isogeny of AsGLP1) overexpression or Tnt1 mutant (glpx-1) in symbiosis with Sinorhizobium meliloti 1021. The glpx-1 mutant displayed hyperinfection and the formation of more infection threads but a decrease in root nodules. RNA sequencing analysis showed that many differentially expressed genes were involved in hormone signaling and symbiosis. Taken together, AsGLP1 and its homology play an essential role in mediating the early symbiotic process through interacting with the OMPs of rhizobia. IMPORTANCE This study is the first report to characterize a legume host plant protein to sense and interact with an outer membrane protein (OMP) of rhizobia. It can be speculated that GLP1 plays an essential role to mediate early symbiotic process through interacting with OMPs of rhizobia. The results provide deeper understanding and novel insights into the molecular interactive mechanism of a legume symbiosis signaling pathway in recognition with rhizobial OMPs. Our findings may also provide a new perspective to improve the symbiotic compatibility and nodulation of legume.

A designed peptide-based vaccine to combat Brucella melitensis, B. suis and B. abortus: Harnessing an epitope mapping and immunoinformatics approach

Vaccines against Brucella abortus, B. melitensis and B. suis have been based on weakened or killed bacteria, however there is no recombinant vaccine for disease prevention or therapy. This study attempted to predict IFN-γ epitopes, T cell cytotoxicity, and T lymphocytes in order to produce a multiepitope vaccine based on BtpA, Omp16, Omp28, virB10, Omp25, and Omp31 antigens against B. melitensis, B. abortus, and B. suis. AAY, GPGPG, and EAAAK peptides were used as epitope linkers, while the PADRE sequence was used as a Toll-like receptor 2 (TLR2) and TLR4 agonist. The final construct included 389 amino acids, and was a soluble protein with a molecular weight of 41.3 kDa, and nonallergenic and antigenic properties. Based on molecular docking studies, molecular dynamics simulations such as Gyration, RMSF, and RMSD, as well as tertiary structure validation methods, the modeled protein had a stable structure capable of interacting with TLR2/4. As a result, this novel vaccine may stimulate immune responses in B and T cells, and could prevent infection by B. suis, B. abortus, and B. melitensis.

A gene expression map of host immune response in human brucellosis

Brucellosis is a common zoonotic disease caused by intracellular pathogens of the genus Brucella. Brucella infects macrophages and evades clearance mechanisms, thus resulting in chronic parasitism. Herein, we studied the molecular changes that take place in human brucellosis both in vitro and ex vivo. RNA sequencing was performed in primary human macrophages (Mφ) and polymorphonuclear neutrophils (PMNs) infected with a clinical strain of Brucella spp. We observed a downregulation in the expression of genes involved in host response, such as TNF signaling, IL-1β production, and phagosome formation in Mφ, and phosphatidylinositol signaling and TNF signaling in PMNs, being in line with the ability of the pathogen to survive within phagocytes. Further transcriptomic analysis of isolated peripheral blood mononuclear cells (PBMCs) and PMNs from patients with acute brucellosis before treatment initiation and after successful treatment revealed a positive correlation of the molecular signature of active disease with pathways associated with response to interferons (IFN). We identified 24 common genes that were significantly altered in both PMNs and PBMCs, including genes involved in IFN signaling that were downregulated after treatment in both cell populations, and IL1R1 that was upregulated. The concentration of several inflammatory mediators was measured in the serum of these patients, and levels of IFN-γ, IL-1β and IL-6 were found significantly increased before the treatment of acute brucellosis. An independent cohort of patients with chronic brucellosis also revealed increased levels of IFN-γ during relapse compared to remissions. Taken together, this study provides for the first time an in-depth analysis of the transcriptomic alterations that take place in human phagocytes upon infection, and in peripheral blood immune populations during active disease.

Case Report: Suspected Case of Brucella-Associated Immune Reconstitution Inflammatory Syndrome

Human brucellosis is one of the most prevalent zoonoses. There are many similarities between the pathogenesis of Mycobacterium tuberculosis (MTB) infection and that of brucellosis. Immune reconstitution inflammatory syndrome (IRIS) may occur during the treatment of MTB infection, but it has not been reported in brucellosis cases thus far. We report the case of a 40-year-old male whose condition initially improved after adequate anti-Brucella therapy. However, 3 weeks later, the patient presented with exacerbation of symptoms and development of a paravertebral abscess. After exclusion of other possible causes of clinical deterioration, immune reconstitution inflammatory syndrome (IRIS) with brucellosis was presumed. After supplementation with anti-Brucella treatment with corticosteroids, the abscess disappeared, and the symptoms completely resolved. Our case suggests that it is necessary to be aware of the possible occurrence of IRIS in patients with brucellosis in clinical practice.

Host F-Box Protein 22 Enhances the Uptake of Brucella by Macrophages and Drives a Sustained Release of Proinflammatory Cytokines through Degradation of the Anti-Inflammatory Effector Proteins of Brucella

Brucella species are intracellular bacterial pathogens, causing the worldwide zoonotic disease brucellosis. Brucella invades professional and nonprofessional phagocytic cells, followed by resisting intracellular killing and establishing a replication permissive niche. Brucella also modulates the innate and adaptive immune responses of the host for its chronic persistence. The complex intracellular cycle of Brucella depends in a major way on multiple host factors, but limited information is available on host and bacterial proteins that play an essential role in the invasion, intracellular replication, and modulation of host immune responses. By employing a small interfering RNA (siRNA) screening, we identified a role for the host protein FBXO22 in the Brucella-macrophage interaction. FBXO22 is the key element in the SCF E3 ubiquitination complex, where it determines the substrate specificity for ubiquitination and degradation of various host proteins. Downregulation of FBXO22 by siRNA or the CRISPR-Cas9 system resulted in diminished uptake of Brucella into macrophages, which was dependent on NF-κB-mediated regulation of phagocytic receptors. FBXO22 expression was upregulated in Brucella-infected macrophages, which resulted in induction of phagocytic receptors and enhanced production of proinflammatory cytokines through NF-κB. Furthermore, we found that FBXO22 recruits the effector proteins of Brucella, including the anti-inflammatory proteins TcpB and OMP25, for degradation through the SCF complex. We did not observe any role for another F-box-containing protein of the SCF complex, β-TrCP, in the Brucella-macrophage interaction. Our findings unravel novel functions of FBXO22 in host-pathogen interaction and its contribution to pathogenesis of infectious diseases.

Tumor Necrosis Factor Alpha Contributes to Inflammatory Pathology in the Placenta during Brucella abortus Infection

Research on Brucella pathogenesis has focused primarily on its ability to cause persistent intracellular infection of the mononuclear phagocyte system. At these sites, Brucella abortus evades innate immunity, which results in low-level inflammation and chronic infection of phagocytes. In contrast, the host response in the placenta during infection is characterized by severe inflammation and extensive extracellular replication of B. abortus. Despite the importance of reproductive disease caused by Brucella infection, our knowledge of the mechanisms involved in placental inflammation and abortion is limited. To understand the immune responses specifically driving placental pathology, we modeled placental B. abortus infection in pregnant mice. B. abortus infection caused an increase in the production of tumor necrosis factor alpha (TNF-α), specifically in the placenta. We found that placental expression levels of Tnfa and circulating TNF-α were dependent on the induction of endoplasmic reticulum stress and the B. abortus type IV secretion system (T4SS) effector protein VceC. Blockade of TNF-α reduced placental inflammation and improved fetal viability in mice. This work sheds light on a tissue-specific response of the placenta to B. abortus infection that may be important for bacterial transmission via abortion in the natural host species.

Immunization with a combination of recombinant Brucella abortus proteins induces T helper immune response and confers protection against wild-type challenge in BALB/c mice

Protective efficiency of a combination of four recombinant Brucella abortus (B. abortus) proteins, namely, ribosomal protein L7/L12, outer membrane protein (OMP) 22, OMP25 and OMP31, was evaluated as a combined subunit vaccine (CSV) against B. abortus infection in RAW 264.7 cell line and murine model. Four proteins were cloned, expressed and purified, and their immunocompetence was analysed. BALB/c mice were immunized subcutaneously with single subunit vaccines (SSVs) or CSV. Cellular and humoral immune responses were determined by ELISA. Results of immunoreactivity showed that these four recombinant proteins reacted with Brucella‐positive serum individually but not with Brucella‐negative serum. A massive production of IFN‐γ and IL‐2 but low degree of IL‐10 was observed in mice immunized with SSVs or CSV. In addition, the titres of IgG2a were heightened compared with IgG1 in SSV‐ or CSV‐immunized mice, which indicated that SSVs and CSV induced a typical T‐helper‐1‐dominated immune response in vivo. Further investigation of the CSV showed a superior protective effect in mice against brucellosis. The protection level induced by CSV was significantly higher than that induced by SSVs, which was not significantly different compared with a group immunized with RB51. Collectively, these antigens of Brucella could be potential candidates to develop subunit vaccines, and the CSV used in this study could be a potential candidate therapy for the prevention of brucellosis.

Brucella spp. Omp25 Promotes Proteasome-Mediated cGAS Degradation to Attenuate IFN-β Production

Type I interferons (IFN), a family of cytokines widely expressed in various tissues, play important roles in anti-infection immunity. Nevertheless, it is not known whether Brucella spp. could interfere with IFN-I production induced by other pathogens. This study investigated the regulatory roles of Brucella outer membrane protein (Omp)25 on the IFN-I signaling pathway and found that Omp25 inhibited the production of IFN-β and its downstream IFN-stimulated genes induced by various DNA viruses or IFN-stimulatory DNA in human, murine, porcine, bovine, and ovine monocyte/macrophages or peripheral blood mononuclear cells. Brucella Omp25 suppressed the phosphorylation of stimulator of IFN genes (STINGs) and IFN regulatory factor 3 and nuclear translocation of phosphorylated IFN regulatory factor 3 in pseudorabies virus- or herpes simplex virus-1-infected murine, human, or porcine macrophages. Furthermore, we found that Brucella Omp25 promoted cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) degradation via the proteasome-dependent pathway, resulting in a decreased cyclic guanosine monophosphate-adenosine monophosphate production and downstream signaling activation upon DNA virus infection or IFN-stimulatory DNA stimulation. Mapping the predominant function domain of Omp25 showed that the amino acids 161 to 184 of Omp25 were required for Omp25-induced cGAS degradation, among which five amino acid residues (R176, Y179, R180, Y181, and Y184) were required for the inhibitory effect of Omp25 on IFN-β induction. Altogether, our results demonstrated that Brucella Omp25 inhibits cGAS STING signaling pathway-induced IFN-β via facilitating the ubiquitin-proteasome-dependent degradation of cGAS in various mammalian monocyte/macrophages.

In Vitro Evaluation of Immunogenicity of Recombinant OMP25 Protein Obtained from Endemic Brucella abortus Biovar 3 as Vaccine Candidate Molecule Against Animal Brucellosis

BACKGROUND

Brucellosis is a zoonotic disease that causes serious economic losses due to factors such as miscarriages and decreased milk yield in animals. Existing live vaccines have some disadvantages, so effective vaccines need to be developed with new technological approaches.

OBJECTIVES

The primary objectives of this study were the expression and purification of recombinant Omp25 fusion protein from B. abortus and the evaluation of the effect of the Omp25 protein on cell viability and inflammatory response.

METHODS

The omp25 gene region was amplified by a polymerase chain reaction and cloned into a Pet102/D-TOPO expression vector. The protein expression was carried out using the procaryotic expression system. The recombinant Omp25 protein was purified with affinity chromatography followed by GPC (Gel Permeation Chromatography). The MTS assay and cytokine-release measurements were carried out to evaluate cell viability and inflammatory response, respectively.

RESULTS

It was determined that doses of the recombinant Omp25 protein doses greater than 0.1 μg/mL are toxic to RAW cells. Doses of 1 µg/mL and lower significantly increased inflammation due to nitric oxide (NO) levels. ELISA results show that IFN-γ was produced in stimulated RAW 264.7 cells at a dose that did not affect the viability (0.05 µg/mL). However, IL-12, which is known to have a dual role in the activation of macrophages, did not show a statistically significant difference at the same dose.

CONCLUSION

Studies of cell viability and Th1-related cytokine release suggest that Omp25 protein is a promising candidate molecule for vaccine development.

Uncovering the Hidden Credentials of Brucella Virulence

Bacteria in the genus Brucella are important human and veterinary pathogens. The abortion and infertility they cause in food animals produce economic hardships in areas where the disease has not been controlled, and human brucellosis is one of the world's most common zoonoses. Brucella strains have also been isolated from wildlife, but we know much less about the pathobiology and epidemiology of these infections than we do about brucellosis in domestic animals. The brucellae maintain predominantly an intracellular lifestyle in their mammalian hosts, and their ability to subvert the host immune response and survive and replicate in macrophages and placental trophoblasts underlies their success as pathogens. We are just beginning to understand how these bacteria evolved from a progenitor alphaproteobacterium with an environmental niche and diverged to become highly host-adapted and host-specific pathogens. Two important virulence determinants played critical roles in this evolution: (i) a type IV secretion system that secretes effector molecules into the host cell cytoplasm that direct the intracellular trafficking of the brucellae and modulate host immune responses and (ii) a lipopolysaccharide moiety which poorly stimulates host inflammatory responses. This review highlights what we presently know about how these and other virulence determinants contribute to Brucella pathogenesis. Gaining a better understanding of how the brucellae produce disease will provide us with information that can be used to design better strategies for preventing brucellosis in animals and for preventing and treating this disease in humans.

Dendritic cells and Brucella spp. interaction: the sentinel host and the stealthy pathogen

As dendritic cells (DCs) are among the first cells to encounter antigens, these cells trigger both innate and T cell responses, and are the most potent antigen-presenting cells. Brucella spp., which is an intracellular facultative and stealthy pathogen, is able to evade the bactericidal activities of professional phagocytes. Several studies have demonstrated that Brucella can survive and replicate intracellularly, thereby provoking impaired maturation of DCs. Therefore, the interaction between DCs and Brucella becomes an interesting model to study the immune response. In this review, we first will describe the most common techniques for DCs differentiation in vitro as well as general features of brucellosis. Then, the interaction of DCs and Brucella, including pathogen recognition, molecular mechanisms of bacterial pathogenesis, and intracellular trafficking of Brucella to subvert innate response, will be reviewed. Finally, we will debate diversity in immunological DC response and the controversial role of DC activation against Brucella infection.

Immunogenic and protective antigens of Brucella as vaccine candidates

Brucella is an intracellular pathogen that causes abortion in domestic animals and undulant fever in humans. Due to the lack of a human vaccine against brucellosis, animal vaccines play an important role in the management of animal and human brucellosis for decades. Strain 19, RB51 and Rev1 are the approved Brucella spp. vaccine strains that are most commonly used to protect livestock against infection and abortion. However, due to some disadvantages of these vaccines, numerous studies have been conducted for the development of effective vaccines that could also be used in other susceptible animals. In this review, we compare different aspects of immunogenic antigens that have been a candidate for the brucellosis vaccine.

Learning from the master: targets and functions of the CtrA response regulator in Brucella abortus and other alpha-proteobacteria

The α-proteobacteria are a fascinating group of free-living, symbiotic and pathogenic organisms, including the Brucella genus, which is responsible for a worldwide zoonosis. One common feature of α-proteobacteria is the presence of a conserved response regulator called CtrA, first described in the model bacterium Caulobacter crescentus, where it controls gene expression at different stages of the cell cycle. Here, we focus on Brucella abortus and other intracellular α-proteobacteria in order to better assess the potential role of CtrA in the infectious context. Comparative genomic analyses of the CtrA control pathway revealed the conservation of specific modules, as well as the acquisition of new factors during evolution. The comparison of CtrA regulons also suggests that specific clades of α-proteobacteria acquired distinct functions under its control, depending on the essentiality of the transcription factor. Other CtrA-controlled functions, for instance motility and DNA repair, are proposed to be more ancestral. Altogether, these analyses provide an interesting example of the plasticity of a regulation network, subject to the constraints of inherent imperatives such as cell division and the adaptations to diversified environmental niches.

Alterations of microRNAs and their predicted targeting mRNAs expression in RAW264.7 macrophages infected with Omp25 mutant Brucella melitensis

Brucellosis is a worldwide zoonosis caused by Brucella species and represents a serious threat to both human and animal health. Omp25 is an important immunogenic and protective antigen in Brucella species; however, the functional mechanism of Omp25 in macrophages has not yet been elucidated. Here, we constructed a Brucella melitensis omp25 deletion mutant (M5-90-Δomp25) and performed microRNA (miRNA) profiling of infected RAW264.7 cells. Eight differentially expressed miRNAs (mmu-miR-146a-5p, mmu-miR-155-5p, mmu-miR-3473a, mmu-miR-149-3p, mmu-miR-671-5p, mmu-miR-1224-5p, mmu-miR-1895, and mmu-miR-5126) were identified, with quantitative real-time PCR (qRT-PCR) analysis confirming the up-regulation of mmu-miR-146-a-5p and mmu-miR-155-5p and down-regulation of mmu-miR-149-3p and mmu-miR-5126. mRNA profiling of B. melitensis M5-90-Δomp25-infected RAW264.7 cells identified 967 differentially expressed genes (DEGs) (fold change ≥ 2). Among these, we focused on genes that were predicted by TargetScan, miRanda, and PicTar to be the potential targets of the differentially expressed miRNAs. The results suggested that 17 separate genes are potentially targeted by mmu-miR-149-3p, with one of these genes, Tbr1, also targeted by mmu-miR-5126. qRT-PCR analysis confirmed the up-regulation of nine of the predicted target genes. Our findings provide important information about the functional molecules in host cells, including miRNA and their target genes, affected by Omp25 from Brucella. This information is particularly valuable for the prophylaxis and treatment of brucellosis.

Diagnostic potential of Brucella melitensis Rev1 native Omp28 precursor in human brucellosis

Serologic tests for brucellosis aim to detect antibodies produced against membranous lipopolysaccharide of bacteria. Diagnostic use of this method is limited due to false positiveness. This study evaluates an alternative antigen to lipopolysaccharides (LPS), outer membrane 28-precursor-protein, of Brucella melitensis Rev1 for its diagnostic value. Omp28 precursor of B. melitensis Rev1 was cloned, expressed, and purified. 6-His and sumo epitope tags were used to tag the protein at N-termini. Omp28 gene was amplified based on the ORF sequence and cloned into a pETSUMO vector. The recombinant construct was propagated in Escherichia coli One Shot^® Mach1™ cells then transformed into E. coli BL21(D3) cells for protein expression. The purified protein was studied in an indirect ELISA for diagnosis of brucellosis. Sera samples from 60 patients were screened by ELISA and the results were compared to Rose Bengal plate test. Recombinant antigen-based iELISA has given a successful outcome with the sensitivity, specificity, positive predictive value, and negative predictive value of 87.8%, 96.2%, 96.6%, and 78.78%, respectively. In conclusion, recombinant production and purification of the immunodominant Omp28 precursor protein has been achieved successfully in a one-step process with efficient yield and can be used for diagnosis of brucellosis in humans.

Brucella Downregulates Tumor Necrosis Factor-α to Promote Intracellular Survival via Omp25 Regulation of Different MicroRNAs in Porcine and Murine Macrophages

Brucella spp. impedes the production of pro-inflammatory cytokines by its outer membrane protein Omp25 in order to promote survival and immune evasion. However, how Omp25 regulates tumor necrosis factor (TNF-α) expression in different mammalian macrophages remains unclear. In this study, we investigated the potential mechanisms by which Omp25 regulates TNF-α expression and found that Omp25-deficient mutant of B. suis exhibited an enhanced TNF-α expression compared with wild-type (WT) B. suis, whereas ectopic expression of Omp25 suppressed LPS-induced TNF-α production at both protein and mRNA levels in porcine alveolar macrophages (PAMs) and murine macrophage RAW264.7 cells. We observed that Omp25 protein as well as WT B. suis upregulated miR-146a, -181a, -181b, and -301a-3p and downregulated TRAF6 and IRAK1 in both PAMs and RAW264.7 cells, but separately upregulates miR-130a-3p in PAMs and miR-351-5p in RAW264.7. The upregulation of miR-146a or miR-351-5p attenuated TNF-α transcription by targeting TRAF6 and IRAK1 at the 3' untranslated region (UTR), resulting in inhibition of NF-kB pathway, while upregulation of miR-130a-3p, -181a, or -301a-3p correlated temporally with decreased TNF-α by targeting its 3'UTR in PAMs or RAW264.7 cells. In contrast, inhibition of miR-130a-3p, -146a, -181a, and -301a-3p attenuated the inhibitory effects of Omp25 on LPS-induced TNF-α in PAMs, while inhibition of miR-146a, -181a, -301a-3p, and -351-5p attenuated the inhibitory effects of Omp25 in RAW264.7, resulting in an increased TNF-α production and decreased intracellular bacteria in both cells. Taken together, our results demonstrate that Brucella downregulates TNF-α to promote intracellular survival via Omp25 regulation of different microRNAs in porcine and murine macrophages.

Evaluation of immune responses induced by polymeric OMP25-BLS Brucella antigen

Brucellosis is one the serious infectious diseases caused deleterious health and economic losses. Vaccination with subunit vaccines is the efficient alternative way than live attenuated vaccines against infectious diseases. Herein a new chimeric OMP25-BLS antigen emulsified in Chitosan Nanoparticles was designed and its immune responses were compared with control groups. Also, the role of heat shock protein 60 kDa in combination with OMP25-BLS antigen was assessed. Structural and antigenic features of chimeric antigen were predicted using bioinformatics tools. Moreover, the humoral and cellular immune responses were measured by ELISA in seven different groups. Observations showed rOMP25-BLS structure was highly stable and antigenic. Cytokines analysis showed rOMP25 and rOMP25-BLS + rHSP60 induced higher titer of INF-γ than rHSP60 and rOMP25-BLS. There was no statistically significant difference between positive control group and rOMP25-BLS + rHSP60 in inducing TNF-α (p < .05). Additionally, the highest titer of IL-4 was dedicated to rOMP25 among other immunized treatments, while there were no significant differences between positive control group and other immunized groups with recombinant proteins (p < .05). In addition, rOMP25-BLS and rHSP60 induced higher titer of total antibody compared to other groups. Also, rHSP60 could improve IgG2a to IgG1 ratio when it used in combination with chimeric antigen. Moreover, the lymphocyte proliferation index was higher in chimeric rOMP25-BLS + HSP60 antigen. In conclusion, while rOMP25-BLS chimeric antigen unable to induce efficient cellular response than individual injection of rOMP25, its injection in combination with rHSP60 could improve cellular immunity.

Outer Membrane Protein 25 of Brucella Activates Mitogen-Activated Protein Kinase Signal Pathway in Human Trophoblast Cells

Outer membrane protein 25 (OMP25), a virulence factor from Brucella, plays an important role in maintaining the structural stability of Brucella. Mitogen-activated protein kinase (MAPK) signal pathway widely exists in eukaryotic cells. In this study, human trophoblast cell line HPT-8 and BALB/c mice were infected with Brucella abortus 2308 strain (S2308) and 2308ΔOmp25 mutant strain. The expression of cytokines and activation of MAPK signal pathway were detected. We found that the expressions of tumor necrosis factor-α, interleukin-1, and interleukin-10 (IL-10) were increased in HPT-8 cells infected with S2308 and 2308ΔOmp25 mutant. S2308 also activated p38 phosphorylation protein, extracellular-regulated protein kinases (ERK), and Jun-N-terminal kinase (JNK) from MAPK signal pathway. 2308ΔOmp25 could not activate p38, ERK, and JNK branches. Immunohistochemistry experiments showed that S2308 was able to activate phosphorylation of p38 and ERK in BABL/c mice. However, 2308ΔOmp25 could weakly activate phosphorylation of p38 and ERK. These results suggest that Omp25 played an important role in the process of Brucella activation of the MAPK signal pathway.

Brucella Omp25 Upregulates miR-155, miR-21-5p, and miR-23b to Inhibit Interleukin-12 Production via Modulation of Programmed Death-1 Signaling in Human Monocyte/Macrophages

Brucella spp. infection results in compromised Type1 (Th1) cellular immune response. Several reports have described an immunomodulatory function for Brucella major outer membrane protein Omp25. However, the mechanism by which Omp25 modulates macrophage dysfunction has not been defined. Herein, we reported that Omp25-deficient mutant of Brucella suis exhibited an enhanced ability to induce interleukin (IL)-12 whereas ectopic expression of Omp25 protein inhibited TLR agonists-induced IL-12 p70 production through suppression of both IL-12 p40 and p35 subunit expression in THP-1 cells. In addition, Omp25 significantly upregulated miR-155, -23b and -21-5p, as well as the immunomodulator molecule programmed death-1 (PD-1) in monocyte/macrophages. The upregulation of miR-155 and -23b correlated temporally with decreased TAB2 levels, IκB phosphorylation and IL-12 p40 levels by targeting TAB2 and il12B 3' untranslated region (UTR), respectively, while miR-21-5p increase directly led to the reduction of lipopolysaccharide (LPS)/R848-induced IL-12 p35 protein by targeting il12A 3'UTR. Consistent with this finding, reduction of miR-155 and -23b attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p40 expression at both transcriptional and posttranscriptional levels, while reduction of miR-21-5p attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p35 expression at the posttranscriptional level, together significantly enhanced IL-12 p70 production upon LPS/R848 stimulation. We also found that blocking PD-1 signaling decreased the expression of miR-155, -23b and -21-5p induced by Omp25 and enhanced IL-12 production in monocyte/macrophages. Altogether, these data demonstrate that Brucella Omp25 induces miR-155, -23b and -21-5p to negatively regulate IL-12 production at both transcriptional and posttranscriptional levels via regulation of PD-1 signaling, which provides an entirely new mechanism underlying monocyte/macrophages dysfunction during Brucella spp. infection.

OMP31 of Brucella melitensis 16M impairs the apoptosis of macrophages triggered by TNF-α

Outer membrane proteins (OMPs) of microorganisms play important roles in directly interacting with host cells. Brucella species inhibit the apoptosis of host cells to benefit their own intracellular survival and replication. However, the association between OMP31 of Brucella and host cell apoptosis, and the underlying mechanism are unclear. In this study, an OMP31 gene deletion mutant based on B. melitensis 16M was constructed. Following the infection of RAW264.7 cells with B. melitensis 16M or the mutant strain, colony formation, apoptosis, tumor necrosis factor (TNF)-α levels and the levels of key downstream factors of the apoptosis pathways triggered by TNF-α, namely caspase-3, -8 and -9, cytochrome c, B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (Bax) were detected. The mutant strain was shown to have the same phenotype as the parent strain using traditional microbiological tests. However, the mutant strain had impaired intracellular survival, with higher levels of apoptosis and TNF-α expression in infected RAW164.7 macrophages than the parent strain. The downstream factors of apoptosis triggered by TNF-α, including increased caspase-8, -3 and -9, cytochrome c and Bax, and decreased Bcl-2, indicated that the classical and mitochondrial cell death pathways were involved. It may be concluded that OMP31 from Brucella inhibited apoptosis and benefitted the intracellular survival of this microorganism. Furthermore, TNF-α may have served as a switch triggering classical death and mitochondrial cell death pathways.

Subclinical sacroiliitis in brucellosis. Clinical presentation and MRI findings

PURPOSE

The aim of this work was to detect subclinical sacroiliac joint involvement in patients with brucellosis and study their clinical and laboratory features.

PATIENTS AND METHODS

The study included 100 brucellosis patients being followed-up in the Gastroenterology and Hepatology Unit, Theodor Bilharz Research Institute and Cairo University outpatient clinics. A thorough history, physical examination, routine laboratory tests, and abdominal ultrasound were obtained for all patients. Extended rheumatological examination was performed including clinical testing for sacroiliitis and enthesitis. None of the patients reported a history of back pain or any symptoms suggestive of sacroiliitis during the course of the infection. Plain x-ray and MRI scan of the sacroiliac joints were performed for all patients.

RESULTS

Asymptomatic sacroiliitis was present in 24 % of the brucellosis patients; none of the patients had tenderness over their spine with preserved lumbar spine mobility. Sacroiliitis was mainly unilateral being bilateral in 20.83 %. There was an obvious relationship with animal contact and occupation of the patients. Osteoarticular involvement was common (67 %) including arthralgias, arthritis, myalgias, spondylitis, enthesitis and bursitis, being clearly higher in those with sacroiliitis. The MRI scan showed blurring of the margins in 66.67 %, widening in 25 %, narrowing in 54.17 %, erosions in 20.83 %, and sclerosis in 12.5 %.

CONCLUSION

Osteoarticular manifestations of brucellosis are prevalent and subclinical sacroiliitis is evident, a finding that may classify these patients as having brucellar spondyloarthropathy (BSA). Referring brucellosis patients for rheumatological assessment has the advantage of early assessment of asymptomatic cases with sacroiliitis which is commonly overlooked.

Deletion of the Small RNA Chaperone Protein Hfq down Regulates Genes Related to Virulence and Confers Protection against Wild-Type Brucella Challenge in Mice

Brucellosis is one of the most common zoonotic epidemics worldwide. Brucella, the etiological pathogen of brucellosis, has unique virulence characteristics, including the ability to survive within the host cell. Hfq is a bacterial chaperone protein that is involved in the survival of the pathogen under stress conditions. Moreover, hfq affects the expression of a large number of target genes. In the present study, we characterized the expression and regulatory patterns of the target genes of Hfq during brucellosis. The results revealed that hfq expression is highly induced in macrophages at the early infection stage and at the late stage of mouse infection. Several genes related to virulence, including omp25, omp31, vjbR, htrA, gntR, and dnaK, were found to be regulated by hfq during infection in BALB/c mice. Gene expression and cytokine secretion analysis revealed that an hfq-deletion mutant induced different cytokine profiles compared with that induced by 16M. Infection with the hfq-deletion mutant induced protective immune responses against 16M challenge. Together, these results suggest that hfq is induced during infection and its deletion results in significant attenuation which affects the host immune response caused by Brucella infection. By regulating genes related to virulence, hfq promotes the virulence of Brucella. The unique characteristics of the hfq-deletion mutant, including its decreased virulence and the ability to induce protective immune response upon infection, suggest that it represents an attractive candidate for the design of a live attenuated vaccine against Brucella.

Cloning, expression and molecular analysis of Iranian Brucella melitensis Omp25 gene for designing a subunit vaccine

Brucellosis is a well-known domestic animal infectious disease, which is caused by Brucella bacterium. The outer membrane protein 25 kDa (Omp25) gene plays an important role in simulating of TNF-α, IFN-α, macrophage, and cytokines cells. In the current study molecular cloning and expression analysis of Omp25 gene for designing a subunit vaccine against Brucella was investigated. Amplifying the full length of candidate gene was performed using specific primers. Sub-cloning of this gene conducted using pTZ57R/T vector in TOP10F strain of Escherichia coli(E.coli) as the host. Also, pET32(a)⁺ vector used for expression in BL21 (DE3) strain of E.coli. Omp25 gene with 642 bp size was amplified and cloned successfully. The expression results were confirmed by sequencing and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analyses which showed 42 kDa protein band correctly. Also, phylogenic analysis showed this gene has a near genetic relation with other Brucella strains. According to our results we can propose this gene as a candidate useful for stimulation of cell-mediated and humoral immunity system in future study.

Blocking the expression of syntaxin 4 interferes with initial phagocytosis of Brucella melitensis in macrophages

Brucella melitensis is the Brucella species most frequently associated with brucellosis in humans. It is also the causative agent of the disease in goats and other ruminants. Although significant aspects of the pathogenesis of infection by this intracellular pathogen have been clarified, several events during invasion of host cells remain to be elucidated. In this study, infections of human macrophages from the THP-1 monocyte cell line were conducted with B. melitensis Bm133 wild-type strain and a strain of Salmonella serovar Enteritidis as a control. A multiplicity of infection of 100 was used in trials focused on defining the relative expression of syntaxin 4 (STX4), a soluble N-ethylmaleimide-sensitive factor attachment protein receptor, in the early events of phagocytosis (at 15, 30, 45, and 60 min). Immunoblot assays were also done to visualize expression of the protein in cells infected with either bacterial strain. The expression of STX4 was not significantly different in cells infected with B. melitensis strain Bm133 compared to that observed in cells infected with S. Enteritidis. When the expression of STX4 mRNA was inhibited with short or small interfering, or silencing, RNA in the THP-1 cells, the survival of B. melitensis was significantly reduced at time 0, when gentamicin treatment of cultures was begun (after 1 h of phagocytosis), and also at 2 h and 12 h after infection.

A novel Omp25-binding peptide screened by phage display can inhibit Brucella abortus 2308 infection in vitro and in vivo

Brucellosis is a globally distributed zoonotic disease affecting animals and humans, and current antibiotic and vaccine strategies are not optimal. The surface-exposed protein Omp25 is involved in Brucella virulence and plays an important role in Brucella pathogenesis during infection, suggesting that Omp25 could be a useful target for selecting potential therapeutic molecules to inhibit Brucella pathogenesis. In this study, we identified, we believe for the first time, peptides that bind specifically to the Omp25 protein of pathogens, using a phage panning technique, After four rounds of panning, 42 plaques of eluted phages were subjected to pyrosequencing. Four phage clones that bound better than the other clones were selected following confirmation by ELISA and affinity constant determination. The peptides selected could significantly inhibit Brucella abortus 2308 (S2308) internalization and intracellular growth in RAW264.7 macrophages, and significantly induce secretion of TNF-α and IL-12 in peptide- and S2308-treated cells. Any observed peptide (OP11, OP27, OP35 or OP40) could significantly inhibit S2308 infection in BALB/c mice. Moreover, the peptide OP11 was the best candidate peptide for inhibiting S2308 infection in vitro and in vivo. These results suggest that peptide OP11 has potential for exploitation as a peptide drug in resisting S2308 infection.

Pluronic P85 enhances the efficacy of outer membrane vesicles as a subunit vaccine against Brucella melitensis challenge in mice

Brucellosis is the most common zoonotic disease worldwide, and there is no vaccine for human use. Brucella melitensis Rev1, a live attenuated strain, is the commercial vaccine for small ruminants to prevent B. melitensis infections but has been associated with abortions in animals. Moreover, strain Rev1 is known to cause disease in humans and cannot be used for human vaccination. Outer membrane vesicles (OMVs) obtained from B. melitensis have been shown to provide protection similar to strain Rev1 in mice against B. melitensis challenge. In the present work, we tested the efficacy of Pluronic P85 as an adjuvant to enhance the efficacy of Brucella OMVs as a vaccine. P85 enhanced the in vitro secretion of TNF-α by macrophages induced with OMVs and P85. Further, P85 enhanced the protection provided by OMVs against B. melitensis challenge. This enhanced protection was associated with higher total IgG antibody production but not increased IFN-γ or IL-4 cytokine levels. Moreover, P85 alone provided significantly better clearance of B. melitensis compared to saline-vaccinated mice. Further studies are warranted to find the mechanism of action of P85 that provides nonspecific protection and enhances the efficacy of OMVs as a vaccine against B. melitensis.

Host-Brucella interactions and the Brucella genome as tools for subunit antigen discovery and immunization against brucellosis

Vaccination is the most important approach to counteract infectious diseases. Thus, the development of new and improved vaccines for existing, emerging, and re-emerging diseases is an area of great interest to the scientific community and general public. Traditional approaches to subunit antigen discovery and vaccine development lack consideration for the critical aspects of public safety and activation of relevant protective host immunity. The availability of genomic sequences for pathogenic Brucella spp. and their hosts have led to development of systems-wide analytical tools that have provided a better understanding of host and pathogen physiology while also beginning to unravel the intricacies at the host-pathogen interface. Advances in pathogen biology, host immunology, and host-agent interactions have the potential to serve as a platform for the design and implementation of better-targeted antigen discovery approaches. With emphasis on Brucella spp., we probe the biological aspects of host and pathogen that merit consideration in the targeted design of subunit antigen discovery and vaccine development.

Cell mediated immune response after challenge in Omp25 liposome immunized mice contributes to protection against virulent Brucella abortus 544

Brucellosis is a disease affecting various domestic and wild life species, and is caused by a bacterium Brucella. Keeping in view the serious economic and medical consequences of brucellosis, efforts have been made to prevent the infection through the use of vaccines. Cell-mediated immune responses [CMI] involving interferon gamma and cytotoxic CD4(+) and CD8(+) T cells are required for removal of intracellular Brucella. Omp25 has been reported to be involved in virulence of Brucella melitensis, Brucella abortus and Brucella ovis. In our previous study, we have shown the protective efficacy of recombinant Omp25, when administered intradermally. In this study, the recombinant Omp25 was formulated in PC-PE liposomes and PLGA microparticles, to enhance the protective immunity generated by it. Significant protection was seen with prime and booster liposome immunization in Balb/c mice against virulent B. abortus 544 as it was comparable to B. abortus S-19 vaccine strain. However, microparticle prime and booster immunization failed to give better protection when compared to B. abortus S-19 vaccine strain. This difference can be attributed to the stimulation of cell mediated immune response in PC-PE liposome immunized mice even after challenge which converted to cytotoxicity seen in CD4(+) and CD8(+) enriched lymphocytes. However, in PLGA microparticle immunized mice, cell mediated immunity was not generated after challenge as observed by decreased cytotoxicity of CD4(+) and CD8(+) enriched lymphocytes. Our study emphasizes on the importance of liposome encapsulating Omp25 immunization in conferring protection against B. abortus 544 challenge in Balb/c mice with a single dose immunization regimen.

Outer membrane vesicles from Brucella abortus promote bacterial internalization by human monocytes and modulate their innate immune response

Outer membrane vesicles (OMVs) released by some Gram-negative bacteria have been shown to exert immunomodulatory effects that favor the establishment of the infection. The aim of the present study was to assess the interaction of OMVs from Brucella abortus with human epithelial cells (HeLa) and monocytes (THP-1), and the potential immunomodulatory effects they may exert. Using confocal microscopy and flow cytometry, FITC-labeled OMVs were shown to be internalized by both cell types. Internalization was shown to be partially mediated by clathrin-mediated endocytosis. Pretreatment of THP-1 cells with Brucella OMVs inhibited some cytokine responses (TNF-α and IL-8) to E. coli LPS, Pam3Cys or flagellin (TLR4, TLR2 and TLR5 agonists, respectively). Similarly, pretreatment with Brucella OMVs inhibited the cytokine response of THP-1 cells to B. abortus infection. Treatment of THP-1 cells with OMVs during IFN-γ stimulation reduced significantly the inducing effect of this cytokine on MHC-II expression. OMVs induced a dose-dependent increase of ICAM-1 expression on THP-1 cells and an increased adhesion of these cells to human endothelial cells. The addition of OMVs to THP-1 cultures before the incubation with live B. abortus resulted in increased numbers of adhered and internalized bacteria as compared to cells not treated with OMVs. Overall, these results suggest that OMVs from B. abortus exert cellular effects that promote the internalization of these bacteria by human monocytes, but also downregulate the innate immune response of these cells to Brucella infection. These effects may favor the persistence of Brucella within host cells.

Intradermal immunization with outer membrane protein 25 protects Balb/c mice from virulent B. abortus 544

Brucella abortus is a causative agent of brucellosis, a zoonosis affecting the endemic areas, which infects domestic animals as well as humans, thus, posing a potential bioterror threat. Outer membrane protein 25 is conserved among the Brucella species. Omp25 mutant strain of Brucella is shown to be attenuated in mice emphasizing on the role of Omp25 in Brucella virulence. Moreover, Omp25 has been shown to inhibit TNF-α production in human macrophages, thereby, abrogating cell mediated immunity. In this study, we evaluated the immunogenic potential of recombinant Omp25 and its protective efficacy against virulent B. abortus challenge in Balb/c mice. Recombinant Omp25 was administered via two routes of immunization: intraperitoneal and intradermal. Dosage reduction was observed with intradermal immunization when compared with intraperitoneal immunization. A higher IgG1:IgG2b ratio suggested a strong Th2 bias of immune response in both the routes of immunization. In vitro stimulation of splenocytes from immunized mice resulted in high level of IL-4 along with increasing levels of IL-12 and IFN-γ indicating a mixed Th1 and Th2 type of immune response. Immunized mice were challenged with virulent B. abortus and splenic colonization of B. abortus reduced significantly in intradermally immunized mice. Intradermal immunization gave protection comparable to that of B. abortus S-19 strain. Cytokine levels in spleen homogenate after challenge revealed a cell mediated immune response with elevated levels of IL-12 and IFN-γ but no detectable amount of IL-4. This can be a possible reason behind the protection observed in mice after rOmp25 immunization. Thus, our study proposes recombinant Omp25 to be a potential subunit vaccine candidate against brucellosis.

Replication of Crohn's disease-associated AIEC within macrophages is dependent on TNF-α secretion

Adherent and invasive Escherichia coli (AIEC) associated with Crohn's disease are able to survive and to replicate extensively in active phagolysosomes within macrophages. AIEC-infected macrophages release large amounts of tumour necrosis factor-alpha (TNF-α) and do not undergo cell death. The aim of the present study was to determine what benefit AIEC bacteria could gain from inducing the release of large amounts of TNF-α by infected macrophages and to what extent the neutralization of TNF-α could affect AIEC intramacrophagic replication. Our results showed that the amount of TNF-α released by infected macrophages is correlated with the load of intramacrophagic AIEC bacteria and their intracellular replication. TNF-α secretion was not related to the number of bacteria entering host cells because when the number of bacteria internalized in macrophage was decreased by blocking lipid raft-dependent and clathrin-coated pits-dependent endocytosis, the amount of TNF-α secreted by infected macrophages was not modified. Interestingly, dose-dependent increases in the number of intracellular AIEC LF82 bacteria were observed when infected macrophages were stimulated with exogenous TNF-α, and neutralization of TNF-α secreted by AIEC-infected macrophages using anti-TNF-α antibodies induced a significant decrease in the number of intramacrophagic bacteria. These results indicate that AIEC bacteria use TNF-α as a Trojan horse to ensure their intracellular replication because replication of AIEC bacteria within macrophages induces the release of TNF-α, which in turn increases the intramacrophagic replication of AIEC. Neutralizing TNF-α secreted by infected macrophages may represent an effective strategy to control AIEC intracellular replication.

Identification of immunoreactive proteins of Brucella melitensis by immunoproteomics

Infection with Brucella causes brucellosis, a chronic disease in humans, which induces abortion and sterility in livestock. Among the different Brucella species, Brucella melitensis is considered the most virulent and is the predominant species associated with outbreaks in China. To date, no safe human vaccine is available against Brucella infection. The currently used live vaccines against Brucella in livestock induce antibodies that interfere with the diagnosis of field infection in vaccinated animals, which is harmful to eradication programs. However, there is as yet no complete profile of immunogenic proteins of B. melitensis. Towards the development of a safer, equally efficacious, and field infection-distinguishable vaccine, we used immunoproteomics to identify novel candidate immunogenic proteins from B. melitensis M5. Eighty-eight immunoreactive protein spots from B. melitensis M5 were identified by Western blotting and were assigned to sixty-one proteins by mass spectrometry, including many new immunoreactive proteins such as elongation factor G, F0F1 ATP synthase subunit beta, and OMP1. These provide many candidate immunoreactive proteins for vaccine development.

DNA vaccination of bison to brucellar antigens elicits elevated antibody and IFN-γ responses

Brucella abortus remains a threat to the health and well-being of livestock in states bordering the Greater Yellowstone Area. During the past several years, cohabitation of infected wildlife with cattle has jeopardized the brucellosis-free status of Idaho, USA; Wyoming, USA; and Montana, USA. Current livestock B. abortus vaccines have not proven to be efficacious in bison (Bison bison) or elk (Cervus elaphus nelsoni). One problem with the lack of vaccine efficacy may stem from the failure to understand wildlife immune responses to vaccines. In an attempt to understand their immune responses, bison were vaccinated with eukaryotic DNA expression vectors encoding the Brucella periplasmic protein, bp26, and the chaperone protein, trigger factor (TF). These DNA vaccines have previously been shown to be protective against Brucella infection in mice. Bison were immunized intramuscularly at weeks 0, 2, and 4 with bp26 and TF DNA vaccines plus CpG adjuvant or empty vector (control) plus CpG. Blood samples were collected before vaccination and at 8, 10, and 12 wk after primary vaccination. The results showed that bison immunized with bp26 and TF DNA vaccines developed enhanced antibody, proliferative T cell, and interferon-gamma (IFN-γ) responses upon in vitro restimulation with purified recombinant bp26 or TF antigens, unlike bison immunized with empty vector. Flow cytometric analysis revealed that the percentages of CD4(+) and CD8(+) T lymphocytes from the DNA-vaccinated groups were significantly greater than they were for those bison given empty vector. These data suggest that DNA vaccination of bison may elicit strong cellular immune responses and serve as an alternative for vaccination of bison for brucellosis.

An evolutionary strategy for a stealthy intracellular Brucella pathogen

Brucella is an intracellular bacterial pathogen that causes abortion and infertility in mammals and leads to a debilitating febrile illness that can progress into a long lasting disease with severe complications in humans. Its virulence depends on survival and replication properties in host cells. In this review, we describe the stealthy strategy used by Brucella to escape recognition of the innate immunity and the means by which this bacterium evades intracellular destruction. We also discuss the development of adaptive immunity and its modulation during brucellosis that in course leads to chronic infections. Brucella has developed specific strategies to influence antigen presentation mediated by cells. There is increasing evidence that Brucella also modulates signaling events during host adaptive immune responses.

TNFRp55 modulates IL-6 and nitric oxide responses following Yersinia lipopolysaccharide stimulation in peritoneal macrophages

While cytokines are major regulators of macrophage activation following host-pathogen interactions, they also act to limit inflammation to avoid tissue damage. In previous studies we reported the development of progressive Yersinia enterocolitica-induced reactive arthritis (ReA) in mice lacking the tumor necrosis factor receptor p55 (TNFRp55). In this work, we analyzed the response of TNFRp55⁻/⁻ macrophages to Y. enterocolitica antigens. We found higher concentration of nitric oxide (NO) in TNFRp55⁻/⁻ compared to wild-type macrophages in response to heat-killed Yersinia (HKY) and Yersinia outer membranes (OM). Moreover, Toll-like receptor (TLR)4 expression was increased in OM-stimulated TNFRp55⁻/⁻ versus wild-type (WT) macrophages. Accordingly, NO production was inhibited in TLR4-deficient macrophages following stimulation with OM, suggesting that LPS may function as a major OM component implicated in these responses. Thus, augmented NO production together with enhanced expression of inducible nitric oxide synthase (iNOS) and higher IL-6 production, may provide a pro-inflammatory setting in Yersinia LPS-stimulated TNFRp55⁻/⁻ macrophages. Augmented synthesis of NO and IL-6 was prevented by treatment with Polymyxin B, or by exposure to a specific NF-κB p65 oligonucleotide antisense, indicating the involvement of TLR4-mediated NF-κB activation in the unleashed pro-inflammatory response triggered by TNFRp55 deficiency. Thus, TNFRp55 modulates macrophage functions in response to Yersinia LPS stimulation through mechanisms involving NO, IL-6 and NF-κB pathways, suggesting an essential regulatory role of TNF via TNFRp55 signaling.

Cell-mediated immunity in human brucellosis

Brucella can parasitize within human antigen-presenting cells modifying phagocytosis, phagolysosome fusion, antigen presentation, cytokine secretion, and apoptosis. Subversion of innate immune mechanisms by Brucella leads to defective Th1 immune responses and T-cell anergy in chronic brucellosis patients. This review summarizes the cellular immune responses in brucellosis, based on data derived exclusively from human cells or cell lines.

Cloning and expression of the immunoreactive Brucella melitensis 28 kDa outer-membrane protein (Omp28) encoding gene and evaluation of the potential of Omp28 for clinical diagnosis of brucellosis

Brucellosis is a disease caused by Gram-negative, facultative, intracellular bacteria belonging to the genus Brucella. It is an emerging zoonosis, and an economically important infection of humans and livestock with a worldwide distribution. Human infection is known to occur through consumption of infected raw milk, milk products and undercooked or raw meat. Serodiagnosis of brucellosis is carried out by detection of antibodies generated against LPS or whole-cell bacterial extracts by ELISA or agglutination tests using colorimetry. The present study was designed to develop a highly sensitive and specific indirect ELISA in both a microtitre plate and dot-blot format employing the recombinant outer-membrane protein 28 (rOmp28). Cloning and expression of Brucella melitensis Omp28 protein, which is a group 3 antigen, was accomplished by PCR amplification and cloning of the gene in a pET-28a expression system, followed by Ni-NTA affinity chromatography purification of the His-tagged recombinant protein. An indirect ELISA in both a microtitre plate and dot-blot format was optimized with sera collected from three groups: culture-confirmed cases, clinically suspected cases and healthy individuals. The rOmp28 protein reacted only with the culture-confirmed positive samples and no reaction was observed with culture-negative samples, confirming the immunoreactivity of the recombinant protein. The test in both formats had a correlation of approximately 90 % with the Rose Bengal plate agglutination test (RBPT) and a standard tube agglutination test, assays that are routinely performed for the serodiagnosis of brucellosis. The sensitivity and specificity of the assay in the plate format were 97.50 and 85.59 %, and in the dot-blot format were 82.05 and 92.43%, respectively, in comparison with RBPT. The specificity of this assay was further confirmed by testing samples that were positive for malaria and typhoid, which gave negative results. This ELISA system in microtitre plates and a dot-blot format will be useful for the rapid screening of large numbers of samples for the diagnosis of human brucellosis in endemic areas.

Comparative proteomics analyses reveal the virB of B. melitensis affects expression of intracellular survival related proteins

BACKGROUND

Brucella melitensis is a facultative, intracellular, pathogenic bacterium that replicates within macrophages. The type IV secretion system encoded by the virB operon (virB) is involved in Brucella intracellular survival. However, the underlying molecular mechanisms, especially the target proteins affected by the virB, remain largely unclear.

METHODOLOGY/PRINCIPAL FINDINGS

In order to define the proteins affected by virB, the proteomes of wild-type and the virB mutant were compared under in vitro conditions where virB was highly activated. The differentially expressed proteins were identified by MALDI-TOF-MS. Forty-four down-regulated and eighteen up-regulated proteins which exhibited a 2-fold or greater change were identified. These proteins included those involved in amino acid transport and metabolism, lipid metabolism, energy production, cell membrane biogenesis, translation, post-translational modifications and protein turnover, as well as unknown proteins. Interestingly, several important virulence related proteins involved in intracellular survival, including VjbR, DnaK, HtrA, Omp25, and GntR, were down-regulated in the virB mutant. Transcription analysis of virB and vjbR at different growth phase showed that virB positively affect transcription of vjbR in a growth phase dependent manner. Quantitative RT-PCR showed that transcription of these genes was also affected by virB during macrophage cell infection, consistent with the observed decreased survival of the virB mutant in macrophage.

CONCLUSIONS/SIGNIFICANCE

These data indicated that the virB operon may control the intracellular survival of Brucella by affecting the expression of relevant proteins.