Synthesis of BLF1-containing trimethyl chitosan nanoparticles and evaluation of its immunogenicity and protection in syrian mice by oral and subcutaneous injections

The bacterium Burkholderia pseudomallei is the cause of melioidosis infectious disease. In this bacterium, the BLF1 protein wide inhibits the synthesis of proteins in human cells. This disease is reported to cause a death rate of 40% in some parts of the world. Currently, no effective vaccine is available against this bacterial infection. In this study, therefore, a Nano vaccine was synthesized based on the trimethyl chitosan (TMC) polymer containing the BLF1 recombinant protein, and its immunogenicity and protection in Syrian mice were evaluated by oral and subcutaneous injections. The BLF1 recombinant protein expression was induced in Escherichia coli Bl21 (DE3) and purified by the affinity chromatography technique. Recombinant protein-containing nanoparticles (NPs) were then synthesized by the ionotropic gelation method. After oral and subcutaneous injections, antibody titration was assessed by the indirect ELISA assay. Finally, murine groups were challenged using the BLF1 toxin. The results indicated that the immune system showed more antibody titration in subcutaneous injection than in the oral form. However, the results were reversed in the challenge results, and the survival rate was more significant in the oral injection.

Diabetes and Infectious Diseases with a Focus on Melioidosis

Diabetes mellitus (DM) leads to impaired innate and adaptive immune responses. This renders individuals with DM highly susceptible to microbial infections such as COVID-19, tuberculosis and melioidosis. Melioidosis is a tropical disease caused by the bacterial pathogen Burkholderia pseudomallei, where diabetes is consistently reported as the most significant risk factor associated with the disease. Type-2 diabetes is observed in 39% of melioidosis patients where the risk of infection is 13-fold higher than non-diabetic individuals. B. pseudomallei is found in the environment and is an opportunistic pathogen in humans, often exhibiting severe clinical manifestations in immunocompromised patients. The pathophysiology of diabetes significantly affects the host immune responses that play a critical role in fighting the infection, such as leukocyte and neutrophil impairment, macrophage and monocyte inhibition and natural killer cell dysfunction. These defects result in delayed recruitment as well as activation of immune cells to target the invading B. pseudomallei. This provides an advantage for the pathogen to survive and adapt within the immunocompromised diabetic patients. Nevertheless, knowledge gaps on diabetes-infectious disease comorbidity, in particular, melioidosis-diabetes comorbidity, need to be filled to fully understand the dysfunctional host immune responses and adaptation of the pathogen under diabetic conditions to guide therapeutic options.

Subtractive proteomics-guided vaccine targets identification and designing of multi-epitopes vaccine for immune response instigation against Burkholderia pseudomallei

In this study, a methodical workflow using subtractive proteomics, vaccine designing, molecular simulation, and agent-based modeling approaches were used to annotate the whole proteome of Burkholderia pseudomallei (strain K96243) for vaccine designing. Among the total 5717 proteins in the whole proteome, 505 were observed to be essential for the pathogen's survival and pathogenesis predicted by the Database of Essential Genes. Among these, 23 vaccine targets were identified, of which fimbrial assembly chaperone (Q63UH5), Outer membrane protein (Q63UH1), and Hemolysin-like protein (Q63UE4) were selected for the subsequent analysis based on the systematic approaches. Using immunoinformatic approaches CTL (cytotoxic T lymphocytes), HTL (helper T lymphocytes), IFN-positive, and B cell epitopes were predicted for these targets. A total of 9 CTL epitopes were added using the GSS linker, 6 HTL epitopes using the GPGPG linker, and 6 B cell epitopes using the KK linker. An adjuvant was added for enhanced antigenicity, an HIV-TAT peptide for improved delivery, and a PADRE sequence was added to form a 466 amino acids long vaccine construct. The construct was classified as non-allergenic, highly antigenic, and experimentally feasible. Molecular docking results validated the robust interaction of MEVC with immune receptors such as TLR2/4. Furthermore, molecular simulation revealed stable dynamics and compact nature of the complexes. The binding free energy results further validated the robust binding. In silico cloning, results revealed GC contents of 50.73 % and a CIA value of 0.978 which shows proper downstream processing. Immune simulation results reported that after the three injections of the vaccine a robust secondary immune response, improved antigen clearance, and effective immune memory generation were observed highlighting its potential for effective and sustained immunity. Future directions should encompass experimental validations, animal model studies, and clinical trials to substantiate the vaccine's efficacy, safety, and immunogenicity.

Flagellin-modulated inflammasome pathways characterize the human alveolar macrophage response to Burkholderia pseudomallei, a lung-tropic pathogen

Melioidosis is an emerging tropical infection caused by inhalation, inoculation, or ingestion of the flagellated, facultatively intracellular pathogen Burkholderia pseudomallei. The melioidosis case fatality rate is often high, and pneumonia, the most common presentation, doubles the risk of death. The alveolar macrophage is a sentinel pulmonary host defense cell, but the human alveolar macrophage in B. pseudomallei infection has never been studied. The objective of this study was to investigate the host-pathogen interaction of B. pseudomallei infection with the human alveolar macrophage and to determine the role of flagellin in modulating inflammasome-mediated pathways. We found that B. pseudomallei infects primary human alveolar macrophages but is gradually restricted in the setting of concurrent cell death. Electron microscopy revealed cytosolic bacteria undergoing division, indicating that B. pseudomallei likely escapes the alveolar macrophage phagosome and may replicate in the cytosol, where it triggers immune responses. In paired human blood monocytes, uptake and intracellular restriction of B. pseudomallei are similar to those observed in alveolar macrophages, but cell death is reduced. The alveolar macrophage cytokine response to B. pseudomallei is characterized by marked interleukin (IL)-18 secretion compared to monocytes. Both cytotoxicity and IL-18 secretion in alveolar macrophages are partially flagellin dependent. However, the proportion of IL-18 release that is driven by flagellin is greater in alveolar macrophages than in monocytes. These findings suggest differential flagellin-mediated inflammasome pathway activation in the human alveolar macrophage response to B. pseudomallei infection and expand our understanding of intracellular pathogen recognition by this unique innate immune lung cell.

BpOmpW Antigen Stimulates the Necessary Protective T-Cell Responses Against Melioidosis

Melioidosis is a potentially fatal bacterial disease caused by Burkholderia pseudomallei and is estimated to cause 89,000 deaths per year in endemic areas of Southeast Asia and Northern Australia. People with diabetes mellitus are most at risk of melioidosis, with a 12-fold increased susceptibility for severe disease. Interferon gamma (IFN-γ) responses from CD4 and CD8 T cells, but also from natural killer (NK) and natural killer T (NKT) cells, are necessary to eliminate the pathogen. We previously reported that immunization with B. pseudomallei OmpW (BpOmpW antigen) protected mice from lethal B. pseudomallei challenge for up to 81 days. Elucidating the immune correlates of protection of the protective BpOmpW vaccine is an essential step prior to clinical trials. Thus, we immunized either non-insulin-resistant C57BL/6J mice or an insulin-resistant C57BL/6J mouse model of type 2 diabetes (T2D) with a single dose of BpOmpW. BpOmpW induced strong antibody responses, stimulated effector CD4+ and CD8+ T cells and CD4+ CD25+ Foxp3+ regulatory T cells, and produced higher IFN-γ responses in CD4+, CD8+, NK, and NKT cells in non-insulin-resistant mice. The T-cell responses of insulin-resistant mice to BpOmpW were comparable to those of non-insulin-resistant mice. In addition, as a precursor to its evaluation in human studies, humanized HLA-DR and HLA-DQ (human leukocyte antigen DR and DQ isotypes, respectively) transgenic mice elicited IFN-γ recall responses in an enzyme-linked immune absorbent spot (ELISpot)-based study. Moreover, human donor peripheral blood mononuclear cells (PBMCs) exposed to BpOmpW for 7 days showed T-cell proliferation. Finally, plasma from melioidosis survivors with diabetes recognized our BpOmpW vaccine antigen. Overall, the range of approaches used strongly indicated that BpOmpW elicits the necessary immune responses to combat melioidosis and bring this vaccine closer to clinical trials.

Septicemic Melioidosis Detection Using Support Vector Machine with Five Immune Cell Types

Melioidosis, caused by Burkholderia pseudomallei (B. pseudomallei), predominantly occurs in the tropical regions. Of various types of melioidosis, septicemic melioidosis is the most lethal one with a mortality rate of 40%. Early detection of the disease is paramount for the better chances of cure. In this study, we developed a novel approach for septicemic melioidosis detection, using a machine learning technique-support vector machine (SVM). Several SVM models were built, and 19 features characterized by the corresponding immune cell types were generated by Cell type Identification Estimating Relative Subsets Of RNA Transcripts (CIBERSORT). Using these features, we trained a binomial SVM model on the training set and evaluated it on the independent testing set. Our findings indicated that this model performed well with means of sensitivity and specificity up to 0.962 and 0.979, respectively. Meanwhile, the receiver operating characteristic (ROC) curve analysis gave area under curves (AUCs) ranging from 0.952 to 1.000. Furthermore, we found that a concise SVM model, built upon a combination of CD8+ T cells, resting CD4+ memory T cells, monocytes, M2 macrophages, and activated mast cells, worked perfectly on the detection of septicemic melioidosis. Our data showed that its mean of sensitivity was up to 0.976 while that of specificity up to 0.993. In addition, the ROC curve analysis gave AUC close to 1.000. Taken together, this SVM model is a robust classification tool and may serve as a complementary diagnostic technique to septicemic melioidosis.

Interactions Between Pathogenic Burkholderia and the Complement System: A Review of Potential Immune Evasion Mechanisms

The genus Burkholderia contains over 80 different Gram-negative species including both plant and human pathogens, the latter of which can be classified into one of two groups: the Burkholderia pseudomallei complex (Bpc) or the Burkholderia cepacia complex (Bcc). Bpc pathogens Burkholderia pseudomallei and Burkholderia mallei are highly virulent, and both have considerable potential for use as Tier 1 bioterrorism agents; thus there is great interest in the development of novel vaccines and therapeutics for the prevention and treatment of these infections. While Bcc pathogens Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia cepacia are not considered bioterror threats, the incredible impact these infections have on the cystic fibrosis community inspires a similar demand for vaccines and therapeutics for the prevention and treatment of these infections as well. Understanding how these pathogens interact with and evade the host immune system will help uncover novel therapeutic targets within these organisms. Given the important role of the complement system in the clearance of bacterial pathogens, this arm of the immune response must be efficiently evaded for successful infection to occur. In this review, we will introduce the Burkholderia species to be discussed, followed by a summary of the complement system and known mechanisms by which pathogens interact with this critical system to evade clearance within the host. We will conclude with a review of literature relating to the interactions between the herein discussed Burkholderia species and the host complement system, with the goal of highlighting areas in this field that warrant further investigation.

Melioidosis Patient Survival Correlates With Strong IFN-γ Secreting T Cell Responses Against Hcp1 and TssM

Melioidosis, caused by the Gram-negative bacterium Burkholderia pseudomallei, is a serious infectious disease with diverse clinical manifestations. The morbidity and mortality of melioidosis is high in Southeast Asia and no licensed vaccines currently exist. This study was aimed at evaluating human cellular and humoral immune responses in Thai adults against four melioidosis vaccine candidate antigens. Blood samples from 91 melioidosis patients and 100 healthy donors from northeast Thailand were examined for immune responses against B. pseudomallei Hcp1, AhpC, TssM and LolC using a variety of cellular and humoral immune assays including IFN-γ ELISpot assays, flow cytometry and ELISA. PHA and a CPI peptide pool were also used as control stimuli in the ELISpot assays. Hcp1 and TssM stimulated strong IFN-γ secreting T cell responses in acute melioidosis patients which correlated with survival. High IFN-γ secreting CD4+ T cell responses were observed during acute melioidosis. Interestingly, while T cell responses of melioidosis patients against the CPI peptide pool were low at the time of enrollment, the levels increased to the same as in healthy donors by day 28. Although high IgG levels against Hcp1 and AhpC were detected in acute melioidosis patients, no significant differences between survivors and non-survivors were observed. Collectively, these studies help to further our understanding of immunity against disease following natural exposure of humans to B. pseudomallei as well as provide important insights for the selection of candidate antigens for use in the development of safe and effective melioidosis subunit vaccines.

Role of Burkholderia pseudomallei-Specific IgG2 in Adults with Acute Melioidosis, Thailand

Melioidosis is a life-threatening infectious disease caused by the gram-negative bacillus Burkholderia pseudomallei. An effective vaccine is needed, but data on protective immune responses in human melioidosis are lacking. We used ELISA and an antibody-dependent cellular phagocytosis assay to identify the major features of protective antibodies in patients with acute melioidosis in Thailand. We found that high levels of B. pseudomallei–specific IgG2 are associated with protection against death in a multivariable logistic regression analysis adjusting for age, diabetes, renal disease, and neutrophil count. Serum from melioidosis survivors enhanced bacteria uptake into human monocytes expressing FcγRIIa-H/R131, an intermediate-affinity IgG2-receptor, compared with serum from nonsurvivors. We did not find this enhancement when using monocytes carrying the low IgG2–affinity FcγRIIa-R131 allele. The findings indicate the importance of IgG2 in protection against death in human melioidosis, a crucial finding for antibody-based therapeutics and vaccine development.

Interactions Between Pathogenic Burkholderia and the Complement System: A Review of Potential Immune Evasion Mechanisms

The genus Burkholderia contains over 80 different Gram-negative species including both plant and human pathogens, the latter of which can be classified into one of two groups: the Burkholderia pseudomallei complex (Bpc) or the Burkholderia cepacia complex (Bcc). Bpc pathogens Burkholderia pseudomallei and Burkholderia mallei are highly virulent, and both have considerable potential for use as Tier 1 bioterrorism agents; thus there is great interest in the development of novel vaccines and therapeutics for the prevention and treatment of these infections. While Bcc pathogens Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia cepacia are not considered bioterror threats, the incredible impact these infections have on the cystic fibrosis community inspires a similar demand for vaccines and therapeutics for the prevention and treatment of these infections as well. Understanding how these pathogens interact with and evade the host immune system will help uncover novel therapeutic targets within these organisms. Given the important role of the complement system in the clearance of bacterial pathogens, this arm of the immune response must be efficiently evaded for successful infection to occur. In this review, we will introduce the Burkholderia species to be discussed, followed by a summary of the complement system and known mechanisms by which pathogens interact with this critical system to evade clearance within the host. We will conclude with a review of literature relating to the interactions between the herein discussed Burkholderia species and the host complement system, with the goal of highlighting areas in this field that warrant further investigation.

Burkholderia pseudomallei triggers canonical inflammasome activation in a human primary macrophage-based infection model

Most of the current knowledge on Burkholderia pseudomallei-induced inflammasome activation and cell death in macrophages is derived from murine systems. Little is known about the involved bacterial structures and mechanisms in primary human macrophages. This is of particular relevance since murine and human macrophages as well as primary cells and cell lines differ in many aspects of inflammasome activation, including the proteins involved in the recognition of bacterial patterns. In this study, we therefore aimed (i) to establish an in vitro B. pseudomallei infection model with human monocyte-derived primary macrophages from single donors as these cells more closely resemble macrophages in the human host and (ii) to analyze B. pseudomallei-triggered cell death and bacterial elimination in those cells. Our results show that B. pseudomallei-infected primary human macrophages not only release the inflammasome-independent pro-inflammatory cytokines IL-8 and TNF-α, but are also engaged in canonical inflammasome activation as evidenced by caspase-1 and gasdermin D processing. Absence of the B. pseudomallei T3SS-3 needle protein BsaL, a potent activator of the canonical inflammasome, abolished lytic cell death, reduced IL-1β release, and caspase-1 and gasdermin D processing. IFN-γ, known to promote non-canonical inflammasome activation, did not influence pyroptosis induction or IL-1β release from infected primary human macrophages. Nevertheless, it reduced intracellular B. pseudomallei loads, an effect which was partially antagonist by the inhibition of NADPH oxidase. Overall, our data implicate T3SS-3 dependent inflammasome activation and IFN-γ induced immune mechanisms as critical defense mechanisms of human macrophages against B. pseudomallei. In addition, our infection model provides a versatile tool to study human host-pathogen interactions and has the potential to elucidate the role of human individual genetic variations in B. pseudomallei infections.

Considering the constantly emerging antibiotic resistance of pathogens, comprehensive analyses of immune response mechanisms against infections are urgently needed to provide the basis for novel therapeutic strategies. Studies based on primary murine cells and cell lines of murine and human origin led to advances in the understanding of immune defense mechanisms against bacterial infections including B. pseudomallei. Nevertheless, results relying on these cell types are not always transferrable to primary human cells due to e.g. pathway alterations. We established and validated a macrophage-based model system derived from human peripheral blood monocytes, which yields high amounts of genetically identical cells more closely resembling cells found in the human host. This model system provides the basis for studying the pathogenesis of B. pseudomallei in primary human macrophages and for developing new human host directed therapies avoiding pitfalls from cell lines. Using our newly established model we demonstrate, that restriction of B. pseudomallei by primary human macrophages is mediated by T3SS-3 dependent canonical inflammasome activation and IFN-γ induced intracellular bacterial restriction.

Distinct classes and subclasses of antibodies to hemolysin co-regulated protein 1 and O-polysaccharide and correlation with clinical characteristics of melioidosis patients

Melioidosis is a tropical infectious disease caused by Burkholderia pseudomallei that results in high mortality. Hemolysin co-regulated protein 1 (Hcp1) and O-polysaccharide (OPS) are vaccine candidates and potential diagnostic antigens. The correlation of classes/subclasses of antibodies against these antigens with clinical characteristics of melioidosis patients is unknown. Antibodies in plasma samples from melioidosis patients and healthy donors were quantified by ELISA and compared with clinical features. In melioidosis patients, Hcp1 induced high IgG levels. OPS induced high IgG and IgA levels. The area under receiver operating characteristic curve (AUROCC) to discriminate melioidosis cases from healthy donors was highest for anti-Hcp1 IgG (0.92) compared to anti-Hcp1 IgA or IgM. In contrast, AUROCC for anti-OPS for IgG (0.91) and IgA (0.92) were comparable. Anti-Hcp1 IgG1 and anti-OPS IgG2 had the greatest AUROCCs (0.87 and 0.95, respectively) compared to other IgG subclasses for each antigen. Survivors had significantly higher anti-Hcp1 IgG3 levels than non-survivors. Male melioidosis patients with diabetes had higher anti-OPS IgA levels than males without diabetes. Thus, diverse and specific antibody responses are associated with distinct clinical characteristics in melioidosis, confirming the diagnostic utility of these responses and providing new insights into immune mechanisms.

Evaluation of Burkholderia mallei ΔtonB Δhcp1 (CLH001) as a live attenuated vaccine in murine models of glanders and melioidosis

Background

Glanders caused by Burkholderia mallei is a re-emerging zoonotic disease affecting solipeds and humans. Furthermore, B. mallei is genetically related to B. pseudomallei, which is the causative agent of melioidosis. Both facultative intracellular bacteria are classified as tier 1 select biothreat agents. Our previous study with a B. mallei ΔtonB Δhcp1 (CLH001) live-attenuated vaccine demonstrated that it is attenuated, safe and protective against B. mallei wild-type strains in the susceptible BALB/c mouse model.

Methodology/Principal finding

In our current work, we evaluated the protective efficacy of CLH001 against glanders and melioidosis in the more disease-resistant C57BL/6 mouse strain. The humoral as well as cellular immune responses were also examined. We found that CLH001-immunized mice showed 100% survival against intranasal and aerosol challenge with B. mallei ATCC 23344. Moreover, this vaccine also afforded significant cross-protection against B. pseudomallei K96243, with low level bacterial burden detected in organs. Immunization with a prime and boost regimen of CLH001 induced significantly greater levels of total and subclasses of IgG, and generated antigen-specific splenocyte production of IFN-γ and IL-17A. Interestingly, protection induced by CLH001 is primarily dependent on humoral immunity, while CD4⁺ and CD8⁺ T cells played a less critical protective role.

Conclusions/Significance

Our data indicate that CLH001 serves as an effective live attenuated vaccine to prevent glanders and melioidosis. The quantity and quality of antibody responses as well as improving cell-mediated immune responses following vaccination need to be further investigated prior to advancement to preclinical studies.

Glanders (caused by Burkholderia. mallei) and melioidosis (caused by B. pseudomallei) are severe infectious diseases of concern worldwide because of the rising number of cases and mortality rate. The low infectious doses of these two pathogens along with their amenability for aerosolization are factors that could be exploited as potential biothreat agents. Once the diseases have developed in humans and animals, intrinsic resistance to broad classes of antibiotics becomes a challenge for treatment and increases the risk for relapse. The progress in vaccine development demonstrates that live attenuated vaccine strains are the most effective in protection and providing long-lasting immune responses against both diseases. Our data indicate that the B. mallei double mutant (ΔtonB Δhcp1) strain CLH001, is a feasible vaccine candidate to prevent glanders and melioidosis, especially for biodefense and public health purposes.

Transcriptional profiling unveils type I and II interferon networks in blood and tissues across diseases

Understanding how immune challenges elicit different responses is critical for diagnosing and deciphering immune regulation. Using a modular strategy to interpret the complex transcriptional host response in mouse models of infection and inflammation, we show a breadth of immune responses in the lung. Lung immune signatures are dominated by either IFN-γ and IFN-inducible, IL-17-induced neutrophil- or allergy-associated gene expression. Type I IFN and IFN-γ-inducible, but not IL-17- or allergy-associated signatures, are preserved in the blood. While IL-17-associated genes identified in lung are detected in blood, the allergy signature is only detectable in blood CD4+ effector cells. Type I IFN-inducible genes are abrogated in the absence of IFN-γ signaling and decrease in the absence of IFNAR signaling, both independently contributing to the regulation of granulocyte responses and pathology during Toxoplasma gondii infection. Our framework provides an ideal tool for comparative analyses of transcriptional signatures contributing to protection or pathogenesis in disease.

Rab32 GTPase, as a direct target of miR-30b/c, controls the intracellular survival of Burkholderia pseudomallei by regulating phagosome maturation

Burkholderia pseudomallei is a gram-negative, facultative intracellular bacterium, which causes a disease known as melioidosis. Professional phagocytes represent a crucial first line of innate defense against invading pathogens. Uptake of pathogens by these cells involves the formation of a phagosome that matures by fusing with early and late endocytic vesicles, resulting in killing of ingested microbes. Host Rab GTPases are central regulators of vesicular trafficking following pathogen phagocytosis. However, it is unclear how Rab GTPases interact with B. pseudomallei to regulate the transport and maturation of bacterial-containing phagosomes. Here, we showed that the host Rab32 plays an important role in mediating antimicrobial activity by promoting phagosome maturation at an early phase of infection with B. pseudomallei. And we demonstrated that the expression level of Rab32 is increased through the downregulation of the synthesis of miR-30b/30c in B. pseudomallei infected macrophages. Subsequently, we showed that B. pseudomallei resides temporarily in Rab32-positive compartments with late endocytic features. And Rab32 enhances phagosome acidification and promotes the fusion of B. pseudomallei-containing phagosomes with lysosomes to activate cathepsin D, resulting in restricted intracellular growth of B. pseudomallei. Additionally, Rab32 mediates phagosome maturation depending on its guanosine triphosphate/guanosine diphosphate (GTP/GDP) binding state. Finally, we report the previously unrecognized role of miR-30b/30c in regulating B. pseudomallei-containing phagosome maturation by targeting Rab32 in macrophages. Altogether, we provide a novel insight into the host immune-regulated cellular pathway against B. pseudomallei infection is partially dependent on Rab32 trafficking pathway, which regulates phagosome maturation and enhances the killing of this bacterium in macrophages.

Caprine humoral response to Burkholderia pseudomallei antigens during acute melioidosis from aerosol exposure

Burkholderia pseudomallei causes melioidosis, a common source of pneumonia and sepsis in Southeast Asia and Northern Australia that results in high mortality rates. A caprine melioidosis model of aerosol infection that leads to a systemic infection has the potential to characterize the humoral immune response. This could help identify immunogenic proteins for new diagnostics and vaccine candidates. Outbred goats may more accurately mimic human infection, in contrast to the inbred mouse models used to date. B. pseudomallei infection was delivered as an intratracheal aerosol. Antigenic protein profiling was generated from the infecting strain MSHR511. Humoral immune responses were analyzed by ELISA and western blot, and the antigenic proteins were identified by mass spectrometry. Throughout the course of the infection the assay results demonstrated a much greater humoral response with IgG antibodies, in both breadth and quantity, compared to IgM antibodies. Pre-infection sera showed multiple immunogenic proteins already reactive for IgG (7-20) and IgM (0-12) in most of the goats despite no previous exposure to B. pseudomallei. After infection, the number of IgG reactive proteins showed a marked increase as the disease progressed. Early stage infection (day 7) showed immune reaction to chaperone proteins (GroEL, EF-Tu, and DnaK). These three proteins were detected in all serum samples after infection, with GroEL immunogenically dominant. Seven common reactive antigens were selected for further analysis using ELISA. The heat shock protein GroEL1 elicited the strongest goat antibody immune response compared to the other six antigens. Most of the six antigens showed the peak IgM reactivity at day 14, whereas the IgG reactivity increased further as the disease progressed. An overall MSHR511 proteomic comparison between the goat model and human sera showed that many immune reactive proteins are common between humans and goats with melioidosis.

Antibodies in Melioidosis: The Role of the Indirect Hemagglutination Assay in Evaluating Patients and Exposed Populations

Melioidosis is a major neglected tropical disease with high mortality, caused by the Gram-negative bacterium Burkholderia pseudomallei (Bp). Microbiological culture remains the gold standard for diagnosis, but a simpler and more readily available test such as an antibody assay is highly desirable. In this study, we conducted a serological survey of blood donors (n = 1,060) and adult melioidosis patients (n = 200) in northeast Thailand to measure the antibody response to Bp using the indirect hemagglutination assay (IHA). We found that 38% of healthy adults (aged 17-59 years) have seropositivity (IHA titer ≥ 1:80). The seropositivity in healthy blood donors was associated with having a declared occupation of rice farmer and with residence in a nonurban area, but not with gender or age. In the melioidosis cohort, the seropositivity rate was higher in adult patients aged between 18 and 45 years (90%, 37/41) compared with those aged ≥ 45 years (68%, 108/159, P = 0.004). The seropositivity rate was significantly higher in people with diabetes (P = 0.008). Seropositivity was associated with decreased mortality on univariable analysis (P = 0.005), but not on multivariable analysis when adjusted for age, diabetes status, preexisting renal disease, and neutrophil count. This study confirms the presence of high background antibodies in an endemic region and demonstrates the limitations of using IHA during acute melioidosis in this population.

Disease progression in mice exposed to low-doses of aerosolized clinical isolates of Burkholderia pseudomallei

Mouse models have been essential to generate supporting data for the research of infectious diseases. Burkholderia pseudomallei, the etiological agent of melioidosis, has been studied using mouse models to investigate pathogenesis and efficacy of novel medical countermeasures to include both vaccines and therapeutics. Previous characterization of mouse models of melioidosis have demonstrated that BALB/c mice present with an acute infection, whereas C57BL/6 mice have shown a tendency to be more resistant to infection and may model chronic disease. In this study, either BALB/c or C57BL/6 mice were exposed to aerosolized human clinical isolates of B. pseudomallei. The bacterial strains included HBPUB10134a (virulent isolate from Thailand), MSHR5855 (virulent isolate from Australia), and 1106a (relatively attenuated isolate from Thailand). The LD₅₀ values were calculated and serial sample collections were performed in order to examine the bacterial burdens in tissues, histopathological features of disease, and the immune response mounted by the mice after exposure to aerosolized B. pseudomallei. These data will be important when utilizing these models for testing novel medical countermeasures. Additionally, by comparing highly virulent strains with attenuated isolates, we hope to better understand the complex disease pathogenesis associated with this bacterium.

Seroepidemiology of Burkholderia pseudomallei, Etiologic Agent of Melioidosis, in the Ouest and Sud-Est Departments of Haiti

Burkholderia pseudomallei, the etiological agent of melioidosis, has been hypothesized to be endemic throughout the Caribbean, including the impoverished nation of Haiti. However, because of the protean clinical manifestations, presence of asymptomatic infections, and limited medical diagnostic capacity, the identification of active melioidosis cases remains challenging. A seroepidemiological study was conducted using a novel enzyme-linked immunosorbent assay (ELISA) to detect antibodies toward B. pseudomallei in the native population. The performance of an indirect ELISA with purified lipopolysaccharide (LPS) from B. pseudomallei was evaluated using serum collected from rhesus macaques exposed to aerosolized B. pseudomallei. After optimization, serum collected from asymptomatic population members (n = 756) was screened for polyvalent (immunoglobulin M [IgM]/ immunoglobulin G [IgG]/ immunoglobulin A) and monoclonal (IgG or IgM) immunoglobulins against B. pseudomallei LPS. The population seroprevalence was 11.5% (95% confidence interval [CI]: 9.2, 13.8) for polyvalent immunoglobulins, 9.8% (95% CI: 7.7, 11.9) for IgG, and 1.7% (95% CI: 0.8, 2.6%) for IgM. The seroprevalence was not significantly different by gender (P = 0.16), but increased significantly (P < 0.001) with age, yielding an estimated annual seroconversion rate of 1.05% (95% CI: 0.81, 1.3). The detection of both recent (IgM+) and previous (IgG+) exposure to B. pseudomallei provides serological evidence that melioidosis is endemic in Haiti.

Caspase-11-dependent pyroptosis of lung epithelial cells protects from melioidosis while caspase-1 mediates macrophage pyroptosis and production of IL-18

Infection with Burkholderia pseudomallei or B. thailandensis triggers activation of the NLRP3 and NLRC4 inflammasomes leading to release of IL-1β and IL-18 and death of infected macrophages by pyroptosis, respectively. The non-canonical inflammasome composed of caspase-11 is also activated by these bacteria and provides protection through induction of pyroptosis. The recent generation of bona fide caspase-1-deficient mice allowed us to reexamine in a mouse model of pneumonic melioidosis the role of caspase-1 independently of caspase-11 (that was also absent in previously generated Casp1^-/- mice). Mice lacking either caspase-1 or caspase-11 were significantly more susceptible than wild type mice to intranasal infection with B. thailandensis. Absence of caspase-1 completely abolished production of IL-1β and IL-18 as well as pyroptosis of infected macrophages. In contrast, in mice lacking caspase-11 IL-1β and IL-18 were produced at normal level and macrophages pyroptosis was only marginally affected. Adoptive transfer of bone marrow indicated that caspase-11 exerted its protective action both in myeloid cells and in radio-resistant cell types. B. thailandensis was shown to readily infect mouse lung epithelial cells triggering pyroptosis in a caspase-11-dependent way in vitro and in vivo. Importantly, we show that lung epithelial cells do not express inflammasomes components or caspase-1 suggesting that this cell type relies exclusively on caspase-11 for undergoing cell death in response to bacterial infection. Finally, we show that IL-18’s protective action in melioidosis was completely dependent on its ability to induce IFNγ production. In turn, protection conferred by IFNγ against melioidosis was dependent on generation of ROS through the NADPH oxidase but independent of induction of caspase-11. Altogether, our results identify two non-redundant protective roles for caspase-1 and caspase-11 in melioidosis: Caspase-1 primarily controls pyroptosis of infected macrophages and production of IL-18. In contrast, caspase-11 mediates pyroptosis of infected lung epithelial cells.

Burkholderia pseudomallei is a bacterium that infect macrophages and other cell types and causes a diseases called melioidosis. Inflammasomes are multiprotein complexes that control activation of the proteases caspase-1 and caspase-11 resulting in production of the inflammatory mediators IL-1β and IL-18 and death of infected cells. Mice deficient of caspase-1 or caspase-11 are more susceptible to infection with B. pseudomallei or the closely related B. thailandensis. Here we show that absence of caspase-1 completely abolished production of IL-1β and IL-18 as well as death of macrophages infected with B. thailandensis. In contrast, in the highly susceptible caspase-11-deficient mice, IL-1β and IL-18 production and macrophages death were not significantly affected. Rather, absence of caspase-11 abolished death of infected lung epithelial cells. Taken together, our results show that caspase-1 and caspase-11 have non-redundant protective roles in melioidosis: Caspase-1 primarily controls cell death of infected macrophages and production of IL-18. In contrast, caspase-11 mediates cell death of infected lung epithelial cells.

Inactivation of bpsl1039-1040 ATP-binding cassette transporter reduces intracellular survival in macrophages, biofilm formation and virulence in the murine model of Burkholderia pseudomallei infection

Burkholderia pseudomallei, a gram-negative intracellular bacillus, is the causative agent of a tropical infectious disease called melioidosis. Bacterial ATP-binding cassette (ABC) transporters import and export a variety of molecules across bacterial cell membranes. At present, their significance in B. pseudomallei pathogenesis is poorly understood. We report here characterization of the BPSL1039-1040 ABC transporter. B. pseudomallei cultured in M9 medium supplemented with nitrate, demonstrated that BPSL1039-1040 is involved in nitrate transport for B. pseudomallei growth under anaerobic, but not aerobic conditions, suggesting that BPSL1039-1040 is functional under reduced oxygen tension. In addition, a nitrate reduction assay supported the function of BPSL1039-1040 as nitrate importer. A bpsl1039-1040 deficient mutant showed reduced biofilm formation as compared with the wild-type strain (P = 0.027) when cultured in LB medium supplemented with nitrate under anaerobic growth conditions. This reduction was not noticeable under aerobic conditions. This suggests that a gradient in oxygen levels could regulate the function of BPSL1039-1040 in B. pseudomallei nitrate metabolism. Furthermore, the B. pseudomallei bpsl1039-1040 mutant had a pronounced effect on plaque formation (P < 0.001), and was defective in intracellular survival in both non-phagocytic (HeLa) and phagocytic (J774A.1 macrophage) cells, suggesting reduced virulence in the mutant strain. The bpsl1039-1040 mutant was found to be attenuated in a BALB/c mouse intranasal infection model. Complementation of the bpsl1039-1040 deficient mutant with the plasmid-borne bpsl1039 gene could restore the phenotypes observed. We propose that the ability to acquire nitrate for survival under anaerobic conditions may, at least in part, be important for intracellular survival and has a contributory role in the pathogenesis of B. pseudomallei.

Immune Control of Burkholderia pseudomallei--Common, High-Frequency T-Cell Responses to a Broad Repertoire of Immunoprevalent Epitopes

Burkholderia pseudomallei (Bp) is an environmental bacterial pathogen that causes potentially lethal sepsis in susceptible individuals and is considered a Category B, Tier-1 biothreat agent. As such, it is crucial to gain an improved understanding of protective immunity and potential vaccine candidates. The nature of immune correlates dictating why most exposed individuals in endemic regions undergo asymptomatic seroconversion while others succumb to life-threatening sepsis is largely uncharted. Bp seroreactive, immunogenic proteins have previously been identified by antigen microarray. We here set out to conduct an analysis of T-cell recognition of the Bp immunome using serodominant antigens represented in the original antigen microarray, examining immune correlates of disease in healthy seropositive individuals and those with acute disease or in convalescence. By screening a library of 739 overlapping peptides representing the sequences of 20 different Bp antigens, we aimed to define immune correlates of protection at the level of immunoprevalent T-cell epitopes. Responses to a large number of epitopes were common in healthy seropositive individuals: we found remarkably broad responsiveness to Bp epitopes, with 235 of 739 peptides recognized by ≥80% of all tested donors. The cumulative response to Bp epitopes in healthy, seropositive, donors from this endemic region were of the order of thousands of spot forming cells per million cells, making Bp recognition a significant component of the T-cell repertoire. Noteworthy among our findings, analysis revealed 10 highly immunoprevalent T-cell epitopes, able to induce Bp-specific IFNγ responses that were high in responding T-cell frequency within the repertoire, and also common across individuals with different human leukocyte antigen types. Acute melioidosis patients showed poor T-cell responses to the immunoprevalent epitopes, but acquired responsiveness following recovery from infection. Our findings suggest that a large repertoire of CD4 T cells, high in frequency and with broad coverage of antigens and epitopes, is important in controlling Bp infection. This offers an attractive potential strategy for subunit or epitope-based vaccines.

Comprehensive analysis of clinical Burkholderia pseudomallei isolates demonstrates conservation of unique lipid A structure and TLR4-dependent innate immune activation

Burkholderia pseudomallei is an environmental bacterium that causes melioidosis, a major community-acquired infection in tropical regions. Melioidosis presents with a range of clinical symptoms, is often characterized by a robust inflammatory response, may relapse after treatment, and results in high mortality rates. Lipopolysaccharide (LPS) of B. pseudomallei is a potent immunostimulatory molecule comprised of lipid A, core, and O-polysaccharide (OPS) components. Four B. pseudomallei LPS types have been described based on SDS-PAGE patterns that represent the difference of OPS-type A, type B, type B2 and rough LPS. The majority of B. pseudomallei isolates are type A. We used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) followed by electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QqTOF MS) and gas chromatography to characterize the lipid A of B. pseudomallei within LPS type A isolates. We determined that B. pseudomallei lipid A is represented by penta- and tetra-acylated species modified with 4-amino-4-deoxy-arabinose (Ara4N). The MALDI-TOF profiles from 171 clinical B. pseudomallei isolates, including 68 paired primary and relapse isolates and 35 within-host isolates were similar. We did not observe lipid A structural changes when the bacteria were cultured in different growth conditions. Dose-dependent NF-κB activation in HEK cells expressing TLR4 was observed using multiple heat-killed B. pseudomallei isolates and corresponding purified LPS. We demonstrated that TLR4-dependent NF-κB activation induced by heat-killed bacteria or LPS prepared from OPS deficient mutant was significantly greater than those induced by wild type B. pseudomallei. These findings suggest that the structure of B. pseudomallei lipid A is highly conserved in a wide variety of clinical and environmental circumstances but that the presence of OPS may modulate LPS-driven innate immune responses in melioidosis.

Structural characterisation of the capsular polysaccharide expressed by Burkholderia thailandensis strain E555:: wbiI (pKnock-KmR) and assessment of the significance of the 2-O-acetyl group in immune protection

Burkholderia pseudomallei and its close relative B. mallei are human pathogens that are classified as Tier 1 bio-threat agents. Both organisms have previously been shown to constitutively produce a capsular polysaccharide (CPS) that is both a virulence determinant and protective antigen. Extraction and purification of CPS for use as a potential vaccine candidate requires containment level 3 laboratories which is expensive and time-consuming. B. thailandensis strain E555 is closely related to B. pseudomallei and B. mallei, but is non-pathogenic to humans and based on immunological cross-reactivity has previously been shown to express a B. pseudomallei-like CPS. In this study, capsular polysaccharide isolated from an O-antigen deficient strain of B. thailandensis E555 was identified by 1H and 13C NMR spectroscopy as -3-)-2-O-acetyl-6-deoxy-β-d-manno-heptopyranose-(-1, and identical to that produced by B. pseudomallei. This was further substantiated by anti-CPS monoclonal antibody binding. In connection with the production of CPS fragments for use in glycoconjugate vaccines, we set out to assess the importance or otherwise of the CPS 2-OAc groups in immune protection. To this end conjugates of the native and de-O-acetylated CPS with the Hc fragment of tetanus toxin (TetHc) were used as vaccines in a mouse model of melioidosis. The level of protection provided by deacetylated CPS was significantly lower than that from native, acetylated CPS. In addition, sera from mice vaccinated with the deacetylated CPS conjugate did not recognise native CPS. This suggests that CPS extracted from B. thailandensis can be used as antigen and that the acetyl group is essential for protection.

Infection with Burkholderia pseudomallei - immune correlates of survival in acute melioidosis

Melioidosis, caused by Burkholderia pseudomallei, is a potentially lethal infection with no licensed vaccine. There is little understanding of why some exposed individuals have no symptoms, while others rapidly progress to sepsis and death, or why diabetes confers increased susceptibility. We prospectively recruited a cohort of 183 acute melioidosis patients and 21 control subjects from Northeast Thailand and studied immune parameters in the context of survival status and the presence or absence of diabetes. HLA-B*46 (one of the commonest HLA class I alleles in SE Asia) and HLA-C*01 were associated with an increased risk of death (odds ratio 2.8 and 3.1 respectively). Transcriptomic analysis during acute infection in diabetics indicated the importance of interplay between immune pathways including those involved in antigen presentation, chemotaxis, innate and adaptive immunity and their regulation. Survival was associated with enhanced T cell immunity to nine of fifteen immunodominant antigens analysed including AhpC (BPSL2096), BopE (BPSS1525), PilO (BPSS1599), ATP binding protein (BPSS1385) and an uncharacterised protein (BPSL2520). T cell immunity to GroEL (BPSL2697) was specifically impaired in diabetic individuals. This characterization of immunity associated with survival during acute infection offers insights into correlates of protection and a foundation for design of an effective multivalent vaccine.