Expression and bactericidal activity of nitric oxide synthase in Brucella suis-infected murine macrophages

Brucella spp. are facultative anaerobic bacteria under denitrifying conditions

IMPORTANCE

Respiration is a fundamental and complex process that bacteria use to produce energy. Despite aerobic respiration being the most common, some bacteria make use of a mode of respiration in the absence of oxygen, called anaerobic respiration, which can yield advantages in adaptation to various environmental conditions. Denitrification is part of this respiratory process ensuring higher respiratory flexibility under oxygen depletion. Here, we report for the first time the evidence of anaerobic growth of Brucella spp. under denitrifying conditions, which implies that this genus should be reconsidered as facultative anaerobic. Our study further describes that efficient denitrification is not equally found within the Brucella genus, with atypical species showing a greater ability to denitrify, correlated with higher expression of the genes involved, as compared to classical species.

Intracellular Growth Inhibition and Host Immune Modulation of 3-Amino-1,2,4-triazole in Murine Brucellosis

Catalase, an antioxidant enzyme widely produced in mammalian cells and bacteria, is crucial to mitigating oxidative stress in hostile environments. This function enhances the intracellular survivability of various intracellular growth pathogens, including Brucella (B.) abortus. In this study, to determine whether the suppression of catalase can inhibit the intracellular growth of B. abortus, we employed 3-amino-1,2,4-triazole (3-AT), a catalase inhibitor, in both RAW 264.7 macrophage cells and an ICR mouse model during Brucella infection. The intracellular growth assay indicated that 3-AT exerts growth-inhibitory effects on B. abortus within macrophages. Moreover, it contributes to the accumulation of reactive oxygen species and the formation of nitric oxide. Notably, 3-AT diminishes the activation of the nucleus transcription factor (NF-κB) and modulates the cytokine secretion within infected cells. In our mouse model, the administration of 3-AT reduced the B. abortus proliferation within the spleens and livers of infected mice. This reduction was accompanied by a diminished immune response to infection, as indicated by the lowered levels of TNF-α, IL-6, and IL-10 and altered CD4+/CD8+ T-cell ratio. These results suggest the protective and immunomodulatory effects of 3-AT treatment against Brucella infection.

Cytokine expression profile of B. melitensis-infected goat monocyte-derived macrophages

Brucella parasitize the macrophage where is able to replicate and modulate the immune response in order to establish a chronic infection. The most adequate response to control and eliminate Brucella infection is a type 1 (Th1) cell-mediated effector immunity. Research in immune response of B. melitensis-infected goats is relatively scarce. In this study, we first evaluated changes in the gene expression of cytokines, a chemokine (CCL2) and the inducible nitric oxide synthase (iNOS) of goat macrophage cultures derived from monocytes (MDMs) infected for 4 and 24 h with Brucella melitensis strain 16 M. TNFα, IL-1β and iNOS, and IL-12p40, IFNγ and also iNOS were significantly expressed (p < 0.05) at 4 and 24 h respectively, in infected compared to non-infected MDMs. Therefore, the in vitro challenge of goat MDMs with B. melitensis promoted a transcriptional profile consistent with a type 1 response. However, when the immune response to B. melitensis infection was contrasted between MDM cultures phenotypically restrictive or permissive to intracellular multiplication of B. melitensis 16 M, it was observed that the relative IL-4 mRNA expression was significantly higher in permissive macrophage cultures with respect to restrictive cultures (p < 0.05), independently of the time p.i. A similar trend, although non-statistical, was recorded for IL-10, but not for pro-inflammatory cytokines. Thus, the up-expression profile of inhibitory instead of pro-inflammatory cytokines could explain, in part, the difference observed in the ability to restrict intracellular replication of Brucella. In this sense, the present results make a significant contribution to the knowledge of the immune response induced by B. melitensis in macrophages of its preferential host species.

Live mucosal vaccination stimulates potent protection via varied CD4+ and CD8+ T cell subsets against wild-type Brucella melitensis 16M challenge

Re-emerging zoonotic pathogen Brucella spp. continues to impact developing countries and persists in expanding populations of wildlife species in the US, constantly threatening infection of our domestic herds. The development of improved animal and human vaccines remains a priority. In this study, immunity to a novel live attenuated B. melitensis strain, termed znBM-mC, was characterized. An oral prime, intranasal (IN) boost strategy conferred exquisite protection against pulmonary challenge, with wild-type (wt) B. melitensis providing nearly complete protection in the lungs and spleens from brucellae colonization. Vaccination with znBM-mC showed an IFN-γ⁺ CD8⁺ T-cell bias in the lungs as opposed to Rev 1-vaccinated mice showing IFN-γ⁺ CD4⁺ T-cell inclination. Lung CD4⁺ and CD8⁺ effector memory T cells (TEMs) increased over 200-fold; and lung CD4⁺ and CD8⁺ resident memory T cells (TRMs) increased more than 250- and 150-fold, respectively. These T cells served as the primary producers of IFN-γ in the lungs, which was essential for vaccine clearance and the predominant cytokine generated pre-and post-challenge with wt B. melitensis 16M; znBM-mC growth could not be arrested in IFN-γ^−/− mice. Increases in lung TNF-α and IL-17 were also induced, with IL-17 being mostly derived from CD4⁺ T cells. Vaccination of CD4^−/−, CD8^−/−, and B6 mice with znBM-mC conferred full protection in the lungs and spleens post-pulmonary challenge with virulent B. melitensis; vaccination of IL-17^−/− mice resulted in the protection of the lungs, but not the spleen. These data demonstrate the efficacy of mucosal vaccine administration for the generation of protective memory T cells against wt B. melitensis.

Idiosyncratic Biogenesis of Intracellular Pathogens-Containing Vacuoles

While most bacterial species taken up by macrophages are degraded through processing of the bacteria-containing vacuole through the endosomal-lysosomal degradation pathway, intravacuolar pathogens have evolved to evade degradation through the endosomal-lysosomal pathway. All intra-vacuolar pathogens possess specialized secretion systems (T3SS-T7SS) that inject effector proteins into the host cell cytosol to modulate myriad of host cell processes and remodel their vacuoles into proliferative niches. Although intravacuolar pathogens utilize similar secretion systems to interfere with their vacuole biogenesis, each pathogen has evolved a unique toolbox of protein effectors injected into the host cell to interact with, and modulate, distinct host cell targets. Thus, intravacuolar pathogens have evolved clear idiosyncrasies in their interference with their vacuole biogenesis to generate a unique intravacuolar niche suitable for their own proliferation. While there has been a quantum leap in our knowledge of modulation of phagosome biogenesis by intravacuolar pathogens, the detailed biochemical and cellular processes affected remain to be deciphered. Here we discuss how the intravacuolar bacterial pathogens Salmonella, Chlamydia, Mycobacteria, Legionella, Brucella, Coxiella, and Anaplasma utilize their unique set of effectors injected into the host cell to interfere with endocytic, exocytic, and ER-to-Golgi vesicle traffic. However, Coxiella is the main exception for a bacterial pathogen that proliferates within the hydrolytic lysosomal compartment, but its T4SS is essential for adaptation and proliferation within the lysosomal-like vacuole.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

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.

Proteomics Investigation of the Time Course Responses of RAW264.7 Macrophages to Infections With the Wild-Type and Twin-Arginine Translocation Mutant Strains of Brucella melitensis

Brucella, a notorious intracellular pathogen, causes chronic infections in many mammals, including humans. The twin-arginine translocation (Tat) pathway transports folded proteins across the cytoplasmic membrane; protein substrates translocated by Brucella include ABC transporters, oxidoreductases, and cell envelope biosynthesis proteins. Previously, we showed that a Tat mutant of Brucella melitensis M28 exhibits reduced survival within murine macrophages. In this study, we compared the host responses elicited by wild-type M28 and its Tat-mutant strains ex vivo. We utilized label-free quantitative proteomics to assess proteomic changes in RAW264.7 macrophages after infection with M28 and its Tat mutants. A total of 6085 macrophage proteins were identified with high confidence, and 79, 50, and 99 proteins were differentially produced upon infection with the Tat mutant at 4, 24, and 48 hpi, respectively, relative to the wild-type infection. Gene ontology and KEGG enrichment analysis indicated that immune response-related proteins were enriched among the upregulated proteins. Compared to the wild-type M28 infection, the most upregulated proteins upon Tat-mutant infection included the cytosolic nucleic acid signaling pathway-related proteins IFIH1, DHX58, IFI202, IFI204, and ISG15 and the NF-κB signaling pathway-related proteins PTGS2, CD40, and TRAF1, suggesting that the host increases the production of these proteins in response to Tat mutant infection. Upregulation of some proteins was further verified by a parallel reaction monitoring (PRM) assay. ELISA and qRT-PCR assays indicated that Tat mutant infection significantly induced proinflammatory cytokine (TNF-α and IL-6) and nitric oxide (NO) production. Finally, we showed that the Tat mutant displays higher sensitivity to nitrosative stress than the wild type and that treatment with the NO synthase inhibitor L-NMMA significantly increases the intracellular survival of the Tat mutant, indicating that NO production contributes to restricting Tat mutant survival within macrophages. Collectively, this work improves our understanding of host immune responses to Tat mutants and provides insights into the mechanisms underlying the attenuated virulence of Tat mutants.

STING regulates metabolic reprogramming in macrophages via HIF-1α during Brucella infection

Macrophages metabolic reprogramming in response to microbial insults is a major determinant of pathogen growth or containment. Here, we reveal a distinct mechanism by which stimulator of interferon genes (STING), a cytosolic sensor that regulates innate immune responses, contributes to an inflammatory M1-like macrophage profile upon Brucella abortus infection. This metabolic reprogramming is induced by STING-dependent stabilization of hypoxia-inducible factor-1 alpha (HIF-1α), a global regulator of cellular metabolism and innate immune cell functions. HIF-1α stabilization reduces oxidative phosphorylation and increases glycolysis during infection with B. abortus and, likewise, enhances nitric oxide production, inflammasome activation and IL-1β release in infected macrophages. Furthermore, the induction of this inflammatory profile participates in the control of bacterial replication since absence of HIF-1α renders mice more susceptible to B. abortus infection. Mechanistically, activation of STING by B. abortus infection drives the production of mitochondrial reactive oxygen species (mROS) that ultimately influences HIF-1α stabilization. Moreover, STING increases the intracellular succinate concentration in infected macrophages, and succinate pretreatment induces HIF-1α stabilization and IL-1β release independently of its cognate receptor GPR91. Collectively, these data demonstrate a pivotal mechanism in the immunometabolic regulation of macrophages during B. abortus infection that is orchestrated by STING via HIF-1α pathway and highlight the metabolic reprogramming of macrophages as a potential treatment strategy for bacterial infections.

The impact of host cell metabolism on pathogen growth or restriction represent an emerging field in immunology and shed light on the intricate network of signaling pathways during immune cells response. Here, we dissected a distinct mechanism by which STING regulates macrophage metabolic reprogramming eliciting an inflammatory profile during Brucella infection. Brucella abortus is an intracellular bacterium that causes brucellosis, an infectious disease that promotes abortion in domestic animals leading to severe economic losses and an inflammatory condition in humans. The metabolite reprogramming orchestrated by STING relies on HIF-1α stabilization through increased succinate and mROS levels. We demonstrated that HIF-1α stabilization enhances nitric oxide production, inflammasome activation and IL-1β release in infected macrophages, and this inflammatory profile participates in the control of bacterial replication. Thus, our findings bring new insights on this intricate circuit by which the host immune senses intracellular pathogens contributing to development of drugs and/or vaccines to control infectious diseases.

Characterization of innate immune response to Brucella melitensis infection in goats with permissive or restrictive phenotype for Brucella intramacrophagic growth

Caprine brucellosis is a chronic, world-wide distributed disease which causes reproductive failure in goats and Brucella melitensis, its causative agent, bears a great zoonotic potential. There is evidence suggesting that some cattle and pigs have an innate ability to resist Brucella infection, but this has not yet been investigated in goats. In this study, we compared caprine macrophages that exhibit extreme restriction and permissiveness to B. melitensis' intracellular growth in vitro. Monocyte derived macrophages (MDMs) from 110 female goats were cultured and challenged in vitro with B. melitensis 16 M. After initial screening, 18 donor goats were selected based on their macrophages ability to restrict or allow bacterial intracellular growth and some elements of humoral and cellular immunity were studied in depth. MDMs that were able to restrict the pathogen's intracellular growth showed enhanced bacterial internalization, although there were no differences between groups in the production of reactive oxygen and nitrogen intermediates following 48 h treatment with heat-killed B. melitensis. Moreover, there were no differences between groups in the level of antibodies reacting with keyhole limpet hemocyanin (natural antibodies, NAbs) or with Brucella LPS antigens (cross-reacting antibodies, CrAbs), although a strong positive correlation between individual levels of IgM NAbs and IgM CrAbs was detected. Altogether, these results represent an initial step in understanding innate primary host response to B. melitensis, and deciphering which mechanisms may determine a successful outcome of the infection in goats.

Crude polysaccharide from the milky mushroom, Calocybe indica, modulates innate immunity of macrophage cells by triggering MyD88-dependent TLR4/NF-κB pathway

OBJECTIVES

Calocybe indica is a famous nutritious food in Asian countries and one of the most widely cultivated mushrooms in the world. Here, we have isolated crude polysaccharides from this mushroom, characterized it and investigated its antioxidant and immunostimulatory potential.

METHODS

The polysaccharide was chemically characterized by spectrophotometry, FTIR and high-performance thin layer chromatography and tested its antioxidant potential by in vitro assays. Immunomodulatory activity and its underlying signalling process were ascertained in RAW 264.7 cells.

KEY FINDINGS

The polysaccharide consisted of D-glucose (β-linked sugars), D-mannose and D-galactose, where backbone was organized in random coil structure. Preliminary investigation of the bioactivity of the polysaccharide revealed its antioxidant potential. The polysaccharide could noticeably induce phagocytic activity and production of immune mediators in macrophage cells. The polysaccharide was found to enhance the expression of pro-inflammatory cytokines and activate NF-κB signalling pathway by overexpressing MyD88, Iκ-Bα and NF-κB. Further studies indicated the polysaccharide binds to the toll-like receptor 4 to manifest its immunostimulatory activity in macrophage cells.

CONCLUSIONS

Our findings indicate potential therapeutic properties of the crude polysaccharide of C. indica which might provide the means to treat various radical induced and immunodeficiency disorders in the days to come.

Modulatory Effect of Linoleic Acid During Brucella abortus 544 Infection in Murine Macrophage RAW264.7 Cells and Murine Model BALB/c Mice

In this study, we investigated the effects of linoleic acid (LA) treatment on Brucella abortus infection in professional phagocyte RAW264.7 cells, particularly during the pathogens invasion and intracellular growth in these cells, as well as in murine model BALB/c mice focusing on bacterial splenic proliferation and immunoregulatory activities. LA inhibited the growth of Brucella in a doseand time-dependent manner. The ability of the pathogen to enter the phagocytes was inhibited as was its survival within these cells. This was accompanied by increased nitrite accumulation in these cells at 24 h post-infection. The concentration of LA used in the present study did not affect the total body weight or liver function of the mice. During Brucella infection, the total splenic weight of these animals was not changed; rather, resistance to bacterial proliferation was enhanced in the spleen. Furthermore, mice treated with LA displayed elevated levels of IL-12 and IFN-γ but reduced levels of IL-10 during infection. The findings in this study showed the regulatory role of LA against B. abortus infection suggesting its potential use in designing intervention strategy for brucellosis.

IFN-γ-dependent nitric oxide suppresses Brucella-induced arthritis by inhibition of inflammasome activation

Brucellosis, caused by the intracellular bacterial pathogen Brucella, is a globally important zoonotic disease for which arthritis is the most common focal complication in humans. Wild-type mice infected systemically with Brucella typically do not exhibit arthritis, but mice lacking IFN-γ develop arthritis regardless of the route of Brucella infection. Here, we investigated mechanisms by which IFN-γ suppresses Brucella-induced arthritis. Several cell types, including innate lymphoid cells, contributed to IFN-γ production and suppression of joint swelling. IFN-γ deficiency resulted in elevated joint IL-1β levels, and severe joint inflammation that was entirely inflammasome dependent, and in particular, reliant on the NLRP3 inflammasome. IFN-γ was vital for induction of the nitric oxide producing enzyme, iNOS, in infected joints, and nitric oxide directly inhibited IL-1β production and inflammasome activation in Brucella-infected macrophages in vitro. During in vivo infection, iNOS deficiency resulted in an increase in IL-1β and inflammation in Brucella-infected joints. Collectively, this data indicate that IFN-γ prevents arthritis both by limiting Brucella infection, and by inhibiting excessive inflammasome activation through the induction of nitric oxide.

Immune response and differentially expressed proteins in the lung tissue of BALB/c mice challenged by aerosolized Brucella melitensis 5

Objective

This study was performed to develop a murine aerosol infection model of brucellosis to investigate the pathogenicity and immune reactions induced by aerosolized Brucella and to identify key proteins associated with Brucella infection in lung tissue.

Methods

BALB/c mice were exposed to aerosolized Brucella melitensis 5 (M5) for 30 minutes and killed at 1, 3, 7, and 15 days post-exposure. Clinical observation, pathological analysis of lung tissue, and cytokine expression detection were then performed. Proteomic analysis based on two-dimensional electrophoresis and mass spectrometry was used to identify proteins exhibiting significant changes in expression in lung tissues during Brucella infection.

Results

Pathological analysis revealed alveolar wall thickening, telangiectasia with hyperemia, inflammatory cell infiltration, large areas of congestion and bleeding, and areas of focal necrosis. The T-helper 1 type immune response played an important role during aerosol infection, and 12 differentially expressed proteins were involved in the infectious process in lung tissue.

Conclusion

These results contribute to our understanding of the pathogenic process of Brucella in the lung tissue of BALB/c mice challenged with aerosolized Brucella. Some of the identified proteins may be potential targets in future therapeutic strategies.

Lipocalin 2 (Lcn2) interferes with iron uptake by Brucella abortus and dampens immunoregulation during infection of RAW 264.7 macrophages

Lipocalin 2 (Lcn2) is an important innate immunity component against bacterial pathogens. In this study, we report that Lcn2 is induced by Brucella (B.) abortus infection and significantly contributes to the restriction of intracellular survival of Brucella in macrophages. We found that Lcn2 prevented iron uptake by B. abortus through two distinct mechanisms. First, Lcn2 is secreted to capture bacterial siderophore(s) and abrogate iron import by Brucella. Second, Lcn2 decreases the intracellular iron levels during Brucella infection, which probably deprives the invading Brucella of the iron source needed for growth. Suppression of Lcn2 signalling resulted in a marked induction of anti-inflammatory cytokine, interleukin 10, which was shown to play a major role in Lcn2-induced antibrucella immunity. Similarly, interleukin 6 was also found to be increased when Lcn2 signalling is abrogated; however, this induction was thought to be an alternative pathway that rescues the cell from infection when the effective Lnc2 pathway is repressed. Furthermore, Lcn2 deficiency also caused a marked decrease in brucellacidal effectors, such as reactive oxygen species and nitric oxide but not the phagolysosome fusion. Taken together, our results indicate that Lcn2 is required for the efficient restriction of intracellular B. abortus growth that is through limiting iron acquisition and shifting cells to pro-inflammatory brucellacidal activity in murine macrophages.

Simultaneous RNA-seq based transcriptional profiling of intracellular Brucella abortus and B. abortus-infected murine macrophages

Brucella is a zoonotic pathogen that survives within macrophages; however the replicative mechanisms involved are not fully understood. We describe the isolation of sufficient Brucella abortus RNA from primary host cell environment using modified reported methods for RNA-seq analysis, and simultaneously characterize the transcriptional profiles of intracellular B. abortus and bone marrow-derived macrophages (BMM) from BALB/c mice at 24 h (replicative phase) post-infection. Our results revealed that 25.12% (801/3190) and 16.16% (515/3190) of the total B. abortus genes were up-regulated and down-regulated at >2-fold, respectively as compared to the free-living B. abortus. Among >5-fold differentially expressed genes, the up-regulated genes are mostly involved in DNA, RNA manipulations as well as protein biosynthesis and secretion while the down-regulated genes are mainly involved in energy production and metabolism. On the other hand, the host responses during B. abortus infection revealed that 14.01% (6071/43,346) of BMM genes were reproducibly transcribed at >5-fold during infection. Transcription of cytokines, chemokines and transcriptional factors, such as tumor necrosis factor (Tnf), interleukin-1α (Il1α), interleukin-1β (Il1β), interleukin-6 (Il6), interleukin-12 (Il12), chemokine C-X-C motif (CXCL) family, nuclear factor kappa B (Nf-κb), signal transducer and activator of transcription 1 (Stat1), that may contribute to host defense were markedly induced while transcription of various genes involved in cell proliferation and metabolism were suppressed upon B. abortus infection. In conclusion, these data suggest that Brucella modulates gene expression in hostile intracellular environment while simultaneously alters the host pathways that may lead to the pathogen's intracellular survival and infection.

Activation of NF-kB-Mediated TNF-Induced Antimicrobial Immunity Is Required for the Efficient Brucella abortus Clearance in RAW 264.7 Cells

In this study, we explore the regulatory roles of pro-inflammatory cytokine tumor necrosis factor alpha (TNF) in the innate immunity of macrophages against B. abortus infection. We show that infection of macrophage with B. abortus induces marked expression and secretion of TNF which subsequently binds to TNF receptor 1 (TNFR-1) and activates a downstream signaling cascade of the innate immunity. Blocking of TNF signaling resulted in a notable increase of B. abortus survival which was associated with an increase of anti-inflammatory cytokine interleukin 10 (IL-10), a beneficial effector of Brucella survival, as well as remarkable decrease of reactive oxygen species (ROS) and nitric oxide (NO), antibrucella molecules. However, surprisingly, the interference of TNF did not show any influence on phagolysosome and cell death events. Furthermore, the transcriptional factor NF-kB was found to be a main mediator of TNF signaling when blocking of NF-kB pathway drastically suppressed the TNF-induced brucellacidal effect. Taken together, these findings clearly indicate that the immune cascade activated by TNF/TNFR-1 is required for the sufficient resistance to B. abortus survival in macrophages.

Peripheral blood RNA gene expression in children with pneumococcal meningitis: a prospective case-control study

INTRODUCTION

Invasive pneumococcal disease (IPD), caused by Streptococcus pneumoniae, is a leading cause of pneumonia, meningitis and septicaemia worldwide, with increased morbidity and mortality in HIV-infected children.

OBJECTIVES

We aimed to compare peripheral blood expression profiles between HIV-infected and uninfected children with pneumococcal meningitis and controls, and between survivors and non-survivors, in order to provide insight into the host inflammatory response leading to poorer outcomes.

DESIGN AND SETTING

Prospective case-control observational study in a tertiary hospital in Malawi.

PARTICIPANTS

Children aged 2 months to 16 years with pneumococcal meningitis or pneumonia.

METHODS

We used the human genome HGU133A Affymetrix array to explore differences in gene expression between cases with pneumococcal meningitis (n=12) and controls, and between HIV-infected and uninfected cases, and validated gene expression profiles for 34 genes using real-time quantitative PCR (RT-qPCR) in an independent set of cases with IPD (n=229) and controls (n=13). Pathway analysis was used to explore genes differentially expressed.

RESULTS

Irrespective of underlying HIV infection, cases showed significant upregulation compared with controls of the following: S100 calcium-binding protein A12 (S100A12); vanin-1 (VNN1); arginase, liver (ARG1); matrix metallopeptidase 9 (MMP9); annexin A3 (ANXA3); interleukin 1 receptor, type II (IL1R2); CD177 molecule (CD177); endocytic adaptor protein (NUMB) and S100 calcium-binding protein A9 (S100A9), cytoskeleton-associated protein 4 (CKAP4); and glycogenin 1 (GYG1). RT-qPCR confirmed differential expression in keeping with microarray results. There was no differential gene expression in HIV-infected compared with HIV-uninfected cases, but there was significant upregulation of folate receptor 3 (FOLR3), S100A12 in survivors compared with non-survivors.

CONCLUSION

Children with IPD demonstrated increased expression in genes regulating immune activation, oxidative stress, leucocyte adhesion and migration, arginine metabolism, and glucocorticoid receptor signalling.

A dual-targeting approach to inhibit Brucella abortus replication in human cells

Brucella abortus is an intracellular bacterial pathogen and an etiological agent of the zoonotic disease known as brucellosis. Brucellosis can be challenging to treat with conventional antibiotic therapies and, in some cases, may develop into a debilitating and life-threatening chronic illness. We used multiple independent assays of in vitro metabolism and intracellular replication to screen a library of 480 known bioactive compounds for novel B. abortus anti-infectives. Eighteen non-cytotoxic compounds specifically inhibited B. abortus replication in the intracellular niche, which suggests these molecules function by targeting host cell processes. Twenty-six compounds inhibited B. abortus metabolism in axenic culture, thirteen of which are non-cytotoxic to human host cells and attenuate B. abortus replication in the intracellular niche. The most potent non-cytotoxic inhibitors of intracellular replication reduce B. abortus metabolism in axenic culture and perturb features of mammalian cellular biology including mitochondrial function and receptor tyrosine kinase signaling. The efficacy of these molecules as inhibitors of B. abortus replication in the intracellular niche suggests “dual-target” compounds that coordinately perturb host and pathogen are promising candidates for development of improved therapeutics for intracellular infections.

Should perioperative immunonutrition for elective surgery be the current standard of care?

Postoperative infectious complications are independently associated with increased hospital length of stay (LOS) and cost and contribute to significant inpatient morbidity. Many strategies such as avoidance of long periods of preoperative fasting, re-establishment of oral feeding as early as possible after surgery, metabolic control and early mobilization have been used to either prevent or reduce the incidence of postoperative infections. Despite these efforts, it remains a big challenge to our current healthcare system to mitigate the cost of postoperative morbidity. Furthermore, preoperative nutritional status has also been implicated as an independent risk factor for postoperative morbidity. Perioperative nutritional support using enteral and parenteral routes has been shown to decrease postoperative morbidity, especially in high-risk patients. Recently, the role of immunonutrition (IMN) in postoperative infectious complications has been studied extensively. These substrates have been found to positively modulate postsurgical immunosuppression and inflammatory responses. They have also been shown to be cost-effective by decreasing both tpostoperative infectious complications and hospital LOS. In this review, we discuss the postoperative positive outcomes associated with the use of perioperative IMN, their cost-effectiveness, current guidelines and future clinical implications.

Brucella abortus Cell Cycle and Infection Are Coordinated

Brucellae are facultative intracellular pathogens. The recent development of methods and genetically engineered strains allowed the description of cell-cycle progression of Brucella abortus, including unipolar growth and the ordered initiation of chromosomal replication. B. abortus cell-cycle progression is coordinated with intracellular trafficking in the endosomal compartments. Bacteria are first blocked at the G1 stage, growth and chromosome replication being resumed shortly before reaching the intracellular proliferation compartment. The control mechanisms of cell cycle are similar to those reported for the bacterium Caulobacter crescentus, and they are crucial for survival in the host cell. The development of single-cell analyses could also be applied to other bacterial pathogens to investigate their cell-cycle progression during infection.

The abcEDCBA-Encoded ABC Transporter and the virB Operon-Encoded Type IV Secretion System of Brucella ovis Are Critical for Intracellular Trafficking and Survival in Ovine Monocyte-Derived Macrophages

Brucella ovis infection is associated with epididymitis, orchitis and infertility in rams. Most of the information available on B. ovis and host cell interaction has been generated using murine macrophages or epithelial cell lines, but the interaction between B. ovis and primary ovine macrophages has not been studied. The aim of this study was to evaluate the role of the B. ovis abcEDCBA-encoded ABC transporter and the virB operon-encoded Type IV Secretion System (T4SS) during intracellular survival of B. ovis in ovine peripheral blood monocyte-derived macrophages. ΔabcBA and ΔvirB2 mutant strains were unable to survive in the intracellular environment when compared to the WT B. ovis at 48 hours post infection (hpi). In addition, these mutant strains cannot exclude the lysosomal marker LAMP1 from its vacuolar membrane, and their vacuoles do not acquire the endoplasmic reticulum marker calreticulin, which takes place in the WT B. ovis containing vacuole. Higher levels of nitric oxide production were observed in macrophages infected with WT B. ovis at 48 hpi when compared to macrophages infected with the ΔabcBA or ΔvirB2 mutant strains. Conversely, higher levels of reactive oxygen species were detected in macrophages infected with the ΔabcBA or ΔvirB2 mutant strains at 48 hpi when compared to macrophages infected with the WT strain. Our results demonstrate that B. ovis is able to persist and multiply in ovine macrophages, while ΔabcBA and ΔvirB2 mutations prevent intracellular multiplication, favor phagolysosome fusion, and impair maturation of the B. ovis vacuole towards an endoplasmic reticulum-derived compartment.

Cervical Lymph Nodes as a Selective Niche for Brucella during Oral Infections

Cervical lymph nodes (CLN) are the first lymph nodes encountered by material taking the oral route. To study their role in orally acquired infections, we analyzed 307 patients of up to 14 years treated in the university clinic of Skopje, Macedonia, for brucellosis, a zoonotic bacterial disease frequently acquired by ingestion of contaminated dairy products. From these children, 36% had lymphadenopathy. Among orally infected children, lymphadenopathy with CLN being the only lymph nodes affected was significantly more frequent as compared to those infected by contact with animals (83% vs. 63%), suggesting a possible involvement of CLN during orally acquired human brucellosis. Using a murine model where bacteria are delivered into the oral cavity, we show that Brucella quickly and selectively colonize the CLN where they proliferate and persist over long periods of time for up to 50 days post-infection. A similar efficient though less specific drainage to CLN was found for Brucella, Salmonella typhimurium and fluorescent microspheres delivered by gavage, a pathway likely representing a mixed infection mode of intragastric and oral infection, suggesting a central pathway of drained material. Microspheres as well as bacteria drained to CLN predominately reside in cells expressing CD68 and no or low levels of CD11c. Even though no systemic response could be detected, Brucella induced a locally restricted inflammatory reaction with increased expression levels of interferon γ, interleukin (IL)-6, IL-12, granzyme B and a delayed induction of Nos2. Inflammation led to pronounced lymphadenopathy, infiltration of macrophages/monocytes expressing high levels of major histocompatibility complex II and to formation of epitheloid granulomas. Together, these results highlight the role of CLN in oral infections as both, an initial and efficient trap for bacterial invaders and as possible reservoir for chronic pathogens. They likewise cast a new light on the significance of oral routes for means of vaccination.

Key role of Toll-like receptor 2 in the inflammatory response and major histocompatibility complex class ii downregulation in Brucella abortus-infected alveolar macrophages

Alveolar macrophages (AM) seem to constitute the main cellular target of inhaled brucellae. Here, we show that Brucella abortus invades and replicates in murine AM without inducing cytotoxicity. B. abortus infection induced a statistically significant increase of tumor necrosis factor alpha (TNF-α), CXCL1 or keratinocyte chemoattractant (KC), interleukin-1β (IL-1β), IL-6, and IL-12 in AM from C57BL/6 mice and BALB/c mice, but these responses were generally weaker and/or delayed compared to those elicited in peritoneal macrophages. Studies using knockout mice for TLR2, TLR4, and TLR9 revealed that TNF-α and KC responses were mediated by TLR2 recognition. Brucella infection reduced in a multiplicity of infection-dependent manner the expression of major histocompatibility complex class II (MHC-II) molecules induced by gamma interferon (IFN-γ) in AM. The same phenomenon was induced by incubation with heat-killed B. abortus (HKBA) or the lipidated form of the 19-kDa outer membrane protein of Brucella (L-Omp19), and it was shown to be mediated by TLR2 recognition. In contrast, no significant downregulation of MHC-II was induced by either unlipidated Omp19 or Brucella LPS. In a functional assay, treatment of AM with either L-Omp19 or HKBA reduced the MHC-II-restricted presentation of OVA peptides to specific T cells. One week after intratracheal infection, viable B. abortus was detected in AM from both wild-type and TLR2 KO mice, but CFU counts were higher in the latter. These results suggest that B. abortus survives in AM after inhalatory infection in spite of a certain degree of immune control exerted by the TLR2-mediated inflammatory response. Both the modest nature of the latter and the modulation of MHC-II expression by the bacterium may contribute to such survival.

Suppression of PTRF alleviates the polymicrobial sepsis induced by cecal ligation and puncture in mice

BACKGROUND

Sepsis and sepsis-associated organ failure are devastating conditions. Understanding the detailed cellular/molecular mechanisms involved in sepsis should lead to the identification of novel therapeutic targets.

METHODS

Cecal ligation and puncture (CLP) was used as a polymicrobial sepsis model in vivo to determine mortality and end-organ damage. Macrophages were adopted as the cellular model in vitro for mechanistic studies.

RESULTS

PTRF+/- mice survived longer and suffered less organ damage after CLP. Reductions in nitric oxide (NO) and iNOS biosynthesis were observed in plasma, macrophages, and vital organs in the PTRF+/- mice. Using an acute sepsis model after CLP, we found that iNOS-/- mice had a comparable level of survival as the PTRF+/- mice. Similarly, polymerase I transcript release factor (PTRF) deficiency resulted in decreased iNOS and NO/ROS production in macrophages in vitro. Mechanistically, lipopolysaccharide (LPS) enhanced the co-localization and interaction between PTRF and TLR4 in lipid rafts. Deletion of PTRF blocked formation of the TLR4/Myd88 complex after LPS. Consistent with this, lack of PTRF impaired the TLR4 signaling, as shown by the decreased p-JNK, p-ERK, and p-p38, which are upstream factors involved in iNOS transcription.

CONCLUSION

PTRF is a crucial regulator of TLR4 signaling in the development of sepsis.

Immunogenic and invasive properties of Brucella melitensis 16M outer membrane protein vaccine candidates identified via a reverse vaccinology approach

Brucella is the etiologic agent of brucellosis, one of the most common and widely distributed zoonotic diseases. Its highly infectious nature, the insidious, systemic, chronic, debilitating aspects of the disease and the lack of an approved vaccine for human use in the United States are features that make Brucella a viable threat to public health. One of the main impediments to vaccine development is identification of suitable antigens. In order to identify antigens that could potentially be used in a vaccine formulation, we describe a multi-step antigen selection approach. We initially used an algorithm (Vaxign) to predict ORF encoding outer membrane proteins with antigenic determinants. Differential gene expression during acute infection and published evidence for a role in virulence were used as criteria for down-selection of the candidate antigens that resulted from in silico prediction. This approach resulted in the identification of nine Brucella melitensis outer membrane proteins, 5 of which were recombinantly expressed and used for validation. Omp22 and Hia had the highest in silico scores for adhesin probability and also conferred invasive capacity to E. coli overexpressing recombinant proteins. With the exception of FlgK in the goat, all proteins reacted to pooled sera from exposed goats, mice, and humans. BtuB, Hia and FlgK stimulated a mixed Th1-Th2 response in splenocytes from immunized mice while BtuB and Hia elicited NO release from splenocytes of S19 immunized mice. The results support the applicability of the current approach to the identification of antigens with immunogenic and invasive properties. Studies to assess immunogenicity and protective efficacy of individual proteins in the mouse are currently underway.

Host interferon-γ inducible protein contributes to Brucella survival

Brucella spp. are highly adapted intracellular pathogens of mammals that cause chronic infections while surving and replicating in host monocytes and macrophages. Although monocytes are normally susceptible to infection, pretreatment with pro-inflammatory cytokine interferon-γ (IFN-γ) activates cellular defense mechanisms that increase intracellular killing of Brucella and prevents bacterial replication. We examined the contribution of the IFN-γ inducible GTPase, LRG-47, to B. abortus 2308 infection in in vitro and in vivo murine models. Infecting non-activated macrophages from LRG-47(-/-) mice revealed that loss of this host protein negatively effected the intracellular survival and replication of IgG opsonized B. abortus. In contrast, survival and replication of non-opsonized B. abortus was the same in both C57/B6 and LRG-47(-/-) peritoneal macrophages. Following IFN-γ activation of LRG-47(-/-) monocytes, IgG opsonized B. abortus survived better than non-opsonized bacteria. The differential fate of opsonized and non-opsonized B. abortus was only observed in macrophages collected from LRG-47(-/-) mice. Given the specific nature of the relationship between this host protein and the mechanism of Brucella internalization, LRG-47(-/-) mice were infected with B. abortus to assess whether the loss of the lrg47 protein would affect the ability of the bacteria to colonize or persist within the host. B. abortus were able to establish and maintain similar numbers of bacteria in both C57/B6 mice and LRG-47(-/-) through 3 weeks post intraperitoneal infection. By 9 weeks p.i. fewer B. abortus were recovered from LRG-47(-/-) mice than controls, suggesting that the host protein has a positive role in maintaining long term persistence of the bacteria within the host. These observations demonstrating a positive role for a host IFN-γ induced protein defense protein has yet to be reported. These results provide interesting insight into the complex interaction between Brucella and their host.

Brucella abortus inhibits IFN-γ-induced FcγRI expression and FcγRI-restricted phagocytosis via toll-like receptor 2 on human monocytes/macrophages

The strategies that allow Brucella abortus to persist for years inside macrophages subverting host immune responses are not completely understood. Immunity against this bacterium relies on the capacity of IFN-γ to activate macrophages, endowing them with the ability to destroy intracellular bacteria. We report here that infection with B. abortus down-modulates the expression of the type I receptor for the Fc portion of IgG (FcγRI, CD64) and FcγRI-restricted phagocytosis regulated by IFN-γ in human monocytes/macrophages. Both phenomena were not dependent on bacterial viability, since they were also induced by heat-killed B. abortus (HKBA), suggesting that they were elicited by a structural bacterial component. Accordingly, a prototypical B. abortus lipoprotein (L-Omp19), but not its unlipidated form, inhibited both CD64 expression and FcγRI-restricted phagocytosis regulated by IFN-γ. Moreover, a synthetic lipohexapeptide that mimics the structure of the protein lipid moiety also inhibited CD64 expression, indicating that any Brucella lipoprotein could down-modulate CD64 expression and FcγRI-restricted phagocytosis. Pre-incubation of monocytes/macrophages with anti-TLR2 mAb blocked the inhibition of the CD64 expression mediated by HKBA and L-Omp19. These results, together with our previous observations establish that B. abortus utilizes its lipoproteins to inhibit the monocytes/macrophages activation mediated by IFN-γ and to subvert host immunonological responses.

Cisplatin reduces Brucella melitensis-infected cell number by inducing apoptosis, oxidant and pro-inflammatory cytokine production

Brucella species are able to survive and replicate within the phagocytic cells and cause chronic infections in domestic animals and humans. Modulation of programmed cell death by Brucella spp. may be one of the reasons of the chronicity of the infection. In this study, whether cisplatin treatment, an apoptotic anticancer agent, would enhance the host resistance against Brucella melitensis-infected human macrophage-like cells was investigated. The infection neither induced inflammation nor oxidative stress. But, Brucella caused a decrease in infected macrophage viability of 36% at 48 h postinfection (p.i.) as compared with uninfected cells. Treatment of infected macrophages with 20 microM cisplatin for 48 h caused a large increase in nitric oxide (NO) levels in a time-dependent manner via induction of iNOS transcription. Cisplatin also enhanced glutathione peroxidase, myeloperoxidase and xanthine oxidase activities, providing evidence of generation of reactive free radicals. N-acetylcysteine was able to decrease cisplatin-induced NO, and prevented the agent-induced apoptosis, similar to effects found in l-NAME (N(G)-nitro-l-arginine methyl ester) treatment. Cisplatin stimulated inflammation through the induction of TNF-alpha and IL-12 secretion, and down-regulated Brucella-stimulated IL-10 transcription. The number of infected cells and their viability were decreased by 80% at 48 h p.i. by cisplatin in comparison with infected cells. Similar to this result, cisplatin treatment resulted in reduced intracellular CFU of B. melitensis being reduced by 80% at 48 h p.i. These findings demonstrate that pharmacological agents such as cisplatin may be considered to influence immune responses and apoptosis to help decrease Brucella-infected cell number.

Survival of the fittest: how Brucella strains adapt to their intracellular niche in the host

Brucella strains produce abortion and infertility in their natural hosts and a zoonotic disease in humans known as undulant fever. These bacteria do not produce classical virulence factors, and their capacity to successfully survive and replicate within a variety of host cells underlies their pathogenicity. Extensive replication of the brucellae in placental trophoblasts is associated with reproductive tract pathology in natural hosts, and prolonged persistence in macrophages leads to the chronic infections that are a hallmark of brucellosis in both natural hosts and humans. This review describes how Brucella strains have efficiently adapted to their intracellular lifestyle in the host.

Psychological stress suppresses innate IFN-gamma production via glucocorticoid receptor activation: reversal by the anxiolytic chlordiazepoxide

Studies in humans and in animals indicate that psychological stress can modulate immune responses. Here we demonstrate that exposure to psychological stress (restraint stress) suppresses innate interferon (IFN)-gamma production in mice following an in vivo lipopolysaccharide (LPS) challenge. IFN-gamma signaling was also impaired by stress, as indicated by reduced STAT1 phosphorylation and reduced expression of the IFN-gamma-inducible genes, inducible nitric oxide synthase (iNOS) and IFN-gamma-inducible protein 10 (IP-10/CXCL10). Furthermore, restraint stress suppressed production of the IFN-gamma inducing cytokine interleukin (IL)-12 and increased production of the anti-inflammatory cytokine IL-10, which can inhibit both IL-12 and IFN-gamma production. However, using IL-10 knockout mice, we demonstrate that IL-10 does not mediate the suppressive effect of restraint stress on innate IFN-gamma production. Restraint stress increased corticosterone concentrations in serum and spleen, and consistent with a role for glucocorticoids in the immunosuppressive actions of stress, pre-treatment with the glucocorticoid receptor antagonist mifepristone completely blocked the stress-related suppression of innate IFN-gamma production. Addition of exogenous IL-12 to LPS-stimulated spleen cells reversed the suppressive effect of both restraint stress and corticosterone on IFN-gamma production. These data suggest that reduced IL-12 production is a key event in stress-induced suppression of innate IFN-gamma production. Finally, we demonstrate that pre-treatment with the anxiolytic drug chlordiazepoxide prevents the suppressive effect of stress on innate IFN-gamma production, and also attenuates the stress-induced increase in circulating corticosterone concentrations.

Activation of macrophages and lymphocytes by methylglyoxal against tumor cells in the host

Methylglyoxal is a normal metabolite and has the potential to affect a wide variety of cellular processes. In particular, it can act selectively against malignant cells. The study described herein was to investigate whether methylglyoxal can enhance the non-specific immunity of the host against tumor cells. Methylglyoxal increased the number of macrophages in the peritoneal cavity of both normal and tumor-bearing mice. It also elevated the phagocytic capacity of macrophages in both these groups of animals. This activation of macrophages was brought about by increased production of Reactive Oxygen Intermediates (ROIs) and Reactive Nitrogen Intermediates (RNIs). The possible mechanism for the production of ROIs and RNIs can be attributed to stimulation of the respiratory burst enzyme NADPH oxidase and iNOS, respectively. IFN-gamma, which is a regulatory molecule of iNOS pathway also showed an elevated level by methylglyoxal. TNF-alpha, which is an important cytokine for oxygen independent killing by macrophage also increased by methylglyoxal in both tumor-bearing and non tumor-bearing animals. Methylglyoxal also played a role in the proliferation and cytotoxicity of splenic lymphocytes. In short, it can be concluded that methylglyoxal profoundly stimulates the immune system against tumor cells.

Interaction of Brucella suis and Brucella abortus rough strains with human dendritic cells

Brucella is a facultative intracellular pathogen of various mammals and the etiological agent of brucellosis. We recently demonstrated that dendritic cells (DCs), which are critical components of adaptive immunity, are highly susceptible to Brucella infection. Furthermore, Brucella prevented the infected DCs from engaging in maturation processes and impaired their capacity to present antigen to naive T cells and to secrete interleukin-12 (IL-12). The lipopolysaccharide (LPS) phenotype is largely associated with the virulence of Brucella. Depending on whether they express the O-side chain of LPS or not, the bacteria display a smooth or rough phenotype. Rough Brucella mutants are attenuated and induce a potent protective T-cell-dependent immune response. Due to the essential role of DCs in the initiation of T-cell-dependent adaptive immune responses, it seemed pertinent to study the interaction between rough Brucella strains and human DCs. In the present paper, we report that, in contrast to smooth bacteria, infection of DCs with rough mutants of Brucella suis or Brucella abortus leads to both phenotypic and functional maturation of infected cells. Rough mutant-infected DCs then acquire the capacity to produce IL-12 and to stimulate naive CD4+ T lymphocytes. Experiments with rough and smooth purified LPS of Brucella supported the hypothesis of an indirect involvement of the O-side chain. These results provide new data concerning the role of LPS in Brucella virulence strategy and illuminate phenomena contributing to immune protection conferred by rough vaccine strains.

Identification and isolation of Brucella suis virulence genes involved in resistance to the human innate immune system

Brucella strains are facultative intracellular pathogens that induce chronic diseases in humans and animals. This observation implies that Brucella subverts innate and specific immune responses of the host to develop its full virulence. Deciphering the genes involved in the subversion of the immune system is of primary importance for understanding the virulence of the bacteria, for understanding the pathogenic consequences of infection, and for designing an efficient vaccine. We have developed an in vitro system involving human macrophages infected by Brucella suis and activated syngeneic gamma9delta2 T lymphocytes. Under these conditions, multiplication of B. suis inside macrophages is only slightly reduced. To identify the genes responsible for this reduced sensitivity, we screened a library of 2,000 clones of transposon-mutated B. suis. For rapid and quantitative analysis of the multiplication of the bacteria, we describe a simple method based on Alamar blue reduction, which is compatible with screening a large library. By comparing multiplication inside macrophages alone and multiplication inside macrophages with activated gamma9delta2 T cells, we identified four genes of B. suis that were necessary to resist to the action of the gamma9delta2 T cells. The putative functions of these genes are discussed in order to propose possible explanations for understanding their exact role in the subversion of innate immunity.

BvrR/BvrS-controlled outer membrane proteins Omp3a and Omp3b are not essential for Brucella abortus virulence

The Brucella abortus two-component regulatory system BvrR/BvrS controls the expression of outer membrane proteins (Omp) Omp3a (Omp25) and Omp3b (Omp22). Disruption of bvrS or bvrR generates avirulent mutants with altered cell permeability, higher sensitivity to microbicidal peptides, and complement. Consequently, the role of Omp3a and Omp3b in virulence was examined. Similar to bvrS or bvrR mutants, omp3a and omp3b mutants displayed increased attachment to cells, indicating surface alterations. However, they showed unaltered permeability; normal expression of Omp10, Omp16, Omp19, Omp2b, and Omp1; native hapten polysaccharide; and lipopolysaccharide and were resistant to complement and polymyxin B at ranges similar to those of the wild-type (WT) counterpart. Likewise, omp3a and omp3b mutants were able to replicate in murine macrophages and in HeLa cells, were resistant to the killing action of human neutrophils, and persisted in mice, like the WT strain. Murine macrophages infected with the omp3a mutant generated slightly higher levels of tumor necrosis factor alpha than the WT, whereas the bvrS mutant induced lower levels of this cytokine. Since the absence of Omp3a or Omp3b does not result in attenuation, it can be concluded that BvrR/BvrS influences additional Brucella properties involved in virulence. Our results are discussed in the light of previous works suggesting that disruption of omp3a generates attenuated Brucella strains, and we speculate on the role of group 3 Omps.

Heterologous immunity revisited

Heterologous immunity, or protection by one invading organism against another across phylogenetic divides, has been recognised for decades. It was initially thought to operate largely through enhancement of phagocytosis, but this explanation became untenable when it was realised it worked extremely well against intraerythrocytic protozoa and killed them while they were free in the circulation. Clearly a soluble mediator was called for. This review summarises the logic that arose from this observation, which led to a wider appreciation of the roles of pro-inflammatory cytokines, and then nitric oxide, in the host's response against invaders, as well as the ability of these mediators to harm the host itself if they are generated too enthusiastically. This has led to a discernable pattern across heterologous immunity as a whole, and its lessons influence a range of areas, including vaccine development.

Gamma interferon loaded onto albumin nanoparticles: in vitro and in vivo activities against Brucella abortus

The aim of this study was to evaluate the activity of gamma interferon (IFN-gamma) when it was either adsorbed onto or loaded into albumin nanoparticles. Brucella abortus-infected macrophages and infected BALB/c mice were selected as the models for testing of the therapeutic potentials of these cytokine delivery systems, in view of the well-established role of IFN-gamma-activated macrophages for the control of Brucella sp. infections. Whereas the encapsulation of IFN-gamma inside the matrix of nanoparticles completely abrogated its activity, adsorbed IFN-gamma increased by 0.75 log unit the bactericidal effect induced by RAW macrophages activated with free IFN-gamma, along with a higher level of production of nitric oxide. In infected BALB/c-mice, IFN-gamma adsorbed onto nanoparticles was also more active than free cytokine in reducing the number of bacteria in the spleens, and the effect was mediated by an increased ratio of IFN-gamma-secreting (Th1) to interleukin-4-secreting (Th2) cells. Overall, albumin nanoparticles would be suitable as carriers that target IFN-gamma to macrophages and, thus, potentiate their therapeutic activity.

Different roles of the two high-oxygen-affinity terminal oxidases of Brucella suis: Cytochrome c oxidase, but not ubiquinol oxidase, is required for persistence in mice

The survival of Brucella suis mutant strains in mice demonstrated different roles of the two high-oxygen-affinity terminal oxidases. The cbb3-type cytochrome c oxidase was essential for chronic infection in oxygen-deficient organs. Lack of the cytochrome bd ubiquinol oxidase led to hypervirulence of bacteria, which could rely on nitrite accumulation inhibiting the inducible nitric oxide synthase of the host.

Evaluation of oxidative stress and inflammation in long term Brucella melitensis infection

The Brucella genus is able to cause chronic infection in a wide range of mammals including humans. Oxidative events, lipid peroxidation and inflammatory response against Brucella infection have not yet been well elucidated in vivo. We have investigated oxidative/antioxidative status and nitric oxide production in plasma, brain, liver and spleen during a 60 day period of B. melitensis infection in a rat model. In addition, inducible nitric oxide synthase (iNOS), IL-10, IL-12, IFN-gamma and TNF-alpha mRNA transcriptions were analyzed by semiquantitative reverse transcriptase PCR (RT-PCR) in brain samples. Animals were infected with B. melitensis and sacrificed at 7th, 15th, 30th, 45th and 60th day of post-inoculation. Malondialdehyde (MDA), as an indicator of lipid peroxidation, and nitric oxide (NO) concentrations were significantly increased after Brucella inoculation and began to decline to basal levels from 45th day in plasma, liver and spleen. However, iNOS transcription was not induced during the infection period in brains. In contrast, MDA level was increased in brain during the late phase of infection without any change in NO production. The infection did not alter the antioxidant enzyme activities in the tissues; although significantly increased catalase activity was observed between days 30 and 45 in the liver. Transcription analyses demonstrated that IL-10, IL-12 and IFN-gamma mRNA level were not induced in the brain. Only TNF-alpha mRNA was weakly up-regulated in brain 30 days after pathogen inoculation. The results obtained in this study demonstrate that B. melitensis induces lipid peroxidation and NO production in the liver and spleen in the early days of infection, but that these levels subsequently decline. Moreover, Brucella does not appear to induce antioxidant enzyme activities and inflammation during two months of infection. However, the pathogen does stimulate cerebral lipid peroxidation in the late phase of infection without causing significant inflammation.

Requirement of norD for Brucella suis virulence in a murine model of in vitro and in vivo infection

A mutant of Brucella suis bearing a Tn5 insertion in norD, the last gene of the operon norEFCBQD, encoding nitric oxide reductase, was unable to survive under anaerobic denitrifying conditions. The norD strain exhibited attenuated multiplication within nitric oxide-producing murine macrophages and rapid elimination in mice, hence demonstrating that norD is essential for Brucella virulence.

Brucella abortusd-alanyl-d-alanine carboxypeptidase contributes to its intracellular replication and resistance against nitric oxide

Brucella spp. are facultative intracellular pathogens that have the ability to survive and multiply in professional and nonprofessional phagocytes, and cause abortion in domestic animals and undulant fever in humans. However, the mechanism and factors of virulence are not fully understood. In the present study, a D-alanyl-D-alanine carboxypeptidase (DAP) mutant of Brucella abortus failed to replicate in mouse macrophages and HeLa cells, and showed less virulence than the wild type in mice. Under nitric oxide (NO) stress, the growth of the DAP mutant in vitro decreased and it also had less capability to reduce NO than the wild type. Intracellular replication of the DAP mutant was partially restored by pretreatment of macrophages with the NO synthase inhibitor, 1-phenyl-imidazole, and the level of expression of the NO reductase gene, norB, in the DAP mutant was lower than that in the wild type. These results suggest that DAP contributes to resistance against NO and that it is required for the intracellular growth of the bacterium.

NnrA is required for full virulence and regulates several Brucella melitensis denitrification genes

We identified two regulators of denitrification genes in Brucella melitensis 16M: NarR, which regulates the nitrate reductase (nar) operon, and NnrA, which is involved in the expression of the last three reductases of the denitrification pathway (nirK, norB, and nosZ). NnrA is required for virulence in mice and for intracellular resistance to nitric oxide.

Regulation of the mitogen-activated protein kinases by Brucella spp. expressing a smooth and rough phenotype: relationship to pathogen invasiveness

By comparing smooth wild-type Brucella spp. to their rough mutants, we show that the LPS O chain restricted the activation of the ERK1/2 and p38 mitogen-activated protein kinase (MAPK) pathways, thus preventing the synthesis of immune mediators that regulate host defense. We conclude that the MAPKs are a target for immune intervention by virulent smooth Brucella.

Opsonized virulent Brucella abortus replicates within nonacidic, endoplasmic reticulum-negative, LAMP-1-positive phagosomes in human monocytes

Cells in the Brucella spp. are intracellular pathogens that survive and replicate within host monocytes. Brucella maintains persistent infections in animals despite the production of high levels of anti-Brucella-specific antibodies. To determine the effect of antibody opsonization on the ability of Brucella to establish itself within monocytes, the intracellular trafficking of virulent Brucella abortus 2308 and attenuated hfq and bacA mutants was followed in the human monocytic cell line THP-1. Early trafficking events of B. abortus 2308-containing phagosomes (BCP) were indistinguishable from those seen for control particles (heat-killed B. abortus 2308, live Escherichia coli HB101, or latex beads). All phagosomes transiently communicated the early-endosomal compartment and rapidly matured into LAMP-1(+), cathepsin D(+), and acidic phagosomes. By 2 h postinfection, however, the number of cathepsin D(+) BCP was significantly lower for live B. abortus 2308-infected cells than for either Brucella mutant strains or control particles. B. abortus 2308 persisted within these cathepsin D(-), LAMP-1(+), and acidic vesicles; however, at the onset of intracellular replication, the numbers of acidic B. abortus 2308 BCP decreased while remaining cathepsin D(-) and LAMP-1(+). In contrast to B. abortus 2308, the isogenic hfq and bacA mutants remained in acidic, LAMP-1(+) phagosomes and failed to initiate intracellular replication. Notably, markers specific for the host endoplasmic reticulum were absent from the BCPs throughout the course of the infection. Thus, opsonized B. abortus in human monocytes survives within phagosomes that remain in the endosomal pathway and replication of virulent B. abortus 2308 within these vesicles corresponds with an increase in intraphagosomal pH.

Brucella lipopolysaccharide acts as a virulence factor

Brucella is a facultative intracellular bacterium responsible for brucellosis. Virulence factors involved in Brucella replication and Brucella's strategies to circumvent the immune response are under investigation. VirB proteins that form the type IV secretion system and that are involved in intracellular replication are considered as one of Brucella's virulence factors. In addition to this secretion system, bacterial outer membrane components have also been described as being implicated in Brucella survival in the host. For example, this bacterium possesses an unconventional non-endotoxic lipopolysaccharide that confers resistance to anti-microbial attacks and modulates the host immune response. These properties make lipopolysaccharide an important virulence factor for Brucella survival and replication in the host.

Cellular bioterrorism: how Brucella corrupts macrophage physiology to promote invasion and proliferation

Brucellosis is a worldwide human zoonosis caused by intracellular bacteria of the genus Brucella. Virulence factors play an important role in allowing Brucella infection and proliferation within macrophages. Brucella enters macrophages through lipid raft microdomains, avoids phagolysosome fusion, and inhibits TNF-alpha secretion and apoptosis. Furthermore, Brucella can perturb bactericidal activity in macrophages by influencing the host cell response to its advantage through its LPS or by activating the cAMP/PKA pathway. To date, small steps have been taken in defining and understanding the virulence factors of Brucella used in macrophage subversion, but further investigation is required to fully explain virulence and persistence.