Smooth and rough lipopolysaccharide phenotypes of Brucella induce different intracellular trafficking and cytokine/chemokine release in human monocytes

SiRNA screens using Drosophila cells to identify host factors required for infection

Drosophila melanogaster offers a powerful model system for interrogating interactions between host cells and human bacterial pathogens. Brucella, a gram-negative, facultative intracellular bacterium is the causative agent of brucellosis, a zoonotic disease of global consequence. Over the past several decades, pathogen factors that mediate Brucella infection have been identified. However, host factors that mediate infection have remained obscure. We have used the power of the Drosophila S2 cell system to identify and characterize host factors that support infection by Brucella melitensis. Host protein inositol-requiring enzyme 1 (IRE1α), a transmembrane kinase and master regulator of the eukaryotic unfolded protein response, was shown to play an important role in regulating Brucella infection, thereby providing the first glimpse of host mechanisms that are subverted by the pathogen to support its intracellular lifestyle. Furthermore, our study also established the Drosophila S2 cell as a powerful system for elucidating Brucella host factors. Here, we describe a protocol for using the Drosophila S2 cell system for studying the Brucella-host interaction.

CD14 mediates binding of high doses of LPS but is dispensable for TNF-α production

Activation of macrophages with lipopolysaccharide (LPS) involves a sequential engagement of serum LPS-binding protein (LBP), plasma membrane CD14, and TLR4/MD-2 signaling complex. We analyzed participation of CD14 in TNF-α production stimulated with 1-1000 ng/mL of smooth or rough LPS (sLPS or rLPS) and in sLPS binding to RAW264 and J744 cells. CD14 was indispensable for TNF-α generation induced by a low concentration, 1 ng/mL, of sLPS and rLPS. At higher doses of both LPS forms (100-1000 ng/mL), TNF-α release required CD14 to much lower extent. Among the two forms of LPS, rLPS-induced TNF-α production was less CD14-dependent and could proceed in the absence of serum as an LBP source. On the other hand, the involvement of CD14 was crucial for the binding of 1000 ng/mL of sLPS judging from an inhibitory effect of the anti-CD14 antibody. The binding of sLPS was also strongly inhibited by dextran sulfate, a competitive ligand of scavenger receptors (SR). In the presence of dextran sulfate, sLPS-induced production of TNF-α was upregulated about 1.6-fold. The data indicate that CD14 together with SR participates in the binding of high doses of sLPS. However, CD14 contribution to TNF α production induced by high concentrations of sLPS and rLPS can be limited.

Entrance and survival of Brucella pinnipedialis hooded seal strain in human macrophages and epithelial cells

Marine mammal Brucella spp. have been isolated from pinnipeds (B. pinnipedialis) and cetaceans (B. ceti) from around the world. Although the zoonotic potential of marine mammal brucellae is largely unknown, reports of human disease exist. There are few studies of the mechanisms of bacterial intracellular invasion and multiplication involving the marine mammal Brucella spp. We examined the infective capacity of two genetically different B. pinnipedialis strains (reference strain; NTCT 12890 and a hooded seal isolate; B17) by measuring the ability of the bacteria to enter and replicate in cultured phagocytes and epithelial cells. Human macrophage-like cells (THP-1), two murine macrophage cell lines (RAW264.7 and J774A.1), and a human malignant epithelial cell line (HeLa S3) were challenged with bacteria in a gentamicin protection assay. Our results show that B. pinnipedialis is internalized, but is then gradually eliminated during the next 72 – 96 hours. Confocal microscopy revealed that intracellular B. pinnipedialis hooded seal strain colocalized with lysosomal compartments at 1.5 and 24 hours after infection. Intracellular presence of B. pinnipedialis hooded seal strain was verified by transmission electron microscopy. By using a cholesterol-scavenging lipid inhibitor, entrance of B. pinnipedialis hooded seal strain in human macrophages was significantly reduced by 65.8 % (± 17.3), suggesting involvement of lipid-rafts in intracellular entry. Murine macrophages invaded by B. pinnipedialis do not release nitric oxide (NO) and intracellular bacterial presence does not induce cell death. In summary, B. pinnipedialis hooded seal strain can enter human and murine macrophages, as well as human epithelial cells. Intracellular entry of B. pinnipedialis hooded seal strain involves, but seems not to be limited to, lipid-rafts in human macrophages. Brucella pinnipedialis does not multiply or survive for prolonged periods intracellulary.

Role of cognitive parameters in dengue hemorrhagic fever and dengue shock syndrome

Dengue is becoming recognized as one of the most important vector-borne human diseases. It is predominant in tropical and subtropical zones but its geographical distribution is progressively expanding, making it an escalating global health problem of today. Dengue presents with spectrum of clinical manifestations, ranging from asymptomatic, undifferentiated mild fever, dengue fever (DF), to dengue hemorrhagic fever (DHF) with or without shock (DSS), a life-threatening illness characterized by plasma leakage due to increased vascular permeability. Currently, there are no antiviral modalities or vaccines available to treat and prevent dengue. Supportive care with close monitoring is the standard clinical practice. The mechanisms leading to DHF/DSS remains poorly understood. Multiple factors have been attributed to the pathological mechanism, but only a couple of these hypotheses are popular in scientific circles. The current discussion focuses on underappreciated factors, temperature, natural IgM, and endotoxin, which may be critical components playing roles in dengue pathogenesis.

Caspase-2 mediates a Brucella abortus RB51-induced hybrid cell death having features of apoptosis and pyroptosis

Programmed cell death (PCD) can play a crucial role in tuning the immune response to microbial infection. Although PCD can occur in different forms, all are mediated by a family of proteases called caspases. Caspase-2 is the most conserved caspase, however, its function in cell death is ill-defined. Previously we demonstrated that live attenuated cattle vaccine strain Brucella abortus RB51 induces caspase-2-mediated and caspase-1-independent PCD of infected macrophages. We also discovered that rough attenuated B. suis strain VTRS1 induces a caspase-2-mediated and caspase-1-independent proinflammatory cell death in infected macrophages, which was tentatively coined "caspase-2-mediated pyroptosis". However, the mechanism of caspase-2-mediated cell death pathway remained unclear. In this study, we found that caspase-2 mediated proinflammatory cell death of RB51-infected macrophages and regulated many genes in different PCD pathways. We show that the activation of proapoptotic caspases-3 and -8 was dependent upon caspase-2. Caspase-2 regulated mitochondrial cytochrome c release and TNFα production, both of which are known to activate caspase-3 and caspase-8, respectively. In addition to TNFα, RB51-induced caspase-1 and IL-1β production was also driven by caspase-2-mediated mitochondrial dysfunction. Interestingly, pore formation, a phenomenon commonly associated with caspase-1-mediated pyroptosis, occurred; however, unlike its role in S. typhimurium-induced pyroptosis, pore formation did not contribute to RB51-induced proinflammatory cell death. Our data suggest that caspase-2 acts as an initiator caspase that mediates a novel RB51-induced hybrid cell death that simulates but differs from typical non-proinflammatory apoptosis and caspase-1-mediated proinflammatory pyroptosis. The initiator role of the caspase-2-mediated cell death was also conserved in cellular stress-induced cell death of macrophages treated with etoposide, naphthalene, or anti-Fas. Caspase-2 also regulated caspase-3 and -8 activation, as well as cell death in macrophages treated with each of the three reagents. Taken together, our data has demonstrated that caspase-2 can play an important role in mediating a proinflammatory response and a hybrid cell death that demonstrates features of both apoptosis and pyroptosis.

Lon Mutant of Brucella abortus Induces Tumor Necrosis Factor-Alpha in Murine J774.A1 Macrophage

Objectives

The objective of this study was to isolate a Brucella lon mutant and to analyze the cytokine response of B. lon mutant during macrophage infection.

Methods

A wild-type Brucella abortus strain was mutagenized by Tn5 transposition. From the mouse macrophage J774.A1 cells, total RNA was isolated at 0 hours, 6 hours, 12 hours, and 24 hours after infection with Brucella. Using mouse cytokine microarrays, we measured transcriptional levels of the cytokine response, and validated our results with a reverse transcriptase-polymerase chain reaction (RT-PCR) assay to confirm the induction of cytokine messenger RNA (mRNA).

Results

In host J774.A1 macrophages, mRNA levels of T helper 1 (Th1)-type cytokines, including tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin-2 (IL-2), and IL-3, were significantly higher in the lon mutant compared to wild-type Brucella and the negative control. TNF-α levels in cell culture media were induced as high as 2 μg/mL after infection with the lon mutant, a greater than sixfold change.

Conclusion

In order to understand the role of the lon protein in virulence, we identified and characterized a novel B. lon mutant. We compared the immune response it generates to the wild-type Brucella response in a mouse macrophage cell line. We demonstrated that the B. lon mutants induce TNF-α expression from the host J774.A1 macrophage.

Entry and elimination of marine mammal Brucella spp. by hooded seal (Cystophora cristata) alveolar macrophages in vitro

A high prevalence of Brucellapinnipedialis serology and bacteriology positive animals has been found in the Northeast Atlantic stock of hooded seal (Cystophoracristata); however no associated gross pathological changes have been identified. Marine mammal brucellae have previously displayed different infection patterns in human and murine macrophages. To investigate if marine mammal Brucella spp. are able to invade and multiply in cells originating from a presumed host species, we infected alveolar macrophages from hooded seal with a B. pinnipedialis hooded seal isolate. Hooded seal alveolar macrophages were also challenged with B. pinnipedialis reference strain (NCTC 12890) from harbor seal (Phocavitulina), B. ceti reference strain (NCTC 12891) from harbor porpoise (Phocoenaphocoena) and a B. ceti Atlantic white-sided dolphin (Lagenorhynchusacutus) isolate (M83/07/1), to evaluate possible species-specific differences. Brucella suis 1330 was included as a positive control. Alveolar macrophages were obtained by post mortem bronchoalveolar lavage of euthanized hooded seals. Phenotyping of cells in the lavage fluid was executed by flow cytometry using the surface markers CD14 and CD18. Cultured lavage cells were identified as alveolar macrophages based on morphology, expression of surface markers and phagocytic ability. Alveolar macrophages were challenged with Brucella spp. in a gentamicin protection assay. Following infection, cell lysates from different time points were plated and evaluated quantitatively for colony forming units. Intracellular presence of B. pinnipedialis hooded seal isolate was verified by immunocytochemistry. Our results show that the marine mammal brucellae were able to enter hooded seal alveolar macrophages; however, they did not multiply intracellularly and were eliminated within 48 hours, to the contrary of B. suis that showed the classical pattern of a pathogenic strain. In conclusion, none of the four marine mammal strains tested were able to establish a persistent infection in primary alveolar macrophages from hooded seal.

Silencing of PrP C (prion protein) expression does not affect Brucella melitensis infection in human derived microglia cells

Cellular prion proteins (PrP(C)) are mainly expressed in the central nervous system where they have antioxidant effects and a role in the endocytosis of bacteria within cells. These proteins also have some crucial biological functions including roles in neurotransmission, signal transduction and programmed cell death. However, the role of prion proteins in neuronal Brucella infection, specifically in the interaction of the pathogen and the host cell is controversial. In the present study, the silencing of PrP(C) mRNA by small interfering RNA (siRNA) transfection was investigated in human microglia cells infected with Brucella melitensis. More than 70% of prion proteins were down-regulated in microglia by siRNA transfection and this caused a slight decrease in the cellular viability of the control cells. Silencing of PrP(C) suppressed the antioxidant systems, though it led to an up-regulation of pro-inflammatory cytokines such as IL-12 and TNF-α as demonstrated by qRT-PCR analysis. B. melitensis infection of prion protein-silenced cells led to increase host viability, but had no effect on bacterial phagocytosis. According to the present study, there is no significant effect of prion proteins on phagocytosis and intracellular killing of B. melitensis in microglia cells.

The Attenuated Brucella abortus Strain 19 Invades, Persists in, and Activates Human Dendritic Cells, and Induces the Secretion of IL-12p70 but Not IL-23

BACKGROUND

Bacterial vectors have been proposed as novel vaccine strategies to induce strong cellular immunity. Attenuated strains of Brucella abortus comprise promising vector candidates since they have the potential to induce strong CD4(+) and CD8(+) T-cell mediated immune responses in the absence of excessive inflammation as observed with other Gram-negative bacteria. However, some Brucella strains interfere with the maturation of dendritic cells (DCs), which is essential for antigen-specific T-cell priming. In the present study, we investigated the interaction of human monocyte-derived DCs with the smooth attenuated B. abortus strain (S) 19, which has previously been employed successfully to vaccinate cattle.

METHODOLOGY/PRINCIPAL FINDINGS

We first looked into the potential of S19 to hamper the cytokine-induced maturation of DCs; however, infected cells expressed CD25, CD40, CD80, and CD86 to a comparable extent as uninfected, cytokine-matured DCs. Furthermore, S19 activated DCs in the absence of exogeneous stimuli, enhanced the expression of HLA-ABC and HLA-DR, and was able to persist intracellularly without causing cytotoxicity. Thus, DCs provide a cellular niche for persisting brucellae in vivo as a permanent source of antigen. S19-infected DCs produced IL-12/23p40, IL-12p70, and IL-10, but not IL-23. While heat-killed bacteria also activated DCs, soluble mediators were not involved in S19-induced activation of human DCs. HEK 293 transfectants revealed cellular activation by S19 primarily through engagement of Toll-like receptor (TLR)2.

CONCLUSIONS/SIGNIFICANCE

Thus, as an immunological prerequisite for vaccine efficacy, B. abortus S19 potently infects and potently activates (most likely via TLR2) human DCs to produce Th1-promoting cytokines.

Inhibitory effects of traditional herbal formula pyungwi-san on inflammatory response in vitro and in vivo

Pyungwi-san (PWS) is a traditional basic herbal formula. We investigated the effects of PWS on induction of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), pro-inflammatory cytokines (interleukin-6 (IL-6) and tumor necrosis factor- α (TNF- α )) and nuclear factor-kappa B (NF- κ B) as well as mitogen-activated protein kinases (MAPKs) in lipopolysaccharide-(LPS-) induced Raw 264.7 cells and on paw edema in rats. Treatment with PWS (0.5, 0.75, and 1 mg/mL) resulted in inhibited levels of expression of LPS-induced COX-2, iNOS, NF- κ B, and MAPKs as well as production of prostaglandin E2 (PGE2), nitric oxide (NO), IL-6, and TNF- α induced by LPS. Our results demonstrate that PWS possesses anti-inflammatory activities via decreasing production of pro-inflammatory mediators through suppression of the signaling pathways of NF- κ B and MAPKs in LPS-induced macrophage cells. More importantly, results of the carrageenan-(CA-) induced paw edema demonstrate an anti-edema effect of PWS. In addition, it is considered that PWS also inhibits the acute edematous inflammations through suppression of mast cell degranulations and inflammatory mediators, including COX-2, iNOS and TNF- α . Thus, our findings may provide scientific evidence to explain the anti-inflammatory properties of PWS in vitro and in vivo.

Human platelets can discriminate between various bacterial LPS isoforms via TLR4 signaling and differential cytokine secretion

Platelets are currently acknowledged as cells of innate immunity and inflammation and play a complex role in sepsis. We examined whether different types of LPS have different effects on the release of soluble signaling/effective molecules from platelets. We used platelet-rich plasma from healthy volunteers and LPS from two strains of gram-negative bacteria with disparate LPS structures. We combined LPS-stimulated platelet supernatants with reporter cells and measured the PBMC cytokine secretion profiles. Upon stimulation of platelets with both Escherichia coli O111 and Salmonella minnesota LPS, the platelet LPS::TLR4 interaction activated pathways to trigger the production of a large number of molecules. The different platelet supernatants caused differential PBMC secretion of IL-6, TNFα, and IL-8. Our data demonstrate that platelets have the capacity to sense external signals differentially through a single type of pathogen recognition receptor and adjust the innate immune response appropriately for pathogens exhibiting different types of 'danger' signals.

The role of a Brucella abortus lipoprotein in intracellular replication and pathogenicity in experimentally infected mice

Brucella abortus, the causative agent of brucellosis, can survive and replicate within host cells. Understanding bacterial virulence factors and bacteria-host cell interactions is critical for controlling brucellosis. However, little is known regarding the pathogenic mechanisms of brucellosis. A lipoprotein mutant (Gene Bank ID: 3339351) of B. abortus showed a lower rate of intracellular replication than did the wild-type strain in HeLa cells and RAW 264.7 macrophages. The adherent activity of the lipoprotein mutant was slightly increased compared to that of the wild-type strain in HeLa cells. After infection into macrophages, the lipoprotein mutant co-localized with either late endosomes or lysosomes. In mice infected with the lipoprotein mutant, fewer lipoprotein mutants were recovered from the spleen at 8 weeks post-infection compared to the wild-type strain. The ability to protect the lipoprotein mutant against infection by the virulent B. abortus strain 544 was similar to that of strain RB51. Our results indicate that the B. abortus lipoprotein is an important factor for survival within phagocytes and mice, and the B. abortus lipoprotein mutant may help improve live vaccines used to control brucellosis.

Caspase-2-dependent dendritic cell death, maturation, and priming of T cells in response to Brucella abortus infection

Smooth virulent Brucella abortus strain 2308 (S2308) causes zoonotic brucellosis in cattle and humans. Rough B. abortus strain RB51, derived from S2308, is a live attenuated cattle vaccine strain licensed in the USA and many other countries. Our previous report indicated that RB51, but not S2308, induces a caspase-2-dependent apoptotic and necrotic macrophage cell death. Dendritic cells (DCs) are professional antigen presenting cells critical for bridging innate and adaptive immune responses. In contrast to Brucella-infected macrophages, here we report that S2308 induced higher levels of apoptotic and necrotic cell death in wild type bone marrow-derived DCs (WT BMDCs) than RB51. The RB51 and S2308-induced BMDC cell death was regulated by caspase-2, indicated by the minimal cell death in RB51 and S2308-infected BMDCs isolated from caspase-2 knockout mice (Casp2KO BMDCs). More S2308 bacteria were taken up by Casp2KO BMDCs than wild type BMDCs. Higher levels of S2308 and RB51 cells were found in infected Casp2KO BMDCs compared to infected WT BMDCs at different time points. RB51-infected wild type BMDCs were mature and activated as shown by significantly up-regulated expression of CD40, CD80, CD86, MHC-I, and MHC-II. RB51 induced the production of cytokines TNF-α, IL-6, IFN-γ and IL12/IL23p40 in infected BMDCs. RB51-infected WT BMDCs also stimulated the proliferation of CD4⁺ and CD8⁺ T cells compared to uninfected WT BMDCs. However, the maturation, activation, and cytokine secretion are significantly impaired in Casp2KO BMDCs infected with RB51 or Salmonella (control). S2308-infected WT and Casp2KO BMDCs were not activated and could not induce cytokine production. These results demonstrated that virulent smooth strain S2308 induced more apoptotic and necrotic dendritic cell death than live attenuated rough vaccine strain RB51; however, RB51, but not its parent strain S2308, induced caspase-2-mediated DC maturation, cytokine production, antigen presentation, and T cell priming.

Newly identified variability in Brucella canis fatty-acid content is associated with geographical origin

This study compared the fatty-acid profiles of Brucella canis blood culture isolates obtained from infected dogs in the UK, Germany, Japan, South Africa, Peru, Mexico, Colombia, and Argentina, and from a human clinical case in Argentina, to a bank of isolates obtained from canine outbreaks in the USA. Analysis of a total of 42 B. canis isolates and one reference strain found a marked variation within the species. Fatty-acid analysis showed that only the isolates from Argentina, Colombia, and Mexico, which included the human B. canis isolate, contained a specific fatty acid, 19:0 cyclopropane (lactobacillic acid), w8c (cis-11,12-methylene octadecanoic acid), and that this fatty acid, when present, made up a large percentage of overall fatty-acid content. Prior to this study, the cellular fatty-acid 19:0 cyclopropane had been identified in all of the species of Brucella considered to be pathogenic to humans (B. abortus, B. melitensis, B. suis) except for B. canis. Discovering that this fatty acid not only occurs in B. canis, but also that it is only present in some strains of the species provides a new focus for investigations aimed at identifying the cause of reported geographical variability in human B. canis infection, and at finding predictors of biological behaviour and human pathogenicity within this Brucella species.

The virB-encoded type IV secretion system is critical for establishment of infection and persistence of Brucella ovis infection in mice

Brucella spp. are gram-negative intracellular bacterial pathogens that cause chronic infections. Brucella virulence factors include a type IV secretion system (T4SS) and its lipopolysaccharide (LPS), which are essential for persistence. However, the role of the virB-encoded T4SS has not been investigated in naturally rough Brucella species such as Brucella ovis. In this study, male 6-week old BALBc mice were infected with B. ovis, Brucella abortus, and their respective ΔvirB2 mutant strains. During early infection, B. ovis and B. abortus wild type strains were similarly recovered from spleen. Interestingly, in contrast to ΔvirB2 B. abortus that was recovered at similar levels when compared to the wild type strain, the ΔvirB2 B. ovis was markedly attenuated as early as 24h post infection (hpi). The ΔvirB2 B. ovis was unable to survive and multiply in murine peritoneal macrophages and extracellularly within the peritoneal cavity at 12 and 24 hpi with lower splenic colonization than the parental strain at 6, 12 and 24 hpi. In contrast, wild type B. abortus and ΔvirB2 B. abortus had a similar kinetics of infection in this model. As expected, the T4SS was essential for intracellular replication of smooth and rough strains in RAW macrophages at 48 hpi. These results suggest that T4SS is important for survival of B. ovis in murine model, and that a T4SS deficient B. ovis strain is cleared at earlier stages of infection when compared to a similar B. abortus mutant.

Internal affairs: investigating the Brucella intracellular lifestyle

Bacteria of the genus Brucella are Gram-negative pathogens of several animal species that cause a zoonotic disease in humans known as brucellosis or Malta fever. Within their hosts, brucellae reside within different cell types where they establish a replicative niche and remain protected from the immune response. The aim of this article is to discuss recent advances in the field in the specific context of the Brucella intracellular 'lifestyle'. We initially discuss the different host cell targets and their relevance during infection. As it represents the key to intracellular replication, the focus is then set on the maturation of the Brucella phagosome, with particular emphasis on the Brucella factors that are directly implicated in intracellular trafficking and modulation of host cell signalling pathways. Recent data on the role of the type IV secretion system are discussed, novel effector molecules identified and how some of them impact on trafficking events. Current knowledge on Brucella gene regulation and control of host cell death are summarized, as they directly affect intracellular persistence. Understanding how Brucella molecules interplay with their host cell targets to modulate cellular functions and establish the intracellular niche will help unravel how this pathogen causes disease.

Differential expression of iron acquisition genes by Brucella melitensis and Brucella canis during macrophage infection

Brucella spp. cause chronic zoonotic disease often affecting individuals and animals in impoverished economic or public health conditions; however, these bacteria do not have obvious virulence factors. Restriction of iron availability to pathogens is an effective strategy of host defense. For brucellae, virulence depends on the ability to survive and replicate within the host cell where iron is an essential nutrient for the growth and survival of both mammalian and bacterial cells. Iron is a particularly scarce nutrient for bacteria with an intracellular lifestyle. Brucella melitensis and Brucella canis share ∼99% of their genomes but differ in intracellular lifestyles. To identify differences, gene transcription of these two pathogens was examined during infection of murine macrophages and compared to broth grown bacteria. Transcriptome analysis of B. melitensis and B. canis revealed differences of genes involved in iron transport. Gene transcription of the TonB, enterobactin, and ferric anguibactin transport systems was increased in B. canis but not B. melitensis during infection of macrophages. The data suggest differences in iron requirements that may contribute to differences observed in the lifestyles of these closely related pathogens. The initial importance of iron for B. canis but not for B. melitensis helps elucidate differing intracellular survival strategies for two closely related bacteria and provides insight for controlling these pathogens.

Analyses of Brucella pathogenesis, host immunity, and vaccine targets using systems biology and bioinformatics

Brucella is a Gram-negative, facultative intracellular bacterium that causes zoonotic brucellosis in humans and various animals. Out of 10 classified Brucella species, B. melitensis, B. abortus, B. suis, and B. canis are pathogenic to humans. In the past decade, the mechanisms of Brucella pathogenesis and host immunity have been extensively investigated using the cutting edge systems biology and bioinformatics approaches. This article provides a comprehensive review of the applications of Omics (including genomics, transcriptomics, and proteomics) and bioinformatics technologies for the analysis of Brucella pathogenesis, host immune responses, and vaccine targets. Based on more than 30 sequenced Brucella genomes, comparative genomics is able to identify gene variations among Brucella strains that help to explain host specificity and virulence differences among Brucella species. Diverse transcriptomics and proteomics gene expression studies have been conducted to analyze gene expression profiles of wild type Brucella strains and mutants under different laboratory conditions. High throughput Omics analyses of host responses to infections with virulent or attenuated Brucella strains have been focused on responses by mouse and cattle macrophages, bovine trophoblastic cells, mouse and boar splenocytes, and ram buffy coat. Differential serum responses in humans and rams to Brucella infections have been analyzed using high throughput serum antibody screening technology. The Vaxign reverse vaccinology has been used to predict many Brucella vaccine targets. More than 180 Brucella virulence factors and their gene interaction networks have been identified using advanced literature mining methods. The recent development of community-based Vaccine Ontology and Brucellosis Ontology provides an efficient way for Brucella data integration, exchange, and computer-assisted automated reasoning.

Characterization of recombinant B. abortus strain RB51SOD toward understanding the uncorrelated innate and adaptive immune responses induced by RB51SOD compared to its parent vaccine strain RB51

Brucella abortus is a Gram-negative, facultative intracellular pathogen for several mammals, including humans. Live attenuated B. abortus strain RB51 is currently the official vaccine used against bovine brucellosis in the United States and several other countries. Overexpression of protective B. abortus antigen Cu/Zn superoxide dismutase (SOD) in a recombinant strain of RB51 (strain RB51SOD) significantly increases its vaccine efficacy against virulent B. abortus challenge in a mouse model. An attempt has been made to better understand the mechanism of the enhanced protective immunity of RB51SOD compared to its parent strain RB51. We previously reported that RB51SOD stimulated enhanced Th1 immune response. In this study, we further found that T effector cells derived from RB51SOD-immunized mice exhibited significantly higher cytotoxic T lymphocyte activity than T effector cells derived from RB51-immunized mice against virulent B. abortus-infected target cells. Meanwhile, the macrophage responses to these two strains were also studied. Compared to RB51, RB51SOD cells had a lower survival rate in macrophages and induced lower levels of macrophage apoptosis and necrosis. The decreased survival of RB51SOD cells correlates with the higher sensitivity of RB51SOD, compared to RB51, to the bactericidal action of either Polymyxin B or sodium dodecyl sulfate (SDS). Furthermore, a physical damage to the outer membrane of RB51SOD was observed by electron microscopy. Possibly due to the physical damage, overexpressed Cu/Zn SOD in RB51SOD was found to be released into the bacterial cell culture medium. Therefore, the stronger adaptive immunity induced by RB51SOD did not correlate with the low level of innate immunity induced by RB51SOD compared to RB51. This unique and apparently contradictory profile is likely associated with the differences in outer membrane integrity and Cu/Zn SOD release.

A review of Brucella infection in marine mammals, with special emphasis on Brucella pinnipedialis in the hooded seal (Cystophora cristata)

Brucella spp. were isolated from marine mammals for the first time in 1994. Two novel species were later included in the genus; Brucella ceti and Brucella pinnipedialis, with cetaceans and seals as their preferred hosts, respectively. Brucella spp. have since been isolated from a variety of marine mammals. Pathological changes, including lesions of the reproductive organs and associated abortions, have only been registered in cetaceans. The zoonotic potential differs among the marine mammal Brucella strains. Many techniques, both classical typing and molecular microbiology, have been utilised for characterisation of the marine mammal Brucella spp. and the change from the band-based approaches to the sequence-based approaches has greatly increased our knowledge about these strains. Several clusters have been identified within the B. ceti and B. pinnipedialis species, and multiple studies have shown that the hooded seal isolates differ from other pinniped isolates. We describe how different molecular methods have contributed to species identification and differentiation of B. ceti and B. pinnipedialis, with special emphasis on the hooded seal isolates. We further discuss the potential role of B. pinnipedialis for the declining Northwest Atlantic hooded seal population.

Brucellosis at the animal/ecosystem/human interface at the beginning of the 21st century

Following the recent discovery of new Brucella strains from different animal species and from the environment, ten Brucella species are nowadays included in the genus Brucella. Although the intracellular trafficking of Brucella is well described, the strategies developed by Brucella to survive and multiply in phagocytic and non-phagocytic cells, particularly to access nutriments during its intracellular journey, are still largely unknown. Metabolism and virulence of Brucella are now considered to be two sides of the same coin. Mechanisms presiding to the colonization of the pregnant uterus in different animal species are not known. Vaccination is the cornerstone of control programs in livestock and although the S19, RB51 (both in cattle) and Rev 1 (in sheep and goats) vaccines have been successfully used worldwide, they have drawbacks and thus the ideal brucellosis vaccine is still very much awaited. There is no vaccine available for pigs and wildlife. Animal brucellosis control strategies differ in the developed and the developing world. Most emphasis is put on eradication and on risk analysis to avoid the re-introduction of Brucella in the developed world. Information related to the prevalence of brucellosis is still scarce in the developing world and control programs are rarely implemented. Since there is no vaccine available for humans, prevention of human brucellosis relies on its control in the animal reservoir. Brucella is also considered to be an agent to be used in bio- and agroterrorism attacks. At the animal/ecosystem/human interface it is critical to reduce opportunities for Brucella to jump host species as already seen in livestock, wildlife and humans. This task is a challenge for the future in terms of veterinary public health, as for wildlife and ecosystem managers and will need a "One Health" approach to be successful.

Proinflammatory caspase-2-mediated macrophage cell death induced by a rough attenuated Brucella suis strain

Brucella spp. are intracellular bacteria that cause an infectious disease called brucellosis in humans and many domestic and wildlife animals. B. suis primarily infects pigs and is pathogenic to humans. The macrophage-Brucella interaction is critical for the establishment of a chronic Brucella infection. Our studies showed that smooth virulent B. suis strain 1330 (S1330) prevented programmed cell death of infected macrophages and rough attenuated B. suis strain VTRS1 (a vaccine candidate) induced strong macrophage cell death. To further investigate the mechanism of VTRS1-induced macrophage cell death, microarrays were used to analyze temporal transcriptional responses of murine macrophage-like J774.A1 cells infected with S1330 or VTRS1. In total 17,685 probe sets were significantly regulated based on the effects of strain, time and their interactions. A miniTUBA dynamic Bayesian network analysis predicted that VTRS1-induced macrophage cell death was mediated by a proinflammatory gene (the tumor necrosis factor alpha [TNF-α] gene), an NF-κB pathway gene (the IκB-α gene), the caspase-2 gene, and several other genes. VTRS1 induced significantly higher levels of transcription of 40 proinflammatory genes than S1330. A Mann-Whitney U test confirmed the proinflammatory response in VTRS1-infected macrophages. Increased production of TNF-α and interleukin 1β (IL-1β) were also detected in the supernatants in VTRS1-infected macrophage cell culture. Hyperphosphorylation of IκB-α was observed in macrophages infected with VTRS1 but not S1330. The important roles of TNF-α and IκB-α in VTRS1-induced macrophage cell death were further confirmed by individual inhibition studies. VTRS1-induced macrophage cell death was significantly inhibited by a caspase-2 inhibitor but not a caspase-1 inhibitor. The role of caspase-2 in regulating the programmed cell death of VTRS1-infected macrophages was confirmed in another study using caspase-2-knockout mice. In summary, VTRS1 induces a proinflammatory, caspase-2- and NF-κB-mediated macrophage cell death. This unique cell death differs from apoptosis, which is not proinflammatory. It is also different from classical pyroptosis, which is caspase-1 mediated.

Lipopolysaccharide-Deficient Brucella Variants Arise Spontaneously during Infection

Lipopolysaccharide-deficient mutants of smooth Brucella species (rough mutants) have been shown to arise spontaneously in culture. However, in situ analysis of Brucella infected macrophages using antibody directed against O-polysaccharide suggested a loss of reactivity of Brucella consistent with the appearance of rough organisms, and a potential contribution to infection. The experiments reported describe the direct recovery of Brucella from macrophages infected in vitro and from the spleens of infected mice at a frequency similar to that described in vitro, suggesting that Brucella dissociation is not simply an in vitro artifact. The frequency of appearance of spontaneous rough organisms deficient in O-polysaccharide expression measured in vitro is approximately 2–3 logs higher than the appearance of mutation to antibiotic resistance, purine auxotrophy, or reversion of erythritol sensitive ΔeryC mutants to tolerance. Genetic trans-complementation using a plasmid-based expression of Brucella manBA successfully restored O-polysaccharide expression in only one-third of O-polysaccharide deficient spontaneous mutants. Suggesting that the appearance of rough mutants is caused by mutation at more than one locus. In addition, Sanger sequencing of the manBA structural genes detected multiple sequence changes that may explain the observed phenotypic differences. The presence of O-polysaccharide resulted in macrophage and neutrophil infiltration into the peritoneal cavity and systemic distribution of the organism. In contrast, rough organisms are controlled by resident macrophages or by extracellular killing mechanisms and rapidly cleared from this compartment consistent with the inability to cause disease. Loss of O-polysaccharide expression appears to be stochastic giving rise to organisms with biological properties distinct from the parental smooth organism during the course of infection.

Cell-mediated immunity in human brucellosis

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

Comparative analysis of the early transcriptome of Brucella abortus--infected monocyte-derived macrophages from cattle naturally resistant or susceptible to brucellosis

Brucellosis is a worldwide zoonotic infectious disease that has a significant economic impact on animal production and human public health. We characterized the gene expression profile of B. abortus-infected monocyte-derived macrophages (MDMs) from naïve cattle naturally resistant (R) or susceptible (S) to brucellosis using a cDNA microarray technology. Our data indicate that (1) B. abortus induced a slightly increased genome activation in R MDMs and a down-regulated transcriptome in S MDMs, during the onset of infection, (2) R MDMs had the ability to mount a type 1 immune response against B. abortus infection which was impaired in S cells, and (3) the host cell activity was not altered after 12 h post-B. abortus infection in R MDMs while the cell cycle was largely arrested in infected S MDMs at 12 h p.i. These results contribute to an improved understanding of how host responses may be manipulated to prevent infection by brucellae.

Brucella-infected hepatocytes mediate potentially tissue-damaging immune responses

BACKGROUND & AIMS

Hepatic involvement is frequent in human brucellosis. While different histopathological lesions have been reported in these patients, the underlying cellular and molecular mechanisms have not been addressed.

METHODS

This study assessed whether Brucella abortus can infect a human hepatoma cell line and induce a proinflammatory response in these cells.

RESULTS

The bacterium not only infected the human hepatoma cell line HepG2 but also exhibited intracellular replication. The infection induced hepatoma cells to secrete IL-8, and supernatants from Brucella-infected hepatoma cells were shown to induce the migration of human neutrophils. The infection also induced the expression of the intercellular adhesion molecule ICAM-1 on hepatoma cells, and the adhesion of neutrophils to these cells was significantly higher than to uninfected hepatoma cells. ICAM-1 expression was also induced by stimulation of hepatoma cells with supernatants from Brucella-infected neutrophils. While Brucella infection did not induce the expression of matrix metalloproteinases (MMPs) in hepatoma cells, it significantly induced MMP-9 in neutrophils. Hepatoma cell apoptosis was significantly induced by B. abortus infection and also by stimulation with supernatants from Brucella-infected neutrophils.

CONCLUSIONS

The present study provides clues regarding potential mechanisms of tissue damage during liver brucellosis.

Direct and monocyte-induced innate immune response of human lung epithelial cells to Brucella abortus infection

Although Brucella frequently infects humans through inhalation, its interaction with pulmonary cells has been overlooked. We examined whether human lung epithelial cells produce proinflammatory mediators in response to Brucella infection. Infection with smooth or rough strains of Brucella abortus induced the secretion of IL-8 and GM-CSF by the bronchial epithelial cell lines Calu-6 and 16HBE14o-, but not by the alveolar epithelial cell line A549. Infected Calu-6 cells also produced low levels of MCP-1. Since monocyte-derived cytokines may induce chemokine secretion in epithelial cells, cocultures of human monocytes (THP-1 cell line) and respiratory epithelial cells were used to study such interaction. IL-8 and MCP-1 levels in B. abortus-infected THP-1:A549 and THP-1:Calu-6 cocultures, and MCP-1 levels in THP-1:16HBE14o- cocultures, were higher than those detected in infected epithelial monocultures. Conditioned medium from infected monocytes induced the secretion of IL-8 and/or MCP-1 by A549 and Calu-6 cells, and these effects were mainly mediated by IL-1 (in A549 cells) or TNF-alpha (in Calu-6 cells). Conversely, culture supernatants from Brucella-infected bronchial epithelial cells induced MCP-1 production by monocytes, an effect largely mediated by GM-CSF. This study shows that human lung epithelial cells mount a proinflammatory response to Brucella, either directly or after interaction with Brucella-infected monocytes.

Cholesterol, ganglioside GM1 and class A scavenger receptor contribute to infection by Brucella ovis and Brucella canis in murine macrophages

The establishment of infection by Brucella ovis and Brucella canis in J774.A1 macrophages was found to be dependent upon cholesterol and ganglioside GM(1), two components of lipid rafts. This process also required a class A scavenger receptor of macrophages, and was not inhibited by smooth and rough lipopolysaccharides from Brucella spp. In response to infection, both bacteria induced a weak degree of macrophage activation. These results demonstrate that B. ovis and B. canis use cell surface receptors common to smooth Brucella spp. for macrophage infection, thus limiting macrophage activation and favouring intracellular multiplication and/or the survival of both bacteria.

Brucella melitensis, B. neotomae and B. ovis elicit common and distinctive macrophage defense transcriptional responses

Brucella spp. establish an intracellular replicative niche in macrophages, while macrophages attempt to eliminate the bacteria by innate defense mechanisms. Brucella spp. possess similar genomes yet exhibit different macrophage infections. Few B. melitensis and B. neotomae enter macrophages with intracellular adaptation occurring over 4-8 hr. Conversely, B. ovis are readily ingested by macrophages and exhibit a persistent plateau of infection. Evaluating early macrophage interaction with Brucella spp. allows discovery of host entry and intracellular translocation mechanisms. Microarray analysis of macrophage transcriptional response following a 4 hr infection by different Brucella spp. revealed common macrophage genes altered in expression compared to uninfected macrophages. Macrophage infection with three different Brucella spp. provokes a common innate immune theme with increased transcript levels of chemokines and defense response genes and decreased transcript levels of GTPase signaling and cytoskeletal function that may affect trafficking of Brucella containing vesicles. For example, transcript levels of genes associated with chemotaxis (IL-1beta, MIP-1alpha), cytokine regulation (Socs3) and defense (Fas, Tnf) were increased, while transcript levels of genes associated with vesicular trafficking (Rab3d) and lysosomal associated enzymes (prosaposin) were decreased. Genes with altered macrophage transcript levels among Brucella spp. infections may correlate with species specific host defenses and intracellular survival strategies. Depending on the infecting Brucella species, gene ontology categorization identified genes differentially involved in cell growth and maintenance, endopeptidase inhibitor activity and G-protein mediated signaling. Examples of decreased gene expression in B. melitensis infection but not other Brucella spp. were growth arrest (Gas2), immunoglobulin receptor (FcgammarI) and chemokine receptor (Cxcr4) genes, suggesting opposing effects on intracellular functions.

Oral bacteria induce a differential activation of human immunodeficiency virus-1 promoter in T cells, macrophages and dendritic cells

INTRODUCTION

The human immunodeficiency virus (HIV) can integrate into T cells, macrophages and dendritic cells resulting in a latent infection. Reports have also demonstrated that various microbial and host cell factors can trigger HIV reactivation leading to HIV recrudescence, potentially undermining highly active antiretroviral therapies.

METHODS

This study evaluated the capacity of oral bacteria associated with chronic periodontal infections to stimulate HIV promoter activation in various cell models of HIV latency.

RESULTS

T cells (1G5) challenged with oral bacteria demonstrated a dose-response of HIV promoter activation with a subset of the bacteria, as well as kinetics that were generally similar irrespective of the stimuli. Direct bacterial challenge of the T cells resulted in increased activation of approximately 1.5- to 7-fold over controls. Challenge of macrophages (BF24) indicated different kinetics for individual bacteria and resulted in consistent increases in promoter activation of five fold to six fold over basal levels for all bacteria except Streptococcus mutans. Dendritic cells showed increases in HIV reactivation of 7- to 34-fold specific for individual species of bacteria.

CONCLUSION

These results suggested that oral bacteria have the capability to reactivate HIV from latently infected cells, showing a relationship of mature dendritic cells > immature dendritic cells > macrophages > or = T cells. Expression of various pattern recognition receptors on these various cell types may provide insight into the primary receptors/signaling pathways used for reactivation by the bacteria.

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.

O-antigen delays lipopolysaccharide recognition and impairs antibacterial host defense in murine intestinal epithelial cells

Although Toll-like receptor (TLR) 4 signals from the cell surface of myeloid cells, it is restricted to an intracellular compartment and requires ligand internalization in intestinal epithelial cells (IECs). Yet, the functional consequence of cell-type specific receptor localization and uptake-dependent lipopolysaccharide (LPS) recognition is unknown. Here, we demonstrate a strikingly delayed activation of IECs but not macrophages by wildtype Salmonella enterica subsp. enterica sv. (S.) Typhimurium as compared to isogenic O-antigen deficient mutants. Delayed epithelial activation is associated with impaired LPS internalization and retarded TLR4-mediated immune recognition. The O-antigen-mediated evasion from early epithelial innate immune activation significantly enhances intraepithelial bacterial survival in vitro and in vivo following oral challenge. These data identify O-antigen expression as an innate immune evasion mechanism during apical intestinal epithelial invasion and illustrate the importance of early innate immune recognition for efficient host defense against invading Salmonella.

The mammalian host recognizes infection by the detection of particular microbial structures. Recognition of these structures leads to activation of host defense effector mechanisms that in turn combat infection. A very potent activating microbial structure is lipopolysaccharide, a cell wall component released by many bacteria such as Salmonella, one of the most frequent causative agents of foodborne infection of the gut. We previously showed that cells lining the gut surface require uptake of bacterial lipopolysaccharide for its detection. The functional consequence of lipopolysaccharide uptake, however, was unknown. Here, we demonstrate that the uptake of lipopolysaccharide released by Salmonella is impaired by its extensive sugar modification. Impaired lipopolysaccharide uptake prevents early activation of host defense mechanisms and thereby allows Salmonella to better survive and proliferate within the host's intestinal cells. Thus, this lipopolysaccharide modification represents a mechanism by which Salmonella impairs recognition by the mammalian host to more efficiently cause infection of the intestinal mucosa.

Caspase-2 mediated apoptotic and necrotic murine macrophage cell death induced by rough Brucella abortus

Brucella species are Gram-negative, facultative intracellular bacteria that cause zoonotic brucellosis. Survival and replication inside macrophages is critical for establishment of chronic Brucella infection. Virulent smooth B. abortus strain 2308 inhibits programmed macrophage cell death and replicates inside macrophages. Cattle B. abortus vaccine strain RB51 is an attenuated rough, lipopolysaccharide O antigen-deficient mutant derived from smooth strain 2308. B. abortus rough mutant RA1 contains a single wboA gene mutation in strain 2308. Our studies demonstrated that live RB51 and RA1, but not strain 2308 or heat-killed Brucella, induced both apoptotic and necrotic cell death in murine RAW264.7 macrophages and bone marrow derived macrophages. The same phenomenon was also observed in primary mouse peritoneal macrophages from mice immunized intraperitoneally with vaccine strain RB51 using the same dose as regularly performed in protection studies. Programmed macrophage cell death induced by RB51 and RA1 was inhibited by a caspase-2 inhibitor (Z-VDVAD-FMK). Caspase-2 enzyme activation and cleavage were observed at the early infection stage in macrophages infected with RB51 and RA1 but not strain 2308. The inhibition of macrophage cell death promoted the survival of rough Brucella cells inside macrophages. The critical role of caspase-2 in mediating rough B. abortus induced macrophage cell death was confirmed using caspase-2 specific shRNA. The mitochondrial apoptosis pathway was activated in macrophages infected with rough B. abortus as demonstrated by increase in mitochondrial membrane permeability and the release of cytochrome c to cytoplasm in macrophages infected with rough Brucella. These results demonstrate that rough B. abortus strains RB51 and RA1 induce apoptotic and necrotic murine macrophage cell death that is mediated by caspase-2. The biological relevance of Brucella O antigen and caspase-2-mediated macrophage cell death in Brucella pathogenesis and protective Brucella immunity is discussed.

Role of inflammation (leukocyte-endothelial cell interactions) in vasospasm after subarachnoid hemorrhage

BACKGROUND

Delayed vasospasm is the leading cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). This phenomenon was first described more than 50 years ago, but only recently has the role of inflammation in this condition become better understood.

METHODS

The literature was reviewed for studies on delayed vasospasm and inflammation.

RESULTS

There is increasing evidence that inflammation and, more specifically, leukocyte-endothelial cell interactions play a critical role in the pathogenesis of vasospasm after aSAH, as well as in other conditions including meningitis and traumatic brain injury. Although earlier clinical observations and indirect experimental evidence suggested an association between inflammation and chronic vasospasm, recently direct molecular evidence demonstrates the central role of leukocyte-endothelial cell interactions in the development of chronic vasospasm. This evidence shows in both clinical and experimental studies that cell adhesion molecules (CAMs) are up-regulated in the perivasospasm period. Moreover, the use of monoclonal antibodies against these CAMs, as well as drugs that decrease the expression of CAMs, decreases vasospasm in experimental studies. It also appears that certain individuals are genetically predisposed to a severe inflammatory response after aSAH based on their haptoglobin genotype, which in turn predisposes them to develop clinically symptomatic vasospasm.

CONCLUSION

Based on this evidence, leukocyte-endothelial cell interactions appear to be the root cause of chronic vasospasm. This hypothesis predicts many surprising features of vasospasm and explains apparently unrelated phenomena observed in aSAH patients. Therapies aimed at preventing inflammation may prevent and/or reverse arterial narrowing in patients with aSAH and result in improved outcomes.

Intracellular copper/zinc superoxide dismutase from bay scallop Argopecten irradians: its gene structure, mRNA expression and recombinant protein

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Two unique and highly compartmentalized bay scallop Argopecten irradians superoxide dismutases: MnSOD and ecCuZnSOD, have been molecularly characterized in our previous study. To complete characterize the SOD family in A. irradians, a novel intracellular copper/zinc SOD from the A. irradians (Ai-icCuZnSOD) was obtained and characterized. The full-length cDNA of Ai-icCuZnSOD was 1047 bp with a 459 bp open reading frame encoding 152 amino acids. The genomic length of the Ai-icCuZnSOD gene was about 4279 bp containing 4 exons and 3 introns. The promoter region containing many putative transcription factor binding sites were analyzed. Furthermore, quantitative reverse transcriptase real-time PCR (qRT-PCR) analysis indicated that the highest expression of the Ai-icCuZnSOD was detected in gill and the expression profiles in hemocytes of bay scallops challenged with bacteria Vibrio anguillarum and lipopolysaccharide (LPS) were different. The result presented an increased expression after injection with LPS whereas no significant changes were observed after V. anguillarum injection. A fusion protein containing Ai-icCuZnSOD was produced in vitro. The rAi-icCuZnSOD is a stable enzyme, retaining more than 80% of its activity between 10 and 60 degrees C and keeping above 88% of its activity at pH values between 5.8 and 9. Ai-icCuZnSOD is more stable under alkaline than acidic conditions.

Role of Salmonella enterica lipopolysaccharide in activation of dendritic cell functions and bacterial containment

In contrast to nonpathogenic bacteria, the Gram-negative pathogen Salmonella enterica is not eradicated, but persists in murine dendritic cells (DC). The molecular basis of this phenotype is unknown. We set out to characterize bacterial and DC functions that are involved in Salmonella persistence. Our data prove that neither bacterial nor host cell de novo protein biosynthesis is required for Salmonella persistence in DC. We identified the Salmonella O-Ag of the LPS of Salmonella as an important factor for controlling the intracellular fate of Salmonella in DC. A Salmonella strain with entirely absent O-Ag showed an increased rate of uptake by DC, altered intracellular processing, and increased degradation, and also boosted the activation of immune functions of DC. These novel findings demonstrate that in addition to the multiple functions of the bacterial LPS in adaptation to the intestinal environment and protection against innate immune function, this molecule also has an important role in interaction of Salmonella with DC.

Chronic brucellosis patients retain low frequency of CD4+ T-lymphocytes expressing CD25 and CD28 after Escherichia coli LPS stimulation of PHA-cultured PBMCs

Chronic brucellosis patients display a defective Th1 response to PHA. We have previously shown that heat-killed B. abortus (HKBA) can downregulate the PHA-induced increase of CD4+/CD25+ and CD14+/CD80+ cells of brucellosis patients. In the present study, we investigate the effect of E. coli LPS, as a potent stimulant of monocytes and autologous T-lymphocytes, on the PHA-cultured PBMCs of the same groups of patients. Thirteen acute brucellosis (AB) patients, 22 chronic brucellosis (CB) patients, 11 “cured” subjects, and 15 healthy volunteers were studied. The percentage of CD4+/CD25+ and CD4+/CD28+ T-lymphocytes as well as CD14+/CD80+ monocytes were analyzed by flow cytometry after PBMCs culture with PHA plus E. coli LPS. A significant decrease in the percentage of CD4+/CD25+ and CD4+/CD28+ T-lymphocytes was observed in CB compared to AB. In HKBA cultures, compared to E. coli LPS-cultures, there was a significant reduction of CD4+/CD25+ T-lymphocytes in all groups and CD14+/CD80+ in patients groups. We suggest that Brucella can modulate host immune response, leading to T-cell anergy and chronic infection.

Modulation of CD163 receptor expression and replication of porcine reproductive and respiratory syndrome virus in porcine macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) has a specific cell tropism for differentiated macrophages, such as porcine alveolar macrophages (PAMs). We analyzed the expression of CD163 on PAMs and macrophages derived from CD14 positive blood monocytes (MDMs), in correlation with PRRSV replication. By flow cytometry analysis, we showed that the levels of CD163 expression correlated well with the overall level of PRRSV replication. We further examined the effects of modulators of macrophage function, including 12-O-tetradecanoylphorbol-13-acetate (TPA), lipopolysaccharide (LPS), and interleukin (IL)-10 on the expression of CD163 and PRRSV replication. Pre-treatment of PAMs or MDMs with TPA or LPS resulted in decreased expression of CD163 and reduction in PRRSV replication. On the contrary, the incubation of CD14 positive monocytes with IL-10 during differentiation into MDMs resulted in up-regulated expression of CD163 with a corresponding increase in PRRSV infection. These data indicate that the expression of CD163 on macrophages in different microenvironments, in vivo, may determine the replication efficiency and subsequent pathogenecity of PRRSV.

Proinflammatory response of human osteoblastic cell lines and osteoblast-monocyte interaction upon infection with Brucella spp

The ability of Brucella spp. to infect human osteoblasts and the cytokine response of these cells to infection were investigated in vitro. Brucella abortus, B. suis, B. melitensis, and B. canis were able to infect the SaOS-2 and MG-63 osteoblastic cell lines, and the first three species exhibited intracellular replication. B. abortus internalization was not significantly affected by pretreatment of cells with cytochalasin D but was inhibited up to 92% by colchicine. A virB10 mutant of B. abortus could infect but not replicate within osteoblasts, suggesting a role for the type IV secretion system in intracellular survival. Infected osteoblasts produced low levels of chemokines (interleukin-8 [IL-8] and macrophage chemoattractant protein 1 [MCP-1]) and did not produce proinflammatory cytokines (IL-1beta, IL-6, and tumor necrosis factor alpha [TNF-alpha]). However, osteoblasts stimulated with culture supernatants from Brucella-infected human monocytes (THP-1 cell line) produced chemokines at levels 12-fold (MCP-1) to 17-fold (IL-8) higher than those of infected osteoblasts and also produced IL-6. In the inverse experiment, culture supernatants from Brucella-infected osteoblasts induced the production of IL-8, IL-1beta, IL-6, and TNF-alpha by THP-1 cells. The induction of TNF-alpha and IL-1beta was largely due to granulocyte-macrophage colony-stimulating factor produced by infected osteoblasts, as demonstrated by inhibition with a specific neutralizing antibody. This study shows that Brucella can invade and replicate within human osteoblastic cell lines, which can directly and indirectly mount a proinflammatory response. Both phenomena may have a role in the chronic inflammation and bone and joint destruction observed in osteoarticular brucellosis.

RNAi screen of endoplasmic reticulum-associated host factors reveals a role for IRE1alpha in supporting Brucella replication

Brucella species are facultative intracellular bacterial pathogens that cause brucellosis, a global zoonosis of profound importance. Although recent studies have demonstrated that Brucella spp. replicate within an intracellular compartment that contains endoplasmic reticulum (ER) resident proteins, the molecular mechanisms by which the pathogen secures this replicative niche remain obscure. Here, we address this issue by exploiting Drosophila S2 cells and RNA interference (RNAi) technology to develop a genetically tractable system that recapitulates critical aspects of mammalian cell infection. After validating this system by demonstrating a shared requirement for phosphoinositide 3-kinase (PI3K) activities in supporting Brucella infection in both host cell systems, we performed an RNAi screen of 240 genes, including 110 ER-associated genes, for molecules that mediate bacterial interactions with the ER. We uncovered 52 evolutionarily conserved host factors that, when depleted, inhibited or increased Brucella infection. Strikingly, 29 of these factors had not been previously suggested to support bacterial infection of host cells. The most intriguing of these was inositol-requiring enzyme 1 (IRE1), a transmembrane kinase that regulates the eukaryotic unfolded protein response (UPR). We employed IRE1α^−/− murine embryonic fibroblasts (MEFs) to demonstrate a role for this protein in supporting Brucella infection of mammalian cells, and thereby, validated the utility of the Drosophila S2 cell system for uncovering novel Brucella host factors. Finally, we propose a model in which IRE1α, and other ER-associated genes uncovered in our screen, mediate Brucella replication by promoting autophagosome biogenesis.

Brucella spp. are facultative intracellular pathogens that cause brucellosis in a broad range of hosts, including humans. Brucella melitensis, B. abortus, and B. suis are highly infectious and can be readily transmitted in aerosolized form, and a human vaccine against brucellosis is unavailable. Therefore, these pathogens are recognized as potential bioterror agents. Because genetic systems for studying host–Brucella interactions have been unavailable, little is known about the host factors that mediate infection. Here, we demonstrate that a Drosophila S2 cell system and RNA interference can be exploited to study the role that evolutionarily conserved Brucella host proteins play in these processes. We also show that this system provides for the identification and characterization of host factors that mediate Brucella interactions with the host cell endoplasmic reticulum. In fact, we identified 52 host factors that, when depleted, inhibited or increased Brucella infection. Among the identified Brucella host factors, 29 have not been previously shown to support bacterial infection. Finally, we demonstrate that the novel host factor inositol-requiring enzyme 1 (IRE1) and its mammalian ortholog (IRE1α) are required for Brucella infection of Drosophila S2 and mammalian cells, respectively. Therefore, this work contributes to our understanding of host factors mediating Brucella infection.

Brucellosis vaccines: assessment of Brucella melitensis lipopolysaccharide rough mutants defective in core and O-polysaccharide synthesis and export

Background

The brucellae are facultative intracellular bacteria that cause brucellosis, one of the major neglected zoonoses. In endemic areas, vaccination is the only effective way to control this disease. Brucella melitensis Rev 1 is a vaccine effective against the brucellosis of sheep and goat caused by B. melitensis, the commonest source of human infection. However, Rev 1 carries a smooth lipopolysaccharide with an O-polysaccharide that elicits antibodies interfering in serodiagnosis, a major problem in eradication campaigns. Because of this, rough Brucella mutants lacking the O-polysaccharide have been proposed as vaccines.

Methodology/Principal Findings

To examine the possibilities of rough vaccines, we screened B. melitensis for lipopolysaccharide genes and obtained mutants representing all main rough phenotypes with regard to core oligosaccharide and O-polysaccharide synthesis and export. Using the mouse model, mutants were classified into four attenuation patterns according to their multiplication and persistence in spleens at different doses. In macrophages, mutants belonging to three of these attenuation patterns reached the Brucella characteristic intracellular niche and multiplied intracellularly, suggesting that they could be suitable vaccine candidates. Virulence patterns, intracellular behavior and lipopolysaccharide defects roughly correlated with the degree of protection afforded by the mutants upon intraperitoneal vaccination of mice. However, when vaccination was applied by the subcutaneous route, only two mutants matched the protection obtained with Rev 1 albeit at doses one thousand fold higher than this reference vaccine. These mutants, which were blocked in O-polysaccharide export and accumulated internal O-polysaccharides, stimulated weak anti-smooth lipopolysaccharide antibodies.

Conclusions/Significance

The results demonstrate that no rough mutant is equal to Rev 1 in laboratory models and question the notion that rough vaccines are suitable for the control of brucellosis in endemic areas.

Genomic island 2 of Brucella melitensis is a major virulence determinant: functional analyses of genomic islands

Brucella genomic islands (GIs) share similarities in their genomic organization to pathogenicity islands from other bacteria and are likely acquired by lateral gene transfer. Here, we report the identification of a GI that is important for the pathogenicity of Brucella melitensis. The deletion of GI-1, GI-5, or GI-6 did not affect bacterial growth in macrophages as well as their virulence in interferon regulatory factor 1-deficient (IRF-1(-/-)) mice, suggesting that these islands do not contribute to Brucella virulence. However, the deletion of GI-2 resulted in the attenuation of bacterial growth in macrophages and virulence in IRF-1(-/-) mice. The GI-2 mutant also displayed a rough lipopolysaccharide (LPS) phenotype indicated by acriflavin agglutination, suggesting that in vitro and in vivo attenuation is a result of LPS alteration. Further, systematic analysis of the entire GI-2 revealed two open reading frames (ORFs), BMEI0997 and I0998, that encode hypothetical sugar transferases and contribute to LPS alteration, as the deletion of either of these ORFs resulted in a rough phenotype similar to that of the GI-2 mutant. Complementation analyses indicated that in addition to I0997 and I0998, I0999 is required to restore the smooth LPS in the GI-2 mutant as well as its full in vitro and in vivo virulence. The I0999 sequence analysis suggested that it might function as a transporter to help facilitate the transport or linking of the O antigen to the LPS. Our study also indicated that the rough LPS resulting from the GI-2 deletion may affect pathogen-associated molecular pattern recognition by Toll-like receptors.

Evidence of Brucella abortus OPS dictating uptake and restricting NF-kappaB activation in murine macrophages

Smooth Brucella abortus S2308 is virulent while rough derivatives are attenuated. Intracellular killing is often blamed for these differences. In the studies described, uptake kinetics and interaction of S2308 and S2308 manBA::Tn5 (CA180) rough mutants with macrophages were investigated. The results revealed that smooth B. abortus was rapidly internalized, achieving a maximum level in less than 5 min without additional uptake over the next 30 min. In contrast, continued uptake of the rough mutant was observed and only achieves a maximum level after 30 min. The results were confirmed by the differences in F-actin polymerization, lipid raft staining, early endosome colocalization and electron microscopic observations after smooth and rough Brucella infection. We also demonstrated for the first time that uptake of S2308, but not rough mutant CA180 was PI3-kinase and toll-like receptor 4 (TLR4) dependent. Differences in uptake were associated with differences in macrophage activation with regard to NF-kappaB translocation and cytokine production. These results provide evidence that the presence of B. abortus OPS dictates the interactions between Brucella and specific cell surface receptors minimizing macrophage activation and enhancing Brucella survival and/or persistence.

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.

Cytotoxicity in macrophages infected with rough Brucella mutants is type IV secretion system dependent

Smooth Brucella spp. inhibit macrophage apoptosis, whereas rough Brucella mutants induce macrophage oncotic and necrotic cell death. However, the mechanisms and genes responsible for Brucella cytotoxicity have not been identified. In the current study, a random mutagenesis approach was used to create a mutant bank consisting of 11,354 mutants by mariner transposon mutagenesis using Brucella melitensis rough mutant 16M delta manBA as the parental strain. Subsequent screening identified 56 mutants (0.49% of the mutant bank) that failed to cause macrophage cell death (release of 10% or less of the lactate dehydrogenase). The absence of cytotoxicity during infection with these mutants was independent of demonstrable defects in in vitro bacterial growth or uptake and survival in macrophages. Interrupted genes in 51 mutants were identified by DNA sequence analysis, and the mutations included interruptions in virB encoding the type IV secretion system (T4SS) (n = 36) and in vjbR encoding a LuxR-like regulatory element previously shown to be required for virB expression (n = 3), as well as additional mutations (n = 12), one of which also has predicted roles in virB expression. These results suggest that the T4SS is associated with Brucella cytotoxicity in macrophages. To verify this, deletion mutants were constructed in B. melitensis 16M by removing genes encoding phosphomannomutase/phosphomannoisomerase (delta manBA) and the T4SS (delta virB). As predicted, deletion of virB from 16M delta manBA and 16M resulted in a complete loss of cytotoxicity in rough strains, as well as the low level cytotoxicity observed with smooth strains at extreme multiplicities of infection (>1,000). Taken together, these results demonstrate that Brucella cytotoxicity in macrophages is T4SS dependent.