Entry and intracellular replication of Mycobacterium tuberculosis in cultured human microvascular endothelial cells

Epithelial and Mesenchymal-like Pancreatic Cancer Cells Exhibit Different Stem Cell Phenotypes Associated with Different Metastatic Propensities

Pancreatic ductal adenocarcinoma (PDAC) is mostly diagnosed at advanced or even metastasized stages, limiting the prognoses of patients. Metastasis requires high tumor cell plasticity, implying phenotypic switching in response to changing environments. Here, epithelial-mesenchymal transition (EMT), being associated with an increase in cancer stem cell (CSC) properties, and its reversion are important. Since it is poorly understood whether different CSC phenotypes exist along the EMT axis and how these impact malignancy-associated properties, we aimed to characterize CSC populations of epithelial and mesenchymal-like PDAC cells. Single-cell cloning revealed CSC (Holoclone) and non-CSC (Paraclone) clones from the PDAC cell lines Panc1 and Panc89. The Panc1 Holoclone cells showed a mesenchymal-like phenotype, dominated by a high expression of the stemness marker Nestin, while the Panc89 Holoclone cells exhibited a SOX2-dominated epithelial phenotype. The Panc89 Holoclone cells showed enhanced cell growth and a self-renewal capacity but slow cluster-like invasion. Contrarily, the Panc1 Holoclone cells showed slower cell growth and self-renewal ability but were highly invasive. Moreover, cell variants differentially responded to chemotherapy. In vivo, the Panc1 and Panc89 cell variants significantly differed regarding the number and size of metastases, as well as organ manifestation, leading to different survival outcomes. Overall, these data support the existence of different CSC phenotypes along the EMT axis in PDAC, manifesting different metastatic propensities.

Changing paradigms in the treatment of tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis, is a disease long dealt with, but still remains the second leading cause of death world-wide. The current anti-tubercular chemotherapy primarily targets the microbial pathogenesis, which however, is failing due to the development of drug resistance. Moreover, with fewer new drugs reaching the market, there is a need to focus on alternate treatment approaches that could be used as stand-alone or adjunct therapy and the existing drugs, referred to as Track II chemotherapy. This article is an attempt to review the changing global patterns of tuberculosis and its treatment. Further, newer drug delivery approaches like multi-particulate drug carriers which increase the therapeutic efficacy and bring down the systemic toxicity associated with drugs have also been discussed. There is also a need to use interventions which can be used as Track II therapy. Host-directed therapeutics (HDT) is an emerging area concept in which host cell functions and hence the response to pathogens can be modulated, which can help manage TB. HDT decreases damage induced due to inflammation and necrosis in the lungs and other parts of the body due to the disease. Various immuno-modulatory pathways have been discussed in this review which could be explored further to treat TB. An in-depth understanding of multi-particulate drug carriers and HDT could help in dealing with tuberculosis; however, there is still a long way to go.

The Missing Link in Correlates of Protective Tuberculosis Immunity: Recognizing the Infected Cell

For most vaccination studies, the assessment of vaccine-induced CD4+ and CD8+ T cells has relied upon the measurement of antigen-specific polyfunctional cells, typically using recombinant antigen or peptide pools. However, this approach leaves open the question as to whether or not these cells are responsive to the Mtb-infected cell within the context of Mtb infection and hence leaves open the possibility that a key parameter of vaccine immunogenicity may be overlooked. In this review, we discuss the case that these measurements almost certainly over-estimate the capacity of both CD4+ and CD8+ T cells to recognize the Mtb-infected cell.

Advanced In Vitro Lung Models for Drug and Toxicity Screening: The Promising Role of Induced Pluripotent Stem Cells

The substantial socioeconomic burden of lung diseases, recently highlighted by the disastrous impact of the coronavirus disease 2019 (COVID-19) pandemic, accentuates the need for interventive treatments capable of decelerating disease progression, limiting organ damage, and contributing to a functional tissue recovery. However, this is hampered by the lack of accurate human lung research models, which currently fail to reproduce the human pulmonary architecture and biochemical environment. Induced pluripotent stem cells (iPSCs) and organ-on-chip (OOC) technologies possess suitable characteristics for the generation of physiologically relevant in vitro lung models, allowing for developmental studies, disease modeling, and toxicological screening. Importantly, these platforms represent potential alternatives for animal testing, according to the 3Rs (replace, reduce, refine) principle, and hold promise for the identification and approval of new chemicals under the European REACH (registration, evaluation, authorization and restriction of chemicals) framework. As such, this review aims to summarize recent progress made in human iPSC- and OOC-based in vitro lung models. A general overview of the present applications of in vitro lung models is presented, followed by a summary of currently used protocols to generate different lung cell types from iPSCs. Lastly, recently developed iPSC-based lung models are discussed.

Cronobacter sakazakii ATCC 29544 Translocated Human Brain Microvascular Endothelial Cells via Endocytosis, Apoptosis Induction, and Disruption of Tight Junction

Cronobacter sakazakii (C. sakazakii) is an emerging opportunistic foodborne pathogen that can cause neonatal necrotizing enterocolitis, meningitis, sepsis in neonates and infants with a relatively high mortality rate. Bacterial transcytosis across the human brain microvascular endothelial cells (HBMEC) is vital for C. sakazakii to induce neonatal meningitis. However, few studies focus on the mechanisms by which C. sakazakii translocates HBMEC. In this study, the translocation processes of C. sakazakii on HBMEC were explored. C. sakazakii strains could effectively adhere to, invade and intracellularly survive in HBMEC. The strain ATCC 29544 exhibited the highest translocation efficiency across HBMEC monolayer among four tested strains. Bacteria-contained intracellular endosomes were detected in C. sakazakii-infected HBMEC by a transmission electron microscope. Endocytosis-related proteins CD44, Rab5, Rab7, and LAMP2 were increased after infection, while the level of Cathepsin L did not change. C. sakazakii induced TLR4/NF-κB inflammatory signal pathway activation in HBMEC, with increased NO production and elevated mRNA levels of IL-8, IL-6, TNF-α, IL-1β, iNOS, and COX-2. C. sakazakii infection also caused LDH release, caspase-3 activation, and HBMEC apoptosis. Meanwhile, increased Dextran-FITC permeability and decreased trans epithelial electric resistance indicated that C. sakazakii disrupted tight junction of HBMEC monolayers, which was confirmed by the decreased levels of tight junction-related proteins ZO-1 and Occludin. These findings suggest that C. sakazakii induced intracellular bacterial endocytosis, stimulated inflammation and apoptosis, disrupted monolayer tight junction in HBMEC, which all together contribute to bacterial translocation.

A protein fragment of Rv3194c located on mycobacterial cell surface efficiently prevents adhesion of recombinant Mycobacterium smegmatis, and promises a new anti-adhesive drug

Adhesins are virulence factors expressed on the surfaces of pathogenic bacteria that mediate pathogen-host interactions, a critical step in the infection process. Here, we show that the Mycobacterium tuberculosis protease Rv3194c functions not only as an enzyme but as an adhesin. The heterologous Rv3194c protein was purified from Escherichia coli and was shown to bind to hyaluronic acid (HA). The HA-binding site was identified as a 20 amino acid peptide between residues 91 and 110 (P91-110). Rv3194c bound to A549 alveolar basal epithelial cells and the interaction was abolished by the addition of hyaluronidase or P91-110. Experimental infection in vitro revealed that Rv3194c participates in the attachment of recombinant Mycobacterium smegmatis (Rv3194c/MS) to A549 cells, and P91-110 treatment of A549 cells largely inhibited the Rv3194c/MS-A549 cell interaction. To provide in vivo evidence, we constructed a reporter strain of M. smegmatis that expressed a derivative of the firefly luciferase that is shifted to red (FFlucRT) in combination with Rv3194c (Rv3194c + FFlucRT/MS) to infect mice and monitor the progression of the disease. In mice, Rv3194c dramatically enhanced M. smegmatis persistence and induced lesions in the lungs. In addition, treatment of intratracheal Rv3194c + FFlucRT/MS- infected mice with P91-110 significantly suppressed the growth of Rv3194c + FFlucRT/MS in vivo and reduced pathological injury caused by infection of the lung with Rv3194c + FFlucRT/MS. Taken together, these results demonstrate that Rv3194c functions as an HA-binding adhesin and that P91-110 may have the potential for treating and preventing mycobacterial infection.

Mycobacterium tuberculosis Dissemination Plays a Critical Role in Pathogenesis

Mycobacterium tuberculosis is primarily a respiratory pathogen. However, 15% of infections worldwide occur at extrapulmonary sites causing additional complications for diagnosis and treatment of the disease. In addition, dissemination of M. tuberculosis out of the lungs is thought to be more than just a rare event leading to extrapulmonary tuberculosis, but rather a prerequisite step that occurs during all infections, producing secondary lesions that can become latent or productive. In this review we will cover the clinical range of extrapulmonary infections and the process of dissemination including evidence from both historical medical literature and animal experiments for dissemination and subsequent reseeding of the lungs through the lymphatic and circulatory systems. While the mechanisms of M. tuberculosis dissemination are not fully understood, we will discuss the various models that have been proposed to address how this process may occur and summarize the bacterial virulence factors that facilitate M. tuberculosis dissemination.

Evaluation of in silico designed inhibitors targeting MelF (Rv1936) against Mycobacterium marinum within macrophages

We recently identified inhibitors targeting Mycobacterium marinum MelF (Rv1936) by in silico analysis, which exhibited bacteriostatic/bactericidal activity against M. marinum and M. tuberculosis in vitro. Herein, we evaluated the effect of best four inhibitors (# 5175552, # 6513745, # 5255829, # 9125618) obtained from the ChemBridge compound libraries, on intracellular replication and persistence of bacteria within IFN-γ activated murine RAW264.7 and human THP-1 macrophages infected with M. marinum. Inhibitors # 5175552 and # 6513745 significantly reduced (p < 0.05) the intracellular replication of bacilli during day 7 post-infection (p.i.) within RAW264.7 and THP-1 macrophages infected at multiplicity of infection (MOI) of ~1.0. These observations were substantiated by electron microscopy, which revealed the protective effect of # 5175552 in clearing the bacilli inside murine macrophages. Strikingly, # 6513745 displayed synergism with isoniazid against M. marinum in murine macrophages, whereas # 5175552 significantly suppressed (p < 0.05) the persistent bacilli during day 10–14 p.i. in infected RAW264.7 and THP-1 macrophages (MOI of ~ 0.1). Moreover, # 5175552 and # 6513745 were non-cytotoxic to host macrophages at both 1X and 5X MIC. Further validation of these inhibitors against M. tuberculosis-infected macrophages and animal models has potential for development as novel anti-tubercular agents.

Beyond the antibody: B cells as a target for bacterial infection

It is well established that B cells play an important role during infections beyond antibody production. B cells produce cytokines and are APCs for T cells. Recently, it has become clear that several pathogenic bacterial genera, such as Salmonella, Brucella, Mycobacterium, Listeria, Francisella, Moraxella, and Helicobacter, have evolved mechanisms such as micropinocytosis induction, inflammasome down-regulation, inhibitory molecule expression, apoptosis induction, and anti-inflammatory cytokine secretion to manipulate B cell functions influencing immune responses. In this review, we summarize our current understanding of B cells as targets of bacterial infection and the mechanisms by which B cells become a niche for bacterial survival and replication away from extracellular immune responses such as complement and antibodies.

Mycobacteria employ two different mechanisms to cross the blood-brain barrier

Central nervous system (CNS) infection by Mycobacterium tuberculosis is one of the most devastating complications of tuberculosis, in particular in early childhood. In order to induce CNS infection, M. tuberculosis needs to cross specialised barriers protecting the brain. How M. tuberculosis crosses the blood-brain barrier (BBB) and enters the CNS is not well understood. Here, we use transparent zebrafish larvae and the closely related pathogen Mycobacterium marinum to answer this question. We show that in the early stages of development, mycobacteria rapidly infect brain tissue, either as free mycobacteria or within circulating macrophages. After the formation of a functionally intact BBB, the infiltration of brain tissue by infected macrophages is delayed, but not blocked, suggesting that crossing the BBB via phagocytic cells is one of the mechanisms used by mycobacteria to invade the CNS. Interestingly, depletion of phagocytic cells did not prevent M. marinum from infecting the brain tissue, indicating that free mycobacteria can independently cause brain infection. Detailed analysis showed that mycobacteria are able to cause vasculitis by extracellular outgrowth in the smaller blood vessels and by infecting endothelial cells. Importantly, we could show that this second mechanism is an active process that depends on an intact ESX-1 secretion system, which extends the role of ESX-1 secretion beyond the macrophage infection cycle.

Endothelial lineage-specific interaction of Mycobacterium tuberculosis with the blood and lymphatic systems

Mycobacterium tuberculosis (Mtb) has plagued humanity for tens of thousands of years, yet still remains a threat to human health. Its pathology is largely associated with pulmonary tuberculosis with symptoms including fever, hemoptysis, and chest pain. Mtb, however, also manifests in other extrapulmonary organs, such as the pleura, bones, gastrointestinal tract, central nervous system, and lymph nodes. Compared to the knowledge of pulmonary tuberculosis, extrapulmonary pathologies of Mtb are quite understudied. Lymph node tuberculosis is one of the most common extrapulmonary manifestations of tuberculosis, and presents significant challenges in its diagnosis, management, and treatment due to its elusive etiologies and pathologies. The objective of this review is to overview the current understanding of the tropism and pathogenesis of Mtb in endothelial cells of the extrapulmonary tissues, particularly, in lymph nodes. Lymphatic endothelial cells (LECs) are derived from blood vascular endothelial cells (BECs) during development, and these two types of endothelial cells demonstrate substantial molecular, cellular and genetic similarities. Therefore, systemic comparison of the differential and common responses of BECs vs. LECs to Mtb invasion could provide new insights into its pathogenesis, and may promote new investigations into this deadly disease.

Lack of intracellular replication of M. tuberculosis and M. bovis BCG caused by delivering bacilli to lysosomes in murine brain microvascular endothelial cells

Invasion and traversal of the blood-brain barrier (BBB) by Mycobacterium tuberculosis cause meningeal tuberculosis (TB) in the central nervous system (CNS). Meningeal TB is a serious, often fatal disease that disproportionately affects young children. The mechanisms involved in CNS invasion by M. tuberculosis bacilli are poorly understood. In this study, we microscopically examined endosomal trafficking and measured survival of M. tuberculosis and M. bovis Bacille Calmette-Guérin (BCG) bacilli in murine brain microvascular endothelial cells (BMECs). The results show that both species internalize but do not replicate in BMECs in the absence of a cytotoxic response. Confocal microscopy indicates that bacilli-containing vacuoles are associated with the early endosomal marker, Rab5, late endosomal marker, Rab7, and lysosomal marker, LAMP2, suggesting that bacilli-containing endosomes mature into endolysosomes in BMECs. Our data also show that a subset of intracellular M. tuberculosis, but not BCG bacilli, escape into the cytoplasm to avoid rapid lysosomal killing. However, the intracellular mycobacteria examined cannot spread cell-to-cell in BMECs. Taken together, these data show that with the exception of the small terminal cytoplasmic population of bacilli, M. tuberculosis does not modulate intracellular trafficking in BMECs as occurs in macrophages and lung epithelial and endothelial cells.

Mycobacteria entry and trafficking into endothelial cells

Endothelial cells are susceptible to infection by mycobacteria, but the endocytic mechanisms that mycobacteria exploit to enter host cells and their mechanisms of intracellular transport are completely unknown. Using pharmacological inhibitors, we determined that the internalization of Mycobacterium tuberculosis (MTB), Mycobacterium smegmatis (MSM), and Mycobacterium abscessus (MAB) is dependent on the cytoskeleton and is differentially inhibited by cytochalasin D, nocodazole, cycloheximide, wortmannin, and amiloride. Using confocal microscopy, we investigated their endosomal trafficking by analyzing Rab5, Rab7, LAMP-1, and cathepsin D. Our results suggest that MSM exploits macropinocytosis to enter endothelial cells and that the vacuoles containing these bacteria fuse with lysosomes. Conversely, the entry of MTB seems to depend on more than one endocytic route, and the observation that only a subset of the intracellular bacilli was associated with phagolysosomes suggests that these bacteria are able to inhibit endosomal maturation to persist intracellularly. The route of entry for MAB depends mainly on microtubules, which suggests that MAB uses a different trafficking pathway. However, MAB is also able to inhibit endosomal maturation and can replicate intracellularly. Together, these findings provide the first evidence that mycobacteria modulate proteins of host endothelial cells to enter and persist within these cells.

Mycobacterium tuberculosis infection and tissue factor expression in macrophages

A number of earlier studies reported the occurrence of thrombotic complications, particularly disseminated intravascular coagulation and deep vein thrombosis, in tuberculosis (TB) patients. The aberrant expression of tissue factor (TF), the primary activator of coagulation cascade, is known to be responsible for thrombotic disorders in many diseases including bacterial infections. Further, expression of TF by cells of the monocyte/macrophage lineage is also shown to contribute to the development and progression of local and systemic inflammatory reactions. In the present study, we have investigated whether Mycobacterium tuberculosis (Mtb) infection induces TF expression in macrophages, and various host and pathogenic factors responsible for TF expression. We have tested the effect of live virulent Mtb H37Rv, gamma-irradiated Mtb H37Rv (γ-Mtb) and various components derived from Mtb H37Rv on TF expression in macrophages. The data presented in the manuscript show that both live virulent Mtb and γ-Mtb treatments markedly increased TF activity in macrophages, predominantly in the CD14⁺ macrophages. Detailed studies using γ-Mtb showed that the increased TF activity in macrophages following Mtb treatment is the result of TF transcriptional activation. The signaling pathways of TF induction by Mtb appears to be distinct from that of LPS-induced TF expression. Mtb-mediated TF expression is dependent on cooperation of CD14/TLR2/TLR4 and probably yet another unknown receptor/cofactor. Mtb cell wall core components, mycolyl arabinogalactan peptidoglycan (mAGP), phosphatidylinositol mannoside-6 (PIM6) and lipomannan (LM) were identified as factors responsible for induction of TF in the order of mAGP>PIM6>LM. A direct contact between bacteria and macrophage and not Mtb-released soluble factors is critical for TF induction by Mtb. In summary, our data show that Mtb induces TF expression in macrophages and Mtb signaling pathways that elicit TF induction require cooperation of multiple receptors, co-receptors/co-factors including Toll-like receptors. The importance of TF in granuloma formation and containment of Mtb is discussed.

Divergent responses of different endothelial cell types to infection with Candida albicans and Staphylococcus aureus

Endothelial cells are important in the pathogenesis of bloodstream infections caused by Candida albicans and Staphylococcus aureus. Numerous investigations have used human umbilical vein endothelial cells (HUVECs) to study microbial-endothelial cell interactions in vitro. However, the use of HUVECs requires a constant supply of umbilical cords, and there are significant donor-to-donor variations in these endothelial cells. The use of an immortalized endothelial cell line would obviate such difficulties. One candidate in this regard is HMEC-1, an immortalized human dermal microvascular endothelial cell line. To determine if HMEC-1 cells are suitable for studying the interactions of C. albicans and S. aureus with endothelial cells in vitro, we compared the interactions of these organisms with HMEC-1 cells and HUVECs. We found that wild-type C. albicans had significantly reduced adherence to and invasion of HMEC-1 cells as compared to HUVECs. Although wild-type S. aureus adhered to and invaded HMEC-1 cells similarly to HUVECs, an agr mutant strain had significantly reduced invasion of HMEC-1 cells, but not HUVECs. Furthermore, HMEC-1 cells were less susceptible to damage induced by C. albicans, but more susceptible to damage caused by S. aureus. In addition, HMEC-1 cells secreted very little IL-8 in response to infection with either organism, whereas infection of HUVECs induced substantial IL-8 secretion. This weak IL-8 response was likely due to the anatomic site from which HMEC-1 cells were obtained because infection of primary human dermal microvascular endothelial cells with C. albicans and S. aureus also induced little increase in IL-8 production above basal levels. Thus, C. albicans and S. aureus interact with HMEC-1 cells in a substantially different manner than with HUVECs, and data obtained with one type of endothelial cell cannot necessarily be extrapolated to other types.

Mycobacterium tuberculosis-induced neutrophil ectosomes decrease macrophage activation

BACKGROUND

The existence of ectosome-like microvesicles released by neutrophils was proposed a few decades ago. Other studies revealed that the innate immune response during mycobacterial infection is accompanied by an intense migration of neutrophils to the site of infection, which may be important during the acute phase of tuberculosis. We found that the ectosomes derived from infected neutrophils are biologically active and can influence the survival of Mycobacterium tuberculosis within macrophages.

METHODS

Mycobacteria were cultured on supplemented Middlebrook-7H9 broth. All strains were grown to the exponential phase and quantitated by serial dilution. Human neutrophils and macrophages were infected with mycobacteria. Ectosomes from neutrophils were isolated post-infection and characterized by transmission electron microscopy and flow cytometry. To determine whether these microvesicles influenced mycobactericidal activity, mycobacteria-infected macrophages were treated with isolated ectosomes.

RESULTS

Ectosomes were released from neutrophils infected with mycobacteria. These ectosomes were derived from neutrophil plasma membrane and a small proportion stained with PKH26. These microvesicles, when incubated with infected macrophages, influenced antimycobacterial activity.

CONCLUSIONS

This is the first study to demonstrate that ectosomes that are shed from infected neutrophils influence mycobactericidal activity in macrophages in vitro, suggesting that these microvesicles have biological significance. Nevertheless, major gaps in our knowledge of microvesicle biology remain.

The pathology of Mycobacterium tuberculosis infection

Mycobacterium tuberculosis is an old enemy of the human race, with evidence of infection observed as early as 5000 years ago. Although more host-restricted than Mycobacterium bovis, which can infect all warm-blooded vertebrates, M. tuberculosis can infect, and cause morbidity and mortality in, several veterinary species as well. As M. tuberculosis is one of the earliest described bacterial pathogens, the literature describing this organism is vast and overwhelming. This review strives to distill what is currently known about this bacterium and the disease it causes for the veterinary pathologist.

Human pulmonary microvascular endothelial cells support productive replication of highly pathogenic avian influenza viruses: possible involvement in the pathogenesis of human H5N1 virus infection

Highly pathogenic avian influenza (HPAI) H5N1 viruses continue to cause sporadic human infections with a high fatality rate. Respiratory failure due to acute respiratory distress syndrome (ARDS) is a complication among hospitalized patients. Since progressive pulmonary endothelial damage is the hallmark of ARDS, we investigated host responses following HPAI virus infection of human pulmonary microvascular endothelial cells. Evaluation of these cells for the presence of receptors preferred by influenza virus demonstrated that avian-like (α2-3-linked) receptors were more abundant than human-like (α2-6-linked) receptors. To test the permissiveness of pulmonary endothelial cells to virus infection, we compared the replication of selected seasonal, pandemic (2009 H1N1 and 1918), and potentially pandemic (H5N1) influenza virus strains. We observed that these cells support productive replication only of HPAI H5N1 viruses, which preferentially enter through and are released from the apical surface of polarized human endothelial monolayers. Furthermore, A/Thailand/16/2004 and A/Vietnam/1203/2004 (VN/1203) H5N1 viruses, which exhibit heightened virulence in mammalian models, replicated to higher titers than less virulent H5N1 strains. VN/1203 infection caused a significant decrease in endothelial cell proliferation compared to other subtype viruses. VN/1203 virus was also found to be a potent inducer of cytokines and adhesion molecules known to regulate inflammation during acute lung injury. Deletion of the H5 hemagglutinin (HA) multibasic cleavage site did not affect virus infectivity but resulted in decreased virus replication in endothelial cells. Our results highlight remarkable tropism and infectivity of the H5N1 viruses for human pulmonary endothelial cells, resulting in the potent induction of host inflammatory responses.

Proinflammatory response of human endothelial cells to Brucella infection

Although vascular pathologies such as vasculitis, endocarditis and mycotic aneurysms have been described in brucellosis patients, the interaction of Brucella with the endothelium has not been characterized. In this study we show that Brucella abortus and Brucella suis can infect and replicate in primary human umbilical vein endothelial cells (HUVEC) and in the microvascular endothelial cell line HMEC-1. Infection led to an increased production of IL-8, MCP-1 and IL-6 in HUVEC and HMEC-1 cells, and an increased expression of adhesion molecules (CD54 in both cells, CD106 and CD62E in HUVEC). Experiments with purified antigens from the bacterial outer membrane revealed that lipoproteins (Omp19) but not lipopolysaccharide mediate these proinflammatory responses. Infection of polarized HMEC-1 cells resulted in an increased capacity of these cells to promote the transmigration of neutrophils from the apical to the basolateral side of the monolayer, and the same phenomenon was observed when the cells were stimulated with live bacteria from the basolateral side. Overall, these results suggest that Brucella spp. can infect and survive within endothelial cells, and can induce a proinflammatory response that might be involved in the vascular manifestations of brucellosis.

Innate response of human endothelial cells infected with mycobacteria

Endothelial cells are susceptible to infection by several pathogens, but little is known about mycobacterial infection. We analyzed some features of mycobacteria-endothelial cell interactions and the innate response to the infection. Intracellular growth in human umbilical vein endothelial cells (HUVECs) of three Mycobacterium species: M. tuberculosis (MTB), M. abscessus (MAB) and M. smegmatis (MSM) was analyzed. M. smegmatis was eliminated; M. abscessus had an accelerate intracellular replication and M. tuberculosis did not replicate or was eliminated. M. abscessus infection induced profound cytoskeleton rearrangements, with M. tuberculosis infection changes were less marked, and with MSM were slight. Nitric oxide (NO) production was induced differentially: M. abscessus induced the highest levels followed by M. tuberculosis and M. smegmatis; the contrary was true for reactive oxygen species (ROS) production. Only M. tuberculosis infection caused beta-1 defensin over-expression. As a whole, our results describe some aspects of the innate response of HUVEC infected by mycobacteria with different virulence and suggest that a strong cytoskeleton mobilization triggers a high NO production in these cells.

Pathogenesis, immunology, and diagnosis of latent Mycobacterium tuberculosis infection

Phagocytosis of tubercle bacilli by antigen-presenting cells in human lung alveoli initiates a complex infection process by Mycobacterium tuberculosis and a potentially protective immune response by the host. M. tuberculosis has devoted a large part of its genome towards functions that allow it to successfully establish latent or progressive infection in the majority of infected individuals. The failure of immune-mediated clearance is due to multiple strategies adopted by M. tuberculosis that blunt the microbicidal mechanisms of infected immune cells and formation of distinct granulomatous lesions that differ in their ability to support or suppress the persistence of viable M. tuberculosis. In this paper, current understanding of various immune processes that lead to the establishment of latent M. tuberculosis infection, bacterial spreading, persistence, reactivation, and waning or elimination of latent infection as well as new diagnostic approaches being used for identification of latently infected individuals for possible control of tuberculosis epidemic are described.

Interferon-gamma-responsive nonhematopoietic cells regulate the immune response to Mycobacterium tuberculosis

Immunity to Mycobacterium tuberculosis in humans and in mice requires interferon gamma (IFN-gamma). Whereas IFN-gamma has been studied extensively for its effects on macrophages in tuberculosis, we determined that protective immunity to tuberculosis also requires IFN-gamma-responsive nonhematopoietic cells. Bone marrow chimeric mice with IFN-gamma-unresponsive lung epithelial and endothelial cells exhibited earlier mortality and higher bacterial burdens than control mice, underexpressed indoleamine-2,3-dioxygenase (Ido1) in lung endothelium and epithelium, and overexpressed interleukin-17 (IL-17) with massive neutrophilic inflammation in the lungs. We also found that the products of IDO catabolism of tryptophan selectively inhibit IL-17 production by Th17 cells, by inhibiting the action of IL-23. These results reveal a previously unsuspected role for IFN-gamma responsiveness in nonhematopoietic cells in regulation of immunity to M. tuberculosis and illustrate the role of IDO in the inhibition of Th17 cell responses.

Potential role for ESAT6 in dissemination of M. tuberculosis via human lung epithelial cells

ESAT6 has recently been demonstrated to cause haemolysis and macrophage lysis. Our studies demonstrate that ESAT6 causes cytolysis of type 1 and type 2 pneumocytes. Both types of pneumocytes express membrane laminin, and ESAT6 exhibits dose-dependent binding to both cell types and to purified human laminin. While minimal ESAT6 was detected on the surface of Mycobacterium tuberculosis grown in vitro, exogenously provided ESAT6 specifically associated with the bacterial cell surface, and the bacterium-associated ESAT6 retained its cytolytic ability. esat6 transcripts were upregulated approximately 4- to approximately 13-fold in bacteria replicating in type 1 cells, and approximately 3- to approximately 5 fold in type 2 cells. In vivo, laminin is primarily concentrated at the basolateral surface of pneumocytes where they rest on the basement membrane, which is composed primarily of laminin and collagen. The upregulation of esat6 transcripts in bacteria replicating in pneumocytes, the specific association of ESAT6 with the bacterial surface, the binding of ESAT6 to laminin and the lysis of pneumocytes by free and bacterium-associated ESAT6 together suggest a scenario wherein Mycobacterium tuberculosis replicating in pneumocytes may utilize surface ESAT6 to anchor onto the basolateral laminin-expressing surface of the pneumocytes, and damage the cells and the basement membrane to directly disseminate through the alveolar wall.

Where are all the Mycobacterium avium subspecies paratuberculosis in patients with Crohn's disease?

Mycobacterium avium subspecies paratuberculosis (MAP) causes a chronic granulomatous inflammation of the intestines, Johne's disease, in dairy cows and every other species of mammal in which it has been identified. MAP has been identified in the mucosal layer and deeper bowel wall in patients with Crohn's disease by methods other than light microscopy, and by direct visualization in small numbers by light microscopy. MAP has not been accepted as the cause of Crohn's disease in part because it has not been seen under the microscope in large numbers in the intestines of patients with Crohn's disease. An analysis of the literature on the pathology of Crohn's disease and on possible MAP infection in Crohn's patients suggests that MAP might directly infect endothelial cells and adipocytes and cause them to proliferate, causing focal obstruction within already existing vessels (including granuloma formation), the development of new vessels (neoangiogenesis and lymphangiogenesis), and the "creeping fat" of the mesentery that is unique in human pathology to Crohn's disease but also occurs in bovine Johne's disease. Large numbers of MAP might therefore be found in the mesentery attached to segments of intestine affected by Crohn's disease rather than in the bowel wall, the blood and lymphatic vessels running through the mesentery, or the mesenteric fat itself. The walls of fistulas might result from the neoangiogenesis or lymphangiogenesis that occurs in the bowel wall in Crohn's disease and therefore are also possible sites of large numbers of MAP. The direct visualization of large numbers of MAP organisms in the tissues of patients with Crohn's disease will help establish that MAP causes Crohn's disease.

Mycobacterium tuberculosis-specific CD8+ T cells require perforin to kill target cells and provide protection in vivo

Optimal immunity to Mycobacterium tuberculosis (Mtb) infection requires CD8(+) T cells, and several current Mtb vaccine candidates are being engineered to elicit enhanced CD8(+) T cell responses. However, the function of these T cells and the mechanism by which they provide protection is still unknown. We have previously shown that CD8(+) T cells specific for the mycobacterial Ags CFP10 and TB10.4 accumulate in the lungs of mice following Mtb infection and have cytolytic activity in vivo. In this study, we determine which cytolytic pathways are used by these CD8(+) T cells during Mtb infection. We find that Mtb-specific CD8(+) T cells lacking perforin have reduced cytolytic capacity in vivo. In the absence of perforin, the residual cytolytic activity is CD95 and TNFR dependent. This is particularly true in Mtb-infected lung tissue where disruption of both perforin and CD95 eliminates target cell lysis. Moreover, adoptive transfer of immune CD8(+) T cells isolated from wild-type, but not perforin-deficient mice, protect recipient mice from Mtb infection. We conclude that CD8(+) T cells elicited following Mtb infection use several cytolytic pathways in a hierarchical and compensatory manner dominated by perforin-mediated cytolysis. Finally, although several cytolytic pathways are available, adoptively transferred Mtb-specific CD8(+) T cells require perforin-mediated cytolysis to protect animals from infection. These data show that CD8(+) T cell-mediated protection during Mtb infection requires more than the secretion of IFN-gamma and specifically defines the CD8(+) cytolytic mechanisms utilized and required in vivo.

Crack cocaine and infectious tuberculosis

We hypothesize that crack cocaine is independently associated with smear-positive tuberculosis (TB). In a case–control study of TB in London, 19 (86%) of 22 crack cocaine users with pulmonary TB were smear positive compared with 302 (36%) of 833 non–drug users. Respiratory damage caused by crack cocaine may predispose drug users to infectivity.

Characterization of Mce4A protein of Mycobacterium tuberculosis: role in invasion and survival

Background

The mce4 operon is one of the four homologues of mammalian cell entry (mce) operons of Mycobacterium tuberculosis. The mce4A (Rv3499c) gene within this operon is homologous to mce1A (Rv0169), that has a role in host cell invasion by M. tuberculosis. Our earlier reports show that mce4 operon is expressed during the stationary phase of growth of the bacillus in culture and during the course of infection in mammalian hosts. M. tuberculosis carrying mutation in mce4 operon shows growth defect and reduced survival in infected mice. However, the intracellular localization of Mce4A protein and its direct role in cell entry or survival of the bacillus has not been demonstrated so far.

Results

By transmission electron microscopy we have demonstrated that recombinant Mce4A protein facilitates the invasion of non-pathogenic strain of E. coli into non-phagocytic HeLa cells. We observe that mce4A gene has a role comparable to mce1A in the survival of recombinant E. coli in human macrophages. Using antibodies raised against Mce4A protein, we show that the protein is localized in the cell wall fraction of M. tuberculosis H37Rv stationary phase culture only.

Conclusion

Mce4A protein is expressed during the stationary phase of broth culture and localizes in the cell wall fraction of M. tuberculosis. Mce4A protein expressed in non-pathogenic E. coli enables it to enter and survive within HeLa cells and the macrophages. As Mce4A protein is expressed during later phase of mycobacterial growth, our results raise the possibility of it playing a role in maintenance of persistent tubercular infection.

Internalization by HeLa cells of latex beads coated with mammalian cell entry (Mce) proteins encoded by the mce3 operon of Mycobacterium tuberculosis

The mammalian cell entry (Mce) operon 3 (mce3) is one of four homologous mce operons of Mycobacterium tuberculosis, encoding six (Mce3A-F) invasin-like membrane-associated proteins. Previous studies have shown that recombinant expression of Mce1A encoded by the mce1 operon in Escherichia coli allows this non-pathogenic bacterium to invade and survive inside macrophages, and latex beads coated with Mce1A are internalized by non-phagocytic HeLa cells. However, the role of other mce1 operon proteins (Mce1B-F) and proteins encoded by the operons mce2-4 in facilitating the internalization of M. tuberculosis in mammalian cells has not been studied. This study was carried out to determine whether Mce proteins encoded by the mce3 operon also facilitated the internalization of latex beads by HeLa cells. Recombinant pure Mce3A and lipoprotein LprM (Mce3E) were expressed and purified from E. coli cells. Mce1A expressed as a fusion protein with glutathione S-transferase (GST-Mce1A) and GST alone, purified similarly from E. coli cells, were used as control proteins. Fluorescent latex beads coated with purified proteins were used to study their uptake by HeLa cells using fluorescence microscopy, flow cytometry and electron microscopy. Fluorescence microscopy and flow cytometry showed an association of HeLa cells with beads coated with both Mce3A and LprM, whilst GST-Mce1A and GST yielded the expected results. Transmission electron microscopy confirmed the uptake of beads coated with Mce3A or LprM by HeLa cells. The data showed that Mce3A encoded by the mce3 operon facilitated the uptake and internalization of latex beads by HeLa cells. The data also showed, for the first time, the role of another Mce protein (LprM/Mce3E) in facilitating the interaction and internalization of M. tuberculosis by mammalian cells.

Cholesterol oxidase is required for virulence ofMycobacterium tuberculosis

Recent reports have indicated that cholesterol plays a crucial role during the uptake of mycobacteria by macrophages. However, the significance of cholesterol modification enzymes encoded by Mycobacterium tuberculosis for bacterial pathogenicity remains unknown. Here, the authors explored whether the well-known cholesterol modification enzyme, cholesterol oxidase (ChoD), is important for virulence of the tubercle bacillus. Homologous recombination was used to replace the choD gene from the M. tuberculosis genome with a nonfunctional copy. The resultant mutant (delta choD) was attenuated in peritoneal macrophages. No attenuation in macrophages was observed when the same strain was complemented with an intact choD gene controlled by a heat shock promoter (delta choDP(hsp)choD). The mice infection experiments confirm the significance of ChoD in the pathogenesis of M. tuberculosis.

The thymus as a target for mycobacterial infections

Mycobacterial infections are among the major health threats worldwide. Ability to fight these infections depends on the host's immune response, particularly on macrophages and T lymphocytes produced by the thymus. Using the mouse as a model, and two different routes of infection (aerogenic or intravenous), we show that the thymus is consistently colonized by Mycobacterium tuberculosis, Mycobacterium avium or Mycobacterium bovis BCG. When compared to organs such as the liver and spleen, the bacterial load reaches a plateau at later time-points after infection. Moreover, in contrast with organs such as the spleen and the lung no granuloma were found in the thymus of mice infected with M. tuberculosis or M. avium. Since T cell differentiation depends, to a large extent, on the antigens encountered within the thymus, infection of this organ might alter the host's immune response to infection. Therefore, from now on, the thymus should be considered in studies addressing the immune response to mycobacterial infection.