Influence of trehalose 6,6'-dimycolate (TDM) during mycobacterial infection of bone marrow macrophages

Generation of Liposomes to Study the Effect of Mycobacterium Tuberculosis Lipids on HIV-1 cis- and trans-Infections

Tuberculosis (TB) is the leading cause of death among HIV-1-infected individuals and Mycobacterium tuberculosis (Mtb) co-infection is an early precipitate to AIDS. We aimed to determine whether Mtb strains differentially modulate cellular susceptibility to HIV-1 infection (cis- and trans-infection), via surface receptor interaction by their cell envelope lipids. Total lipids from pathogenic (lineage 4 Mtb H37Rv, CDC1551 and lineage 2 Mtb HN878, EU127) and non-pathogenic (Mycobacterium bovis BCG and Mycobacterium smegmatis) Mycobacterium strains were integrated into liposomes mimicking the lipid distribution and antigen accessibility of the mycobacterial cell wall. The resulting liposomes were tested for modulating in vitro HIV-1 cis- and trans-infection of TZM-bl cells using single-cycle infectious virus particles. Mtb glycolipids did not affect HIV-1 direct infection however, trans-infection of both R5 and X4 tropic HIV-1 strains were impaired in the presence of glycolipids from M. bovis, Mtb H37Rv and Mtb EU127 strains when using Raji-DC-SIGN cells or immature and mature dendritic cells (DCs) to capture virus. SL1, PDIM and TDM lipids were identified to be involved in DC-SIGN recognition and impairment of HIV-1 trans-infection. These findings indicate that variant strains of Mtb have differential effect on HIV-1 trans-infection with the potential to influence HIV-1 disease course in co-infected individuals.

Understanding Host Immunity and the Gut Microbiota Inspires the New Development of Vaccines and Adjuvants

Vaccinations improve the mortality and morbidity rates associated with several infections through the generation of antigen-specific immune responses. Adjuvants are often used together with vaccines to improve immunogenicity. However, the immune responses induced by most on-going vaccines and adjuvants approved for human use vary in individuals; this is a limitation that must be overcome to improve vaccine efficacy. Several reports have indicated that the symbiotic bacteria, particularly the gut microbiota, impact vaccine-mediated antigen-specific immune responses and promote the induction of nonspecific responses via the "training" of innate immune cells. Therefore, the interaction between gut microbiota and innate immune cells should be considered to ensure the optimal immunogenicity of vaccines and adjuvants. In this review, we first introduce the current knowledge on the immunological mechanisms of vaccines and adjuvants. Subsequently, we discuss how the gut microbiota influences immunity and highlight the relationship between gut microbes and trained innate immunity, vaccines, and adjuvants. Understanding these complex interactions will provide insights into novel vaccine approaches centered on the gut microbiota.

The thick waxy coat of mycobacteria, a protective layer against antibiotics and the host's immune system

Tuberculosis, caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb), is the leading cause of death from an infectious disease, with a mortality rate of over a million people per year. This pathogen's remarkable resilience and infectivity is largely due to its unique waxy cell envelope, 40% of which comprises complex lipids. Therefore, an understanding of the structure and function of the cell wall lipids is of huge indirect clinical significance. This review provides a synopsis of the cell envelope and the major lipids contained within, including structure, biosynthesis and roles in pathogenesis.

Variations in Antimicrobial Activities of Human Monocyte-Derived Macrophage and Their Associations With Tuberculosis Clinical Manifestations

Macrophages play a significant role in preventing infection through antimicrobial activities, particularly acidification, and proteolysis. Mycobacterium tuberculosis (Mtb) infection can lead to diverse outcomes, from latent asymptomatic infection to active disease involving multiple organs. Monocyte-derived macrophage is one of the main cell types accumulating in lungs following Mtb infection. The variation of intracellular activities of monocyte-derived macrophages in humans and the influence of these activities on the tuberculosis (TB) spectrum are not well understood. By exploiting ligand-specific bead-based assays, we investigated macrophage antimicrobial activities real-time in healthy volunteers (n = 53) with 35 cases of latent TB (LTB), and those with active TB (ATB), and either pulmonary TB (PTB, n = 70) or TB meningitis (TBM, n = 77). We found wide person-to-person variations in acidification and proteolytic activities in response to both non-immunogenic IgG and pathogenic ligands comprising trehalose 6,6'−dimycolate (TDM) from Mtb or β-glucan from Saccharamyces cerevisiase. The variation in the macrophage activities remained similar regardless of stimuli; however, IgG induced stronger acidification activity than immunogenic ligands TDM (P = 10⁻⁵, 3 × 10⁻⁵ and 0.01 at 30, 60, and 90 min) and β-glucan (P = 10⁻⁴, 3 × 10⁻⁴ and 0.04 at 30, 60, and 90 min). Variation in proteolysis activity was slightly higher in LTB than in ATB (CV = 40% in LTB vs. 29% in ATB, P = 0.03). There was no difference in measured antimicrobial activities in response to TDM and bacterial killing in macrophages from LTB and ATB, or from PTB and TBM. Our results indicate that antimicrobial activities of monocyte-derived macrophages vary among individuals and show immunological dependence, but suggest these activities cannot be solely responsible for the control of bacterial replication or dissemination in TB.

The Pathogenesis of Tuberculosis-The Koch Phenomenon Reinstated

Research on the pathogenesis of tuberculosis (TB) has been hamstrung for half a century by the paradigm that granulomas are the hallmark of active disease. Human TB, in fact, produces two types of granulomas, neither of which is involved in the development of adult type or post-primary TB. This disease begins as the early lesion; a prolonged subclinical stockpiling of secreted mycobacterial antigens in foamy alveolar macrophages and nearby highly sensitized T cells in preparation for a massive necrotizing hypersensitivity reaction, the Koch Phenomenon, that produces caseous pneumonia that is either coughed out to form cavities or retained to become the focus of post-primary granulomas and fibrocaseous disease. Post-primary TB progresses if the antigens are continuously released and regresses when they are depleted. This revised paradigm is supported by nearly 200 years of research and suggests new approaches and animal models to investigate long standing mysteries of human TB and vaccines that inhibit the early lesion to finally end its transmission.

Mycobacterium tuberculosis cords within lymphatic endothelial cells to evade host immunity

The ability of Mycobacterium tuberculosis to form serpentine cords is intrinsically related to its virulence, but specifically how M. tuberculosis cording contributes to pathogenesis remains obscure. Here, we show that several M. tuberculosis clinical isolates form intracellular cords in primary human lymphatic endothelial cells (hLECs) in vitro and in the lymph nodes of patients with tuberculosis. We identified via RNA-Seq a transcriptional program that activated, in infected-hLECs, cell survival and cytosolic surveillance of pathogens pathways. Consistent with this, cytosolic access was required for intracellular M. tuberculosis cording. Mycobacteria lacking ESX-1 type VII secretion system or phthiocerol dimycocerosates expression, which failed to access the cytosol, were indeed unable to form cords within hLECs. Finally, we show that M. tuberculosis cording is a size-dependent mechanism used by the pathogen to avoid its recognition by cytosolic sensors and evade either resting or IFN-γ-induced hLEC immunity. These results explain the long-standing association between M. tuberculosis cording and virulence and how virulent mycobacteria use intracellular cording as strategy to successfully adapt and persist in the lymphatic tracts.

Each Mycobacterium Requires a Specific Culture Medium Composition for Triggering an Optimized Immunomodulatory and Antitumoral Effect

Mycobacterium bovis bacillus Calmette-Guérin (BCG) remains the first treatment option for non-muscle-invasive bladder cancer (BC) patients. In research laboratories, M. bovis BCG is mainly grown in commercially available media supplemented with animal-derived agents that favor its growth, while biomass production for patient treatment is performed in Sauton medium which lacks animal-derived components. However, there is not a standardized formulation of Sauton medium, which could affect mycobacterial characteristics. Here, the impact of culture composition on the immunomodulatory and antitumor capacity of M. bovis BCG and Mycolicibacterium brumae, recently described as efficacious for BC treatment, has been addressed. Both mycobacteria grown in Middlebrook and different Sauton formulations, differing in the source of nitrogen and amount of carbon source, were studied. Our results indicate the relevance of culture medium composition on the antitumor effect triggered by mycobacteria, indicating that the most productive culture medium is not necessarily the formulation that provides the most favorable immunomodulatory profile and the highest capacity to inhibit BC cell growth. Strikingly, each mycobacterial species requires a specific culture medium composition to provide the best profile as an immunotherapeutic agent for BC treatment. Our results highlight the relevance of meticulousness in mycobacteria production, providing insight into the application of these bacteria in BC research.

Impact of Aging and HIV Infection on the Function of the C-Type Lectin Receptor MINCLE in Monocytes

Both aging and HIV infection are associated with an enhanced pro-inflammatory environment that contributes to impaired immune responses and is mediated in part by innate immune pattern-recognition receptors. MINCLE is a C-type lectin receptor that recognizes trehalose-6,6'-dimycolate or "cord factor," the most abundant glycolipid in Mycobacterium tuberculosis. Here, we evaluated MINCLE function in monocytes in a cohort of HIV-infected and uninfected young (21-35 years) and older adults (≥60 years) via stimulation of peripheral blood mononuclear cells with trehalose-6,6-dibehenate, a synthetic analog of trehalose-6,6'-dimycolate and measurement of cytokine production (interleukin [IL]-10, IL-12, IL-6, tumor necrosis factor-α) by multicolor flow cytometry. Our studies show an age- and HIV-associated increase in cytokine multifunctionality of monocytes both at the population and single cell level that was dominated by IL-12, IL-10, and IL-6. These findings provide insight into the host response to M. tuberculosis and possible sources for the pro-inflammatory environment seen in aging and HIV infection.

Underestimated Manipulative Roles of Mycobacterium tuberculosis Cell Envelope Glycolipids During Infection

The Mycobacterium tuberculosis cell envelope has been evolving over time to make the bacterium transmissible and adaptable to the human host. In this context, the M. tuberculosis cell envelope contains a peripheral barrier full of lipids, some of them unique, which confer M. tuberculosis with a unique shield against the different host environments that the bacterium will encounter at the different stages of infection. This lipid barrier is mainly composed of glycolipids that can be characterized by three different subsets: trehalose-containing, mannose-containing, and 6-deoxy-pyranose-containing glycolipids. In this review, we explore the roles of these cell envelope glycolipids in M. tuberculosis virulence and pathogenesis, drug resistance, and further, how these glycolipids may dictate the M. tuberculosis cell envelope evolution from ancient to modern strains. Finally, we address how these M. tuberculosis cell envelope glycolipids are impacted by the host lung alveolar environment, their role in vaccination and masking host immunity, and subsequently the impact of these glycolipids in shaping how M. tuberculosis interacts with host cells, manipulating their immune response to favor the establishment of an infection.

Mycobacterial Trehalose 6,6'-Dimycolate-Induced M1-Type Inflammation

Murine models of Mycobacterium tuberculosis (Mtb) infection demonstrate progression of M1-like (proinflammatory) and M2-like (anti-inflammatory) macrophage morphology following primary granuloma formation. The Mtb cell wall cording factor, trehalose 6,6'-dimycolate (TDM), is a physiologically relevant and useful molecule for modeling early macrophage-mediated events during establishment of the tuberculosis-induced granuloma pathogenesis. Here, it is shown that TDM is a major driver of the early M1-like macrophage response as seen during initiation of the granulomas of primary pathology. Proinflammatory cytokines tumor necrosis factor-α, IL-1β, IL-6, and IL-12p40 are produced in lung tissue after administration of TDM to mice. Furthermore, CD11b⁺CD45⁺ macrophages with a high surface expression of the M1-like markers CD38 and CD86 were found present in regions of pathology in lungs of mice at 7 days post-TDM introduction. Conversely, only low phenotypic marker expression of M2-like markers CD206 and EGR-2 were present on macrophages. These findings suggest that TDM plays a role in establishment of the M1-like shift in the microenvironment during primary tuberculosis.

Selective delipidation of Mycobacterium bovis BCG enables direct pulmonary vaccination and enhances protection against Mycobacterium tuberculosis

Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis (TB), is the leading killer due to an infectious organism. Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only vaccine approved against TB, however, its efficacy against pulmonary TB is poor. While BCG is currently inoculated intradermally, the natural route of M.tb infection is through the lung. Excessive lung pathology caused by pulmonary inoculation of BCG has prevented the use of this immunization route. Here, we show that selective chemical treatment of BCG with petroleum ether removes inflammatory lipids from the bacterial surface while keeping BCG viable. Pulmonary vaccination using this modified BCG attenuated inflammatory responses, prevented immunopathology of the lung, and significantly increased protection against M.tb infection in mice. We further directly linked IL-17A as the responsible contributor of improved immunity against M.tb infection. These results provide evidence that selective removal of cytotoxic lipids from the BCG surface attenuates inflammation and offers a safer and superior vaccine against TB causing less damage post-infectious challenge with M.tb.

Mycobacteriophage Lysis Enzymes: Targeting the Mycobacterial Cell Envelope

Mycobacteriophages are viruses that specifically infect mycobacteria, which ultimately culminate in host cell death. Dedicated enzymes targeting the complex mycobacterial cell envelope arrangement have been identified in mycobacteriophage genomes, thus being potential candidates as antibacterial agents. These comprise lipolytic enzymes that target the mycolic acid-containing outer membrane and peptidoglycan hydrolases responsive to the atypical mycobacterial peptidoglycan layer. In the recent years, a remarkable progress has been made, particularly on the comprehension of the mechanisms of bacteriophage lysis proteins activity and regulation. Notwithstanding, information about mycobacteriophages lysis strategies is limited and is mainly represented by the studies performed with mycobacteriophage Ms6. Since mycobacteriophages target a specific group of bacteria, which include Mycobacterium tuberculosis responsible for one of the leading causes of death worldwide, exploitation of the use of these lytic enzymes demands a special attention, as they may be an alternative to tackle multidrug resistant tuberculosis. This review focuses on the current knowledge of the function of lysis proteins encoded by mycobacteriophages and their potential applications, which may contribute to increasing the effectiveness of antimycobacterial therapy.

Cell envelope lipids in the pathophysiology of Mycobacterium tuberculosis

Mycobacterium tuberculosis is an intracellular bacterium that persists and replicates inside macrophages. The bacterium possesses an unusual lipid-rich cell envelope that provides a hydrophobic impermeable barrier against many environmental stressors and allows it to survive extremely hostile intracellular surroundings. Since the lipid-rich envelope is crucial for M. tuberculosis virulence, the components of the cell wall lipid biogenesis pathways constitute an attractive target for the development of vaccines and antimycobacterial chemotherapeutics. In this review, we provide a detailed description of the mycobacterial cell envelope lipid components and their contributions to the physiology and pathogenicity of mycobacteria. We also discussed the current status of the antimycobacterial drugs that target biosynthesis, export and regulation of cell envelope lipids.

Association of IL4, IL6, and IL10 polymorphisms with pulmonary tuberculosis in a Tibetan Chinese population

Background

Pulmonary tuberculosis (PTB) is an infectious disease with a high incidence worldwide. Genes encoding cytokines IL4, IL6, and IL10 are highly polymorphic and can influence the susceptibility to PTB.

Results

We found correlations between one SNP in IL6 (rs2069837 p = 6.63E-11), seven SNPs in IL10 (rs1554286 p = 6.87E-20, rs1518111 p = 6.11E-11, rs3021094 p = 6.75E-29, rs3790622 p = 2.40E-06, rs3024490 p = 6.73E-11, rs1800872 p = 6.18E-11, rs1800871 p = 6.73E-11) and incidences of PTB. The SNPs rs2069837, rs1554286, rs1518111, rs3024490, rs1800872, and rs1800871 increased PTB risk by 1.95-fold, 2.34-fold, 1.84-fold, 1.84-fold, 1.84-fold and 1.84-fold, respectively. The SNPs rs3021094 and rs3790622 decreased PTB risk by 0.33-fold and 0.38-fold, respectively. We also found two linkage disequilibrium blocks in the studied IL SNPs. The IL4 haplotype TCCCGGA (OR = 1.33, p = 0.014) increased PTB risk, the IL10 haplotypes ATGGATA (OR = 0.39, p = 4.84E-06) provided a protective effect and decreased PTB risk.

Materials and Methods

For this study, we recruited 467 subjects with PTB and 503 healthy subjects from a Tibetan population living in Lhasa and nearby, China. Association analyses of sixteen single-nucleotide polymorphisms (SNPs) in IL4, IL6, and IL10 were performed.

Conclusions

Our findings demonstrate an association between polymorphisms in IL6 and IL10 and risk of PTB.

Down-regulation of PE11, a cell wall associated esterase, enhances the biofilm growth of Mycobacterium tuberculosis and reduces cell wall virulence lipid levels

PE11 (Rv1169c or LipX) is a cell wall associated esterase/lipase of Mycobacterium tuberculosis (Mtb). Evidences suggest that PE11 is expressed by Mtb both in vitro and in vivo. Previous studies have shown that PE11 leads to modification in cell wall lipid content and enhanced virulence when expressed in the non-pathogenic surrogate Mycobacterium smegmatis. Since cell wall lipids often play different roles in pathogenic and non-pathogenic mycobacteria, we investigated the role of PE11 in its host, Mtb. Mtb with lowered expression of PE11 (PE11 knock-down) displayed significant changes in colony morphology and cell wall lipid profile, confirming the role of PE11 in cell wall architecture. In addition, the levels of phthiocerol dimycocerosates, a cell wall virulence factor, were decreased. Levels of trehalose esters and free mycolic acids were increased. In contrast to M. smegmatis expressing Mtb PE11, a role reversal was observed in Mtb with respect to pellicle/biofilm formation. The PE11 knock-down Mtb strain showed significantly enhanced aggregation and early biofilm growth in detergent-free medium, compared to the wild-type. Knock-down strain also showed nearly 27-fold up-regulation of a fibronectin attachment protein (Rv1759c), linking biofilm growth with over-expression of bacterial proteins that help in aggregation and/or binding to host extracellular matrix. The knock-down also resulted in poor virulence of Mtb in PMA (phorbol 12-myristate 13-acetate) treated and PMA+IFN-γ treated THP-1 macrophages. Therefore, the study not only links PE11 to cell wall virulence lipids but also reveals the involvement of this cell wall associated esterase in down-regulation of biofilm in Mtb.

Association of pellicle growth morphological characteristics and clinical presentation of Mycobacterium tuberculosis isolates

Trehalose 6,6'dimycolate (TDM) is a glycolipid found in nearly pure form on the surface of virulent Mycobacterium tuberculosis (MTB). This manuscript investigated the production of TDM, growth rate and colony morphology of multiple strains of MTB, each of which had been isolated from both pulmonary (sputum) and extrapulmonary sites of multiple patients. Since sputum contains MTB primarily from cavities and extrapulmonary biopsies are typically granulomas, this provided an opportunity to compare the behavior of single strains of MTB that had been isolated from cavities and granulomas. The results demonstrated that MTB isolated from pulmonary sites produced more TDM (3.23 ± 1.75 μg TDM/mg MTB), grew more rapidly as thin spreading pellicles, demonstrated early cording, and climbed culture well walls. In contrast, extrapulmonary isolates produced less TDM (1.42 ± 0.58 μg TDM/mg MTB) (p < 0.001) and grew as discrete patches with little tendency to spread or climb. Both Beijing pulmonary isolates and the non-Beijing pulmonary isolates produced significantly more TDM (1.64 ± 0.46 μg TDM/mg MTB) and grew faster than the Beijing and non-Beijing extrapulmonary isolates (1.14 ± 0.63 μg TDM/mg MTB) (p < 0.001 and p < 0.005 respectively). These results indicate that MTB from pulmonary sites (cavities) grows faster and produces more TDM than strains isolated from extrapulmonary sites (granulomas). This report suggests a critical role for TDM in cavitary TB.

Cord factor as an invisibility cloak? A hypothesis for asymptomatic TB persistence

Mycobacterium tuberculosis (MTB) has long been known to persist in grossly normal tissues even in people with active lesions and granulomas in other parts of the body. We recently reported that post-primary TB begins as an asymptomatic infection that slowly progresses, accumulating materials for a massive necrotizing reaction that results in cavitation. This paper explores the possible roles of trehalose 6,6' dimycolate (TDM) or cord factor in the ability of MTB to persist in such lesions without producing inflammation. TDM is unique in that it has three distinct sets of biologic activities depending on its physical conformation. As a single molecule, TDM stimulates macrophage C-type lectin receptors including Mincle. TDM can also form three crystal like structures, cylindrical micelles, intercalated bilayer and monolayer, that have distinct non receptor driven activities that depend on modulation of interactions with water. In the monolayer form, TDM is highly toxic and destroys cells in minutes upon contact. The cylindrical micelles and an intercalated bilayer have surfaces composed entirely of trehalose which protect MTB from killing in macrophages. Here we review evidence that these trehalose surfaces bind water. We speculate that this immobilized water constituites of an "invisibility cloak" that facilitates the persistence of MTB in multiple cell types without producing inflammation, even in highly immune individuals.

Oral recombinant human or mouse lactoferrin reduces Mycobacterium tuberculosis TDM induced granulomatous lung pathology

Trehalose 6'6-dimycolate (TDM) is the most abundant glycolipid on the cell wall of Mycobacterium tuberculosis (MTB). TDM is capable of inducing granulomatous pathology in mouse models that resembles those induced by MTB infection. Using the acute TDM model, this work investigates the effect of recombinant human and mouse lactoferrin to reduce granulomatous pathology. C57BL/6 mice were injected intravenously with TDM at a dose of 25 μg·mouse^-1. At day 4 and 6, recombinant human or mouse lactoferrin (1 mg·(100 μL)^-1·mouse^-1) were delivered by gavage. At day 7 after TDM injection, mice were evaluated for lung pathology, cytokine production, and leukocyte populations. Mice given human or mouse lactoferrin had reduced production of IL-12p40 in their lungs. Mouse lactoferrin increased IL-6 and KC (CXCL1) in lung tissue. Increased numbers of macrophages were observed in TDM-injected mice given human or mouse lactoferrin. Granulomatous pathology, composed of mainly migrated leukocytes, was visually reduced in mice that received human or mouse lactoferrin. Quantitation of granulomatous pathology demonstrated a significant decrease in mice given human or mouse lactoferrin compared with TDM control mice. This report is the first to directly compare the immune modulatory effects of both heterologous recombinant human and homologous mouse lactoferrin on the development of TDM-induced granulomas.

Trehalose 6,6-Dimycolate from Mycobacterium tuberculosis Induces Hypercoagulation

Tuberculosis (TB) remains a global health concern. Trehalose 6'6-dimycolate (TDM) activates innate inflammation and likely also stimulates chronic inflammation observed during disease progression. Noninfectious models using purified TDM oil/water emulsions elicit pathologic findings observed in patients with TB. We introduce a new TDM model that promotes inflammatory lung pathologic findings and vascular occlusion and hemorrhage. C57BL/6 and BALB/c mice were injected with 10 μg of i.p. TDM in light mineral oil (TDM-IP). At day 7, another injection of 10 μg of i.v. TDM in oil/water emulsion was given (TDM-IV). The i.p./i.v. TDM (TDM-IVIP) group was compared with mice injected once with i.v. or i.p. TDM. The responses to TDM-IP, TDM-IV, or TDM-IPIV were consistent between mouse strains. Mice that received TDM-IV and TDM-IPIV had inflammatory pathologic findings with increases in inflammatory and T-cell cytokines, and the TDM-IPIV group had further enhancement of IL-10 and granulocyte-macrophage colony-stimulating factor. The TDM-IPIV group had increased CD4(+) T cells in lung tissue, significantly increased coagulation, decreased clot formation time, and increased maximum clot firmness. Masson's trichrome staining revealed increased deposition of collagen in the occluded vasculature. TDM-IPIV promotes a hypercoagulopathy state, independent of inflammation. This new model argues that TDM is sufficient to generate the hypercoagulopathy observed in patients with TB.

Single Nucleotide Polymorphisms in IL17A and IL6 Are Associated with Decreased Risk for Pulmonary Tuberculosis in Southern Brazilian Population

In Mycobacterium tuberculosis (MTB) infection, the complex interaction of host immune system and the mycobacteria is associated with levels of cytokines production that play a major role in determining the outcome of the disease. Several single-nucleotide polymorphisms (SNPs) in cytokine genes have been associated with tuberculosis (TB) outcome. The aim of this study was to evaluate the association between previously reported SNPs IL2-330 T>G (rs2069762); IL4-590 C>T (rs2243250); IL6-174 G>C (rs1800795); IL10-592 A>C (rs1800872); IL10-1082 G>A (rs1800896); IL17A -692 C>T (rs8193036); IL17A -197 G>A (rs2275913); TNF -238 G>A (rs361525); TNF -308 G>A (rs1800629) and IFNG +874 T>A (rs2430561) and pulmonary TB (PTB) susceptibility. We conducted a case-control study in individuals from Southern Brazil who were recruited between February 2012 and October 2013 in a high incidence TB city. We performed a multiplex genotyping assay in 191 patients with PTB and 175 healthy subjects. Our results suggest a decreased risk for PTB development associated with the IL17A -197A allele (OR = 0.29; p = 0.04), AA genotype (OR = 0.12; p = 0.04) and A carrier (AG/AA) (OR = 0.29; p = 0.004) and IL6 -174C carrier (CC/CG) (OR = 0.46; p = 0.04). We could not properly analyze IL17A -692 C>T (rs8193036) and IFNG +874T>A due to genotypic inconsistencies and found no evidence of association for the IL2, IL4, IL10 and TNF polymorphisms and PTB. In conclusion, our results show a protective effect of IL17 and IL6 polymorphisms on PTB outcome in Southern Brazilian population.

Lactoferrin: A Modulator for Immunity against Tuberculosis Related Granulomatous Pathology

There is great need for a therapeutic that would limit tuberculosis related pathology and thus curtail spread of disease between individuals by establishing a "firebreak" to slow transmission. A promising avenue to increase current therapeutic efficacy may be through incorporation of adjunct components that slow or stop development of aggressive destructive pulmonary pathology. Lactoferrin, an iron-binding glycoprotein found in mucosal secretions and granules of neutrophils, is just such a potential adjunct therapeutic agent. The focus of this review is to explore the utility of lactoferrin to serve as a therapeutic tool to investigate "disruption" of the mycobacterial granuloma. Proposed concepts for mechanisms underlying lactoferrin efficacy to control immunopathology are supported by data generated based on in vivo models using nonpathogenic trehalose 6,6'-dimycolate (TDM, cord factor).

Purification and proteomics of pathogen-modified vacuoles and membranes

Certain pathogenic bacteria adopt an intracellular lifestyle and proliferate in eukaryotic host cells. The intracellular niche protects the bacteria from cellular and humoral components of the mammalian immune system, and at the same time, allows the bacteria to gain access to otherwise restricted nutrient sources. Yet, intracellular protection and access to nutrients comes with a price, i.e., the bacteria need to overcome cell-autonomous defense mechanisms, such as the bactericidal endocytic pathway. While a few bacteria rupture the early phagosome and escape into the host cytoplasm, most intracellular pathogens form a distinct, degradation-resistant and replication-permissive membranous compartment. Intracellular bacteria that form unique pathogen vacuoles include Legionella, Mycobacterium, Chlamydia, Simkania, and Salmonella species. In order to understand the formation of these pathogen niches on a global scale and in a comprehensive and quantitative manner, an inventory of compartment-associated host factors is required. To this end, the intact pathogen compartments need to be isolated, purified and biochemically characterized. Here, we review recent progress on the isolation and purification of pathogen-modified vacuoles and membranes, as well as their proteomic characterization by mass spectrometry and different validation approaches. These studies provide the basis for further investigations on the specific mechanisms of pathogen-driven compartment formation.

Bacterial iron-sulfur cluster sensors in mammalian pathogens

Iron-sulfur clusters act as important cofactors for a number of transcriptional regulators in bacteria, including many mammalian pathogens. The sensitivity of iron-sulfur clusters to iron availability, oxygen tension, and reactive oxygen and nitrogen species enables bacteria to use such regulators to adapt their gene expression profiles rapidly in response to changing environmental conditions. In this review, we discuss how the [4Fe-4S] or [2Fe-2S] cluster-containing regulators FNR, Wbl, aconitase, IscR, NsrR, SoxR, and AirSR contribute to bacterial pathogenesis through control of both metabolism and classical virulence factors. In addition, we briefly review mammalian iron homeostasis as well as oxidative/nitrosative stress to provide context for understanding the function of bacterial iron-sulfur cluster sensors in different niches within the host.

Trehalolipid biosurfactants from nonpathogenic Rhodococcus actinobacteria with diverse immunomodulatory activities

Actinobacteria of the genus Rhodococcus produce trehalolipid biosurfactants with versatile biochemical properties and low toxicity. In recent years, these biosurfactants are increasingly studied as possible biomedical agents with expressed immunological activities. Applications of trehalolipids from Rhodococcus, predominantly cell-bound, in biomedicine are also attractive because their cost drawback could be less significant for high-value products. The review summarizes recent findings in immunomodulatory activities of trehalolipid biosurfactants from nonpathogenic Rhodococcus and related actinobacteria and compares their biomedical potential with well-known immunomodifying properties of trehalose dimycolates from Mycobacterium tuberculosis. Molecular mechanisms of trehalolipid interactions with immunocompetent cells are also discussed.

Isolation of bead phagosomes to study virulence function of M. tuberculosis cell wall lipids

Following pathogen recognition by macrophages, the causative agent of human tuberculosis, Mycobacterium tuberculosis, is internalized by receptor-mediated phagocytosis. Phagosomes containing nonpathogenic bacteria usually follow a stepwise maturation process to phagolysosomes where bacteria are eliminated. However, as a hallmark of M. tuberculosis virulence, pathogenic mycobacteria inhibit phagosome maturation in order to generate an intracellular niche for persistence and replication in resting macrophages. In contrast, activation by interferon gamma and tumor necrosis alpha activates microbicidal effectors of macrophages such as nitric oxide synthase, NO-mediated apoptosis and LRG-47-linked autophagy, which drives M. tuberculosis into phagolysosomes. Glycolipid compounds of the mycobacterial cell wall have been suggested as virulence factors and several studies revealed their contribution to mycobacterial interference with phagosome maturation. To study their effect on phagosome maturation and to characterize phagosomal protein and lipid compositions, we developed a reductionist mycobacterial lipid-coated bead model. Here, we provide protocols to "infect" macrophages with lipid-coated magnetic beads for subsequent purification and characterization of bead phagosomes. This model has been successfully employed to characterize the virulence properties of trehalose dimycolate, as one of the cell wall glycolipids essential for inhibition of phagosome maturation.

Trehalose 6,6'-dimycolate--a coat to regulate tuberculosis immunopathogenesis

Tuberculosis (TB) remains a significant public health burden worldwide. Treatment of this disease requires a minimum of six months and there is no vaccine available for the most common form of the disease. Increasing evidence suggests that the mycobacterial glycolipid trehalose 6,6' dimycolate (TDM; cord factor) plays a key role in the pathogenesis of TB disease. TDM protects the TB bacilli from macrophage-mediated killing, inhibits effective antigen presentation, and reduces the formation of protective T-cell responses. TDM promotes initiation of granuloma formation and likely plays a role in caseation. Furthermore, TDM may contribute to the development of post primary disease. Receptors for TDM were recently described and are expected to contribute to our knowledge of the molecular pathogenesis of TB disease. In this manner, understanding TDM may prove promising towards development of targeted TB therapeutics to limit clinical pathologies.

The cell envelope glycoconjugates of Mycobacterium tuberculosis

Tuberculosis (TB) remains the second most common cause of death due to a single infectious agent. The cell envelope of Mycobacterium tuberculosis (Mtb), the causative agent of the disease in humans, is a source of unique glycoconjugates and the most distinctive feature of the biology of this organism. It is the basis of much of Mtb pathogenesis and one of the major causes of its intrinsic resistance to chemotherapeutic agents. At the same time, the unique structures of Mtb cell envelope glycoconjugates, their antigenicity and essentiality for mycobacterial growth provide opportunities for drug, vaccine, diagnostic and biomarker development, as clearly illustrated by recent advances in all of these translational aspects. This review focuses on our current understanding of the structure and biogenesis of Mtb glycoconjugates with particular emphasis on one of the most intriguing and least understood aspect of the physiology of mycobacteria: the translocation of these complex macromolecules across the different layers of the cell envelope. It further reviews the rather impressive progress made in the last 10 years in the discovery and development of novel inhibitors targeting their biogenesis.

Mycobacterial Lipidomics

Lipidomics is a distinct subspecialty of metabolomics concerned with hydrophobic molecules that organize into membranes. Most of the lipid classes present in Mycobacterium tuberculosis are found only in Actinobacteria and show extreme structural diversity. This article highlights the conceptual basis and the practical challenges associated with the mass spectrometry–based lipidomic study of M. tuberculosis to solve basic questions about the virulence of this lipid-laden organism.

Mycolic acids: structures, biosynthesis, and beyond

Mycolic acids are major and specific lipid components of the mycobacterial cell envelope and are essential for the survival of members of the genus Mycobacterium that contains the causative agents of both tuberculosis and leprosy. In the alarming context of the emergence of multidrug-resistant, extremely drug-resistant, and totally drug-resistant tuberculosis, understanding the biosynthesis of these critical determinants of the mycobacterial physiology is an important goal to achieve, because it may open an avenue for the development of novel antimycobacterial agents. This review focuses on the chemistry, structures, and known inhibitors of mycolic acids and describes progress in deciphering the mycolic acid biosynthetic pathway. The functional and key biological roles of these molecules are also discussed, providing a historical perspective in this dynamic area.

Recognition of the mycobacterial cord factor by Mincle: relevance for granuloma formation and resistance to tuberculosis

The world's most successful intracellular bacterial pathogen, Mycobacterium tuberculosis (MTB), survives inside macrophages by blocking phagosome maturation and establishes chronic infection characterized by the formation of granulomas. Trehalose-6,6-dimycolate (TDM), the mycobacterial cord factor, is the most abundant cell wall lipid of virulent mycobacteria, is sufficient to cause granuloma formation, and has long been known to be a major virulence factor of MTB. Recently, TDM has been shown to activate the Syk-Card9 signaling pathway in macrophages through binding to the C-type lectin receptor Mincle. The Mincle-Card9 pathway is required for activation of macrophages by TDM in vitro and for granuloma formation in vivo following injection of TDM. Whether this pathway is also exploited by MTB to reprogram the macrophage into a comfortable niche has not been explored yet. Several recent studies have investigated the phenotype of Mincle-deficient mice in mycobacterial infection, yielding divergent results in terms of a role for Mincle in host resistance. Here, we review these studies, discuss possible reasons for discrepant results and highlight open questions in the role of Mincle and other C-type lectin receptors in the infection biology of MTB.

Cord factors from atypical mycobacteria (Mycobacterium alvei, Mycobacterium brumae) stimulate the secretion of some pro-inflammatory cytokines of relevance in tuberculosis

The ability to induce several cytokines relevant to tuberculosis (TNF-α, IL-1β, IL-6, IL-12p40 and IL-23) by cord factor (trehalose dimycolate) from Mycobacterium alvei CR-21(T) and Mycobacterium brumae CR-270(T) was studied in the cell lines RAW 264.7 and THP-1, and compared to the ability of cord factor from Mycobacterium tuberculosis H37Rv, where this glycolipid appears to be implicated in the pathogenesis of tuberculosis. Details of the fine structure of these molecules were obtained by NMR and MS. The mycoloyl residues were identified as α and (ω-1)-methoxy in M. alvei CR-21(T) and α in M. brumae CR-270(T); in both cases they were di-unsaturated instead of cyclopropanated as found in M. tuberculosis. In RAW 264.7 cells, cord factors from M. alvei CR-21(T), M. brumae CR-270(T) and M. tuberculosis differed in their ability to stimulate IL-6, the higher levels corresponding to the cord factor from M. tuberculosis. In THP-1 cells, a similar overall profile of cytokines was found for M. alvei CR-21(T) and M. brumae CR-270(T), with high proportions of IL-1β and TNF-α, and different from M. tuberculosis, where IL-6 and IL-12p40 prevailed. The data obtained indicate that cord factors from the atypical mycobacteria M. alvei CR-21(T) and M. brumae CR-270(T) stimulated the secretion of several pro-inflammatory cytokines, although there were some differences with those of M. tuberculosis H37Rv. This finding seems to be due to their particular mycoloyl substituents and could be of interest when considering the potential adjuvanticity of these molecules.

Nocardia brasiliensis cell wall lipids modulate macrophage and dendritic responses that favor development of experimental actinomycetoma in BALB/c mice

Nocardia brasiliensis is a Gram-positive facultative intracellular bacterium frequently isolated from human actinomycetoma. However, the pathogenesis of this infection remains unknown. Here, we used a model of bacterial delipidation with benzine to investigate the role of N. brasiliensis cell wall-associated lipids in experimental actinomycetoma. Delipidation of N. brasiliensis with benzine resulted in complete abolition of actinomycetoma without affecting bacterial viability. Chemical analyses revealed that trehalose dimycolate and an unidentified hydrophobic compound were the principal compounds extracted from N. brasiliensis with benzine. By electron microscopy, the extracted lipids were found to be located in the outermost membrane layer of the N. brasiliensis cell wall. They also appeared to confer acid-fastness. In vitro, the extractable lipids from the N. brasiliensis cell wall induced the production of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and CCL-2 in macrophages. The N. brasiliensis cell wall extractable lipids inhibited important macrophage microbicidal effects, such as tumor necrosis factor alpha (TNF-α) and nitric oxide (NO) production, phagocytosis, bacterial killing, and major histocompatibility complex class II (MHC-II) expression in response to gamma interferon (IFN-γ). In dendritic cells (DCs), N. brasiliensis cell wall-associated extractable lipids suppressed MHC-II, CD80, and CD40 expression while inducing tumor growth factor β (TGF-β) production. Immunization with delipidated N. brasiliensis induced partial protection preventing actinomycetoma. These findings suggest that N. brasiliensis cell wall-associated lipids are important for actinomycetoma development by inducing inflammation and modulating the responses of macrophages and DCs to N. brasiliensis.

Complement factor C7 contributes to lung immunopathology caused by Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) remains a significant global health burden despite the availability of antimicrobial chemotherapy. Increasing evidence indicates a critical role of the complement system in the development of host protection against the bacillus, but few studies have specifically explored the function of the terminal complement factors. Mice deficient in complement C7 and wild-type C57BL/6 mice were aerosol challenged with MTB Erdman and assessed for bacterial burden, histopathology, and lung cytokine responses at days 30 and 60 post-infection. Macrophages isolated from C7 −/− and wild-type mice were evaluated for MTB proliferation and cytokine production. C7 −/− mice had significantly less liver colony forming units (CFUs) at day 30; no differences were noted in lung CFUs. The C7 deficient mice had markedly reduced lung occlusion with significantly increased total lymphocytes, decreased macrophages, and increased numbers of CD4+ cells 60 days post-infection. Expression of lung IFN-γ and TNF-α was increased at day 60 compared to wild-type mice. There were no differences in MTB-proliferation in macrophages isolated from wild-type and knock-out mice. These results indicate a role for complement C7 in the development of MTB induced immunopathology which warrants further investigation.

Towards understanding the functional diversity of cell wall mycolic acids of Mycobacterium tuberculosis

Mycolic acids constitute the waxy layer of the outer cell wall of Mycobacterium spp. and a few other genera. They are diverse in structure, providing a unique chromatographic foot-print for almost each of the more than 70 Mycobacterium species. Although mainly esterified to cell wall arabinogalactan, trehalose or glucose, some free mycolic acid is secreted during in vitro growth of Mycobacterium tuberculosis. In M. tuberculosis, α-, keto- and methoxy-mycolic acids are the main classes, each differing in their ability to attract neutrophils, induce foamy macrophages or adopt an antigenic structure for antibody recognition. Of interest is their particular relationship to cholesterol, discovered by their ability to attract cholesterol, to bind Amphotericin B or to be recognised by monoclonal antibodies that cross-react with cholesterol. The structural elements that determine this diverse functionality include the carboxylic acid in the mycolic motif, as well as the nature and stereochemistry of the two functional groups in the merochain. The functional diversity of mycolic acid classes implies that much information may be contained in the selective expression and secretion of mycolic acids to establish tuberculosis after infection of the host. Their cholesteroid nature may relate to how they utilize host cholesterol for their persistent survival.

RL, Actor JK. IL-6 mediates 11βHSD type 2 to effect progression of the mycobacterial cord factor trehalose 6,6'-dimycolate-induced granulomatous response

Granulomatous structures are highly dynamic during active mycobacterial infection, with accompanying responsive inflammation contributing to modulation of pathology throughout the course of disease. The heightened inflammatory response coinciding with initiation and maintenance of newly developing granulomatous structures must be limited to avoid excessive damage to bystander tissue. Modulating the cellular bioavailability of glucocorticoids by local regulation of 11βHSD enzymes within responding tissue and parenchyma would allow controlled inflammatory response during infection. Mycobacterial glycolipid trehalose 6,6'-dimycolate was used to induce strong pulmonary granulomatous inflammation immunopathology. Pulmonary corticosterone was significantly increased at days 3 and 5 after administration. An inverse relationship of 11βHSD1 and 11βHSD2 message correlated with pathology development. Immunohistochemical analysis also demonstrated that 11βHSD2 is expressed in proximity to granulomatous lesions. A role for pro-inflammatory IL-6 cytokine in regulation of converting enzymes to control the granulomatous response was confirmed using gene-disrupted IL-6-/- mice. A model is proposed linking IL-6 to endocrine-derived factors which allows modification of active corticosterone into inert 11-dehydrocorticosterone at the site of granuloma formation to limit excessive parenchymal damage.

Biosynthesis and Virulent Behavior of Lipids Produced by Mycobacterium tuberculosis: LAM and Cord Factor: An Overview

Mycobacterium tuberculosis is the causative agent of tuberculosis disease, which has developed a myriad of exceptional features contributing to its survival within the hostile environment of host cell. Unique cell wall structure with high lipid content plays an imperative role in the pathogenicity of mycobacteria. Cell wall components of MTB such as lipoarabinomannan and Trehalose dimycolate (cord factor) are virulent in nature apart from its virulence genes. Virulent effect of these factors on host cells reduces host cell immunity. LAM has been known to inhibit phagosome maturation by inhibiting the Ca²⁺/calmodulin phosphatidyl inositol-3-kinase hvps34 pathways. Moreover, TDM (Trehalose dimycolate) also inhibits fusion between phospholipid vesicles and migration of polymorphonuclear neutrophils. The objective of this paper is to understand the virulence of LAM and cord factor on host cell which might be helpful to design an effective drug against tuberculosis.

Histopathological features and expression profiles of cytokines, chemokines and SOCS family proteins in trehalose 6,6'-dimycolate-induced granulomatous lesions

OBJECTIVE AND DESIGN

The objective of this paper is to elucidate the factors contributing to the development and regression of trehalose 6,6'-dimycolate (TDM)-induced model of tuberculous granulomatous lesions.

MATERIALS AND TREATMENT

BALB/c mice were twice injected i.p. with a 100 μl of w/o/w emulsion (100 μg of TDM, 3.2 μl of Freund's incomplete adjuvant, 3.2 μl of PBS, and 93.6 μl of saline containing 0.2% Tween 20) at a 1 week interval. The mice were killed at days 0, 3, 7, 14, or 21 after the last injection. Three mice were used per group.

METHODS

We examined histopathological changes of the lesions and defined the expression levels of cytokines and suppressor of cytokine signaling (SOCS) family proteins by real-time PCR.

RESULTS

The levels of inflammatory cytokine, such as TNF-α and IL-1β, paralleled with the size of the lesions and the levels of TGF-β and SOCS-3 were high at regression phase.

DISCUSSION

Our results demonstrated that both the down-regulation of inflammatory cytokines and up-regulation of TGF-β and SOCS-3 are crucial for histopathological changes including alteration in the sizes of the lesions and changes in inflammatory cell populations.

Lactoferrin modulation of mycobacterial cord factor trehalose 6-6'-dimycolate induced granulomatous response

The immune system responds to tuberculosis (TB) infection by forming granulomas. However, subsequent immune-mediated destruction of lung tissue is a cause of significant morbidity and contributes to disease transmission. Lactoferrin, an iron-binding glycoprotein, has demonstrated immunomodulatory properties that decrease tissue destruction and promote T(H)1 immune responses, both of which are essential for controlling TB infection. The cord factor trehalose 6,6'-dimycolate (TDM) model of granuloma formation mimics many aspects of TB infection with a similar histopathology accompanied by proinflammatory cytokine production. C57BL/6 mice were injected intravenously with TDM. A subset of mice was given 1 mg of bovine lactoferrin 24 h post-TDM challenge. Lung tissue was analyzed for histological response and for the production of proinflammatory mediators. C57BL/6 mice demonstrated a granuloma formation that correlated with an increased production of interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α,) IL-12p40, interferon-gamma (IFN-γ), and IL-10 protein. Mice treated with lactoferrin postchallenge had significantly fewer and smaller granulomas compared with those given TDM alone. Proinflammatory and T(H)1 cytokines essential to the control of mycobacterial infections, such as TNF-α and IFN-γ, were not significantly different in mice treated with lactoferrin. Furthermore, the anti-inflammatory cytokines IL-10 and transforming growth factor-β were increased. A potential mechanism for decreased tissue damage observed in the lactoferrin-treated mice is proposed. Because of its influence to modulate immune responses, lactoferrin may be a useful adjunct in the treatment of granulomatous inflammation occurring during mycobacterial infection.

Spotlight on Mycobacteria and dendritic cells: will novel targets to fight tuberculosis emerge?

Over thousands of years microbes and mammals have co-evolved, resulting in extraordinarily sophisticated molecular mechanisms permitting the organisms to survive together. Mycobacterium tuberculosis is one of the best examples of successful co-evolution, since the bacilli have infected one third of the human population, but in 90% of the cases without causing overt disease. Despite this, increasing incidence of Human Immunodeficiency Virus (HIV) infection and the emergence of drug-resistant strains means that tuberculosis is in fact an extremely serious emerging threat to global health. Decades of work have focused on the interaction of this pathogen with its established cellular host, the macrophage, but still novel therapeautics remain elusive. While the macrophage is clearly important, recent evidence suggests that understanding the role of dendritic cells, which are key regulators of immunity, may be a crucial step in identifying new means of controlling this disease. Novel technologies, in particular genome-wide transcriptome analyses, are advancing our ability to dissect the complex dynamic relationships between dendritic cells and mycobacteria, highlighting new areas for study that have not been previously explored.

Mycobacteriophage Ms6 LysB specifically targets the outer membrane of Mycobacterium smegmatis

LysB, a mycobacteriophage Ms6-encoded protein, was previously identified as a lipolytic enzyme able to hydrolyse the ester bond in lipase and esterase substrates. In the present work, we show that LysB can hydrolyse lipids containing mycolic acids from the outer membrane of the mycobacterial cell wall. LysB was shown to hydrolyse the mycolic acids from the mycolyl-arabinogalactan-peptidoglycan complex where the mycolates of the inner leaflet of the outer membrane are covalently attached to an arabinosyl head group. In addition, treatment of the extractable lipids from Mycobacterium smegmatis, Mycobacterium bovis BCG and Mycobacterium tuberculosis H37Ra with LysB showed that trehalose 6,6'-dimycolate (TDM), a trehalose diester of two mycolic acid molecules, was hydrolysed by the enzyme. We have also determined the structures of the mycolic acid molecules that form the M. smegmatis TDM. The identification of a phage-encoded enzyme that targets the outer membrane of the mycobacterial cell wall enhances our understanding of the mechanism of mycobacteriophage lysis.

Direct recognition of the mycobacterial glycolipid, trehalose dimycolate, by C-type lectin Mincle

Tuberculosis remains a fatal disease caused by Mycobacterium tuberculosis, which contains various unique components that affect the host immune system. Trehalose-6,6′-dimycolate (TDM; also called cord factor) is a mycobacterial cell wall glycolipid that is the most studied immunostimulatory component of M. tuberculosis. Despite five decades of research on TDM, its host receptor has not been clearly identified. Here, we demonstrate that macrophage inducible C-type lectin (Mincle) is an essential receptor for TDM. Heat-killed mycobacteria activated Mincle-expressing cells, but the activity was lost upon delipidation of the bacteria; analysis of the lipid extracts identified TDM as a Mincle ligand. TDM activated macrophages to produce inflammatory cytokines and nitric oxide, which are completely suppressed in Mincle-deficient macrophages. In vivo TDM administration induced a robust elevation of inflammatory cytokines in sera and characteristic lung inflammation, such as granuloma formation. However, no TDM-induced lung granuloma was formed in Mincle-deficient mice. Whole mycobacteria were able to activate macrophages even in MyD88-deficient background, but the activation was significantly diminished in Mincle/MyD88 double-deficient macrophages. These results demonstrate that Mincle is an essential receptor for the mycobacterial glycolipid, TDM.

TB research at UT-Houston--a review of cord factor: new approaches to drugs, vaccines and the pathogenesis of tuberculosis

Tuberculosis remains a major threat as drug resistance continues to increase. Pulmonary tuberculosis in adults is responsible for 80% of clinical cases and nearly 100% of transmission of infection. Unfortunately, since we have no animal models of adult type pulmonary tuberculosis, the most important type of disease remains largely out of reach of modern science and many fundamental questions remain unanswered. This paper reviews research dating back to the 1950's providing compelling evidence that cord factor (trehalose 6,6 dimycolate [TDM]) is essential for understanding tuberculosis. However, the original papers by Bloch and Noll were too far ahead of their time to have immediate impact. We can now recognize that the physical and biologic properties of cord factor are unprecedented in science, especially its ability to switch between two sets of biologic activities with changes in conformation. While TDM remains on organisms, it protects them from killing within macrophages, reduces antibiotic effectiveness and inhibits the stimulation of protective immune responses. If it comes off organisms and associates with lipid, TDM becomes a driver of tissue damage and necrosis. Studies emanating from cord factor research have produced (1) a rationale for improving vaccines, (2) an approach to new drugs that overcome natural resistance to antibiotics, (3) models of caseating granulomas that reproduce multiple manifestations of human tuberculosis. (4) evidence that TDM is a key T cell antigen in destructive lesions of tuberculosis, and (5) a new understanding of the pathology and pathogenesis of postprimary tuberculosis that can guide more informative studies of long standing mysteries of tuberculosis.