Pathology of postprimary tuberculosis in humans and mice: contradiction of long-held beliefs

Understanding the development of tuberculous granulomas: insights into host protection and pathogenesis, a review in humans and animals

Granulomas, organized aggregates of immune cells which form in response to Mycobacterium tuberculosis (Mtb), are characteristic but not exclusive of tuberculosis (TB). Despite existing investigations on TB granulomas, the determinants that differentiate host-protective granulomas from granulomas that contribute to TB pathogenesis are often disputed. Thus, the goal of this narrative review is to help clarify the existing literature on such determinants. We adopt the a priori view that TB granulomas are host-protective organelles and discuss the molecular and cellular determinants that induce protective granulomas and those that promote their failure. While reports about protective TB granulomas and their failure may initially seem contradictory, it is increasingly recognized that either deficiencies or excesses of the molecular and cellular components in TB granuloma formation may be detrimental to the host. More specifically, insufficient or excessive expression/representation of the following components have been reported to skew granulomas toward the less protective phenotype: (i) epithelioid macrophages; (ii) type 1 adaptive immune response; (iii) type 2 adaptive immune response; (iv) tumor necrosis factor; (v) interleukin-12; (vi) interleukin-17; (vii) matrix metalloproteinases; (viii) hypoxia in the TB granulomas; (ix) hypoxia inducible factor-1 alpha; (x) aerobic glycolysis; (xi) indoleamine 2,3-dioxygenase activity; (xii) heme oxygenase-1 activity; (xiii) immune checkpoint; (xiv) leukotriene A4 hydrolase activity; (xv) nuclear-factor-kappa B; and (xvi) transforming growth factor-beta. Rather, more precise and timely coordinated immune responses appear essential for eradication or containment of Mtb infection. Since there are several animal models of infection with Mtb, other species within the Mtb complex, and the surrogate Mycobacterium marinum - whether natural (cattle, elephants) or experimental (zebrafish, mouse, guinea pig, rabbit, mini pig, goat, non-human primate) infections - we also compared the TB granulomatous response and other pathologic lung lesions in various animals infected with one of these mycobacteria with that of human pulmonary TB. Identifying components that dictate the formation of host-protective granulomas and the circumstances that result in their failure can enhance our understanding of the macrocosm of human TB and facilitate the development of novel remedies - whether they be direct therapeutics or indirect interventions - to efficiently eliminate Mtb infection and prevent its pathologic sequelae.

Association of polymorphism of the glutathione-s-transferase M1 gene and tumor necrosis factor alpha with the formation and size of decay cavities in patients with pulmonary tuberculosis

The aim. To study the association of polymorphic variants of the GSTM1 (E/D) and TNF-s (308G>A (rs1800629) genes with the formation of decay cavity sizes in patients with pulmonary tuberculosis.

Material and methods. The study group is represented by 335 patients suffering from pulmonary tuberculosis (212 people were diagnosed with pulmonary tuberculosis for the first time; 123 people with chronic pulmonary tuberculosis) aged 18 to 65  years; receiving an intensive phase of chemotherapy. To conduct molecular genetic studies; 335 people had whole blood taken from a vein into a test tube with EDTA. Genomic DNA was isolated using Arrow Blood DNA 500 reagent kits from whole blood (at the NorDiag Arrow station). After; the polymerase chain reaction was staged in real time using sets of reagents for genotyping SNPs: GSTM1 (E/D) and TNF-s (–308G>A (rs1800629).

Results and discussion. In patients with pulmonary tuberculosis; the genotype DD of the gene GSTM1 (E/D) and the genotype GG of the gene TNF-s –308G>A (rs1800629) is most often associated with the formation of the size of decay cavities.

Conclusion. It is advisable to introduce genotyping of the GSTM1 and TNF-s genes into the practice of a phthisiologist in order to predict the probability of the formation of the size of decay cavities in patients with pulmonary tuberculosis.

 

B cells in perivascular and peribronchiolar granuloma-associated lymphoid tissue and B-cell signatures identify asymptomatic Mycobacterium tuberculosis lung infection in Diversity Outbred mice

Because most humans resist Mycobacterium tuberculosis infection, there is a paucity of lung samples to study. To address this gap, we infected Diversity Outbred mice with M. tuberculosis and studied the lungs of mice in different disease states. After a low-dose aerosol infection, progressors succumbed to acute, inflammatory lung disease within 60 days, while controllers maintained asymptomatic infection for at least 60 days, and then developed chronic pulmonary tuberculosis (TB) lasting months to more than 1 year. Here, we identified features of asymptomatic M. tuberculosis infection by applying computational and statistical approaches to multimodal data sets. Cytokines and anti-M. tuberculosis cell wall antibodies discriminated progressors vs controllers with chronic pulmonary TB but could not classify mice with asymptomatic infection. However, a novel deep-learning neural network trained on lung granuloma images was able to accurately classify asymptomatically infected lungs vs acute pulmonary TB in progressors vs chronic pulmonary TB in controllers, and discrimination was based on perivascular and peribronchiolar lymphocytes. Because the discriminatory lesion was rich in lymphocytes and CD4 T cell-mediated immunity is required for resistance, we expected CD4 T-cell genes would be elevated in asymptomatic infection. However, the significantly different, highly expressed genes were from B-cell pathways (e.g., Bank1, Cd19, Cd79, Fcmr, Ms4a1, Pax5, and H2-Ob), and CD20+ B cells were enriched in the perivascular and peribronchiolar regions of mice with asymptomatic M. tuberculosis infection. Together, these results indicate that genetically controlled B-cell responses are important for establishing asymptomatic M. tuberculosis lung infection.

Systems genetics uncover new loci containing functional gene candidates in Mycobacterium tuberculosis-infected Diversity Outbred mice

Mycobacterium tuberculosis infects two billion people across the globe, and results in 8-9 million new tuberculosis (TB) cases and 1-1.5 million deaths each year. Most patients have no known genetic basis that predisposes them to disease. Here, we investigate the complex genetic basis of pulmonary TB by modelling human genetic diversity with the Diversity Outbred mouse population. When infected with M. tuberculosis, one-third develop early onset, rapidly progressive, necrotizing granulomas and succumb within 60 days. The remaining develop non-necrotizing granulomas and survive longer than 60 days. Genetic mapping using immune and inflammatory mediators; and clinical, microbiological, and granuloma correlates of disease identified five new loci on mouse chromosomes 1, 2, 4, 16; and three known loci on chromosomes 3 and 17. Further, multiple positively correlated traits shared loci on chromosomes 1, 16, and 17 and had similar patterns of allele effects, suggesting these loci contain critical genetic regulators of inflammatory responses to M. tuberculosis. To narrow the list of candidate genes, we used a machine learning strategy that integrated gene expression signatures from lungs of M. tuberculosis-infected Diversity Outbred mice with gene interaction networks to generate scores representing functional relationships. The scores were used to rank candidates for each mapped trait, resulting in 11 candidate genes: Ncf2, Fam20b, S100a8, S100a9, Itgb5, Fstl1, Zbtb20, Ddr1, Ier3, Vegfa, and Zfp318. Although all candidates have roles in infection, inflammation, cell migration, extracellular matrix remodeling, or intracellular signaling, and all contain single nucleotide polymorphisms (SNPs), SNPs in only four genes (S100a8, Itgb5, Fstl1, Zfp318) are predicted to have deleterious effects on protein functions. We performed methodological and candidate validations to (i) assess biological relevance of predicted allele effects by showing that Diversity Outbred mice carrying PWK/PhJ alleles at the H-2 locus on chromosome 17 QTL have shorter survival; (ii) confirm accuracy of predicted allele effects by quantifying S100A8 protein in inbred founder strains; and (iii) infection of C57BL/6 mice deficient for the S100a8 gene. Overall, this body of work demonstrates that systems genetics using Diversity Outbred mice can identify new (and known) QTLs and functionally relevant gene candidates that may be major regulators of complex host-pathogens interactions contributing to granuloma necrosis and acute inflammation in pulmonary TB.

Clinical and Imaging Characteristics of Smear Negative Pulmonary Tuberculosis Patients: A Comparative Study

Background

Prevalence surveys in Ethiopia indicate smear negative pulmonary tuberculosis (SNPTB) taking the major share of the overall TB burden. It has also been a diagnostic dilemma worldwide leading to diagnostic delays and difficulty in monitoring treatment outcomes. This study determines and compares the clinical and imaging findings in SNPTB and smear positive PTB (SPPTB). Methodology. A case-control study was conducted on 313 PTB (173 SNPTB) patients. Data and sputum samples were collected from consented patients. Smear microscopy, GeneXpert, and culture analyses were performed on sputum samples. Data were analyzed using Stata version 17; a P value < 0.05 was considered statistically significant.

Results

Of the 173 SNPTB patients, 42% were culture positive with discordances between test results reported by health facilities and Armauer Hansen Research Institute laboratory using concentrated smear microscopy. A previous history of TB and fewer cavitary lesions were significantly associated with SNPTB.

Conclusions

Though overall clinical presentations of SNPTB patients resemble those seen in SPPTB patients, a prior history of TB was strongly associated with SNPTB. Subject to further investigations, the relatively higher discrepancies seen in TB diagnoses reflect the posed diagnostic challenges in SNPTB patients, as a higher proportion of these patients are also seen in Ethiopia.

Systems genetics uncover new loci containing functional gene candidates in Mycobacterium tuberculosis-infected Diversity Outbred mice

Mycobacterium tuberculosis, the bacillus that causes tuberculosis (TB), infects 2 billion people across the globe, and results in 8-9 million new TB cases and 1-1.5 million deaths each year. Most patients have no known genetic basis that predisposes them to disease. We investigated the complex genetic basis of pulmonary TB by modelling human genetic diversity with the Diversity Outbred mouse population. When infected with M. tuberculosis, one-third develop early onset, rapidly progressive, necrotizing granulomas and succumb within 60 days. The remaining develop non-necrotizing granulomas and survive longer than 60 days. Genetic mapping using clinical indicators of disease, granuloma histopathological features, and immune response traits identified five new loci on mouse chromosomes 1, 2, 4, 16 and three previously identified loci on chromosomes 3 and 17. Quantitative trait loci (QTLs) on chromosomes 1, 16, and 17, associated with multiple correlated traits and had similar patterns of allele effects, suggesting these QTLs contain important genetic regulators of responses to M. tuberculosis. To narrow the list of candidate genes in QTLs, we used a machine learning strategy that integrated gene expression signatures from lungs of M. tuberculosis-infected Diversity Outbred mice with gene interaction networks, generating functional scores. The scores were then used to rank candidates for each mapped trait in each locus, resulting in 11 candidates: Ncf2, Fam20b, S100a8, S100a9, Itgb5, Fstl1, Zbtb20, Ddr1, Ier3, Vegfa, and Zfp318. Importantly, all 11 candidates have roles in infection, inflammation, cell migration, extracellular matrix remodeling, or intracellular signaling. Further, all candidates contain single nucleotide polymorphisms (SNPs), and some but not all SNPs were predicted to have deleterious consequences on protein functions. Multiple methods were used for validation including (i) a statistical method that showed Diversity Outbred mice carrying PWH/PhJ alleles on chromosome 17 QTL have shorter survival; (ii) quantification of S100A8 protein levels, confirming predicted allele effects; and (iii) infection of C57BL/6 mice deficient for the S100a8 gene. Overall, this work demonstrates that systems genetics using Diversity Outbred mice can identify new (and known) QTLs and new functionally relevant gene candidates that may be major regulators of granuloma necrosis and acute inflammation in pulmonary TB.

Comparative pathology of experimental pulmonary tuberculosis in animal models

Research in human tuberculosis (TB) is limited by the availability of human tissues from patients, which is often altered by therapy and treatment. Thus, the use of animal models is a key tool in increasing our understanding of the pathogenesis, disease progression and preclinical evaluation of new therapies and vaccines. The granuloma is the hallmark lesion of pulmonary tuberculosis, regardless of the species or animal model used. Although animal models may not fully replicate all the histopathological characteristics observed in natural, human TB disease, each one brings its own attributes which enable researchers to answer specific questions regarding TB immunopathogenesis. This review delves into the pulmonary pathology induced by Mycobacterium tuberculosis complex (MTBC) bacteria in different animal models (non-human primates, rodents, guinea pigs, rabbits, cattle, goats, and others) and compares how they relate to the pulmonary disease described in humans. Although the described models have demonstrated some histopathological features in common with human pulmonary TB, these data should be considered carefully in the context of this disease. Further research is necessary to establish the most appropriate model for the study of TB, and to carry out a standard characterisation and score of pulmonary lesions.

The host-directed therapeutic imatinib mesylate accelerates immune responses to Mycobacterium marinum infection and limits pathology associated with granulomas

Infections caused by members of the mycobacterium tuberculosis complex [MTC] and nontuberculous mycobacteria [NTM] can induce widespread morbidity and mortality in people. Mycobacterial infections cause both a delayed immune response, which limits rate of bacterial clearance, and formation of granulomas, which contain bacterial spread, but also contribute to lung damage, fibrosis, and morbidity. Granulomas also limit access of antibiotics to bacteria, which may facilitate development of resistance. Bacteria resistant to some or all antibiotics cause significant morbidity and mortality, and newly developed antibiotics readily engender resistance, highlighting the need for new therapeutic approaches. Imatinib mesylate, a cancer drug used to treat chronic myelogenous leukemia [CML] that targets Abl and related tyrosine kinases, is a possible host-directed therapeutic [HDT] for mycobacterial infections, including those causing TB. Here, we use the murine Mycobacterium marinum [Mm] infection model, which induces granulomatous tail lesions. Based on histological measurements, imatinib reduces both lesion size and inflammation of surrounding tissue. Transcriptomic analysis of tail lesions indicates that imatinib induces gene signatures indicative of immune activation and regulation at early time points post infection that resemble those seen at later ones, suggesting that imatinib accelerates but does not substantially alter anti-mycobacterial immune responses. Imatinib likewise induces signatures associated with cell death and promotes survival of bone marrow-derived macrophages [BMDMs] in culture following infection with Mm. Notably, the capacity of imatinib to limit formation and growth of granulomas in vivo and to promote survival of BMDMs in vitro depends upon caspase 8, a key regulator of cell survival and death. These data provide evidence for the utility of imatinib as an HDT for mycobacterial infections in accelerating and regulating immune responses, and limiting pathology associated with granulomas, which may mitigate post-treatment morbidity.

Association of Polymorphic Gene Variants of Xenobiotic Biotransformation Enzymes with Lung Tissue Destruction in Tuberculosis Patients

The objective: to investigate the association of polymorphic gene variants of xenobiotic biotransformation enzymes (NAT2, CYP2E1, ABCB1, GSTM1, GSTT1) and cytokines (IL1B, IL-4, IL-10, TNF) with lung tissue destruction in pulmonary tuberculosis patients.

Subjects and Methods. An ethnically homogeneous population sample of unrelated individuals of Slavic nationalities (mainly Russians) living in Kursk Oblast suffering from new pulmonary tuberculosis was examined.

Results. New pulmonary tuberculosis with no destructive changes in the lungs was associated with the EE genotype of the GSTM1 gene (p < 0.0001) in 89.5%, while the DD genotype of the GSTM1 gene (p < 0.0001) was associated with the presence of destructive changes in the lungs in 56.1% of cases; the dominant GG genotype of the TNF-α gene was associated with destructive changes in the lungs in 93.3% (p = 0.027), and the recessive GA genotype of the TNF-α gene was associated with no destructive changes in the lungs in 71.9% (p = 0.027).

PRMT5 epigenetically regulates the E3 ubiquitin ligase ITCH to influence lipid accumulation during mycobacterial infection

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), triggers enhanced accumulation of lipids to generate foamy macrophages (FMs). This process has been often attributed to the surge in the expression of lipid influx genes with a concomitant decrease in those involved in lipid efflux. Here, we define an Mtb-orchestrated modulation of the ubiquitination of lipid accumulation markers to enhance lipid accretion during infection. We find that Mtb infection represses the expression of the E3 ubiquitin ligase, ITCH, resulting in the sustenance of key lipid accrual molecules viz. ADRP and CD36, that are otherwise targeted by ITCH for proteasomal degradation. In line, overexpressing ITCH in Mtb-infected cells was found to suppress Mtb-induced lipid accumulation. Molecular analyses including loss-of-function and ChIP assays demonstrated a role for the concerted action of the transcription factor YY1 and the arginine methyl transferase PRMT5 in restricting the expression of Itch gene by conferring repressive symmetrical H4R3me2 marks on its promoter. Consequently, siRNA-mediated depletion of YY1 or PRMT5 rescued ITCH expression, thereby compromising the levels of Mtb-induced ADRP and CD36 and limiting FM formation during infection. Accumulation of lipids within the host has been implicated as a pro-mycobacterial process that aids in pathogen persistence and dormancy. In line, we found that perturbation of PRMT5 enzyme activity resulted in compromised lipid levels and reduced mycobacterial survival in mouse peritoneal macrophages (ex vivo) and in a therapeutic mouse model of TB infection (in vivo). These findings provide new insights into the role of PRMT5 and YY1 in augmenting mycobacterial pathogenesis. Thus, we posit that our observations could help design novel adjunct therapies and combinatorial drug regimen for effective anti-TB strategies.

Mycobacterium tuberculosis infection leads to the formation of lipid-laden cells (foamy macrophages-FMs) that offer a favorable shelter for its persistence. During infection, we observe a significant reduction in the expression of the E3 ubiquitin ligase, ITCH. This repression allows the sustenance of key lipid accretion molecules (ADRP and CD36), by curbing their proteasomal degradation. Further, we show the repression of ITCH to be dependent on the concerted action of the bifunctional transcription factor, YY1 and the arginine methyl transferase, PRMT5. NOTCH signaling pathway was identified as a master-regulator of YY1 expression. In vitro and in vivo analyses revealed the significance of PRMT5 in regulating FM formation and consequently mycobacterial burden.

Direct Attachment with Erythrocytes Augments Extracellular Growth of Pathogenic Mycobacteria

Pathogenic intracellular mycobacteria, such as Mycobacterium tuberculosis and Mycobacterium avium, which cause lung diseases, can grow in macrophages. Extracellular mycobacteria have been reported in the lungs, blood, and sputum of patients, indicating the involvement of these pathogens in disease progression. Erythrocytes are involved in the symptoms associated with pulmonary mycobacterial diseases, such as bloody sputum and hemoptysis; however, little attention has been paid to the role of erythrocytes in mycobacterial diseases. Herein, we found that Mycobacterium avium subsp. hominissuis (MAH) and Mycobacterium intracellulare colocalized with erythrocytes at the sites of lung infection, inside capillaries and necrotic areas of granulomas, using histopathological examinations. Electron microscopy showed that MAH adhered and entered human erythrocytes when they were cocultured in vitro. MAH adhered to erythrocytes through complement receptor 1 and cell-surface sialo-glycoproteins. Importantly, MAH grew vigorously without causing any pronounced damage to erythrocytes. This erythrocyte-mediated enhancement of MAH growth occurred extracellularly depending on its direct attachment to erythrocytes. In contrast, MAH failed to multiply inside erythrocytes. Similarly, erythrocytes augmented the growth of other pathogenic mycobacteria, such as M. intracellulare and M. tuberculosis. THP-1 cell-derived human macrophages preferentially phagocytosed erythrocytes that were attached to mycobacteria (compared to bacteria alone), suggesting that erythrocyte-attached mycobacteria are an efficient infectious source for macrophages. Our findings provide new insights into the pathogenesis of mycobacterial diseases and offer an alternative and useful strategy for treating mycobacterial disease. IMPORTANCE Pathogenic mycobacteria, such as Mycobacterium tuberculosis, Mycobacterium avium subsp. hominissuis (MAH), and Mycobacterium intracellulare, cause pulmonary infections as intracellular parasites of lung macrophages and epithelial cells. Here, using histopathological examinations we found that MAH and M. intracellulare colocalized with erythrocytes in lung infection sites. Subsequent studies demonstrated that direct interaction with erythrocytes enhances the extracellular proliferation of mycobacteria based on the following results: 1. MAH adhered and invaded human erythrocytes upon coculture in vitro; 2. MAH adhered to erythrocytes through complement receptor 1 and cell-surface sialo-glycoproteins; 3. MAH rapidly proliferated when directly attached to erythrocytes but not within them; 4. other mycobacteria, such as M. intracellulare and M. tuberculosis, also proliferated in the same way as MAH. The finding that pathogenic mycobacteria grow extracellularly in an erythrocyte-dependent manner is of considerable clinical importance for understanding disease progression and latent infection.

Foam Cell Macrophages in Tuberculosis

Mycobacterium tuberculosis infects primarily macrophages in the lungs. Infected macrophages are surrounded by other immune cells in well organised structures called granulomata. As part of the response to TB, a type of macrophage loaded with lipid droplets arises which we call Foam cell macrophages. They are macrophages filled with lipid laden droplets, which are synthesised in response to increased uptake of extracellular lipids, metabolic changes and infection itself. They share the appearance with atherosclerosis foam cells, but their lipid contents and roles are different. In fact, lipid droplets are immune and metabolic organelles with emerging roles in Tuberculosis. Here we discuss lipid droplet and foam cell formation, evidence regarding the inflammatory and immune properties of foam cells in TB, and address gaps in our knowledge to guide further research.

The Tuberculous Granuloma and Preexisting Immunity

Pulmonary granulomas are widely considered the epicenters of the immune response to Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Recent animal studies have revealed factors that either promote or restrict TB immunity within granulomas. These models, however, typically ignore the impact of preexisting immunity on cellular organization and function, an important consideration because most TB probably occurs through reinfection of previously exposed individuals. Human postmortem research from the pre-antibiotic era showed that infections in Mtb-naïve individuals (primary TB) versus those with prior Mtb exposure (postprimary TB) have distinct pathologic features. We review recent animal findings in TB granuloma biology, which largely reflect primary TB. We also discuss our current understanding of postprimary TB lesions, about which much less is known. Many knowledge gaps remain, particularly regarding how preexisting immunity shapes granuloma structure and local immune responses at Mtb infection sites.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Pharmacological and genetic activation of cAMP synthesis disrupts cholesterol utilization in Mycobacterium tuberculosis

There is a growing appreciation for the idea that bacterial utilization of host-derived lipids, including cholesterol, supports Mycobacterium tuberculosis (Mtb) pathogenesis. This has generated interest in identifying novel antibiotics that can disrupt cholesterol utilization by Mtb in vivo. Here we identify a novel small molecule agonist (V-59) of the Mtb adenylyl cyclase Rv1625c, which stimulates 3', 5'-cyclic adenosine monophosphate (cAMP) synthesis and inhibits cholesterol utilization by Mtb. Similarly, using a complementary genetic approach that induces bacterial cAMP synthesis independent of Rv1625c, we demonstrate that inducing cAMP synthesis is sufficient to inhibit cholesterol utilization in Mtb. Although the physiological roles of individual adenylyl cyclase enzymes in Mtb are largely unknown, here we demonstrate that the transmembrane region of Rv1625c is required during cholesterol metabolism. Finally, the pharmacokinetic properties of Rv1625c agonists have been optimized, producing an orally-available Rv1625c agonist that impairs Mtb pathogenesis in infected mice. Collectively, this work demonstrates a role for Rv1625c and cAMP signaling in controlling cholesterol metabolism in Mtb and establishes that cAMP signaling can be pharmacologically manipulated for the development of new antibiotic strategies.

Association of TyG Index with CT Features in Patients with Tuberculosis and Diabetes Mellitus

Background

The purpose of this study was to investigate the association of the triglyceride glucose (TyG) index, a surrogate marker of insulin resistance (IR) with a high sensitivity of 96.5% and a specificity of 85.0% for the diagnosis of IR, with computed tomography (CT) features in patients with tuberculosis and diabetes mellitus.

Methods

A total of 247 subjects were enrolled from July, 2020 to May, 2021. The basic clinical features and CT features were analyzed. In addition, multivariate logistic regression analysis models were employed to evaluate the association of the TyG indicator with CT features in participants.

Results

In the quartile groups of TyG index, air bronchial sign detection rate was 11.7%, 14.5%, 23.2%, and 44.1%; large segmented leafy shadow detection rate was 27.9%, 40.6%, 46.4%, and 66.2%; thick-walled cavity was found in 38.2%, 43.4%, 57.9%, and 69.1%; the rate of multiple cavities was 17.6%, 27.5%, 36.2%, 52.9%; the rate of lymph node enlargement was 22.1%, 17.4%, 28.9%, and 38.2%, respectively. In addition, the positive relation with the TyG index and the prevalence of abnormal CT signs was observed in the fully adjusted model: TyG, per one-unit increase: air bronchial sign: adjusted odds ratio (AOR) 3.92, 95% CI 1–15.35, P = 0.049; multiple cavities: AOR 4.1, 95% CI 1.26–13.31, P = 0.019; thick-walled cavity: AOR 2.89, 95% CI 1.05–8.03, P = 0.041. In quartile of TyG index, compared with patients in quartile 1, the AOR (95% CI) values for air bronchial sign in quartile 4 was 8.1 (1.7–44), p = 0.011; multiple cavities was 7.1 (1.7–32), p = 0.008; thick-walled cavity was 7.8 (1.9–34.7), p = 0.005.

Conclusion

The present study showed that an increased TyG index was positively related to the severity of patients with T2DM-PTB.

Early Lesion of Post-Primary Tuberculosis: Subclinical Driver of Disease and Target for Vaccines and Host-Directed Therapies

The characteristic lesion of primary tuberculosis is the granuloma as is widely studied in human tissues and animal models. Post-primary tuberculosis is different. It develops only in human lungs and begins as a prolonged subclinical obstructive lobular pneumonia that slowly accumulates mycobacterial antigens and host lipids in alveolar macrophages with nearby highly sensitized T cells. After several months, the lesions undergo necrosis to produce a mass of caseous pneumonia large enough to fragment and be coughed out to produce a cavity or be retained as the focus of a post-primary granuloma. Bacteria grow massively on the cavity wall where they can be coughed out to infect new people. Here we extend these findings with the demonstration of secreted mycobacterial antigens, but not acid fast bacilli (AFB) of M. tuberculosis in the cytoplasm of ciliated bronchiolar epithelium and alveolar pneumocytes in association with elements of the programmed death ligand 1 (PD-L1), cyclo-oxygenase (COX)-2, and fatty acid synthase (FAS) pathways in the early lesion. This suggests that M. tuberculosis uses its secreted antigens to coordinate prolonged subclinical development of the early lesions in preparation for a necrotizing reaction sufficient to produce a cavity, post-primary granulomas, and fibrocaseous disease.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb's development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound's effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound's development.

Understanding Metabolic Regulation Between Host and Pathogens: New Opportunities for the Development of Improved Therapeutic Strategies Against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) causes chronic granulomatous lung disease in humans. Recently, novel strategies such as host-directed therapeutics and adjunctive therapies that enhance the effect of existing antibiotics have emerged to better control Mtb infection. Recent advances in understanding the metabolic interplay between host immune cells and pathogens have provided new insights into how their interactions ultimately influence disease outcomes and antibiotic-treatment efficacy. In this review, we describe how metabolic cascades in immune environments and relevant metabolites produced from immune cells during Mtb infection play critical roles in the progression of diseases and induction of anti-Mtb protective immunity. In addition, we introduce how metabolic alterations in Mtb itself can lead to the development of persister cells that are resistant to host immunity and can eventually evade antibiotic attacks. Further understanding of the metabolic link between host cells and Mtb may contribute to not only the prevention of Mtb persister development but also the optimization of host anti-Mtb immunity together with enhanced efficacy of existing antibiotics. Overall, this review highlights novel approaches to improve and develop host-mediated therapeutic strategies against Mtb infection by restoring and switching pathogen-favoring metabolic conditions with host-favoring conditions.

Initiation of Post-Primary Tuberculosis of the Lungs: Exploring the Secret Role of Bone Marrow Derived Stem Cells

Mycobacterium tuberculosis (Mtb), the causative organism of pulmonary tuberculosis (PTB) now infects more than half of the world population. The efficient transmission strategy of the pathogen includes first remaining dormant inside the infected host, next undergoing reactivation to cause post-primary tuberculosis of the lungs (PPTBL) and then transmit via aerosol to the community. In this review, we are exploring recent findings on the role of bone marrow (BM) stem cell niche in Mtb dormancy and reactivation that may underlie the mechanisms of PPTBL development. We suggest that pathogen's interaction with the stem cell niche may be relevant in potential inflammation induced PPTBL reactivation, which need significant research attention for the future development of novel preventive and therapeutic strategies for PPTBL, especially in a post COVID-19 pandemic world. Finally, we put forward potential animal models to study the stem cell basis of Mtb dormancy and reactivation.

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.

Fatty acid oxidation of alternatively activated macrophages prevents foam cell formation, but Mycobacterium tuberculosis counteracts this process via HIF-1α activation

The ability of Mycobacterium tuberculosis (Mtb) to persist inside host cells relies on metabolic adaptation, like the accumulation of lipid bodies (LBs) in the so-called foamy macrophages (FM), which are favorable to Mtb. The activation state of macrophages is tightly associated to different metabolic pathways, such as lipid metabolism, but whether differentiation towards FM differs between the macrophage activation profiles remains unclear. Here, we aimed to elucidate whether distinct macrophage activation states exposed to a tuberculosis-associated microenvironment or directly infected with Mtb can form FM. We showed that the triggering of signal transducer and activator of transcription 6 (STAT6) in interleukin (IL)-4-activated human macrophages (M(IL-4)) prevents FM formation induced by pleural effusion from patients with tuberculosis. In these cells, LBs are disrupted by lipolysis, and the released fatty acids enter the β-oxidation (FAO) pathway fueling the generation of ATP in mitochondria. Accordingly, murine alveolar macrophages, which exhibit a predominant FAO metabolism, are less prone to become FM than bone marrow derived-macrophages. Interestingly, direct infection of M(IL-4) macrophages with Mtb results in the establishment of aerobic glycolytic pathway and FM formation, which could be prevented by FAO activation or inhibition of the hypoxia-inducible factor 1-alpha (HIF-1α)-induced glycolytic pathway. In conclusion, our results demonstrate that Mtb has a remarkable capacity to induce FM formation through the rewiring of metabolic pathways in human macrophages, including the STAT6-driven alternatively activated program. This study provides key insights into macrophage metabolism and pathogen subversion strategies.

Foam Cells Control Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) infects macrophages and macrophage-derived foam cells, a hallmark of granulomata in tuberculous lesions. We analyzed the effects of lipid accumulation in human primary macrophages and quantified strong triglyceride and phospholipid remodeling which depended on the dietary fatty acid used for the assay. The enrichment of >70% in triglyceride and phospholipids can alter cell membrane properties, signaling and phagocytosis in macrophages. In conventional macrophage cultures, cells are heterogeneous, small or large macrophages. In foam cells, a third population of 30% of cells with increased granularity can be detected. We found that foam cell formation is heterogenous and that lipid accumulation and foam cell formation reduces the phagocytosis of Mtb. Under the conditions tested, cell death was highly prevalent in macrophages, whereas foam cells were largely protected from this effect. Foam cells also supported slower Mtb replication, yet this had no discernible impact on the intracellular efficacy of four different antitubercular drugs. Foam cell formation had a significant impact in the inflammatory potential of the cells. TNF-α, IL-1β, and prototypical chemokines were increased. The ratio of inflammatory IL-1β, TNF-α, and IL-6 vs. anti-inflammatory IL-10 was significantly higher in response to Mtb vs. LPS, and was increased in foam cells compared to macrophages, suggestive of increased pro-inflammatory properties. Cytokine production correlated with NF-κB activation in our models. We conclude that foam cell formation reduces the host cell avidity for, and phagocytosis of, Mtb while protecting the cells from death. This protective effect is associated with enhanced inflammatory potential of foam cells and restricted intracellular growth of Mtb.

The Echo of Pulmonary Tuberculosis: Mechanisms of Clinical Symptoms and Other Disease-Induced Systemic Complications

Clinical symptoms of active tuberculosis (TB) can range from a simple cough to more severe reactions, such as irreversible lung damage and, eventually, death, depending on disease progression. In addition to its clinical presentation, TB has been associated with several other disease-induced systemic complications, such as hyponatremia and glucose intolerance. Here, we provide an overview of the known, although ill-described, underlying biochemical mechanisms responsible for the clinical and systemic presentations associated with this disease and discuss novel hypotheses recently generated by various omics technologies. This summative update can assist clinicians to improve the tentative diagnosis of TB based on a patient's clinical presentation and aid in the development of improved treatment protocols specifically aimed at restoring the disease-induced imbalance for overall homeostasis while simultaneously eradicating the pathogen. Furthermore, future applications of this knowledge could be applied to personalized diagnostic and therapeutic options, bettering the treatment outcome and quality of life of TB patients.

Caseum: a Niche for Mycobacterium tuberculosis Drug-Tolerant Persisters

Caseum, the central necrotic material of tuberculous lesions, is a reservoir of drug-recalcitrant persisting mycobacteria. Caseum is found in closed nodules and in open cavities connecting with an airway. Several commonly accepted characteristics of caseum were established during the preantibiotic era, when autopsies of deceased tuberculosis (TB) patients were common but methodologies were limited. These pioneering studies generated concepts such as acidic pH, low oxygen tension, and paucity of nutrients being the drivers of nonreplication and persistence in caseum. Here we review widely accepted beliefs about the caseum-specific stress factors thought to trigger the shift of Mycobacterium tuberculosis to drug tolerance. Our current state of knowledge reveals that M. tuberculosis is faced with a lipid-rich diet rather than nutrient deprivation in caseum. Variable caseum pH is seen across lesions, possibly transiently acidic in young lesions but overall near neutral in most mature lesions. Oxygen tension is low in the avascular caseum of closed nodules and high at the cavity surface, and a gradient of decreasing oxygen tension likely forms toward the cavity wall. Since caseum is largely made of infected and necrotized macrophages filled with lipid droplets, the microenvironmental conditions encountered by M. tuberculosis in foamy macrophages and in caseum bear many similarities. While there remain a few knowledge gaps, these findings constitute a solid starting point to develop high-throughput drug discovery assays that combine the right balance of oxygen tension, pH, lipid abundance, and lipid species to model the profound drug tolerance of M. tuberculosis in caseum.

Lineage-specific differences in lipid metabolism and its impact on clinical strains of Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) is the causative agent of TB and its incidences has been on the rise since 1993. Lipid metabolism is an imperative metabolic process, which grants M. tb the ability to utilize host-derived lipids as a secondary source of nutrition during infection. In addition to degrading host lipids, M. tb is proficient at using lipids, such as cholesterol, to facilitate its entry into macrophages. Mycolic acids, constituents of the mycobacterial cell wall, offer protection and aid in persistence of the bacterium. These are effectively synthesized using a complex fatty acid synthase system. Many pathogenesis studies have reported differences in lipid-metabolism of clinical strains of M. tb that belongs to diverse lineages of the Mycobacterium tuberculosis complex (MTBC). East-Asian and Euro-American lineages possess "unique" cell wall-associated lipids compared to the less transmissible Ethiopian lineage, which may offer these lineages a competitive advantage. Therefore, it is crucial to comprehend the complexities among the MTBC lineages with lipid metabolism and their impact on virulence, transmissibility and pathogenesis. Thus, this review provides an insight into lipid metabolism in various lineages of the MTBC and their impact on virulence and persistence during infection, as this may provide critical insight into developing novel therapeutics to combat TB.

Proteomic Profiling Reveals the Architecture of Granulomatous Lesions Caused by Tuberculosis and Mycobacterium avium Complex Lung Disease

Tuberculosis (TB) and Mycobacterium avium complex lung disease (MAC-LD) are both characterized pathologically by granuloma lesions, which are typically composed of a necrotic caseum at the center surrounded by fibrotic cells and lymphocytes. Although the histological characterization of TB and MAC-LD granulomas has been well-documented, their molecular signatures have not been fully evaluated. In this research we applied mass spectrometry-based proteomics combined with laser microdissection to investigate the unique protein markers in human mycobacterial granulomatous lesions. Comparing the protein abundance between caseous and cellular sub-compartments of mycobacterial granulomas, we found distinct differences. Proteins involved in cellular metabolism in transcription and translation were abundant in cellular regions, while in caseous regions proteins related to antimicrobial response accumulated. To investigate the determinants of their heterogeneity, we compared the protein abundance in caseous regions between TB and MAC-LD granulomas. We found that several proteins were significantly abundant in the MAC-LD caseum of which proteomic profiles were different from those of the TB caseum. Immunohistochemistry demonstrated that one of these proteins, Angiogenin, specifically localized to the caseous regions of selected MAC-LD granulomas. We also detected peptides derived from mycobacterial proteins in the granulomas of both diseases. This study provides new insights into the architecture of granulomatous lesions in TB and MAC-LD.

[Immunological aspects of tuberculosis pathogenesis]

The morphological aspects of TB pathogenesis are well described in the publications. Much is also known about the main stages of development and formation of specific adaptive immunity. However, from our point of view, not enough attention is being paid to the involvement of the immune system in the pathogenesis of clinically relevant TB abnormalities, as well as various forms of the disease. Nevertheless, there is no doubt that the variety of clinical manifestations of any disease associated with the penetration of a foreign agent into the body, and Mycobacterium tuberculosis (MTB) in particular, is due to the collective interaction of the infectious agent and the individual response of the macroorganism to this infectious agent. The mosaic of such interactions usually imposes its own adjustments on the development of different forms of the process, its speed and direction, as well as the outcomes. Certainly, the response of a macroorganism to MTB is an integral part of pathogenesis and consists of many general components including the responses associated with the mechanisms of natural and acquired immunity. Intensity of these reactions depends on the characteristics of an agent (MTB) and a macroorganism. For the development of TB disease, massiveness of TB infection, dose and duration of MTB exposure to the human body, as well as virulence of MTB and the level of body's protection during the exposure play a very important role. TB pathogenesis is somewhat different in primary MTB infection and re - infection. With primary infection, 88-90% of individuals do not have clinical manifestations, and only the tuberculin skin test conversion signals the onset of infection. In some cases, without any use of anti-TB drugs limited abnormalities may result in spontaneous cure with the minimal residual changes in the lungs, intrathoracic lymph nodes and tissues of other organs, often in the form of calcifications and limited areas of fibrosis in more advanced cases. Only 10-12% of newly infected individuals develop TB with severe clinical manifestations requiring TB therapy. The absence of clinical manifestations of primary TB infection can be explained by a high level of natural resistance of the human body to tuberculosis, and sometimes can be an effect of acquired protection due to BCG vaccination. This review attempts to discuss the role of immune mechanisms in the pathogenesis both at the beginning of disease development, and in the process of its various manifestations. Issues of genetically determined resistance or susceptibility to TB are not being covered in detail in this manuscript.

Impact of the Polymorphism of the PACRG and CD80 Genes on the Development of the Different Stages of Tuberculosis Infection

BACKGROUND

Tuberculosis (TB) is one of the most significant health-care problems worldwide. The host's genetics play an important role in the development of TB in humans. The disease progresses through several stages, each of which can be under the control of different genes. The precise genes influencing the different stages of the disease are not yet identified. The aim of the current study was to determine the associations between primary and secondary TB and the polymorphisms of novel candidate genes for TB susceptibility, namely CD79A, HCST, CXCR4, CD4, CD80, CP, PACRG, and CD69.

METHODS

A total of 357 patients with TB (130 cases with primary TB and 227 cases with secondary TB) from the Siberian region of Russia as well as 445 healthy controls were studied. The study was performed at the Research Institute of Medical Genetics, Tomsk NRMC, Tomsk, Russia, between July 2015 and November 2016. Genotyping was carried out using MALDI-TOF mass spectrometry and PCR-RFLP. The associations between the single-nucleotide polymorphisms and TB were assessed using logistic regression adjusting for covariates (age and gender). Multiple testing was addressed via the experiment-wise permutation approach. The statistical significance threshold was a P value less than 0.05 for the permutation P values. The analyses were done in R 3.2 statistical software.

RESULTS

An association was established between the rs1880661 variant of the CD80 gene and secondary TB and the rs10945890 variant of the PACRG gene and both primary and secondary TB. However, the same allele of PACRG appeared to be both a risk factor for reactivation (secondary TB) and a protector against primary infection.

CONCLUSION

The results suggested that the CD80 and PACRG genes were associated with susceptibility to different forms of TB infection in the Russian population.

The pathogenesis of post-primary tuberculosis. A game changer for vaccine development

A vaccine that prevents transmission of infection is urgently needed in the fight against tuberculosis (TB). Results of clinical trials have been disappointing. Major problems include lack of biomarkers and understanding of the mechanisms of disease and protection. A more fundamental problem is that the scientific community seldom recognizes that primary and post-primary TB are distinct disease entities. Nearly all vaccine candidates have been designed and tested in models of primary TB, while transmission of infection is mediated by post-primary TB. Post-primary TB is seldom studied because no animal develop complete symptoms of the disease as it exists in humans. Nevertheless, mice, guinea pigs and rabbits all develop infections that at certain points appear to be models of human post-primary TB. Slowly progressive pulmonary TB in immunocompetent mice is an example. It is characterized by an alveolitis with infected foamy macrophages that have multiple characteristics of the human disease. We demonstrated that inclusion of an immune modulating agent, lactoferrin, with a BCG vaccine in this model induced a sustained reduction in lung pathology, but not numbers of organisms in tissue. Since the animals die of expanding pathology, this demonstrates the feasibility of using selected animal models for studies of vaccines against post-primary TB.

Modeling Infectious Diseases in Mice with a "Humanized" Immune System

Human immune system (HIS) mice are created by transplanting human immune cells or their progenitor cells into highly immunodeficient recipient mouse hosts, thereby "humanizing" their immune systems. Over past decades, the field of HIS mice has evolved rapidly, as modifications of existing immunodeficient mouse strains have been developed, resulting in increasing levels of human tissue engraftment as humanization is optimized. Current HIS mouse models not only permit elevated levels of human cell engraftment but also demonstrate graft stability. As such, HIS mice are being extensively used to study the human innate and adaptive immune response against microbial infections in vivo. Compared to nonhumanized animal models, which are frequently infected with surrogate or adapted microbes, the HIS mouse models allow the analysis of interactions between human immune cells and bona fide pathogenic microbes, making them a more clinically relevant model. This article reviews the development of HIS mice and covers the different strategies used to humanize mice, as well as discussing the use of HIS mice for studying bacterial infections that cause human disease.

The genetic requirements of fatty acid import by Mycobacterium tuberculosis within macrophages

Mycobacterium tuberculosis (Mtb) imports and metabolizes fatty acids to maintain infection within human macrophages. Although this is a well-established paradigm, the bacterial factors required for fatty acid import are poorly understood. Previously, we found that LucA and Mce1 are required for fatty acid import in Mtb (Nazarova et al., 2017). Here, we identified additional Mtb mutants that have a reduced ability to import a fluorescent fatty acid substrate during infection within macrophages. This screen identified the novel genes as rv2799 and rv0966c as be necessary for fatty acid import and confirmed the central role for Rv3723/LucA and putative components of the Mce1 fatty acid transporter (Rv0200/OmamB, Rv0172/Mce1D, and Rv0655/MceG) in this process.

A new model for chronic and reactivation tuberculosis: Infection with genetically attenuated Mycobacterium tuberculosis in mice with polar susceptibility

TB infection in mice develops relatively rapidly which interferes with experimental dissection of immune responses and lung pathology features that differ between genetically susceptible and resistant hosts. Earlier we have shown that the M. tuberculosis strain lacking four of five Rpf genes (ΔACDE) is seriously attenuated for growth in vivo. Using this strain, we assessed key parameters of lung pathology, immune and inflammatory responses in chronic and reactivation TB infections in highly susceptible I/St and more resistant B6 mice. ΔACDE mycobacteria progressively multiplied only in I/St lungs, whilst in B6 lung CFU counts decreased with time. Condensed TB foci apeared in B6 lungs at week 4 of infection, whilst in I/St their formation was delayed. At the late phase of infection, in I/St lungs TB foci fused resulting in extensive pneumonia, whereas in B6 lungs pathology was limited to condensed foci. Macrophage and neutrophil populations characteristically differed between I/St and B6 mice at early and late stages of infection: more neutrophils accumulated in I/St and more macrophages in B6 lungs. The expression level of chemokine genes involved in neutrophil influx was higher in I/St compared to B6 lungs. B6 lung cells produced more IFN-γ, IL-6 and IL-11 at the early and late phases of infection. Overall, using a new mouse model of slow TB progression, we demonstrate two important features of ineffective infection control underlined by shifts in lung inflammation: delay in early granuloma formation and fusion of granulomas resulting in consolidated pneumonia late in the infectious course.

The Pathogenesis of Tuberculosis: The Early Infiltrate of Post-primary (Adult Pulmonary) Tuberculosis: A Distinct Disease Entity

It has long been recognized that tuberculosis (TB) induces both protective and tissue damaging immune responses. This paper reviews nearly two centuries of evidence that protection and tissue damage are mediated by separate disease entities in humans. Primary TB mediates protective immunity to disseminated infection while post-primary TB causes tissue damage that results in formation of cavities. Both are necessary for continued survival of Mycobacterium tuberculosis (MTB). Primary TB has been extensively studied in humans and animals. Post-primary TB, in contrast, is seldom recognized or studied. It begins as an asymptomatic early infiltrate that may resolve or progress by bronchogenic spread to caseous pneumonia that either fragments to produce cavities or is retained to produce post-primary granulomas and fibrocaseous disease. Primary and post-primary TB differ in typical age of onset, histopathology, organ distribution, x-ray appearance, genetic predisposition, immune status of the host, clinical course and susceptibility to protection by BCG. MTB is a highly successful human parasite because it produces both primary and post-primary TB as distinct disease entities in humans. No animal reproduces this sequence of lesions. Recognition of these facts immediately suggests plausible solutions, animal models and testable hypotheses to otherwise inaccessible questions of the immunity and pathogenesis of TB.

Delineating the Physiological Roles of the PE and Catalytic Domains of LipY in Lipid Consumption in Mycobacterium-Infected Foamy Macrophages

Within tuberculous granulomas, a subpopulation of Mycobacterium tuberculosis resides inside foamy macrophages (FM) that contain abundant cytoplasmic lipid bodies (LB) filled with triacylglycerol (TAG). Upon fusion of LB with M. tuberculosis-containing phagosomes, TAG is hydrolyzed and reprocessed by the bacteria into their own lipids, which accumulate as intracytosolic lipid inclusions (ILI). This phenomenon is driven by many mycobacterial lipases, among which LipY participates in the hydrolysis of host and bacterial TAG. However, the functional contribution of LipY's PE domain to TAG hydrolysis remains unclear. Here, enzymatic studies were performed to compare the lipolytic activities of recombinant LipY and its truncated variant lacking the N-terminal PE domain, LipY(ΔPE). Complementarily, an FM model was used where bone marrow-derived mouse macrophages were infected with M. bovis BCG strains either overexpressing LipY or LipY(ΔPE) or carrying a lipY deletion mutation prior to being exposed to TAG-rich very-low-density lipoprotein (VLDL). Results indicate that truncation of the PE domain correlates with increased TAG hydrolase activity. Quantitative electron microscopy analyses showed that (i) in the presence of lipase inhibitors, large ILI (ILI⁺³) were not formed because of an absence of LB due to inhibition of VLDL-TAG hydrolysis or inhibition of LB-neutral lipid hydrolysis by mycobacterial lipases, (ii) ILI⁺³ profiles in the strain overexpressing LipY(ΔPE) were reduced, and (iii) the number of ILI⁺³ profiles in the ΔlipY mutant was reduced by 50%. Overall, these results delineate the role of LipY and its PE domain in host and mycobacterial lipid consumption and show that additional mycobacterial lipases take part in these processes.

Ferritin H Deficiency in Myeloid Compartments Dysregulates Host Energy Metabolism and Increases Susceptibility to Mycobacterium tuberculosis Infection

Iron is an essential factor for the growth and virulence of Mycobacterium tuberculosis (Mtb). However, little is known about the mechanisms by which the host controls iron availability during infection. Since ferritin heavy chain (FtH) is a major intracellular source of reserve iron in the host, we hypothesized that the lack of FtH would cause dysregulated iron homeostasis to exacerbate TB disease. Therefore, we used knockout mice lacking FtH in myeloid-derived cell populations to study Mtb disease progression. We found that FtH plays a critical role in protecting mice against Mtb, as evidenced by increased organ burden, extrapulmonary dissemination, and decreased survival in Fth-/- mice. Flow cytometry analysis showed that reduced levels of FtH contribute to an excessive inflammatory response to exacerbate disease. Extracellular flux analysis showed that FtH is essential for maintaining bioenergetic homeostasis through oxidative phosphorylation. In support of these findings, RNAseq and mass spectrometry analyses demonstrated an essential role for FtH in mitochondrial function and maintenance of central intermediary metabolism in vivo. Further, we show that FtH deficiency leads to iron dysregulation through the hepcidin-ferroportin axis during infection. To assess the clinical significance of our animal studies, we performed a clinicopathological analysis of iron distribution within human TB lung tissue and showed that Mtb severely disrupts iron homeostasis in distinct microanatomic locations of the human lung. We identified hemorrhage as a major source of metabolically inert iron deposition. Importantly, we observed increased iron levels in human TB lung tissue compared to healthy tissue. Overall, these findings advance our understanding of the link between iron-dependent energy metabolism and immunity and provide new insight into iron distribution within the spectrum of human pulmonary TB. These metabolic mechanisms could serve as the foundation for novel host-directed strategies.

De Novo Fatty Acid Synthesis During Mycobacterial Infection Is a Prerequisite for the Function of Highly Proliferative T Cells, But Not for Dendritic Cells or Macrophages

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis, is able to efficiently manipulate the host immune system establishing chronic infection, yet the underlying mechanisms of immune evasion are not fully understood. Evidence suggests that this pathogen interferes with host cell lipid metabolism to ensure its persistence. Fatty acid metabolism is regulated by acetyl-CoA carboxylase (ACC) 1 and 2; both isoforms catalyze the conversion of acetyl-CoA into malonyl-CoA, but have distinct roles. ACC1 is located in the cytosol, where it regulates de novo fatty acid synthesis (FAS), while ACC2 is associated with the outer mitochondrial membrane, regulating fatty acid oxidation (FAO). In macrophages, mycobacteria induce metabolic changes that lead to the cytosolic accumulation of lipids. This reprogramming impairs macrophage activation and contributes to chronic infection. In dendritic cells (DCs), FAS has been suggested to underlie optimal cytokine production and antigen presentation, but little is known about the metabolic changes occurring in DCs upon mycobacterial infection and how they affect the outcome of the immune response. We therefore determined the role of fatty acid metabolism in myeloid cells and T cells during Mycobacterium bovis BCG or Mtb infection, using novel genetic mouse models that allow cell-specific deletion of ACC1 and ACC2 in DCs, macrophages, or T cells. Our results demonstrate that de novo FAS is induced in DCs and macrophages upon M. bovis BCG infection. However, ACC1 expression in DCs and macrophages is not required to control mycobacteria. Similarly, absence of ACC2 did not influence the ability of DCs and macrophages to cope with infection. Furthermore, deletion of ACC1 in DCs or macrophages had no effect on systemic pro-inflammatory cytokine production or T cell priming, suggesting that FAS is dispensable for an intact innate response against mycobacteria. In contrast, mice with a deletion of ACC1 specifically in T cells fail to generate efficient T helper 1 responses and succumb early to Mtb infection. In summary, our results reveal ACC1-dependent FAS as a crucial mechanism in T cells, but not DCs or macrophages, to fight against mycobacterial infection.

Formation of Foamy Macrophages by Tuberculous Pleural Effusions Is Triggered by the Interleukin-10/Signal Transducer and Activator of Transcription 3 Axis through ACAT Upregulation

The ability of Mycobacterium tuberculosis (Mtb) to persist in its human host relies on numerous immune evasion strategies, such as the deregulation of the lipid metabolism leading to the formation of foamy macrophages (FM). Yet, the specific host factors leading to the foamy phenotype of Mtb-infected macrophages remain unknown. Herein, we aimed to address whether host cytokines contribute to FM formation in the context of Mtb infection. Our approach is based on the use of an acellular fraction of tuberculous pleural effusions (TB-PE) as a physiological source of local factors released during Mtb infection. We found that TB-PE induced FM differentiation as observed by the increase in lipid bodies, intracellular cholesterol, and expression of the scavenger receptor CD36, as well as the enzyme acyl CoA:cholesterol acyl transferase (ACAT). Importantly, interleukin-10 (IL-10) depletion from TB-PE prevented the augmentation of all these parameters. Moreover, we observed a positive correlation between the levels of IL-10 and the number of lipid-laden CD14⁺ cells among the pleural cells in TB patients, demonstrating that FM differentiation occurs within the pleural environment. Downstream of IL-10 signaling, we noticed that the transcription factor signal transducer and activator of transcription 3 was activated by TB-PE, and its chemical inhibition prevented the accumulation of lipid bodies and ACAT expression in macrophages. In terms of the host immune response, TB-PE-treated macrophages displayed immunosuppressive properties and bore higher bacillary loads. Finally, we confirmed our results using bone marrow-derived macrophage from IL-10^-/- mice demonstrating that IL-10 deficiency partially prevented foamy phenotype induction after Mtb lipids exposure. In conclusion, our results evidence a role of IL-10 in promoting the differentiation of FM in the context of Mtb infection, contributing to our understanding of how alterations of the host metabolic factors may favor pathogen persistence.

Tuberculosis and lung damage: from epidemiology to pathophysiology

A past history of pulmonary tuberculosis (TB) is a risk factor for long-term respiratory impairment. Post-TB lung dysfunction often goes unrecognised, despite its relatively high prevalence and its association with reduced quality of life. Importantly, specific host and pathogen factors causing lung impairment remain unclear. Host immune responses probably play a dominant role in lung damage, as excessive inflammation and elevated expression of lung matrix-degrading proteases are common during TB. Variability in host genes that modulate these immune responses may determine the severity of lung impairment, but this hypothesis remains largely untested. In this review, we provide an overview of the epidemiological literature on post-TB lung impairment and link it to data on the pathogenesis of lung injury from the perspective of dysregulated immune responses and immunogenetics.

Host factors driving lung injury in TB likely contribute to variable patterns of pulmonary impairment after TBhttp://ow.ly/a3of30hBsxB

The in vivo evidence for regulated necrosis

Necrosis is a hallmark of several widespread diseases or their direct complications. In the past decade, we learned that necrosis can be a regulated process that is potentially druggable. RIPK3- and MLKL-mediated necroptosis represents by far the best studied pathway of regulated necrosis. During necroptosis, the release of damage-associated molecular patterns (DAMPs) drives a phenomenon referred to as necroinflammation, a common consequence of necrosis. However, most studies of regulated necrosis investigated cell lines in vitro in a cell autonomous manner, which represents a non-physiological situation. Conclusions based on such work might not necessarily be transferrable to disease states in which synchronized, non-cell autonomous effects occur. Here, we summarize the current knowledge of the pathophysiological relevance of necroptosis in vivo, and in light of this understanding, we reassess the morphological classification of necrosis that is generally used by pathologists. Along these lines, we discuss the paucity of data implicating necroptosis in human disease. Finally, the in vivo relevance of non-necroptotic forms of necrosis, such as ferroptosis, is addressed.

Pathogenesis and Animal Models of Post-Primary (Bronchogenic) Tuberculosis, A Review

Primary and post-primary tuberculosis (TB) are different diseases caused by the same organism. Primary TB produces systemic immunity. Post-primary TB produces cavities to support massive proliferation of organisms for transmission of infection to new hosts from a person with sufficient immunity to prevent systemic infection. Post-primary, also known as bronchogenic, TB begins in humans as asymptomatic bronchial spread of obstructive lobular pneumonia, not as expanding granulomas. Most lesions regress spontaneously. However, some undergo caseation necrosis that is coughed out through the necrotic bronchi to form cavities. Caseous pneumonia that is not expelled through the bronchi is retained to become the focus of fibrocaseous disease. No animal reproduces this entire process. However, it appears that many mammals utilize similar mechanisms, but fail to coordinate them as do humans. Understanding this makes it possible to use human tuberculous lung sections to guide manipulation of animals to produce models of particular human lesions. For example, slowly progressive and reactivation TB in mice resemble developing human bronchogenic TB. Similarly, bronchogenic TB and cavities resembling those in humans can be induced by bronchial infection of sensitized rabbits. Granulomas in guinea pigs have characteristics of both primary and post primary TB. Mice can be induced to produce a spectrum of human like caseating granulomas. There is evidence that primates can develop bronchogenic TB. We are optimistic that such models developed by coordinated study of human and animal tissues can be used with modern technologies to finally address long-standing questions about host/parasite relationships in TB, and support development of targeted therapeutics and vaccines.

Ex vivo expansion of alveolar macrophages with Mycobacterium tuberculosis from the resected lungs of patients with pulmonary tuberculosis

Tuberculosis (TB), with the Mycobacterium tuberculosis (Mtb) as the causative agent, remains to be a serious world health problem. Traditional methods used for the study of Mtb in the lungs of TB patients do not provide information about the number and functional status of Mtb, especially if Mtb are located in alveolar macrophages. We have developed a technique to produce ex vivo cultures of cells from different parts of lung tissues surgically removed from patients with pulmonary TB and compared data on the number of cells with Mtb inferred by the proposed technique to the results of bacteriological and histological analyses used for examination of the resected lungs. The ex vivo cultures of cells obtained from the resected lungs of all patients were largely composed of CD14-positive alveolar macrophages, foamy or not, with or without Mtb. Lymphocytes, fibroblasts, neutrophils, and multinucleate Langhans giant cells were also observed. We found alveolar macrophages with Mtb in the ex vivo cultures of cells from the resected lungs of even those TB patients, whose sputum smears and lung tissues did not contain acid-fast Mtb or reveal growing Mtb colonies on dense medium. The detection of alveolar macrophages with Mtb in ex vivo culture as soon as 16-18 h after isolation of cells from the resected lungs of all TB patients suggests that the technique proposed for assessing the level of infection in alveolar macrophages of TB patients has higher sensitivity than do prolonged bacteriological or pathomorphological methods. The proposed technique allowed us to rapidly (in two days after surgery) determine the level of infection with Mtb in the cells of the resected lungs of TB patients and, by the presence or absence of Mtb colonies, including those with cording morphology, the functional status of the TB agent at the time of surgery.

Lung Infections

A review of pulmonary infections of all types with diagnostic and morphological features.

Hemostasis and Lipoprotein Indices Signify Exacerbated Lung Injury in TB With Diabetes Comorbidity

BACKGROUND

Exacerbated immunopathology is a frequent consequence of TB that is complicated by diabetes mellitus (DM); however, the underlying mechanisms are still poorly defined.

METHODS

In the two groups of age- and sex-matched patients with TB and DM (DM-TB) and with TB and without DM, we microscopically evaluated the areas of caseous necrosis and graded the extent of perinecrotic fibrosis in lung biopsies from the sputum smear-negative (SN) patients. We scored acid-fast bacilli in sputum smear-positive (SP) patients and compiled CT scan data from both the SN and SP patients. We compared inflammatory biomarkers and routine hematologic and biochemical parameters. Binary logistic regression analyses were applied to define the indices associated with the extent of lung injury.

RESULTS

Enlarged caseous necrotic areas with exacerbated fibrotic encapsulations were found in SN patients with DM-TB, consistent with the higher ratio of thick-walled cavities and more bacilli in the sputum from SP patients with DM-TB. Larger necrotic foci were detected in men compared with women within the SN TB groups. Significantly higher fibrinogen and lower high-density lipoprotein cholesterol (HDL-C) were observed in SN patients with DM-TB. Regression analyses revealed that diabetes, activation of the coagulation pathway (shown by increased platelet distribution width, decreased mean platelet volume, and shortened prothrombin time), and dyslipidemia (shown by decreased low-density lipoprotein cholesterol, HDL-C, and apolipoprotein A) are risk factors for severe lung lesions in both SN and SP patients with TB.

CONCLUSIONS

Hemostasis and dyslipidemia are associated with granuloma necrosis and fibroplasia leading to exacerbated lung damage in TB, especially in patients with DM-TB.

Microbial Offense vs Host Defense: Who Controls the TB Granuloma?

The granuloma is the hallmark of tuberculosis and simultaneously signifies acquisition of an infection and induction of a host immune response. But who benefits more from the development of the granuloma, the host or the pathogen? Is microbe or man dictating disease course and progression? Mycobacterial diseases affect humans and animals alike, and the concepts presented in this review reflect host-pathogen interactions that influence not only mycobacterial granulomas in humans and animals but also other infectious granulomatous diseases that are encountered in veterinary medicine. Current dogma supports that an organized granuloma is a mark of an adequate and “restrictive” host immune response. However, the formation of a granuloma also provides a niche for the maturation, growth, and persistence of numerous infectious agents, and these pathogens devote some portion of their genetic machinery to ensuring these structures’ form. An understanding of pathogens’ contributions to granuloma formation can aid the development of host-directed therapies and other antimicrobial and antiparasitic therapies that can tip this balance in favor of a restrictive host response and elimination—not just containment—of the infectious organism. This review discusses animal models that have aided our understanding of pathogens’ contribution to the host response and how mycobacterial virulence genes direct host pathology in ways that may aid disease transmission and/or persistence in the form of latent infection.

Animal Models of Tuberculosis: An Overview

This article provides an overview of the animal models currently used in tuberculosis research, both for understanding the basic science of the disease process and also for practical issues such as testing new vaccine candidates and evaluating the activity of potential new drugs. Animals range in size, from zebrafish to cattle, and in degrees of similarity to the human disease from both an immunological and pathologic perspective. These models have provided a great wealth of information (impossible to obtain simply from observing infected humans), but we emphasize here that one must use care in interpreting or applying this information, and indeed the true art of animal modeling is in deciding what is pertinent information and what might not be. These ideas are discussed in the context of current approaches in vaccine and drug development, including a discussion of certain limitations the field is currently facing in such studies.

An alert of Mycobacterium tuberculosis infection of rhesus macaques in a wild zoo in China

Mycobacterium tuberculosis, the pathogen that causes tuberculosis (TB), is becoming increasingly recognized as an important cause of fatal chronic illnesses in China. In this study, we report an infectious disease among 84 rhesus macaques at a Chinese zoo. Their clinical signs and symptoms were very similar with the manifestations of TB in humans. To determine the potential pathogens of this outbreak, many methods were used. First, tuberculin skin tests showed that none of the monkeys displayed significant skin reactions. Subsequently, the sera were tested for specific antibody IgG; 29 (34.5%) and 39 (46.4%) blood samples tested positive by TB-IgG and TB-DOT, respectively. Radiographic examination showed characteristic imageology changes in 14 (16.7%) monkeys. One individual determined as positive by the above three methods was euthanized, and histopathological analysis demonstrated typical granulomas and caseous necrosis in the lung, liver, spleen, and intestine. Furthermore, the pathogenic mycobacteria were isolated from lung lobe, cultured on acidic Lowenstein-Jensen culture medium, and identified as M. tuberculosis by real-time PCR and DNA sequencing. Nevertheless, the origin of the infection remained unknown. These findings emphasize the need to strengthen the management and training of staff, especially those working at animal shelters.