Interferon-γ Regulates the Death of M. tuberculosis-Infected Macrophages

Latent Tuberculosis Patients Have an Increased Frequency of IFN-γ-Producing CD5+ B Cells, Which Respond Efficiently to Mycobacterial Proteins

Tuberculosis (TB) remains a public health problem worldwide and is one of the deadliest infectious diseases, only after the current COVID-19 pandemic. Despite significant advances in the TB field, there needs to be more immune response comprehension; for instance, the role played by humoral immunity is still controversial. This study aimed to identify the frequency and function of B1 and immature/transitional B cells in patients with active and latent TB (ATB and LTB, respectively). Here we show that LTB patients have an increased frequency of CD5+ B cells and decreased CD10+ B cells. Furthermore, LTB patients stimulated with mycobacteria's antigens increase the frequency of IFN-γ-producing B cells, whereas cells from ATB do not respond. Moreover, under the mycobacterial protein stimulus, LTB promotes a pro-inflammatory environment characterized by a high level of IFN-γ but also can produce IL-10. Regarding the ATB group, they cannot produce IFN-γ, and mycobacterial lipids and proteins stimulate only the IL-10 production. Finally, our data showed that in ATB, but not in LTB, B cell subsets correlate with clinical and laboratory parameters, suggesting that these CD5+ and CD10+ B cell subpopulations have the potential to be biomarkers to differentiate between LTB and ATB. In conclusion, LTB has increased CD5+ B cells, and these cells can maintain a rich microenvironment of IFN-γ, IL-10, and IL-4. In contrast, ATB only maintains an anti-inflammatory environment when stimulated with mycobacterial proteins or lipids.

Expression profile of KIR3DS1/KIR3DL1 receptors in association with immunological responses in TB, HIV and HIV/TB infected patients

Several studies investigated KIR3DS1 and KIR3DL1 in the context of various infections. However, none of the studies were performed on KIR3DS1/L1 in association with IFN-ɣ/IL-10 in TB, HIV-1, and their confections. We aimed to evaluate KIR3DS1/KIR3DL1 expression in association with IFNɣ/IL-10 in HIV-1 and TB mono-infections and HIV-1/TB confection and compared with uninfected controls using RTq PCR. We also performed correlation analysis between KIR3DS1, KIR3DL1, IFN-ɣ and IL-10 in the respective cohorts. The overall expression of KIR3DS1 was found to be downregulated in all groups, whereas in HIV-1 and HIV-1/TB, the frequency of KIR3DS1⁽⁺⁾ expression was significantly (p < 0.05) associated with undetected HIV-1 viral load. However, expression of KIR3DL1 was found to be significantly (p < 0.05) upregulated in HIV-1 only. In addition, IFNɣ expression was significantly (p < 0.05) decreased in TB, whereas in HIV-1/TB, IFNɣ expression was significantly (p < 0.05) increased. In contrast, IL-10 expression was significantly (p < 0.05) increased in HIV-1 and HIV-1/TB but not in TB. Also, we found significant positive correlation (p < 0.05, r = 0.61) between KIR3DL1 and IFNɣ expression in TB and negative correlation (p < 0.05, r = - 0.62) between KIR3DS1 and IL-10 in HIV-1/TB. In conclusion, we suggest that expression of KIR3DS1/L1 is associated with IFNɣ/IL-10 responses and it is involved in modulating disease severity in HIV-1 and TB infections.

It Takes a Village: The Multifaceted Immune Response to Mycobacterium tuberculosis Infection and Vaccine-Induced Immunity

Despite co-evolving with humans for centuries and being intensely studied for decades, the immune correlates of protection against Mycobacterium tuberculosis (Mtb) have yet to be fully defined. This lapse in understanding is a major lag in the pipeline for evaluating and advancing efficacious vaccine candidates. While CD4+ T helper 1 (TH1) pro-inflammatory responses have a significant role in controlling Mtb infection, the historically narrow focus on this cell population may have eclipsed the characterization of other requisite arms of the immune system. Over the last decade, the tuberculosis (TB) research community has intentionally and intensely increased the breadth of investigation of other immune players. Here, we review mechanistic preclinical studies as well as clinical anecdotes that suggest the degree to which different cell types, such as NK cells, CD8+ T cells, γ δ T cells, and B cells, influence infection or disease prevention. Additionally, we categorically outline the observed role each major cell type plays in vaccine-induced immunity, including Mycobacterium bovis bacillus Calmette-Guérin (BCG). Novel vaccine candidates advancing through either the preclinical or clinical pipeline leverage different platforms (e.g., protein + adjuvant, vector-based, nucleic acid-based) to purposefully elicit complex immune responses, and we review those design rationales and results to date. The better we as a community understand the essential composition, magnitude, timing, and trafficking of immune responses against Mtb, the closer we are to reducing the severe disease burden and toll on human health inflicted by TB globally.

A recombinant selective drug-resistant M. bovis BCG enhances the bactericidal activity of a second-line anti-tuberculosis regimen

Drug-resistant tuberculosis (DR-TB) poses a new threat to global health; to improve the treatment outcome, therapeutic vaccines are considered the best chemotherapy adjuvants. Unfortunately, there is no therapeutic vaccine approved against DR-TB. Our study assessed the therapeutic efficacy of a recombinant drug-resistant BCG (RdrBCG) vaccine in DR-TB. We constructed the RdrBCG overexpressing Ag85B and Rv2628 by selecting drug-resistant BCG strains and transformed them with plasmid pEBCG or pIBCG to create RdrBCG-E and RdrBCG-I respectively. Following successful stability testing, we tested the vaccine's safety in severe combined immune deficient (SCID) mice that lack both T and B lymphocytes plus immunoglobulins. Finally, we evaluated the RdrBCG's therapeutic efficacy in BALB/c mice infected with rifampin-resistant M. tuberculosis and treated with a second-line anti-TB regimen. We obtained M. bovis strains which were resistant to several second-line drugs and M. tuberculosis resistant to rifampin. Notably, the exogenously inserted genes were lost in RdrBCG-E but remained stable in the RdrBCG-I both in vitro and in vivo. When administered adjunct to a second-line anti-TB regimen in a murine model of DR-TB, the RdrBCG-I lowered lung M. tuberculosis burden by 1 log10. Furthermore, vaccination with RdrBCG-I adjunct to chemotherapy minimized lung tissue pathology in mice. Most importantly, the RdrBCG-I showed almost the same virulence as its parent BCG Tice strain in SCID mice. Our findings suggested that the RdrBCG-I was stable, safe and effective as a therapeutic vaccine. Hence, the "recombinant" plus "drug-resistant" BCG strategy could be a useful concept for developing therapeutic vaccines against DR-TB.

Association of Polymorphism +874 T/A Interferon Gamma Gene with Susceptibility to Pulmonary Tuberculosis in Medan, Indonesia

BACKGROUND: Pulmonary tuberculosis (TB) is still a disease that concerns in the world due to its high incidence, especially in developing countries, including Indonesia. Polymorphism +874 T/A interferon-gamma (IFN-γ) is one of the host genetic factors that have been widely studied and has been shown to be associated with susceptibility to pulmonary TB. AIM: This study aims to determine the association polymorphism +874 T/A IFN-γ gene with susceptibility to pulmonary TB in Medan population. METHODS: A total of 82 pulmonary TB patients and 85 healthy controls were examined in this case–control study. SPSS 25 is used to process and analyze all data where the Pearson Chi-square is used to analyze the association between genotype and susceptibility to pulmonary TB. RESULTS: The polymorphism +874 T/A IFN-γ gene was not significantly associated with susceptibility to pulmonary TB in patients compared to controls (p = 0.395) and there was no association between allele frequency and susceptibility to pulmonary TB (p = 0.158). CONCLUSION: Our study suggests no association of polymorphism +874 T/A IFN-γ gene with pulmonary TB in Medan, Sumatera Utara, Indonesia.

Transcriptional signatures of human peripheral blood mononuclear cells can identify the risk of tuberculosis progression from latent infection among individuals with silicosis

Host immune factor plays an important role in the progression of latent tuberculosis infection (LTBI) to active tuberculosis (TB) disease. However, whether global gene expression measured in blood biomarkers allows the identification of prospective signatures for TB risk remains unknown. Hence, we aimed to assess the ability of the transcriptome signatures in the human peripheral blood mononuclear cells (PBMCs) of LTBI subjects to differentiate future TB progressors from non-progressors. In a randomized clinical trial of TB preventive treatment of 513 participants with silicosis, we randomly collected PBMC samples from 50 LTBI subjects in the observational group, which was monitored for TB disease progression for 37 months. The prospective signatures of TB risk between the two participants who developed active TB (progressors) and four matched individuals who remained healthy (non-progressors) were compared using differential expression analysis, Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis, and Weighted Gene Co-expression Network Analysis. The 20 TB-specific differentially expressed genes, which were significantly downregulated in TB progressors, were revealed to be associated with interferon-gamma response-related genes. Therefore, the PBMC transcriptome profiles analyzed in this study may help identify LTBI individuals who are at risk of progressing to active TB among silicosis patients and may provide new insights for targeted intervention to prevent disease progression.

Association of gene polymorphisms and environmental factors in tuberculosis patients and their household contacts

BACKGROUND

Tuberculosis (TB) is an important public health problem in China and environmental and genetic factors have an impact on its occurrence and development. We explored the relationship between environmental factors, genetic susceptibility genes and gene-environment interactions and the incidence of TB, as well as their high-risk combination, which can provide a scientific basis for prevention of the disease.

METHODS

The 242 individuals, which included 82 TB patients, 67 family genetically related patients and 93 healthy controls, all of whom were of the Han population in Guangdong Province. The basic information of subjects was collected, including general conditions, behaviour habits, family environmental factors and blood samples. Two single nucleotides with potential functions (interleukin-10 [IL-10] rs1800896, interferon-γ [IFN-γ] rs2430561) were screened by bioinformatics tools and identified by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

We found that gender, education, TB exposure history, fitness activities, residential areas and indoor hygiene conditions were all associated with the occurrence of TB. In the dominant model, AG+GG of IL-10 and AA of IFN-γ are high-risk genotypes. Multifactor dimensionality reduction (MDR) analysis of TB-prone families shows that a combination of male sex, IL-10 AA and AG genotypes and smoking history are elements of high risk for TB infection (prediction accuracy 62.45%, cross-validation consistency 10/10). The MDR analysis of the TB patients group and the healthy control group showed that the combination of low education level, history of TB exposure, and IFN-γ AA genotype represented a higher risk of TB infection (prediction accuracy 80.34%, cross-validation consistency 10/10).

CONCLUSIONS

The occurrence of TB in TB-prone families in the Han population of Guangdong Province is related to environmental factors as well as cytokines IL-10 and IFN-γ. We also found high-risk combinations of genes and environmental factors, providing clues for the timely detection of high-risk groups.

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.

PD-1 blockade exacerbates Mycobacterium tuberculosis infection in rhesus macaques

Boosting immune cell function by targeting the coinhibitory receptor PD-1 may have applications in the treatment of chronic infections. Here, we examine the role of PD-1 during Mycobacterium tuberculosis (Mtb) infection of rhesus macaques. Animals treated with anti-PD-1 monoclonal antibody developed worse disease and higher granuloma bacterial loads compared with isotype control-treated monkeys. PD-1 blockade increased the number and functionality of granuloma Mtb-specific CD8 T cells. In contrast, Mtb-specific CD4 T cells in anti-PD-1-treated macaques were not increased in number or function in granulomas, expressed increased levels of CTLA-4, and exhibited reduced intralesional trafficking in live imaging studies. In granulomas of anti-PD-1-treated animals, multiple proinflammatory cytokines were elevated, and more cytokines correlated with bacterial loads, leading to the identification of a role for caspase 1 in the exacerbation of tuberculosis after PD-1 blockade. Last, increased Mtb bacterial loads after PD-1 blockade were found to associate with the composition of the intestinal microbiota before infection in individual macaques. Therefore, PD-1-mediated coinhibition is required for control of Mtb infection in macaques, perhaps because of its role in dampening detrimental inflammation and allowing for normal CD4 T cell responses.

Host-Pathogen Interaction as a Novel Target for Host-Directed Therapies in Tuberculosis

Tuberculosis (TB) has been a transmittable human disease for many thousands of years, and M. tuberculosis is again the number one cause of death worldwide due to a single infectious agent. The intense 6- to 10-month process of multi-drug treatment, combined with the adverse side effects that can run the spectrum from gastrointestinal disturbances to liver toxicity or peripheral neuropathy are major obstacles to patient compliance and therapy completion. The consequent increase in multidrug resistant TB (MDR-TB) and extensively drug resistant TB (XDR-TB) cases requires that we increase our arsenal of effective drugs, particularly novel therapeutic approaches. Over the millennia, host and pathogen have evolved mechanisms and relationships that greatly influence the outcome of infection. Understanding these evolutionary interactions and their impact on bacterial clearance or host pathology will lead the way toward rational development of new therapeutics that favor enhancing a host protective response. These host-directed therapies have recently demonstrated promising results against M. tuberculosis, adding to the effectiveness of currently available anti-mycobacterial drugs that directly kill the organism or slow mycobacterial replication. Here we review the host-pathogen interactions during M. tuberculosis infection, describe how M. tuberculosis bacilli modulate and evade the host immune system, and discuss the currently available host-directed therapies that target these bacterial factors. Rather than provide an exhaustive description of M. tuberculosis virulence factors, which falls outside the scope of this review, we will instead focus on the host-pathogen interactions that lead to increased bacterial growth or host immune evasion, and that can be modulated by existing host-directed therapies.

Regulation of mitogen-activated protein kinase signaling pathway and proinflammatory cytokines by ursolic acid in murine macrophages infected with Mycobacterium avium

Mycobacterium avium, one of the closest relatives of Mycobacterium tuberculosis (MTB), offers an advantage in studying MTB because of its tuberculosis-like effect in humans and host immune tolerance. This study examined the antimycobacterial action of ursolic acid and its regulation in macrophages during infection. Colonyforming units of the bacteria were determined in the cell lysate of macrophages and in the supernatant. The effect of ursolic acid on macrophages during infection was determined by analyzing the phosphorylation of the mitogen-activated protein kinase signaling pathway and the concentrations of tumor necrosis factor-α, interleukin-1β, interleukin-6, and nitrite. The colony-forming units analysis demonstrated that ursolic acid reduced the presence of Mycobacterium avium both intracellularly (in macrophages) and extracellularly. It decreased the levels of tumor necrosis factor- α and interleukin-6 but increased the concentrations of interleukin-1β and nitrite during infection. It also inhibited the phosphorylation of ERK1/2 but phosphorylated the C-Jun N-terminal kinase signaling pathway. The antimycobacterial effect of ursolic acid correlated with its ability to regulate the activation of macrophages. This dual ability made the ursolic acid-related elimination of the mycobacteria more effective.

Genetic variants in IFNG and IFNGR1 and tuberculosis susceptibility

BACKGROUND

Tuberculosis (TB) is the type of chronic infectious disease which majorly caused by Mycobacterium tuberculosis (M. TB). Emerging data suggest that interferon gamma (IFNG) and its receptor IFNGR1 may be involved in the risk of TB.

METHODS

A total of 636 TB patients and 608 healthy controls were selected. The association between single nucleotide polymorphisms (SNPs) and TB was estimated by logistic analyses adjusting for age, gender and smoking status. SNPs genotyping was done by using the improved multiplex ligase detection reaction (iMLDR).

RESULTS

The IFNG rs1861494 allele C was related to an increased risk for TB (OR = 1.25, 95%CI: 1.06-1.48; P = 0.009). Compared with TT genotype, CT (OR = 1.28, 95%CI: 1.01-1.63; P = 0.040) and CC (OR = 1.51, 95%CI: 1.04-2.19; P = 0.031) were also risk factors for TB. In the subgroup analysis, the association was stronger among participants < 25 years (OR = 2.40, 95%CI: 1.70-3.38; P < 0.001) and male groups (OR = 1.31, 95%CI: 1.03-1.66; P = 0.030). In addition, IFNG rs1861494 was associated with anti-TB treatment outcome (OR = 0.70, 95%CI: 0.52-0.94; P = 0.017). We also detected that IFNGR1 rs2234711 influenced the IFNG production.

CONCLUSION

IFNG rs1861494 polymorphism was associated with TB, particularly in the younger and male subgroups.

Immunometabolism of Phagocytes During Mycobacterium tuberculosis Infection

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains as a leading killer among infectious diseases worldwide. The nature of the host immune response dictates whether the initial Mtb infection is cleared or progresses toward active disease, and is ultimately determined by intricate host-pathogen interactions that are yet to be fully understood. The early immune response to infection is mediated by innate immune cells, including macrophages and neutrophils that can phagocytose Mtb and mount an antimicrobial response. However, Mtb can exploit these innate immune cells for its survival and dissemination. Recently, it has become clear that the immune response and metabolic remodeling are interconnected, which is highlighted by the rapid evolution of the interdisciplinary field of immunometabolism. It has been proposed that the net outcome to Mtb infection—clearance or chronic disease—is likely a result of combined immunologic and metabolic activities of the immune cells. Indeed, host cells activated by Mtb infection have strikingly different metabolic requirements than naïve/non-infected cells. Macrophages activated by Mtb-derived molecules or upon phagocytosis acquire a phenotype similar to M1 with elevated production of pro-inflammatory molecules and rely on glycolysis and pentose phosphate pathway to meet their bioenergetic and metabolic requirements. In these macrophages, oxidative phosphorylation and fatty acid oxidation are dampened. However, the non-infected/naive, M2-type macrophages are anti-inflammatory and derive their energy from oxidative phosphorylation and fatty acid oxidation. Similar metabolic adaptations also occur in other phagocytes, including dendritic cells, neutrophils upon Mtb infection. This metabolic reprogramming of innate immune cells during Mtb infection can differentially regulate their effector functions, such as the production of cytokines and chemokines, and antimicrobial response, all of which can ultimately determine the outcome of Mtb-host interactions within the granulomas. In this review, we describe key immune cells bolstering host innate response and discuss the metabolic reprogramming in these phagocytes during Mtb infection. We focused on the major phagocytes, including macrophages, dendritic cells and neutrophils and the key regulators involved in metabolic reprogramming, such as hypoxia-inducible factor-1, mammalian target of rapamycin, the cellular myelocytomatosis, peroxisome proliferator-activator receptors, sirtuins, arginases, inducible nitric acid synthase and sphingolipids.

Genetic Polymorphisms of IFNG and IFNGR1 with Latent Tuberculosis Infection

Previous studies indicated that single-nucleotide polymorphisms (SNPs) of interferon gamma (IFNG) and IFNG receptor 1 (IFNGR1) may be involved in the pathogenesis of pulmonary tuberculosis (PTB) in different populations. In order to further explore the results in a Chinese Han population, this study was designed to investigate potential associations between the polymorphisms in IFNG and IFNGR1 and susceptibility to latent tuberculosis infection (LTBI) and/or PTB in a Chinese Han population. A total of 209 PTB, 173 LTBI, and 183 healthy control subjects (HCS) were enrolled in our study. Genotyping was conducted using an improved multiplex ligase detection reaction (iMLDR). We performed a logistic regression including sex and age as covariates to test the effect of alleles/genotypes on LTBI and/or TB. All six markers studied in IFNG and IFNGR1 conformed to the Hardy-Weinberg equilibrium (HWE). The IFNG rs1861494 was significantly associated with LTBI in recessive model, and the CC+CT genotype decreased risk of LTBI by 50% (P = 0.046, OR = 0.50, 95%CI: 0.25-0.99). The IFNGR1 rs2234711 was significantly associated with LTBI, and allele A increased the risk of LTBI by 55% (P = 0.047, OR = 1.55, 95%CI: 1.00-2.40). In the present study, we found that IFNG and IFNGR1 polymorphisms were associated with LTBI.

Mycobacterium tuberculosis promotes genomic instability in macrophages

BACKGROUND

Mycobacterium tuberculosis is an intracellular pathogen, which may either block cellular defensive mechanisms and survive inside the host cell or induce cell death. Several studies are still exploring the mechanisms involved in these processes.

OBJECTIVES

To evaluate the genomic instability of M. tuberculosis-infected macrophages and compare it with that of uninfected macrophages.

METHODS

We analysed the possible variations in the genomic instability of Mycobacterium-infected macrophages using the DNA breakage detection fluorescence in situ hybridisation (DBD-FISH) technique with a whole human genome DNA probe.

FINDINGS

Quantitative image analyses showed a significant increase in DNA damage in infected macrophages as compared with uninfected cells. DNA breaks were localised in nuclear membrane blebs, as confirmed with DNA fragmentation assay. Furthermore, a significant increase in micronuclei and nuclear abnormalities were observed in infected macrophages versus uninfected cells.

MAIN CONCLUSIONS

Genomic instability occurs during mycobacterial infection and these data may be seminal for future research on host cell DNA damage in M. tuberculosis infection.

The Role of Mast Cells in Tuberculosis: Orchestrating Innate Immune Crosstalk?

Tuberculosis causes more annual deaths globally than any other infectious disease. However, progress in developing novel vaccines, diagnostics, and therapies has been hampered by an incomplete understanding of the immune response to Mycobacterium tuberculosis (Mtb). While the role of many immune cells has been extensively explored, mast cells (MCs) have been relatively ignored. MCs are tissue resident cells involved in defense against bacterial infections playing an important role mediating immune cell crosstalk. This review discusses specific interactions between MCs and Mtb, their contribution to both immunity and disease pathogenesis, and explores their role in orchestrating other immune cells against infections.

Association of IFNGR1 and IFNG genetic polymorphisms with the risk for pulmonary tuberculosis in the Chinese Tibetan population

Interferon-gamma (IFNG) and its receptor (IFNGR1) are principal genes that associated with tuberculosis. In the current study we aimed to explore the genetic association of polymorphisms of IFNG and IFNGR1 with the risk of pulmonary tuberculosis (PTB) in the Chinese Tibetan population. We selected 467 PTB patients and 503 healthy controls to genotype 9 single nucleotide polymorphisms (SNPs). The unconditional logistic regression analysis was applied for assessing the associations, and the risk of PTB were evaluated by calculating the odds ratio (OR) and 95% confidence interval (CI). The results showed that mutants of rs9376268, rs1327475 and rs1327474 in IFNGR1 played a protective role in the PTB risk under genotype, dominant and additive model (P<0.05). On the contrary, minor allele “A” of rs2069705 in IFNG significantly increased the risk of PTB under genotype, dominant and additive model (P<0.05). However, after Bonferroni's multiple adjustment was applied to our data, which level of significant was set at P<0.0011 (0.05/45). Only variant of rs9376268 was significantly associated decrease the PTB susceptibility under additive model (OR=0.73, 95%CI=0.61-0.88, P<0.001). Furthermore, in the haplotype analysis, we found that the haplotypes “C-G-G-A-C”, “C-G-A-G-T” and “T-A-G-G-T” of rs9376267-rs9376268-rs1327475-rs7749390-rs1327474 block were extremely decreased the PTB risk (P<0.01), however, the haplotypes “C-G-G-A-T”, “T-G-G-G-T” and “C-G-G-G-T” of the block were extremely increased the PTB risk (P<0.01). These results suggested that variants of IFNGR1 may have a close relation with the PTB risk in Chinese Tibetan population.

A single nucleotide polymorphism in the interferon-γ gene (IFNG +874 T/A) is associated with susceptibility to tuberculosis

Interferon-γ (Interferon gamma, IFNG) is an important cytokine involved in providing resistance to mycobacterial diseases. Common variants of IFNG, such as IFNG +874 T/A(rs2430561), may be related to tuberculosis susceptibility, but this association has not been consistently observed. We performed an updated meta-analysis to evaluate the association between the IFNG +874 T/A (rs2430561) polymorphism and tuberculosis susceptibility. PubMed and SinoMed databases were searched up to October 2016, and odds ratios (OR) and 95% confidence intervals (CI) were used to assess the association strength. Based on search criteria for manuscripts reporting tuberculosis susceptibility and its relationship with the IFNG +874 T/A(rs2430561)polymorphism, 42 case-control studies from 39 different articles were retrieved. Significantly positive, decreased, and protective associations were found between the IFNG +874 T/A(rs2430561)polymorphism and tuberculosis risk in five genetic models. Moreover, in the stratified subgroup analysis, a protective relationship was detected in four different ethnicities and sources of the control groups. Furthermore, the IFNG +874 T/A(rs2430561)polymorphism played an important role in protecting individuals from both pulmonary tuberculosis and extra-pulmonary tuberculosis. Our meta-analysis suggests that the IFNG +874 T/A(rs2430561)polymorphism is potentially associated with tuberculosis susceptibility and may be used as a predictive biomarker. Further studies with larger sample sizes and consideration of gene-environment interactions should be conducted to elucidate the role of IFNG +874 T/A(rs2430561) polymorphism in tuberculosis susceptibility.

Mycobacterium tuberculosis replicates within necrotic human macrophages

Mycobacterium tuberculosis triggers macrophage cell death by necrosis, but it is unclear how this affects bacterial replication. Lerner et al. show that this pathogen replicates within necrotic human macrophages before disseminating to other cells upon loss of plasma membrane integrity.

Mycobacterium tuberculosis modulation of macrophage cell death is a well-documented phenomenon, but its role during bacterial replication is less characterized. In this study, we investigate the impact of plasma membrane (PM) integrity on bacterial replication in different functional populations of human primary macrophages. We discovered that IFN-γ enhanced bacterial replication in macrophage colony-stimulating factor–differentiated macrophages more than in granulocyte–macrophage colony-stimulating factor–differentiated macrophages. We show that permissiveness in the different populations of macrophages to bacterial growth is the result of a differential ability to preserve PM integrity. By combining live-cell imaging, correlative light electron microscopy, and single-cell analysis, we found that after infection, a population of macrophages became necrotic, providing a niche for M. tuberculosis replication before escaping into the extracellular milieu. Thus, in addition to bacterial dissemination, necrotic cells provide first a niche for bacterial replication. Our results are relevant to understanding the environment of M. tuberculosis replication in the host.

SP110b Controls Host Immunity and Susceptibility to Tuberculosis

RATIONALE

How host genetic factors affect Mycobacterium tuberculosis (Mtb) infection outcomes remains largely unknown. SP110b, an IFN-induced nuclear protein, is the nearest human homologue to the mouse Ipr1 protein that has been shown to control host innate immunity to Mtb infection. However, the function(s) of SP110b remains unclear.

OBJECTIVES

To elucidate the role of SP110b in controlling host immunity and susceptibility to tuberculosis (TB), as well as to identify the fundamental immunological and molecular mechanisms affected by SP110b.

METHODS

Using cell-based approaches and mouse models of Mtb infection, we characterized the function(s) of SP110b/Ipr1. We also performed genetic characterization of patients with TB to investigate the role of SP110 in controlling host susceptibility to TB.

MEASUREMENTS AND MAIN RESULTS

SP110b modulates nuclear factor-κB (NF-κB) activity, resulting in downregulation of tumor necrosis factor-α (TNF-α) production and concomitant upregulation of NF-κB-induced antiapoptotic gene expression, thereby suppressing IFN-γ-mediated monocyte and/or macrophage cell death. After Mtb infection, TNF-α is also downregulated in Ipr1-expressing mice that have alleviated cell death, less severe necrotic lung lesions, more efficient Mtb growth control in the lungs, and longer survival. Moreover, genetic studies in patients suggest that SP110 plays a key role in modulating TB susceptibility in concert with NFκB1 and TNFα genes.

CONCLUSIONS

These results indicate that SP110b plays a crucial role in shaping the inflammatory milieu that supports host protection during infection by fine-tuning NF-κB activity, suggesting that SP110b may serve as a potential target for host-directed therapy aimed at manipulating host immunity against TB.

Evaluation of interferon-induced transmembrane protein-3 (IFITM3) rs7478728 and rs3888188 polymorphisms and the risk of pulmonary tuberculosis

The current study aimed to examine the possible association between the interferon-induced transmembrane protein-3 (IFITM3) gene polymorphisms and risk of pulmonary tuberculosis (PTB) in a sample population. This case-control study was conducted on 188 PTB patients and 169 healthy subjects. The rs7478728 and rs3888188 variants of IFITM3 were genotyped using polymerase chain reaction-restriction fragment length polymorphism. The findings showed no significant association between rs7478728 polymorphism and risk of PTB. Regarding rs3888188 polymorphism, the TG genotype as well as G allele significantly increased the risk of PTB [odds ratio (OR)=2.48, 95% confidence interval (CI): 1.42-4.53; P=0.002, and OR=2.26, 95% CI: 1.33-3.86; P=0.003, respectively]. In conclusion, the findings revealed that rs3888188 polymorphism increased the risk of PTB in a sample of Iranian population. Additional investigation with larger sample sizes and different ethnicities are needed to verify our findings.

CD4 T Cell-Derived IFN-γ Plays a Minimal Role in Control of Pulmonary Mycobacterium tuberculosis Infection and Must Be Actively Repressed by PD-1 to Prevent Lethal Disease

IFN-γ–producing CD4 T cells are required for protection against Mycobacterium tuberculosis (Mtb) infection, but the extent to which IFN-γ contributes to overall CD4 T cell-mediated protection remains unclear. Furthermore, it is not known if increasing IFN-γ production by CD4 T cells is desirable in Mtb infection. Here we show that IFN-γ accounts for only ~30% of CD4 T cell-dependent cumulative bacterial control in the lungs over the first six weeks of infection, but >80% of control in the spleen. Moreover, increasing the IFN-γ–producing capacity of CD4 T cells by ~2 fold exacerbates lung infection and leads to the early death of the host, despite enhancing control in the spleen. In addition, we show that the inhibitory receptor PD-1 facilitates host resistance to Mtb by preventing the detrimental over-production of IFN-γ by CD4 T cells. Specifically, PD-1 suppressed the parenchymal accumulation of and pathogenic IFN-γ production by the CXCR3⁺KLRG1^-CX3CR1^- subset of lung-homing CD4 T cells that otherwise mediates control of Mtb infection. Therefore, the primary role for T cell-derived IFN-γ in Mtb infection is at extra-pulmonary sites, and the host-protective subset of CD4 T cells requires negative regulation of IFN-γ production by PD-1 to prevent lethal immune-mediated pathology.

The development of novel tuberculosis vaccines has been hindered by the poor understanding of the mechanisms of host-protection. It has been long-held that IFN-γ is the principle effector of CD4 T cell-mediated resistance to Mtb infection, but Mtb-specific CD4 T cells produce low amounts of IFN-γ in vivo, leading to the possibility that increasing IFN-γ production by Th1 cells might enhance control of Mtb infection. However, the precise contribution of IFN-γ to CD4 T cell-dependent protection and the outcome of increasing IFN-γ production by CD4 T cells have not been evaluated. Here we show that IFN-γ accounts for only ~30% of the cumulative CD4 T cell-mediated reduction in lung bacterial loads over the first 1.5 months of infection. Moreover, we find that increasing the per capita production of IFN-γ by CD4 T cells leads to the early death of the host. Lastly, we show that suppression of CD4 T cell-derived IFN-γ by the inhibitory receptor PD-1 is essential to prevent lethal disease. Therefore, poor control Mtb infection does not result from defective production of IFN-γ, and strategies to selectively boost it are unwarranted. Furthermore, identifying the primary mechanisms of CD4 T cell-dependent control of Mtb infection should be a priority.

Differences between Mycobacterium-Host Cell Relationships in Latent Tuberculous Infection of Mice Ex Vivo and Mycobacterial Infection of Mouse Cells In Vitro

The search for factors that account for the reproduction and survival of mycobacteria, including vaccine strains, in host cells is the priority for studies on tuberculosis. A comparison of BCG-mycobacterial loads in granuloma cells obtained from bone marrow and spleens of mice with latent tuberculous infection and cells from mouse bone marrow and peritoneal macrophage cultures infected with the BCG vaccine in vitro has demonstrated that granuloma macrophages each normally contained a single BCG-Mycobacterium, while those acutely infected in vitro had increased mycobacterial loads and death rates. Mouse granuloma cells were observed to produce the IFNγ, IL-1α, GM-CSF, CD1d, CD25, CD31, СD35, and S100 proteins. None of these activation markers were found in mouse cell cultures infected in vitro or in intact macrophages. Lack of colocalization of lipoarabinomannan-labeled BCG-mycobacteria with the lysosomotropic LysoTracker dye in activated granuloma macrophages suggests that these macrophages were unable to destroy BCG-mycobacteria. However, activated mouse granuloma macrophages could control mycobacterial reproduction in cells both in vivo and in ex vivo culture. By contrast, a considerable increase in the number of BCG-mycobacteria was observed in mouse bone marrow and peritoneal macrophages after BCG infection in vitro, when no expression of the activation-related molecules was detected in these cells.

Association of Genetic Polymorphisms of IFNGR1 with the Risk of Pulmonary Tuberculosis in Zahedan, Southeast Iran

Aim. The present study was undertaken to find out the possible association between interferon-gamma (IFN-γ) receptor 1 (IFNGR1) gene polymorphisms and risk of pulmonary tuberculosis (PTB) in a sample of Iranian population. Methods. Polymorphisms of IFNGR1 rs1327474 (−611 A/G), rs11914 (+189 T/G), rs7749390 (+95 C/T), and rs137854905 (27-bp ins/del) were determined in 173 PTB patients and 164 healthy subjects. Results. Our findings showed that rs11914 TG genotypes decreased the risk of PTB in comparison with TT (OR = 0.36, 95% CI = 0.21–0.62, and p = 0.0002). The rs11914 G allele decreased the risk of PTB compared with T allele (OR = 0.41, 95% CI = 0.25–0.68, and p = 0.0006). IFNGR1 rs7749390 CT genotype decreased the risk of PTB in comparison with CC genotype (OR = 0.55, 95% CI = 0.32–0.95, and p = 0.038). No significant association was found between IFNGR1 rs1327474 A/G polymorphism and risk/protective of PTB. The rs137854905 (27-bp I/D) variant was not polymorphic in our population. Conclusion. Our findings showed that IFNGR1 rs11914 and rs7749390 variants decreased the risk of PTB susceptibility in our population.

Versatile myeloid cell subsets contribute to tuberculosis-associated inflammation

Tuberculosis (TB), a chronic bacterial infectious disease caused by Mycobacterium tuberculosis (Mtb), typically affects the lung and causes profound morbidity and mortality rates worldwide. Recent advances in cellular immunology emphasize the complexity of myeloid cell subsets controlling TB inflammation. The specialization of myeloid cell subsets for particular immune processes has tailored their roles in protection and pathology. Among myeloid cells, dendritic cells (DCs) are essential for the induction of adaptive immunity, macrophages predominantly harbor Mtb within TB granulomas and polymorphonuclear neutrophils (PMNs) orchestrate lung damage. However, within each myeloid cell population, diverse phenotypes with unique functions are currently recognized, differentially influencing TB pneumonia and granuloma functionality. More recently, myeloid-derived suppressor cells (MDSCs) have been identified at the site of Mtb infection. Along with PMNs, MDSCs accumulate within the inflamed lung, interact with granuloma-residing cells and contribute to exuberant inflammation. In this review, we discuss the contribution of different myeloid cell subsets to inflammation in TB by highlighting their interactions with Mtb and their role in lung pathology. Uncovering the manifold nature of myeloid cells in TB pathogenesis will inform the development of future immune therapies aimed at tipping the inflammation balance to the benefit of the host.

Interferon gamma induces protective non-canonical signaling pathways in primary neurons

The signal transduction molecule, Stat1, is critical for the expression of type I and II interferon (IFN)-responsive genes in most cells; however, we previously showed that primary hippocampal mouse neurons express low basal Stat1, with delayed and attenuated expression of IFN-responsive genes. Moreover, IFNγ-dependent resolution of a neurotropic viral challenge in permissive mice is Stat1-independent. Here, we show that exogenous IFNγ has no deleterious impact on neuronal viability, and staurosporine-induced apoptosis in neurons is significantly blunted by the addition of IFNγ, suggesting that IFNγ confers a pro-survival signal in neurons. To identify the pathways induced by IFNγ in neurons, the activation of alternative signal transducers associated with IFNγ signaling was assessed. Rapid and pronounced activation of extracellular signal regulated kinase (Erk1/2) was observed in neurons, compared to a modest response in fibroblasts. Moreover, the absence of Stat1 in primary fibroblasts led to enhanced Erk activation following IFNγ addition, implying that the cell-specific availability of signal transducers can diversify the cellular response following IFN engagement.

Extracellular traps and macrophages: new roles for the versatile phagocyte

MΦ are multipurpose phagocytes with a large repertoire of well-characterized abilities and functions, including regulation of inflammation, wound healing, maintenance of tissue homeostasis, as well as serving as an integral component of the innate-immune defense against microbial pathogens. Working along with neutrophils and dendritic cells, the other myeloid-derived professional phagocytes, MΦ are one of the key effector cells initiating and directing the host reaction to pathogenic organisms and resolving subsequent responses once the threat has been cleared. ETs are a relatively novel strategy of host defense involving expulsion of nuclear material and embedded proteins from immune cells to immobilize and kill bacteria, fungi, and viruses. As research on ETs expands, it has begun to encompass many immune cell types in unexpected ways, including various types of MΦ, which are not only capable of generating METs in response to various stimuli, but recent preclinical data suggest that they are an important agent in clearing ETs and limiting ET-mediated inflammation and tissue damage. This review aims to summarize historical and recent findings of biologic research regarding ET formation and function and discuss the role of MΦ in ET physiology and associated pathologies.

Bacillary replication and macrophage necrosis are determinants of neutrophil recruitment in tuberculosis

We previously determined that burst size necrosis is the chief mode of mononuclear cell death in the lungs of mice with tuberculosis. The present study explored the link between infection-induced necrosis of mononuclear phagocytes and neutrophil accumulation in the lungs of mice challenged with one of four Mycobacterium tuberculosis strains of increasing virulence (RvΔphoPR mutant, H37Ra, H37Rv and Erdman). At all time points studied, Erdman produced the highest bacterial load and the highest proportion and number of M. tuberculosis-infected neutrophils. These parameters, and the proportion of TUNEL-positive cells, tracked with virulence across all strains tested. Differences in neutrophil infection were not reflected by levels of chemoattractant cytokines in bronchoalveolar lavage fluid, while interferon-γ (reported to suppress neutrophil trafficking to the lung in tuberculosis) was highest in Erdman-infected mice. Treating Erdman-infected mice with ethambutol decreased the proportion of mononuclear phagocytes with high bacterial burden and the ratio of infected neutrophils to infected mononuclear cells in a dose-dependent manner. We propose that faster replicating M. tuberculosis strains cause more necrosis which in turn promotes neutrophil recruitment. Neutrophils infected with M. tuberculosis constitute a biomarker for poorly controlled bacterial replication, infection-induced mononuclear cell death, and increased severity of immune pathology in tuberculosis.

Variability in tuberculosis granuloma T cell responses exists, but a balance of pro- and anti-inflammatory cytokines is associated with sterilization

Lung granulomas are the pathologic hallmark of tuberculosis (TB). T cells are a major cellular component of TB lung granulomas and are known to play an important role in containment of Mycobacterium tuberculosis (Mtb) infection. We used cynomolgus macaques, a non-human primate model that recapitulates human TB with clinically active disease, latent infection or early infection, to understand functional characteristics and dynamics of T cells in individual granulomas. We sought to correlate T cell cytokine response and bacterial burden of each granuloma, as well as granuloma and systemic responses in individual animals. Our results support that each granuloma within an individual host is independent with respect to total cell numbers, proportion of T cells, pattern of cytokine response, and bacterial burden. The spectrum of these components overlaps greatly amongst animals with different clinical status, indicating that a diversity of granulomas exists within an individual host. On average only about 8% of T cells from granulomas respond with cytokine production after stimulation with Mtb specific antigens, and few “multi-functional” T cells were observed. However, granulomas were found to be “multi-functional” with respect to the combinations of functional T cells that were identified among lesions from individual animals. Although the responses generally overlapped, sterile granulomas had modestly higher frequencies of T cells making IL-17, TNF and any of T-1 (IFN-γ, IL-2, or TNF) and/or T-17 (IL-17) cytokines than non-sterile granulomas. An inverse correlation was observed between bacterial burden with TNF and T-1/T-17 responses in individual granulomas, and a combinatorial analysis of pair-wise cytokine responses indicated that granulomas with T cells producing both pro- and anti-inflammatory cytokines (e.g. IL-10 and IL-17) were associated with clearance of Mtb. Preliminary evaluation suggests that systemic responses in the blood do not accurately reflect local T cell responses within granulomas.

The characteristic feature of Mycobacterium tuberculosis (Mtb) infection is the formation of lesions, which are organized structures of immune cells in the lungs called granulomas, which contain the bacteria. When the granuloma functions effectively, it can kill the bacteria. T cells (a type of immune cell, also present in granulomas) are known to play an important role in control of tuberculosis. However, functions of T cells at individual granuloma levels are unknown. Here, we studied the functional characteristics of T cells, which are defined by the production of chemical messengers (cytokines) at the granuloma level in a non-human primate model. We compared the relationship between cytokine response and the number of bacteria (Mtb) in each granuloma. Each granuloma was found to be unique, suggesting different types exist within an animal. Only a small proportion of T cells produced any cytokine, but different types of cytokines were observed within each granuloma. A balance between different types of cytokine was associated with more killing of bacteria in granulomas. Understanding how to improve the T cell responses to obtain killing of bacteria in the granuloma will be important for vaccine development.

Cell death and autophagy in tuberculosis

Mycobacterium tuberculosis has succeeded in infecting one-third of the human race though inhibition or evasion of innate and adaptive immunity. The pathogen is a facultative intracellular parasite that uses the niche provided by mononuclear phagocytes for its advantage. Complex interactions determine whether the bacillus will or will not be delivered to acidified lysosomes, whether the host phagocyte will survive infection or die, and whether the timing and mode of cell death works to the advantage of the host or the pathogen. Here we discuss cell death and autophagy in TB. These fundamental processes of cell biology feature in all aspects of TB pathogenesis and may be exploited to the treatment or prevention of TB disease.

Genetic polymorphisms of IFNG and IFNGR1 in association with the risk of pulmonary tuberculosis

OBJECTIVE

Genetic host factors play an important role in controlling individual's susceptibility to the pathogen. This study aims to explore the single and joint effect of genetic polymorphisms of interferon-gamma (IFNG) and its receptor (IFNGR1) in association with the pulmonary tuberculosis in a Chinese Han population.

METHODS

This population-based case control study consisted of 1434 pulmonary tuberculosis patients and 1412 healthy controls. Six tag SNPs in IFNG/IFNGR1 were genotyped using TaqMan allelic discrimination technology. The logistic regression model was carried out to analyze the associations between the genotypes and haplotypes and the risk of tuberculosis by calculating the odds ratio (OR) and 95% confidence interval (CI).

RESULTS

After the Bonferroni correction for multiple comparisons, three SNPs (rs2234711, rs1327475 and rs7749390) in IFNGR1 gene were observed to be significantly associated with the altered risks of tuberculosis. For the SNP rs2234711, individuals carrying C allele (vs. T) showed a decreased risk, with the adjusted OR(95% CI) of 0.82(0.76-0.91). The additive model revealed that each additional allele contributed about 14% decreased risk (OR: 0.86, 95% CI: 0.77-0.95). Moreover, we observed a strong linkage disequilibrium between rs2234711 and rs3799488. Compared with the common rs2234711C-rs3799488C haplotype, the haplotype rs2234711T-rs3799488C contributed to a significant increase in the risk of tuberculosis (adjusted OR: 1.24, 95% CI: 1.09-1.41).

CONCLUSIONS

Our results suggest that genetic polymorphisms in IFNGR1 gene are involved in the risk of tuberculosis in the Chinese population. Future studies should include a comprehensive sequencing analysis to identify the specific causative sequence variants underlying the observed associations.

Macrophages from elders are more permissive to intracellular multiplication of Mycobacterium tuberculosis

The elderly account for a disproportionate share of all tuberculosis cases, and the population ageing may not fully explain this phenomenon. We have performed in vitro infection experiments to investigate whether there is an immunological basis for the apparent susceptibility of elders to tuberculosis. In our infection model, Mycobacterium tuberculosis induces a higher production of interleukin (IL)-6 and reactive oxygen species in macrophages from elders than from younger adults. This response did not prevent, however, an increased multiplication of M. tuberculosis in macrophages from elders as compared with the growth observed within cells from adults. By performing a factorial experiment, we have found that IFN-γ, but not IL-1β, IL-6 or TNF-α, stimulate the macrophages to restrict the multiplication of the bacterium in macrophages from elders. Although monocytes from elders seem to be in a higher level of activation, we present evidences that protein tyrosine phosphorylation response induced by M. tuberculosis is stronger in monocytes from adults than from elders. Using a protein array that detects 71 tyrosine phosphorylated kinases, we identified Pyk2 as the only kinase that displayed a difference of intensity larger than 50 % in adults than in elders. Furthermore, monocytes from elders that were incubated in the presence of tyrosine kinase inhibitors (genistein and PP2) allowed a higher level of bacterial multiplication. These observations may help to explain the susceptibility of elders to tuberculosis. An unexpected result was that both genistein and its negative control, daidzein, abundant soy isoflavones, promoted intracellular mycobacterial growth.

A functional promoter polymorphism of IFITM3 is associated with susceptibility to pediatric tuberculosis in Han Chinese population

A susceptibility locus for tuberculosis, a re-emerging infectious disease throughout the world, was previously discovered to exist on chromosome 11p15. IFITM3 gene encoding for interferon inducible transmembrane protein 3, is located at 11p15. It acts as an effector molecule for interferon-gamma, which is essential for anti-tuberculosis immune response. In order to investigate the association between susceptibility to TB and genetic polymorphisms of the IFITM3 core promoter, a case-control study including 368 TB patients and 794 healthy controls was performed in Han Chinese children in northern China. The rs3888188 polymorphism showed significant association with susceptibility to TB. The rs3888188 G allele, acting recessively, was more frequent in TB patients (95% confidence interval: 1.08–1.56, Bonferroni P-value: 0.039). We further assessed the effect of rs3888188 polymorphism on IFITM3 transcription in vitro. As based on luciferase promoter assays, the promoter activity of haplotypes with rs3888188 G allele was lower than that of haplotypes with rs3888188 T allele. Moreover, peripheral-blood mononuclear cells carrying rs3888188 GG genotype showed a reduced IFITM3 mRNA level compared to cells carrying TT or GT genotype. In conclusion, rs3888188, a functional promoter polymorphism of IFITM3, was identified to influence the risk for pediatric TB in Han Chinese population.

Differential effects of type I and II interferons on myeloid cells and resistance to intracellular bacterial infections

The type I and II interferons (IFNs) play important roles in regulating immune responses during viral and bacterial infections and in the context of autoimmune and neoplastic diseases. These two IFN types bind to distinct cell surface receptors that are expressed by nearly all cells to trigger signal transduction events and elicit diverse cellular responses. In some cases, type I and II IFNs trigger similar cellular responses, while in other cases, the IFNs have unique or antagonistic effects on host cells. Negative regulators of IFN signaling also modulate cellular responses to the IFNs and play important roles in maintaining immunological homeostasis. In this review, we provide an overview of how IFNs stimulate cellular responses. We discuss the disparate effects of type I and II IFNs on host resistance to certain intracellular bacterial infections and provide an overview of models that have been proposed to account for these disparate effects. Mechanisms of antagonistic cross talk between type I and II IFNs are also introduced.

IFNG polymorphisms are associated with tuberculosis in Han Chinese pediatric female population

Host genetic factors play a major role in determining differential susceptibility to human tuberculosis (TB), a re-emerging infectious disease throughout the world. Genetic variations in the IFNG gene coding for interferon gamma (IFN-γ), have been identified in TB patients. To investigate the association of the IFNG polymorphisms with TB susceptibility in Chinese pediatric population. A case-control study of 189 TB patients and 164 controls was performed using single-nucleotide polymorphism (SNP) analysis. Genomic DNA was extracted from leukocytes in peripheral blood. Three SNPs of IFNG, including -1616C/T (rs2069705), +874A/T (rs2430561), and +3234C/T (rs2069718), were selected for genotyping and analysis. The +874A and +3234C alleles were more frequent among TB patients (P = 0.108 and P = 0.088), especially in females (both P = 0.029), although this difference was not significant since Bonferroni corrected significance threshold was 0.025 (two of three SNPs were found to be in linkage disequilibrium). More pronounced differences for the +874 and +3234 polymorphisms were found under the genotype comparison between TB cases and controls in the total population [P = 0.026 (borderline non-significance) and P = 0.020, respectively], and in the female subgroup (P = 0.020 and P = 0.020). The dominant model of inheritance was shown to be significant for +874A and +3234C alleles (both P = 0.019) in the female subgroup. The +874A and +3234C alleles were more frequently found in extrapulmonary TB patients than in controls (P = 0.039). Haplotype analysis carried out on these three SNPs showed the TTT haplotype to be more frequent in controls than in TB cases, and this difference showed a strong significance (P = 0.005). The +874A and +3234C alleles may be related to TB susceptibility in the female subgroup in the Chinese pediatric population of North China. The higher rate of +874A (known to correlate with lower IFN-γ expression) in the extrapulmonary TB subgroup suggests a sufficient IFN-γ expression to be not only an important factor for the onset of TB disease but also for limiting its dissemination to lungs.

Mycobacterium tuberculosis exploits human interferon γ to stimulate macrophage extracellular trap formation and necrosis

Human neutrophils form extracellular traps during M. tuberculosis infection, but a similar phenomenon has not been reported in human macrophages. Here we demonstrate that M. tuberculosis induces release of extracellular traps from human macrophages. This process is regulated by elastase activity, previously shown to regulate formation of extracellular traps by neutrophils. Interestingly, formation of extracellular traps by macrophages during M. tuberculosis infection is inducible by interferon γ (IFN-γ). These traps are mainly produced by heavily infected macrophages. Accordingly, IFN-γ is found to stimulate M. tuberculosis aggregation in macrophages. Both IFN-γ–inducible events, extracellular trap formation and mycobacterial aggregation, require the ESX-1 secretion system. In addition, IFN-γ is found to enhance ESX-1–mediated macrophage necrosis. In the absence of ESX-1, IFN-γ does not restore any extracellular trap formation, mycobacterial aggregation, or macrophage necrosis. Thus, initial characterization of macrophage extracellular trap formation due to M. tuberculosis infection led to the uncovering of a novel role for IFN-γ in amplifying multiple effects of the mycobacterial ESX-1.

ALOX5 is associated with tuberculosis in a subset of the pediatric population of North China

BACKGROUND

Genetic factors are involved in the etiology of Mycobacterium tuberculosis infection. Recently, ALOX5 has been identified as a candidate gene for tuberculosis (TB) susceptibility. We investigated whether an association between ALOX5 and TB exists in a Chinese pediatric population from northern China.

METHODS

We conducted a case-control study comprising 488 individuals aged 2 months to 17 years by genotyping 18 tag-single-nucleotide polymorphisms (SNPs) from the ALOX5 gene. The tag-SNPs were selected from the international HapMap project. An Illumina BeadXpress Scanner was utilized for genotyping, supported by the high-density BeadArray technology in combination with an allele-specific extension, adapter ligation, and amplification assay. Statistical analyses were performed to determine correlations between genetic variation and disease.

RESULTS

Our study is the first to show that ALOX5 is associated with susceptibility to pediatric TB in a subset of children in northern China. The rs2115819 T allele of ALOX5 presents a risk factor for childhood TB disease.

Intracellular bacillary burden reflects a burst size for Mycobacterium tuberculosis in vivo

We previously reported that Mycobacterium tuberculosis triggers macrophage necrosis in vitro at a threshold intracellular load of ∼25 bacilli. This suggests a model for tuberculosis where bacilli invading lung macrophages at low multiplicity of infection proliferate to burst size and spread to naïve phagocytes for repeated cycles of replication and cytolysis. The current study evaluated that model in vivo, an environment significantly more complex than in vitro culture. In the lungs of mice infected with M. tuberculosis by aerosol we observed three distinct mononuclear leukocyte populations (CD11b⁻ CD11c^+/hi, CD11b^+/lo CD11c^lo/−, CD11b^+/hi CD11c^+/hi) and neutrophils hosting bacilli. Four weeks after aerosol challenge, CD11b^+/hi CD11c^+/hi mononuclear cells and neutrophils were the predominant hosts for M. tuberculosis while CD11b^+/lo CD11c^lo/− cells assumed that role by ten weeks. Alveolar macrophages (CD11b⁻ CD11c^+/hi) were a minority infected cell type at both time points. The burst size model predicts that individual lung phagocytes would harbor a range of bacillary loads with most containing few bacilli, a smaller proportion containing many bacilli, and few or none exceeding a burst size load. Bacterial load per cell was enumerated in lung monocytic cells and neutrophils at time points after aerosol challenge of wild type and interferon-γ null mice. The resulting data fulfilled those predictions, suggesting a median in vivo burst size in the range of 20 to 40 bacilli for monocytic cells. Most heavily burdened monocytic cells were nonviable, with morphological features similar to those observed after high multiplicity challenge in vitro: nuclear condensation without fragmentation and disintegration of cell membranes without apoptotic vesicle formation. Neutrophils had a narrow range and lower peak bacillary burden than monocytic cells and some exhibited cell death with release of extracellular neutrophil traps. Our studies suggest that burst size cytolysis is a major cause of infection-induced mononuclear cell death in tuberculosis.

Macrophages patrol the lung to ingest and destroy inhaled microbes. Mycobacterium tuberculosis, the bacteria causing tuberculosis, can survive within macrophages and use them as a protected environment for growth. Macrophages by themselves are poorly equipped to kill M. tuberculosis but may undergo programmed cell death (apoptosis) to limit bacterial replication. Virulent M. tuberculosis has evolved the capacity to inhibit macrophage apoptosis, thereby protecting the replication niche. In previous studies we showed that upon reaching a threshold intracellular number (burst size), virulent M. tuberculosis kills macrophages by necrosis and escapes for spreading infection. The present study was designed to test whether this mechanism seen in vitro operates during pulmonary tuberculosis in vivo. The distribution of M. tuberculosis numbers inside lung phagocytes of mice with tuberculosis conformed to predictions based on the burst size hypothesis, as did the appearance of dying cells. We identified four different types of phagocytes hosting intracellular M. tuberculosis. The distribution of M. tuberculosis load within individual phagocytes and between different types of phagocyte changed over the course of tuberculosis disease. These studies reveal the complexity of host defense in tuberculosis that must be considered as new therapies are sought.

Discovery and evaluation of novel inhibitors of mycobacterium protein tyrosine phosphatase B from the 6-Hydroxy-benzofuran-5-carboxylic acid scaffold

Mycobacterium tuberculosis (Mtb) protein tyrosine phosphatase B (mPTPB) is a virulence factor secreted by the pathogen and mediates mycobacterial survival in macrophages by targeting host cell immune responses. Consequently, mPTPB represents an exciting new target to combat tuberculosis (TB) infection. We describe a medicinal chemistry oriented approach that transforms a benzofuran salicylic acid scaffold into a highly potent (IC(50) = 38 nM) and selective mPTPB inhibitor (>50 fold against a large panel of PTPs). Importantly, the inhibitor is capable of reversing the altered host immune responses induced by the bacterial phosphatase and restoring the macrophage's full capacity to secrete IL-6 and undergo apoptosis in response to interferon-γ stimulation, validating the concept that chemical inhibition of mPTPB may be therapeutically useful for novel TB treatment. The study further demonstrates that bicyclic salicylic acid pharmacophores can be used to deliver PTP inhibitors with high potency, selectivity, and cellular efficacy.

Mendelian susceptibility to mycobacterial disease in egyptian children

BACKGROUND

Tuberculosis remains a major health problem in developing countries especially with the emergence of multidrug resistant strains. Mendelian Susceptibility to Mycobacterial Disease (MSMD) is a rare disorder with impaired immunity against mycobacterial pathogens. Reported MSMD etiologies highlight the crucial role of the Interferon gamma /Interleukin 12 (IFN-γ/ IL-12) axis and the phagocyte respiratory burst axis.

PURPOSE

Screen patients with possible presentations for MSMD.

METHODS

Patients with disseminated BCG infection following vaccination, atypical mycobacterial infections or recurrent tuberculosis infections were recruited from the Primary Immune Deficiency Clinic at Cairo University Specialized Pediatric Hospital, Egypt and immune and genetic laboratory investigations were conducted at Human Genetic of Infectious Diseases laboratory in Necker Medical School, France from 2005-2009. IFN-γ level in patient's plasma as well as mutations in the eight previously identified MSMD-causing genes were explored.

RESULTS

Nine cases from eight (unrelated) kindreds were evaluated in detail. We detected a high level of IFN-γ in plasma in one patient. Through Sanger sequencing, a homozygous mutation in the IFNGR1 gene at position 485 corresponding to an amino acid change from serine to phenylalanine (S485F), was detected in this patient.

CONCLUSION

We report the first identified case of MSMD among Egyptian patients, including in particular a new IFNGR1 mutation underlying IFN-γR1 deficiency. The eight remaining patients need to be explored further. These findings have implications regarding the compulsory Bacillus.

Human macrophages infected with a high burden of ESAT-6-expressing M. tuberculosis undergo caspase-1- and cathepsin B-independent necrosis

Mycobacterium tuberculosis (Mtb) infects lung macrophages, which instead of killing the pathogen can be manipulated by the bacilli, creating an environment suitable for intracellular replication and spread to adjacent cells. The role of host cell death during Mtb infection is debated because the bacilli have been shown to be both anti-apoptotic, keeping the host cell alive to avoid the antimicrobial effects of apoptosis, and pro-necrotic, killing the host macrophage to allow infection of neighboring cells. Since mycobacteria activate the NLRP3 inflammasome in macrophages, we investigated whether Mtb could induce one of the recently described inflammasome-linked cell death modes pyroptosis and pyronecrosis. These are mediated through caspase-1 and cathepsin-B, respectively. Human monocyte-derived macrophages were infected with virulent (H37Rv) Mtb at a multiplicity of infection (MOI) of 1 or 10. The higher MOI resulted in strongly enhanced release of IL-1β, while a low MOI gave no IL-1β response. The infected macrophages were collected and cell viability in terms of the integrity of DNA, mitochondria and the plasma membrane was determined. We found that infection with H37Rv at MOI 10, but not MOI 1, over two days led to extensive DNA fragmentation, loss of mitochondrial membrane potential, loss of plasma membrane integrity, and HMGB1 release. Although we observed plasma membrane permeabilization and IL-1β release from infected cells, the cell death induced by Mtb was not dependent on caspase-1 or cathepsin B. It was, however, dependent on mycobacterial expression of ESAT-6. We conclude that as virulent Mtb reaches a threshold number of bacilli inside the human macrophage, ESAT-6-dependent necrosis occurs, activating caspase-1 in the process.