Establishment of CD1b-restricted immunity to lipid antigens in the pulmonary response to Mycobacterium tuberculosis infection.

CD1 is an antigen presenting glycoprotein homologous to MHC I; however, CD1 proteins present lipid rather than peptide antigen. CD1 proteins are well established to present lipid antigens of Mycobacterium tuberculosis (Mtb) to T cells, but understanding the role of CD1-restricted immunity in vivo in response to Mtb infection has been limited by availability of animal models naturally expressing the CD1 proteins implicated in human response: CD1a, CD1b and CD1c. Guinea pigs, in contrast to other rodent models, express four CD1b orthologs, and here we utilize the guinea pig to establish the kinetics of gene and protein expression of CD1b orthologs, as well as the Mtb lipid-antigen and CD1b-restricted immune response at the tissue level over the course of Mtb infection. Our results indicate transient upregulation of CD1b expression during the effector phase of adaptive immunity that wanes with disease chronicity. Gene expression indicates that upregulation of CD1b is the result of transcriptional induction across all CD1b orthologs. We show high CD1b3 expression on B cells, and identify CD1b3 as the predominant CD1b ortholog in pulmonary granuloma lesions. We identify ex vivo cytotoxic activity directed against CD1b that closely paralleled the kinetic changes in CD1b expression in Mtb infected lung and spleen. This study confirms that CD1b expression is modulated by Mtb infection in lung and spleen, leading to pulmonary and extrapulmonary CD1b-restricted immunity as a component of the antigen-specific response to Mtb infection.

Gliosis, misfolded protein aggregation, and neuronal loss in a guinea pig model of pulmonary tuberculosis.

Tuberculosis, caused by Mycobacterium tuberculosis infection, is an ongoing epidemic with an estimated ten million active cases of the disease worldwide. Pulmonary tuberculosis is associated with cognitive and memory deficits, and patients with this disease are at an increased risk for Parkinson's disease and dementia. Although epidemiological data correlates neurological effects with peripheral disease, the pathology in the central nervous system is unknown. In an established guinea pig model of low-dose, aerosolized Mycobacterium tuberculosis infection, we see behavior changes and memory loss in infected animals. We correlate these findings with pathological changes within brain regions related to motor, cognition, and sensation across disease progression. This includes microglial and astrocytic proliferation and reactivity. These cellular changes are followed by the aggregation of neurotoxic amyloid ß and phosphorylated tau and, ultimately, neuronal degeneration in the hippocampus. Through these data, we have obtained a greater understanding of the neuropathological effects of a peripheral disease that affects millions of persons worldwide.

The Impact of Vitamin A Deficiency on Tuberculosis Progression.

BACKGROUND: Although previous studies have shown that vitamin A deficiency is associated with incident tuberculosis (TB) disease, the direction of the association has not been established. We investigated the impact of vitamin A deficiency on TB disease progression. METHODS: We conducted a longitudinal cohort study nested within a randomized clinical trial among HIV-infected patients in Haiti. We compared serial vitamin A levels in individuals who developed TB disease to controls matched on age, gender, follow-up time, and time to antiretroviral therapy initiation. We also evaluated histopathology, bacterial load, and immune outcomes in TB infection in a guinea pig model of dietary vitamin A deficiency. RESULTS: Among 773 participants, 96 developed incident TB during follow-up, 62.5% (60) of whom had stored serum samples obtained 90-365 days before TB diagnosis. In age- and sex- adjusted and multivariate analyses, respectively, incident TB cases were 3.99 times (95% confidence interval [CI], 2.41 to 6.60) and 3.59 times (95% CI, 2.05 to 6.29) more likely to have been vitamin A deficient than matched controls. Vitamin A-deficient guinea pigs manifested more extensive pulmonary pathology, atypical granuloma morphology, and increased bacterial growth after experimental TB infection. Reintroduction of dietary vitamin A to deficient guinea pigs after established TB disease successfully abrogated severe disease manifestations and altered cellular immune profiles. CONCLUSIONS: Human and animal studies support the role of baseline vitamin A deficiency as a determinant of future TB disease progression.

Lactate Metabolism and Signaling in Tuberculosis and Cancer: A Comparative Review.

Infection with Mycobacterium tuberculosis (Mtb) leading to tuberculosis (TB) disease continues to be a major global health challenge. Critical barriers, including but not limited to the development of multi-drug resistance, lack of diagnostic assays that detect patients with latent TB, an effective vaccine that prevents Mtb infection, and infectious and non-infectious comorbidities that complicate active TB, continue to hinder progress toward a TB cure. To complement the ongoing development of new antimicrobial drugs, investigators in the field are exploring the value of host-directed therapies (HDTs). This therapeutic strategy targets the host, rather than Mtb, and is intended to augment host responses to infection such that the host is better equipped to prevent or clear infection and resolve chronic inflammation. Metabolic pathways of immune cells have been identified as promising HDT targets as more metabolites and metabolic pathways have shown to play a role in TB pathogenesis and disease progression. Specifically, this review highlights the potential role of lactate as both an immunomodulatory metabolite and a potentially important signaling molecule during the host response to Mtb infection. While long thought to be an inert end product of primarily glucose metabolism, the cancer research field has discovered the importance of lactate in carcinogenesis and resistance to chemotherapeutic drug treatment. Herein, we discuss similarities between the TB granuloma and tumor microenvironments in the context of lactate metabolism and identify key metabolic and signaling pathways that have been shown to play a role in tumor progression but have yet to be explored within the context of TB. Ultimately, lactate metabolism and signaling could be viable HDT targets for TB; however, critical additional research is needed to better understand the role of lactate at the host-pathogen interface during Mtb infection before adopting this HDT strategy.

Metformin enhances protection in guinea pigs chronically infected with Mycobacterium tuberculosis.

Tuberculosis (TB) is a chronic inflammatory disease that is often associated with alterations in systemic and cellular metabolism that resolves following successful antimicrobial drug treatment. We hypothesized that altered systemic glucose metabolism as a consequence of Mycobacterium tuberculosis (Mtb) infection, contributes to TB pathogenesis, and when normalized with anti-glycemic drugs would improve clinical outcomes. To test this hypothesis, guinea pigs were treated daily with the anti-diabetic drug metformin starting 4 weeks prior or concurrent with aerosol exposure to the H37Rv strain of Mtb. In the chronic stages of infection, Mtb infected metformin-treated animals had restored systemic insulin sensitivity but remained glucose intolerant as determined by oral glucose tolerance testing. Despite persistent glucose intolerance, metformin-treated guinea pigs had a 2.8-fold reduction in lung lesion burden and a 0.7 log decrease in CFUs. An alternative hypothesis that metformin treatment improved clinical disease by having a direct effect on immune cell energy metabolism was tested using extracellular flux analysis and flow cytometry. The proinflammatory immune response to Mtb infection in untreated guinea pigs was associated with a marked increase in energy metabolism (glycolysis and mitochondrial respiration) of peripheral blood mononuclear cells (PBMCs), which was normalized in metformin-treated guinea pigs. Moreover, both CD4+ and CD8+ T lymphocytes from Mtb infected, metformin treated animals maintained a more normal mitochondrial membrane potential while those isolated from untreated animals had persistent mitochondrial hyperpolarization. These data suggest that metformin promotes natural host resistance to Mtb infection by maintaining immune cell metabolic homeostasis and function during the chronic stages of active TB disease.

Cyclin-Dependent Kinases 8 and 19 Regulate Host Cell Metabolism during Dengue Virus Serotype 2 Infection.

Dengue virus infection is associated with the upregulation of metabolic pathways within infected cells. This effect is common to infection by a broad array of viruses. These metabolic changes, including increased glucose metabolism, oxidative phosphorylation and autophagy, support the demands of viral genome replication and infectious particle formation. The mechanisms by which these changes occur are known to be, in part, directed by viral nonstructural proteins that contact and control cellular structures and metabolic enzymes. We investigated the roles of host proteins with overarching control of metabolic processes, the transcriptional regulators, cyclin-dependent kinase 8 (CDK8) and its paralog, CDK19, as mediators of virally induced metabolic changes. Here, we show that expression of CDK8, but not CDK19, is increased during dengue virus infection in Huh7 human hepatocellular carcinoma cells, although both are required for efficient viral replication. Chemical inhibition of CDK8 and CDK19 with Senexin A during infection blocks virus-induced expression of select metabolic and autophagic genes, hexokinase 2 (HK2) and microtubule-associated protein 1 light chain 3 (LC3), and reduces viral genome replication and infectious particle production. The results further define the dependence of virus replication on increased metabolic capacity in target cells and identify CDK8 and CDK19 as master regulators of key metabolic genes. The common inhibition of CDK8 and CDK19 offers a host-directed therapeutic intervention that is unlikely to be overcome by viral evolution.

A mouse model of pulmonary Mycobacteroides abscessus infection.

There is no preclinical mouse model to investigate pulmonary Mycobacteroides abscessus (formerly Mycobacterium abscessus) infection in an immunocompetent mouse strain, especially in the context of antibiotic testing and regimen development. We developed a mouse model of pulmonary M. abscessus infection using the aerosolized route of infection that leads to an increase in bacterial burden post- implantation and develops pathology as a result. In this mouse model, treatment with corticosteroid allows for initial proliferation and sustained M. abscessus pulmonary infection and permits evaluation of efficacies of antibiotics. Administration of corticosteroids that permitted higher levels of bacterial burden in the lungs were more likely to have pathology. Treatment of mice with antibiotics administered intranasally or subcutaneously significantly reduced lung M. abscessus burden. In addition to the reference strain, independent clinical isolates of M. abscessus also readily establish infection and proliferate in the lungs of mice in this model.

2-aminoimidazoles collapse mycobacterial proton motive force and block the electron transport chain.

There is an urgent need to develop new drugs against tuberculosis. In particular, it is critical to target drug tolerant Mycobacterium tuberculosis (M. tuberculosis), responsible, in part, for the lengthy antibiotic regimen required for treatment. We previously postulated that the presence of in vivo biofilm-like communities of M. tuberculosis could contribute to this drug tolerance. Consistent with this hypothesis, certain 2-aminoimidazole (2-AIs) molecules with anti-biofilm activity were shown to revert mycobacterial drug tolerance in an in vitro M. tuberculosis biofilm model. While exploring their mechanism of action, it was serendipitously observed that these 2-AI molecules also potentiated ß-lactam antibiotics by affecting mycobacterial protein secretion and lipid export. As these two bacterial processes are energy-dependent, herein it was evaluated if 2-AI compounds affect mycobacterial bioenergetics. At low concentrations, 2B8, the lead 2-AI compound, collapsed both components of the proton motive force, similar to other cationic amphiphiles. Interestingly, however, the minimum inhibitory concentration of 2B8 against M. tuberculosis correlated with a higher drug concentration determined to interfere with the mycobacterial electron transport chain. Collectively, this study elucidates the mechanism of action of 2-AIs against M. tuberculosis, providing a tool to better understand mycobacterial bioenergetics and develop compounds with improved anti-mycobacterial activity.

Analogue synthesis reveals decoupling of antibiofilm and ß-lactam potentiation activities of a lead 2-aminoimidazole adjuvant against Mycobacterium smegmatis.

Biofilm formation is one of the many mechanisms bacteria utilize to survive antibiotic treatment. It has been demonstrated that when Mycobacterium tuberculosis exists in a biofilm in vitro, it expresses phenotypic resistance to antimicrobial drugs. As the in vivo survival of M. tuberculosis following drug treatment is potentially linked to a biofilm-like expression of drug tolerance, it is hypothesized that biofilm dispersion should increase antibiotic susceptibility and reduce the duration of the current antibiotic treatment regimen. Previously, we have identified a 2-aminoimidazole (2-AI) compound capable of dispersing and inhibiting M. tuberculosis and M. smegmatis biofilms in vitro. Additionally, this compound potentiated the activity of carbenicillin against M. tuberculosis and, to a lesser degree, M. smegmatis. Here, we describe a SAR study on this compound evaluating each derivative for biofilm dispersion and ß-lactam potentiation capabilities against M. smegmatis. This study identified a compound that improved upon the biofilm dispersion capabilities of the lead compound. Interestingly, a different compound was identified with an increased ability to potentiate a subset of ß-lactam antibiotics. These compounds indicate that biofilm dispersion and potentiation capabilities may not be associated.

Topical therapy for refractory rhinosinusitis caused by methicillin-resistant Staphylococcus aureus: First report in a prospective series.

OBJECTIVE: The incidence of refractory chronic rhinosinusitis (CRS) associated with methicillin-resistant Staphylococcus aureus (MRSA) is rising and remains a therapeutic challenge. The goal of this study is to demonstrate the efficacy of a non-invasive topical therapy against MRSA in these patients. METHODS: Seventeen patients with refractory CRS caused by MRSA were treated with a topical therapy protocol. Treatment consisted of weekly endoscopic sinus debridement followed by intra-sinus installation of a hydroxyl-ethylcellulose gel that releases mometasone and a culture-directed antibiotic for a period of 6 weeks, along with daily nasal nebulization of mometasone with the same antibiotic and saline rinses. Clinical outcome was assessed using the Lund-Kennedy (LK) symptom and endoscopic appearance scores. Sinus mucosal tissue was homogenized and cultured, and microbial biofilm burden was assessed based on colony forming units (CFUs) counts. RESULTS: Rhinotopic therapy resulted in clearance of MRSA in 13 of 16 patients (81.2%). Treated patients also demonstrated significant improvement clinically as measured by the LK scores. In addition, a significant decrease in mucosal CFUs was observed post-therapy. CONCLUSION: Our findings demonstrate that topical therapy is an effective method for treating MRSA-associated refractory CRS.

2-aminoimidazoles potentiate ß-lactam antimicrobial activity against Mycobacterium tuberculosis by reducing ß-lactamase secretion and increasing cell envelope permeability.

There is an urgent need to develop new drug treatment strategies to control the global spread of drug-sensitive and multidrug-resistant Mycobacterium tuberculosis (M. tuberculosis). The ß-lactam class of antibiotics is among the safest and most widely prescribed antibiotics, but they are not effective against M. tuberculosis due to intrinsic resistance. This study shows that 2-aminoimidazole (2-AI)-based small molecules potentiate ß-lactam antibiotics against M. tuberculosis. Active 2-AI compounds significantly reduced the minimal inhibitory and bactericidal concentrations of ß-lactams by increasing M. tuberculosis cell envelope permeability and decreasing protein secretion including ß-lactamase. Metabolic labeling and transcriptional profiling experiments revealed that 2-AI compounds impair mycolic acid biosynthesis, export and linkage to the mycobacterial envelope, counteracting an important defense mechanism reducing permeability to external agents. Additionally, other important constituents of the M. tuberculosis outer membrane including sulfolipid-1 and polyacyltrehalose were also less abundant in 2-AI treated bacilli. As a consequence of 2-AI treatment, M. tuberculosis displayed increased sensitivity to SDS, increased permeability to nucleic acid staining dyes, and rapid binding of cell wall targeting antibiotics. Transcriptional profiling analysis further confirmed that 2-AI induces transcriptional regulators associated with cell envelope stress. 2-AI based small molecules potentiate the antimicrobial activity of ß-lactams by a mechanism that is distinct from specific inhibitors of ß-lactamase activity and therefore may have value as an adjunctive anti-TB treatment.

Mycobacterial Biofilms: Revisiting Tuberculosis Bacilli in Extracellular Necrotizing Lesions.

Under detergent-free in vitro conditions, Mycobacterium tuberculosis, the etiological agent of tuberculosis in humans, spontaneously forms organized multicellular structures called biofilms. Moreover, in vitro biofilms of M. tuberculosis are more persistent against antibiotics than their single-cell planktonic counterparts, thereby raising questions about the occurrence of biofilms in the host tissues and their significance in persistence during chemotherapy of tuberculosis. In this article, we present arguments that extracellular M. tuberculosis in necrotizing lesions likely grows as biofilms.

Pathology of Tuberculosis: How the Pathology of Human Tuberculosis Informs and Directs Animal Models.

Tuberculosis (TB) is a chronic inflammatory disease caused by the pathogenic bacterium Mycobacterium tuberculosis. A wide variety of host- and pathogen-associated variables influence the clinical manifestation of TB in different individuals within the human population. As a consequence, the characteristic granulomatous lesions that develop within the lung are heterogeneous in size and cellular composition. Due to the lack of appropriate tissues from human TB patients, a variety of animal models are used as surrogates to study the basic pathogenesis and to test experimental vaccines and new drug therapies. Few animal models mimic the clinical course and pathological response of M. tuberculosis seen in the naturally occurring disease in people. In particular, post-primary TB, which accounts for the majority of cases of active TB and is responsible for transmission between individuals via aerosol exposers, cannot be reproduced in animals and therefore cannot be adequately modeled experimentally. This article describes a new paradigm that explains the pathogenesis of post-primary TB in humans. This new evidence was derived from histological examination of tissues from patients with different stages of M. tuberculosis infection and that had not been treated with antimicrobial drugs. Gaining a better understanding of this unique stage of TB disease will lead to more effective treatment, diagnostic, and prevention strategies.

The Discovery of 2-Aminobenzimidazoles That Sensitize Mycobacterium smegmatis and M.†tuberculosis to ß-Lactam Antibiotics in a Pattern Distinct from ß-Lactamase Inhibitors.

A library of 2-aminobenzimidazole derivatives was screened for the ability to suppress ß-lactam resistance in Mycobacterium smegmatis. Several non-bactericidal compounds were identified that reversed intrinsic resistance to ß-lactam antibiotics in a manner distinct from ß-lactamase inhibitors. Activity also translates to M. tuberculosis, with a lead compound from this study potently suppressing carbenicillin resistance in multiple M. tuberculosis strains (including multidrug-resistant strains). Preliminary mechanistic studies revealed that the lead compounds act through a mechanism distinct from that of traditional ß-lactamase inhibitors.

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment.

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes ß-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by ß-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and ß-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.

Host-directed therapy targeting the Mycobacterium tuberculosis granuloma: a review.

Infection by the intracellular bacterial pathogen Mycobacterium tuberculosis (Mtb) is a major cause of morbidity and mortality worldwide. Slow progress has been made in lessening the impact of tuberculosis (TB) on human health, especially in parts of the world where Mtb is endemic. Due to the complexity of TB disease, there is still an urgent need to improve diagnosis, prevention, and treatment strategies to control global spread of disease. Active research targeting avenues to prevent infection or transmission through vaccination, to diagnose asymptomatic carriers of Mtb, and to improve antimicrobial drug treatment responses is ongoing. However, this research is hampered by a relatively poor understanding of the pathogenesis of early infection and the factors that contribute to host susceptibility, protection, and the development of active disease. There is increasing interest in the development of adjunctive therapy that will aid the host in responding to Mtb infection appropriately thereby improving the effectiveness of current and future drug treatments. In this review, we summarize what is known about the host response to Mtb infection in humans and animal models and highlight potential therapeutic targets involved in TB granuloma formation and resolution. Strategies designed to shift the balance of TB granuloma formation toward protective rather than destructive processes are discussed based on our current knowledge. These therapeutic strategies are based on the assumption that granuloma formation, although thought to prevent the spread of the tubercle bacillus within and between individuals contributes to manifestations of active TB disease in human patients when left unchecked. This effect of granuloma formation favors the spread of infection and impairs antimicrobial drug treatment. By gaining a better understanding of the mechanisms by which Mtb infection contributes to irreversible tissue damage, down regulates protective immune responses, and delays tissue healing, new treatment strategies can be rationally designed. Granuloma-targeted therapy is advantageous because it allows for the repurpose of existing drugs used to treat other communicable and non-communicable diseases as adjunctive therapies combined with existing and future anti-TB drugs. Thus, the development of adjunctive, granuloma-targeted therapy, like other host-directed therapies, may benefit from the availability of approved drugs to aid in treatment and prevention of TB. In this review, we have attempted to summarize the results of published studies in the context of new innovative approaches to host-directed therapy that need to be more thoroughly explored in pre-clinical animal studies and in human clinical trials.

Second generation 2-aminoimidazole based advanced glycation end product inhibitors and breakers.

The formation of advanced glycation end-products (AGE) as a result of the action of reducing sugars on host macromolecules plays a role in increased morbidity of diabetic patients. There are currently no clinically available therapeutics for the prevention or eradication of AGEs. Following our previous identification of 2-aminoimidazole (2-AI) based AGE inhibitors and breakers, we now report the use of a rapid, scalable, two-step procedure to access a second generation of 2-AI based anti-AGE compounds from commercially available amino acids. Several second generation compounds exhibit increased AGE inhibition and breaking activty compared to the first generation compounds and to the known AGE inhibitor aminoguanidine.

Inhibition and breaking of advanced glycation end-products (AGEs) with bis-2-aminoimidazole derivatives.

Advanced glycation end-products (AGEs), unregulated modifications to host macromolecules that occur as a result of metabolic dysregulation, play a role in many diabetes related complications, inflammation and aging, and may lead to increased cardiovascular risk. Small molecules that have the ability to inhibit AGE formation, and even break preformed AGEs have enormous therapeutic potential in the treatment of these disease states. We report the screening of a series of 2-aminoimidazloles for anti-AGE activity, and the identification of a bis-2-aminoimidazole lead compound that possesses superior AGE inhibition and breaking activity compared to the known AGE inhibitor aminoguanidine.

Presence of multiple lesion types with vastly different microenvironments in C3HeB/FeJ mice following aerosol infection with Mycobacterium tuberculosis.

Cost-effective animal models that accurately reflect the pathological progression of pulmonary tuberculosis are needed to screen and evaluate novel tuberculosis drugs and drug regimens. Pulmonary disease in humans is characterized by a number of heterogeneous lesion types that reflect differences in cellular composition and organization, extent of encapsulation, and degree of caseous necrosis. C3HeB/FeJ mice have been increasingly used to model tuberculosis infection because they produce hypoxic, well-defined granulomas exhibiting caseous necrosis following aerosol infection with Mycobacterium tuberculosis. A comprehensive histopathological analysis revealed that C3HeB/FeJ mice develop three morphologically distinct lesion types in the lung that differ with respect to cellular composition, degree of immunopathology and control of bacterial replication. Mice displaying predominantly the fulminant necrotizing alveolitis lesion type had significantly higher pulmonary bacterial loads and displayed rapid and severe immunopathology characterized by increased mortality, highlighting the pathological role of an uncontrolled granulocytic response in the lung. Using a highly sensitive novel fluorescent acid-fast stain, we were able to visualize the spatial distribution and location of bacteria within each lesion type. Animal models that better reflect the heterogeneity of lesion types found in humans will permit more realistic modeling of drug penetration into solid caseous necrotic lesions and drug efficacy testing against metabolically distinct bacterial subpopulations. A more thorough understanding of the pathological progression of disease in C3HeB/FeJ mice could facilitate modulation of the immune response to produce the desired pathology, increasing the utility of this animal model.

Human IL-32 expression protects mice against a hypervirulent strain of Mycobacterium tuberculosis.

Silencing of interleukin-32 (IL-32) in a differentiated human promonocytic cell line impairs killing of Mycobacterium tuberculosis (MTB) but the role of IL-32 in vivo against MTB remains unknown. To study the effects of IL-32 in vivo, a transgenic mouse was generated in which the human IL-32γ gene is expressed using the surfactant protein C promoter (SPC-IL-32γTg). Wild-type and SPC-IL-32γTg mice were infected with a low-dose aerosol of a hypervirulent strain of MTB (W-Beijing HN878). At 30 and 60 d after infection, the transgenic mice had 66% and 85% fewer MTB in the lungs and 49% and 68% fewer MTB in the spleens, respectively; the transgenic mice also exhibited greater survival. Increased numbers of host-protective innate and adaptive immune cells were present in SPC-IL-32γTg mice, including tumor necrosis factor-alpha (TNFα) positive lung macrophages and dendritic cells, and IFN-gamma (IFNγ) and TNFα positive CD4(+) and CD8(+) T cells in the lungs and mediastinal lymph nodes. Alveolar macrophages from transgenic mice infected with MTB ex vivo had reduced bacterial burden and increased colocalization of green fluorescent protein-labeled MTB with lysosomes. Furthermore, mouse macrophages made to express IL-32γ but not the splice variant IL-32ß were better able to limit MTB growth than macrophages capable of producing both. The lungs of patients with tuberculosis showed increased IL-32 expression, particularly in macrophages of granulomas and airway epithelial cells but also B cells and T cells. We conclude that IL-32γ enhances host immunity to MTB.