Growth of Mycobacterium tuberculosis in vivo segregates with host macrophage metabolism and ontogeny

Restriction of mitochondrial oxidation of glutamine or fatty acids enhances intracellular growth of Mycobacterium abscessus in macrophages

Mycobacterium abscessus (Mab), a nontuberculous mycobacterium, is increasing in prevalence worldwide and causes treatment-refractory pulmonary diseases. However, how Mab rewires macrophage energy metabolism to facilitate its survival is poorly understood. We compared the metabolic profiles of murine bone marrow-derived macrophages (BMDMs) infected with smooth (S)- and rough (R)-type Mab using extracellular flux technology. Mab infection shifted BMDMs towards a more energetic phenotype, marked by increased oxidative phosphorylation (OXPHOS) and glycolysis, with a significantly greater enhancement in OXPHOS. This metabolic adaptation was characterized by enhanced ATP production rates, particularly in cells infected with S-type Mab, highlighting OXPHOS as a key energy source. Notably, Mab infection also modulated mitochondrial substrate preferences, increasing fatty acid oxidation capabilities while revealing significant changes in glutamine dependency and flexibility. R-type Mab infections exhibited a marked decrease in glutamine reliance but enhanced metabolic flexibility and capacity. Furthermore, targeting metabolic pathways related to glutamine and fatty acid oxidation exacerbated Mab growth within macrophages, suggesting these pathways play a protective role against infection. These insights advance our understanding of Mab's impact on host cell metabolism and propose a novel avenue for therapeutic intervention. By manipulating host mitochondrial metabolism, we identify a potential host-directed therapeutic strategy against Mab, offering a promising alternative to conventional treatments beleaguered by drug resistance. This study underscores the importance of exploring metabolic interventions to combat Mab infection, paving the way for innovative approaches in the fight against this formidable pathogen.

Alveolar macrophages: guardians of the alveolar lipid galaxy

PURPOSE OF REVIEW

As the primary guardians at the air-surface interface, the functional profile of alveolar macrophages (AM) is wide-ranging from establishment of the alveolar niche, homeostatic maintenance of surfactant levels, to pathogen clearance and resolution and repair processes. Alveolar lipid homeostasis is disturbed in chronic lung diseases and contributes to disease pathogenesis through extracellular localization in the alveolar lumen or intracellular accumulation in AM. This review aims to provide a focused overview of the state of knowledge of AM, their ontogeny and development during health and disease, and how dysregulated AM lipids play a key role in disease processes, from initiation to resolution.

RECENT FINDINGS

While lipid-laden macrophages are observed across a broad spectrum of lung diseases, their occurrence has largely been considered consequential. Recent advances in lipidomic profiling of single cell types has revealed that disturbances to lipid homeostasis occur early in disease in tissue-resident cells. Comparisons between inflammatory and fibrotic injury models reveal specific alveolar macrophage subsets with different lipid utilization that contribute to the disease process.

SUMMARY

Understanding the intricate web of AM population seeding and development and how this niche is perturbed by lipid disturbances may help provide leverage for new interventions.

Using host and bacterial genetic approaches to define virulence strategies and protective immunity during Mycobacterium tuberculosis infection

Infections with Mycobacterium tuberculosis (Mtb) resulted in over one million deaths in 2024, the highest number for any infectious disease. With no vaccines that protect against pulmonary tuberculosis (TB) and the challenges associated with antibiotic therapy, there is a critical need to better understand host-Mtb interactions to help curb this major public health problem. Mtb is arguably the most successful human pathogen, and it survives in diverse environments, resulting in heterogeneous disease outcomes in patients. Five years ago, in my commentary in mSphere, I discussed how Mtb virulence strategies that sense, adapt, and evade killing in the host can be uncovered using genetic approaches. Here, I will come full circle to highlight genetic approaches that recently uncovered new mechanisms regulating protective host responses and Mtb survival tactics. The goal is to highlight a genetic framework to probe a range of unexplored Mtb phenotypes, increase our understanding of host-Mtb interactions, and identify new therapeutic targets that may help prevent TB.

Limitation of Deleterious iNOS-Expressing Interstitial Macrophages Is Dependent on Protective IL-1α and IL-17 in Tuberculosis and Existing Obesity

IL-1α, IL-1β, IFN-γ, IL-17 and the expression of inducible nitric oxide synthase (iNOS) enzyme by macrophages, which generate nitric oxide, are protective against tuberculosis, a disease caused by Mycobacterium tuberculosis. The severity of tuberculosis can be dependent on bacterial load and/or lung immunopathology. Tuberculosis is aggravated by existing comorbidities such as obesity. Obesity induces metabolic dysfunction, meta inflammation and dysbiosis, which increase the prevalence of respiratory diseases and worsen immunopathology. The deficiency of IL-1α (IL-1α-/-) induces deleterious lung monocytic inflammation and functional activation of the adaptive immune response mediated by T cells during M. tuberculosis infection in non-obese mice. Although iNOS and IFN-γ have been described as protective in experimental tuberculosis, using a model of obesity induced by high-fat diet, we show here an increase in iNOS-expressing interstitial macrophages positively correlated with M. tuberculosis numbers in the lungs of IL-1α-/- animals, followed by increased frequency of IFN-γ and decreased frequency of IL-17-producing T cells, showing that IFN-γ and iNOS contribute to immunopathology and pulmonary damage. The protective effect of IL-1α, characterised by reduction of lung immunopathology, is dependent on IL-17-producing CD4+ cells that negatively regulate iNOS expression on macrophages. Our data provide important implications for tuberculosis with existing obesity that aggravates lung immunopathology associated with an exacerbation of IFN-γ-producing and iNOS-expressing cells.

Mycobacterium tuberculosis curli pili reduces oxygen consumption rate of THP-1 macrophages during early infection

The development of improved anti-tuberculosis (TB) strategies to address drug-resistance and ineffectual TB treatment regimens should focus on interrupting the initial host-pathogen interaction. This study aimed to elucidate the effect of surface-located adhesin, Mycobacterium tuberculosis (Mtb) curli pili (MTP), on the bioenergetic and metabolomic profiles of THP-1 macrophages during initial stages of infection. Differentiated THP-1 macrophages were infected with wildtype (WT), ∆mtp, or mtp-complemented strains of Mtb. Bioenergetic profiles and metabolic flux were determined and statistical analysis highlighted differences/similarities amongst the THP-1 macrophage groups. The ∆mtp infected THP-1 macrophages mimicked the higher oxygen consumption rate (OCR) for basal respiration, ATP production, maximal respiration and spare respiratory capacity of the uninfected THP-1 macrophages, relative to the WT and mtp-complement infected THP-1 macrophages. The ∆mtp infected THP-1 macrophages displayed the highest compensatory glycolytic rate. Mtb infection caused the redirection of carbon from the tricarboxylic acid cycle to glycolysis, in addition to an increased flux through the pentose phosphate pathway. However, in the ∆mtp infected THP-1 macrophages, the total metabolite abundance was lower, similar to the uninfected THP-1 macrophages. Data indicates that the absence of MTP facilitates prompt clearance of the intracellular pathogen before it establishes a successful infection. This implies that the presence of MTP facilitates the survival of the pathogen during the early stages until infection is established. These findings support the growing evidence that the MTP adhesin is an important virulence factor and interruption of the interaction between pathogen and host, will facilitate swift clearance of the infection by the host.

A review on biomacromolecular ligand-directed nanoparticles: New era in macrophage targeting

Traditional drug delivery strategies often have side effects due to uneven drug distribution leading to the subtherapeutic impacts. Ligand-modified nanoparticles offer a revolutionary approach to precise drug delivery. These modified nanoparticles can potentially target macrophages, which is crucial for defense and disease progression efficiently. Out of many classes of ligands, biomacromolecular ligands emerged as potential ligands for directing these nanoparticles to macrophages due to their consecutive receptors over the macrophage surface, assisting easy internalization and thus supporting elevated efficacy and reduced toxicity. This approach could significantly improve treatment for diseases like cancer, tuberculosis, etc. by directing drugs to macrophages and reducing side effects. By leveraging nanotechnology and biomacromolecular-based ligand-directed targeting, we can achieve more precise and effective treatments, paving the way for advancements in precision medicine.

How macrophage heterogeneity affects tuberculosis disease and therapy

Macrophages are the primary host cell type for infection by Mycobacterium tuberculosis in vivo. Macrophages are also key immune effector cells that mediate the control of bacterial growth. However, the specific macrophage phenotypes that are required for optimal immune control of M. tuberculosis infection in vivo remain poorly defined. There are two distinct macrophage lineages in the lung, comprising embryonically derived, tissue-resident alveolar macrophages and recruited, blood monocyte-derived interstitial macrophages. Recent studies have shown that these lineages respond divergently to similar immune environments within the tuberculosis granuloma. Here, we discuss how the differing responses of macrophage lineages might affect the control or progression of tuberculosis disease. We suggest that the ability to reprogramme macrophage responses appropriately, through immunological or chemotherapeutic routes, could help to optimize vaccines and drug regimens for tuberculosis.

Genetically Diverse Mycobacterium tuberculosis Isolates Manipulate Inflammasome and Interleukin 1β Secretion Independently of Macrophage Metabolic Rewiring

The diversity of Mycobacterium tuberculosis impacts the outcome of tuberculosis. We previously showed that M. tuberculosis isolates obtained from patients with severe disease induced low inflammasome activation and interleukin 1β (IL-1β) production by infected macrophages. Here we questioned whether this differential modulation of macrophages by M. tuberculosis isolates depended on distinct metabolic reprogramming. We found that the macrophage metabolic landscape was similar regardless of the infecting M. tuberculosis isolate. Paralleling single-Toll-like receptor (TLR) activated macrophages, glycolysis inhibition during infection impaired IL-1β secretion. However, departing from TLR -based models, in infected macrophages, IL-1β secretion was independent of mitochondrial metabolic changes and hypoxia-inducible factor 1α (HIF-1α). Additionally, we found an unappreciated impact of a host metabolic inhibitor on the pathogen, and show that inflammasome activation and IL-1β production by macrophages require metabolically active bacteria. Our study highlights the potential confounding effect of host metabolic inhibitors on the pathogen and uncoupling of M. tuberculosis-inflammasome modulation from the host metabolic reprogramming.

Chemokine CXCL14 Inhibits the Survival of Mycobacterium smegmatis inside Macrophages by Upregulating A20 to Promote ROS Production

Tuberculosis remains a major global health threat, with traditional antibiotic treatments facing challenges such as drug resistance. Host-directed therapy (HDT) has emerged as a promising approach to combat tuberculosis by enhancing the host immune response. CXCL14, a chemokine family member, plays a crucial role in regulating host antipathogenic immune responses. To elucidate the role of CXCL14 and its key regulatory molecules in mycobacterial infections, we identified new targets for host-directed therapy. RAW264.7 macrophages were pretreated with CXCL14 and infected with Mycobacterium smegmatis. CFU, ROS levels, and apoptosis were assessed. Cell RNA was extracted for high-throughput sequencing, and significantly differentially expressed genes were screened and identified. The effects of candidate genes were verified using knockdown and overexpression techniques. A mouse model of mycobacterial infection was established to validate the role of CXCL14 in vivo. CXCL14 pretreatment significantly reduced intracellular mycobacteria and increased ROS levels in macrophages without affecting apoptosis. Transcriptome analysis identified A20 as a key differentially expressed gene. A20 overexpression promoted ROS production and decreased intracellular mycobacteria, while A20 knockdown reversed these effects. The combination of CXCL14 and A20 overexpression effectively inhibited mycobacterial survival in macrophages. CXCL14 significantly inhibited mycobacterial survival in mice and reduced organ damage in vivo. CXCL14 promoted ROS production in macrophages by upregulating A20 expression, thereby inhibiting mycobacterial survival. In the mouse model, CXCL14 alleviated inflammatory responses and histopathological damage caused by mycobacterial infection. These findings suggest that CXCL14 is a promising new HDT molecule for the treatment of mycobacterial infections.

Host-directed therapy for tuberculosis

Current TB treatment regimens are hindered by drug resistance, numerous adverse effects, and long treatment durations, highlighting the need for 'me-better' treatment regimens. Host-directed therapy (HDT) has gained recognition as a promising approach in TB treatment. It allows the repurposing of existing drugs approved for other conditions and aims to enhance the effectiveness of existing anti-TB therapies, minimize drug resistance, decrease treatment duration, and adverse effects. By modulating the host immune response, HDT ameliorates immunopathological damage and improves overall outcomes by promoting autophagy, antimicrobial peptide production, and other mechanisms. It holds promise for addressing the challenges posed by multiple and extensively drug-resistant Mycobacterium tuberculosis strains, which are increasingly difficult to treat using conventional therapies. This article reviews various HDT candidates, including repurposed drugs, explores their underlying mechanisms such as autophagy promotion and inflammation reduction, while emphasizing their potential to improve TB treatment outcomes and outlining future research directions.

Deconvoluting the interplay of innate and adaptive immunity in BCG-induced nonspecific and TB-specific host resistance

BCG is the oldest vaccine in continuous use. While current intradermal vaccination regimens confer limited protection outside the context of pediatric extrapulmonary tuberculosis (TB), promising new data indicate that when administered mucosally or intravenously at a higher dose, BCG can induce sterilizing immunity against pulmonary TB in nonhuman primates. BCG is also known to promote nonspecific host resistance against a variety of unrelated infections and is a standard immunotherapy for bladder cancer, suggesting that this innate immune function may contribute to its protective role against TB. Here, we propose that both the mycobacterial-specific and off-target effects of BCG depend on the interplay of adaptive and innate cells and the cytokines they produce, and that the elucidation of this interaction should be a major strategy in the development of more effective BCG-based vaccines and immunotherapies.

Macrophage Differentiation and Metabolic Adaptation in Mycobacterial Infections

The adaptation of macrophages-the most common tissue-resident immune cells-to metabolic and microbial cues with high local variability is essential for the maintenance of organ integrity. In homeostasis, macrophages show largely predictable tissue-specific differentiation, as recently revealed by multidimensional methods. However, chronic infections with human-adapted pathogens substantially contribute to the differentiation complexity of tissue macrophages, which has been only partially resolved. Specifically, the response to mycobacterial species-which range from Mycobacterium tuberculosis (with highest specificity for humans, broad organ tropism, yet tissue-specific disease phenotypes) to environmental mycobacteria with humans as accidental hosts-may serve as a paradigm of tissue macrophage adaptation mechanisms. While mycobacterial species-specific tissue preferences are partially related to the mode of acquisition and pathogen characteristics, evolutionary convergence with macrophages driven by metabolic features of the target organ likely contributes to infection resistance and immunopathology. In this review, we unravel the mechanisms of tissue-specific macrophage differentiation and its limitations in mycobacterial infections.

Interleukin-1 receptor antagonist is a conserved early factor for exacerbating tuberculosis susceptibility

Mycobacterium tuberculosis (Mtb) causes 1.25 million deaths a year. However, tuberculosis (TB) pathogenesis remains poorly understood and is not fully recapitulated in standard mouse models. Here we find that gene signatures from three different Mtb-susceptible mouse models predict active TB disease in humans significantly better than a signature from resistant C57BL/6 (B6) mice. Conserved among susceptible mice, non-human primates, and humans, but largely absent from B6 mice, was Mtb-induced differentiation of macrophages into an Spp1 + differentiation state. Spp1 + macrophages expressed high levels of immunosuppressive molecules including IL-1 receptor antagonist (IL-1Ra). IL-1Ra was previously reported to cause Mtb susceptibility in one mouse model, but whether IL-1Ra is broadly important remains uncertain. Here we report that enhancement of IL-1 signaling via deletion of IL-Ra promoted bacterial control across three susceptible mouse models. We found IL-1 signaling amplified production of multiple cytokines by lymphoid and stromal cells, providing a multifactorial mechanism for how IL-1 promotes Mtb control. Our results indicate that myeloid cell expression of immunosuppressive molecules, in particular IL-1 receptor antagonist, is a conserved early mechanism limiting Mtb control in mice, non-human primates, and humans.

Impaired fatty acid import or catabolism in macrophages restricts intracellular growth of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infection of macrophages reprograms cellular metabolism to promote lipid retention. While it is clearly known that intracellular Mtb utilize host-derived lipids to maintain infection, the role of macrophage lipid processing on the bacteria's ability to access the intracellular lipid pool remains undefined. We utilized a CRISPR-Cas9 genetic approach to assess the impact of sequential steps in fatty acid metabolism on the growth of intracellular Mtb. Our analyses demonstrate that macrophages that cannot either import, store, or catabolize fatty acids restrict Mtb growth by both common and divergent antimicrobial mechanisms, including increased glycolysis, increased oxidative stress, production of pro-inflammatory cytokines, enhanced autophagy, and nutrient limitation. We also show that impaired macrophage lipid droplet biogenesis is restrictive to Mtb replication, but increased induction of the same fails to rescue Mtb growth. Our work expands our understanding of how host fatty acid homeostasis impacts Mtb growth in the macrophage.

Shared and distinct responses of human and murine alveolar macrophages and monocyte-derived macrophages to Mycobacterium tuberculosis

Macrophages serve as important sites of bacterial replication and host immune response during Mycobacterium tuberculosis (Mtb) infection with distinct roles for alveolar macrophages (AMs) early in infection and monocyte-derived (MDMs) during later stages of disease. Here, we leverage data from human and mouse models to perform a cross-species analysis of macrophage responses to Mtb infection. Overall, we find that both subsets of human and murine macrophages mount a strong interferon response to Mtb infection. However, AM across both species do not generate as strong a pro-inflammatory response as human MDMs or murine bone marrow-derived macrophages (BMDMs), as characterized by TNFA signaling and inflammatory response pathways. Interestingly, AMs from mice that were previously vaccinated with BCG (scBCG) or from a model of contained TB (coMtb) had Mtb responses that were more similar to human AMs than control mice. We also identify species-specific pathways altered by infection differently in mouse and human macrophages, specifically in pathways related to cholesterol in AMs as well as MYC targets and Hedgehog signaling in MDMs/BMDMs. Lastly, to investigate downstream effects of the macrophage interferon responses, we examine macrophage expression of IL-10, an immunosuppressive cytokine induced by Type I Interferons, and c-Maf, a transcription factor required for IL-10 expression in myeloid cells. We find that c-Maf and IL-10 have significantly lower expression in AMs compared to MDMs in both humans and mice, suggesting one possible mechanism by which AMs mount a stronger interferon response following Mtb infection. Overall, these results highlight the dynamics of innate myeloid responses over the course of Mtb infection and the benefit of a combined analysis across species to reveal conserved and unique responses.

Differential expression of genes associated with lipid import, β-oxidation and lactate oxidation induced by Mycobacterium tuberculosis curli pili in broth culture compared to intracellular bacilli within THP-1 macrophages

Introduction. The adhesin, Mycobacterium tuberculosis curli pili (MTP), assists the pathogen in attachment, invasion and disease progression. Previously, this adhesin was demonstrated to contribute to the pathogen's cell wall functions and fatty acid metabolism and affects total metabolite abundance in central carbon metabolism and fatty acid metabolism of the host. The accumulation/depletion of metabolites is reliant on the gene expression of proteins involved in the import, transport and breakdown of substrates.Gap statement. MTP has not been investigated in relation to genes involved in import/transport/breakdown of substrates.Aim. This study aimed to investigate the possible regulatory role of MTP in modulating metabolic changes of the pathogen in different microenvironments.Methods. Ribonucleic acid was harvested from bacterial broth cultures of adhesin-proficient and adhesin-deficient M. tuberculosis. These strains were also used to infect differentiated THP-1 macrophages for 4 h prior to isolation of intracellular bacteria, RNA extraction and reverse transcription real-time quantitative PCR. The expression levels of selected genes involved in fatty acid transport (lucA, mce1D, mceG, Rv2799, Rv0966c and omamB), β-oxidation (fadA5 and fadB), lactate oxidation (lldD1 and lldD2) and gluconeogenic carbon flow (pckA) were analysed by absolute quantification.Results. The gene expression levels of lucA, mce1D and pckA were significantly lower, and those of Rv2799, Rv0966c, mceG, fadA5 and lldD2 were significantly higher in the adhesin-proficient cultured bacterial strains relative to the Δmtp strain. The intracellular adhesin-proficient bacteria displayed significantly higher gene expression levels of Rv2799 and significantly lower gene expression levels of Rv0966c, fadA5, lldD1 and pckA relative to the Δmtp strain. Interestingly, during early infection, the intracellular Δmtp displayed significantly increased expression of omamB, mceG, fadB, lldD1 and lldD2 relative to the broth culture. This trend was inverted in the WT models.Conclusion. MTP are significantly associated with the regulation of genes involved in lipid transport, β-oxidation and lactate oxidation.

Differences in glycolytic metabolism between tissue-resident alveolar macrophages and recruited lung macrophages

Immunometabolism has emerged as a key area of focus in immunology and has the potential to lead to new treatments for immune-related diseases. It is well-established that glycolytic metabolism is essential for adaptation to hypoxia and for macrophage inflammatory function. Macrophages have been shown to upregulate their glycolytic metabolism in response to pathogens and pathogen-associated molecular patterns such as LPS. As a direct link to the external environment, the lungs' distinctive nutrient composition and multiple macrophage subtypes provide a unique opportunity to study macrophage metabolism. This review aims to highlight how the steady-state airway and severely inflamed airway offer divergent environments for macrophage glycolytic metabolism. We describe the differences in glycolytic metabolism between tissue-resident alveolar macrophages, and other lung macrophages at steady-state and during inflammation/injury. We also provide an overview of experimental guidelines on how to assess metabolism at the cellular level using Seahorse-based bioenergetic analysis including a review of pharmacologic agents used to inhibit or activate glycolysis.

The immunometabolic topography of tuberculosis granulomas governs cellular organization and bacterial control

Despite being heavily infiltrated by immune cells, tuberculosis (TB) granulomas often subvert the host response to Mycobacterium tuberculosis (Mtb) infection and support bacterial persistence. We previously discovered that human TB granulomas are enriched for immunosuppressive factors typically associated with tumor-immune evasion, raising the intriguing possibility that they promote tolerance to infection. In this study, our goal was to identify the prime drivers for establishing this tolerogenic niche and to determine if the magnitude of this response correlates with bacterial persistence. To do this, we conducted a multimodal spatial analysis of 52 granulomas from 16 non-human primates (NHP) who were infected with low dose Mtb for 9-12 weeks. Notably, each granuloma's bacterial burden was individually quantified allowing us to directly ask how granuloma spatial structure and function relate to infection control. We found that a universal feature of TB granulomas was partitioning of the myeloid core into two distinct metabolic environments, one of which is hypoxic. This hypoxic environment associated with pathologic immune cell states, dysfunctional cellular organization of the granuloma, and a near-complete blockade of lymphocyte infiltration that would be required for a successful host response. The extent of these hypoxia-associated features correlated with worsened bacterial burden. We conclude that hypoxia governs immune cell state and organization within granulomas and is a potent driver of subverted immunity during TB.

Building Spatiotemporal Understanding of Mycobacterium tuberculosis-Host Interactions

Heterogeneity during Mycobacterium tuberculosis (Mtb) infection greatly impacts disease outcome and complicates treatment. This heterogeneity encompasses many facets, spanning local differences in the host immune response to Mtb and the environment experienced by the bacterium, to nonuniformity in Mtb replication state. All of these facets are interlinked and each can affect Mtb susceptibility to antibiotic treatment. In-depth spatiotemporal understanding of Mtb-host interactions is thus critical to both fundamental comprehension of Mtb infection biology and for the development of effective therapeutic regimens. Such spatiotemporal understanding dictates the need for analysis at the single bacterium/cell level in the context of intact tissue architecture, which has been a significant technical challenge. Excitingly, innovations in spatial single cell methodology have opened the door to such studies, beginning to illuminate aspects ranging from intergranuloma differences in cellular composition and phenotype, to sublocation differences in Mtb physiology and replication state. In this perspective, we discuss recent studies that demonstrate the potential of these methodological advancements to reveal critical spatiotemporal insight into Mtb-host interactions, and highlight future avenues of research made possible by these advances.

In vivo regulation of the monocyte phenotype by Mycobacterium marinum and the ESX-1 type VII secretion system

Pathogenic mycobacteria require the conserved ESX-1 type VII secretion system to cause disease. In a murine Mycobacterium marinum infection model we previously demonstrated that infiltrating monocytes and neutrophils represent the major bacteria-harbouring cell populations in infected tissue. In the current study we use this model, in combination with scRNA sequencing, to assess the impact of M. marinum infection on the transcriptional profile of infiltrating Ly6C⁺MHCII⁺ monocytes in vivo. Our findings demonstrate that infection of infiltrating monocytes with M. marinum alters their cytokine expression profile, induces glycolytic metabolism, hypoxia-mediated signaling, nitric oxide synthesis, tissue remodeling, and suppresses responsiveness to IFNγ. We further show that the transcriptional response of bystander monocytes is influenced by ESX-1-dependent mechanisms, including a reduced responsiveness to IFNγ. These findings suggest that mycobacterial infection has pleiotropic effects on monocyte phenotype, with potential implications in bacterial growth restriction and granuloma formation.

Tuberculosis as an unconventional interferonopathy

Tuberculosis is caused by Mycobacterium tuberculosis, a bacterium that accounts for more human mortality than any other. Evidence is accumulating for the view that tuberculosis is an interferonopathy - a disease driven by type I interferons. However, how type I interferons exacerbate tuberculosis remains poorly understood. As an infection, tuberculosis is distinct from conventional interferonopathies, which are autoinflammatory diseases. Here I consider the hypothesis that type I interferons promote bacterial replication by impairing key antibacterial immune responses, including those orchestrated by interleukin-1 and interferon γ. Paradoxically, during tuberculosis, the underlying state of impaired antibacterial immunity co-exists with overt (but ineffective) inflammation. Conceiving of tuberculosis as an unconventional interferonopathy may suggest fruitful avenues for therapeutic intervention.

BATF2/SINHCAF regulates the quantity and function of macrophages infected with Mycobacterium Tuberculosis via regulation of TTC23 through Wnt/β-catenin pathway

Elucidating the pathogenic mechanism of Tuberculosis (TB) can contribute to control TB. Basic leucine zipper transcription factor ATF-like 2 (BATF2) belonging to a large family of leucine zipper transcription factors (TFs) termed bZip proteins, had been verified to have important value in the diagnosis of TB. However, its role and mechanism in TB had not been elucidated. The study aimed to explore its function and molecular mechanism in macrophages infected with Mycobacterium tuberculosis (Mtb). The results indicated that BATF2 inhibited cell proliferation, promoted inflammatory response and impaired the antibacterial and antigen-presenting capacity in macrophages for T cells through regulating its downstream gene TTC23 by interacting with SINHCAF. Above roles and regulations were dependent on β-catenin functions in macrophages infected with Mtb. Clinical samples verified that the expressions of BATF2 and TTC23 were significantly higher in the blood of patients with pulmonary TB compared with health controls. Altogether, BATF2 interacted with SINHCAF to regulate the quantity and function of macrophages during Mtb infection by targeting TTC23 through Wnt/β-catenin pathway.

Inducible antibacterial responses in macrophages

Macrophages destroy bacteria and other microorganisms through phagocytosis-coupled antimicrobial responses, such as the generation of reactive oxygen species and the delivery of hydrolytic enzymes from lysosomes to the phagosome. However, many intracellular bacteria subvert these responses, escaping to other cellular compartments to survive and/or replicate. Such bacterial subversion strategies are countered by a range of additional direct antibacterial responses that are switched on by pattern-recognition receptors and/or host-derived cytokines and other factors, often through inducible gene expression and/or metabolic reprogramming. Our understanding of these inducible antibacterial defence strategies in macrophages is rapidly evolving. In this Review, we provide an overview of the broad repertoire of antibacterial responses that can be engaged in macrophages, including LC3-associated phagocytosis, metabolic reprogramming and antimicrobial metabolites, lipid droplets, guanylate-binding proteins, antimicrobial peptides, metal ion toxicity, nutrient depletion, autophagy and nitric oxide production. We also highlight key inducers, signalling pathways and transcription factors involved in driving these different antibacterial responses. Finally, we discuss how a detailed understanding of the molecular mechanisms of antibacterial responses in macrophages might be exploited for developing host-directed therapies to combat antibiotic-resistant bacterial infections.

3D Hydrogel Culture System Recapitulates Key Tuberculosis Phenotypes and Demonstrates Pyrazinamide Efficacy

The mortality caused by tuberculosis (TB) infections is a global concern, and there is a need to improve understanding of the disease. Current in vitro infection models to study the disease have limitations such as short investigation durations and divergent transcriptional signatures. This study aims to overcome these limitations by developing a 3D collagen culture system that mimics the biomechanical and extracellular matrix (ECM) of lung microenvironment (collagen fibers, stiffness comparable to in vivo conditions) as the infection primarily manifests in the lungs. The system incorporates Mycobacterium tuberculosis (Mtb) infected human THP-1 or primary monocytes/macrophages. Dual RNA sequencing reveals higher mammalian gene expression similarity with patient samples than 2D macrophage infections. Similarly, bacterial gene expression more accurately recapitulates in vivo gene expression patterns compared to bacteria in 2D infection models. Key phenotypes observed in humans, such as foamy macrophages and mycobacterial cords, are reproduced in the model. This biomaterial system overcomes challenges associated with traditional platforms by modulating immune cells and closely mimicking in vivo infection conditions, including showing efficacy with clinically relevant concentrations of anti-TB drug pyrazinamide, not seen in any other in vitro infection model, making it reliable and readily adoptable for tuberculosis studies and drug screening.

Metabolomics in the Diagnosis of Bacterial Infections

One of the essential factors in the appropriate treatment of infections is accurate and timely laboratory diagnosis. The correct diagnosis of infections plays a vital role in determining desirable therapy and controlling the spread of pathogens. Traditional methods of infection diagnosis are limited by several factors such as insufficient sensitivity and specificity, being time-consuming and laborious, having a low ability to distinguish infection from non-infectious inflammatory conditions and a low potential to predict treatment outcomes. Therefore, it is necessary to find innovative strategies for detecting specific biomarkers in order to diagnose infections. The rapid advancement of metabolomics makes it possible to determine the pattern of metabolite changes in the both of pathogen and the host during an infection. Metabolomics is a method used to assess the levels and type of metabolites in an organism. Metabolites are of low-molecular-weight compounds produced as a result of metabolic processes and pathways within cells. Metabolomics provides valuable data to detect accurate biomarkers of specific biochemical features directly related to certain phenotypes or conditions. This study aimed to review the applications and progress of metabolomics as a biomarker for the diagnosis of bacterial infections.

Impaired fatty acid import or catabolism in macrophages restricts intracellular growth of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infection of macrophages reprograms cellular metabolism to promote lipid retention. While it is clearly known that intracellular Mtb utilize host derived lipids to maintain infection, the role of macrophage lipid processing on the bacteria's ability to access the intracellular lipid pool remains undefined. We utilized a CRISPR-Cas9 genetic approach to assess the impact of sequential steps in fatty acid metabolism on the growth of intracellular Mtb. Our analyzes demonstrate that macrophages which cannot either import, store or catabolize fatty acids restrict Mtb growth by both common and divergent anti-microbial mechanisms, including increased glycolysis, increased oxidative stress, production of pro-inflammatory cytokines, enhanced autophagy and nutrient limitation. We also show that impaired macrophage lipid droplet biogenesis is restrictive to Mtb replication, but increased induction of the same fails to rescue Mtb growth. Our work expands our understanding of how host fatty acid homeostasis impacts Mtb growth in the macrophage.

High-dose intravenous BCG vaccination induces enhanced immune signaling in the airways

Intradermal Bacillus Calmette-Guérin (BCG) is the most widely administered vaccine, but it does not sufficiently protect adults against pulmonary tuberculosis. Recent studies in nonhuman primates show that intravenous BCG administration offers superior protection against Mycobacterium tuberculosis (Mtb). We used single-cell analysis of bronchoalveolar lavage cells from rhesus macaques vaccinated via different routes and doses of BCG to identify alterations in the immune ecosystem in the airway following vaccination. Our findings reveal that high-dose intravenous BCG induces an influx of polyfunctional T cells and macrophages in the airways, with alveolar macrophages from high-dose intravenous BCG displaying a basal activation state in the absence of purified protein derivative stimulation, defined in part by interferon signaling. Enhanced intercellular immune signaling and stronger T helper 1-T helper 17 transcriptional responses were observed following purified protein derivative stimulation. These results suggest that high-dose intravenous BCG vaccination creates a specialized immune environment that primes airway cells for effective Mtb clearance.

Eosinophils Enhance Granuloma-Mediated Control of Persistent Salmonella Infection

Salmonella enterica can persist asymptomatically within tissues for extended periods. This remarkable feat is achieved through intricate host-pathogen interactions in immune cell aggregates called granulomas, wherein Salmonella find favorable cellular niches to exploit while the host limits its expansion and tissue dissemination. Here, using a mouse model of persistent Salmonella infection, we identify a host-protective role of eosinophils in control of Salmonella Typhimurium (STm) infection within the mesenteric lymph nodes (MLN), the main lymphoid tissue of STm persistence. Combining spatial transcriptomics and experimental manipulations, we found that macrophages responding to STm infection recruited eosinophils in a C-C motif chemokine ligand 11 (CCL11)-dependent manner and enhanced their activation. Eosinophil deficiencies increased Salmonella burdens, which was associated with altered granuloma size and impaired type-1 immunity in the MLN. Thus, eosinophils play a vital role in restraining Salmonella exploitation of granuloma macrophages at a key site of bacterial persistence.

Metformin improves Mycobacterium avium infection by strengthening macrophage antimicrobial functions

Introduction

The incidence and prevalence of infections with non-tuberculous mycobacteria such as Mycobacterium avium (Mav) are increasing. Prolonged drug regimens, inherent antibiotic resistance, and low cure rates underscore the need for improved treatment, which may be achieved by combining standard chemotherapy with drugs targeting the host immune system. Here, we examined if the diabetes type 2 drug metformin could improve Mav-infection.

Methods

Metformin was administered to C57BL/6 mice infected intranasally with Mav and C57BL/6 mice were infected intranasally with Mav and treated with metformin over 3 weeks. Organ bacterial loads and lung pathology, inflammatory cytokines and immune cell profiles were assessed. For mechanistic insight, macrophages infected with Mav were treated with metformin alone or in combination with inhibitors for mitochondrial ROS or AMPK and assessed for bacterial burden and phagosome maturation.

Results and discussion

Three weeks of metformin treatment significantly reduced the lung mycobacterial burden in mice infected with Mav without major changes in the overall lung pathology or immune cell composition. Metformin treatment had no significant impact on tissue inflammation except for a tendency of increased lung IFNγ and infiltration of Mav-specific IFNγ-secreting T cells. Metformin did, however, boost the antimicrobial capacity of infected macrophages directly by modulating metabolism/activating AMPK, increasing mitochondrial ROS and phagosome maturation, and indirectly by bolstering type I immunity. Taken together, our data show that metformin improved the control of Mav-infection in mice, mainly by strengthening antimicrobial defenses in macrophages, and suggest that metformin has potential as an adjunct treatment of Mav infections.

Tax1bp1 enhances bacterial virulence and promotes inflammatory responses during Mycobacterium tuberculosis infection of alveolar macrophages

Crosstalk between autophagy, host cell death, and inflammatory host responses to bacterial pathogens enables effective innate immune responses that limit bacterial growth while minimizing coincidental host damage. Mycobacterium tuberculosis (Mtb) thwarts innate immune defense mechanisms in alveolar macrophages (AMs) during the initial stages of infection and in recruited bone marrow-derived cells during later stages of infection. However, how protective inflammatory responses are achieved during Mtb infection and the variation of the response in different macrophage subtypes remain obscure. Here, we show that the autophagy receptor Tax1bp1 plays a critical role in enhancing inflammatory cytokine production and increasing the susceptibility of mice to Mtb infection. Surprisingly, although Tax1bp1 restricts Mtb growth during infection of bone marrow-derived macrophages (BMDMs) (Budzik et al. 2020) and terminates cytokine production in response to cytokine stimulation or viral infection, Tax1bp1 instead promotes Mtb growth in AMs, neutrophils, and a subset of recruited monocyte-derived cells from the bone marrow. Tax1bp1 also leads to increases in bacterial growth and inflammatory responses during infection of mice with Listeria monocytogenes, an intracellular pathogen that is not effectively targeted to canonical autophagy. In Mtb-infected AMs but not BMDMs, Tax1bp1 enhances necrotic-like cell death early after infection, reprogramming the mode of host cell death to favor Mtb replication in AMs. Tax1bp1's impact on host cell death is a mechanism that explains Tax1bp1's cell type-specific role in the control of Mtb growth. Similar to Tax1bp1-deficiency in AMs, the expression of phosphosite-deficient Tax1bp1 restricts Mtb growth. Together, these results show that Tax1bp1 plays a crucial role in linking the regulation of autophagy, cell death, and pro-inflammatory host responses and enhancing susceptibility to bacterial infection.

Ferroptosis: A new way to intervene in the game between Mycobacterium tuberculosis and macrophages

Mycobacterium tuberculosis (Mtb), the main pathogen responsible for the high mortality and morbidity of tuberculosis (TB) worldwide, primarily targets and invades macrophages. Infected macrophages activate a series of immune mechanisms to clear Mtb, however, Mtb evades host immune surveillance through subtle immune escape strategies to create a microenvironment conducive to its own proliferation, growth, and dissemination, while inducing immune cell death. The course of TB is strongly correlated with the form of cell death, including apoptosis, pyroptosis, and necrosis. Recent studies have revealed that ferroptosis, a novel type of programmed cell death characterized by iron-dependent lipid peroxidation, is closely linked to the regulatory mechanisms of TB. The central role of ferroptosis in the pathologic process of TB is increasingly becoming a focal point for exploring new therapeutic targets in this field. This paper will delve into the dynamic game between Mtb and host immune cells, especially the role of ferroptosis in the pathogenesis of TB. At the same time, this paper will analyze the regulatory pathways of ferroptosis and provide unique insights and innovative perspectives for TB therapeutic strategies based on the ferroptosis mechanism. This study not only expands the theoretical basis of TB treatment, but also points out the direction of future drug development, providing new possibilities for overcoming this global health problem.

HUMAN ALVEOLAR MACROPHAGE FUNCTION IS IMPAIRED IN TUBERCULOSIS CONTACTS WITH DIABETES

Type 2 diabetes (T2D) increases susceptibility to tuberculosis (TB) with the underlying mechanisms remaining unknown. To determine whether immune dysfunction in the lung contributes to TB susceptibility, we obtained paired human alveolar macrophages (HAMs) and monocyte-derived macrophages (MDMs) from TB-exposed individuals with/without T2D. Upon infection with Mycobacterium tuberculosis (M.tb), T2D-HAMs had more M.tb growth and produced more TNF. There were fewer neutrophils in the bronchoalveolar lavage of T2D patients which was inversely correlated with M.tb growth. Both T2D-HAMs and MDMs expressed less CD32, with T2D patients having fewer M1-like MDMs. T2D-MDMs produced less IL-1RA and CSF2. Overall M.tb-induced gene expression was delayed in T2D-HAMs, but genes involved in negative regulation of neutrophil migration were upregulated. T2D-HAM DNA was hypermethylated compared to control HAMs, however genes linked to TNF signalling were hypomethylated. We show here the first in-depth analysis of T2D-HAMs providing an explanation for more severe TB in T2D patients.

Lung-resident alveolar macrophages regulate the timing of breast cancer metastasis

Breast disseminated cancer cells (DCCs) can remain dormant in the lungs for extended periods, but the mechanisms limiting their expansion are not well understood. Research indicates that tissue-resident alveolar macrophages suppress breast cancer metastasis in lung alveoli by inducing dormancy. Through ligand-receptor mapping and intravital imaging, it was found that alveolar macrophages express transforming growth factor (TGF)-β2. This expression, along with persistent macrophage-cancer cell interactions via the TGF-βRIII receptor, maintains cancer cells in a dormant state. Depleting alveolar macrophages or losing the TGF-β2 receptor in cancer cells triggers metastatic awakening. Aggressive breast cancer cells are either suppressed by alveolar macrophages or evade this suppression by avoiding interaction and downregulating the TGF-β2 receptor. Restoring TGF-βRIII in aggressive cells reinstates TGF-β2-mediated macrophage growth suppression. Thus, alveolar macrophages act as a metastasis immune barrier, and downregulation of TGF-β2 signaling allows cancer cells to overcome macrophage-mediated growth suppression.

Mycobacterium tuberculosis virulence lipid PDIM inhibits autophagy in mice

Mycobacterium tuberculosis (Mtb) infects several lung macrophage populations, which have distinct abilities to restrict Mtb. What enables Mtb survival in certain macrophage populations is not well understood. Here we used transposon sequencing analysis of Mtb in wild-type and autophagy-deficient mouse macrophages lacking ATG5 or ATG7, and found that Mtb genes involved in phthiocerol dimycocerosate (PDIM) virulence lipid synthesis confer resistance to autophagy. Using ppsD mutant Mtb, we found that PDIM inhibits LC3-associated phagocytosis (LAP) by inhibiting phagosome recruitment of NADPH oxidase. In mice, PDIM protected Mtb from LAP and classical autophagy. During acute infection, PDIM was dispensable for Mtb survival in alveolar macrophages but required for survival in non-alveolar macrophages in an autophagy-dependent manner. During chronic infection, autophagy-deficient mice succumbed to infection with PDIM-deficient Mtb, with impairments in B-cell accumulation in lymphoid follicles. These findings demonstrate that PDIM contributes to Mtb virulence and immune evasion, revealing a contributory role for autophagy in B-cell responses.

Extracellular Vesicles Derived From Entamoeba histolytica Have an Immunomodulatory Effect on THP-1 Macrophages

Recent studies have shown that extracellular vesicles (EVs) secreted by various parasites are capable of modulating the host's innate immune responses, such as by altering macrophage (Mϕ) phenotypes and functions. Studies have shown that Mϕ promote early host responses to amoebic infection by releasing proinflammatory cytokines that are crucial to combating amoebiasis. Here, we are reporting for the first time the effect of EVs released by Entamoeba histolytica (EhEVs) on human THP-1 differentiated Mϕ (THP-1 Mϕ). We show that the EhEVs are internalized by THP-1 Mϕ which leads to differential regulation of various cytokines associated with both M1 and M2 Mϕ. We also saw that EhEV treatment thwarted Type 2 immune-response-related transcriptome pSTAT6 in the THP-1 Mϕ. Furthermore, EhEVs stimulated Mϕ to reduce their energy demand by suppressing oxidative phosphorylation (OXPHOS) and adenosine triphosphate (ATP) production. Hence, the human parasite E. histolytica-derived EVs are capable of eliciting an immune response from Mϕ that may contribute to overall infection status.

Genome-wide screen of Mycobacterium tuberculosis-infected macrophages revealed GID/CTLH complex-mediated modulation of bacterial growth

The eukaryotic Glucose Induced Degradation/C-Terminal to LisH (GID/CTLH) complex is a highly conserved E3 ubiquitin ligase involved in a broad range of biological processes. However, a role of this complex in host anti-microbial defenses has not been described. We exploited Mycobacterium tuberculosis (Mtb) induced cytotoxicity in macrophages in a FACS based CRISPR genetic screen to identify host determinants of intracellular Mtb growth restriction. Our screen identified 5 (GID8, YPEL5, WDR26, UBE2H, MAEA) of the 12 predicted members of the GID/CTLH complex as determinants of intracellular growth of both Mtb and Salmonella serovar Typhimurium. We show that the anti-microbial properties of the GID/CTLH complex knockout macrophages are mediated by enhanced GABAergic signaling, activated AMPK, increased autophagic flux and resistance to Mtb induced necrotic cell death. Meanwhile, Mtb isolated from GID/CTLH knockout macrophages are nutritionally starved and oxidatively stressed. Our study identifies the GID/CTLH complex activity as broadly suppressive of host anti-microbial responses against intracellular bacterial infections.

Antibody-Fab and -Fc features promote Mycobacterium tuberculosis restriction

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death by an infectious disease globally, with no efficacious vaccine. Antibodies are implicated in Mtb control, but the mechanisms of antibody action remain poorly understood. We assembled a library of TB monoclonal antibodies (mAb) and screened for the ability to restrict Mtb in mice, identifying protective antibodies targeting known and novel antigens. To dissect the mechanism of mAb-mediated Mtb restriction, we optimized a protective lipoarabinomannan-specific mAb through Fc-swapping. In vivo analysis of these Fc-variants revealed a critical role for Fc-effector function in Mtb restriction. Restrictive Fc-variants altered distribution of Mtb across innate immune cells. Single-cell transcriptomics highlighted distinctly activated molecular circuitry within innate immune cell subpopulations, highlighting early activation of neutrophils as a key signature of mAb-mediated Mtb restriction. Therefore, improved antibody-mediated restriction of Mtb is associated with reorganization of the tissue-level immune response to infection and depends on the collaboration of antibody Fab and Fc.

Differential requirement of formyl peptide receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. Here, we investigate the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed in a murine TB model utilizing hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion had no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1-/- mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased Mtb persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1-/- neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

CD4+ T cells re-wire granuloma cellularity and regulatory networks to promote immunomodulation following Mtb reinfection

Immunological priming-in the context of either prior infection or vaccination-elicits protective responses against subsequent Mycobacterium tuberculosis (Mtb) infection. However, the changes that occur in the lung cellular milieu post-primary Mtb infection and their contributions to protection upon reinfection remain poorly understood. Using clinical and microbiological endpoints in a non-human primate reinfection model, we demonstrated that prior Mtb infection elicited a long-lasting protective response against subsequent Mtb exposure and was CD4+ T cell dependent. By analyzing data from primary infection, reinfection, and reinfection-CD4+ T cell-depleted granulomas, we found that the presence of CD4+ T cells during reinfection resulted in a less inflammatory lung milieu characterized by reprogrammed CD8+ T cells, reduced neutrophilia, and blunted type 1 immune signaling among myeloid cells. These results open avenues for developing vaccines and therapeutics that not only target lymphocytes but also modulate innate immune cells to limit tuberculosis (TB) disease.

The frequency of CD38+ alveolar macrophages correlates with early control of M. tuberculosis in the murine lung

Tuberculosis, caused by Mycobacterium tuberculosis, remains an enduring global health challenge due to the limited efficacy of existing treatments. Although much research has focused on immune failure, the role of host macrophage biology in controlling the disease remains underappreciated. Here we show, through multi-modal single-cell RNA sequencing in a murine model, that different alveolar macrophage subsets play distinct roles in either advancing or controlling the disease. Initially, alveolar macrophages that are negative for the CD38 marker are the main infected population. As the infection progresses, CD38+ monocyte-derived and tissue-resident alveolar macrophages emerge as significant controllers of bacterial growth. These macrophages display a unique chromatin organization pre-infection, indicative of epigenetic priming for pro-inflammatory responses. Moreover, intranasal BCG immunization increases the numbers of CD38+ macrophages, enhancing their capability to restrict Mycobacterium tuberculosis growth. Our findings highlight the dynamic roles of alveolar macrophages in tuberculosis and open pathways for improved vaccines and therapies.

Metabolically active neutrophils represent a permissive niche for Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb)-infected neutrophils are often found in the airways of patients with active tuberculosis (TB), and excessive recruitment of neutrophils to the lung is linked to increased bacterial burden and aggravated pathology in TB. The basis for the permissiveness of neutrophils for Mtb and the ability to be pathogenic in TB has been elusive. Here, we identified metabolic and functional features of neutrophils that contribute to their permissiveness in Mtb infection. Using single-cell metabolic and transcriptional analyses, we found that neutrophils in the Mtb-infected lung displayed elevated mitochondrial metabolism, which was largely attributed to the induction of activated neutrophils with enhanced metabolic activities. The activated neutrophil subpopulation was also identified in the lung granulomas from Mtb-infected non-human primates. Functionally, activated neutrophils harbored more viable bacteria and displayed enhanced lipid uptake and accumulation. Surprisingly, we found that interferon-γ promoted the activation of lung neutrophils during Mtb infection. Lastly, perturbation of lipid uptake pathways selectively compromised Mtb survival in activated neutrophils. These findings suggest that neutrophil heterogeneity and metabolic diversity are key to their permissiveness for Mtb and that metabolic pathways in neutrophils represent potential host-directed therapeutics in TB.

Resilience of dermis resident macrophages to inflammatory challenges

The skin serves as a complex barrier organ populated by tissue-resident macrophages (TRMs), which play critical roles in defense, homeostasis, and tissue repair. This review examines the functions of dermis resident TRMs in different inflammatory settings, their embryonic origins, and their long-term self-renewal capabilities. We highlight the M2-like phenotype of dermal TRMs and their specialized functions in perivascular and perineuronal niches. Their interactions with type 2 immune cells, autocrine cytokines such as IL-10, and their phagocytic clearance of apoptotic cells have been explored as mechanisms for M2-like dermal TRM self-maintenance and function. In conclusion, we address the need to bridge murine models with human studies, with the possibility of targeting TRMs to promote skin immunity or restrain cutaneous pathology.

Molecular and microbiological methods for the identification of nonreplicating Mycobacterium tuberculosis

Chronic tuberculosis (TB) disease, which requires months-long chemotherapy with multiple antibiotics, is defined by diverse pathological manifestations and bacterial phenotypes. Targeting drug-tolerant bacteria in the host is critical to achieving a faster and durable cure for TB. In order to facilitate this field of research, we need to consider the physiology of persistent MTB during infection, which is often associated with the nonreplicating (NR) state. However, the traditional approach to quantifying bacterial burden through colony enumeration alone only informs on the abundance of live bacilli at the time of sampling, and provides an incomplete picture of the replicative state of the pathogen and the extent to which bacterial replication is balanced by ongoing cell death. Modern approaches to profiling bacterial replication status provide a better understanding of inter- and intra-population dynamics under different culture conditions and in distinct host microenvironments. While some methods use molecular markers of DNA replication and cell division, other approaches take advantage of advances in the field of microfluidics and live-cell microscopy. Considerable effort has been made over the past few decades to develop preclinical in vivo models of TB infection and some are recognized for more closely recapitulating clinical disease pathology than others. Unique lesion compartments presenting different environmental conditions produce significant heterogeneity between Mycobacterium tuberculosis populations within the host. While cellular lesion compartments appear to be more permissive of ongoing bacterial replication, caseous foci are associated with the maintenance of M. tuberculosis in a state of static equilibrium. The accurate identification of nonreplicators and where they hide within the host have significant implications for the way novel chemotherapeutic agents and regimens are designed for persistent infections.

Fatty acid metabolism in neutrophils promotes lung damage and bacterial replication during tuberculosis

Mycobacterium tuberculosis (Mtb) infection induces a marked influx of neutrophils into the lungs, which intensifies the severity of tuberculosis (TB). The metabolic state of neutrophils significantly influences their functional response during inflammation and interaction with bacterial pathogens. However, the effect of Mtb infection on neutrophil metabolism and its consequent role in TB pathogenesis remain unclear. In this study, we examined the contribution of glycolysis and fatty acid metabolism on neutrophil responses to Mtb HN878 infection using ex-vivo assays and murine infection models. We discover that blocking glycolysis aggravates TB pathology, whereas inhibiting fatty acid oxidation (FAO) yields protective outcomes, including reduced weight loss, immunopathology, and bacterial burden in lung. Intriguingly, FAO inhibition preferentially disrupts the recruitment of a pathogen-permissive immature neutrophil population (Ly6Glo/dim), known to accumulate during TB. Targeting carnitine palmitoyl transferase 1a (Cpt1a)-a crucial enzyme in mitochondrial β-oxidation-either through chemical or genetic methods impairs neutrophils' ability to migrate to infection sites while also enhancing their antimicrobial function. Our findings illuminate the critical influence of neutrophil immunometabolism in TB pathogenesis, suggesting that manipulating fatty acid metabolism presents a novel avenue for host-directed TB therapies by modulating neutrophil functions.

Uncovering the Bronchoalveolar Single-Cell Landscape of Patients With Pulmonary Tuberculosis With Human Immunodeficiency Virus Type 1 Coinfection

BACKGROUND

Coinfection of human immunodeficiency virus type 1 (HIV-1) is the most significant risk factor for tuberculosis (TB). The immune responses of the lung are essential to restrict the growth of Mycobacterium tuberculosis and avoid the emergence of the disease. Nevertheless, there is still limited knowledge about the local immune response in people with HIV-1-TB coinfection.

METHODS

We employed single-cell RNA sequencing (scRNA-seq) on bronchoalveolar lavage fluid from 9 individuals with HIV-1-TB coinfection and 10 with pulmonary TB.

RESULTS

A total of 19 058 cells were grouped into 4 major cell types: myeloid cells, T/natural killer (NK) cells, B cells, and epithelial cells. The myeloid cells and T/NK cells were further divided into 10 and 11 subsets, respectively. The proportions of dendritic cell subsets, CD4+ T cells, and NK cells were lower in the HIV-1-TB coinfection group compared to the TB group, while the frequency of CD8+ T cells was higher. Additionally, we identified numerous differentially expressed genes between the CD4+ and CD8+ T-cell subsets between the 2 groups.

CONCLUSIONS

HIV-1 infection not only affects the abundance of immune cells in the lungs but also alters their functions in patients with pulmonary TB.

TGFβ primes alveolar-like macrophages to induce type I IFN following TLR2 activation

Alveolar macrophages (AMs) are key mediators of lung function and are potential targets for therapies during respiratory infections. TGFβ is an important regulator of AM differentiation and maintenance, but how TGFβ directly modulates the innate immune responses of AMs remains unclear. This shortcoming prevents effective targeting of AMs to improve lung function in health and disease. Here we leveraged an optimized ex vivo AM model system, fetal-liver derived alveolar-like macrophages (FLAMs), to dissect the role of TGFβ in AMs. Using transcriptional analysis, we first globally defined how TGFβ regulates gene expression of resting FLAMs. We found that TGFβ maintains the baseline metabolic state of AMs by driving lipid metabolism through oxidative phosphorylation and restricting inflammation. To better understand inflammatory regulation in FLAMs, we next directly tested how TGFβ alters the response to TLR2 agonists. While both TGFβ (+) and TGFβ (-) FLAMs robustly responded to TLR2 agonists, we found an unexpected activation of type I interferon (IFN) responses in FLAMs and primary AMs in a TGFβ-dependent manner. Surprisingly, mitochondrial antiviral signaling protein and the interferon regulator factors 3 and 7 were required for IFN production by TLR2 agonists. Together, these data suggest that TGFβ modulates AM metabolic networks and innate immune signaling cascades to control inflammatory pathways in AMs.

Antibodies as key mediators of protection against Mycobacterium tuberculosis

Tuberculosis (TB) is caused by infection with the bacterial pathogen Mycobacterium tuberculosis (M.tb) in the respiratory tract. There was an estimated 10.6 million people newly diagnosed with TB, and there were approximately 1.3 million deaths caused by TB in 2022. Although the global prevalence of TB has remained high for decades and is an annual leading cause of death attributed to infectious diseases, only one vaccine, Bacillus Calmette-Guérin (BCG), has been approved so far to prevent/attenuate TB disease. Correlates of protection or immunological mechanisms that are needed to control M.tb remain unknown. The protective role of antibodies after BCG vaccination has also remained largely unclear; however, recent studies have provided evidence for their involvement in protection against disease, as biomarkers for the state of infection, and as potential predictors of outcomes. Interestingly, the antibodies generated post-vaccination with BCG are linked to the activation of innate immune cascades, providing further evidence that antibody effector functions are critical for protection against respiratory pathogens such as M.tb. In this review, we aim to provide current knowledge of antibody application in TB diagnosis, prevention, and treatment. Particularly, this review will focus on 1) The role of antibodies in preventing M.tb infections through preventing Mtb adherence to epithelium, antibody-mediated phagocytosis, and antibody-mediated cellular cytotoxicity; 2) The M.tb-directed antibody response generated after vaccination and how humoral profiles with different glycosylation patterns of these antibodies are linked with protection against the disease state; and 3) How antibody-mediated immunity against M.tb can be further explored as early diagnosis biomarkers and different detection methods to combat the global M.tb burden. Broadening the paradigm of differentiated antibody profiling and antibody-based detection during TB disease progression offers new directions for diagnosis, treatment, and preventative strategies. This approach involves linking the aforementioned humoral responses with the disease state, progression, and clearance.

Mycobacterium tuberculosis Utilizes Serine/Threonine Kinase PknF to Evade NLRP3 Inflammasome-driven Caspase-1 and RIPK3/Caspase-8 Activation in Murine Dendritic Cells

Dendritic cells (DCs) are crucial for initiating the acquired immune response to infectious diseases such as tuberculosis. Mycobacterium tuberculosis has evolved strategies to inhibit activation of the NLRP3 inflammasome in macrophages via its serine/threonine protein kinase, protein kinase F (PknF). It is not known whether this pathway is conserved in DCs. In this study, we show that the pknF deletion mutant of M. tuberculosis (MtbΔpknF) compared with wild-type M. tuberculosis-infected cells induces increased production of IL-1β and increased pyroptosis in murine bone marrow-derived DCs (BMDCs). As shown for murine macrophages, the enhanced production of IL-1β postinfection of BMDCs with MtbΔpknF is dependent on NLRP3, ASC, and caspase-1/11. In contrast to macrophages, we show that MtbΔpknF mediates RIPK3/caspase-8-dependent IL-1β production in BMDCs. Consistently, infection with MtbΔpknF results in increased activation of caspase-1 and caspase-8 in BMDCs. When compared with M. tuberculosis-infected cells, the IL-6 production by MtbΔpknF-infected cells was unchanged, indicating that the mutant does not affect the priming phase of inflammasome activation. In contrast, the activation phase was impacted because the MtbΔpknF-induced inflammasome activation in BMDCs depended on potassium efflux, chloride efflux, reactive oxygen species generation, and calcium influx. In conclusion, PknF is important for M. tuberculosis to evade NLRP3 inflammasome-mediated activation of caspase-1 and RIPK3/caspase-8 pathways in BMDCs.

Lung-resident CD3-NK1.1+CD69+CD103+ Cells Play an Important Role in Bacillus Calmette-Guérin Vaccine-Induced Protective Immunity against Mycobacterium tuberculosis Infection

Tissue-resident immune cells play important roles in local tissue homeostasis and infection control. There is no information on the functional role of lung-resident CD3-NK1.1+CD69+CD103+ cells in intranasal Bacillus Calmette-Guérin (BCG)-vaccinated and/or Mycobacterium tuberculosis (Mtb)-infected mice. Therefore, we phenotypically and functionally characterized these cells in mice vaccinated intranasally with BCG. We found that intranasal BCG vaccination increased CD3-NK1.1+ cells with a tissue-resident phenotype (CD69+CD103+) in the lungs during the first 7 d after BCG vaccination. Three months post-BCG vaccination, Mtb infection induced the expansion of CD3-NK1.1+CD69+CD103+ (lung-resident) cells in the lung. Adoptive transfer of lung-resident CD3-NK1.1+CD69+CD103+ cells from the lungs of BCG-vaccinated mice to Mtb-infected naive mice resulted in a lower bacterial burden and reduced inflammation in the lungs. Our findings demonstrated that intranasal BCG vaccination induces the expansion of CD3-NK1.1+CD69+CD103+ (lung-resident) cells to provide protection against Mtb infection.

Single-cell transcriptome sequencing reveals altered peripheral blood immune cells in patients with severe tuberculosis

Tuberculosis is a serious global health burden, resulting in millions of deaths each year. Several circulating cell subsets in the peripheral blood are known to modulate the host immune response to Mycobacterium tuberculosis (Mtb) infection in different ways. However, the characteristics and functions of these subsets to varying stages of tuberculosis infection have not been well elucidated. Peripheral blood immune cells (PBICs) were isolated from healthy donors (HD group), individuals with mild tuberculosis (MI group), and individuals with severe tuberculosis (SE group). CD4+ naive T cells and CD8+ T cells were decreased in the SE and MI groups, while CD14+ monocytes were increased in the SE group. Further analysis revealed increased activated CD4+ T cells, transitional CD8+ T cells, memory-like NK cells, and IGHG3highTTNhighFCRL5high B cells were increased in all patients with tuberculosis (SE and MI group). In contrast, Th17 cells, cytotoxic NK cells, and cytotoxic CD4+ T cells were decreased. Moreover, the increase of CD14+CD16+ monocytes correlated with severe tuberculosis, and the GBP5highRSAD2high neutrophils were unique to patients with severe tuberculosis. Cellular communication analysis revealed that CD8+ T cells exhibited the highest incoming interaction strength in the SE group. The increased CD8+ T cell incoming interactions are associated with the MHC-I and LCK pathways, with HLA-(A-E)-CD8A, HLA-(A-E)-CD8B, and LCK-(CD8A+CD8B) being ligand-receptor pairs. Patients with tuberculosis, especially severe tuberculosis, have profound changes in peripheral blood immune cell profiles. CD8+ T cells showed the highest incoming interaction strength in patients with severe tuberculosis, with the main signals being MHC-I and LCK pathways.