Neutrophil degranulation, NETosis and platelet degranulation pathway genes are co-induced in whole blood up to six months before tuberculosis diagnosis

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.

The role of neutrophil response in lung damage and post-tuberculosis lung disease: a translational narrative review

It is estimated that more than 150 million individuals alive in 2020 had survived tuberculosis (TB). A portion of this large population continues to experience chronic respiratory abnormalities, with or without symptoms, due to previous active pulmonary TB. This condition known as Post-TB Lung Disease (PTLD), involves a complex interaction between pathogen, host and environmental factors. These interactions are believed to drive a hyperinflammatory process in the lungs during active TB, resulting in tissue damage, which may lead to radiological sequelae, impaired pulmonary function, clinical symptoms, such as cough, dyspnea, hemoptysis, and respiratory infections. Such complications impose significant health, financial, and social burdens, which remain poorly understood and inadequately addressed by health care systems. Given the heterogeneity of immune cells and their products infiltrating the airways and the lung parenchyma during acute and chronic inflammation caused by Mycobacterium tuberculosis infection, it is evident that TB immunopathology is multifactorial. Among the various components involved, neutrophils have recently emerged as critical contributors to the deleterious immune response against TB, leading to severe pulmonary damage. In this translational narrative review, we aim to summarize the role of neutrophils and their primary products - proteases (such as elastase), matrix metalloproteinases and neutrophils extracellular traps (NETs) - in pulmonary TB. We highlight new concepts and emerging evidence of neutrophil involvement during the active disease, translating these insights from "bench to bedside" to facilitate dialogue between fundamental researchers and clinical practitioners. Additionally, we present potential targets for future treatment strategies that could mitigate or even prevent PTLD.

Systematic review of innate immune responses against Mycobacterium tuberculosis complex infection in animal models

Background

Mycobacterium tuberculosis (Mtb) complex (MTBC) includes ten species that affect mammals and pose a significant global health concern. Upon infection, Mtb induces various stages in the host, including early bacterial elimination, which may or may not involve memory responses. Deciphering the role of innate immune responses during MTBC infection is crucial for understanding disease progression or protection. Over the past decade, there has been growing interest in the innate immune response to Mtb, with new preclinical models emerging.

Methods

We conducted a systematic review following PRISMA guidelines, focused on innate immune mediators linked to protection or disease progression in animal models of MTBC infection. We searched two databases: National Library of Medicine and Web of Science. Two researchers independently extracted data based on specific inclusion and exclusion criteria.

Results

Eighty-three articles were reviewed. Results were categorized in four groups: MTBC species, animal models, soluble factors and innate pathways, and other molecules (metabolites and drugs). Mtb and M. bovis were the only species studied. P2X7R receptor's role in disease progression and higher macrophage recruitment were observed differentially after infection with hypervirulent Mtb strains. Mice and non-human primates (NHPs) were the most used mammals, with emerging models like Galleria mellonella and planarians also studied. NHPs provided insights into age-dependent immunity and markers for active tuberculosis (ATB). Key innate immune factors/pathways identified included TNF-α, neutrophil recruitment, ROS/RNS responses, autophagy, inflammasomes, and antimicrobial peptides, with homologous proteins identified in insects. Metabolites like vitamin B5 and prostaglandin E2 were associated with protection. Immunomodulatory drugs targeting autophagy and other mechanisms were studied, exhibiting their potential as therapeutic alternatives.

Conclusion

Simpler, physiologically relevant, and ethically sound models, such as G. mellonella, are needed for studying innate responses in MTBC infection. While insects lack adaptive immunity, they could provide insights into "pure" innate immune responses. The dissection of "pure," "sustained" (later than 7 days post-infection), and trained innate immunity presents additional challenges that require high-resolution temporospatial analytical methods. Identifying early innate immune mediators and targetable pathways in the blood and affected tissues could identify biomarkers for immunization efficiency, disease progression, and potential synergistic therapies for ATB.

Pathogenic role for CD101-negative neutrophils in the type I interferon-mediated immunopathogenesis of tuberculosis

Neutrophils are vital for immunity against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), yet their heterogeneous nature suggests a complex role in TB pathogenesis. Here, we identify two distinct neutrophil populations based on CD101 expression, highlighting their divergent roles in TB. CD101-negative (CD101-ve) neutrophils, which resemble immature, pro-inflammatory granulocytes, exhibit reduced Mtb phagocytosis compared to their mature, CD101-positive (CD101+ve) counterparts. Our findings reveal that type I interferons (IFN-Is) suppress neutrophil Mtb uptake and drive the recruitment of CD101-ve neutrophils to the lungs. Infiltration of these cells promotes Mtb extracellular persistence, exacerbates epithelial damage, and impairs surfactant production. Furthermore, we demonstrate that granulocyte colony-stimulating factor (G-CSF) and chemokine receptor CXCR2 are essential for the pulmonary accumulation of CD101-ve neutrophils. Our study uncovers a pathogenic role for CD101-ve neutrophils in TB and highlights the IFN-I-dependent recruitment of this functionally compromised immature neutrophil as a driver of TB immunopathogenesis.

Marked IDO2 expression and activity related to autophagy and apoptosis in brain tissue of fatal tuberculous meningitis

In about 1% of tuberculosis (TB) patients, Mycobacterium tuberculosis (M. tuberculosis) can disseminate to the meninges, causing tuberculous meningitis (TBM) with mortality rate up to 60%. Chronic granulomatous inflammation (non-necrotizing and necrotizing) in the brain is the histological hallmark of TBM. The tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase 1 (IDO1) and the generated kynurenine metabolites exert major effector functions relevant to TB granuloma functioning. Here we have assessed immunohistochemically IDO1 expression and activity and its effector function and that of its isoform, IDO2, in post-mortem brain tissue of patients that demised with neurotuberculosis. We also related these findings to brain tissue of fatal/severe COVID-19. In this study, IDO1 and IDO2 were abundantly expressed and active in tuberculoid granulomas and were associated with the presence of M. tuberculosis as well as markers of autophagy and apoptosis. Like in fatal/severe COVID-19, IDO2 was also prominent in specific brain regions, such as the inferior olivary nucleus of medulla oblongata and cerebellum, but not associated with granulomas or with M. tuberculosis. Spatially associated apoptosis was observed in TBM, whereas in fatal COVID-19 autophagy dominated. Together, our findings highlight IDO2 as a potentially relevant effector enzyme in TBM, which may relate to the symptomology of TBM.

Neutrophil extracellular trap formation and gene programs distinguish TST/IGRA sensitization outcomes among Mycobacterium tuberculosis exposed persons living with HIV

Persons living with HIV (PLWH) have an increased risk for tuberculosis (TB). After prolonged and repeated exposure, some PLWH never develop TB and show no evidence of immune sensitization to Mycobacterium tuberculosis (Mtb) as defined by persistently negative tuberculin skin tests (TST) and interferon gamma release assays (IGRA). This group has been identified and defined as HIV+ persistently TB, tuberculin and IGRA negative (HITTIN). To investigate potential innate mechanisms unique to individuals with the HITTIN phenotype we compared their neutrophil Mtb infection response to that of PLWH, with no TB history, but who test persistently IGRA positive, and tuberculin positive (HIT). Neutrophil samples from 17 HITTIN (PMNHITTIN) and 11 HIT (PMNHIT) were isolated and infected with Mtb H37Rv for 1h and 6h. RNA was extracted and used for RNAseq analysis. Since there was no significant differential transcriptional response at 1h between infected PMNHITTIN and PMNHIT, we focused on the 6h timepoint. When compared to uninfected PMN, PMNHITTIN displayed 3106 significantly upregulated and 3548 significantly downregulated differentially expressed genes (DEGs) (absolute cutoff of a log2FC of 0.2, FDR < 0.05) whereas PMNHIT demonstrated 3816 significantly upregulated and 3794 significantly downregulated DEGs following 6h Mtb infection. Contrasting the log2FC 6h infection response to Mtb from PMNHITTIN against PMNHIT, 2285 genes showed significant differential response between the two groups. Overall PMNHITTIN had a lower fold change response to Mtb infection compared to PMNHIT. According to pathway enrichment, Apoptosis and NETosis were differentially regulated between HITTIN and HIT PMN responses after 6h Mtb infection. To corroborate the blunted NETosis transcriptional response measured among HITTIN, fluorescence microscopy revealed relatively lower neutrophil extracellular trap formation and cell loss in PMNHITTIN compared to PMNHIT, showing that PMNHITTIN have a distinct response to Mtb.