GPX4 regulates cellular necrosis and host resistance in Mycobacterium tuberculosis infection.

Cellular necrosis during Mycobacterium tuberculosis (Mtb) infection promotes both immunopathology and bacterial dissemination. Glutathione peroxidase-4 (Gpx4) is an enzyme that plays a critical role in preventing iron-dependent lipid peroxidation-mediated cell death (ferroptosis), a process previously implicated in the necrotic pathology seen in Mtb-infected mice. Here, we document altered GPX4 expression, glutathione levels, and lipid peroxidation in patients with active tuberculosis and assess the role of this pathway in mice genetically deficient in or overexpressing Gpx4. We found that Gpx4-deficient mice infected with Mtb display substantially increased lung necrosis and bacterial burdens, while transgenic mice overexpressing the enzyme show decreased bacterial loads and necrosis. Moreover, Gpx4-deficient macrophages exhibited enhanced necrosis upon Mtb infection in vitro, an outcome suppressed by the lipid peroxidation inhibitor, ferrostatin-1. These findings provide support for the role of ferroptosis in Mtb-induced necrosis and implicate the Gpx4/GSH axis as a target for host-directed therapy of tuberculosis.

The Immune Interaction between HIV-1 Infection and Mycobacterium tuberculosis.

The modulation of tuberculosis (TB)-induced immunopathology caused by human immunodeficiency virus (HIV)-1 coinfection remains incompletely understood but underlies the change seen in the natural history, presentation, and prognosis of TB in such patients. The deleterious combination of these two pathogens has been dubbed a "deadly syndemic," with each favoring the replication of the other and thereby contributing to accelerated disease morbidity and mortality. HIV-1 is the best-recognized risk factor for the development of active TB and accounts for 13% of cases globally. The advent of combination antiretroviral therapy (ART) has considerably mitigated this risk. Rapid roll-out of ART globally and the recent recommendation by the World Health Organization (WHO) to initiate ART for everyone living with HIV at any CD4 cell count should lead to further reductions in HIV-1-associated TB incidence because susceptibility to TB is inversely proportional to CD4 count. However, it is important to note that even after successful ART, patients with HIV-1 are still at increased risk for TB. Indeed, in settings of high TB incidence, the occurrence of TB often remains the first presentation of, and thereby the entry into, HIV care. As advantageous as ART-induced immune recovery is, it may also give rise to immunopathology, especially in the lower-CD4-count strata in the form of the immune reconstitution inflammatory syndrome. TB-immune reconstitution inflammatory syndrome will continue to impact the HIV-TB syndemic.

Understanding and intervening in HIV-associated tuberculosis.

HIV-associated tuberculosis can present as extremes, ranging from acute life-threatening disseminated disease to occult asymptomatic infection. Both ends of this spectrum have distinct pathological correlates and require specific diagnostic and treatment approaches. Novel therapeutics, targeting both pathogen and host, are needed to augment pathogen clearance. In latent tuberculosis infection, enhancement of immune activation could be desirable. Antiretroviral therapy augments the beneficial effects of antitubercular therapy. However, in the context of high bacillary burden, antiretroviral therapy can also result in pathology (tuberculosis immune reconstitution inflammatory syndrome). In the immune reconstituting patient, modulation of immune activation controls tissue destruction. Interventions should also be appropriate and sustainable within the programmatic setting.

The road to drug resistance in Mycobacterium tuberculosis.

Sequencing of serial isolates of extensively drug-resistant tuberculosis highlights how drug resistance develops within a single patient and reveals unexpected levels of pathogen diversity.

Immunological characterisation of an unmasking TB-IRIS case.

BACKGROUND: Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is an early complication of combination antiretroviral therapy (cART). Two forms are recognised: (i) paradoxical - recurrent or new TB symptoms develop after cART initiation in patients receiving TB treatment prior to cART; and (ii) unmasking TB-IRIS - active TB presents within 3 months of cART in patients not receiving TB treatment at cART initiation. The latter has heightened clinical manifestations and a marked inflammatory presentation. AIM: To gain insight into the immune pathogenesis of a case of unmasking TB-IRIS. METHODS: The patient was recruited when starting cART and followed up at 4, 12 and 24 weeks of treatment. Peripheral blood mononuclear cells were used for flow cytometry. RESULTS: Immunological analysis indicated increased CD4+ T-cell proportions from 1.1% at baseline to 14% at 24 weeks (the CD4 count increased from 4 cells/µl at baseline to 41 cells/µl at 24 weeks). HIV viral load fell from 460 774 to 1 405 copies/ml during the same period. The proportion of TB antigen (PPD)-specific CD4+IFN-γ+ cells increased from 0.4% at baseline and 4 weeks (IRIS onset) to 7.8% at 12 weeks (after resolution of the IRIS episode); this fell to 0.7% at 24 weeks. The surface phenotype of CD4+IFN-γ+ cells during the episode was CD45RO+, CD45RA-, CCR7-, CD62L-, CCR5+/- and CD69-. We found a distorted balance between central memory and effector memory T-cells at cART commencement that might have predisposed the patient to unmasking TB-IRIS. We showed that this might have reflected compromised thymic output. Discussion. While it has been suggested that tuberculin-specific Th1-responses induce TB-IRIS in HIV co-infected patients, our data in this case indicated that these cells were expanded only after IRIS onset and were therefore not inducing TB-IRIS. CONCLUSION: We describe, in hitherto unpublished detail, the immunological characterisation of an unmasking TB-IRIS case; we show that thymic output may be compromised at IRIS onset.

Hypoxia induces an immunodominant target of tuberculosis specific T cells absent from common BCG vaccines.

M. tuberculosis (MTB) species-specific antigenic determinants of the human T cell response are important for immunodiagnosis and vaccination. As hypoxia is a stimulus in chronic tuberculosis infection, we analyzed transcriptional profiles of MTB subject to 168 hours of hypoxia to test the hypothesis that upregulation by hypoxia might result in gene products being recognized as antigens. We identified upregulation of two region of difference (RD) 11 (Rv2658C and Rv2659c), and one RD2 (Rv1986) absent from commonly used BCG strains. In MTB infected persons, the IL-2 ELISpot response to Rv1986 peptides was several times greater than the corresponding IFN-γ response to the reference immunodominant ESAT-6 or CFP-10 antigens. The IL-2 response was confined to two epitopic regions containing residues 61-80 and 161-180. The biggest population of IL-2 secreting T cells was single cytokine positive central memory T cells. The IL-2 response to live MTB bacilli lacking Rv1986 was significantly lower than the response to wild type or mutant complemented with Rv1986. In addition, the IL-2 response to Rv1986 was significantly lower in HIV-TB co-infected persons than in HIV uninfected persons, and significantly increased during antiretroviral therapy. These findings demonstrate that Rv1986 is an immunodominant target of memory T cells and is therefore of relevance when considering the partial efficacy of currently used BCG vaccines and provide evidence for a clinical trial comparing BCG strains.

Association between tuberculin skin test reactivity, the memory CD4 cell subset, and circulating FoxP3-expressing cells in HIV-infected persons.

BACKGROUND: Lack of reactivity to the tuberculin skin test (TST) is widely observed in individuals with advanced human immunodeficiency virus type 1 (HIV-1) infection. METHODS: Biopsy specimens from the TST reaction site and from skin not infiltrated with purified protein derivative were obtained from 15 HIV-1-infected and 23 uninfected persons who did not have active tuberculosis and who were from a community in which the incidence of tuberculosis was very high. Histologic sections (size, 8 mum) were immunohistochemically stained for CD4, CD8, CD28, CD45RA, CD45RO, CD62L, CD1a, human leukocyte antigen (HLA)-DR, granulysin, interferon-gamma, and FoxP3 and were analyzed by single-cell in situ digital imaging. Peripheral blood mononuclear cells were analyzed using a fluorescence-activated cell sorter. RESULTS: Biopsy specimens obtained from TST-reactive skin of HIV-1-infected persons demonstrated fewer CD4(+) T cells at the TST site (P = .36) but more HLA-DR(+) T cells (P = .037) than did such biopsy specimens obtained from HIV-1-uninfected persons. Among HIV-1-infected persons, the total number of cells (P = .008) and numbers of CD45RO(+) memory T cells (P = .003) were significantly higher in TST-reactive persons than in TST-unreactive persons. For HIV-1-infected persons, TST induration was inversely correlated with the numbers of FoxP3(+) T cells in the blood (P = .026) but was unrelated to the number of circulating CD4(+) T cells. CONCLUSIONS: For HIV-1 infected persons, the TST depends on memory T cells and is more strongly associated with the numbers of circulating FoxP3(+)CD4(+) T cells than with the total number of CD4(+) T cells.

Type 1 helper T cells and FoxP3-positive T cells in HIV-tuberculosis-associated immune reconstitution inflammatory syndrome.

RATIONALE: Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) induced by combination antiretroviral therapy (cART) has been attributed to dysregulated expansion of tuberculin PPD-specific IFN-gamma-secreting CD4(+) T cells. OBJECTIVES: To investigate the role of type 1 helper T cell expansions and regulatory T cells in HIV-TB IRIS. METHODS: Longitudinal and cross-sectional studies of Mycobacterium tuberculosis-specific IFN-gamma enzyme-linked immunospot responses and flow cytometric analysis of blood cells from a total of 129 adults with HIV-1-associated tuberculosis, 98 of whom were prescribed cART. MEASUREMENTS AND MAIN RESULTS: In cross-sectional analysis the frequency of IFN-gamma-secreting T cells recognizing early secretory antigenic target (ESAT)-6, alpha-crystallins 1 and 2, and PPD of M. tuberculosis was higher in patients with TB-IRIS than in similar patients treated for both HIV-1 and tuberculosis who did not develop IRIS (non-IRIS; P