Keith D. Kauffman

IFNγ is considered the primary mediator of adaptive immunity to Mycobacterium tuberculosis (Mtb) infection. In mice, control of Mtb requires IFNγ. In humans, IFNγ is critical for resistance to infection with non-tuberculous mycobacteria (NTM), but its relative requirement for control of pulmonary tuberculosis (TB) is less clear. Here we block IFNγR1 signaling in macaques at different times following Mtb infection. IFNγ blockade from day 45 to 49 post-infection rapidly reduced ¹⁸ FDG-PET/CT scores and broadly enhanced anti-viral-like inflammatory responses. Strikingly, IFNγR1 blockade for the first three months of infection had no impact on bacterial loads despite suppression of bioactive IFNγ in granulomas and changes to host immune responses and granuloma structure. We find individuals from Mtb endemic regions with anti-IFNγ neutralizing autoantibodies who develop NTM disease and not TB despite evidence of previous exposure to Mtb. Lastly, we show that mice over-estimate the importance IFNγ in host resistance to TB due to a species-specific induction of iNOS by IFNγ. Thus, while IFNγ has immunoregulatory effects in granulomas, normal resistance to TB in macaques and humans likely requires little IFNγR1 signaling during infection, indicating that the major mechanisms of adaptive immunity to Mtb infection remain unknown.

Oxidative stress triggers ferroptosis, a form of cellular necrosis characterized by iron-dependent lipid peroxidation, and has been implicated in Mycobacterium tuberculosis (Mtb) pathogenesis. We investigated whether Bach1, a transcription factor that represses multiple antioxidant genes, regulates host resistance to Mtb. We found that BACH1 expression is associated clinically with active pulmonary tuberculosis. Bach1 deletion in Mtb-infected mice increased glutathione levels and Gpx4 expression that inhibit lipid peroxidation. Bach1^−/− macrophages exhibited increased resistance to Mtb-induced cell death, while Mtb-infected Bach1-deficient mice displayed reduced bacterial loads, pulmonary necrosis and lipid peroxidation concurrent with increased survival. Single-cell RNA-seq analysis of lungs from Mtb-infected Bach1^−/− mice revealed an enrichment of genes associated with ferroptosis suppression. Bach1 depletion in Mtb-infected B6.Sst1^S mice that display human-like necrotic lung pathology also markedly reduced necrosis and increased host resistance. These findings identify Bach1 as a key regulator of cellular and tissue necrosis and host resistance in Mtb infection.

Control of Mycobacterium tuberculosis (Mtb) infection requires generation of T cells that migrate to granulomas, complex immune structures surrounding sites of bacterial replication. Here we compared the gene expression profiles of T cells in pulmonary granulomas, bronchoalveolar lavage, and blood of Mtb-infected rhesus macaques to identify granuloma-enriched T cell genes. TNFRSF8/CD30 was among the top genes upregulated in both CD4 and CD8 T cells from granulomas. In mice, CD30 expression on CD4 T cells is required for survival of Mtb infection, and there is no major role for CD30 in protection by other cell types. Transcriptomic comparison of WT and CD30−/− CD4 T cells from the lungs of Mtb-infected mixed bone marrow chimeric mice showed that CD30 directly promotes CD4 T cell differentiation and the expression of multiple effector molecules. These results demonstrate that the CD30 co-stimulatory axis is highly upregulated on granuloma T cells and is critical for protective T cell responses against Mtb 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.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily replicates in mucosal sites, and more information is needed about immune responses in infected tissues. Here, we used rhesus macaques to model protective primary immune responses in tissues during mild coronavirus disease 2019 (COVID-19). Viral RNA levels were highest on days 1 to 2 after infection and fell precipitously thereafter. ¹⁸ F-fluorodeoxyglucose ( ¹⁸ FDG)–avid lung abnormalities and interferon (IFN)–activated monocytes and macrophages in the bronchoalveolar lavage (BAL) were found on days 3 to 4 after infection. Virus-specific effector CD8 ⁺ and CD4 ⁺ T cells became detectable in the BAL and lung tissue on days 7 to 10 after viral RNA, radiologic evidence of lung inflammation, and IFN-activated myeloid cells had substantially declined. SARS-CoV-2–specific T cells were not detectable in the nasal turbinates, salivary glands, and tonsils on day 10 after infection. Thus, SARS-CoV-2 replication wanes in the lungs, as well as the nasal and oral mucosa, of rhesus macaques before antigen-specific effector T cells arrive at those sites, suggesting that innate immunity efficiently restricts viral replication during mild COVID-19.

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the activities of multiple leukocyte subsets, yet the roles of the different innate effector cells during tuberculosis are incompletely understood. Here we uncover an unexpected association between eosinophils and Mtb infection. In humans, eosinophils are decreased in the blood but enriched in resected human tuberculosis lung lesions and autopsy granulomas. An influx of eosinophils is also evident in infected zebrafish, mice, and nonhuman primate granulomas, where they are functionally activated and degranulate. Importantly, using complementary genetic models of eosinophil deficiency, we demonstrate that in mice, eosinophils are required for optimal pulmonary bacterial control and host survival after Mtb infection. Collectively, our findings uncover an unexpected recruitment of eosinophils to the infected lung tissue and a protective role for these cells in the control of Mtb infection in mice.