Dual neutrophil subsets exacerbate or suppress inflammation in tuberculosis via IL-1ß or PD-L1.

Neutrophils can be beneficial or deleterious during tuberculosis (TB). Based on the expression of MHC-II and programmed death ligand 1 (PD-L1), we distinguished two functionally and transcriptionally distinct neutrophil subsets in the lungs of mice infected with mycobacteria. Inflammatory [MHC-II-, PD-L1lo] neutrophils produced inflammasome-dependent IL-1ß in the lungs in response to virulent mycobacteria and "accelerated" deleterious inflammation, which was highly exacerbated in IFN-γR-/- mice. Regulatory [MHC-II+, PD-L1hi] neutrophils "brake" inflammation by suppressing T-cell proliferation and IFN-γ production. Such beneficial regulation, which depends on PD-L1, is controlled by IFN-γR signaling in neutrophils. The hypervirulent HN878 strain from the Beijing genotype curbed PD-L1 expression by regulatory neutrophils, abolishing the braking function and driving deleterious hyperinflammation in the lungs. These findings add a layer of complexity to the roles played by neutrophils in TB and may explain the reactivation of this disease observed in cancer patients treated with anti-PD-L1.

Sterile Lung Inflammation Induced by Silica Exacerbates Mycobacterium tuberculosis Infection via STING-Dependent Type 2 Immunity.

Lung inflammation induced by silica impairs host control of tuberculosis, yet the underlying mechanism remains unclear. Here, we show that silica-driven exacerbation of M. tuberculosis infection associates with raised type 2 immunity. Silica increases pulmonary Th2 cell and M2 macrophage responses, while reducing type 1 immunity after M. tuberculosis infection. Silica induces lung damage that prompts extracellular self-DNA release and activates STING. This STING priming potentiates M. tuberculosis DNA sensing by and activation of cGAS/STING, which triggers enhanced type I interferon (IFNI) response and type 2 immunity. cGAS-, STING-, and IFNAR-deficient mice are resistant to silica-induced exacerbation of M. tuberculosis infection. Thus, silica-induced self-DNA primes the host response to M. tuberculosis-derived nucleic acids, which increases type 2 immunity while reducing type 1 immunity, crucial for controlling M. tuberculosis infection. These data show how cGAS/STING pathway activation, at the crossroads of sterile inflammation and infection, may affect the host response to pathogens such as M. tuberculosis.

STING-dependent sensing of self-DNA drives silica-induced lung inflammation.

Silica particles induce lung inflammation and fibrosis. Here we show that stimulator of interferon genes (STING) is essential for silica-induced lung inflammation. In mice, silica induces lung cell death and self-dsDNA release in the bronchoalveolar space that activates STING pathway. Degradation of extracellular self-dsDNA by DNase I inhibits silica-induced STING activation and the downstream type I IFN response. Patients with silicosis have increased circulating dsDNA and CXCL10 in sputum, and patients with fibrotic interstitial lung disease display STING activation and CXCL10 in the lung. In vitro, while mitochondrial dsDNA is sensed by cGAS-STING in dendritic cells, in macrophages extracellular dsDNA activates STING independent of cGAS after silica exposure. These results reveal an essential function of STING-mediated self-dsDNA sensing after silica exposure, and identify DNase I as a potential therapy for silica-induced lung inflammation.