Microanatomic Distribution of Myeloid Heme Oxygenase-1 Protects against Free Radical-Mediated Immunopathology in Human Tuberculosis

摘要

class="head no_bottom_margin" id="sec1title">IntroductionMycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB) disease, is a highly contagious pathogen that is spread via inhalation of infectious droplets released from the lungs of infected individuals. While the disease is mostly asymptomatic, active pulmonary TB, characterized by extensive hemoptysis and extensive tissue damage, is often lethal. The formation of caseous granulomas is a hallmark of Mtb infection that involves accumulation of myeloid cells, including neutrophils, macrophages, and myeloid-derived suppressor cells (MDSCs) to infected sites (, , ). While the formation of granulomas can be beneficial for the host, it may also serve as a safe niche for the bacterium (). In addition, the uncontrolled infiltration of myeloid cells and subsequent inflammation, including reactive oxygen intermediates (ROIs) and reactive nitrogen intermediates (RNIs), may contribute to disease pathology (). However, most studies on myeloid-mediated inflammation in TB have relied on animal models or blood from TB patients. Assessing the clinical relevance of these findings is difficult, because animal models and ex vivo blood analysis have limitations in recapitulating human disease (). Further, the microanatomic architecture of human pulmonary TB is mostly unexplored, largely due to the paucity of resected human tuberculous lung tissue. Not surprisingly, correlating the immune state of the patient and the clinicopathological manifestations of pulmonary TB lesions has been difficult, as is evident by few reports dated decades ago (, ).Heme oxygenase-1 (HO-1) is a redox-sensitive cytoprotective enzyme that degrades heme, a potent oxidant, to yield equimolar ratios of carbon monoxide (CO), iron, and bilirubin (). HO-1 protects cells from heme-mediated oxidative and nitrosative stress and injury and is involved in myeloid cell recruitment and T cell responses in many pathological conditions (, , , ). We and others have shown that HO-1 is upregulated in response to Mtb infection in mice and responds independently of the interferon-γ (IFN-γ)itric oxide (NO) pathway and that HO-1-generated CO is required for the induction of the Mtb Dos dormancy regulon (, ). HO-1 is required to control Mycobacterium avium and Mtb infections in mice (href="#bib45" rid="bib45" class=" bibr popnode">Regev et al., 2012, href="#bib53" rid="bib53" class=" bibr popnode">Silva-Gomes et al., 2013). In addition, it was recently shown that the free heme iron released by HO-1 enzymatic activity is bound by ferritin H, which is required to control Mtb infection in mice (href="#bib44" rid="bib44" class=" bibr popnode">Reddy et al., 2018). Also, HO-1 levels in the plasma of TB can distinguish patients with active TB from latently infected individuals (href="#bib1" rid="bib1" class=" bibr popnode">Andrade et al., 2013), as a readout for the efficacy of TB therapy or diagnosis of TB-HIV co-infection (href="#bib47" rid="bib47" class=" bibr popnode">Rockwood et al., 2017). Furthermore, HO-1 levels in plasma were reported to be inversely correlated with the levels of matrix metalloproteinases, which contribute to tissue destruction in TB (href="#bib3" rid="bib3" class=" bibr popnode">Andrade et al., 2015, href="#bib48" rid="bib48" class=" bibr popnode">Salgame, 2011). More recently, studies have challenged the beneficial role of HO-1 in TB disease, reporting that pharmacological inhibition of HO-1 in mice leads to a decrease in Mtb burden (href="#bib16" rid="bib16" class=" bibr popnode">Costa et al., 2016, href="#bib49" rid="bib49" class=" bibr popnode">Scharn et al., 2016). These conflicting findings, in addition to the fact that the essentiality of HO-1 in humans and mice varies significantly, represent a substantial gap in our understanding of the role of HO-1 in TB.In this study, we tested the hypothesis that HO-1 is essential for effective immune and oxidative stress control to limit TB pathology in mice and human tuberculous lungs. To test this hypothesis, we used multiparameter flow cytometry and immunohistochemistry to examine HO-1 expression in freshly resected and fixed lung tissues of TB patients. The spatial distribution of HO-1 within the microenvironment of human pulmonary TB lesions was also examined. Using global HO-1 knockout (HO-1^−/−) and myeloid cell-specific HO-1 knockout (HO-1^LysM−/−) mice, we studied the survival, disease progression, transcriptional changes, and immune responses upon Mtb infection. Overall, our data show that the expression of HO-1, especially within myeloid cells, is essential for host defense against TB disease.