Rationale Idiopathic subglottic stenosis (iSGS) is a rare and devastating extrathoracic obstruction involving the lower laryngeal and upper tracheal airway. It arises without known antecedent injury or associated disease process. Persistent mucosal inflammation and a localized fibrotic response are hallmarks of the disease. Despite the initial clinical description of iSGS more than 40 year ago, there have been no substantive investigations into the pathogenesis of this enigmatic and progressive airway obstruction. Objectives In these studies, we present the initial characterization of the molecular pathogenesis underlying the fibrosing phenotype of iSGS. Methods Utilizing 20 human iSGS and healthy control specimens we applied histologic, immunohistochemical, molecular and immunologic techniques. Main Results We demonstrate significant activation of the canonical IL-23/IL-17A pathway in the tracheal mucosa of iSGS patients, as well as identify γδ T cells as the primary cellular source of IL-17A. Conclusions Our results suggest that aberrant mucosal immune activation is a component in of the pathogenesis of iSGS. Most critically, our work offers new targets for future therapeutic intervention. Level of Evidence NA

Rationale Idiopathic subglottic stenosis (iSGS) is an unexplained obstruction involving the lower laryngeal and upper tracheal airway. Persistent mucosal inflammation is a hallmark of the disease. Epithelial microbiota dysbiosis is found in other chronic inflammatory mucosal diseases; however, the relationship between tracheal microbiota composition and iSGS is unknown. Objectives Given the critical role for host defense at mucosal barriers, we analyzed tissue specimens from iSGS patients for the presence of microbial pathogens. Methods Utilizing 20 human iSGS, 20 intubation-related tracheal stenosis (iLTS) and 10 healthy control specimens we applied molecular, immunohistochemical, electron microscopic, immunologic and Sanger™ sequencing techniques. Main Results With unbiased culture-independent nucleic acid, protein, and immunologic approaches, we demonstrate that Mycobacterium species are uniquely associated with iSGS. Phylogenetic analysis of the mycobacterial virulence factor rpoB suggests that rather than Mycobacterium Tuberculosis (Mtb), a variant member of the Mycobacterium Tuberculosis Complex (MtbC), or a closely related novel mycobacterium is present in iSGS specimens. Conclusions These studies identify a novel pathogenic role for established large airway bacteria, and provide new targets for future therapeutic intervention. Level of Evidence NA.

Patients with progressive sarcoidosis exhibit increased expression of programmed death-1 (PD-1) receptor on their CD41 T cells. Upregulation of this marker of T cell exhaustion is associated with a reduction in the proliferative response to T cell receptor (TCR) stimulation, a defect that is reversed by PD-1 pathway blockade. Genome-wide association studies and microarray analyses have correlated signaling downstream from the TCR with sarcoidosis disease severity, but the mechanism is not yet known. Reduced phosphatidylinositol 3-kinase (PI3K)/AKT expression inhibits proliferation by inhibiting cell cycle progression. To test the hypothesis that PD-1 expression attenuates TCR-dependent activation of PI3K/AKT activity in progressive systemic sarcoidosis, we analyzed PI3K/AKT/mechanistic target of rapamycin (mTOR) expression at baseline and after PD-1 pathway blockade in CD4 1 T cells isolated from patients with sarcoidosis and healthy control subjects. We confirmed an increased percentage of PD-1 1 CD4 1 T cells and reduced proliferative capacity in patients with sarcoidosis compared with healthy control subjects (P , 0.001). There was a negative correlation with PD-1 expression and proliferative capacity (r = 20.70, P , 0.001). Expression of key mediators of cell cycle progression, including PI3K and AKT, were significantly decreased. Gene and protein expression levels reverted to healthy control levels after PD-1 pathway blockade. Reduction in sarcoidosis CD41 T cell proliferative capacity is secondary to altered expression of key mediators of cell cycle progression, including the PI3K/AKT/mTOR pathway, via PD-1 up-regulation. This supports the concept that PD-1 up-regulation drives the immunologic deficits associated with sarcoidosis severity by inducing signaling aberrancies in key mediators of cell cycle progression.

Investigation of the Th1 immune response in sarcoidosis CD4+ T cells has revealed reduced proliferative capacity and cytokine expression upon TCR stimulation. In other disease models, such cellular dysfunction has been associated with a step-wise, progressive loss of T cell function that results from chronic antigenic stimulation. T cell exhaustion is defined by decreased cytokine production upon TCR activation, decreased proliferation, increased expression of inhibitory cell surface receptors, and increased susceptibility to apoptosis. We characterized sarcoidosis CD4+ T cell immune function in systemic and local environments among subjects undergoing disease progression compared to those experiencing disease resolution. Spontaneous and TCR-stimulated Th1 cytokine expression and proliferation assays were performed in 53 sarcoidosis subjects and 30 healthy controls. PD-1 expression and apoptosis were assessed by flow cytometry. Compared to healthy controls, sarcoidosis CD4+ T cells demonstrated reductions in Th1 cytokine expression, proliferative capacity (p < 0.05), enhanced apoptosis (p < 0.01), and increased PD-1 expression (p < 0.001). BAL-derived CD4+ T cells also demonstrated multiple facets of T cell exhaustion (p < 0.05). Reversal of CD4+ T cell exhaustion was observed in subjects undergoing spontaneous resolution (p < 0.05). Sarcoidosis CD4+ T cells exhibit loss of cellular function during progressive disease that follows the archetype of T cell exhaustion.

Sarcoidosis is a granulomatous disease of unknown cause. Prior molecular and immunologic studies have confirmed the presence of mycobacterial virulence factors, such as catalase peroxidase and superoxide dismutase A, within sarcoidosis granulomas. Molecular analysis of granulomas can identify targets of known antibiotics classes. Currently, major antibiotics are directed against DNA synthesis, protein synthesis, and cell wall formation. We conducted molecular analysis of 40 sarcoidosis diagnostic specimens and compared them with 33 disease control specimens for the presence of mycobacterial genes that encode antibiotic targets. We assessed for genes involved in DNA synthesis (DNA gyrase A [gyrA] and DNA gyrase B), protein synthesis (RNA polymerase subunit β), cell wall synthesis (embCAB operon and enoyl reductase), and catalase peroxidase. Immunohistochemical analysis was conducted to investigate the locale of mycobacterial genes such as gyrA within 12 sarcoidosis specimens and 12 disease controls. Mycobacterial DNA was detected in 33 of 39 sarcoidosis specimens by quantitative real-time polymerase chain reaction compared with 2 of 30 disease control specimens (P < 0.001, two-tailed Fisher's test). Twenty of 39 were positive for three or more mycobacterial genes, compared with 1 of 30 control specimens (P < 0.001, two-tailed Fisher's test). Immunohistochemistry analysis localized mycobacterial gyrA nucleic acids to sites of granuloma formation in 9 of 12 sarcoidosis specimens compared with 1 of 12 disease controls (P < 0.01). Microbial genes encoding enzymes that can be targeted by currently available antimycobacterial antibiotics are present in sarcoidosis specimens and localize to sites of granulomatous inflammation. Use of antimicrobials directed against target enzymes may be an innovative treatment alternative.

Sarcoidosis is an idiopathic multisystem disorder characterized by noncaseating epithelioid granulomas predominately affecting lungs and lymph nodes, but with potential to affect any organ system. Sarcoidosis shares similarities in development to other infectious granulomatous diseases, such as berylliosis and tuberculosis; however, its elusive etiology and non-distinctive histology have provided many diagnostic challenges. Evidence of a transferrable antigen combined with a high incidence rate in the lungs has focused efforts primarily on antigens with airborne transmissibility. While Mycobacterium tuberculosis and Propionibacterium acnes have provided strong associations to implicate each as a contributor to sarcoidosis pathogenesis, detection challenges remain and consensus of a definitive antigen is lacking.