Idiopathic subglottic stenosis arises at the interface of host and pathogen

Idiopathic subglottic stenosis (iSGS) is a rare fibrotic disease of the proximal airway affecting adult Caucasian women nearly exclusively. Life-threatening ventilatory obstruction occurs secondary to pernicious subglottic mucosal scar. Diverse diseases in divergent organ systems are associated with fibrosis, suggesting common biologic mechanisms. One well characterized pathway is chronic inflammation secondary to pathogen. In the present study, we explored the role of the proximal airway microbiome in iSGS pathogenesis. In human samples, abundant bacteria are detectable in iSGS scar as well as in health subglottic controls or patients that developed subglottic stenosis following endotracheal intubation. Interestingly, the community structure of the iSGS proximal airway microbiome does not appear disrupted. Rather, in iSGS defects in the airway epithelial barrier allow displacement of the native microbiome into the immunoprivileged lamina propria and are associated with adaptive immune activation. Animal models of iSGS confirm both bacteria and an adaptive immune response are necessary for pathologic proximal airway fibrosis. Single cell RNA sequencing of the affected airway in iSGS offers an unbiased characterization of the observed epithelial barrier dysfunction. The airway scar in iSGS patients demonstrates basal cell depletion and epithelial acquisition of a mesenchymal phenotype. The epithelial alterations are associated with the observed microbiome displacement, dysregulated immune activation, and localized fibrosis. These results refine our understanding of iSGS and implicate shared pathogenic mechanisms with distal airway fibrotic diseases.