**Cohort Description ** The Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) is a multi-center, observational, longitudinal case-control study designed to guide fu
Background: The small airway epithelium (SAE, >6th generations), the initiation site of smoking-induced airway disorders, is highly sensitive to the stress of smoking. Lymphocyte antigen-6 (Ly6)/uroki
