UBC and bronchiolitis obliterans syndrome: In parallel, gene sets related to ubiquitin-protein ligase activity, ubiquitin-like protein ligase binding, regulation of protein ubiquitination, and ubiquitin-mediated proteolysis were significantly enriched in the BO group (Figures 7A–D), supporting a central role of ubiquitin dysregulation in fibroblast activation and airway fibrosis.