Immunophenotypic and structural signatures of severe granulation tissue in airway implant patients

Abstract Background Granulation tissue formation is a frequent complication following airway implant procedures such as endobronchial valve (EBV) therapy in patients with chronic obstructive pulmonary disease (COPD). This hyperplastic response can impair implant function and clinical outcomes, yet the underlying immunological mechanisms remain poorly understood. Methods In a cohort of EBV patients (n = 147), we developed an optical scaling and scoring system to classify the severity of granulation tissue in relation to clinical outcomes. Based on this system, we prospectively collected endobronchial biopsies from EBV (n = 41) and stent patients (n = 11) for immune and structural profiling across different severity grades. Granulation tissue was analysed by histology, immunofluorescence, and flow cytometry. Results Using the optical scoring system, almost 75% of EBV patients developed hyperplastic granulation tissue (34.7% moderate, 38.8% severe). In many moderate to severe cases, valve dysfunction, dislocation, and the need for revision was observed. Increasing severity of granulation tissue was associated with profound extracellular matrix (ECM) disruption and increased immune cell infiltration. Immunophenotyping revealed elevated neutrophils and regulatory T cells (Tregs) with a central memory phenotype. Macrophages in patients with severe granulation tissue formation showed a shift toward a CD163+ M2-like polarisation. Structural analyses demonstrated a loss of epithelial integrity and an upregulation of ECM remodelling markers, fibronectin, and tenascin C. Conclusion This study provides the first systematic immune-morphological classification of airway granulation tissue following EBV therapy. Our findings revealed distinct immune and ECM signatures associated with clinical complications identify potential mechanisms and therapeutic targets, particularly relevant for COPD patients in whom current anti-inflammatory strategies are insufficient. Graphical abstract Overview of the study design and main findings on the immunological and structural characterisation of granulation tissue following endobronchial valve (EBV) or stent implantation. Granulation tissue was obtained by forceps biopsy during bronchoscopy. Scoring was performed according to severity, followed by histological and immunofluorescence analysis for immune cell infiltration, immunophenotyping by flow cytometry, and assessment of extracellular matrix (ECM) remodelling. Increased granulation grade was associated with clinical complications including EBV dislocation, dysfunction, and need for revision procedures. Key immune cell types [neutrophils, type 2 T helper (Th2) cells, regulatory T cells (Treg), central memory cells (CM), CD16high natural killer cells (NK), CD163+ macrophages], goblet cells, fibroblasts, endothelial cells (endoglin, ICAM), and ECM components (β-Catenin, fibronectin, collagen IV, tenascin C, pan-laminin).