Pulmonary Markers of Epithelial Cell Activation and Injury in Chronic Lung Allograft Dysfunction

Abstract

Airway epithelial injury is thought to be a key event in the pathogenesis of CLAD. We investigated whether markers of epithelial activation and injury in bronchoalveolar lavage (BAL) correlate with CLAD diagnosis and the major CLAD phenotypes: bronchiolitis obliterans syndrome (BOS) vs. restrictive allograft syndrome (RAS) / mixed phenotype. This was a retrospective, cohort study of all consecutive adult, first, bilateral lung transplants performed 2010-2015. CLAD status and phenotypes were retrospectively determined based on 2019 ISHLT definitions. All patients with RAS/mixed phenotype were included and 1:1 matched with BOS patients based on time from transplant to CLAD-onset. CLAD-free controls were randomly selected. Proteins that maintain the barrier function of the airway epithelial mucosa (club cell secretory protein (CCSP), surfactant protein-D (SP-D) and epithelial mucins: MUC1, MUC5AC, MUC5B, MUC16), as well as epithelial cell death markers (M30&M65 representing epithelial cell apoptosis and overall death, respectively) were measured in BAL obtained within 6-months from CLAD onset using a double-sandwich ELISA or a multiplex bead assay. Protein levels were compared using Kruskal-Wallis and Mann-Whitney-U-test. Forty-five CLAD (27 BOS, 11 RAS, 7 mixed) and 26 CLAD-free controls were included. BAL levels of M30, MUC1 and MUC16 were significantly higher in patients with CLAD compared to CLAD-free controls. When comparing CLAD phenotypes, only M30 demonstrated a difference between RAS/mixed and BOS with a significantly higher M30 level in RAS/mixed patients. Airway epithelial mucin and cell death markers are enhanced in the BAL fluid of patients with CLAD and can assist in differentiating between CLAD phenotypes. Abnormal airway mucin expression and epithelial cell death may be involved in the airway inflammatory response of CLAD and thus aid in future selection of targeted therapies.