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Airway epithelial injury is thought to be a key event in the pathogenesis of Chronic lung allograft dysfunction (CLAD). We investigated whether markers of epithelial activity and injury in bronchoalveolar lavage (BAL) correlate with CLAD diagnosis and major CLAD phenotypes: bronchiolitis obliterans syndrome (BOS) vs. restrictive allograft syndrome (RAS)-related phenotypes (including RAS, mixed phenotype, and all other patients with RAS-like opacities).
CLAD status and phenotypes were retrospectively determined in a cohort of all consecutive adult, first, bilateral lung transplants performed 2010-2015. All patients with RAS-related phenotypes were included and 1:1 matched with BOS patients based on time from transplant to CLAD-onset. CLAD-free subjects were used as controls. 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 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. Association between protein levels and graft survival was assessed using Cox proportional hazards models, adjusted for CMV serology mismatch status and phenotype.
Fifty-four CLAD (27 BOS, 11 RAS, 7 mixed, 9 others with RAS-like opacities) patients and 26 CLAD-free controls were included. Median BAL levels were significantly higher in patients with CLAD compared to CLAD-free controls for M30 (124.5 vs. 88.9), MUC1 (6.8 vs. 3.28) and MUC16 (121.0 vs. 31.1). When comparing CLAD phenotypes, M30 was significantly higher in patients with RAS-related phenotypes compared to BOS (160.9 vs. 114.6). In multivariable models, levels of M30 and MUC5B were associated with allograft survival after CLAD onset independent of phenotype (P<0.05 for all).
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.
© 2021 Published by Elsevier Inc.