Altered pIgR/IgA mucosal immunity in bronchiolitis obliterans syndrome

Aims: Long-term survival after lung transplantation (LT) is hampered by the occurrence of chronic lung allograft dysfunction (CLAD), manifesting as bronchiolitis obliterans syndrome (BOS) or restrictive allograft syndrome (RAS). CLAD is triggered by several factors, e.g. recurrent infections. As immunoglobulin (Ig) A is crucial to ensure mucosal immunity and limit airway microbial load, we explored whether IgA and its epithelial receptor, the polymeric Ig receptor (pIgR) are impaired in BOS. Methods: Bronchoalveolar lavages (BAL, n=120) from LT recipients included in the Cohort for Lung Transplantation were collected at pre-defined timepoints prior to the diagnosis of functional stability (BOS-free, n=30) or BOS (pre-BOS, n=30), and assessed for secretory (S)-IgA. Bronchiolar epithelium pIgR expression was quantified in transbronchial biopsies from BOS-free (n=20), pre-BOS (n=19) and BOS LT recipients (n=12), as well as in end-stage BOS explants (n=15). Results: S-IgA levels were reduced in BAL from pre-BOS LT recipients versus BOS-free (16.1 vs 33.4 µg/ml, p<0.01). pIgR bronchiolar expression was reduced in transbronchial biopsies from BOS (p<0.05 vs BOS-free and pre-BOS), with further decrease in end-stage BOS explants (p