Impaired IgA mucosal immunity following lung transplantation: a potential trigger for bronchiolitis obliterans...

Bronchiolitis obliterans syndrome (BOS) limits long-term survival after lung transplantation (LuTx) and may be triggered by infections. As immunoglobulin (Ig)A is crucial to ensure adequate mucosal immunity, we explored whether IgA-related mucosal immunity is impaired in BOS.

60 LuTx recipients from the Cohort for Lung Transplantation (COLT) cohort were included retrospectively. All participants were in stable condition within the first year post-transplant. At 3.5 years post-LuTx, 30 remained stable and 30 had developed BOS. Bronchoalveolar lavage fluid (BALF) and sera collected pre-transplant and at 6 (M6) and 12 months (M12) post-transplant were assessed for monomeric IgA, secretory (S)-IgA, secretory component and cytokine profiling. Second, bronchiolar polymeric Ig receptor (pIgR) expression and subepithelial IgA-producing B-cell numbers were compared across graft tissue samples from 54 LuTx recipients classified as stable, pre-BOS, BOS or end-stage BOS.

S-IgA levels in BALF decreased between M6 and M12 (p=0.0001) and were reduced in BOS patients at M12 (p=0.0018). Patients with lower S-IgA levels had higher infection rates. BOS patients exhibited elevated secretory component levels in serum (p<0.01). Both reduced S-IgA in BALF and increased secretory component in serum were associated with higher risk of BOS. Lastly, a reduction in bronchiolar pIgR expression was observed in BOS patients (p=0.0001), that paralleled BOS severity.

This study demonstrates an early impairment of mucosal IgA immunity in LuTx patients, which was linked to the later development of BOS, suggesting that IgA-related markers may serve as early predictors of BOS onset.