Abstract
Chronic lung allograft dysfunction (CLAD) is a common cause of death among lung transplant recipients (LTxRs). Two phenotypes of CLAD have been recognized; bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS), each with distinct clinical presentations, radiologic features, and prognosis. We have demonstrated increased levels of circulating exosomes containing lung self-antigens (SAgs), transcription factors, co-stimulatory molecules, and microRNA (miRNA) in LTxRs with BOS. Goal is to determine immunologic and molecular differences between LTxRs with BOS and RAS.
Antibodies (Abs) to SAgs (Kα1Tubulin, Collagen V) were identified using ELISA from LTxRs with BOS (n=12) and RAS (n=8). Donor specific antibodies (DSA) to HLA-DR, DQ were quantified using Luminex single antigen. Exosomes were isolated using ultracentrifugation, purified by 0.2µ filtration followed by size determination by Nanosight. Exosome contents were determined by western blot with Abs to SAgs, NFkB, 20S proteasome, HLA-DQ, DR, and poly immunoglobulin receptor protein (PIGR). Nanostring was done to identify miRNAs.
Three of 12 (25.0%) LTxRs with BOS, 1 of 8 (12.5%) with RAS developed Abs against SAgs (p=0.0027). All 8 (100%) LTxRs with RAS, 5 (41.7%) with BOS developed DSA to HLA-DR, DQ (p<0.0001). Compared to stable, all patients with CLAD contained exosomes with increased SAgs, NFkB, CIITA, 20S proteasome, PIGR, HLA-DQ, DR. However, there were significant quantitative differences between LTxRs with BOS and RAS (Table 1). In addition, miRNA profiling showed a higher concentration of 5 different miRNAs in LTxRs with BOS and 9 different miRNAs in LTxRs with RAS. miRNAs in BOS and RAS are related to TGF-β signaling pathways.
This study demonstrates that Abs to SAgs, DSA to HLA DR, DQ, and exosome content differs between LTxRs with BOS and RAS. These differences suggest that humoral immunity may play a prominent role in the pathogenesis of RAS compared to BOS.