Circulating exosomes with distinct properties during chronic lung allograft rejection

Circulating exosomes containing donor HLA and lung-associated self-antigens (SAg) are thought to play an important role in allograft rejection after human lung transplantation. We characterized exosomes isolated from serum of 10 lung transplant recipients (LTxR) diagnosed with bronchiolitis obliterans syndrome (BOS) and compared them with exosomes isolated from serum of 10 stable LTxR. Lung-associated SAg (K-a-1-tubulin [Ka1T] and collagen V [Col-V]), MHC class II molecules, costimulatory molecules CD40, CD80, and CD86, and transcription factors class II MHC trans-activator, NF-kB, hypoxia-inducible factor 1-a, IL-1R–associated kinase 1, MyD88, and 20S proteasome were detected in exosomes from BOS, but not stable LTxR. In contrast, adhesion molecules were present in both groups. C57BL/6 mice immunized with exosomes from BOS but not stable LTxR demonstrated Ab to SAg (Col-V, 33.5 6 15.7 versus 10.4 6 6.4, p = 0.021; Ka1T, 925 6 403 versus 317 6 285, p = 0.044) and HLA (mean fluorescence intensity: BOS, 8450; stable, 632; p < 0.05). Furthermore, splenic lymphocytes demonstrated increased frequency of lung SAg-specific IL-17 (Col-V, 128 6 46 versus 31 6 21, p = 0.013; Ka1T, 194 6 47 versus 67 6 43, p = 0.014) and IFN-g (Col-V, 165 6 79 versus 38 6 40, p = 0.042; Ka1T, 232 6 64 versus 118 6 39, p = 0.012). Reduced levels of IL-10–producing cells were seen in BOS exosome immunized mice compared with mice immunized with stable exosomes (Col-V, 59 6 23 versus 211 6 85, p = 0.016; Ka1T, 78 6 49 versus 295 6 104, p = 0.017). Owing to the unique immune-stimulating properties of exosomes induced during rejection, we propose that they play an important role in eliciting both alloantigen- and SAg-specific immunity, leading to chronic rejection after lung transplantation.