The over-represented gene classes that were enriched as intestinal components of BO consisted of intermediate filaments and binding proteins (e.g., KRT5, 8, 15 and 37, Periplankin, PKP1, EVPL, SOS1), interleukin superfamily members (e.g., RGS12, IL12A, IL36G, IL20, IL1RN), major histocompatibility complex antigens (e.g., HLA-F, HLA-DRB5, HLA-DQB2, ODC1) and protease inhibitors (e.g., CASP6-7, PRKD1, KLK7, CST6, SERPINB2) (Fig. 1D). Here, PRKD1 is linked to bronchiolitis obliterans syndrome.