PDCD1LG2 and bronchiolitis obliterans syndrome: Levels of PD-L2 mRNA were significantly reduced in BO tissue compared with normal oesophageal tissue and trended toward a significant increase in the mRNA levels of PD-L2 in OAC tissue compared with BO tissue (normal:14.31 ± 1.6% vs. BO:9.6 ± 0.9%, OAC:13.53 ± 0.9% p = 0.02 and p = 0.06, respectively) (Fig. 1C.).