PDCD1 and bronchiolitis obliterans syndrome: PD-1 expression was higher (p < 0.001) on MAIT cells (Figure 3A) and T cells (Figure 3B) from all oesophageal tissue types (BO-adjacent control, BO, and OAC) when compared to blood, but no differences were detected between tissue types, with uniform high expression observed in all oesophageal tissues.