The expression of cleaved caspase-9 was significantly increased in the BO-group (Control (n = 10) vs. BO (n = 9); 1.0 ± 0.1 vs. 1.3 ± 0.2 A.U., P < 0.01 vs. Control), but propranolol blocked this increase (BO (n = 9) vs. Pro + BO (n = 11); 1.3 ± 0.2 vs. 1.1 ± 0.1 A.U., P < 0.05 vs. BO) (Fig. 4E). Here, CASP9 is linked to bronchiolitis obliterans syndrome.