BAX and bronchiolitis obliterans syndrome: We examined the effects of BO on the ratio of Bcl-2-associated protein (Bax), an accelerator of apoptosis, and B cell lymphoma-2 protein (Bcl-2), a regulator of apoptosis, in the atrium of the three groups (Fig. 4D) and found that it was significantly increased in the atrium of the BO group (Control (n = 6) vs. BO (n = 8); 1.0 ± 0.2 vs. 1.3 ± 0.2 A.U., P < 0.01 vs. Control).