MPO and bronchiolitis obliterans syndrome: The level of MPO and NE expression in the lung tissue of both 2,3-butanedione and nitric acid-induced BO mice was found to be significantly elevated (p < 0.01 and p < 0.001, respectively, for MPO; p < 0.01 and p < 0.0001, respectively, for NE) (Fig. 6B–E)compared to control mice.