High ROS levels in AML patients are associated with reduced p38^MAPKphosphorylation. (A) Representative Western blot of primary AML blasts showing phospho-p38^MAPK and total p38^MAPK protein expression in relation to superoxide production (total photons). (B) Summary data showing phospho-p38^MAPK in relation to total superoxide production in a cohort of 49 AML patients. (C) Western blot of AML blasts showing GSTM1 protein expression in relation to superoxide production. (D) Relative GSTM1 mRNA expression (normalized to a calibrator sample) in samples from the upper and lower quartiles of superoxide production in a separate cohort of 39 AML patients was analyzed by quantitative real-time polymerase chain reaction using the following GSTM1-specific primers as previously described³³ : 5′-TGATGTCCTTGACCTCCACCGT-3′ (forward), 5′-GCTGCACTTCATGTAGGCAGAG-3′ (reverse). The significance of difference was determined by the Mann-Whitney U test. **P < .01.