Signaling response to H₂O₂modulation in the presence of antioxidant enzyme inhibitors or exogenous catalase. (A) CLL cells were pretreated with the catalase inhibitor ATZ (1 mM), the GPX inhibitor MCA (100 µM), the CuZnSOD inhibitor DDTC (70 µM), or vehicle for 24 hours and then modulated with 3.3 mM H₂O₂ for 10 minutes. Response to H₂O₂ modulation was measured as sum of log2-fold change of pSYK, pERK1/2, and pp38 and then converted to percentage with respect to vehicle response. (B) Representative contour plots of pSYK expression in response to H₂O₂ modulation in presence of the catalase inhibitor ATZ, the GPX inhibitor MCA, the CuZnSOD inhibitor DDTC, or vehicle. (C) CLL cells were pretreated with 1000 U/mL exogenous catalase from bovine liver for 30 minutes and then modulated with 3.3 mM H₂O₂ for 10 minutes. Response to H₂O₂ modulation was measured as sum of log2-fold autofluorescence of pSYK, pERK1/2, and pp38. (D) Representative contour plots of pSYK expression in response to H₂O₂ modulation in presence of exogenous catalase, or vehicle. Comparisons were performed using the paired Student t test. Data are expressed as mean ± SEM. *P ≤ .05; ***P ≤ .001.