Antioxidants prevent the radiation-mediated increase in CD20 expression. The kinetics of CD20 expression was measured with respect to untreated control by flow cytometry after treatment with either PEG-SOD or PEG-catalase, radiation, or H2O2, or a combination of PEG-SOD or PEG-catalase with radiation or H2O as described under Materials and methods. CD20 expression was determined in (A) Daudi and (B) Raji cells using anti-CD20 phycoerythrin-conjugated antibody at 20 and 12 h, respectively. The data were analyzed using FlowJo 6.4.1 and the results expressed as fold change of CD20 expression with respect to control. Statistical comparison was performed using ANOVA (*p<0.05 for control vs H2O2, **p<0.05 for control vs radiation, #p<0.05 for PEG-catalase vs H2O2, ##p < 0.05 for PEG-catalase vs radiation, ###p < 0.05 PEG-SOD vs radiation).