ROS levels in bone marrow cell subpopulations of MDS/sAML patients. (A) Flow cytometry quantification of ROS in BM cells (ie, monocytic, granulocytic, lymphocytic, erythroblastic subpopulations and CD34^pos, CD34^posCD38^low, and CD34^posCD38^high progenitors) of healthy controls. ROS levels were evaluated by DCFDA mean fluorescence intensity (DCFDA-MFI) and results are expressed as % of DCFDA MFI of monocytes (± standard error of the mean [SEM]). The highest level of ROS was found in monocytic cells in all samples, and the lowest level in the erythroblastic subpopulation. *Significant difference with monocytic cells, P < .05; #significant difference, P < .05. (B) Absolute ROS levels (DCFDA-MFI) in the BM monocytic subpopulation from healthy controls, MDS subgroups, and sAML are not statistically different (P = .77, Kruskal-Wallis test). (C) ROS levels in the BM subpopulations of MDS/sAML patients compared with healthy controls, after normalization with the respective DCFDA-MFI value of monocytes in each sample. Increased ROS levels were observed exclusively in myeloid and especially progenitor subpopulations. The most important oxidative stress was found in the erythroblastic subpopulation in MDS-SLD-RS and MDS-MLD with ring sideroblasts, enriched in ring sideroblasts, and in the CD34^posCD38^low progenitors in all pathologies, especially in sAML. Data are expressed as mean ± SEM (n = 65). *Significant difference with the healthy controls, P < .05. #Significant difference with healthy controls and with MDS subgroups, P < .05. ns, nonsignificant difference with the healthy controls.