The number of MDSCs and their expression of Arg-1/iNOS in the peripheral blood. (A) The representative scatter-gram of CD11b⁺CD33⁺HLA-DR^low cells within the gate of PBMCs. Histograms of Arg-1 and iNOS in CD11b⁺CD33⁺HLA-DR^low cells from healthy control patients and patients with ITP before any treatment was initiated. (B) The percentage of CD11b⁺CD33⁺HLA-DR^low cells in hemolyzed whole blood from primary active patients with ITP (n = 21) and healthy control patients (n = 18). (C-D) The expression (mean fluorescence intensity) of Arg-1 (C) and iNOS (D) in circulating MDSCs compared between patients with ITP (n = 21) and control patients (n = 18). Significance between the 2 groups was determined by Student-Newman-Keuls test. Bars represent SD. **P < .01.