Total B cells, immature B cells, naive B cells, and memory B cells of patients with ITP and HCs. (A) Elimination of adherent cells and fragments, and gate settings for lymphocytes from BM and PB. (B, C) patients with ITP had fewer CD19⁺ B cells in BM (7.81 ± 0.84% vs 15.26 ± 1.84%; P < .001) but more in PB (6.94 ± 0.63% vs 4.83 ± 0.41%; P = .013) compared with HCs. (D, E) No statistical difference was found in the proportion of CD19⁺ B cells between BM and PB in patients with ITP (P = .893), whereas the proportion of BM CD19⁺ B cells was significantly higher than its PB counterparts in HCs (15.26 ± 1.84% vs 4.83 ± 0.41%; P = .002). (F, G) No difference was found in CD19⁺CD127⁺ immature B-cell compartments in BM CD19⁺ cells between patients with ITP and HCs (4.91 ± 0.94% vs 4.01 ± 0.58%; P = .504), whereas a lower frequency of CD19⁺CD127⁺ B cells in lymphocytes was observed in patients with ITP (0.22 ± 0.07% vs 0.53 ± 0.12%; P = .029). (H) Density plots of CD27 and CD38 double staining from CD19⁺ cells in flow cytometry. CD19⁺CD27^– cells (Q1 + Q3) were naive B cells, and CD19⁺CD27⁺CD38^–/low cells (Q4) were memory B cells. (I, J) The percentage of naive B cells was significantly lower in BM B cells from patients with ITP compared with HCs (64.04 ± 3.04% vs 77.33 ± 2.33%; P = .011), whereas no statistical difference was found in PB naive B cells between patients with ITP and HCs (median [range], 69.36% [47.66%-93.53%] vs 67.69% [49.45%-85.50%]; P = .817). (K, L) No statistical difference was observed in naive B cells between BM and PB from patients with ITP (median [range], 69.82% [12.78%-89.30%] vs 69.36% [47.66%-93.53%]; P = .731), whereas more naive B cells existed in BM B cells than in PB from HCs (78.10 ± 2.38% vs 64.53 ± 3.24%; P < .001). (M, N) The frequency of memory B cells was higher in BM B cells of patients with ITP than that of HCs (26.23 ± 3.20% vs 12.61 ± 2.57%; P = .002), but no difference was observed in PB memory B cells between patients with ITP and HCs (25.17 ± 2.98% vs 22.84 ± 4.42%; P = .654). (O, P) No statistical difference was found in percentage of memory B cells in CD19⁺ cells between BM and PB in patients with ITP (26.23 ± 3.20% vs 25.17 ± 2.98%; P = .813). HCs had remarkably decreased frequency of memory B cells in BM compared with PB (12.61 ± 2.57% vs 22.84 ± 4.42%; P = .021). *P < .05; **P < .01; ***P < .001. APC, allophycocyanin; FITC, fluorescein isothiocyanate; FSC-A, forward scatter pulse area; SSC-A, side scatter pulse area.