Plasmablasts, SLPCs, and LLPCs in patients with ITP and HCs. (A) CD19⁺CD27⁺CD38^hi cells were gated for analysis of CD19⁺CD27⁺CD38^hiKi67⁺CD138⁺ plasmablasts (Q2) and CD19⁺CD27⁺CD38^hiKi67^–CD138⁺ SLPCs (Q1). (B-E) No statistical difference in frequency of BM or PB plasmablasts in CD19⁺ cells was found between patients with ITP and HCs. Moreover, no significant difference in percentage of plasmablasts in CD19⁺ cells was observed between BM and PB from patients with ITP or HCs. (F, G) There was no remarkable difference in percentage of SLPCs in CD19⁺ cells between patients with ITP and HCs. (H, I) patients with ITP (median [range], 4.32% [1.32%-34.93%] vs 0.34% [0.06%-1.07%]; P < .001) and HCs (median [range], 10.70% [0.72%-20.39%] vs 0.10% [0.01%-0.93%]; P = .016) have more SLPCs in BM B cells than in PB B cells. (J) CD19^–CD38^hiCD138⁺ LLPCs were analyzed from autoantibody-negative or antibody-positive patients and HCs, respectively. (K) No statistical difference was found between all patients with ITP and HCs (median [range], 0.16% [0.01%-1.38%] vs 0.10% [0.02%-0.42%]; P = .273). The proportion of BM LLPCs from autoantibody-positive patients was significantly higher than that from HCs (median [range], 0.27% [0.13%-1.38%] vs 0.10% [0.02%-0.42%]; P = .021) and autoantibody-negative patients (median [range], 0.27% [0.13%-1.38%] vs 0.08% [0.01%-0.15%]; P < .001), whereas no significant difference was found between autoantibody-negative patients and HCs (P = .485). *P < .05; **P < .01; ***P < .001. APC, allophycocyanin; PE, phycoerythrin; SSC, side scatter.