CD19 expressed by peripheral B-cell subsets from healthy donors and systemic lupus erythematosus patients. Peripheral blood mononuclear cells from 33 systemic lupus erythematosus (SLE) patients and 10 controls were stained for CD3, CD14, CD20, CD19 (clone SJ25C1) and CD27. (a) Lymphocytes including large cells were gated based on forward scatter (FSC) and side scatter (SSC) properties; cell aggregates were excluded in a dotplot depicting forward-scatter height (H) versus area (A) signals. Dead cells, T cells and monocytes were excluded from the analysis, and B cells were identified by gating on the DAPI-CD3-CD14-CD19+ population. (b) Geometric mean fluorescence intensity (MFI) values reflecting CD19 expression were compared among B-cell subsets in SLE patients vs. healthy controls (HD); that is, CD27-CD20+ naive and CD27+CD20+ memory B cells and CD27highCD20-/low plasmablasts. (c) SLE patients were subdivided into three equally sized groups according to ascending expression levels of CD19 by CD27- B cells, CD27+ B cells or plasmablasts (indicated by the triangles below the graph) and analyzed for disease activity (Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)). (d) SLE patients were divided into two groups according to disease activity (SLEDAI <6 vs. SLEDAI ≥6) and analyzed for B-cell CD19 expression levels. Horizontal lines represent median values. P < 0.05 was considered to reflect a statistically significant difference according to the Wilcoxon or Mann-Whitney test used for intra-donor or inter-group comparisons, respectively. (e) CD19 expression levels by CD27- and CD27+ B cells and plasmablasts were analyzed between the individual B-cell subsets using Spearman's rank correlation, demonstrating close relations between their CD19 surface expression levels. *P < 0.05, **P < 0.01 and ***P < 0.001 classify significant values. DAPI, 4',6-diamidino-2-phenylindole.