Objective: To determine phenotypic and functional characteristics of memory B cells in patients with systemic lupus erythematosus (SLE). Methods: The percentage of memory B cell subsets in peripheral blood mononuclear cells (PBMC) from normal control (n=11), inactive (n=15) and active (n=10) SLE patients was determined by Fluorescence Activated Cell Sorter (FACS). In addition, the activation status of memory B cells was measured by the surface expression of CD86 (B7-2). The production of antibodies to chromatin and dsDNA (IgG and IgM type) by isolated memory B cell subsets was examined by enzyme-linked immunosorbent assay (ELISA). Results: In this study, we analyzed 2 subtypes of memory B cells: FSC (Forward Side Scatter)^low and FSC^high memory B cell. The percentage of both subtypes from active and inactive SLE patients was significantly reduced compared to that of normal controls (p＜0.01). In addition, the expression of activation markers, CD86 on FSC^high memory B cells from active SLE patients was higher than those of inactive SLE patients and normal controls (p=0.014). Upon stimulation with CpG and IL-15 in vitro for 8 days, isolated FSC^high memory B cells from active SLE patients revealed augmented production of autoantibodies to chromatin and dsDNA. Conclusion: Our results suggest that abnormally activated FSC^high memory B cells from active SLE patients might be involved in spontaneous production of autoantibodies and induce transition from inactive to active phase of the patients.

Keywords: Systemic lupus erythematosus, Anti nuclear autoantibodies, Memory B cell CD86 (B7-2), CPG