Abstract
Purpose Complement receptor 2 (CR2) levels on circulating B cells in patients with systemic lupus erythematosus (SLE) are decreased. In SLE, altered homeostasis of the circulating B-cell pool leads to increased frequency of subsets that express low CR2. We hypothesized that these shifts could account for the decreased CR2 levels demonstrated on bulk B cells of patients with SLE. Methods Peripheral blood mononuclear cells were prepared from nine subjects with SLE and eight healthy controls using a Ficoll density gradient. Cells were stained with fluorescently labeled monoclonal antibodies to CD19, CR2 (HB5 clone), IgD, CD27, and CD38. Ethidium monoazide bromide (EMA) was used as a viability marker. Previously defined peripheral blood B-cell subsets were identified using polychromatic flow cytometry: transitional (CD27−IgD+CD38++), mature naive (CD27−IgD+CD38low), marginal zone-like (CD27+IgD+), class-switched memory (CD27+IgD−CD38low), and plasmablast (CD27+/++IgD−CD38++). SimplyCellular quantification beads (Bangs Labs) were used to quantify CR2 levels. Results are expressed as mean antibody binding capacity (ABC) ± standard deviation. Results Naive B cells comprised the largest subset of circulating B cells in both healthy (43%) and lupus (43%) subjects. Transitional cells were increased in frequency in SLE subjects (17%) compared with healthy controls (3%) (p = .0047). Marginal zone-like cells were decreased in frequency in SLE subjects (6%) compared with healthy controls (20%) (p Conclusions As previously described, subjects with SLE have changes in B-cell subsets leading to increased frequency of CR2low cells. However, B cells in subjects with SLE have lower CR2 across all subsets and demonstrate a blunting of the increases in CR2 levels typically seen with maturation. Therefore, expansion of a CR2low B cell subset does not provide the mechanism for reduced B-cell CR2 levels in SLE.
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