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 naïve (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 < .001), as were class-switched memory cells (12% vs 17%). There was a slight expansion of plasmablasts in subjects with SLE (5% vs 2%). Levels of CR2 on bulk B cells were decreased by 45% in subjects with SLE compared with healthy controls (mean antibody binding capacity 29,829 ± 5,139 vs. 16,305 ± 6,147), and this decrease was observed in all subsets except plasmablasts. In healthy controls, CR2 levels increased with B-cell maturation consistent with the developmentally restricted pattern previously described. This pattern was blunted in subjects with SLE.
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.
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.