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275 CHANGES IN B-CELL SUBSETS DO NOT ACCOUNT FOR DECREASED COMPLEMENT RECEPTOR 2 LEVELS IN HUMAN SYSTEMIC LUPUS ERYTHEMATOSUS.
  1. D. W. Pearson1,
  2. S. A. Boackle1
  1. 1Colorado Health Sciences Center, Denver, CO.

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 (CD27IgD+CD38++), mature naïve (CD27IgD+CD38low), marginal zone-like (CD27+IgD+), class-switched memory (CD27+IgDCD38low), and plasmablast (CD27+/++IgDCD38++). 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.

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