Background To examine B-cell subsets in peripheral blood of patients (pts) with systemic lupus erythematosus (SLE), and to analyze the association between the B-cell subsets and SLE activity.

Methods Peripheral blood of 20 healthy donors, 21 SLE pts (16F/5M, Me(IQR) age 33 (29–40) years, disease duration 6,0 (0,2–12,0) months, SLEDAI-2K 6 (4–9), SDI 0 (0–1)) were assessed for B-cell subpopulations. CD19+B cells, memory B cells (CD19+CD27+), non-switched memory B cells (CD19+IgD+CD27+), switched memory B cells (CD19+IgD-CD27+), naïve (CD19+IgD+CD27-), double negative (CD19+IgD-CD27-), transitional (CD19+IgD+CD10+CD38++CD27-) B cells, and plasmablasts (CD19+CD38+++IgD-CD27+CD20-) were assessed by multicolor flow cytometry.

Results In pts with SLE, compared to healthy donors was found the higher percentage and abs level of memory B cells (14.4 (12.8–23.3) vs 2.15 (1.05–2.95) and 0.016 (0.007–0.03) vs 0.0025

(0.01–0.007)), the higher percentage of non-switched memory B cells (11 (8.7–19.4) vs7.35 (3.7–11.05)), the higher percentage and abs level of plasmatic cells (2.8 (1.3–4.7) vs 0.1 (0.1–0.2) and 0.002 (0.001–0.006) vs 0.0002 (0.00009–0.0004) and higher percentage and abs level of transitional cells (17.1 (9.0–30.0) vs 0.1 (0.0–0.1) and 0.019 (0.009–0.03) vs 0.0001 (0.0–0.00025)), p<0.05 for all cases.

In pts with SLE we found a significant correlation between the percentage of CD19+B cells and La-SSB (r=0.54), abs memory B cells and La-SSB (r=0.53); abs negative correlation between non-switched memory B cells and C3 (r=0.67) and C4 (r=0.66), p<0.05 for all cases.

Conclusions Patients with SLE showed an increase in the percentage and absolute levels of memory B cells, non-switched memory B cells, plasmatic cells and transitional cells. We found a positive correlation between the B-cell subsets and autoantibody levels and negative correlation with the level of compliment components.