Increased Frequencies of Switched Memory B Cells and Plasmablasts in Peripheral Blood from Patients with ANCA-Associated Vasculitis

Abstract

B cells are thought to play a central role in the pathogenesis of antineutrophil cytoplasmic antibody- (ANCA-) associated vasculitis (AAV). ANCAs have been proposed to cause vasculitis by activating primed neutrophils to damage small blood vessels. We studied a cohort of AAV patients of which a majority were in remission and diagnosed with granulomatosis with polyangiitis (GPA). Using flow cytometry, the frequencies of CD19⁺ B cells and subsets in peripheral blood from 106 patients with AAV and 134 healthy controls were assessed. B cells were divided into naive, preswitch memory, switched memory, and exhausted memory cells. Naive and switched memory cells were further subdivided into transitional cells and plasmablasts, respectively. In addition, serum concentrations of immunoglobulin A, G, and M were measured and clinical data were retrieved. AAV patients displayed, in relation to healthy controls, a decreased frequency of B cells of lymphocytes (5.1% vs. 8.3%) and total B cell number. For the subsets, a decrease in percentage of transitional B cells (0.7% vs. 4.4%) and expansions of switched memory B cells (22.3% vs. 16.5%) and plasmablasts (0.9% vs. 0.3%) were seen. A higher proportion of B cells was activated (CD95⁺) in patients (20.6% vs. 10.3%), and immunoglobulin levels were largely unaltered. No differences in B cell frequencies between patients in active disease and remission were observed. Patients in remission with a tendency to relapse had, compared to nonrelapsing patients, decreased frequencies of B cells (3.5% vs. 6.5%) and transitional B cells (0.1% vs. 1.1%) and an increased frequency of activated exhausted memory B cells (30.8% vs. 22.3%). AAV patients exhibit specific changes in frequencies of CD19⁺ B cells and their subsets in peripheral blood. These alterations could contribute to the autoantibody-driven inflammatory process in AAV.

Figure 1

Comparisons of B cells and subsets between vasculitis patients and healthy blood donors. (a) Percentage of CD19⁺ B cells of lymphocytes, (b) percentage of transitional B cells (of CD19⁺ B cells), (c) percentage of switched memory B cells (of CD19⁺ B cells), and (d) percentage of plasmablasts (of CD19⁺ B cells), in peripheral blood from patients with antineutrophil cytoplasmic autoantibody- (ANCA-) associated vasculitis (AAV, n = 106) and healthy blood donors (HBD, n = 134). The Mann-Whitney test was used to calculate the level of significance. Data are presented with medians and interquartile ranges. In figure (d), one data point (20.56) in the AAV group is not shown for presentation purposes but included in statistical calculations.

Figure 2

Comparison of CD95⁺ B cells (of CD19⁺ B cells) in peripheral blood from patients with antineutrophil cytoplasmic autoantibody- (ANCA-) associated vasculitis (AAV, n = 106) and healthy blood donors (HBD, n = 134). The Mann-Whitney test was used to calculate the level of significance. Data are presented with medians and interquartile ranges.

Figure 3

Comparisons of B cells and subsets between patients in remission with and without a tendency to relapse. (a) Concentration of CD19⁺ B cells in peripheral blood from patients with antineutrophil cytoplasmic autoantibody- (ANCA-) associated vasculitis (AAV) in remission with (n = 28) and without (n = 33) tendency to relapse. (b) Percentage of transitional B cells (of CD19⁺ B cells), (c) percentage of CD95⁺ exhausted memory B cells (of exhausted memory B cells), in peripheral blood from patients with AAV in remission with (n = 29) and without (n = 36) tendency to relapse. The Mann-Whitney test was used to calculate the level of significance. Data are presented with medians and interquartile ranges.