Breg Cells Are Numerically Decreased and Functionally Impaired in Patients With Systemic Sclerosis.

Abstract

Breg cells, a regulatory cell subset that produces interleukin-10 (IL-10), play a significant role in suppressing autoimmune responses and preventing autoimmunity. This study was undertaken to examine the number and function of Breg cells in patients with systemic sclerosis (SSc), a disease with many autoantibodies. Forty-five patients with SSc (12 with early SSc, 33 with established disease including 16 with SSc-associated pulmonary fibrosis [PF]), 12 healthy control subjects, and 10 patients with rheumatoid arthritis (RA)-associated PF were studied. The phenotypes of immature/transitional Breg cells (CD19+CD24(high) CD38(high) ) and memory Breg cells (CD19+CD27+CD24(high) ) were evaluated by flow cytometry. The function of Breg cells was assessed by measuring the production of IL-10 after B cell activation. In addition, activation of p38 MAPK and STAT-3 was measured following stimulation of the cells with B cell receptor (BCR) and Toll-like receptor 9 (TLR-9). Percentages of memory Breg cells were decreased in patients with early SSc (mean ± SEM 1.85 ± 0.38%), those with established SSc (1.6 ± 0.88%), those with SSc-associated PF (1.52 ± 0.17%), and those with RA-associated PF (1.58 ± 0.26%), compared to healthy controls (6.3 ± 0.49%; each P < 0.001). Percentages of transitional Breg cells were also decreased. Expression of IL-10 by Breg cells after stimulation with TLR-9 was impaired in patients with SSc, particularly those with SSc-associated PF. Activation of STAT-3 and p38 MAPK was impaired in naive and memory B cells from patients with SSc after stimulation with BCR and TLR-9. Expression of the stimulatory CD19 receptor was increased in B cells and also increased, to a lesser extent, in Breg cells from patients with SSc compared to healthy controls. Percentages of memory B cells were decreased in patients with SSc, particularly in those with SSc-associated PF. This is the first study to demonstrate that Breg cells are phenotypically and functionally impaired in patients with SSc. Furthermore, in SSc, B cells exhibit impaired p38 MAPK and STAT-3 activation upon stimulation with BCR and TLR-9. The findings of decreased numbers of Breg cells along with increased expression of CD19 support the idea of B cell autoaggression acting as an immunopathogenic mediator in SSc.