Abstract

B cells are implicated in rheumatoid arthritis (RA) based on the presence of autoantibodies and the therapeutic response to B cell depletion. IL-21 has a significant role in B cell development and function. Here we assess B cell responses to IL-21 and the mechanisms responsible for altered IL-21R expression in RA. Flow cytometry of PBMC and cultured B cells was used to quantify protein and mRNA levels of IL-21R, IL-21 signaling through pSTAT3, specificity protein 1 (SP1) and to determine cytokine production (IL-6) and maturation status of B cells in RA and healthy control subjects. SP1 binding to the IL21R promoter region in B cells was assessed with ChIP-qPCR. We demonstrate an increase in IL-21R expression in total and memory B cells from RA subjects, which correlated with responsiveness to IL-21 stimulation. Stimulation of naïve RA B cells with IL-21 and CD40L resulted in an increase in differentiation into plasmablasts and an increase in IL-6 production in comparison to healthy controls, which was dose dependent on IL-21 stimulation. IL-21R expression on memory B cells in RA synovial fluid was comparable to peripheral blood making our study pertinent to understanding B cell responses in the joint and site of inflammation. We identified an increase in SP1 protein and mRNA in RA B cells and demonstrate an increase in binding of SP1 to the IL21R promoter region, which suggests a mechanism by which IL-21R expression is enhanced on B cells in RA. Taken together, our results indicate a mechanism by which IL-21 enhances B cell development and function in RA through an SP1 mediated increase in IL-21R expression on B cells.

Highlights

  • Rheumatoid arthritis (RA) is a chronic inflammatory and destructive joint disease characterized by the presence of rheumatoid factor and anti-cyclic citrullinated peptide autoantibodies (ACPA) [1, 2]

  • We demonstrate an increase in the expression of IL-21R on total and memory B cells in RA compared to controls, which positively correlated with pSTAT3 levels following IL-21 stimulation

  • Example gating for B cell populations and IL-21R gating of a bimodal population is visualized in Figure 1A and is applied throughout the paper

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Summary

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory and destructive joint disease characterized by the presence of rheumatoid factor and anti-cyclic citrullinated peptide autoantibodies (ACPA) [1, 2]. The. SP1 Enhances IL-21R in RA development of ACPA and rheumatoid factor autoantibodies precede disease development and expansion of ACPA and rheumatoid factor specific plasmablasts in RA patients with significant levels of somatic mutation, further indicating dysregulation in B cell maturation [4]. B cell depletion with rituximab is efficacious in RA [5] and response to therapy with rituximab and abatacept [6] correlate with decreases in the level of ACPA. This highlights the need to better understand how B cells escape tolerance in RA and their role in propagating disease

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