Fibroblast‐like synoviocytes preferentially induce terminal differentiation of IgD+ memory B cells instead of naïve B cells.

Rheumatoid arthritis (RA) is a systemic autoimmune disease driven by highly active autoantibody‐producing B cells. Activation of B cells is maintained within ectopic germinal centres found in affected joints. Fibroblast‐like synoviocytes (FLS) present in inflamed joints support B‐cell survival, activation, and differentiation. CD27+ memory B cells and naive B cells show very different responses to activation, particularly by CD40 ligand (CD40L). We show that FLS‐dependent activation of human B cells is dependent on interleukin‐6 (IL‐6) and CD40L. FLS have been shown to activate both naive and memory B cells. Whether the activating potential of FLS is different for naive and memory B cells has not been investigated. Our results suggest that FLS‐induced activation of B cells is dependent on IL‐6 and CD40L. While FLS are able to induce plasma cell differentiation, isotype switching, and antibody production in memory B cells, the ability of FLS to activate naive B cells is significantly lower. [ABSTRACT FROM AUTHOR]