Systemic immunosuppression depletes peripheral blood regulatory B cells in patients with immune thrombocytopenia

Regulatory B (Breg) cells are potentially implicated in the pathogenesis of immune thrombocytopenia (ITP). We analysed a prospective cohort of newly diagnosed steroid naïve ITP patients enrolled in the multicentre FLIGHT trial and found that the numbers of Bregs in their peripheral blood were similar to healthy controls. In contrast, Breg numbers were significantly reduced in ITP patients treated with systemic immunosuppression (glucocorticoids or mycophenolate mofetil). We also demonstrate that glucocorticoid treatment impairs Breg interleukin-10 production via an indirect T-cell-mediated mechanism.