Characterization of human IL-10-producing regulatory B cells.

Regulatory B cells (Bregs) play a pivotal role in the maintenance of immune tolerance. Such critical roles of Bregs have been demonstrated in multiple disease types, including inflammatory diseases, organ transplantation, allergic asthma, and cancer. However, surface phenotypes and functional characteristics of human Bregs have not been fully investigated. Herein, we report that CD24hiCD38hi transitional B cells (TBs) and CD24hiCD27+ B cells (human equivalent of murine B10 cells) are the major IL-10-producing B cells that are capable of suppressing CD4+ T cell proliferation as well as IFNγ/IL-17 expression. Impaired frequency and function of CD24hiCD38hi TBs and CD24hiCD27+ B10 cells were also found in liver allograft recipient with plasma cell hepatitis (PCH). Further investigation of human Bregs revealed that CD24hiCD27+ B cells consist of two major subsets, CD24hiCD27+CD39hiIgD+IgMhiCD1chi and CD24hiCD27+CD39hiIgD-IgMloCD1c+/lo B cells. These two subsets of Bregs expressed not only IL-10, a major anti-inflammatory cytokine, but also CD39, programmed death-ligand 1 (PD-L1), transforming growth factor beta 1 (TGFβ1), granzyme B, and T-cell immunoreceptor with Ig and ITIM domains (TIGIT). In line with their ability to express such immunosuppressive molecules, they were efficient at suppressing CD4+ T cell proliferation as well as inflammatory cytokine expression. RNA-Seq data further showed that the two CD24hiCD27+ B cell subsets exhibited common as well as distinct transcriptomic signatures. However, they were distinct from TBs and others B cells in many different aspects. Finally, we showed that both frequency and function of CD24hiCD27+CD39hiIgD+IgMhiCD1chi and CD24hiCD27+CD39hiIgD-IgMloCD1c+/lo Bregs were significantly reduced in liver allograft recipients with donor specific alloantibody (DSA+) than DSA- patients and age-sex matched healthy control subjects. Data from this study are fundamental for our understanding of the biology of human Bregs as well as for a rational design of Breg-targeted therapy in future.