CD24^hiCD38^hi and CD24^hiCD27⁺ human regulatory B cells display common and distinct functional characteristics

Although IL-10-producing regulatory B cells (Bregs) play important roles in immune regulation, their surface phenotypes and functional characteristics have not been fully investigated. In this study, we report that the frequency of IL-10-producing Bregs in human peripheral blood, spleens, and tonsils is similar, but they display heterogenous surface phenotypes. Nonetheless, CD24^hiCD38^hi transitional B cells (TBs) and CD24^hiCD27⁺ B cells (human equivalent of murine B10 cells) are the major IL-10-producing B cells. They both suppress CD4⁺ T cell proliferation as well as IFN-γ/IL-17 expression. However, CD24^hiCD27⁺ B cells were more efficient than TBs at suppressing CD4⁺ T cell proliferation and IFN-γ/IL-17 expression, whereas they both coexpress IL-10 and TNF-α. TGF-β1 and granzyme B expression were also enriched within CD24^hiCD27⁺ B cells, when compared with TBs. Additionally, CD24^hiCD27⁺ B cells expressed increased levels of surface integrins (CD11a, CD11b, α1, α4, and β1) and CD39 (an ecto-ATPase), suggesting that the in vivo mechanisms of action of the two Breg subsets are not the same. Lastly, we also report that liver allograft recipients with plasma cell hepatitis had significant decreases of both Breg subsets.