Effects of Wiskott-Aldrich Syndrome Protein Deficiency on IL-10-Producing Regulatory B Cells in Humans and Mice.

The Wiskott-Aldrich syndrome protein (WASp) is an important regulator of the actin cytoskeleton and is required for immune cell function. WASp deficiency causes a marked reduction in major mature peripheral B cell subsets, particularly marginal zone (MZ) B cells. We hypothesized that WASp deficiency may also lead to a reduction of regulatory B cells (known as B10 cells) belonging to a novel subset of B cells. And in consideration of the key role of B10 cells play in maintaining peripheral tolerance, we conjectured that a deficit of these cells could contribute to the autoimmunity in patients with Wiskott-Aldrich syndrome (WAS). The effects of WASp deficiency on B10 cells have been reported by only one group, which used an antigen-induced arthritis model. To add more information, we measured the percentage of B10 cells, regulatory T cells (Tregs) and Th1 cells in WASp knockout (WASp KO) mice. We also measured the percentage of B10 cells in patients with WAS by flow cytometry. Importantly, we used the non-induced autoimmune WASp KO mouse model to investigate the association between B10 cell frequency and the Treg/Th1 balance. We found that the percentage of B10 cells was reduced in both mice (steady state and inflammatory state) and in humans and that the lower B10 population correlated with an imbalance in the Treg/Th1 ratio in old WASp KO mice with autoimmune colitis. These findings suggest that WASp plays a crucial role in B10 cell development and that WASp-deficient B10 cells may contribute to autoimmunity in WAS.