FCER2 and arthritic joint disease: To investigate whether the reduction in Breg cells contribute directly to altered Treg- and Th17-cell equilibrium and exacerbated arthritis in WAS KO mice, we isolated B220+CD21+CD23+ T2-MZP B cells from C57BL/6 mice with arthritis and adoptively transferred these into WAS KO mice prior to arthritis induction.