CD19 and type 1 diabetes mellitus: Furthermore, to investigate whether we could discern a systemic immunoregulatory defect in these patients, we also assessed the production of IL-10 in purified CD19+ B cells following IL-21 stimulation, which revealed an association between polymorphisms of the T1D locus IL2–IL21 and IL-10 production in memory B cells and, in a follow-up analysis, in autoreactive T cells.