SDC1 and systemic lupus erythematosus: B-cell-intrinsic T-bet deletion in lupus mice showed no effect on ABC production, where TBX21−/− ABCs and WT ABCs had identical surface phenotypes, including increased cell size, equivalent IgM and IgD expression, reduced CD21, CD23, and CD138 expression, and upregulated expression of co-stimulatory molecules CD86, MHC II, and CD95.