XBP1 and systemic lupus erythematosus: Interestingly, B cells from SLE patients cultured with TGF-β3 showed reduced B-cell survival, proliferation, and differentiation into plasmablasts and IgG, IgA, and IgM production and decreased the expression of IFN regulatory factor 4 (IRF4), B lymphocyte-induced maturation protein-1 (Blimp-1), X-box-binding protein 1 (XBP1), Smad1/5, and Syk (111).