FCER2 and systemic lupus erythematosus: Additionally, the activated naive B cells that expanded in systemic lupus erythematosus (SLE) were characterized by low expression of surface CXCR5, CD21, and CD23, in addition to high expression of CD11c and T-bet (107), suggesting that PAX5lo naive B cells might be a different subpopulation compared with the one expanded in SLE.