CD27 and systemic lupus erythematosus: Purified SLE B cell subsets (T-betlo BN, T-betlo CD11cnegCXCR5+ CD27negIgDneg DN1 memory cells, T-betlo CD27+ memory B cells (Bmem) and T-bethi CD11c+CXCR5neg DN2 cells) were stimulated with cytokines (IFNγ, IL-21, IL-2, BAFF) and R848 for 2.5 days then counted and transferred to anti-IgG ELISPOT plates for 6 hr.