CD27 and systemic lupus erythematosus: In particular, studies in SLE, a condition that uniquely combines strong, simultaneous activation of both new naïve B cells and pre-existing memory cells, indicates that the majority of T-bet++, CD11c++, CXCR5–, CD21lo cells (all ABC-associated markers) reside within activated IgD+ naïve and IgD/CD27– DN2 cells with a smaller fraction of CD21lo cells with intermediate levels of expression of T-bet and CD11c, identified within the CD27+ memory population and in particular within the CD21lo activated memory subset (Figure 3B) (41, 42).