CD27 and rheumatoid arthritis: Interestingly, a significant reduction in naive (IgD+CD27–) B cells and a dramatic increase in the frequency of switched memory and double-negative memory B cells in RA SF (P < 0.0001 for all) and synovial tissue (P < 0.0001, P = 0.01, P = 0.0002, respectively) compared with peripheral blood was observed (Figure 2, A–C).