Since the CD27−IgD− cell subset, which appears to be enhanced in the peripheral blood of patients with SLE [36], [37] might include B cells which may have undergone class switching simply by exposure to TLR-ligands or cytokines such as IL-10 or IL-21 or BAFF [38], [39], [40], [41], this subset was considered to be heterogeneous. Here, TNFSF13B is linked to systemic lupus erythematosus.