As far as infectious diseases are concerned, DN B cells seem to play an inhibitory role in the humoral responses.19,20,35,36 Actually, these cells express a variety of inhibitor receptors, such as FcRL4, and exhibit many features of exhaustion,19,20,35,36 in contrast to DN2 B cells, which are very active in SLE.13,21–23 Moreover, the absence of FcRL4 in SLE DN B cells,13,17 further suggests that DN B cells in infectious diseases differ from DN2 cells. This evidence concerns the gene FCRL4 and systemic lupus erythematosus.