TLR9 and systemic lupus erythematosus: Different roles of TLR7 and TLR9 were indicated by Christensen et al., who reported that TLR9−/− mice showed an exacerbation of lupus activities including the activation of lymphocytes, i.e., plasmatoid dendritic cells (pDCs) with an upregulation of IFN-α activity, in contrast to the pathologic condition observed in TLR7−/− mice [88].