In this study, we report the generation of an anti-BDCA2 mAb, 24F4A, that can potently inhibit TLR7 and TLR9-induced IFN-I in human pDCs from healthy and SLE patients, as has been shown with a previously described anti-BDCA2 mAb (Dzionek et al, 2001; Blomberg et al, 2003; Fanning et al, 2006; Cao et al, 2007; Rock et al, 2007). Here, TLR9 is linked to systemic lupus erythematosus.