TLR9 and systemic lupus erythematosus: Data from Kwok et al. [90] seemed to indicate that type I IFN production by pDC upon TLR9 engagement was diminished in SLE patients, leading them to hypothesize that the persistent presence of endogenous IFNα-inducing factors induces TLR tolerance in pDCs of SLE patients, resulting in impaired production of IFNα.