Plasmacytoid dendritic cells (pDCs) and neutrophils are detected in psoriatic skin lesions and implicated in the pathogenesis of psoriasis. pDCs specialize in the production of type I interferon (IFNI), a cytokine that plays an important role in chronic autoimmune-like inflammation, including psoriasis. Here, we demonstrate that IFNI production in pDCs is stimulated by DNA structures containing the neutrophil serine protease cathepsin G (CatG) and the secretory leukocyte protease inhibitor (SLPI), which is a controlling inhibitor of serine proteases. We also demonstrate the presence of neutrophil-derived DNA structures containing CatG and SLPI in lesional skin samples from psoriasis patients. These findings suggest a previously unappreciated role for CatG in psoriasis by linking CatG and its inhibitor SLPI to the IFNI-dependent regulation of immune responses by pDCs in psoriatic skin
