In 2003, Tim Behrens' group (13), the team of Virginia Pascual and Jacques Banchereau (14), and Mary Crow (15) published their discovery that SLE patient blood contain active type I interferon (IFN) and a high expression level of IFN-stimulated genes (ISGs), now referred to as the “IFN signature.” Although indications that IFNα may be important in the lupus pathogenesis had been published earlier (16–18), this still was a surprising finding because the principal function of type I IFN is in host defense against viral infection, while SLE is not an infectious disease. The gene discussed is IFNA1; the disease is systemic lupus erythematosus.