While exogenous DNA is cleared by DNase I (Napirei et al, 2000), human serum lacks nuclease activity against RNA:DNA hybrids (R.E.R., unpublished data), so hybrids could persist extracellularly, thereby contributing to the activation of IFN-producing pDCs in lupus (Ronnblom et al, 2003). Here, IFNA1 is linked to systemic lupus erythematosus.