This effect was even more pronounced in cells additionally exposed to environmental genotoxic stress in the form of ultraviolet light, a well-known trigger of SLE flares, suggesting that ultraviolet light could promote type I IFN activation in TREX1-deficient cells by enhancing formation of ssDNA byproducts resulting from repair of DNA photodamage. Here, TREX1 is linked to systemic lupus erythematosus.