Absence of lymphoproliferation and regression of skin lesions in As₂O₃-treated MRL/lpr mice. Two-month-old mice had been treated daily for 2 months with PBS or As₂O₃ (5 μg/g). (A) Spleens and mesenteric LNs from 4-month-old MRL/lpr and MRL⁺/+ mice. (B) Skin lesions on the back and ears from 4-month-old MRL/lpr mice. Light microscopy histology of these skin lesions (bottom panels, original magnification ×50, with 5×/0.15 NA objective).