As₂O₃-induces regression of pulmonary and renal inflammatory infiltrates and inhibits immune-complex deposition in kidneys of MRL/lpr mice. Histologic examination of mononuclear-cell infiltrates (arrows) in (A) lung (original magnification ×50, with 5×/0.15 NA objective) and (B) kidney (original magnification ×200, with 20×/0.50 NA objective) sections from a 4-month-old MRL/lpr mouse that had been treated daily for 2 months with As₂O₃ (5 μg/g) or PBS. (C) Glomerular IgG deposits in frozen kidney sections labeled with HRP-conjugated goat anti–mouse IgG (original magnification ×200, with 20×/0.50 NA objective).