Macroscopic appearance of skin vasculitis. (A) 6-19–treated FcRγ+/− mice developed purpura in the ear, tail, and footpads (upper mouse), whereas 6-19–treated FcRγ−/− mice failed to develop vascular purpura (lower mouse). (B) 6-19–treated FcRγ−/− mice were SC inoculated with 1 × 10⁶ BMMC in the left ear and with PBS in the right ear as a control. After 1 to 2 days, vascular purpura appeared in the restricted site of the BMMC injection (arrow).