Representative histological appearance of 6-19–induced skin lesions. The sections of the ear from untreated normal mice (A) and 6-19–treated FcRγ+/− (B), FcRγ−/− (C), and TNFβ−/− (D) mice were prepared 12 days after IP injection of 6-19 hybridoma cells. Tissues sections were stained with HE (original magnification × 100). FcRγ+/− mice developed leukocytoclastic vasculitis characterized by the infiltration of PMNs and the extravasation of erythrocytes (B). FcRγ−/− and TNF−/− mice did not develop leukocytoclastic vascular lesions (C and D). Note that in (D), darkly stained cells were melanocytes due to 129 background and that small numbers of PMNs had infiltrated the skin of TNF−/− mice.