Systemic vasculitis and granulomatous inflammation in Rag2^–/– mice 13 days after receiving 1 × 10⁸ anti-MPO splenocytes. (a) Necrotizing arteritis in lymph node with transmural fibrinoid necrosis (arrow) (H&E stain). (b) Necrotizing arteritis in spleen with transmural fibrinoid necrosis (arrow) (Masson trichrome stain). (c) Intense acute arteritis in lung with transmural and perivascular infiltration of predominantly neutrophils (Masson trichrome stain). (d) Early focal arteritis in lung with neutrophils and mononuclear leukocytes invading the intima (arrow) (Masson trichrome stain). (e) Pulmonary hemorrhagic capillaritis showing numerous neutrophils marginated within alveolar septal capillaries (arrow) and red blood cells in air spaces. (f) Granulomatous inflammation with multinucleated giant cells in a lymph node.