WKY rats immunized with hMPO develop focal necrotizing crescentic glomerulonephritis and pulmonary hemorrhage. (A) No histologic abnormalities in a rat immunized with HSA (Periodic acid Schiff; UplanApo 40×/0.85 NA); (B) severe crescentic glomerulonephritis (arrows) in a rat immunized with hMPO (Periodic acid Schiff; UplanApo 10×/0.40 NA); (C) tubulo-interstitial nephritis with red cell cast (arrow) in a rat immunized with hMPO (hematoxylin and eosin [H&E]; UplanApo 10×/0.40 NA); (D) focal glomerular necrosis, with an adjacent glomerulus showing normal architecture in a rat immunized with hMPO (H&E; UplanApo 20×/0.70 NA); (E) focal necrotizing lesion with early crescent formation (arrow) in a rat immunized with hMPO (H&E; UplanApo 40×/0.85 NA); (F) circumferential glomerular crescent (arrow) in a rat immunized with hMPO (H&E; UplanApo 10×/0.40 NA); (G) normal lung architecture in a rat immunized with HSA (H&E; UplanApo 10×/0.40 NA). (H) Pulmonary vasculitis (arrow) in a rat immunized with hMPO (H&E; UplanApo 20×/0.70 NA); (I) pulmonary hemorrhage in a rat immunized with hMPO, with extensive blood in the alveolar spaces (H&E; UplanApo 10×/0.40 NA).