Renal histopathology in an animal in Group 3 (sublethal E coli plus C4bBP) versus an animal in Group 4 (7E3 F[ab′]₂ plus sublethal E coli plus C4bBP): (A) The renal histopathology of the untreated animal in Group 3 was characterized by numerous capillary and arteriolar thrombi, which stained positive for fibrin with the PTAH stain (see arrows). In some cases, the capillary walls were thickened with eosinophilic hyaline or granular material between the basement membrane and endothelium. Kidneys from untreated animals also showed focal areas of hemorrhage, tubular changes, and mononuclear leukocyte infiltration. (B) The renal histopathology of a treated animal in Group 4, which was characterized by mild congestion with no thrombin, hemorrhage, or leukocyte infiltration.