Immunopathogenesis of Heymann's nephritis

Renal localization of the C5b-9 membrane attack complex (MAC) in relation to other complement components and immunoglobulins was studied at different stages of Heymann's nephritis and following reimmunization of Lew rats with stage IV disease. Trace amounts of the MAC were found during stages I and IV of disease, whereas during stages II to III, a period of active glomerular and tubular injury, moderate deposits of MAC were observed in glomeruli, periluminal cytoplasm of proximal tubular epithelial cells, and desquamated intraluminal brush border material. Following reimmunization of stage IV animals, a striking increase in the amount of MAC was observed. Moderate to marked deposition of IgG and C3 was also found during stages II and III at sites containing the MAC. Although a slight decrease in detectable IgG was noted during stage IV, a bright, confluent ribbon-like staining pattern was present in reimmunized animals. These data suggest that the MAC is a mediator for acute in situ immune-complex-induced glomerular and tubular cytoplasmic injury, although subsequent proteinuria may persist without continued complement pathway activation and assembly of the MAC.