An electron microscopic study of the endothelial changes and the nature of “fibrinoid” produced in the generalized Shwartzman reaction

Abstract

An electron microscopic study of the intravascular material formed and the changes occurring in vascular endothelium in the generalized Shwartzman reaction was performed in rabbits in which this reaction was produced by two intravenous injections of a lipopolysaccharide of E. coli. The intravascular material, often referred to as “fibrinoid”, was found to be identical with fibrin. Intracellular vesicles and extracellular projections were a feature of normal endothelium, particularly that of the renal glomerular capillaries. These structures were increased in number in the generalized Shwartzman reaction, and many of the endothelial cells were swollen. Phagocytosis of fibrin was observed in cells lining the liver sinusoids, raising the possibility that phagocytosis of this material by endothelial cells in certain sites may be a mechanism whereby the intravascular deposition of fibrin is inhibited.