Hepatic expression of type A and type B receptors for tumor necrosis factor

We have examined the in-situ distribution of type A and type B receptors for tumor necrosis factor (TNF) in normal and diseased human liver biopsy specimens. In normal liver tissue, no or very small amounts of TNF receptors were found. In acute and chronic inflammatory liver diseases, a strong up-regulation of the expression of both TNF receptors was found on hepatocytes, bile duct epithelium, sinusoidal lining cells and mononuclear inflammatory cells. With immunoelectronmicroscopy, all these cells showed cytoplasmic, in addition to membranous staining, suggesting active synthesis of the receptor or, alternatively, internalization of the receptor and its ligand. This up-regulated expression of both type A and type B receptors for TNF was similar in acute and chronic active hepatitis, and was not related to the etiology of the liver disease, nor restricted to areas of liver inflammation. Our results indicate that hepatocytes, sinusoidal endothelial cells, bile duct epithelial cells and mononuclear inflammatory cells, by displaying receptors for TNFs, represent target cells for both these cytokines. Up-regulated expression of type A and type B receptors for TNFs endows these cells with augmented responsiveness for the pleiomorphic biological activities of these cytokines during liver injury.