Role of primary intrahepatic T-cell activation in the 'liver tolerance effect'

There is accumulating evidence suggesting that hepatic permeability to both naive and activated T lymphocytes may be unique among the solid organs. The possibility that the liver may act as a site of primary activation for CD8+ T lymphocytes is supported by experimental data and may contribute to some of the unique immunological properties of this organ, particularly its ability to induce antigen-specific tolerance. This review discusses the nature of the liver APC inducing primary T-cell activation within the liver: Kupffer cells, liver dendritic cells, liver sinusoidal endothelial cells and hepatocytes are favourably located to allow physical contact with circulating T lymphocytes. Here, we examine the capability of each cell type to act as APC for naive CD4+ or CD8+ T cells and to induce tolerance.