The liver as an immune organ

Abstract

The liver accommodates a variety of cell populations, some of which are primarily engaged in immune activities. The intrahepatic immunologic processes result from a complex interplay between parenchymal and nonparenchymal cells [18, 19, 22, 26]. The knowledge of the characteristic liver architecture, the distinct hepatic circulation, and the specific cellular composition of the organ form the basis for understanding the immunological role of the liver. Immunologically important molecules, such as complement factors and acute phase proteins are synthesized in the liver. The liver harbors a large fraction of the reticuloendothelial system of the human body, thereby participating in nonspecific immune defense reactions. If antigens expressed on hepatocytes are the targets of an immune reaction, the liver itself becomes the center of the "immunologic battle" (see Chapter 18). On the other hand, primary nonhepatic immunologic disorders, such as the collagen vascular diseases, may secondarily affect the liver. The morphology of the liver and of its cellular elements is discussed extensively in Chapters 2 and 3. The liver is situated strategically between the splanchnic area and the systemic circulation. Its dual blood supply from the portal vein and the hepatic artery leads to a continuous exposure to intestinal, pancreatic, splenic and systemic antigens. Gut microorganisms, after overcoming the intestinal barrier, gain access to the liver via the portal circulation and may elicit intrahepatic immune reactions. This early antigenic contact suggests that the liver must accommodate the components of the innate immune system in order to avert gut derived infectious, toxic and carcinogenic injuries. The composition of immunocompetent cells in the liver corroborates the assumption that innate, nonspecific immune reactions belong to the most important immunologic tasks of the organ. © Springer-Verlag Berlin Heidelberg 2010.