Liver Transplant Immunology 1: Fundamentals of Liver Immunology and Allorecognition

The liver is a multifunctional organ responsible for complex metabolic and immune functions. Although not a classic lymphoid organ, the liver is enriched with traditional immune cells as well as parenchymal and nonparenchymal cells that play a key role in immune homeostasis. Due to its location and unique anatomic structure, the liver must finely balance immunity and tolerance to avoid undue inflammation in the setting of constant antigenic exposure from portal blood flow while maintaining appropriate immunity against pathogens. Since the first successful liver transplantation in humans in 1967 at the University of Colorado, our knowledge of hepatic immunity and tolerance, in the context of both liver disease and liver transplantation, has evolved dramatically. With these advancements, therapeutic modalities have been developed that have revolutionized the care of liver transplant recipients. In Part 1: Fundamentals of Liver Immunology and Allorecognition, we review current knowledge of hepatic immunity, including anatomic features and cellular components that give the liver its unique properties. In addition, we describe critical concepts of innate and adaptive immune function to provide a context for understanding allograft injury and rejection. This review contains 4 figures, 4 tables and 26 references. Key Words: adaptive immunity; allorecognition; antigen presenting cells; innate immunity; liver transplantation; T lymphocytes