Liver Transplant Immunology 2: Application to Liver Allograft Immunity

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 2: Application to Liver Allograft Immunity, we apply the basic principles of liver immunology and allorecognition to our current management of liver transplant recipients in the context of both immunosuppression and the holy grail of transplantation, operational tolerance. This review contains 4 figures, 3 tables, and 32 references Key Words: adaptive immunity; allograft rejection; allograft tolerance; allorecognition; antigen presenting cells; immunosuppression; innate immunity; liver transplantation; T lymphocytes