The liver as an immune-privileged site

The liver is well known as an organ with important functions in the metabolism of lipids, proteins, and carbohydrates. Besides these functions, it is getting increasingly clear that the liver has also a central role in initiating and modulating immune responses. Special attention is linked to the fact that 75% of the liver's blood supply comes as venous blood from the gut, not only rich in nutrients but also rich in microbial degradation products. To protect the organ and the body from these immunostimulatory microbial products, the liver has an extraordinary scavenger function clearing all these molecules. At the same time, the liver itself is protected by establishing a tolerogenic state by modulating immune responses. Adaptive and innate immune reactions are suppressed to avoid unnecessary immune activation. Here we describe the parenchymal and non-parenchymal cell populations contributing to the tolerogenic status. An organ that represses immune reactions is a well-suited target for pathogens. Here we describe the viral pathogens targeting the liver, their infection behavior, and potential therapeutic options.