Innate Immune Mechanisms in the Liver

Having been ignored by immunologists for years, the liver is now known to be a site of complex immune activity and to play a key role in some of the most important pathologies, including septicemia, metastases, and hepatotropic infections. Even in its healthy state, the liver is presented with an intricate combination of immunological challenges for which it is surprisingly well equipped. These challenges include massive antigenic loads of harmless dietary and commensal products borne by the portal tract, which must be immunologically tolerated, but which may be laced with pathogens or toxins, requiring a swift response. Its blood supply of approx 1.5 L per minute ensures that the liver is the organ most frequently exposed to blood-borne metastatic stimuli, while products of hepatic metabolism may be carcinogenic. The liver immune system must therefore provide protection against pathogens, transformed liver cells, and metastasic cells while at the same time tolerating harmless self and foreign antigens.