Dendritic cell dynamics in the liver and hepatic lymph.

Dendritic cells (DC) are bone-marrow-derived cells that function as professional antigen-presenting cells (APC). Liver is an essential organ for a host defense. It not only is armed with a powerful macrophage system but also is constantly surveyed by a heavy traffic of DC and lymphocytes. In case of emergency, such as infection and inflammation, DC traffic in the liver is accelerated. DC in the liver (interstitial DC) capture and process antigens, enter the draining lymph (DC in hepatic lymph) and accumulate in the T-cell area of hepatic lymph nodes (LN). DC in the LN present antigens to T and B cells to initiate immune responses. In accelerated states, DC precursors are recruited to the liver and soon translocate to hepatic lymph. Even mature lymph DC can undergo a blood-lymph translocation from the liver to hepatic LN after i.v. injection into normal rats. Rat Kupffer cells in the hepatic sinusoids are capable of selectively trapping DC from the blood in vivo and in vitro, suggesting involvement of certain adhesion molecules. Kupffer cells presumably elaborate chemokines to attract and trap the recruited DC via selective adhesion, leading to DC extravasation. The accelerated traffic and the presence of blood-lymph translocation would induce rapid and efficient immune responses and thus contribute to the local defense to antigens within liver tissues as well as systemic defense to blood-borne antigens. DC progenitors are also present in the liver, and these may play an important role in tolerance induction in liver transplantation.