Dendritic Cells in Hepatitis and Liver Transplantation

Dendritic cells (DCs) play a key role in innate immune responses and are also the most effective cells for the activation of T cell immunity. They acquire antigen and process it; then they display it on the cell surface bound in a noncovalent complex with human leukocyte antigen molecules of class I (human leukocyte antigens A, B, and C) and class II (human leukocyte antigen DR). These cells are subdivided into 3 main subsets: 2 called myeloid dendritic cells (mDC) or classical DCs of types 1 and 2, and 1 called plasmacytoid dendritic cells (pDCs). The mDCs process and present antigen while the pDCs also strongly respond to viral signals by secreting type 1 interferon. In the liver, all of these subsets are present. However, their relative abundance is different from the peripheral blood, and it is further modified by liver disease. It appears that in relation to T cell tolerance, both mDCs and pDCs are influenced by the liver milieu and promote T cell inactivation. However, in antiviral responses and in ischemia/reperfusion injury, where innate immune functions are more important, mDCs and pDCs have distinct roles.