Dendritic cells and chronic hepatitis virus carriers.

Many individuals infected with hepatitis B virus (HBV) and hepatitis C virus (HCV) are unable to clear these viruses following an acute infection and become chronically infected. There are more than 400 million HBV and HCV carriers in the world and a considerable number of these patients would eventually develop more severe complications like liver cirrhosis and hepatocellular carcinoma. It is not clearly known how an individual develops a chronic hepatitis virus carrier state; however, a defective immune response of the host is thought to play a critical role in the underlying pathogenetic mechanism. On the other hand, dendritic cells (DCs), the most potent antigen-presenting cells, are widely distributed in both lymphoid and nonlymphoid tissues. Recognition of the microbes or microbial antigens by DCs is one of critical events for the initiation of an immune response. DCs also play a cardinal role during the progression and termination of an immune response. The aim of this overview is to provide information regarding the role of DCs in the pathogenesis of chronic hepatitis due to HBV and HCV in humans and in animal models of HBV and HCV carrier states. First, we summarize our current understanding of the pathogenesis of hepatitis virus carrier states and also of general properties of DCs. Next, we discuss the data on the phenotypes and functions of DCs in both human and murine HBV and HCV carriers. We also discuss vaccine therapy in murine HBV carriers because activation of DCs due to vaccination-initiated HBsAg-specific immune responses in HBV transgenic mice (HBV-Tg), which in turn resulted in complete clearance of hepatitis B surface antigen and hepatitis B e antigen and decreased levels of HBV DNA in some HBV-Tg. Finally, we discuss the extracted questions and future research directions.