Immune (T cell) response in viral hepatitis

Abstract

The immune system is of central importance in the course of viral diseases and increasing evidence suggests that this is also true for viral hepatitis B and C. On the one hand immune responses to viral antigens are believed to be responsible for viral clearance in acute hepatitis B and C, and on the other hand, if they fail to eliminate or control the virus, they most likely cause chronic inflammatory liver disease. The uncompromised human immune system is equipped with humoral and cellular components, that in most viral infections can eliminate the virus or at least achieve viral control. In the natural course of viral hepatitis, however, persistence of the infecting virus is common and numerous observations suggest that both viral and host factors may contribute to viral persistence. Since HBV and HCV are non-cytopathic viruses, liver tissue damage in chronic hepatitis is the result of a permanent inflammatory process within the liver mediated by effector cells of the immune system which obviously cannot eliminate the virus-infected hepatocytes and therefore cannot terminate infection. The decisive role of the immune system becomes evident in acute hepatitis B and C virus infection when the immune system of the infected host holds the key to decide whether there will be viral clearance or control and self-limited disease or viral persistence and chronic hepatitis. Although acute infection displays similar features in hepatitis B and C there are numerous and not only virologically important differences in the course of both viral infections. In acute hepatitis B infection, at least in healthy adults, only a minority (5-10%) of infected individuals will develop chronic disease. In acute hepatitis C infection the majority will run an asymptomatic course of disease that in about 85% will progress to chronic hepatitis. Only those patients who display symptomatic acute hepatitis C, however, clear the infection in about 50%, suggesting that a vigorous immune response contributes to viral clearance in these patients.