Bystander Activation by Cytokines of Intrahepatic T Cells in Chronic Viral Hepatitis

: Although immune responses to hepatitis viruses are initiated by virus-specific T cells, there is evidence that many more intrahepatic T cells are activated than those specific for the pathogen. Recent evidence suggests that cytokine combinations, such as IL-2, IL-6, and TNF alpha, can activate both naive and memory T cells in vitro. The inflammatory cytokine milieu in the liver of patients with chronic viral hepatitis may therefore favor bystander activation of T cells. This may play an important role in enhancing effector T-cell function in the liver, and in maintaining peripheral memory T cells in the absence of antigenic stimulation, such as after virus clearance.