Vδ1T lymphocytes expressing a Th1 phenotype are the major γδ T cell subset infiltrating the liver of HCV-infected persons

Background: Hepatitis C infection induces an acute and chronic liver inflammation that may lead to cirrhosis, liver failure, or hepatocarcinoma. Since the role of alpha beta T lymphocytes in hepatitis C virus (HCV) immunopathology has been analyzed extensively, we investigated the distribution and functional activation of gamma delta T cell subsets in chronically HCV-infected patients. Materials and Methods: Blood samples and liver biopsies from 35 patients with compensated chronic HCV infection were compared in terms of T cell subset distribution, expression of activation markers, gamma delta T cell receptor (TCR) repertoire, and pattern of cytokine production. Moreover, we analyzed whether these immunological parameters were associated with other clinical observations (plasma viremia, ALT levels, Ishak index). Results: Differing from peripheral blood distribution, a specific compartmentalization of V delta1 T cells (p < 0.001) was observed in the liver of HCV patients. These cells represented a relevant fraction of intrahepatic T lymphocytes (1.8-8.7%) and expressed the memory/effector phenotype (CD62-L(-)CD45-RO(+)CD95(+)). This phenotype was consistent with selective homing upon antigen recognition. Mitogenic stimulation of V<delta>1(+) T lymphocytes recruited in the liver revealed the T helper cell type 1 (Th1) pattern of cytokine secretion. Interestingly, the frequency of interferon-gamma (IFN-gamma)-producing V delta1 T cells was associated with an higher degree of liver necroinflammation. measured by the Ishak index. Finally, the T-cell repertoire analysis revealed the absence of V gamma selection in the TCR repertoire of intrahepatic V delta1 T cells. Conclusions: gamma delta T cell distribution in the peripheral blood differs from the V delta1 T cell subset because it is policlonally activated and recruited in the liver of chronic HCV-infected patients. During HCV-infection, this T cell subset may release Th1 cytokines and contribute to the necroinflammatory liver disease.