Expression of a novel activation antigen on intrahepatic CD8+ T lymphocytes in viral chronic active hepatitis.

It has been suggested that CD8+ T lymphocytes play an important role in the pathogenesis of liver cell injury in viral chronic active hepatitis. However, the mere presence of T lymphocytes with cytotoxic/suppressor phenotype in the hepatic inflammatory infiltrate does not necessarily imply that these cells are actively involved in an immune reaction. In the present study, the expression of different activation antigens have been investigated, such as the interleukin-2 and the transferrin receptors and a recently described T-cell activation molecule termed "activation-inducer molecule" on the different lymphocyte subsets of both peripheral blood and liver-infiltrating lymphocytes from patients with virus-induced chronic active hepatitis. Studies of double immunostaining clearly showed that the majority of intrahepatic CD8+ T lymphocytes selectively coexpressed the activation-inducer molecule, whereas no significant expression of this molecule was found on either intrahepatic CD4+ T lymphocytes or peripheral blood lymphocytes of the same patients. Furthermore, lymphocytes from both peripheral blood or liver compartments did not express other activation antigens such as the interleukin-2 and the transferrin-receptor molecules. These results suggest that the CD8+ T-cell subset bearing the activation-inducer molecule may represent the main activated intrahepatic lymphoid cell population in virus-related chronic active hepatitis.