Immune CD8+ T lymphocytes lyse Listeria monocytogenes-infected hepatocytes by a classical MHC class I-restricted mechanism

Hepatocytes constitute the principal site of listerial replication in the livers of mice infected i.v. CD8+ T lymphocytes play a predominant role in the host defenses to Listeria monocytogenes. In vitro experiments by others undertaken to delineate the functions of CD8+ T lymphocytes have focused primarily on their interaction with Listeria-infected macrophages. Such experiments do not address directly the role of CD8+ T lymphocytes in eliminating the bulk of Listeria replicating within the liver. Here, we report that immune CD8+ T cells at an E:T cell ratio > or = 10:1 lysed Listeria-infected hepatocytes as judged by the following two criteria. Aspartate aminotransferase activity in the culture supernatants, indicative of hepatocyte damage, increased significantly. Conversely, infected hepatocytes cocultured with immune CD8+ T cells exhibited a marked reduction in viable intracellular Listeria assessed by CFUs. Neither immune CD4+ T cells nor nonimmune CD8+ T cells caused a similar increase in aspartate aminotransferase activity released or a decrease in intracellular bacteria. Immune CD8+ T cell-mediated lysis of infected hepatocytes was restricted by classical MHC class I (H-2Kb) molecules and was inhibited by the presence of either brefeldin A or mAb specific for CD8. These results suggest that the predominant role of CD8+ T lymphocytes in host resistance to listerial infections of the liver may be due to their capacity to lyse infected hepatocytes.