Large number of T cells traffic through the liver. In order to examine the effects of such traffic on the phenotype of hepatocytes, we vaccinated mice using DNA vaccines encoding antigens with MHC class I-binding epitopes. Small numbers of activated CD8(+) T blasts (10(5)-10(6)/liver) changed the surface phenotype and cytokine expression profile of hepatocytes (HCs). HCs upregulate surface expression of major histocompatibility complex (MHC) class I molecules and CD1d but not MHC class II molecules Qa-1, CD80, CD86, CD54, or CD95; in addition, they expressed/secreted interleukin (IL)-10 and IL-4 but not IL-1, IL-6, IL-13, interferon (IFN)-gamma, tumor necrosis factor (TNF), IL-4, or IL-27 (i.e., they acquire the HC* phenotype). HCs* (but not HCs) induced specific activation, proliferation, and IFN-gamma, TNF, and IL-13 release of cocultured naïve CD8(+) T cells. In contrast to the specific activation of naïve CD8(+) T cells by dendritic cells (DCs), specific CD8(+) T cell activation by HC* was not down-modulated by IFN-alphabeta. Only recently activated CD8(+) T blasts (but not recently activated CD4(+) T blasts or activated cells of the innate immune system, including natural killer T [NKT] cells) induced the HC* phenotype that is prominent from day 10 to day 20 postvaccination (i.e., time points at which peak numbers of recently primed CD8(+) T blasts are found in the liver). In conclusion, recently activated CD8(+) T blasts that enter the liver postimmunization in small numbers can transiently modulate the phenotype of HC, allowing them to activate naïve CD8(+) T cells with unrelated specificities.