Antigen-specific primary activation of CD8+ T cells within the liver

It is generally accepted that naive T cells recirculate via the blood and lymph, but do not enter nonlymphoid tissues without prior activation and differentiation. In this study, we demonstrate that the liver is an exception to this rule. Naive Des-TCR transgenic CD8(+) T cells specific for H-2K(b) were selectively retained in the liver within a few minutes of adoptive transfer into transgenic Met-Kh mice expressing H-2K(b) in the liver. Activated CD8(+) cells were found in the liver, but not the blood, as soon as 2 h after transfer and underwent cell division and started to recirculate within 24 h of transfer. In contrast, CD8(+) cells activated in the lymph nodes remained sequestered at that site for 2 days before entering the blood. Our results therefore suggest that, in addition to its previously described role as a non Ag-specific activated T cell graveyard, the liver is involved in Ag-specific activation of naive recirculating CD8(+) T cells. This particular property of the liver, combined with the previously demonstrated ability of hepatocytes to induce tolerance by means of premature CD8(+) T cell death, may be a major mechanism contributing to the acceptance of liver allografts and the chronicity of viral hepatitis.