The liver promotes antigen-specific clearance of naïve CD8+ T cells activated in situ

Abstract

The liver has unique immunological properties as transplants are accepted in many animal models and infections of the liver (e.g. Hepatitis C virus) often become chronic. Although several hypothesis have been proposed, the mechanisms for the liver tolerance effect still remain unknown. Methods: Naive CD8+ Des-TCR transgenic T cells (H-2k) specific for the MHC class I H-2Kb were adoptively transferred into B6 (H-2b), which express the antigen ubiquitously, or B10.BR (H-2k) mice as negative controls. The cells were tracked using gamma counting, flow cytometry, confocal and electron microscopy. Results: Most radioactive labeled Des cells were retained in the liver of B6 mice with little change between 1 and 22h after transfer while they preferentially homed to lymphoid tissues of B10.BR mice. Single cell suspensions revealed that the liver retention in B6 was accompanied by a drop of cell numbers by 80–90% of Des cells after 22h with almost no change in B10.BR mice. This decrease was independent of the cell numbers transferred and not due to rejection by host NK cells as it also occurred in F1 mice. TUNEL staining suggested a non-apoptotic cell death and neither the blockage of phosphatidylserine receptors nor the depletion of macrophages could prevent the deletion of Des cells. Instead, Des cell remnants were present in lysosomes inside hepatocytes. In vitro studies confirmed that Des-TCR T cells actively invaded antigen-bearing hepatocytes, a process termed emperipolesis, and we could identify an inhibitor of this process which was able to break tolerance in vivo. Conclusion: We identify a new mechanism by which the liver eliminates T cells in an antigen-specific way. As 80–90% of the naive T cells that are initially retained in the liver are destroyed within 22h, we propose that this suicidal emperipolesis is a highly efficient and fast process for the deletion of antigen-specific T cells that contributes to the tolerogenic properties of the liver.