Adult Human Liver Contains CD8pos T Cells with Naive Phenotype, but Is Not a Site for Conventional αβ T Cell Development

Abstract

Normal adult human liver (AHL) contains populations of unconventional lymphocytes that have been shown in the mouse to mature locally. The presence of lymphoid progenitors together with IL-7, recombinase-activating gene, and pre-TCR-α expression in AHL suggests similar local T cell development activity in humans. Flow cytometry was used to characterize potentially naive hepatic αβ-T cells. We looked for evidence of TCR-αβ cell development in AHL by quantifying δ deletion TCR excision circles (TRECs) in CD3pos populations isolated from the liver and matched blood of eight individuals. Phenotypic analysis of hepatic T cells suggests the presence of Ag-inexperienced populations. TRECs were detected in all blood samples (mean, 164.10 TRECs/μg DNA), whereas only two hepatic samples were positive at low levels (59.40 and 1.92). The relatively high level of CD8pos T cells in these livers with a naive phenotype suggests that in addition to its role as a graveyard for Ag-specific activated CD8pos T cells, naive CD8pos T cells may enter the liver without prior activation. The almost complete absence of TRECs suggests that normal AHL is not a site for the development of conventional αβ T cells.