Induction of TCR-gamma delta+ cells from thymocytes stimulated by a fetal liver-derived hepatocyte clone

We have previously reported that a fetal liver-derived hepatocyte clone, FHC-4D2, can support hematopoiesis in vitro. Here, we show that fetal thymocytes (FT) or adult thymocytes (AT) proliferate on the monolayer of FHC-4D2 cells in the presence of rIL-2. Fresh thymocytes contained few TCR-gamma delta+ cells (< 4% for FT and < 1% for AT); significant numbers of TCR-gamma delta+ cells were detected (2-11% for FT and 15-33% for AT) after the coculture with FHC-4D2 and rIL-2. Although FT-derived TCR-gamma delta+ cells predominantly used the V gamma 5 chain, the major population in AT-derived TCR-gamma delta+ cells used V gamma 1, V gamma 4, or V gamma 7 chains. Both FT- and AT-derived TCR-gamma delta+ cells killed FcR-bearing target cells when incubated with anti-TCR-gamma delta Ab. Half of FT-derived TCR-gamma delta+ cells were CD4-CD8 alpha+8 beta-; the rest were CD4-CD8 alpha-8 beta-. AT-derived TCR-gamma delta+ cells expressed neither CD4 nor CD8 molecules. Separation of thymocytes from FHC-4D2 cells with a membrane filter reduced the proliferative response by two- to threefold. Taken together, these results demonstrate that a fetal hepatocyte clone supports thymocytes to develop preferentially into TCR-gamma delta+ cells in cooperation with rIL-2 through cell-cell contact, that the repertoire and the phenotype of induced TCR-gamma delta+ cells are determined by the age of the mice, and that hepatocytes might thus play an active role in T lymphopoiesis in the fetal liver.