Reciprocal T cell responses in the liver and thymus of mice injected with syngeneic tumor cells

We investigated the T cell responses in various tissues, especially in the liver and thymus, of mice injected with syngeneic tumors. This study was undertaken since recent evidence indicated that the liver is one of the important immune organs for T cell proliferation. When C3H/He mice were intraperitoneally injected with mitomycin-treated syngeneic MH134 tumors (1 × 10⁷/mouse), a transient increase of liver mononuclear cells (MNC) was induced, showing a peak at Day 4 after injection. Histological study of such liver showed a sinusoidal dilatation and an accumulation of MNC in the sinusoids. The most predominant MNC induced were double negative (CD4P^-8^-) αβ T cells and γδ T cells. These γδ T cells varied, showing unique time-kinetics. Despite a continuous increase of whole liver MNC and αβ T cells, the proportion of γδ T cells in the liver decreased beginning 4 days after injection. In contrast with the response in the liver, a striking decrease in the cell number of thymocytes was induced after tumor injection, showing a basal level at Day 6. This hypocellularity in the thymus appears to be an inverted response of the lymphocytosis in the liver. At this time, a corresponding decrease in the proportion of double positive (CD4⁺8⁺) T cells was always seen in the thymus. Analysis of cell proliferative response showed that the increase of liver MNC after tumor injection was accompanied by augmented proliferation, whereas the decrease of thymocytes was accompanied by depressed proliferation. The present results indicate that there exists a unique, reciprocal response of T lymphocytes between the liver and thymus, and that the presence of tumor appears to stimulate T cell response in the liver but alternatively inactivates such response in the thymus.