Immunosuppression by fetal liver as a model for tolerance to self.

The embryonic liver chimera system was used as a model to study the development of tolerance to self antigens. It was found that the permanent tolerant state which was induced in (C3H/eb x C57BL/6)F1 irradiated hosts following reconstitution with parental C57BL liver cells could be due to the development of suppressor cells within the liver cell inoculum, which specifically prevent reactivity of immunocompetent cells. General suppressor activity could be found in embryonic liver cells at early stages of gestation. However, the differentiation of such cells into specific suppressor of "self" antigens is dependent on the presence of the thymus.