Precursors of T-Cell Mitogen Reactive Cells and their Suppressors in the Mouse Fetal Liver

Abstract

A considerable volume of information has been accumulated on the development of T cell lineages from the embryonic thymus (Ceredig et al., 1982). However, the original source of the stem cells and the developmental processes preceding the earliest phase in which the thymus becomes lymphoid have not yet been clearly delineated. An intriguing possibility is that the stem cells originate from, and/or temporarily reside in, the fetal liver. It should be noted in this respect that although the fetal liver is recognized as an early B cell organ (Owen et al., 1974), it also contains pre-thymic and post-thymic cells that can develop into T cells (Stutman, 1978). Indeed, chimeras obtained by reconstitution of lethally irradiated mice with 14-day fetal liver cells developed a wide spectrum of liver type cells expressing T cell functions (Rabinowich et al., 1983). By the 14th day of gestation, embryonic liver cells could be induced to elicit a graft-versus-host response (Umiel et al., 1968), suggesting that embryonic liver may contain cells which can contribute to the T cell compartment even before the thymus itself is established as a lymphoid or secretory organ. Yet the ability to produce a response required thymic induction. On the other hand, the embryonic liver is a major source of suppressor cells during ontogeny (Globerson et al., 1975).