Detection of Thy-1, T-200, Lyt-1 and Lyt-2-bearing cells in the developing lymphoid organs of the mouse embryo in vivo and in vitro.

The appearance of cell membrane antigens on lymphoid cells of the embryonic thymus in vivo and in vitro using monoclonal antibodies in immunoperoxidase tests on frozen sections and in two-color immunofluorescence tests on cells suspensions was studied. It was shown that cells are heterogeneous with respect to Lyt antigen expression from the earliest stages of ontogeny. Thus, after 16 days gestation, some cells are Lyt-1+2-, others are Lyt-1-2+ and some are Lyt-1+2+. However, for various reasons which are discussed, we hesitate to suggest that this finding demonstrates independent derivation of the various T cell subsets. In the absence of cell migration, organ cultures of embryonic thymus generate enriched populations of Lyt-1+2- and Lyt-1-2+ cells, i.e. cells with functional "mature" phenotypes. It was not found that cells bearing T cell antigens are generated in organ cultures of fetal liver and spleen. This result argues against the thymus-independent generation of T cells in these organs.