T cell maturation: thymocyte and thymus migrant subpopulations defined with monoclonal antibodies to the antigens Lyt-1, Lyt-2, and ThB1.

The phenotypes of thymus cells for the antigens Lyt-1, Lyt-2 and ThB have been analyzed by using immunofluorescence techniques. Cells throughout the intrathymic maturation sequence have been tested, including the primitive subcapsular lymphoblasts, all size classes of cortical and medullary thymocytes, and thymus cell emigrants. ThB antigen is not detectable on migrant cells, but all subpopulations in the thymus are subdivided into two categories, bright and dull. Thus, it is possible that the bright and dull phenotypes represent a lineage specific rather than a stage-specific marker, at least inside the thymus. The Lyt-defined thymocyte subclasses Lyt1+2+-(Lyt-1) and Lyt 1+2+ (lyt-1,2) are also both represented in all subpopulations, including subcapsular lymphoblasts. This suggests that they may represent two separate lineages, and that the Lyt-12(3) class is not a precursor of the Lyt-1 class, although the possibility of a very early Lyt-(12(3) cell precursor common to both lines cannot be ruled out.