Lyt markers on thymus cell migrants

Abstract

THE lymphocyte antigens Lyt-1 and Lyt-2 have been clearly shown to be differentially expressed on distinct, functionally defined subsets of precursor and effector T cells. The cell population expressing only Lyt-1 includes ‘helper cells’ and cells which react in mixed lymphocyte cultures. The population expressing only Lyt-2 includes ‘suppressor’ and cytotoxic cells, whereas cells bearing both antigens (Lyt-1,2) seem to function as precursors of cytotoxic and suppressor cells and in some systems, as amplifiers (reviewed in ref. 1). Peripheral T cells consist of about 50% Lyt-1,2 cells, 30–40% Lyt-1 cells and 10% Lyt-2 cells², although the proportions vary somewhat from organ to organ (R.S. and I.W., unpublished data). More than 90% of all thymic lymphocytes are immuno-incompetent and Lyt-1,2, but the relatively infrequent (less than 10% of all thymocytes) cortisone-resistant cells have properties of immuno-competence and Lyt phenotype distribution more like those of peripheral T cells (∼45% Lyt-1,2, 50% Lyt-1 and <5% Lyt-2 (ref. 2, and R.S. and I.W., unpublished data)). Speculation concerning the phenotype of thymic emigrants has centred on the hypothesis that the thymus migrants are Lyt-1,2 precursor cells which differentiate peripherally, but no experiments directly testing this hypothesis have been published. Here we report experiments which demonstrate that cells leaving the thymus are already divided into subpopulations defined by the Lyt antigens.