Lymphocyte Emigration from the Ovine Thymus: Characterization of Lymphatic Emigrants and Venous Emigrants

Although it has been generally agreed that mammalian thymus produces lymphocytes of the T lineage and releases them as T cells into the general circulation, there have been differences in opinion expressed concerning the rate of thymocyte emigration compared to that of production and also concerning the maturity of emigrant cells. Cell traffic studies by the use of an intrathymic injection technique by Scollay and his associates indicated that, in the mouse thymus, only a small fraction of the cells produced in the thymus emigrate and that those emigrant cells are functionally mature (Scollay, Chen and Shortman, 1984). In contrast, experiments in other animal species often yielded results which indicated a high rate of thymocyte emigration with the emigrants being at least phenotypi-cally immature (Williams et al., 1971).