Development of γδ T cells in the adult murine thymus

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Abstract
The development of T cells belonging to the γδ lineage is not well understood. We have analyzed the cells in the adult murine thymus which express the γδ TcR on the surface in order to learn more about this process. Our data demonstrate a number of clear subpopulations of γδ expressing cells in the thymus based on the expression of Thy‐1 and HSA (heat‐stable antigen). Only one of these subpopulations, the one expressing both Thy‐1 and HSA, contains dividing cells or has a significant rate of turnover. Together with the fact that emigrant γδ cells are HSA+Thy‐1+, this suggests that this thymic subpopulation is the sole, or major, source of exported cells. However, the turnover of cells from this population is 5 × 104 ‐ 10 × 104 cells per day, while previous estimates of the rate of export of γδ cells are in the order of 104 cells per day. Furthermore the Vγ profile of recent γδ+ emigrants differs from that of the thymic HSA+Thy‐1+ cells. This raises the possibility that only a selected subpopulation of the thymic γδ+HSA+Thy‐l+ population is exported, and that some γδ cells may die in situ in the thymus. The function of the other γδ thymic subpopulations, which are turning over very slowly or not at all, (i.e. the HAS−Thy‐l− and HAS−Thy‐l+ subpopulations) remains unclear.