DEVELOPMENT OF GAMMA-DELTA T-CELLS IN THE ADULT MURINE THYMUS

The development of T cells belonging to the gammadelta lineage is not well understood.We have analyzed the cells in the adult murine thymus which express the gammadelta TcR on the surface in order to learn more about this process. Our data demonstrate a number of clear subpopulat ions of gammadelta expressing cells in the thymus based on the express ion of Thy-1 and HSA (heat-stable antigen). Only one of these subpopul ations, the one expressing both Thy-1 and HSA, contains dividing cells or has a significant rate of turnover. Together with the fact that em igrant gammadelta cells are HSA+Thy-1+, this suggests that this thymic subpopulation is the sole, or major, source of exported cells. Howeve r, the turnover of cells from this population is 5 x 10(4) - 10 x 10(4 ) cells per day, while previous estimates of the rate of export of gam madelta cells are in the order of 10(4) cells per day. Furthermore the Vgamma profile of recent gammadelta+ emigrants differs from that of t he thymic HSA+Thy-1+ cells. This raises the possibility that only a se lected subpopulation of the thymic gammadelta+HSA+Thy-1+ population is exported, and that some gammadelta cells may die in situ in the thymu s. The function of the other gammadelta thymic subpopulations, which a re turning over very slowly or not at all, (i.e. the HSA-Thy-1- and HS A-Thy-1+ subpopulations) remains unclear.