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.