γδ T-cell precursor-derived CD4- CD8- αβ T cells retain γδ cell function

We have previously shown that some of the DN alpha beta(+) T cells arising in TcR alpha-chain transgenic mice are of gamma delta T cell origin, based on phenotypic data and on their status of TcR gene rearrangements. In the present report we investigated the impact of alpha beta TcR expression on the functional programme of the mature gamma delta precursor-derived DN alpha beta(+) T cells. Our results demonstrate that both their proliferative capacity and their cytokine production profile are similar to that of gamma delta T cells. Furthermore, both transgenic DN alpha beta(+) T cells and DN gamma delta(+) T cells up-regulate CD8 alpha expression after activation, but, in contrast to CD4(+) alpha beta T cells, are unable to induce proliferation of naive B cells. Thus, our results suggest that the effector functions of mature T cells are determined independently of the TcR isotype, probably at an early stage of differentiation, and thereby have important implications for current models of T-cell lineage commitment.