The Eδ enhancer controls the generation of CD4-CD8- αβTCR-expressing T cells that can give rise to different lineages of αβ T cells

It is well established that the pre-T cell receptor for antigen ( TCR) is responsible for efficient expansion and differentiation of thymocytes with productive TCR beta rearrangements. However, Ptcra- as well as Tcra-targeting experiments have suggested that the early expression of Tcra in CD4(-)CD8(-) cells can partially rescue the development of alpha beta CD4(+)CD8(+) cells in Ptcra-deficient mice. In this study, we show that the TCR E delta but not E.. enhancer function is required for the cell surface expression of alpha beta TCR on immature CD4(-)CD8(-) T cell precursors, which play a crucial role in promoting alpha beta T cell development in the absence of pre-TCR. Thus, alpha beta TCR expression by CD4(-)CD8(-) thymocytes not only represents a transgenic artifact but occurs under physiological conditions.