Signals involved in gamma/delta T cell versus alpha/beta T cell lineage commitment.

In seeking an explanation for the complexity of tissue development, biologists are obliged to explain lineage commitment, the events that dictate whether or not a progenitor cell will differentiate into one cell type or another. Such explanations have been sought across a broad spectrum of biological systems, although in no case has a full under- standing been developed. For immunologists, attention has been focused on the lineage commitment of a T cell progenitor to becoming either a gammadelta T cell or an alphabeta T cell. In this review, we compare the signals that thymocytes may receive from the pre T cell receptor (preTCR) with signalling from TCRgammadelta. These signals may determine, co-determine, facilitate, or cement the alphabeta/gammadelta lineage decision, in concert with signals from additional molecules, such as Notch and cytokine receptors. Elucidating the pleiotropic signalling events, particularly those elicited by the preTCR, may in the near future contribute to a molecular definition of lineage commitment.