[The molecular mechanisms governing T cell development in the thymus].

Intracellular signaling events required for T cell development in the thymus have been investigated using various gene deficient and transgenic mice. Here, we summarize and discuss the recent results. Immature thymocytes immigrated from bone marrow are found to be committed to lymphoid lineage. First, the lymphoid progenitor proliferates in IL-7-dependent manner, and differentiates into the cells expressing preTCR complex. The expression of preTCR is required for differentiation to CD4+ CD8+ cells. Then, CD4+ CD8+ cells express TCR alpha beta and are subjected to positive and negative selection. Essential molecules for these selection events and gene activation required for lineage commitment to CD4 or CD8 T cells are getting clear. In the near future, molecular mechanisms governing each developmental step of T cells will be clarified.