Thymic education--T cells do it for themselves.

The phenomenon of positive selection of developing T cells is well established. However, the cellular interactions that are responsible for selecting the restriction element are still ill defined. Here, Tomasz Pawlowski and Uwe Staerz discuss the latest developments in the field, as well as some new evidence suggesting that cells of epithelial or hematopoietic origin are not the only ones capable of selecting the restriction element for T cells expressing the alpha beta T-cell receptor.