Phosphatidylinositol 3-kinase regulates thymic exit.

To understand the role of PI3K during T cell development, we generated transgenic mice expressing the N terminus of the PI3K catalytic subunit (p110(ABD); ABD, adaptor binding domain) in thymocytes. Expression of p110(ABD) activates endogenous p110 and results in the accumulation of mature single-positive CD3(high)heat-stable Ag(low) thymocytes. This is mostly due to a defect in emigration of those cells, as shown by the delayed appearance of peripheral T cells in neonatal transgenic mice and by competitive adoptive transfer experiments. Although the mechanisms underlying these effects of PI3K are not yet clear, our results show an important role for PI3K activity in the regulation of mature thymocyte exit to the periphery.