Development and function of CD25+CD4+ regulatory T cells

The essential role played by CD25+CD4+ regulatory T cells (TR cells) in the control of physiological as well as pathological immunity is now well established, but many aspects of their biology still remain unclear. One of the unresolved issues regards their development: where does this occur, what signals are required, and how do TR cells fit into the larger taxonomy of the T-cell family? Recent data has begun to shed light on the development and function of these important cells.