Development and function of CD25+CD4+ regulatory T cells

The essential role played by CD25(+)CD4(+) regulatory T cells (T-R 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 T-R 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.