A paragon of self-tolerance: CD25+CD4+ regulatory T cells and the control of immune responses.

The interest in naturally arising regulatory T (TR) cells as a paradigm for maintaining immunological self-tolerance has undergone an explosive re-emergence in recent years. This renaissance was triggered by several key experimental observations and the identification of specific molecular markers that have enabled the isolation and experimental manipulation of these cells. Although their existence was once controversial, a large body of evidence now highlights the critical roles of TR cells in maintaining immunological self-tolerance. Furthermore, abnormality of natural TR cells can be a primary cause of autoimmune and other inflammatory diseases in humans.