T Regulatory Cells
T regulatory (Treg) cells are CD4+ T helper cells that are critical to the maintenance of immune cell homeostasis as evidenced by the catastrophic consequences of genetic or physical ablation of the Treg population. Specifically, Treg cells maintain order in the immune system by enforcing a dominant negative regulation on other immune cells. Treg cells manifest their function through a myriad of mechanisms that include the secretion of soluble factors, cell contact mediated regulation, and cytolytic activity. Treg cells are characterized by their expression of the Foxp3 transcription factor that specifies differentiation of the lineage.