T Regulatory Cells
Tregs are a well characterized T cell subset that mediates antigen-specific immune suppression—a critical component in the maintenance of self-tolerance, as well as tempering of normal immune responses and immune homeostasis. Both CD8+ and CD4+ Tregs exist, with CD4+ CD25+ cells being responsible for maintaining self-tolerance. Expression of the transcription factor Foxp3 stabilizes and drives Treg function and also blocks expression of the Th17 cytokine, IL-17. Several Treg types exist and may be identified using flow cytometry with specific phenotypic markers. Natural Tregs and Induced Tregs (Tr1 and Th3) are distinguished based on their expression of CD4, CD25, CD127, CTLA4, GITR, CD45RB, and Foxp3. Activated functional Tregs may also upregulate LAP (TGF-β1) and GARP, while down regulating expression of CD45RA.