Based upon this observation, it has become possible to ask whether there is evidence of recipient anti-donor Tregs

Based upon this observation, it has become possible to ask whether there is evidence of recipient anti-donor Tregs. active process that is characterized by a central and peripheral component (17). Central tolerance is a thymic dependent process that involves the deletion of autoreactive clones through the induction of apoptosis. Peripheral tolerance can be subdivided into at least three major categories: clonal deletion, anergy, and suppression. A subset of T cells has been identified that specifically regulate the suppression process. These cells are known as regulatory T cells (Tregs). Even though these cells are frequently alpha-hederin grouped under one category, they can be divided into two developmental subsets, thymic-derived (natural) Tregs (tTregs or alpha-hederin nTregs), and induced (adaptive) peripheral Tregs (iTregs or pTregs) (8) (Figure 1). Although these cells are predominantly CD4+, CD8+Foxp3+cells have been identified that are also suppressive in nature. Natural Tregs are produced in the thymus and most express the IL-2 receptor alpha chain (CD25) (9). Their development and functionality depend on the expression alpha-hederin of the transcriptional factor forkhead box P3 (Foxp3) (10, 11). Induced Tregs are derived in the periphery from nave T cells following specific antigenic stimulation. There are also several populations of CD4+Foxp3T cells that are suppressive, including IL-10 producing T regulatory 1 (Tr1) alpha-hederin cells, transforming growth factor beta (TGF-) T helper a few (Th3) cells, and T regulatory type 35 (Tr35) cells that produce IL-35, which is related to the IL-12 superfamily (1, 3, 12) (Figure 2). This review will focus on the biology of Tregs, the role that they play in kidney allograft acceptance, and the ways that our knowledge about Tregs is being leveraged in the clinic. == Figure 1 . == Origin of Foxp3+Tregs. During thymic ontogeny, double positive (CD4+CD8+) thymocytes with low affinity for self-peptide + self-MHC undergo positive selection, becoming single positive CD8+or CD4+thymocytes which eventually are exported into the peripheral lymphoid compartment as nave T cells. Under certain conditions (seefigure 2for more details), these nave T cells can be induced to express Foxp3, and these cells are known as pTregs (for Tregs of peripheral origin). Double positive thymocytes with moderate affinity for self-peptide+self-MHC are induced to express Foxp3, and these cells, known as tTregs because of their thymic origin, are exported into the periphery as fully formed Tregs. Abbreviations: Foxp3+Tregs, Foxp3 positive regulatory T cells; MHC, major histocompatibility complex; tTregs, thymic-derived Tregs; IL, interleukin; TCR, T cell receptor; pTreg, induced peripheral regulatory T cells. == Determine 2 . == Induction of Tregs from nave T cells. In the periphery, conditions which favor the induction of pTregs from nave T cells include low level continuous antigen exposure, the absence of inflammatory signals (especially IL-6), the presence of cytokines such as IL-2 and TGF-, and other factors such Rabbit polyclonal to ABCB1 as retinoic acid. High levels of IL-10 can also induce a regulatory T cell phenotype, however these cells, known as Tr1 cells, do not express Foxp3 and themselves produce IL-10. Abbreviations; Foxp3+Treg, Foxp3 positive regulatory T cell; pTreg, induced peripheral regulatory T cells; IL, interleukin; TGF-, transforming growth factor beta; APC, antigen-presenting cell. == Treg biology == == Basic Concepts alpha-hederin == Foxp3+Tregs constitute 5 to 10% of peripheral CD4+T cells in both mice and humans (13) and are critical for maintaining immune homeostasis. Mutations inFoxp3leading to an absence of functional Tregs is the cause of severe autoimmunity as observed inscurfymice and in humans with IPEX (immune dysregulation, polyendocrinopathy, enteropathy,.