Editing T cell (section)

====Regulatory CD4<sup>+</sup> T cells====
{{Main|Regulatory T cell}}

[[Regulatory T cell]]s are crucial for the maintenance of [[immunological tolerance]]. Their major role is to shut down T cell–mediated immunity toward the end of an immune reaction and to suppress [[autoreactive T cell]]s that escaped the process of negative selection in the thymus.

Two major classes of CD4<sup>+</sup> T<sub>reg</sub> cells have been described—FOXP3<sup>+</sup> T<sub>reg</sub> cells and FOXP3<sup>−</sup> T<sub>reg</sub> cells.

Regulatory T cells can develop either during normal development in the thymus, and are then known as thymic Treg cells, or can be induced peripherally and are called peripherally derived Treg cells. These two subsets were previously called "naturally occurring" and "adaptive" (or "induced"), respectively.<ref name="pmid23507634">{{cite journal|vauthors=Abbas AK, Benoist C, Bluestone JA, Campbell DJ, Ghosh S, Hori S, Jiang S, Kuchroo VK, Mathis D, Roncarolo MG, Rudensky A, Sakaguchi S, Shevach EM, Vignali DA, Ziegler SF|title=Regulatory T cells: recommendations to simplify the nomenclature|journal=Nat. Immunol.|volume=14|issue=4|pages=307–8|year=2013|pmid=23507634|doi=10.1038/ni.2554|s2cid=11294516|url=http://www.escholarship.org/uc/item/75m8c11s|doi-access=free}}</ref> Both subsets require the expression of the [[transcription factor]] [[FOXP3]] which can be used to identify the cells. Mutations of the ''FOXP3'' gene can prevent regulatory T cell development, causing the fatal [[autoimmune disease]] [[IPEX (syndrome)|IPEX]].

Several other types of T cells have suppressive activity, but do not express FOXP3 constitutively. These include [[Type 1 regulatory T cell|Tr1]] and [[T helper 3 cell|Th3]] cells, which are thought to originate during an immune response and act by producing suppressive molecules. Tr1 cells are associated with IL-10, and Th3 cells are associated with [[TGF-beta]]. Recently, [[Th17 cells]] have been added to this list.<ref name="pmid24434314">{{cite journal|vauthors=Singh B, Schwartz JA, Sandrock C, Bellemore SM, Nikoopour E|title=Modulation of autoimmune diseases by interleukin (IL)-17 producing regulatory T helper (Th17) cells|journal=Indian J. Med. Res.|volume=138|issue=5|pages=591–4|year=2013|pmid=24434314|pmc=3928692}}</ref>