Treg细胞是一类能够负向调节免疫反应的细胞，《Kuby Immunology, 7th Edition》中将这种具有维持外周免疫耐受的Treg细胞分为iTreg(induced Treg)和nTreg(natural Treg)。其中nTreg来源于胸腺，iTreg来源于次级淋巴组织。

    在T Regulatory Cells Overview中将Treg分为三类，nTreg和另外两种iTreg(Tr1与Th3)，并总结了他们之间的区别。

    Property Natural Treg (nTreg) Induced Treg (iTreg) - Tr1 Induced Treg (iTreg) - Th3
    Development Thymus Periphery (MALT) Periphery (MALT)
    Phenotype CD4CD25CD127 CD4CD25 CD4CD25 from CD25 precursors
    Other Associated Markers CTLA-4GITRFoxp3 CD45RBFoxp3 CD25CD45RBFoxp3
    Suppression Contact-, Granzyme-B dependent, makes TGF beta IL-10 mediated TGF beta mediated
    Target Cells APC and Effector T Cells Effector T Cells Unknown
    CD28 Involvement Thymic development and maintenance in periphery Unnecessary for development or function Unnecessary for development or function
    in vivo Role Suppression of autoreactive T cells Mucosal immunity, inflammatory response Mucosal immunity, inflammatory response
    in vitro Expansion TCR/CD28 stimulation and IL-2 CD3, IL-10, Retinoic Acid CD3, TGF beta