T cell receptor signalling in the control of regulatory T cell differentiation and function

Regulatory T (TReg) cells are a distinct lineage of CD4+ T cells that differentiate in response to agonist self antigens in the thymus and to non-pathogenic foreign antigens in the periphery.The involvement of T cell receptor (TCR) signalling modules that have opposing activities in T cell lineage specification favours a TReg cell repertoire that, in general, reacts to low-abundance, high-affinity antigens.Compared with ubiquitous antigens, low-abundance, high-affinity antigens will probably induce inefficient clonal deletion of T cells, and thus the existence of these antigens justifies the necessity of TReg cell-mediated dominant immune tolerance.Depending on the expression of activation markers, mature TReg cells can be divided into resting and activated TReg cell subsets, and these discrete populations probably accompany conventional T cells to control their activation and effector functions in secondary lymphoid organs and target tissues.Distinct TCR signalling modules are selectively involved in the control of trafficking, maintenance and suppressive activities of resting and activated TReg cells.