Regulatory T cell‐mediated suppression: potential role of ICER

How regulatory T (T R ) cells dampen T cell responses remains unclear. Multiple modes of action have been proposed, including cell contact‐dependent and/or cytokine‐dependent mechanisms. Suppression may involve direct contact between T R cells and responder T cells. Alternatively, T R cells may act on dendritic cells to reduce their abiity to prime T cells by modulating costimulation, inducing the secretion of suppressive cytokines or the increase of tryptophan metabolism. Here, we review emerging, novel mechanisms involved in contact‐dependent, T R ‐mediated suppression of IL‐2 production in responder CD25 − T lymphocytes and the potential involvement of inducible cAMP early repressor (ICER) in this suppression. Finally, cytokines such as TGF‐β and IL‐10, produced by T R cells or other cells, may exert local suppression, which can be conveyed by basic mechanism(s) acting in a similar manner as contact‐dependent, T R ‐mediated suppression.