Mechanisms of Treg cell function. Treg cells exert their suppressive function by cell-to-cell contact to inhibit effector T cells, metabolic disruption via CD25, CD39 and CD73, modulating the activation and function of antigen-presenting cells via CTLA-4 and PD1, secreting of inhibitory cytokines such as IL-10, TGF-β and IL-35, cytolysis via secreting granzyme B/A and perforin, and/or IL-2 deprivation. Loss of Foxp3 expression occurred in response to microenvironments can induce Treg cells to Th-like cells. In addition, Treg cells can promote tissue repair and regeneration via the secretion of growth factors and other pathways. APCs: antigen-presenting cells; CTLA4: cytotoxic T-lymphocyte-associated protein 4; PD1: programmed death 1; Teff: effector Th cells