Tregs (T regulatory cells)

T regulatory cells are a specialised CD4+ T-cell subset defined by expression of the transcription factor FOXP3 that suppresses excessive immune responses and maintains self-tolerance. They act through multiple mechanisms including secretion of the anti-inflammatory cytokines IL-10 and TGF-β, expression of inhibitory co-receptors such as CTLA-4, and direct cytotoxicity toward activated effector cells. In the context of aging, Treg numbers in peripheral blood generally increase or are maintained, but their suppressive function may be impaired; paradoxically, elevated Treg activity has been proposed both to contribute to immunodeficiency by dampening anti-tumour immunity and, in some tissues, to limit chronic inflammation. In the tumour microenvironment, high Treg infiltration is associated with immune evasion and worse prognosis.