This article or section should be merged with regulatory T cell

There were debates over the existence of suppressor cells, but recent years studies have confirmed a central role of suppressor cell populations in regulating immunity. Naturally occurring suppressor T lymphocyte populations (renamed regulatory T cells - T reg) belong to CD4+ subpopulations and express all or some of the following markers: CD25+ (interleukin-2 IL-2 alpha chain), transcription factor FoxP3 (forkhead box p3), CTLA-4 (cytotoxic T-lymphocyte associated molecule-4) and GITR (glucocorticoid-induced TNF receptor). They mature in the thymus and comprise ~5-10% of the peripheral blood CD4+ helper T cell subpopulation in mice. Absence of T regs or their dysfunction are associated with severe autoimmunity and tumors. Evidence is now accumulating that T regulatory activity is amplified in a variety of infectious contexts, mediating suppression during retroviral and bacterial infections. Moreover, CD4+CD25+ T cells curtail immunity to Leishmania and malaria parasites in mouse models. There is also some suggestion that the pathogens themselves can manipulate the regulatory cells to immunosuppress the host and so potentiate their own survival. T regs exhibit suppressor-regulatory activity by producing anti-inflammatory cytokines TGF-beta and interleukin-10 (IL-10) and may exert direct suppression of T cell proliferation.