any functional anomaly of the specialized subpopulation of T cells that act to suppress activation of the immune system and thus maintain immune system homeostasis and prevent pathological self-reactivity; these may include T cells that express the CD8 transmembrane glycoprotein (CD8-positive T cells), those that express CD4 and CD25 (CD4-positive, CD25-positive regulatory T cells or Tregs) and other T cell types that have suppressor function (Mammalian Phenotype Ontology, MP_0004946)
