Table 1.

Classification of dysfunctional T cells.

T cell dysfunction	Functional and Phenotypic features
Ignorance	Self-reactive T cells that do not sense self-antigens due to physical sequestration or low antigen expression.
Tolerance	Central tolerance accounts for negative selection of thymocytes expressing high-affinity TCRs to self-antigens. Thymocytes which escape negative selection are inactivated by different mechanisms of the peripheral tolerance.
Exhaustion	Persistent antigen stimulation of T cells during chronic diseases (infections or cancer) induce progressive loss of T cell effector functions and lead to exhaustion.
Anergy	A hyporesponsive state of T cells arise in suboptimal costimulatory signal during T cell-antigen recognition.
Senescence	State of non-reversible cell cycle arrest caused by telomere shortening.