Anergy is a state in which the immune system is unable to mount a normal immune response against a specific antigen. This may be caused by a defect in the molecular mechanisms that initiate T-cell activation or by a block in the signal transduction pathway downstream of the T-cell receptor.
Exhaustion is a state of T cell dysfunction that results from many chronic infections or cancer. It is characterized by the loss of cytolytic function, inability to produce cytokines, and downregulation of markers of activation.
Clonal deletion is the process whereby self-reactive T cells die as a result of apoptosis. The process of clonal deletion is an important mechanism for maintaining self-tolerance and preventing autoimmunity.