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→Anergy
'''Ignorance''' can occur when self-reactive T cells cannot penetrate an endothelial barrier, when self-antigen is present in very low amounts, when self-antigen is present on cells that do not express or express low amounts of MHC or when self-antigen is presented without co-stimulation, which can lead to ignorance or anergy, depending on the type of antigen and the affinity to the TCR. Ignorance also occurs when the T cells are not present in sufficient numbers to mount an effective response.
'''Ignorance''' can occur when self-reactive T cells cannot penetrate an endothelial barrier, when self-antigen is present in very low amounts, when self-antigen is present on cells that do not express or express low amounts of MHC or when self-antigen is presented without co-stimulation, which can lead to ignorance or anergy, depending on the type of antigen and the affinity to the TCR. Ignorance also occurs when the T cells are not present in sufficient numbers to mount an effective response.
'''Anergy''' is defined as a state where the T cell is still alive, but they fail to respond to stimulation from its specific T cell receptor and other receptors are required for activation.
Anergy is easily induced in T cells ''in vivo'' by activation of T cell receptors without co-stimulation; it can be induced ''in vitro'' by the injection of potent superantigens (antigens that stimulate T cells with different receptor types, using the same T cell receptor V gene). Anergy occurs naturally when there is a downregulation of T cell receptors as a result of chronic stimulation. Anergy induced without co-stimulation can be reversed by IL-2.
===Cell death===
===Cell death===