The ligand is made by other cells, including immune cells. This mechanism is used by the immune system to delete activated T lymphocytes after the immune response. TNF induced apoptosis. I receptors, present on endothelial cells and lymphocytes among others, transduce death domain mediated apoptosis by mechanisms analogous to those in the Fas system. I is involved in immune deletion or activation, and in endothelial apoptosis during shock.
Many cells are dependent on hormones, cytokines or growth factors for their survival.
The mitochondrial damage that results triggers caspases, and cell death. If DNA repair is not successful, p53 initiates complex biochemical events which result in apoptosis. Mutant p53 forms or absent p53 is not permissive for this type of cellular deletion, with or without DNA damage, and is thus permissive for carcinogenesis. Cancers, specially those with p53 mutations. Hormone dependent tumors such as breast, prostate, ovary.