Detection of Apoptosis using Fluorescent In Situ Nick Translation

Apoptosis is the most common mechanism of cell death (Kerr et al., 1972). It is also known as Programmed Cell Death and it is dependent on specific enzymatic activity. Apoptosis takes place in embryogenesis, tumor regression, tissue atrophy and cell death induced by cytotoxic T-lymphocytes (Duvall and Wyllie, 1986). It can be induced by a number of factors, including glucocorticosteroids, tumor necrosis factor, lymphotoxin and radiation. The tumor suppressor gene bcl-2 blocks apoptosis as has been reviewed by Williams (1991). Wild-type p53 also functions as a tumor suppressor gene and induces apoptosis (Yonish-Rouach et al. 1991). Sellins and Cohen (1987) proved that, in contrast to necrosis, apoptosis is an active process by showing that induction of gene expression takes place after γ-irradiation. This gene expression is required for DNA fragmentation by endonucleases, an early event in apoptosis. Growth factors promote cell survival which means that they suppress apoptosis in haemopoietic cells (Williams et al., 1990, Nieto et al., 1989). Resting lymphocytes are very sensitive for irradiation and die via apoptosis. This process is known as Interphase Death. Sellins and Cohen (1987) suggested that this mechanism has a role in the elimination of cells that could be potentially harmful to the organism, because they might possibly turn into tumor cells by errors in the DNA repair process. Therefore they called this mechanism a ‘better dead than wrong’ mechanism that defends the organism against these potentially dangerous irradiated clonogenic lymphocytes.