ABSTRACT

Cytotoxicity mediated by T lymphocytes represents the most specific weapon available to the immune system. Cytotoxic T lymphocytes (CTL) can recognize virally infected or chemically modified cells and eliminate them without damaging normal cells. Models of CTL-mediated cytolysis favoring internal damage emphasize the differences in the morphological and biochemical changes induced in the target cell during CTL-mediated vs. complement mediated cytolysis. One of the morphological changes in targets of CTL is widespread condensation of nuclear chromatin, the hallmark of apoptosis. To investigate the changes in target cell DNA during CTL-mediated cytolysis, DNA fragmentation and 51Cr release were determined during 4 hr dose-response experiments employing various effector to target ratios. While the CTL could directly transfer the nuclear-modifying enzymes to the target, there is little evidence to support such an idea. In CTL-mediated cytolysis, the CTL interacts with the target via specific target cell membrane proteins, and induces DNA fragmentation and cytolysis in a protein synthesis independent fashion.