Differences between ATP-mediated cytotoxicity and cell-mediated cytotoxicity

There has been considerable recent interest in the possible role of extracellular ATP in cell-mediated cytotoxicity. To investigate the similarities and differences between ATP-mediated lysis and CTL-mediated lysis, we studied in detail the ATP-mediated lysis of EL-4 cells, which are highly susceptible to lysis by extracellular ATP. ATP-mediated lysis was time and concentration dependent; most lysis occurred within 4 to 6 h of incubation. The kinetics of ATP- and cell-mediated lysis were similar. However, in contrast to CTL-mediated lysis, ATP-mediated lysis of EL-4 cells did not appear to be accompanied by characteristic chromosomal degradation (apoptosis). In order to compare these cytotoxic processes in greater detail, ATP-resistant clones were derived by growing EL-4 cells continuously in the presence of high concentrations of ATP. These cloned EL-4 lines showed marked resistance to ATP-mediated cytotoxicity across a wide range of concentrations but were as susceptible as the parent EL-4 cells to cell-mediated cytotoxicity by an alloreactive effector population from a MLC. Thus, there appear to be a number of differences between ATP-mediated and cell-mediated cytotoxicity in this system; most notable is the identification of cell lines that are resistant to ATP but susceptible to CTL-mediated lysis.