PROGRAMMED CELL-DEATH OF THE NORMAL HUMAN NEUTROPHIL - AN IN-VITRO MODEL OF SENESCENCE

The present study provides experimental data which indicate that the n eutrophil is ideal for studying programmed cell death or apoptosis in vitro. Neutrophils can be obtained from human peripheral blood in larg e numbers with minimal experimental manipulation and are easily separa ted from other leukocytes, providing nearly pure cell suspensions. The neutrophil life span in vitro is sufficiently short to allow observat ions to be made within eight hours after experimental manipulation. Ne utrophils can also be easily maintained in serum-free, chemically defi ned media which can be systematically altered, thereby defining specif ic variables that influence the apoptotic process. Since the neutrophi ls do not need an exogenous trigger to undergo programmed cell death, it is also an excellent model to study senescence. It was determined f rom this study that neutrophils undergo apoptosis most efficiently at 37 degrees C, a temperature requirement for physiologic cell death. Ne utrophils undergo apoptosis at a slightly faster rate and maintain mem brane integrity better when incubated in a tissue culture medium (e.g. , RPMI 1640) compared with a balanced salt solution (e.g., HBBB). Cycl oheximide, an inhibitor of protein synthesis, was shown to accelerate apoptosis in a dose-dependent manner. The presence of Zn++ significant ly decreased the rate of apoptosis, whereas the presence of Ca++ and M g++ had no apparent effect. These studies indicate that the process of senescence, culminating in cell death, is subject to modulation by a variety of agents and experimental conditions. In addition, the ultras tructural features of neutrophils undergoing programmed cell death in vitro were compared in detail to those occurring in vivo and were foun d to be comparable. (C) 1994 Wiley-Liss, Inc.