Interphase death in human peripheral blood lymphocytes after moderate and high doses of low and high LET radiation: an electron microscopic approach.

Peripheral blood lymphocytes irradiated with low and moderate doses of low linear energy transfer (LET) gamma-rays are known to die by an apoptotic process. In the present study, the type of interphase death occuring after administration of moderate and high doses of low LET gamma-rays and high LET fast neutrons was investigated. Lymphocytes were irradiated in vitro with radiation doses of 5 and 20 gray (Gy) of both radiation qualities. They were cultured for 24 or 48 hours and the type of cell death induced was determined by electron microscopy. After neutron irradiation, a slight increase in the incidence of apoptosis from 5 to 20 Gy was found, whereas after gamma-irradiation, the incidence of apoptosis was lower at 20 Gy as compared to 5 Gy. However, unlike the other radiation doses, the 20 Gy dose of gamma-rays, besides apoptosis also induced oncosis (classical necrosis). According to our experiments, membranes are probably an important target for the induction of interphase death. It is suggested that a great amount of ionisations distributed all over the cell surface, as caused by high doses of gamma-rays, lead to a high influx of Ca++ which induces oncosis instead of apoptosis.