Induction of apoptosis of splenic lymphocytes in mice by accelerated carbon ions

To assess the capacity of heavy ions to induce apoptosis in lymphocytes, mice have been irradiated with accelerated carbon ions (95 MeV/nucleon) at doses ranging from 0.1 to 4 Gy. Their spleens were removed 24 h later and gently dissociated to prepare a single cell suspension. Mononuclear cells were then maintained in culture at 37 degrees C, and the occurrence of apoptosis in these cells was analysed 24 h later. Lymphocytes were also irradiated in vitro, in the presence of Ac-DEVD-CHO, a potent caspase-3 and -7 inhibitor. Results from three experiments performed at the Grand Accelerateur National d'Ions Lourds (GANIL, Caen, France) are reported here. They indicate that carbon ions induce a marked, dose-dependent, reduction of the spleen weight and cellularity. However, in sharp contrast with spleen cells prepared from X-ray irradiated mice, only a slight increase of apoptosis is evidenced in cultured lymphocytes from mice irradiated with heavy ions. The significance of such results is discussed. So far, few data exist concerning the biological effects of heavy ions, in particular their capacity to induce apoptosis in lymphocytes; the present study provides useful clues for further investigations.