Ex vivo determination of the effect of whole-body exposure to fast neutrons on murine spleen cell viability and apoptosis

The effects of high-linear energy transfer (LET) radiations on lymphoid tis sues and lymphocytes are not well understood. As a first approach to deline ate these effects, the present work was conducted to assess the effects of high-LET radiations on murine spleen cells ex vivo and in vitro. BALB/c mic e were irradiated whole-body with 65 MeV neutrons or 15 MV X rays at doses ranging from 0.2 to 3 Gy. Spleens were removed 1 day postirradiation and we ighed, and single cell suspensions were prepared and cultured for several d ays. Apoptosis occurring itt vitro was determined at different times by flo w cytometry analysis of cells labeled with propidium iodide. It was found t hat irradiation with fast neutrons reduced spleen weight and cellularity to a greater extent than photons, Considering the spleen cellularity as end p oint, the relative biological effectiveness (RBE) of fast neutrons was 2. H owever, for both modes of irradiation, apoptosis of recovered spleen cells in vitro increased as a function of dose and the duration of culture. The l evel of apoptosis occurring at various times postirradiation was found to b e identical for high- and low-LET radiations. Taken together, these results suggest that external as well as cellular factors might differentially mod ulate the sensitivity of lymphocytes to fast neutrons and photons. (C) 2000 by Radiation Research Society.