Programmed cell death in whole body and organ systems by low dose radiation

An extremely sensitive in vivo method to detect interphase cell death in the thymus, spleen and intestinal crypt was established by using frozen sections of these organs and tissues. The frozen sections as thick as 8 μm were made after X-irradiation of the whole body or removed organs, and stained with 0.02% erythrosin B solution. When a single whole bode dose of X rays was given to various strains of mice, clusters of erythrosin positive cells were produced. They appear at 2 hr after irradiation and reached the maximuim at 4 hr, remaining at a similar level until 8 hr. The number of erythrosin B positive cells decreased after then by the elimination of dead cells. The cells were observed as a single cell death, observed in non-irradiated controls, at 24 hr after irradiation. The maximum erythrosin B positive cells and the associated number of clusters increased with increasing doses of X rays from 0.05 to 0.5 Gy. There were large differences in the radiation susceptivility among the inbred strains of mice for the induction of interphase cell death of thymic lymhocytes: radiation sesceptivility was high in C57BL/6J and AKR/J, intermediate in N4, A/J, PT and ST, and low in C3H/HeJ, HT, 101/H and DBA/2J. Similar results were observed in organ specificity to chemical mutagens. Erythrosin B positive cells was extremely increased in the thymus and spleen but not in the intestinal crypt with methylprednisolone, and vice versa with bleomycin. In vitro number of erythrosin B positive cells reached the maximum at 5 hr after X-irradiation; e.g., slightly later than in vivo method. The efficiency was about 60% in C57BL/6J mice when compared with in vivo method. (N.K.)