A Direct Measurement of the Radiation Sensitivity of Normal Mouse Bone Marrow Cells

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Abstract
A technique has been developed for estimating the number of cells in a suspension of mouse bone marrow capable of continued proliferation. Various dilutions of the marrow suspension are injected intravenously into 2-4-month-old isologous test animals, pre-irradiated (total body) with 950 of X-rays, a dose that prevents gross or microscopic regeneration of marrow cells in the spleen during the period of the experiment. When the spleens of these animals are examined after 10 days, colonies of proliferating hematopoietic cells are seen. Over approximately a tenfold range of cell concentration, colonies are discrete and may be enumerated macroscopic ally. The number of colonies thus determined is linearly related to the number of cells injected. On the average, about 10 colonies per spleen are formed when 105 unirradiated, nucleated marrow cells are injected. Using this technique, a radiation survival curve has been obtained for normal mouse bone marrow cells irradiated in vitro but proliferating in vivo. The curve has a mean lethal dose (MLD) of 115 [plus or minus] 8 rads ( of Co60 gamma rays) and a hit number of about 2. Experiments on C3Hf and C57BI mice yielded similar results.