OBSERVATIONS ON THE EFFECT OF SPLEEN-SHIELDING 



and re-suspension of the bone marrow cells in saline or Locke's solution 

 considerably reduce the deleterious effect. 



To determine the length of time during which ladiation damage is rever- 

 sible, non-irradiated bone marrow suspensions were injected intravenously 

 into irradiated mice from 1 to 5 days after 900 r. Some beneficial 

 effect was still obtained when the bone marrow was injected as late as 

 5 days after X-irradiation. 



Effect of cell suspensions on survival of mice exposed to 750 r — Experiments 

 similar to those described above are in progress. These differ only in that 

 the recipients are being exposed to 750 r. The mice are irradiated without 

 anaesthesia in plastic tubes. The target distance is 79 cm and the dosage 

 rate, approximately 60 r per min. The animals that were exposed to 900 r 

 were anaesthetized with Nembutal during irradiation ; the target distance 

 was 57 cm and the dosage rate, 69 r per min. 



Preliminary data indicate that 50 per cent survival is obtained when as 

 few as 0-5 X 10^ nucleated cells are injected intravenously after the mice 

 have been exposed to 750 r. The survival rate is the same with cells obtained 

 from 2-day liver or embryo liver or spleen and with cells from the bone 

 marrow of 4- to 5-week mice. 



In a preliminary experiment, 6 of 10 mice survived with 0-075 x 10^ 

 (75,000) embryo cells ; 22 of 32 survived with 0-150 to 0-2 X 10« (150,000- 

 200,000) embryo cells; 4 of 10 with 0-175 (175,000) cells from 2-day 

 spleens ; 6 of 16 with 0-225 to 0-3 (225,000-300,000) cells from 2-day liver ; 

 and 6 of 8 have survived 28 days that received 150,000 bone marrow cells 

 obtained from 4- to 5-week-old mice. 



Comments 



It is obvious from our data that (1) a relatively small total number of cells is 

 sufficient to insure significant survival when these are injected into mice that 

 have been irradiated with 900 r, and (2) embryo liver cells and baby mouse 

 spleen or marrow cells are more effective than adult liver, spleen, or marrow 

 cells. As one reduces the total-body exposure to the recipient mice (750r), 

 an even smaller number of cells is required to significantly enhance survival. 

 In view of the observation that cells from the liver are effective, it is perhaps 

 important to determine whether the vital cells are parenchymal ectopic 

 primitive blood cells or some other cellular constituent of liver, e.g. the 

 Kiipffer cells. It should be possible to obtain information on the cell type 

 or types involved in the elaboration of the factor(s) responsible for the 

 recovery of irradiated animals by such techniques as differential centrifugation 

 and by a study of their morphologic characteristics. 



Cole and his co-workers^ claim to have prepared splenic suspensions from 

 the mouse in which only the nuclei of the cells were intact. According to 

 their report, these preparations administered intraperitoneally to mice that 

 have been exposed to 750 r routinely increase survival. If their suspensions 

 contained as many as 50,000 morphologically intact cells or if the induced 

 damage was reversible, the experiments must be extended to include larger 

 numbers of animals and the absence of intact cells (less than 100,000) 

 must be established before Cole's interpretation of his results can be 

 accepted. 



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