Increase of Survival of X-Irradiated Mice by Postirradiation Injections of a Splenic Extract Prepared from Vaccine or Endotoxin-treated Syngenic Animals

Spleens of mice which had been treated with E. coli endotoxin or typhoid-paratyphoid vaccine were extracted with an isotonic saline. The extract was filtered through an asbesto filter and chromatographed on a Sephadex G-200 column. The fraction which was excluded at around 2.5-void volume (molecular weight, about 20, 000) was significantly effective in increasing survival of animals, when it was repeatedly injected in mice after X-irradiation (600R). The injection caused an increase of the weight of spleen of the animals with increased number of endogenous spleen colonies. The result sxggests that the life-saving effect of the spleen extract is based on its effect of stimulating repopulation of autochthonous hematopoietic cells in the X-irradiated animals. Similar splenic extract prepared from normal mice gave an ambiguous effect on the survival of X-irradiated animals.