Prevention of x-ray-induced leukemia in mice. I. Action of a radiation leukemia protection factor in several mouse strains following leukemogenic or sublethal doses of x-ray.

Leukemia was induced in 6 to 8-week-old male and female mice by exposure to fractional doses of X-irradiation. Half the ani mals were given injections immediately after exposure of 40% extracts of sheep spleen according to the procedure of Berenblum et al. (2) or with 10% extracts. The extracts caused a highly signi ficant difference in leukemia incidence in C57BL/6 and BALB/C mico, and no effect on a small group of RF mice. There was no significant difference in leukemia indidence between the sexes. Xirradiated C3H/eb mice died within hours of the 4th or 5th injec tion, apparently in anaphylactic shock. Similar highly significant decreases in leukemia incidence in C57BL/6 mice were produced by 40% bovine spleen extracts. Bovine serum albumin was devoid of effect, whereas bovine serum 7-globulin exerted a significantly protective action. Three strains of mice were used in an attempt to demonstrate anantilethal effect of the sheep spleen extracts. In 2 experiments in which Swiss mice and 1 in which C57BL/6 mice were exposed to single doses of 550 r, significant decreases in mortality, meas ured at 30 days, were noted. In the remaining 15 experiments, the differences either were not significant, or the extracts seemed to exert a deleterious action. An experiment with BALB/C mice infected with Rauscher virus failed to demonstrate an antiviral effect of sheep spleen extract.