Colony-Forming Cells in Irradiated, Partially Shielded, Endotoxin-Treated Mice

The kinetics of the regeneration of colony-forming units (CFU) were studied in endotoxin-treated or nontreated, one-leg-shielded mice at 30 minutes, 6 hours, and 3, 7, and 10 days after irradiation with 500 R. Eight micrograms of Serratia marcescens endotoxin given 20 minutes after irradiation was found to significantly influence CFU regeneration kinetics. As compared to the whole-body-irradiated animals, CFU regeneration was accelerated in the partially shielded ones; 10 days after irradiation the CFU reached 59% of the control value in the exposed tibia of the partially shielded animals, as against the 35% measured in the whole-body-irradiated ones. A significant CFU decrease in the shielded tibia was measured at 30 minutes after irradiation and was presumably a consequence of the so-called "abscopal effect." CFU regeneration kinetics changed in a characteristic way in the exposed tibia of the endotoxin-treated animals: (1) Abortive regeneration failed to occur at the sixth hour; (2) the CFU level was appreciably higher in the endotoxin-treated animals in the initial phase of regeneration; and (3) the 10-day value was appreciably lower as compared to that found for the irradiated control animals. Reduced CFU level was measured in the shielded tibia of the endotoxin-treated mice during the whole experimental period.