Transient Increase in Resistance of Mice to Experimental Infection Following a Small Dose of X-Radiation.

CF-1 female mice, 9-10 weeks old, were exposed to a small dose of whole body X-radiation (50, 75, or 100 r) and together with unirradiated controls were challenged at various intervals by intraperitoneal injection of graded inocula of Pseudomonas aeruginosa. Comparison of the LD50's (30 days) of irradiated and control mice in each challenge showed a small but significant increase in resistance to the experimental infection during the 4th week following irradiation with 75 or 100 r. Exposure to 75 r was more effective than 100 r. The results suggest a possible explanation of “acquired radio-resistance.”