Impact of total-body irradiation on the response to a live bacterial challenge

Purpose: Concern regarding radiation effects on human health continues to increase worldwide. Given that infection is a major cause of morbidity and mortality after exposure, the aim of this study was to evaluate decrements in immune cell populations using a mammalian model subjected to a live bacterial infection. Materials and methods: C57BL/6 mice were exposed to total-body irradiation (TBI) with 3 Gy protons (70 cGy/min). One, 2, 4, 8 or 16 days later, subsets of mice were injected intraperitoneally with live Escherichia coli [055: K59(B5)]. Control groups received no radiation and vehicle (no bacteria). The mice were euthanized for analyses 90-120 min after injection of the bacteria. Results: There were no unexpected effects of radiation or E. coli alone. Despite dramatic radiation-induced decreases in all leukocyte populations in both the blood and spleen, irradiated mice were still able to respond to an immune challenge based on capacity to generate an oxidative burst and secrete inflammatory cytokines, i.e., tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). However, these responses were generally elevated above control values. Conclusions: Together, these results suggest the possibility for enhanced inflammation-associated tissue injury and increased risk for chronic inflammation.