Keywords: anti-tumour activity, cytotoxicity, low dose, X-rays, macrophages, natural killer cells, NK cells, mice, low radiation, tumour cells, NK lymphocytes, ionising radiation
Modulation of anti-tumour functions of NK cells and macrophages after single low-level exposures of mice to X-rays
Based on the reports suggesting that exposures to low doses of ionising radiation may impede tumour development and/or trigger the activity of natural anti-neoplastic defence mechanisms we demonstrate in the present study that single whole-body irradiations of mice with 0.1 or 0.2 Gy X-rays significantly decreased the number of the induced tumour colonies in the lungs and that the effect was accompanied by a marked stimulation of the Natural Killer (NK) cell- and macrophage-mediated lysis of susceptible tumour cells in vitro. The enhanced cytotoxicity of the two cell types coincided with the elevated expression of Fas ligand on NK lymphocytes as well as the increased production of nitric oxide, superoxide anions, and tumour necrosis factor-α in the activated macrophages. Importantly, suppression of the activity of NK cells or macrophages in vivo abrogated the anti-neoplastic effect of the low-level exposures to X-rays.