Single and fractionated Whole-Body Irradiation (WBI) of the BALB/c mice with total doses of 0.1 or 0.2 Gy X-rays led to reductions in the number of pulmonary tumour colonies. Single and fractionated WBI with 0.1 or 0.2 Gy, as well as the fractionated exposure to 1.0 Gy X-rays, significantly stimulated: the cytotoxicity of macrophages (Mφ) and Natural Killer (NK) cells mediated mainly by nitric oxide (NO) (Mφ) and perforin and Fas ligand (FasL) (NK cells); and production of IL-1β, IL-12 and TNF-α by Mφ, as well as the synthesis of IFN-γ by NK cells and IL-2 by splenocytes. Single exposures of the isolated NK cells and Mφ to X-rays did not boost the cytotoxic activities of these cell populations. The results indicate that the suppression of the development of pulmonary tumour colonies by single and fractionated WBI may be due to the stimulation of natural defence reactions mediated by NK lymphocytes and/or cytotoxic Mφ.
Keywords: low dose X-rays, single irradiation, fractionated irradiation, macrophages, natural killer cells, NK cells, anti-tumour activity, immune mechanisms, cytotoxicity, low radiation, whole-body irradiation, mice, pulmonary tumours, natural defence reactions