Anti-neoplastic and immunostimulatory effects of low-dose X-ray fractions in mice

Abstract

Purpose: The exploration of immune mechanisms of the tumour-inhibitory effect of exposures to low-level fractions of X-rays.

Materials and methods: BALB/c mice were exposed to whole-body daily irradiations with 0.01, 0.02, or 0.1 Gy X-rays per day for 5 days/week for two weeks. Then, mice were intravenously injected with L1 tumour cells, killed 14 days later, and neoplastic colonies were counted in the lungs. Natural killer (NK) cell-enriched splenocytes and activated peritoneal macrophages (Mϕ) were collected and cytotoxic activities of these cells against susceptible tumour targets were assayed. Concanamycin A (CMA) and antibody against the ligand for the Fas receptor (FasL) were used to inhibit the NK cell-mediated cytotoxicity. Production of nitric oxide (NO) was quantified using the Griess reagent. Secretion of interferon-γ (IFN-γ), interleukin-1β (IL-1β), interleukin-12 (IL-12), and tumour necrosis factor-α (TNF-α) was measured using the enzyme-linked immunosorbent assays.

Results: All the exposures to X-rays significantly reduced the number of the induced tumour colonies and enhanced cytotoxic properties of the NK cell-enriched splenocytes and activated Mϕ.

Conclusion: Suppression of the growth of pulmonary tumour colonies by irradiations of mice with low-dose fractions of X-rays may result from stimulation of anti-tumour reactions mediated by NK cells and/or cytotoxic macrophages.

Keywords:

• low doses of X-rays
• fractionated irradiations
• induced tumour colonies
• NK cells
• activated macrophages
• cytotoxic function
• cytokines

Acknowledgements

This study was supported by the Polish Ministry of the National Defence and by the grants No. 2P05D05028 and No. N40400532/0161 from the Polish Ministry of Science and Higher Education.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Notes

1 According to the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) Report (1986), acute doses above 2 Gy, between 2 and 0.2 Gy, and below 0.2 Gy are regarded as high, intermediate, and low, respectively. The more recent UNSCEAR (2006) and BEIR (2006) publications set the upper boundary of the acute low dose region at 0.1 Gy.