Keywords: low-dose radiation, Th1 immunity, immunity balance, tumour growth, cell-mediated immunity, NK cells, cytotoxic T lymphocytes, CTLs, glutathione, GSH, low radiation, gamma irradiation, mice, macrophage levels
The enhancement of Th1 immunity and the suppression of tumour growth by low-dose γ-radiation
To address if the modulation of immunity balance by low dose radiation is involved in the enhancement of the anti-tumour function, we examined the effect of 0.5 Gy γ-irradiation on the Th1/Th2 immunity balance in Ehrlich Solid Tumour (EST)-bearing mice. Repeated 0.5 Gy γ-irradiation significantly delayed the growth of tumours. The cytotoxic activities of Natural Killer (NK) cells and Cytotoxic T Lymphocytes (CTLs) were enhanced after repeated irradiation. Irradiation at 0.5 Gy significantly increased the Interferon (IFN)-γ production by splenocytes of tumour-bearing mice with their Interleukin (IL)-4 unchanged, resulting in the increased ratio of IFN-γ/IL-4, a hallmark of Th1 shift. Irradiation also increased the IL-12 production and cellular-reduced Glutathione (GSH) level of macrophages. The increase in the GSH level was found to be sustained for a few days after irradiation. These results indicate that low dose radiation shifts the immunity balance towards Th1 and consequently enhances the anti-tumour activity. The elevation of the GSH of macrophages by irradiation is suggested to be involved in the shift of the immunity balance.