Low dose γ-rays activate immune functions via induction of glutathione and delay tumor growth

We examined whether the increase of glutathione level induced by low dose gamma-ray irradiation is involved in the appearance of enhanced natural killer (NK) activity and antibody-dependent cellular cytotoxicity (ADCC), leading to delayed tumor growth in Ehrlich solid tumor-bearing mice. NK activity in ICR mouse splenocytes significantly increased from 4 h to 6 h after whole-body gamma-ray irradiation at 0.5 Gy, and thereafter decreased almost to the zero-time level by 24 h post-irradiation. ADCC also increased significantly in a similar way. Reduced glutathione exogenously added to splenocytes obtained from normal mice enhanced both NK activity and ADCC in a dose-dependent manner. Since immune functions were enhanced through the induction of cellular glutathione after low-dose irradiation, the inhibitory effect of the radiation on tumor growth was then examined in Ehrlich solid tumor-bearing mice. Tumor growth after inoculation was significantly delayed by the radiation. These results suggest that low-dose gamma-rays activate immune functions via an induction of glutathione, leading to a delay of tumor growth.