Augmentation of NO production and cytolytic activity of Mφ obtained from mice irradiated with a low dose of γ-rays

The activation of macrophages (Mφ) by low-dose irradiation (4cGy) was examined. The irradiated Mφ were obtained from mice exposed to a low dose of γ-rays. The addition of excess irradiated Mφ suppressed more the concanavalin A-induced proliferation of splenocytes than that of unirradiated Mφ. This was attributed to large nitric oxide (NO) production from irradiated Mφ. In addition, low-dose irradiation augmented NO production and glucose consumption in Mφ treated with interferon-γ alone or interferon-γ/lipopolysaccharide. Furthermore, low-dose-irradiated Mφ showed a higher cytolytic activity against P-815 mastocytoma cells than unirradiated Mφ, indicating that the NO production was involved in the activity. On the other hand, the Mφ irradiated with a low dose in vitro did not enhance the NO production. These findings suggest that whole-body irradiation with a low dose of γ-rays activates Mφ indirectly and consequently enhances NO production from Mφ, by which the self-defense systems such as the tumoricidal activity will be augmented. (author)