Augmentation of NO production and cytolytic activity of M phi obtained from mice irradiated with a low dose of gamma-rays.

The activation of macrophages (M phi) by low-dose irradiation (4cGy) was examined. The irradiated M phi were obtained from mice exposed to a low dose of gamma-rays. The addition of excess irradiated M phi suppressed more the concanavalin A-induced proliferation of splenocytes than that of unirradiated M phi. This was attributed to large nitric oxide (NO) production from irradiated M phi. In addition, low-dose irradiation augmented NO production and glucose consumption in M phi treated with interferon-gamma alone or interferon-gamma/lipopolysaccharide. Furthermore, low-dose-irradiated M phi showed a higher cytolytic activity against P-815 mastocytoma cells than unirradiated M phi, indicating that the NO production was involved in the activity. On the other hand, the M phi 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 gamma-rays activates M phi indirectly and consequently enhances NO production from M phi, by which the self-defense systems such as the tumoricidal activity will be augmented.