Enhancement of O-2(-) production from resident peritoneal macrophages by low-doses in vivo gamma-irradiation

Superoxide anion (O-2(-)) production after very low-dose in vivo irradiatio n (4cGy) was examined in resident peritoneal macrophages. The level of prod uction rapidly increased following treatment with the PKC activator, phorbo l 12-myristate 13-acetate (PMA), but no fur ther enhancement by low-dose in vivo irradiation was observed. On the other hand, treatment with zymosan A gradually induced O-2(-) production, which was further increased in low-do se in vivo irradiated macrophages. The amounts of phagocytosis of zymosan A were not changed by in vivo irradiation. This indicated that the enhanceme nt of O-2(-) production was not due to an increase in phagocytotic activity by low-dose in vivo irradiation. Our results show that low-dose in vivo ir radiation induces production of reactive oxygen species by macrophages, not only nitric oxide as reported in our previous paper but also O-2(-). This may contribute to the increase of cytolytic activity of macrophages after l ow-dose in vivo irradiation.