The development of classically and alternatively activated macrophages has different effects on the varied stages of radiation-induced pulmonary injury in mice

The classical and alternative activation of macrophages has been proposed to play a role in radiation-induced pneumonitis and fibrosis,respectively. to test this hypothesis,the thoraces of c57bl/6 mice were irradiated with 12 gy x-rays,and irradiated and control mice were euthanized at 1,8,12,24 and 72 hours,and 2,4,8,16 and 24 weeks after irradiation. the expression of inducible nitric oxide synthase (inos) and arginase type 1 (arg-1) was evaluated at the mrna and protein levels at different stages post-irradiation. we demonstrated that the enhanced mrna and protein expression of inos occurred within the pneumonic stage,whereas the high levels of arg-1 expression occurred within the fibrotic phase. immunohistochemistry revealed that inos and arg-1 were mainly expressed in macrophages. the expression of inos and arg-1 may be associated with acute radiation pneumonitis and the development of radiation fibrosis,respectively. although the function of macrophages cannot explain the whole process of radiation-induced pulmonary injury development,it may play an important regulatory role during this process.