Activation of MAP kinases during progression of radiation-induced pneumonitis in rats

Radiation-induced pneumonitis is closely associated with the interplay of various stress-activated signals and immune responses related to the progression of lung injury. Mitogen-activated protein (MAP) kinase pathways play critical roles in the progression of inflammation via a cellular damage. Here, we examined the regional distribution of phosphorylated MAP kinases (p-JNK, p-ERK, and p-p38) in the progression of pneumonitis after exposure of a single dose irradiation with 10 Gy for 0, 4, and 8 weeks in rats. Also, we identified positive cells for these kinases using specific cell-type markers related to inflammation and type II pneumocyte. p-JNK was present abundantly in activated macrophages, CD8 ⁺T-cells, peribronchiolar smooth muscle cells, and weakly type II pneumocytes at 4 weeks or 8 weeks after irradiation. p-p38 and p-ERK was predominantly expressed in macrophages, CD4 ⁺ T-cells, fibrotic cells as well as present in various lung parenchymal cells including alveolar epithelial cells and type II pneumocytes. In conclusion, it is considered that MAP kinase pathways play a pivotal role in early damage of residual cells as well as in the long-term regulation of distinct inflammatory cells during the progression of radiation-induced pneumonitis.