Objective To investigate the effects of normal mouse serum (NMS) on radiation-induced lung injury (RILI) in mice.

Methods Radiation pneumonitis models were established by whole-lung irradiation with 13 Gy, and radiation-induced pulmonary fibrosis models were established by right-lung irradiation with 17 Gy in mice. Twenty-four mice were assigned through stratified randomization into control, serum, irradiation, and irradiation+serum groups, with 6 mice in each group. Mice in the serum and irradiation+serum groups received intravenous injections of 100 μl of NMS via the tail vein after irradiation, whereas mice in the control and irradiation groups received 100 μl of normal saline via the same route. Injections were administered every other day for a total of eight doses. Tissue and blood samples were collected at 1.5 and 7 months post-irradiation. Levels of inflammatory factors in mice serum and lung tissue were quantified through enzyme-linked immunosorbent assay kit. Lung morphological changes and collagen deposition were assessed through hematoxylin–eosin and Masson′s trichrome staining. The expression levels of fibrosis-related genes were detected by quantitative reverse transcription polymerase chain reaction, whereas the expression levels of corresponding fibrosis-associated proteins were evaluated through immunohistochemistry and Western Blot analysis. The comparison between two groups of measurement data was conducted using t-test.

Results The lung organ coefficient in the irradiation+serum group was significantly lower than that in the irradiation group ((0.766±0.076) % vs. (0.649±0.050) %) 1.5 months after 13 Gy whole-lung irradiation, and the difference was statistically significant (t=2.626, P<0.05). The levels of pneumonia-related inflammatory factors, transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α), interleukin (IL)-1α, and IL-6 in the supernatant of mice lung tissue decreased ((457.100±46.900) pg/ml vs. (382.500±24.700) pg/ml; (426.200±56.250) pg/ml vs. (349.600±41.830) pg/ml; (16.680±1.015) pg/ml vs. (14.550±0.523) pg/ml; (40.650±4.345) pg/ml vs. (32.830±3.640) pg/ml); the levels of TGF-β, TNF-α, IL-1α, and IL-6 in the serum also decreased ((482.800±41.190) pg/ml vs. (401.900±53.980) pg/ml; (492.300±38.690) pg/ml vs. (403.500±39.990) pg/ml; (18.740±2.172) pg/ml vs.(15.83±1.028) pg/ml; (41.920±2.865) pg/ml vs. (32.980±3.193) pg/ml), and the differences were statistically significant (t=2.464–5.104; all P<0.05). Furthermore, compared with the irradiation group, the pathological manifestations of collagen deposition and morphological alterations in the right lung tissue of the irradiation+serum group were markedly improved 7 months after 17 Gy irradiation. The expression levels of fibrosis-related genes, including Mmp2, fibronectin, Mcp1, TNF-α, Col1a1, and Mmp13 (1.862±0.456 vs. 1.240±0.245; 5.314±2.022 vs. 2.681±1.115; 3.123±0.573 vs. 1.608±0.283; 1.975±0.365 vs. 1.192±0.352; 2.646±0.551 vs. 1.473±0.677; 2.492±0.444 vs. 1.136±0.475) and the expression levels of fibrosis-related proteins Col1a1 and α-SMA (2.732±0.612 vs. 1.433±0.282; 1.888±0.174 vs. 1.220±0.372) were significantly decreased, and the differences were statistically significant (t=2.550–5.236; all P<0.05).

Conclusions NMS can effectively alleviate the severity of radiation pneumonia and radiation pulmonary fibrosis in mice, demonstrating a certain therapeutic effect for RILI. Early intervention during the early phase of radiation pneumonitis may effectively reduce and delay the progression of radiation-induced pulmonary fibrosis.