Expression of interleukin-17A in lung tissues of irradiated mice and the influence of dexamethasone

Abstract

Purpose: To investigate the expressions of IL-17A in different phases of radiation-induced lung injury and the effect of dexamethasone.

Methods: The thorax of C57BL/6 mice was irradiated with 15 Gy rays. Mice from dexamethasone-treated group were injected intraperitoneally with dexamethasone (0.42 mg/kg/day) every day for the first month after irradiation. IL-17A in lung tissues was detected by immunohistochemistry. IL-17A, TGF-β1, and IL-6 in bronchoalveolar lavage fluid were detected by ELISA. Lung inflammation and collagen deposition were observed by H&E and Masson methods. The degree of alveolitis and fibrosis was judged according to scoring.

Results: IL-17A expression was appreciable at 1 week, peaked at 4 weeks, and subsequently declined at 8 weeks after irradiation. IL-17A was reduced after dexamethasone application at all the observation periods. Dexamethasone also inhibited expressions of TGF-β, IL-6, and TNF-α in bronchoalveolar lavage fluid. Moreover, dexamethasone attenuated the severity of lung injury by reducing the infiltration of inflammatory cells and collagen deposition. Terms of survival and the time of death in mice of treatment group were postponed and survival rate was improved.

Conclusions: IL-17A plays an important role in the process of radiation-induced lung injury. And dexamethasone may provide a protective role in lung injury induced by radiation.

Figures

Figure 1

IL-17A expression in lung tissue detected by immunohistochemical method. It can be seen that cytoplasmic staining of RT group gradually deepened from the 1st week, peaked in the 4th week, declined in the 8th week, and reached a lower level in the 16th week but slightly higher than Sham group (Table 1, Figure 1). DXM application reduced mice IL-17A expression of RT group at indicated time points. The position of black arrows points to IL-17A-positive cells.

Figure 2

Expression of IL-17A in BALF at the indicated time points. The mice were sacrificed at the time of 1, 4, 8, and 16 weeks after irradiation, and BALF was collected for analysis of IL-17A contents. The contents of IL-17A in the BALF were analyzed by ELISA kits. Radiation stimulated an increase in the levels of IL-17A, but dexamethasone attenuated the IL-17A level in BALF. #P < 0.05 versus RT group at corresponding time points. Data are presented as the mean ± SD (n = 8/group/experiment).

Figure 3

Representative samples of pathological changes in Sham group (a), (d), RT group (b), (e), and RT + DXM group (c), (f). Dexamethasone attenuates radiation-induced pneumonitis and pulmonary fibrosis. Mice were administered dexamethasone (0.42 mg/kg/day) intraperitoneally on days 1 to 30 after irradiation. Mice were sacrificed on specific time point, and lung tissue was fixed and excised into tissue sections for the detection of pulmonary inflammation and collagen deposition by H&E or Masson staining. In (a), (b), and (c), dexamethasone promoted the resolution of the radiation-induced pulmonary inflammation in the 4th week as indicated by H&E staining of the lung sections. (a) Sham group. (b) RT group, significant radiation pneumonitis and inflammatory cell infiltration (black arrows position). (c) RT + DXM group, inflammatory cell infiltration was significantly reduced without significant leakage. In (d), (e), and (f), dexamethasone promoted the resolution of the radiation-induced pulmonary fibrosis in the 16th week as indicated by Masson staining of the lung sections. (d) Sham group. (e) RT group, fibrosis stage, a large number of collagen depositions (black arrow position). (f) RT + DXM group, collagen deposition was significantly reduced compared with RT group; the alveolar structure is relatively intact.

Figure 4

Content of lung hydroxyproline was determined by alkaline hydrolysis assay. Hydroxyproline content was significantly higher at 16 weeks than Sham group. Dexamethasone reduced lung hydroxyproline content which can reflect the content of collagen. *P < 0.001 versus RT group and Sham group at corresponding time points. Data are presented as the mean ± SD (n = 8/group/experiment).

Figure 5

Effect of dexamethasone on the survival of mice after irradiation. C57BL/6J mice were treated with a single dose (15 Gy) to the entire thorax. Dexamethasone treatment increased the survival rates of irradiated mice. The survival rates at 180 days in Sham (n = 10), RT group (n = 20), and RT + DXM group (n = 20) are 100.0%, 35.0%, and 70.0%, respectively (RT versus RT + DXM group, P = 0.0323). The survival rate was analyzed using the Kaplan-Meier method.