Early administration of IL-6RA does not prevent radiation-induced lung injury in mice

Abstract

Background: Radiation pneumonia and subsequent radiation lung fibrosis are major dose-limiting complications for patients undergoing thoracic radiotherapy. Interleukin-6 (IL-6) is a pleiotropic cytokine and plays important roles in the regulation of immune response and inflammation. The purpose of this study was to investigate whether anti-IL-6 monoclonal receptor antibody (IL-6RA) could ameliorate radiation-induced lung injury in mice.

Methods: BALB/cAnNCrj mice having received thoracic irradiation of 21 Gy were injected intraperitoneally with IL-6RA (MR16-1) or control rat IgG twice, immediately and seven days after irradiation. Enzyme-linked immunosorbent assay was used to examine the plasma level of IL-6 and serum amyloid A (SAA). Lung injury was assessed by histological staining with haematoxylin and eosin or Azan, measuring lung weight, and hydroxyproline.

Results: The mice treated with IL-6RA did not survive significantly longer than the rat IgG control. We observed marked up-regulation of IL-6 in mice treated with IL-6RA 150 days after irradiation, whereas IL-6RA temporarily suppressed early radiation-induced increase in the IL-6 release level. Histopathologic assessment showed no differences in lung section or lung weight between mice treated with IL-6RA and control.

Conclusions: Our findings suggest that early treatment with IL-6RA after irradiation alone does not protect against radiation-induced lung injury.

Figure 1

Kaplan-Meier analysis of survival curves and body weights for IL-6RA- (white circle) and IgG control (black circle)-injected mice. (A) Survival curves. The p value was calculated with the log-rank test. Kaplan-Meier plots were calculated from data for 7 IL-6RA-treated mice and 8 nontreated mice. (B) Body weights. Data are presented as means + SD.

Figure 2

Effects of IL-6RA treatment in lungs of lethally irradiated IL-6RA (white square) and IgG control (black square) mice on radiation-induced increases in IL-6 (A) and SAA (B) production. Each bar represents the mean ± SD (n = 5 per group). Asterisks indicate statistical significance. Dotted line represents each from average value of non-irradiated mice + SD to average value of them -SD.

Figure 3

Effects of IL-6RA treatment on radiation-induced lung injury indices. (A) Lung weight after 21 Gy of single irradiation to whole thorax with (white square) or without (black square) IL-6RA treatment. (B) Hydroxyproline levels in lung homogenates obtained from IL-6RA injected mice (white square) or control (black square). Data obtained from 5 animals in each group are presented as means ± SD. Dotted line shows each from mean value of non-irradiated mice + SD to mean value of them -SD.

Figure 4

Histological analyses using H&E staining for irradiated murine lung tissue.

Figure 5

Histological analyses using Azan staining for irradiated murine lung tissue.