Interleukin-18: A Novel Participant in the Occurrence, Development, and Drug Therapy of Obliterative Bronchiolitis Postlung Transplantation

Abstract

Background. Obliterative bronchiolitis (OB) was a main cause of deterioration of long-term prognosis in lung transplant recipients after the first posttransplant year. Proinflammatory cytokine interleukin-18 (IL-18) strengthened both the natural immunity and acquired immunity and played an important role in organ transplantation. The roles of IL-18 in the occurrence, development, and drug treatment of OB remained unclear. Methods. Small interfering RNA (siRNA) against mouse IL-18 (siRNA-IL-18) was used to silence IL-18 expression. Mouse heterotopic tracheal transplantation model was used to simulate OB. Recipient mice were divided into 5 groups ( $n=12$ ) according to donor mouse strains and drug treatment: isograft group, allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group. The luminal obliteration rates were pathological evaluation. Expressions of cytokines and MMPs were detected by real-time PCR, western blot, and enzyme chain immunosorbent assay (ELISA). Results. The luminal obliteration rates of IL-18 of the siRNA-IL-18 group were significantly lower than those of the negative control group ( $p<0.0001$ ) and the blank control group ( $p=0.0002$ ). mRNA expressions of IFN-γ, EMMPRIN, MMP-8, and MMP-9 of the siRNA-IL-18 group were significantly lower than those of the negative and blank control groups. No tracheal occlusion occurred in grafts of the isograft group. The rates of tracheal occlusion of the allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group were $72.17\pm 4.66$ %, $40.33\pm 3.00$ %, $38.50\pm 2.08$ %, and $23.33\pm 3.24$ %, respectively. There were significant differences between the 4 groups ( $p<0.001$ ). Serum protein expressions of IL-17 ( $p=0.0017$ ), IL-18 ( $p=0.0036$ ), IFN-γ ( $p=0.0102$ ), and MMP-9 ( $p=0.0194$ ) were significantly decreased in the allograft+tacrolimus+azithromycin group compared to the allograft group. Conclusions. IL-18 could be a novel molecular involved in the occurrence, development, and drug treatment of OB.