BackgroundThe rejection following keratoplasty still is a leading cause of corneal transplantation failure.Studies showed that the interleukin-22 (IL-22), one of the effector molecules of T helper cell 17 (Th17) participated on the rejection after heart, liver and bone marrow transplantation.However, the effect of IL-22 on corneal graft rejection is not well understood.

ObjectiveThis study was to investigate the expression of IL-22 mRNA in the corneal grafts and the role of IL-22 in the immune rejection after corneal transplantation in rats.

MethodsSeventy-two Wistar rats were randomized into autologous keratoplasty group, allograft keratoplasty group and anti-rejection group, and other 4 normal Wistar rats served as normal control group.Autologous keratoplasty was operated on the Wistar rats of the autologous keratoplasty group, and allograft keratoplasty were carried out with the 24 SD rats as donors and 48 Wistar rats as recipients.Tobramycin and dexamethasone eye drops were topically administrated after autologous keratoplasty for 2 weeks in the anti-rejection group.The experimental eyes were examined by slit lamp microscope after surgery and graft survival was evaluated based on the rejection scoring criteria of Larkin.Intergroup accumulated survival rates of grafts were compared using Kaplan-Meier analysis.Histopathological examination of grafts was carried out in 5 and 14 days after operation respectively, and the related expression levels of IL-22 mRNA and aryl hydrocar-bon receptor (AhR) mRNA were carried out by real-time fluorescence quantitative PCR.The feeding and use of the experimental animals followed the Guangdong provincial regulations on the management of experimental animals.The experimental design was approved by the ethics committee of Southern Medical University.

ResultsThe median survival time of grafts in the allograft keratoplasty group was 10 days, and that in the anti-rejection group was 17 days, showing a significant survival extention in the anti-rejection group ( χ ²=16.442, P=0.000). Significant differences were found among the 4 groups in the related expression levels of IL-22 mRNA in both 5 days and 14 days after surgery (postoperative 5 days: F=2.44, P=0.00; postoperative 14 days: F=267.92, P=0.00), and the related expression levels of IL-22 mRNA were remarkably higher in the allograft keratoplasty group than those in the anti-rejection group at different time points (postoperative 5 days: 9.70±0.35 vs.0.46±0.21; postoperative 14 days: 23.12±1.89 vs.3.14±0.94 ) (both at P<0.05). The related expression levels of AhR mRNA in the grafts were considerably different among the 4 groups (postoperative 5 days: F=395.73, P=0.00; postoperative 14 days: F=942.37, P=0.00), and the expression levels were significantly elevated in the allograft keratoplasty group compared with the anti-rejection group at various time points (postoperative 5 days: 2.52±0.32 vs. 1.89±0.10; postoperative 14 days: 7.20±0.25 vs.2.60±0.17) (both at P<0.05).

ConclusionsThe expression level of IL-22 RNA up-regulates in the grafts with immuno-rejection.Topical administration of tobramycin and dexamethasone eye drops inhibits the rejection after keratoplasty.AhR plays a regulative role to the expression of IL-22 in rats after keratoplasty.