Il-17 Produced By Non-T Cell Leukocytes Targets Late-onset Cornea Allograft Rejection

Abstract

Purpose: : The role that IL-17 plays in corneal allograft rejection has been the subject of several recent studies. However these studies have not conclusively determined a role for this cytokine during rejection. Consequently, we decided to evaluate IL-17 during both early-onset rejection (2-5 weeks postoperative) and late-onset rejection (>6weeks postoperative).

Methods: : Donor corneas (C57BL/6) were grafted orthotopically onto BALB/c recipients. Corneas, draining lymph nodes and spleen were removed at various times and subjected to Bio-Plex analysis to determine the levels of Th1 and Th17 cytokines. Similarly, immuofluorescent analyses were performed on grafts to determine the phenotype of infiltrate cells and the cytokines they produced. We also isolated cells from LNs and spleens to perform intracellular cytokine analysis for IL-17 and IFN-γ by flow cytometry. Finally we tested the effect of neutralizing IL-17 during early-onset rejection.

Results: : We did not observe any significant increase of IL-17 at any time in mice undergoing acute early-onset rejection. However, we did note a vigorous upregulation of IL-17 in corneas which were undergoing late-onset rejection. In contrast IFN-γ expression was slightly elevated during early-onset rejection but not at later time points, while intracellular cytokine staining of LN cells did not reveal any increases in either IL-17⁺ or IFN-γ⁺ cells at any time points evaluated. Surprisingly the IL-17⁺ cells did not express T cell markers but were Gr-1⁺ suggesting that they might be granulocytes or monocytes. Finally, treatment of mice with anti-IL-17 during early onset rejection did not result in any changes in rejection frequency or kinetics of rejection.

Conclusions: : Our data do not support the notion that IL-17 plays a significant role during early onset rejection, which likely is mediated by other proinflammatory cytokines such as IFNγ. In contrast, the fact that there is a significant increase in IL-17 production and the development of Gr-1⁺, IL-17⁺ cells during late-onset rejection suggests that this cytokine might be important for this form of corneal allograft rejection. The underlying mechanism responsible for late-onset corneal allograft rejection, which is a clinically important problem, is not known. Our data suggest that the underlying pathogenesis might be the mechanism of chronic allorejection and chronic endothelium dysfunction may in part be mediated by IL-17.

Keywords: cornea: basic science • transplantation • cytokines/chemokines