The local and systemic secretion of the pro-inflammatory cytokine interleukin-6 after transplantation of retinal pigment epithelium cells in a rabbitmodel

The rejection of retinal pigment epithelium (RPE) allografts is one of the major problems for long-term success after retinal transplantation. However , the details of the immunological interactions in the subretinal space aft er transplantation are still unknown. The aim of our study was to investiga te the role of IL-6 in the rejection process in the subretinal space and to use IL-6 monitoring for a possible early sign of rejection after transplan tation of allogeneic RPE cells. For this we used a model of transplanting p igmented RPE cells, either activated in vitro with 1000 U/ml interferon-gam ma (IFN-gamma) for 8 days or non-activated, into 30 albino rabbits. The IL- 6 was investigated 3, 5, 7, 9 and 14 days after transplantation. Additional ly, sham operated animals and the untreated eyes served as controls. At the se time-points the animals were killed, the liquid in the vitreous cavity a nd serum was collected and the IL-6 present in these samples was quantified with an enzyme-linked immunosorbent assay. Under these conditions, IL-6 wa s detected in the liquid of the vitreous cavity and in the serum of all RPE -transplanted rabbits. In the group receiving activated RPE two cytokine pe aks were measured, 3 and 7 days after transplantation in the vitreous cavit y. In non-activated grafts, a maximum was detected on the 5th day after tra nsplantation. Generally, the detected quantity of IL-6 depended on the host status and on the phase of rejection. No significant changes were seen in the sera from either group. Possibly, the host RPE cells are the main sourc e of this interleukin in the transplantation area. The measuring of IL-6 in the rejection model suggests that it plays a role in the immune cascade in the subretinal space.