Autoantibodies in a Patient with Cone-rod Degeneration Triggers Death of Retinal Ganglion (RGC-5) Cells by Complement Mediated Lysis

Abstract

Abstract: : Purpose: Autoantibodies may directly contribute to pathologic processes. We have recently identified anti-retinal antibodies in a patient with progressive retinal degeneration. In this study we evaluated mechanisms by which these anti-retinal antibodies induce retinal cell death. Methods: Using immunohistochemistry, sera obtained from a patient with cone-rod degeneration were evaluated for the presence of anti-retinal antibodies. Both mouse and rat ocular tissues were used as substrates. Autoantibodies were further characterized using an immortalized rat retinal ganglion (RGC-5) cell line. Sera reactivity to RGC-5 cells was examined by immunofluorescent staining. The patient sera were then examined for toxicity to RGC-5 cells. First, cells were incubated with patient sera to determine if the sera were toxic to the cells. Second, IgG purified from the patient sera and normal human IgG were evaluated in a complement mediated cytotoxicity assay. CellTiter 96 Aqueous One Solution Cell Proliferation Assay (Promega, Madison, WI) was used to evaluate RGC-5 cell viability. Results: Staining of ocular tissue revealed that patient sera reacted with retinal ganglion cells and the inner nuclear layer. The sera were positive to a titer of 640. This patient had no significant past medical history and presented with symptoms of a progressive retinal disease with gradual loss of vision over five years. Immunofluorescent staining of RGC-5 cells with the patient sera were localized to the nuclei with a punctate pattern. Incubating RGC-5 cells with media containing 5% patient sera resulted in 50% cell death after 2 hours and 75% cell death after 6 hours. Media containing either 5% control human sera or 5% heat-inactivated patient sera or control human sera had no effect on RGC-5 cell viability. IgG purified from patient sera killed RGC-5 cells in a dose dependent manner when the cells were incubated with IgG and guinea pig complement. Cell death did not occur when cells were incubated with either patient IgG or guinea pig complement alone. Conclusions:Autoantibodies to retinal proteins were discovered in a patient with cone-rod degeneration. The antibodies reacted strongly to an antigen in the nuclei of retinal ganglion cells. In vitro these autoantibodies were able to cause retinal ganglion cell death by complement mediated lysis.

Keywords: autoimmune disease • retina: proximal(bipolar, amacrine, and gangli • retinal degenerations: cell biology