Purpose: The present study focuses on the role of CD81, the target of the anti-proliferative antibody (TAPA), in the regulation of the growth of retinal pigment epithelium (RPE).
Methods: RPE of 8-day-old rat pups was cultured. The level of CD81 in the cultures was defined by immunoblot methods, and the distribution of the protein was examined using indirect immunohistochemical methods. In addition, the effects of the antibody binding were tested in culture.
Results: CD81 was found in all layers of the normal retina with a distinct absence of labeling in the inner and outer segments of the photoreceptors. Based on the authors' original immunohistochemical analysis, it was difficult to determine whether CD81 was expressed by RPE. By examining cultures of RPE it was demonstrated that CD81 was expressed on the surface of these cells and that it was concentrated at regions of cell-cell contact. Indirect immunohistochemical methods using a peroxidase-labeled secondary antibody in albino mice revealed heavy labeling of the RPE in the intact eye. When the AMP1 antibody (directed against the large extracellular loop of CD81) was added to cultured RPE, the mitotic activity of the cells was depressed.
Conclusions: CD81 was found in the normal rat retina. Previous studies demonstrated that CD81 was expressed in retinal glia, the Müller cells that span the thickness of the retina, and astrocytes found in the ganglion cell layer. The present study demonstrated that CD81 was also expressed by RPE. The dramatic effects of the AMP1 antibody and the location of CD81 at regions of cell-cell contact support the hypothesis that this molecule is part of a molecular switch controlling contact inhibition.