Cytoskeleton in normal and reactive human retinal pigment epithelial cells

The cytoskeleton of normal and reactive retinal pigment epithelium (RPE) was analyzed immunohistochemically in five light microscopically normal formalin-fixed, paraffin-embedded human eyes enucleated because of orbital tumor and in 44 eyes with a uveal melanoma. In 26 eyes, the RPE overlying the tumor was morphologically normal or atrophic; in 18 eyes, hyperplastic changes were present. Normal RPE cells lacked vimentin, but it was present in 35 of 44 eyes with uveal melanoma. Antibodies that recognize cytokeratins CK8 and CK18 labeled normal and reactive RPE cells in all specimens. Although CAM 5.2 and CY-90 detected RPE cells strongly and quantitatively, clones CK5, KS-B17.2, and pancytokeratin antibody lu-5 reacted weakly and did not label some specimens. Immunoblotting supported the presence of CK8 and CK18 in human RPE. Normal RPE cells did not express other simple epithelial cytokeratins, but both atrophic and hyperplastic reactive RPE cells were labeled with antibodies to CK7 or CK19 in 24 of the 44 eyes. Hyperplastic proliferating RPE cells that formed subretinal membranes reacted positively for alpha-smooth muscle actin in 13 of 18 eyes. Antibodies to CK8 and CK18 are valuable markers of normal and reactive human RPE cells, but a panel of reagents is necessary to document reactive changes in the cytoskeleton. Acquisition of alpha-smooth muscle actin by human RPE cells may be related to their ability to form periretinal membranes and contribute to intraocular proliferative diseases.