The identification of cells comprising
epiretinal membranes is difficult because of the phenotypic changes that occur. Examination of intermediate filament
protein content by immunocytochemical analysis can help to identify some cells with altered ultrastructure but is not always definitive because altered expression of
intermediate filament proteins can also occur. To examine this issue further, the authors utilized a postembedding immunocytochemical technique with
epiretinal membranes in which they were able to double label for
keratin, a useful marker for identifying
retinal pigment epithelial cells, and
glial fibrillary acidic protein (GFAP), a useful marker for identifying glial cells. Nine of ten idiopathic
epiretinal membranes contained cells that labeled for GFAP and not
keratin. Two of these membranes also contained cells that labeled only for
keratin and one membrane contained cells that simultaneously labeled for both GFAP and
keratin. Other types of
epiretinal membranes had an equal participation by cells that expressed only GFAP or
keratin (12 of 17 membranes contained cells positive for
keratin; 13 of 17 contained cells positive for GFAP). Ten of 17 nonidiopathic membranes contained cells simultaneously expressing GFAP and
keratin, although they comprised only a minor subpopulation of the total number of cells present. These findings demonstrate that
keratin and GFAP are not mutually exclusive
intermediate filament proteins in cells of
epiretinal membranes and that, although each may provide a helpful adjunct for cell type identification, neither is an absolutely specific marker.