The intermediate filament
protein types of normal choroid plexus and ependymal tissue and their putative
tumors were investigated. In normal human choroid plexus tissue, but not in ependyma,
keratin could be demonstrated immunohistochemically. By immunoblotting,
keratins 8, 18, and 19 were found, but
glial fibrillary acidic protein (GFAP) was absent. In mouse and rat, choroid plexus epithelium and ependymal lining cells were
keratin-positive. In addition, many ependymal cells were
vimentin-positive.
Keratin was immunohistochemically found in three of four
choroid plexus papillomas, two of two choroid plexus
carcinomas, and the lining cells of three neuroepithelial
cysts. GFAP-positive cells were present in some
choroid plexus tumors. In contrast, none of the eight
ependymomas contained
keratin, but all were strongly positive for GFAP. The results show that choroid plexus lining cells and
choroid plexus tumors have true epithelial characteristics in their cytoskeleton, in contrast to
ependymomas, which do not show
keratin positivity but show glial filaments, as would be seen in astrocytic
tumors.