Localization of human prealbumin in choroid plexus epithelium

Cerebrospinal fluid (CSF) is generally considered to be derived from plasma through a combined process of ultrafiltration and secretion by the choroid plexus. However, the mechanisms ultimately responsible for achieving the final protein composition of CSF are uncertain. Some proteins, in particular prealbumin, are present in quantities not easily explained by usual physicochemical considerations. To investigate the possibility of de novo synthesis by choroid epithelium, we have examined human choroid plexus and ependyma for the presence of prealbumin. Using the peroxidase-antiperoxidase method at the light and electron microscopic level, as well as immunofluorescence, we localized prealbumin in choroid epithelial cytoplasm on the endoplasmic reticulum and in association with the Golgi apparatus. Ependymal cells and stroma did not reveal immunocytochemical labeling. These findings indicate that the choroid plexus epithelium contributes to the final CSF composition by de novo protein synthesis.