Choroid plexus as a barrier to immunoglobulin delivery into cerebrospinal fluid

The concentration of gamma globulins is greatly increased in the cerebrospinal fluid (CSF) during inflammatory and degenerative disorders of the central nervous system (CNS). The mechanism by which immunoglobulins enter the CSF under normal conditions is unknown. The extent of participation of the blood-brain barrier in protein delivery to the CSF is unclear, although the choroid plexus is known to have primary responsibility for the formation and movement of certain proteins into the CSF. To investigate the role of the choroid plexus in immunoglobulin delivery to the CSF, the authors evaluated rat brain tissue by light and electron microscopic immunohistochemical technique using the peroxidase technique of immunoglobulin (Ig)G and IgA detection. Peanut agglutinin was used to identify macrophages, cells known to have important immune functions and which have been reported as a normal component of the choroid plexus. Antisera to IgG' and IgA demonstrated diffuse surface staining of the choroidal epithelial cells with light and electron microscopy; the cytoplasm and nuclei did not contain immunoglobulins. Macrophages were not present in the choroid plexus, in contrast to previous reports. The results demonstrate that immunoglobulins do not enter the CSF via the choroid plexus, unlike other proteins in similar concentrations in the CSF. In addition, macrophages are shown to be an insignificant component of the plexus, thereby further diminishing the likelihood of participation-of the choroid plexus in the regulation of immunoglobulin entry into the CNS under normal conditions.