Ultrastructural localization of adhesion molecules in the healthy and inflamed choroid plexus of the mouse

The functional expression of vascular cell adhesion molecule-1 (VCAM-1), in tercellular adhesion molecule-1 (ICAM-1) and MAdCAM-1 in the choroid plexus is indicative of a role of this structure in the communication of the immu ne system with the central nervous system (CNS). In order to gain further i nsight into the possible functions of adhesion molecules expressed in the c horoid plexus, we investigated the exact ultrastructural localization of VC AM-1, ICAM-1 and MAdCAM-1 on semithin and ultrathin cryosections of the cho roid plexus of healthy mice and of mice suffering from experimental autoimm une encephalomyelitis (EAE). In the healthy choroid plexus VCAM-1 and ICAM- 1, but not MAdCAM-1, could be detected on the apical surface of the choroid plexus epithelial cells. During EAE, immunoreactivity for VCAM-1 and ICAM- 1 was dramatically increased. Additionally, apical expression of MAdCAM-1 w as observed on individual choroid plexus epithelial cells during EAE. At th e same time, VCAM-1, ICAM-1 or MAdCAM-1 were never present on the endotheli al cells of the fenestrated capillaries within the choroid plexus. The pola r expression of VCAM-1, ICAM-1 and MAdCAM-1 on the apical surface of choroi d plexus epithelial cells, which form the blood-cerebrospinal fluid barrier , implies a previously unappreciated function of this barrier in the immuno surveillance of the CNS.