Choroid Plexus and Immune Response of the Brain - New Insights to Neuroimmune Biology - page 68

Figure 4.1 Photograph of freshly isolated neonatal porcine CP. Note the epithelial cells on the
top portion overlying a dense, highly vascularized stroma.
The lined epithelial cells are connected by tight junctions that physically restrict the
movement of substances between blood and cerebrospinal fluid, fittingly called the
blood-CSF barrier ( Figure 4.2(B) ). The complex configuration of the CP is further
revealed by the capillaries of the vascular bed, which are large, with thin fenestrated
endothelial walls and bridging diaphragms overlying the fenestrations. This special-
ized CP structure resembles that of the gastrointestinal tract, characterized by succes-
sively smaller folds that provide increased surface area and thereby enhance mixing
of fluids. The abundance of organelles may be related to the CP's multiple secretory
functions, such as metabolism and protein synthesis ( Figure 4.2(C) ).
Foremost among the many established functions of the CP is CSF production [6] .
The importance of this CP role cannot be understated, in view of the fact that
humans require maintenance of CSF volume at about 80-150 ml, requiring new
CSF production at a rate of approximately 500 ml/day. The blood-CSF barrier is
critical to CSF production, in that CSF is generated primarily by active secretion,
with water entering the CSF from the blood along an osmotic gradient or via spe-
cific water channels such as aquaporin. The barrier function of CSF containment
transfers to the CP as CSF shifts from the vasculature to the epithelium, where tight
junctions form between the epithelial cells to confer the permeability properties of
the individual cells [7] ; this further exemplifies the prominent role of the CP in CSF
production.
An equally major role of the CP in brain functioning relates to guarding the CSF
from, and monitoring for, the presence of noxious compounds or potentially damaging