Basement membrane type IV collagen molecules in the choroid plexus, pia mater and capillaries in the mouse brain

We investigated the differential distribution of basement membrane type IV collagen α chains in the mouse brain by immunohistochemistry using α chain-specific monoclonal antibodies. Subendothelial basement membranes were found to contain α1 and α2 chains. Basement membranes surrounding smooth muscle cells on blood vascular walls were immunoreactive for α1 and α2 chains but not for α5 and α6 chains. Interestingly, the pia mater contained a thin basement membrane which was positive for α1, α2, α5, and α6 chains, suggesting that glia limitans superficialis coheres basement membranes containing [α1(IV)]₂α2(IV) and [α5(IV)₂α6(IV) molecules. In contrast, capillaries always possessed thin basement membranes of [α1(IV)]₂α2(IV) molecules. Cerebrospinal fluid is produced through filtration of blood at the choroid plexus, where two distinct basement membranes were detected by anti-α1 and anti-α2 antibodies. The subendothelial basement membrane appeared to consist of [α1(IV)]₂α2(IV) molecules, whereas the subependymal basement membrane in the choroid plexus was strongly positive for α3, α4, and α5 chains, indicating that the filtering unit was composed of α3(IV)α4(IV)α5(IV) molecules. That the specific localizations of these molecules are shared by renal glomeruli and the choroid plexus leads us to hypothesize that the supramolecular network containing a3(IV) α4(IV)α5(IV) molecules may function as a permeability selective barrier.