Cellular glycoconjugates and their potential endogenous receptors in the cerebral microvasculature of man: a glycohistochemical study

Protein-carbohydrate interactions are supposed to play a pivotal role in mediation of recognitive interactions, relevant to cellular interactions and transport. The brain microvasculature is the site of numerous cell-cell and cell-matrix recognitive interactions. Assuming carbohydrate-protein interactions play important physiological roles here, then specific carbohydrate-binding proteins should be prominent components of this microvasculature, in addition to the wealth of endogenous glycoconjugates reported by other authors. Human brain and brain tumor microvessels were analyzed histochemically for expression of endogenous sugar-binding proteins using a panel of biotin-conjugated, chemically glycosylated probes with specificities for alpha-/beta-D-galactosides and -D-glucosides, alpha-L-fucosides, alpha-D-mannosides, and beta-D-xylosides, and for expression of endogenous glycoconjugates using a panel of biotin-conjugated plant lectins with specificities for fucoside, galactoside, mannoside and glucoside moieties. Wax-embedded aldehyde- or Bouin-fixed tissues or acetone-fixed frozen sections were examined. Blood-brain barrier function was checked by ascertaining immunohistochemically the extravasation of serum albumin in these tissues. Microvessels in normal human brain tissues (with intact blood-brain barrier) contained abundant endogenous sugar-binding proteins with specificities for beta-galactosides, alpha-mannosides and beta-xylosides, and lesser amounts of proteins binding alpha-galactosides, alpha-fucosides and glucosides. Endogenous glycoconjugates bearing beta-galactoside, alpha-D-mannoside/alpha-D-glucoside or alpha-L-fucoside moieties were also abundant. In brain tumors (with defective blood brain barrier) the microvessels contained altered patterns of endogenous sugar-binding proteins, particularly noticeable in glioblastomas, in which there were notable alterations in galactoside-binding proteins in the microvessels.