HETEROGENEITY OF MICROFIBRILS - ROLE OF T HROMBOSPONDIN-MICROFIBRILS IN THE THROMBOGENICITY OF THE SUBENDOTHELIUM

We report the results of an immunogold electron microscopical analysis on microfibrils from the arterial subendothelium showing that thrombo spondin (TSP) is present on 40 nm-diameter structures joining 8-10 nm- diameter microfibrils containing fibrillin. They differ from type VI c ollagen which forms 3-5 nm-diameter microfibrils. TSP containing micro fibrils (TSP-MF) extracted from human umbilical arteries did not conta in fibrillin or type VI collagen. Blood platelet interactions with TSP -MF were not modified by anti-fibrillin or anti-type VI collagen antib odies. In situ, uWF war bound to cross-linked microfibrils, at the lev el of their 40 nm junction, and a double-labeling with the anti-thromb ospondin and and-uWF antibodies was observed. In vitro, uWF binding to TSP-MF was not inhibited by anti-fibrillin or anti-type VI collagen a ntibodies. These results suggest a structural and functional heterogen eity of microfibrils and emphasize the role of TSP-MF in the thromboge nicity of the subendothelium.