[Plasma fibronectin].

Abstract

Fibronectin (FN) is a glycoprotein (disulfite-bonded dimer of 200 to 220 Kd submits) found in a soluble form in blood (concentration 250--500 microg/ml), it can be removed from it by cryoprecipitation and affinity chromatography on gelatin or heparin-agarose. It is also found in an insoluble fibrillar form as a component of connective tissue matrix like collagen, proteoglycans... FN fundamentally forms molecular complexes with collagen, fibrinogen or fibrin, heparin, activated factor XIII, bacteria, cellular membranes..., these various proteins binding with now well known functional "domains" on subunits. Thus FN mediates adhesion of cells to cells as well to biomaterials or tissue, cell migration and chemotactic activity, tissue stromal organization... The transformed cultured cells in presence of oncogen virus loose ability to secrete FN which contribute to their invasive tendency. FN also interacts with hemostatic and fibrinolytic systems, as component of the subendothelium (secreted, like Willbrand factor, by endothelial cells) and of platelet alpha-granules released by stimulated platelets. FN could then provoke platelet spreading on the subendothelium surface after collagen-platelet adhesion, triggered by Willebrand factor, has happened. FN is a part of the fibrinous clot. It participates in anchorage of the clot to subendothelium and mediates its colonisation by fibroblasts, first step to wound reparation. Lastly FN probably has an important role in organism defence. It acts as a non-immunological opsonin, promoting phagocytosis by RES macrophages of bacteria, cellular or fibrin fragments, immune complexes... present in blood. Plasmatic FN concentration is strongly decreased in several ill patients following major trauma, extensive burns, shock, sepsis, with or not evidence of DIVC, of respiratory distress... SABA and various other authors have obtained good results after injections of FN (as cryoprecipitates or concentrated fractions). It is yet necessary to confirm therapeutic role of FN.