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pubmed:abstractText |
Glycocalicin (Gc) is the large, water soluble fragment, obtained by cleavage of one of the major membrane glycoproteins, GP Ib, of human platelets by means of the endogenous, calcium-dependent neutral protease (CNP) obtained from lysed platelets. GP Ib has been proposed as the receptor for von Willebrand factor (vWF) as well as for the Fc-receptor of the platelet surface. We have investigated, whether Gc was involved in a receptor function for aggregated human IgG, which is a powerful activator of platelets. Neither Gc nor asialo-Gc inhibited the stimulation of human blood platelets by bisdiazoniumbenzidine-aggregated human IgG (BDB-IgG). Moreover, platelets, after treatment with a crude preparation of CNP, which removes Gc, could be stimulated by BDB-IgG as well as or better than control platelets, but were unreactive with bovine vWF. We conclude that the Gc-moiety of GP Ib, which is involved in the bovine vWF binding site, is not the Fc-receptor on platelets. Thus, the inhibition, by human or rabbit IgG aggregates or monomeric rabbit IgG, of vWF-induced platelet agglutination, as reported by other authors, is either due to a steric effect resulting from a vicinal position of both receptors or involves the residual part of GP Ib after cleavage of Gc.
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