Heparin-Associated Thrombocytopenia: The Effects of Various Intravenous lgG Preparations on Antibody Mediated Platelet Activation - A Possible New Indication for High Dose i.v. IgG

Abstract

SummaryThe immunologic type of heparin-associated thrombocytopenia (HAT) is caused by antibodies which activate platelets via the Fc-re- ceptor in the presence of polysulfated oligosaccharides. The antigen is formed by a releasable platelet protein (in many cases PF4) complexed to heparin. Since the role of GP Ilb/IIIa in platelet activation by HAT antibodies is controversial, we investigated platelet activation by antibodies related to HAT. We used normal platelets and platelets from a patient with Glanzmann’s thrombasthenia (GT) lacking GP Ilb/IIIa. Heparin and sera from patients with HAT stimulated GT platelets in the same manner as determined by 14C-serotonin release and the changes in phosphorylation of p20 and p47. Platelet activation could be inhibited by an anti FcRII monoclonal antibody (IV. 3, Fab-fragments), and by Fc-fragments, but not by F(ab’)2-fragments of human IgG. The effect of four different, commercially available preparations of intact i.v. IgG on the platelet activation by six HAT sera was investigated by 14C-seroto- nin release. The inhibitory effect was strongly dependent upon the manufacturing process. At a concentration of 20 mg/ml only IgG that had been subjected to low pH and traces of pepsin sufficiently inhibited platelet activation. IgG treated with polyethylenglycol or sulfitolysis was less effective, whereas beta-propiolactone-treated IgG almost completely lost the ability to inhibit platelet activation by antibodies related to HAT. We conclude that inhibition of GP Ilb/IIIa-fibrinogen interaction is insufficient for preventing platelet activation in HAT. This is, however, possible by high dose i.v. IgG, whereby inhibition of FcRII on platelets strongly depends upon the process by which the i.v. IgG preparation was manufactured.