Demonstration of a marked reduction in the amount of GPIIb in most type II patients with Glanzmann's thrombasthenia

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Abstract
Summary. In this study employing a sensitive immunoblot assay, we have characterized GPIIb and GPIIIa in thrombasthenic platelets from seven type II and four type I patients from 10 unrelated families. The amounts of GPIIb and GPIIIa were both markedly reduced in all these patients, and abnormal molecular weight GPIIb or GPIIIa was not detected. In all of four type I patients the amount of GPIIb was much lower than that of GPIIIa. In this study, however, we found that the amount of GPIIb was also lower even in six out of seven type II patients. Immunodepletion of patients’platelets with AP2 (a monoclonal antibody specific for the GPIIb‐IIIa complex), AP3 (specific for GPIIIa) or AMF7 (specific for αv) further confirmed that GPIIIa existed in excess, and demonstrated that excess GPIIIa were mostly in free form and not associated with GPIIb or αv. The reduction of GPIIb may represent an abnormality in GPIIb processing in these type II and type I thrombasthenic platelets. It remains unclear whether these two subgroups represent distinct categories.