PLASMA PROTEIN REQUIREMENTS FOR HUMAN PLATELET AGGREGATION

Summary 1. Three cationic proteins–fibrinogen, Hageman factor, and gamma globulin-are all capable of restoring aggregation capability of washed human platelets. 2. The aggregation-restoring effect of gamma globulin is inhibited by acetic proteins in subfractions of Cohn fraction IV and fractions V and VI. 3. Artificial enhancement of the net negative charge of plasma proteins through acylation produces derivatives capable of inhibiting platelet aggregation in platelet-rich plasma. 4. It is proposed that the rate of platelet aggregation is regulated in part by the equilibrium between cationic and anionic proteins in plasma and on the platelet membrane surface. This concept finds support in the following clinical observations. 5. Platelets of Glanzmann's thrombasthenia incapable of aggregation fail to adsorb cationic proteins to their surface. 6. Purified myeloma proteins from patients with platelet dysfunction do not restore aggregation of normal washed platelets and inhibit the aggregation-restoring effect of normal IgG. 7. Enhanced platelet aggregation demonstrable in chronic, active glomerular disease may result from the loss in the urine of plasma proteins normally inhibiting platelet aggregation.