Inhibition of platelet-aggregating activity in thrombotic thrombocytopenic purpura plasma by normal adult immunoglobulin G.

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of autologous and homologous platelets, and effect which was inhibited by normal plasma. IgG purified from seven normal adults at a concentration of 0.7 mg/ml completely inhibited the platelet aggregation induced by plasma obtained from two TTP patients with active disease. The inhibition of platelet aggregation by human adult IgG was concentration dependent, and the inhibitory activity of human IgG was neutralized by rabbit antihuman IgG. Fab fragments inhibited the TTP plasma-induced platelet aggregation as well as intact IgG, whereas Fc fragments had no effect. Platelet aggregation caused by ADP, collagen, epinephrine, or thrombin was not affected by purified human IgG. The prior incubation of IgG with TTP plasma caused a significantly greater reduction of platelet aggregation by TTP plasma than that of IgG and platelet suspension, suggesting that the IgG inhibits TTP plasma-induced platelet aggregation through direct interaction with platelet aggregating factor in TTP plasma. IgG obtained initially from five infants and young children under the age of 4 yr did not possess any inhibitory activity. When one of the children reached 3 yr of age, his IgG inhibited the aggregation induced by one TTP plasma, but not that caused by another plasma. The IgG procured from the same boy at 4 yr of age inhibited the aggregation induced by both TTP plasmas. The IgG purified from the TTP plasma during active disease failed to inhibit the aggregation caused by the same plasma. After recovery, however, the IgG effectively inhibited aggregation. These observations suggest that platelet-aggregating factors present in the TTP plasma are heterogeneous in nature and that the IgG present in the normal adult plasma, which inhibits the TTP plasma-induced platelet aggregation, may be partially responsible for the success of plasma infusion therapy in TTP.

Purification and some properties of a protein obtained from normal human plasma which inhibits the platelet aggregation induced by thrombotic thrombocytopenic purpura plasma.

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of washed human platelets, which was inhibited by preincubation with normal plasma. Using salt fractionation, ion exchange chromatography, and preparative agarose gel electrophoresis, we purified a protein from normal plasma which inhibited the platelet aggregation caused by TTP plasma. On SDS polyacrylamide gel, the purified inhibitor gave a single band with a M.W. of 150,000. The antiserum against the purified protein neutralized the activity of the inhibitor and formed an identical precipitin line against normal and TTP plasma.

Cross-linking of actin and fibrin by fibrin-stabilizing factor.

Fibrin-stabilizing factor is known to cross-link fibrin monomers. This study was undertaken to explore whether a similar interaction might occur between actin and fibrin. Purified actin and fibrinogen were labeled with 131I and 125I, respectively. The interaction of actin and fibrin, under different conditions, was evaluated by gel electrophoresis. The data show that actin and fibrin are cross-linked in the presence of fibrin-stabilizing factor.

Isolation and properties of a low molecular weight antiplasmin of human blood platelets and serum.

A low molecular weight antiplasmin has been detected in human blood platelets. The antiplasmin is dialysable and a similar material is present in normal plasma. A simple method for rapid isolation of the antiplasmin based on ultrafiltration is described. The inhibition of plasmin by these materials under different conditions has been studied. In the ultracentrifuge, both antiplasmins showed a single broad peak with an approximate sedimentation coefficient of 0.5S. Paper chromatography and paper electrophoresis indicated the isolated material to be heterogeneous. The individual components were isolated by paper chromatography and the antiplasmin activity was measured by the fibrin plate method. Preliminary studies on the fraction with maximal antiplasmin activity suggest that the inhibitory effect might be due to enzyme-inhibitor complex formation. Based on the present data, it is concluded that the platelet antiplasmin and the serum antiplasmin are very similar. This antiplasmin material may be useful in fibrinolytic therapy.