Thrombotic Thrombocytopenic Purpura Patients Research Articles

Platelet-agglutinating protein P37 from a thrombotic thrombocytopenic purpura plasma forms a complex with human immunoglobulin G

We have previously reported the purification of a 37-kd platelet- agglutinating protein (PAP p37) from the plasma of a patient with thrombotic thrombocytopenic purpura (TTP) that was shown to be present in a subset of TTP patients. The platelet agglutination induced by PAP p37 has been shown to be inhibited by IgG from normal human adults and the same TTP patient after recovery. To elucidate the mechanism of inhibition of IgG, the interaction between PAP p37 and IgG was studied. The complex formation was demonstrated by the binding of fluid-phase IgG from normal adults and the same TTP patient after recovery to adsorbed PAP by using an enzyme-linked immunosorbent assay. The binding was specific, concentration dependent, and saturable. IgG purified from a 5-month-old baby and the same TTP patient during active disease did not form complex with PAP p37. The IgG covalently cross-linked to Sepharose 4B bound 125I-PAP p37 but not 125I-fibrinogen. Sucrose density gradient ultracentrifugation of a mixture of 125I-PAP p37 and IgG also revealed the fluid-phase complex formation with a sedimentation value of 19S. Complexes of molecular weight ranging from 180,000 to over 350,000 daltons were also detected by molecular sieve chromatography. The IgG that was bound to PAP p37 conjugated to Sepharose 4B inhibited the agglutination of washed platelets induced by TTP plasma containing PAP p37, whereas the IgG that was not bound to PAP p37 did not have a significant inhibitory effect. The complex formation between PAP p37 and specific IgG is likely to account for the in vitro inhibition of TTP plasma-induced agglutination and, at least partly, the in vivo successful treatment with specific IgG-containing normal plasma.

Platelet-Agglutinating Protein P37 From a Thrombotic Thrombocytopenic Purpura Plasma Forms a Complex With Human Immunoglobulin G

We have previously reported the purification of a 37-kd platelet-agglutinating protein (PAP p37) from the plasma of a patient with thrombotic thrombocytopenic purpura (TTP) that was shown to be present in a subset of TTP patients. The platelet agglutination induced by PAP p37 has been shown to be inhibited by IgG from normal human adults and the same TTP patient after recovery. To elucidate the mechanism of inhibition of IgG, the interaction between PAP p37 and IgG was studied. The complex formation was demonstrated by the binding of fluid-phase IgG from normal adults and the same TTP patient after recovery to adsorbed PAP by using an enzyme-linked immunosorbent assay. The binding was specific, concentration dependent, and saturable. IgG purified from a 5-month-old baby and the same TTP patient during active disease did not form complex with PAP p37. The IgG covalently cross-linked to Sepharose 4B bound 125I-PAP p37 but not 125I-fibrinogen. Sucrose density gradient ultracentrifugation of a mixture of 125I-PAP p37 and IgG also revealed the fluid-phase complex formation with a sedimentation value of 19S. Complexes of molecular weight ranging from 180,000 to over 350,000 daltons were also detected by molecular sieve chromatography. The IgG that was bound to PAP p37 conjugated to Sepharose 4B inhibited the agglutination of washed platelets induced by TTP plasma containing PAP p37, whereas the IgG that was not bound to PAP p37 did not have a significant inhibitory effect. The complex formation between PAP p37 and specific IgG is likely to account for the in vitro inhibition of TTP plasma-induced agglutination and, at least partly, the in vivo successful treatment with specific IgG-containing normal plasma.

Thrombotic thrombocytopenic purpura.

Platelet thrombus formation in small vessels is triggered by certain stimuli, including vascular injury, primary platelet agglutination, or both. The formation and dissolution of platelet thrombi is modulated by proteolysis, plasma factors, PGI2 synthesis and stability, and immune mechanisms. Some recent evidence now suggests that there is a subset of thrombotic thrombocytopenic purpura (TTP) patients possessing a specific platelet agglutinating factor that triggers the intravascular platelet agglutination. Identification and classification of TTP patients into subgroups with common triggering agents, and further clarification of the role of modifying factors will enable us to understand the disease better and to improve therapy.

Treatment of Three Patients of Thrombotic Thrombocytopenic Purpura with Plasma Exchange

Treatment of Three Patients of Thrombotic Thrombocytopenic Purpura with Plasma Exchange

Calcium-dependent cysteine protease activity in the sera of patients with thrombotic thrombocytopenic purpura

Plasma and serum from patients with thrombotic thrombocytopenic purpura (TTP) can cause activation and aggregation of normal human platelets in vitro. It is possible that this platelet-activating factor contributes to the disease. In this report we describe studies designed to identify the platelet-activating factor in TTP. Platelet activation by sera from 15 patients with TTP was inhibited by leupeptin, iodoacetamide, and antipain but not by phenylmethylsulphonylfluoride, epsilon-aminocaproic acid, soybean trypsin inhibitor, aprotinin, and D-phenylanyl-1-prolyl-1- arginine chloromethyl ketone. These studies suggested that the platelet- activating factor in TTP serum was a cysteine protease. We confirmed that a calcium-dependent cysteine protease (CDP) was present in the sera of each of the 15 patients when we used an assay based on the ability of CDP to proteolyse platelet membrane glycoprotein 1b (GP1b) and hence to abolish the ability of CDP-treated normal platelets to agglutinate in the presence of ristocetin and von Willebrand factor. This proteolytic activity was inhibited by EDTA, leupeptin, antipain, iodoacetamide, and by N-ethyl-maleamide (NEM) but not by the serine protease inhibitors. Activity was detected in 15 of 15 patients with TTP tested before therapy was begun. In contrast, no activity was detected in the serum of any of five of the TTP patients tested in remission or in any of the sera from 36 patients with thrombocytopenia and 423 nonthrombocytopenic controls. To look for in vivo CDP activity in patients with TTP, we studied platelets from two patients with acute TTP (drawn into acid-citrate-dextrose, NEM, and leupeptin). These platelets showed a loss of GP1b from the platelet surface. Both patients were also studied in remission: GP1b on the platelet surface had returned to normal. These studies provide evidence that CDP is present in the sera of patients with TTP, that it is specific to this disease, and that is is active in vivo as well as in vitro. We postulate that a disorder of CDP homeostasis plays a major role in the pathophysiology of TTP.

Calcium-Dependent Cysteine Protease Activity in the Sera of Patients With Thrombotic Thrombocytopenic Purpura

Plasma and serum from patients with thrombotic thrombocytopenic purpura (TTP) can cause activation and aggregation of normal human platelets in vitro. It is possible that this platelet-activating factor contributes to the disease. In this report we describe studies designed to identify the platelet-activating factor in TTP. Platelet activation by sera from 15 patients with TTP was inhibited by leupeptin, iodoacetamide, and antipain but not by phenylmethylsulphonylfluoride, epsilon-aminocaproic acid, soybean trypsin inhibitor, aprotinin, and D-phenylanyl-1-prolyl-1-arginine chloromethyl ketone. These studies suggested that the platelet-activating factor in TTP serum was a cysteine protease. We confirmed that a calcium-dependent cysteine protease (CDP) was present in the sera of each of the 15 patients when we used an assay based on the ability of CDP to proteolyse platelet membrane glycoprotein 1b (GP1b) and hence to abolish the ability of CDP-treated normal platelets to agglutinate in the presence of ristocetin and von Willebrand factor. This proteolytic activity was inhibited by EDTA, leupeptin, antipain, iodoacetamide, and by N-ethyl-maleamide (NEM) but not by the serine protease inhibitors. Activity was detected in 15 of 15 patients with TTP tested before therapy was begun. In contrast, no activity was detected in the serum of any of five of the TTP patients tested in remission or in any of the sera from 36 patients with thrombocytopenia and 423 nonthrombocytopenic controls. To look for in vivo CDP activity in patients with TTP, we studied platelets from two patients with acute TTP (drawn into acid-citrate-dextrose, NEM, and leupeptin). These platelets showed a loss of GP1b from the platelet surface. Both patients were also studied in remission: GP1b on the platelet surface had returned to normal. These studies provide evidence that CDP is present in the sera of patients with TTP, that it is specific to this disease, and that is is active in vivo as well as in vitro. We postulate that a disorder of CDP homeostasis plays a major role in the pathophysiology of TTP.

Studies Investigating Platelet Aggregation and Release Initiated by Sera From Patients With Thrombotic Thrombocytopenic Purpura

Abstract Many patients with thrombotic thrombocytopenic purpura (TTP) have a platelet aggregating factor in their serum that may be pathologically linked with the disease process. To help characterize the type of platelet aggregation and platelet release induced by the sera from seven TTP patients, we measured the ability of a variety of inhibitors of platelet function as well as the ability of monoclonal antibodies (MoAbs) against platelet glycoproteins to inhibit TTP sera-induced platelet aggregation and release. These results were compared with the ability of the same inhibitors to block platelet aggregation induced by ristocetin, collagen, ADP, thrombin, and IgG-immune complexes. Monoclonal antibody directed against platelet glycoprotein Ib totally inhibited ristocetin-induced aggregation and release but had no effect on aggregation and release induced by the TTP sera or by any of the other platelet agonists. However, the MoAb against glycoproteins IIb/IIIa inhibited aggregation and release caused by TTP sera as well as by collagen, thrombin, and ADP but had no effect on aggregation and release induced by ristocetin. The aggregating activity could be abolished by heparin but not by the serine protease inhibitor PMSF (1 mmol/L). And although monomeric human IgG and purified Fc fragments of IgG inhibited IgG-immune complex-induced aggregation and release, they had no effect on TTP sera-induced aggregation and release nor on aggregation and release induced by any of the other agonists. Consistent with these in vitro studies showing no effect of IgG were the in vivo observations that intravenous (IV) IgG was without effect when administered to three patients with TTP. This study indicates that although a von Willebrand factor (vWF)-rich preparation of cryoprecipitate enhances the in vitro platelet aggregation and release caused by sera from the seven TTP patients we studied, the pathway of aggregation and release is not via platelet glycoprotein Ib. Also the aggregating factor of TTP sera is not neutralized in vitro or in vivo by IgG.

Studies investigating platelet aggregation and release initiated by sera from patients with thrombotic thrombocytopenic purpura

Many patients with thrombotic thrombocytopenic purpura (TTP) have a platelet aggregating factor in their serum that may be pathologically linked with the disease process. To help characterize the type of platelet aggregation and platelet release induced by the sera from seven TTP patients, we measured the ability of a variety of inhibitors of platelet function as well as the ability of monoclonal antibodies (MoAbs) against platelet glycoproteins to inhibit TTP sera-induced platelet aggregation and release. These results were compared with the ability of the same inhibitors to block platelet aggregation induced by ristocetin, collagen, ADP, thrombin, and IgG-immune complexes. Monoclonal antibody directed against platelet glycoprotein Ib totally inhibited ristocetin-induced aggregation and release but had no effect on aggregation and release induced by the TTP sera or by any of the other platelet agonists. However, the MoAb against glycoproteins IIb/IIIa inhibited aggregation and release caused by TTP sera as well as by collagen, thrombin, and ADP but had no effect on aggregation and release induced by ristocetin. The aggregating activity could be abolished by heparin but not by the serine protease inhibitor PMSF (1 mmol/L). And although monomeric human IgG and purified Fc fragments of IgG inhibited IgG-immune complex-induced aggregation and release, they had no effect on TTP sera-induced aggregation and release nor on aggregation and release induced by any of the other agonists. Consistent with these in vitro studies showing no effect of IgG were the in vivo observations that intravenous (IV) IgG was without effect when administered to three patients with TTP. This study indicates that although a von Willebrand factor (vWF)-rich preparation of cryoprecipitate enhances the in vitro platelet aggregation and release caused by sera from the seven TTP patients we studied, the pathway of aggregation and release is not via platelet glycoprotein Ib. Also the aggregating factor of TTP sera is not neutralized in vitro or in vivo by IgG.

蛇毒を用いたプロテインＣ活性の測定 先天性プロテインＣ欠乏症，播種性血管内凝固症候群，血栓性血小板減少性紫斑病，糖尿病，肝障害およびワーファリン服用患者におけるプロテインＣ抗原との比較

Functional protein C (PC) activity (both anticoagulant and amidolytic) was measured using a specific PC activator extracted from the venom of Agkistrodon contortrix in 4 patients with hereditary PC deficiency, 37 with disseminated intravascular coagulation (DIC), 9 with thrombotic thrombocytopenic purpura (TTP), 8 with diabetes mellitus (DM), 8 with liver injury and 30 under long-term warfarin therapy. The results were compared with those obtained by an immunological assay (ELISA). In patients with hereditary PC deficiency, DIC and TTP, PC activity was closely related with PC antigen levels. Both functional and immunological PC were decreased in many patients with DIC, while most TTP patients had normal PC levels. Some DM patients had high PC antigen levels, and their PC activity was somewhat lower than the antigen levels. PC activity and antigen were decreased in patients with hepatic injury, but in some of them functional assays (especially anticoagulant assay) gave lower PC values than the immunoassay. During stabilized warfarin treatment, PC antigen and amidolytic activity were decreased in parallel, but a decrease in anticoagulant activity was more pronounced. In addition, only anticoagulant activity correlated significantly with thrombotest values.These results indicate that the measurement of PC activity is valuable for the assessment of the behavior of PC in various disease states. Only anticoagulat PC assay can evaluate the PC function in patients under oral anticoagulant therapy and in some patients with hepatic injury.

Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) is classically highlighted by a pentad of features: fever, hemolytic anemia, thrombocytopenia purpura, transient or permanent central nervous system signs, and renal disease. The antemortem diagnosis is reliant upon the multisystem clinical signs and symptoms in conjunction with severe hemolytic anemia and thrombocytopenia. Relapse is common within the first six months after initial presentation. Laboratory findings have been generally nonspecific per se, and antemortem tissue biopsy findings are frequently unrewarding. Recently, however, unusually large multimers of the Factor VIII:Ag molecule (von Willebrand protein) have been identified in the plasma of patients with TTP who have recovered from an acute attack. This observation is very important because it may lead to essential information on the nature of the inciting event in this devastating illness. The differential diagnosis includes several multisystem disease processes such as the hemolytic uremic syndrome, toxemia of pregnancy, systemic lupus erythematosus, subacute bacterial endocarditis, nonbacterial thrombotic endocarditis, immune thrombocytopenic purpura, and the postpartum renal failure syndrome. The hemolytic uremic syndrome, toxemia of pregnancy, and TTP may resemble each other, exhibit many overlapping features, and are probably related. The cause of TTP remains unknown; the overwhelming majority of cases occur in otherwise healthy people without any recognizable underlying illness. Since 1965 45 to 70% of patients survive, a significant improvement in contrast to the early 1900s when the mortality rate was greater than 90%. The most dramatic advance has been observed in therapeutics, namely the utilization of some mode of plasma therapy (either infusion alone or plasmapheresis followed by plasma infusion). Corticosteroids remain very important in the management of patients with TTP. Vincristine may be very helpful, but additional studies are needed. The efficacy of vinca alkaloids, chronic immunosuppressive therapy, and sple. nectomy remains undefined. At present there is very little, if any, evidence that antiplatelet agents, aspirin, and prostacyclin are beneficial to patients with TTP. Prompt diagnosis and vigorous aggressive therapy is critical for successful management of TTP patients.

7 Thrombotic Thrombocytopenic Purpura and the Haemolytic-Uraemic Syndrome: Evolving Concepts of Pathogenesis and Therapy

Thrombotic thrombocytopenic purpura (TTP) and the haemolytic-uraemic syndrome (HUS) are caused by platelet thrombi in the microcirculation (i.e. arterioles and capillaries) throughout the body (TTP) or predominantly in the kidneys (HUS). Plasma factors that induce intravascular platelet agglutination have been a focus of investigation into the pathogenesis of these disorders. Von Willebrand factor (vWF) multimeric forms that are larger than those present in normal plasma are found in the plasma of patients with the chronic relapsing form of TTP. These unusually large vWF multimers are similar to those produced by normal human endothelial cells, but never allowed into the normal circulation. Unusually large vWF multimers in chronic relapsing TTP patients are most apparent in plasma during remission. They disappear, presumably in the process of attaching to platelets and inducing the formation of platelet thrombi, during relapses in chronic TTP. The disappearance of the largest plasma vWF multimeric forms during acute episodes of non-relapsing TTP and HUS has also been seen. These syndromes may be the result of damage to systemic or renal endothelial cells. A cofactor which induces the attachment of large vWF multimers to platelets during episodes of TTP has recently been detected, but not yet characterized biochemically. The cryosupernatant (i.e. vWF-depleted) fraction of normal plasma contains an activity that converts, or potentiates the conversion of, unusually large vWF multimers to the somewhat smaller circulating vWF forms as the bloodstream. There is clinical evidence that an autoantibody may prevent the effect of this 'unusually large vWF depolymerase' in some chronic relapsing TTP patients. Transfusions of normal plasma or cryosupernatant as prophylaxis against, or therapy for, episodes of TTP may transiently provide this missing unusually large vWF depolymerase activity, as well as additional plasma proteins to bind and eliminate the vWF cofactor proposed as the inciting agent of TTP episodes. In some patients, partial removal of unusually large vWF multimers (and possibly the inciting vWF cofactor) by plasmapheresis may be required along with the transfusion of normal plasma or cryosupernatant, in order to control in vivo platelet agglutination. Plasma manipulation has greatly improved the survival of patients with relapsing and non-relapsing forms of TTP. Corticosteroids may also be beneficial. The effectiveness of ancillary measures (splenectomy, vinca alkaloids or other immunosuppressive drugs) is not precisely defined. There is no convincing evidence that aspirin, dipyridamole or PGI2 are helpful in TTP.(ABSTRACT TRUNCATED AT 400 WORDS)

Novel platelet-agglutinating protein from a thrombotic thrombocytopenic purpura plasma.

A novel platelet-agglutinating protein (PAP) was purified approximately 2,000-fold from the plasma of a patient with thrombotic thrombocytopenic purpura (TTP) by ammonium sulfate fractionation, DEAE-Sephacel and concanavalin A-Sepharose chromatographies. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with and without reduction, this preparation revealed a major protein band with a molecular weight of 37,000, and a minor band with a molecular weight of 32,000-34,000. After elution from the gel, only the 37,000-mol wt protein corresponding to the major band induced the platelet agglutination. When four normal plasmas and the recovery plasma from the same TTP patient were subjected to the similar purification steps, the 37,000-mol wt major band was absent. The 125I-PAP bound to the platelets in a concentration-dependent manner. The platelet agglutination induced by PAP was not inhibited by hirudin, heparin in the presence of antithrombin III, phenylmethylsulfonyl fluoride, apyrase, aspirin, or prostaglandin I2. However, it was inhibited by IgG from normal adults and from the same TTP patient after recovery. The anti-37,000-mol wt PAP antiserum prepared in the rabbit formed a single precipitin line against the highly purified PAP. Using this antiserum in the Western immunoblotting, the 37,000-mol wt protein band was found in the three TTP plasmas, of which the platelet-agglutinating activity was inhibited by the anti-37,000-mol wt PAP IgG. The 37,000-mol wt immunoprecipitin band was absent in the plasmas obtained from another two TTP patients, two normal subjects, two patients with idiopathic thrombocytopenic purpura, and two patients with disseminated intravascular coagulation. These results suggest that the 37,000-mol wt PAP is present only in certain cases of TTP, and is likely to be responsible for the formation of platelet thrombi in the microcirculation.

Effects of Fresh-Frozen Plasma and Its Cryosupernatant Fraction on von Willebrand Factor Multimeric Forms in Chronic Relapsing Thrombotic Thrombocytopenic Purpura

Abstract Remission plasma samples of some patients with chronic relapsing thrombotic thrombocytopenic purpura (TTP) contain unusually large von Willebrand factor (vWF) multimers similar to those produced by normal human endothelial cells in culture. The infusion of the cryosupernatant fraction of normal plasma is as effective as normal fresh-frozen plasma (FFP) in the treatment or prevention of TTP episodes in patients with the chronic relapsing form of TTP. Three patients with chronic relapsing TTP during remission have unusually large vWF multimers present in their plasma. Two of the patients were transfused once with FFP, one of the two received cryosupernatant on three occasions, and the third patient was studied before and immediately after plasma exchange. Unusually large vWF multimers decreased or disappeared from patient plasma samples within 1/2 to 1 1/2 hours following the transfusion of FFP (on two occasions) or cryosupernatant (on two of three occasions), and immediately after plasma exchange (on one occasion). The patient who received cryosupernatant was studied serially after the infusions. Unusually large vWF multimers returned to her plasma within ten to 24 hours and persisted thereafter. Unusually large vWF multimers did not disappear from patient remission plasma samples, or from the culture medium removed from normal human endothelial cells, when these fluids were incubated in vitro with either normal FFP or cryosupernatant. We conclude that an activity in FFP, and its cryosupernatant fraction, promoted the rapid in vivo disappearance of unusually large vWF multimers from the plasma of two patients with chronic relapsing TTP in remission, and plasma exchange reversed the abnormality in a third patient who was in partial remission. Neither FFP nor cryosupernatant directly converted unusually large multimers to smaller vWF forms in vitro in the fluid phase. These results indicate that an activity in the cryosupernatant fraction of normal plasma is involved in vivo in controlling the metabolism of unusually large vWF multimers, and that this process is defective in some chronic relapsing TTP patients.

Effects of fresh-frozen plasma and its cryosupernatant fraction on von Willebrand factor multimeric forms in chronic relapsing thrombotic thrombocytopenic purpura

Remission plasma samples of some patients with chronic relapsing thrombotic thrombocytopenic purpura (TTP) contain unusually large von Willebrand factor (vWF) multimers similar to those produced by normal human endothelial cells in culture. The infusion of the cryosupernatant fraction of normal plasma is as effective as normal fresh-frozen plasma (FFP) in the treatment or prevention of TTP episodes in patients with the chronic relapsing form of TTP. Three patients with chronic relapsing TTP during remission have unusually large vWF multimers present in their plasma. Two of the patients were transfused once with FFP, one of the two received cryosupernatant on three occasions, and the third patient was studied before and immediately after plasma exchange. Unusually large vWF multimers decreased or disappeared from patient plasma samples within 1/2 to 1 1/2 hours following the transfusion of FFP (on two occasions) or cryosupernatant (on two of three occasions), and immediately after plasma exchange (on one occasion). The patient who received cryosupernatant was studied serially after the infusions. Unusually large vWF multimers returned to her plasma within ten to 24 hours and persisted thereafter. Unusually large vWF multimers did not disappear from patient remission plasma samples, or from the culture medium removed from normal human endothelial cells, when these fluids were incubated in vitro with either normal FFP or cryosupernatant. We conclude that an activity in FFP, and its cryosupernatant fraction, promoted the rapid in vivo disappearance of unusually large vWF multimers from the plasma of two patients with chronic relapsing TTP in remission, and plasma exchange reversed the abnormality in a third patient who was in partial remission. Neither FFP nor cryosupernatant directly converted unusually large multimers to smaller vWF forms in vitro in the fluid phase. These results indicate that an activity in the cryosupernatant fraction of normal plasma is involved in vivo in controlling the metabolism of unusually large vWF multimers, and that this process is defective in some chronic relapsing TTP patients.

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.

Pathologic Effects of Plasma From Patients With Thrombotic Thrombocytopenic Purpura on Platelets and Cultured Vascular Endothelial Cells

The pathologic hallmarks of thrombotic thrombocytopenic purpura (TTP) include endothelial cell proliferation and subendothelial hyalin deposits in the microvasculature leading to symptomatic thrombotic occlusions. Plasma or sera from three consecutive patients with TTP were subjected to multiple analyses to determine whether they induce endothelial injury and/or platelet activation, two pathogenic mechanisms that may account for this disorder. Sera were utilized in a microcytotoxicity assay against cultured human umbilical vein endothelial cells (EC). These cells were assessed ultrastructurally and with immunofluorescence techniques to ascertain the nature of inflicted cell damage. Control plasmas were obtained from healthy volunteers as well as patients with immune complex disease and the adult hemolytic uremic syndrome. In the presence of TTP serum, cell kill of 3H-proline-labeled EC averaged 42% versus 8.6% for control sera. Cytotoxicity induced by an IgG fraction of TTP sera averaged 70% versus 16.8% for control IgG. Removal of IgG by immune precipitation diminished cytotoxicity by 70%. Using indirect immunofluorescence, IgG was detected on EC incubated with TTP serum but not on EC treated with control serum. Ultrastructural changes became apparent within 30 min after exposure of cultured EC to TTP serum. Virtually every cell developed numerous cytoplasmic inclusions rarely seen in EC in the presence of normal serum. Prolonged incubation with the TTP serum led to progressive cytolysis, terminating with complete cytoplasmic and nuclear degeneration. Plasma from all three patients with TTP caused spontaneous aggregation of normal washed platelets as monitored by aggregometry. No spontaneous aggregation occurred in response to control plasmas. These results indicate that the sera of the three TTP patients studied were able to mediate time-dependent immune destruction of human cultured endothelial cells and that their plasmas were capable of causing spontaneous aggregation of normal human platelets in vitro. It would seem likely that these mechanisms are also operative in vivo to produce the endothelial destruction as well as the thrombotic vascular occlusions seen in this disorder.

Pathologic effects of plasma from patients with thrombotic thrombocytopenic purpura on platelets and cultured vascular endothelial cells

The pathologic hallmarks of thrombotic thrombocytopenic purpura (TTP) include endothelial cell proliferation and subendothelial hyalin deposits in the microvasculature leading to symptomatic thrombotic occlusions. Plasma or sera from three consecutive patients with TTP were subjected to multiple analyses to determine whether they induce endothelial injury and/or platelet activation, two pathogenic mechanisms that may account for this disorder. Sera were utilized in a microcytotoxicity assay against cultured human umbilical vein endothelial cells (EC). These cells were assessed ultrastructurally and with immunofluorescence techniques to ascertain the nature of inflicted cell damage. Control plasmas were obtained from healthy volunteers as well as patients with immune complex disease and the adult hemolytic uremic syndrome. In the presence of TTP serum, cell kill of 3H-proline- labeled EC averaged 42% versus 8.6% for control sera. Cytotoxicity induced by an IgG fraction of TTP sera averaged 70% versus 16.8% for control IgG. Removal of IgG by immune precipitation diminished cytotoxicity by 70%. Using indirect immunofluorescence, IgG was detected on EC incubated with TTP serum but not on EC treated with control serum. Ultrastructural changes became apparent within 30 min after exposure of cultured EC to TTP serum. Virtually every cell developed numerous cytoplasmic inclusions rarely seen in EC in the presence of normal serum. Prolonged incubation with the TTP serum led to progressive cytolysis, terminating with complete cytoplasmic and nuclear degeneration. Plasma from all three patients with TTP caused spontaneous aggregation of normal washed platelets as monitored by aggregometry. No spontaneous aggregation occurred in response to control plasmas. These results indicate that the sera of the three TTP patients studied were able to mediate time-dependent immune destruction of human cultured endothelial cells and that their plasmas were capable of causing spontaneous aggregation of normal human platelets in vitro. It would seem likely that these mechanisms are also operative in vivo to produce the endothelial destruction as well as the thrombotic vascular occlusions seen in this disorder.