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

Abstract

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.

Characterization of platelet glycoproteins and platelet/endothelial cell antibodies in patients with thrombotic thrombocytopenic purpura

“…Agglutination of autologous and homologous platelets by TTP plasma has been demonstrated. A 37 kD protein has been isolated from plasma of some patients with acute TTP, and it has been suggested that this protein, which is not found in all patients with TTP, agglutinates platelets through interaction with CD36 ( Siddiqui & Lian, 1988; Lian et al , 1991 ). It has been previously observed that 23/27 TTP sera showed anti‐CD36 reactivity by at least one method ( Tandon et al , 1994 ).…”

Binding of Platelet Agglutinating Protein p 37 from the Plasma of a Patient with Thrombotic Thrombocytopenic Purpura to Human Platelets

“…It was found that normal adult human IgG decreased the binding of PAP p37 to platelets. The reduced binding of PAP p37 to platelets in presence of adult IgG is likely due to the specific antigen-antibody complex formation between PAP p37 and IgG as demonstrated by us (19).…”

“…The clinical manifestations of thrombotic thrombocytopenic purpura are thought to be caused by the deposition of platelet thrombi in the arterioles and capillaries (3,4). The platelet thrombi formation is initiated by platelet agglutination/aggregation as a primary event, secondary to vascular injury, or resulting from both of the above (18,19). The agglutination of platelets by TTP plasma has been demonstrated by us (5) and others (6)(7)(8)(9).…”

Plasma from patients with thrombotic thrombocytopenic purpura induces activation of human monocytes and polymorphonuclear neutrophils

“…Most studies on the pathophysiology of TTP have focused on the investigation of platelet‐aggregation‐promoting factors. These included ULVWF multimers, released from injured endothelial cells or as a consequence of deficient metalloprotease activity (Moake et al , 1986; Furlan et al , 1998; Tsai & Lian, 1998), defects in prostacyclin metabolism (Remuzzi et al , 1987), soluble aggregating factors (Siddiqui & Lian, 1988) or antibodies against the platelet glycoprotein IV (CD36) (Tandon et al , 1994). Others have found poorly defined factors in TTP plasma that induce endothelial cell damage or apoptosis (Mitra et al , 1997; Jimenez et al , 2001).…”