Specific antiplatelet autoantibodies in patients with antiphospholipid antibodies and thrombocytopenia

Abstract

By means of immunoblotting and monoclonal antibody immobilization of platelet antigens (MAIPA) we have studied the specificity of antiplatelet antibodies in patients with antiphospholipid antibodies and thrombocytopenia defined as presence of anticardiolipin IgG and a platelet count below 100 x 10y/l. The study group consisted of 10 patients with systemic lupus erythematosus (SLE), 8 patients with primary anti-phospholipid syndrome (PAPS) and 16 patients with idiopathic thrombocytopenic purpura (ITP). The comparison group was formed by 17 patients with classical chronic ITP without anticardiolipin IgG. We identified the 80-100, 130-150 and 150-170 KD surface proteins that comigrate with GPIIIa, GPIIb and GPIb and a 50-70 KD cytoplasm band by immunoblot. In patients with classical chronic ITP, the prevalence of the antiplatelet antibodies against GPIIIa was 53 % on immunoblot assay and 47% on MAIPA. In ITP patients who had also anti-phospholipid antibodies in serum, the percentage of reactivity to GPIIIa declined to 37% on immunoblot and 21% on MAIPA but it was not statistically different from the percentage observed in patients with classical ITP. Autoantibodies to platelet surface glycoproteins were almost absent in SLE and PAPS patients, who showed a significant prevalence (78 %) of IgG reactivity to the 50-70 KD internal platelet protein which was frequently encountered also in patients with ITP and aPL (56%). Our study provides additional evidence that platelet antigens in patients with phospholipid-associated secondary immune thrombocytopenia are different from those of primary I ITP, and that surface glycoproteins were not involved.

Hematologic Abnormalities in the Antiphospholipid Syndrome

“…In addition, increased concentrations of aPL have been found to be common in patients with idiopathic thrombocytopenic purpura, but these aPL did not shown any clinical significance [26]. Finally, increased plasma levels of antibodies against glycoprotein IIb/IIIa and Ib/IX have been found in 40% of aPLpositive patients [24,27,28]. This prevalence is similar to that described in idiopathic thrombocytopenic purpura patients [29].…”

The Significance and Management of Thrombocytopenia in Antiphospholipid Syndrome

“…Severe thrombocytopenia in APS correlates more closely with antiplatelet-GP antibodies than aPL [35,36,39]. The prevalence of these antibodies in APS patients with no thrombocytopenia, however, is approximately 10 % [36,37].…”

“…Based on monoclonal antibody immobilization of platelet antigens (MAIPA) assays [35][36][37][38][39], antibodies directed against GP on the cell wall of platelets (GPIIb/IIIa, GPIb/IX, GPIa/IIa, and GPIV) have been identified in 40-70 % of thrombocytopenic patients with APS. Severe thrombocytopenia in APS correlates more closely with antiplatelet-GP antibodies than aPL [35,36,39].…”

Antiphospholipid-associated thrombocytopenia or autoimmune hemolytic anemia in patients with or without definite primary antiphospholipid syndrome according to the Sapporo revised classification criteria: a 6-year follow-up study

“…13 Thrombocytopenia in APS also has been associated with antiplatelet glycoprotein antibodies that at times correlate more closely than either aPL or clinical manifestations. [14][15][16] Spontaneous and induced murine models of APS develop thrombocytopenia as one of their relevant disease features. [17][18][19] Interestingly, one of these models (NZW ϫ NXSB) F1 has been proposed as an experimental model of idiopathic thrombocytopenic purpura.…”