Antibodies against platelet glycoproteins and antiphospholipid antibodies in autoimmune thrombocytopenia

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Abstract
Autoantibodies against platelet glycoproteins (anti‐GP) are found in the majority of patients with autoimmune thrombocytopenia (AITP) as well as in thrombocytopenia associated with systemic lupus erythematosus (SLE). Some of these patients may have anti‐phospholipid antibodies (anti‐PL). To evaluate the pathogenetic significance of anti‐PL and anti‐GP antibodies in AITP and SLE patients, we investigated anti‐cardiolipin (anti‐CL), anti‐phosphatidylserine (anti‐PS) and anti‐GP antibodies (anti‐GPIIb‐IIIa and anti‐GPIb‐IX) in 71 patients with AITP and 3 thrombocytopenic patients with SLE. Anti‐GP antibodies were detected in 52 (70%) patients. Fifty‐six (73%) patients showed anti‐PL antibodies. Seven patients (6 AITP, 1 SLE) with both anti‐GPIIb‐IIIa and IgG anti‐PL antibodies were followed during treatment with corticosteroids. Antibodies were measured before treatment and at the time of platelet‐peak. Anti‐GPIIb‐IIIa antibodies decreased in all or became undetectable in five. In contrast, IgG anti‐PS and IgG anti‐CL antibodies decreased only moderately or remained positive. Adsorption experiments, using gelfiltered platelets, erythrocyte (Ec)‐inside‐out‐vesicles and purified GPIIb‐IIIa, showed that anti‐GP and anti‐PL antibodies have distinct specificities and do not crossreact. We conclude that anti‐PL and anti‐GP antibodies may be present simultaneously in some patients with immune mediated thrombocytopenia. Although anti‐PS as well as anti‐CL antibodies may be responsible for thrombocytopenia, we speculate that anti‐GPIIb‐IIIa antibodies are more related to the severity of thrombocytopenia.