ANTIBODIES AGAINST PLATELET GLYCOPROTEINS AND ANTIPHOSPHOLIPID ANTIBODIES IN AUTOIMMUNE THROMBOCYTOPENIA

Autoantibodies against platelet glycoproteins (anti-GP) are found in t he majority of patients with autoimmune thrombocytopenia (AITP) as wel l as in thrombocytopenia associated with systemic lupus erythematosus (SLE). Some of these patients may have anti-phospholipid antibodies (a nti-FL). To evaluate the pathogenetic significance of anti-FL and anti -GF antibodies in AITP and SLE patients, we investigated anti-cardioli pin (anti-CL), anti-phosphatidylserine (anti-FS) and anti-GF antibodie s (anti-GPIIb-IIIa and anti-GPIb-IX) in 71 patients with AITP and 3 th rombocytopenic patients with SLE. Anti-GP antibodies were detected in 52 (70%) patients. Fifty-six (73%) patients showed anti-FL antibodies. Seven patients (6 AITP, 1 SLE) with both anti-GPIIb-IIIa and IgG anti -FL antibodies were followed during treatment with corticosteroids. An tibodies were measured before treatment and at the time of platelet-pe ak. Anti-GPIIb-IIIa antibodies decreased in all or became undetectable in five. In contrast, IgG anti-PS and IgG anti-CL antibodies decrease d only moderately or remained positive. Adsorption experiments, using gelfiltered platelets, erythrocyte (Ec)-inside-out-vesicles and purifi ed GFIIb-IIIa, showed that anti-GP and anti-PL antibodies have distinc t specificities and do not crossreact. We conclude that anti-PL and an ti-GP antibodies may be present simultaneously in some patients with i mmune mediated thrombocytopenia. Although anti-PS as well as anti-CL a ntibodies may be responsible for thrombocytopenia, we speculate that a nti-GPIIb-IIIa antibodies are more related to the severity of thromboc ytopenia.