SPECIFICITIES OF PLATELET AUTOANTIBODIES IN PATIENTS WITH LUPUS ANTICOAGULANTS IN PRIMARY ANTIPHOSPHOLIPID SYNDROME

We have studied target platelet antigens in 22 patients with lupus ant icoagulants and a primary antiphospholipid syndrome in order to determ ine whether any specificities of platelet autoantibodies are correlate d with thromboembolism, and if these antibodies cross-reacte with phos pholipids, which would suggest their role in the development of thromb oembolic disease. Platelet counts were median 203 x 10(9)/l, range 100 -298 x 10(9)/l. Platelet antibodies were found in six thrombocytopenic patients and in further nine patients. All these 15 patients had anti bodies against GPIIb/IIIa, five patients against GPIb/IX, and six pati ents against GPIV. Anti-GPIb/IX and -GPIV occurred only in combination with anti-GPIIb/IIIa antibodies. There was no correlation between the presence of detectable platelet antibodies or any of their glycoprote in specificity and thrombocytopenia or the history of a thromboembolic disease. Eluates from platelets contained only GPIIb/IIIa reactivitie s, but neither anti-GPIb/IX nor anti-GPIV. None of the eluates contain ed lupus anticoagulant activity. In one case, the platelet eluates con tained anti-GPIIb/IIIa and anticardiolipin IgG antibodies. These resul ts suggest that in patients with a primary antiphospholipid syndrome t he presence of platelet autoantibodies neither indicate a risk for thr omboembolic disorder nor have lupus anticoagulant activity.