Thrombocytopenia in systemic lupus erythematosus: association with antiplatelet and anticardiolipin antibodies.

Serum platelet bindable immunoglobulin G (SPbIgG) and anticardiolipin antibodies (ACA) have been assayed in SLE patients with (group A, n = 8) and without thrombocytopenia (group B, n = 8). Moreover, we studied the binding of serum IgG on platelet proteins using a Western blotting procedure. Increased levels of SPbIgG were found in all thrombocytopenic patients and in five cases of group B. A binding of serum IgG on platelet proteins (80 and 53 kDa) was seen in seven of eight thrombocytopenic patients and in only one case of group B. ACA were present in the serum of four patients in each group and a significant inhibition of ACA IgG by entire washed platelets was achieved in only two severe thrombocytopenic cases. These data suggest that participation of ACA to the platelet destruction can be evoked for a few SLE patients, whereas recognition of platelet protein determinants by lupus autoantibodies is necessary to the thrombocytopenia.