Antiphospholipid antibodies and complement activation in patients with cerebral ischemia.

Antiphospholipid antibodies (aPL) have been linked to stroke and TIA. The mechanism for aPL-associated thrombosis is uncertain, but could be related to complement-mediated membrane damage. Indirect evidence for complement activation (low C4 levels) has been associated with aPL, with variable correlation with disease manifestations. We measured complement activation directly using an ELISA for SC5b-9 in 26 patients with stroke/TIA; 13 with and 13 without aPL. Patient plasma levels of SC5b-9 were measured along with standard positive and 5 normal control samples. Nine patients with, whereas only one without, aPL had an abnormal SC5b-9 level (p = 0.0018, Fisher's Exact Test). These data confirm a relationship between aPL and complement activation, which argues for an active autoimmune process in aPL-associated thrombosis and suggests that complement activation may play a pathogenic role.