Affinity purified human antiphospholipid antibodies bind normal term placenta

Antiphospholipid antibodies (aPL) are associated with an increased incidence of fetal loss, but the pathophysiology remains unclear. One mechanism may involve the binding of aPL directly to the placenta where they may initiate placental thrombosis and infarction. We have developed an immunofluorescent technique to detect human aPL binding to human placenta. Endogenous immunoglobulins were eluted by extensive washing and residual staining was prevented by incorporating multiple blocking steps. APL were affinity purified on both cardiolipin and phosphatidylserine liposomes from the sera of six patients with aPL (five antiphospholipid syndrome (APS) patients and one post bone marrow transplant patient). Heterogeneous binding to normal term placenta, involving either the trophoblast microvillous surface, stromal and peri-vascular regions was demonstrated by affinity purified aPL from five of six patients. Preliminary sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting studies have demonstrated that aPL bind a number of placental proteins. beta2GPI was not the predominant protein bound by aPL using this technique. This study provides further evidence for the involvement of aPL in mediating placental damage.