Affinity purified human antiphospholipid antibodies bind normal term placenta

Antiphospholipid antibodies (aPL) are associated with an increased incidenc e of fetal loss, but the pathophysiology remains unclear. One mechanism may involve the binding of aPL directly to the placenta where they may initiat e placental thrombosis and infarction. We have developed an immunofluoresce nt technique to detect human aPL binding to human placenta. Endogenous immu noglobulins were eluted by extensive washing and residual staining was prev ented by incorporating multiple blocking steps. APL were affinity purified on both cardiolipin and phosphatidylserine liposomes from the sera of six p atients with aPL (five antiphospholipid syndrome (,APS) patients and one po st bone marrow transplant patient). Heterogeneous binding to normal term pl acenta, involving either the trophoblast microvillous surface, stromal and perivascular regions was demonstrated by affinity purified aPL from five of six patients. Preliminary sodium dodecyl sulphate-polyacrylamide gel elect rophoresis (SDS-PAGE) and western blotting studies have demonstrated that a PL bind a number of placental proteins. beta(2)GPI was not the predominant protein bound by aPL using this technique. This study provides further evid ence for the involvement of aPL in mediating placental damage.