MONOCLONAL ANTIPHOSPHATIDYLSERINE ANTIBODY REACTIVITY AGAINST HUMAN FIRST-TRIMESTER PLACENTAL TROPHOBLASTS

OBJECTIVE: To investigate the binding of antibodies against negatively charged phospholipids (antiphospholipid antibodies) to human placenta , we tested the reactivity of three mouse monoclonal antiphospholipid antibodies against first-trimester human placenta. STUDY DESIGN: Forma lin-fixed and frozen sections of first trimester placentas were staine d by immunoperoxidase with three mouse monoclonal antibodies. Each mon oclonal antibody reacted differently with cardiolipin and phosphatidyl serine, 3SB9b reacted with phosphatidylserine, D11A4 reacted with card iolipin, and BA3B5C4 reacted with both. RESULTS: 3SB9b reacted strongl y with the syncytiotrophoblastic layer of both formalin-fixed and froz en placental tissue. Sporadic reactivity was observed against the cyto trophoblastic layer. BA3B5C4 reacted strongly and specifically with cy totrophoblastic cells. D11A4 reacted minimally or, more commonly, not at all. CONCLUSION: The trophoblastic layer directly in contact with t he maternal circulation is most reactive with antiphospholipid antibod ies that react with phosphatidylserine rather than cardiolipin, sugges ting that the trophoblasts may potentially be directly damaged by anti phospholipid antibodies through mechanisms unrelated to thrombosis. In addition, the differential reactivity of 3SB9b and BA3B5C4 suggests t hat the antigenic conformation involving phosphatidylserine on the cyt otrophoblast is altered concurrent with fusion into the syncytium.