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PROBLEM: The antiphospholipid (aPL) antibody syndrome is characterized by severe pregnancy complications, the cause of which remains unknown. We hypothesized that the placental trophoblast is a target for aPLs. METHOD OF STUDY: The effects of monoclonal aPLs on trophoblast function, including the invasion of JAR into matrigel-coated filters and the effects of annexin V expression on BeWo, were investigated using choriocarcinoma models. RESULTS: aPLs against phosphatidylserine (PS) significantly (P < 0.001) decreased the migration of JAR across the membrane. In the annexin V studies, undifferentiated BeWo did not express surface annexin V. After differentiation, BeWo expressed surface annexin V, which was removed in the presence of aPLs, resulting in increased binding of prothrombin. CONCLUSIONS: PS is expressed on the trophoblast surface during differentiation and invasion of extracellular matrix. Our data suggest that aPLs against PS can directly affect trophoblast function by limiting the depth of decidual invasion and by concurrently creating a procoagulant surface on trophoblast exposed to the maternal circulation.

OBJECTIVE: Trophoblast differentiation is associated with externalization of phosphatidylserine from the inner to the outer surface of the plasma membrane. In this study we tested the hypothesis that concurrent externalization and binding of annexin-V blocks the phosphatidylserine-rich surface from acting as a site for activation of coagulation and that antiphospholipid antibodies lead to a procoagulant state by preventing annexin-V binding. STUDY DESIGN: A choriocarcinoma model of trophoblast differentiation, forskolin-activated BeWo cells and immunoperoxidase techniques were used to determine surface and cytoplasmic localization of annexin-V related to differentiation. Monoclonal immunoglobulin M antibodies against phosphatidylserine- and cardiolipin-dependent antigens were used to determine the effects of antiphospholipid antibodies on annexin-V localization and on the binding of prothrombin to the BeWo surface. RESULTS: During differentiation BeWo cells externalized phosphatidylserine and increased the expression of surface annexin-V. Monoclonal antibody against phosphatidylserine removed annexin-V from the BeWo surface and increased binding of prothrombin. CONCLUSION: Antiphosphatidylserine antibody induces sites for prothrombin binding on the surface of a BeWo model of trophoblast, most likely by removing annexin-V. This mechanism could explain the frequent observation of increased thrombosis at the maternal-fetal interface in miscarriages associated with antiphospholipid antibodies. (Am J Obstet Gynecol 1997;177:964-72.)

OBJECTIVE: Antiphospholipid antibodies are associated with clinical intrauterine growth restriction. In this study we investigated whether immunoglobulin M monoclonal antibodies against phosphatidylserine or cardiolipin or cross-reactive with both phospholipids would induce intrauterine growth restriction in an experimental model of the antiphospholipid antibody syndrome. STUDY DESIGN: Balb/c or CD-1 mice were injected intraperitoneally on day 8 of pregnancy with three immunoglobulin M monoclonal antibodies that differentiated between cardiolipin- and phosphatidylserine-dependent antigens or with control immunoglobulin M monoclonal antibodies against irrelevant antigens. The animals were killed on day 15 of pregnancy and placental and fetal weights were measured. RESULTS: Monoclonal antibody 3SB9b, which reacted in enzyme-linked immunosorbent assays with phosphatidylserine but not cardiolipin, induced a significant reduction in both fetal and placental weights. Monoclonal antibodies BA3B5C4, which was cross-reactive with cardiolipin and phosphatidylserine, and D11A4, which reacted with cardiolipin, did not alter fetoplacental weights. CONCLUSION: An antiphospholipid antibody that reacts with phosphatidylserine induces significant fetal and placental intrauterine growth restriction in a mouse model for the antiphospholipid antibody syndrome, but those that react with cardiolipin do not. (AM J OBSTET GYNECOL 1996;174:700-7.)

The antiphospholipid antibody syndrome (aPL syndrome) is characterized by elevated levels of autoantibodies against negatively charged phospholipids (aPLs) associated with several severe obstetrical complications, including recurrent pregnancy loss, pregnancy-induced hypertension and preeclampsia before 34 weeks’gestation, and intrauterine growth retardation (reviewed in 1, 2). The syndrome appears to be a prothrombotic state in which the patients are at risk for thrombosis at virtually any site. The most thoroughly studied aPLs are the lupus anticoagulant and antibodies against the phospholipid cardiolipin (aCLs). It is commonly proposed that aCLs, which are cross-reactive with other phospholipids, are primarily responsible for the thrombosis. The obstetric complications have been attributed to aCL-induced placental damage resulting from placental or decidual thrombosis.

Naturally occurring antibodies against the negatively charged phospholipids cardiolipin (CL) and phosphatidylserine (PS) have been associated with recurrent pregnancy loss. One prevalent hypothesis proposes that antiphospholipid antibody (aPL) mediated pathophysiology is through increased placental thrombosis. In this study we investigated the reactivity of three mouse monoclonal aPLs with term and 26 week human placental preparations. Each monoclonal antibody reacted differently with CL and PS; 3SB9b reacted with PS (CL − /PS + ), D11A4 reacted with CL (CL + /PS − ) and BA3B5C4 reacted with both CL and PS (CL + /PS + ). 3SB9b reacted strongly with the syncytiotrophoblastic layer of both formalin fixed and frozen placental tissue. Sporadic reactivity was observed against the cytotrophoblastic layer. BA3B5C4 reacted strongly and specifically with cytotrophoblastic cells. D11A4 had only weak reactivity in the subtrophoblastic stromal region of the placenta in frozen sections. aPL staining was also observed against extravillous cytotrophoblast. BA3B5C4 stained cytoplasmic structures, whereas 3SB9b stained the plasma membrane region with little cytoplasmic staining. These data suggest that the trophoblastic layer is reactive with aPLs and may potentially be directly damaged through mechanisms unrelated to thrombosis. In addition, the trophoblastic layer directly in contact with the maternal circulation is most reactive with aPLs that are PS + rather than CL + . The differential reactivity of 3SB9b and BA3B5C4 suggests that the antigenic conformation involving PS on the cytotrophoblast is altered concurrent with fusion into the syncytium.