Monoclonal antiphosphatidylserine antibody inhibits intercellular fusion of the choriocarcinoma line, JAR.

Naturally occurring antiphospholipid antibodies are strongly associated with placental dysfunction and severe obstetrical complications. We have produced three monoclonal antiphospholipid antibodies that differentiate between phosphatidylserine (PS)- and cardiolipin (CL)-dependent antigens, 3SB9b (CL-/PS+), BA3B5C4 (CL+/PS+), and D11A4 (CL+/PS-). We tested these monoclonal antiphospholipid antibodies in an assay for intertrophoblastic fusion. A JAR choriocarcinoma cell line was induced to undergo intercellular fusion by forskolin in the presence or absence of monoclonal antiphospholipid antibodies. The amount of syncytium formation was quantified by using fluorescein isothiocyanate (FITC)-conjugated anti-desmosome antibody to visualize intercellular membranes and propidium iodide to stain nuclei and by counting those cells with multiple nuclei. Without the presence of antiphospholipid antibodies, and in cultures containing BA3B5C4 (CL+/PS+) or D11A4 (CL+/PS-), approximately 70% of JAR formed syncytial cells after 24 h of forskolin treatment. Less than 13% of the cells formed synctia in 2-day cultures that were not exposed to forskolin or that contained forskolin in the presence of 3SB9b (CL-/PS+). These data suggest that phosphatidylserine is externalized during intertrophoblastic fusion and that antiphospholipid antibody with reactivity against PS, but not CL, can affect placental development by interfering with the normal formation of syncytiotrophoblast.