MONOCLONAL ANTIPHOSPHATIDYLSERINE ANTIBODY INHIBITS INTERCELLULAR FUSION OF THE CHORIOCARCINOMA LINE, JAR

Naturally occurring antiphospholipid antibodies are strongly associate d with placental dysfunction and severe obstetrical complications. We have produced three monoclonal antiphospholipid antibodies that differ entiate between phosphatidylserine (PS)- and cardiolipin (CL)-dependen t antigens, 3SB9b (CL-/PS+), BA3B5C4 (CL+/PS+), and D11A4 (CL+/PS-). W e 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 absen ce of monoclonal antiphospholipid antibodies. The amount of syncytium formation was quantified by using fluorescein isothiocyanate (FITC)-co njugated 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-), appro ximately 70% of JAR formed syncytial cells after 24 h of forskolin tre atment. Less than 13% of the cells formed syncytia in 2-day cultures t hat were not exposed to forskolin or that contained forskolin in the p resence of 3SB9b (CL-/PS+). These data suggest that phosphatidylserine is externalized during intertrophoblastic fusion and that antiphospho lipid antibody with reactivity against PS, but not CL, can affect plac ental development by interfering with the normal formation of syncytio trophoblast.