REDUCTION OF ANNEXIN-V (PLACENTAL ANTICOAGULANT PROTEIN-I) ON PLACENTAL VILLI OF WOMEN WITH ANTIPHOSPHOLIPID ANTIBODIES AND RECURRENT SPONTANEOUS-ABORTION

OBJECTIVE: The mechanism by which antiphospholipid antibodies are asso ciated with pregnancy loss and thromboembolic conditions has yet to be elucidated. Annexin-V, an anticoagulant phospholipid-binding protein, is normally present in syncytiotrophoblasts lining the placental vill i, where it may play a role in the maintenance of intervillous blood f luidity. We therefore investigated the distribution of annexin-V in pl acentas of patients with antiphospholipid antibodies in situ and then used short-term villous cultures to study the direct effect of antipho spholipid antibodies on the immunolocation of annexin-V. STUDY DESIGN: We performed a blinded study by means of computerized morphometric an alysis of placental tissues that were stained for annexin-V with affin ity-purified polyclonal antibody in an avidin-biotin peroxidase system . The distribution of villous surface annexin-V on cross sections of p lacentas of patients with antiphospholipid antibodies was compared wit h that of placentas from patients with uncomplicated pregnancies, elec tive abortions, and pregnancy losses not associated with antiphospholi pid antibodies (n = 8 for each group). We quantitated villous surface annexin-V in cultured placental villi that were incubated with antipho spholipid antibodies immunoglobulin G compared with normal immunoglobu lin G and measured annexin-V levels by enzyme-linked immunosorbent ass ay in conditioned media and in the villi. RESULTS: The mean villous su rface annexin-V of the group with antiphospholipid antibodies was 26.2 % +/- 17% (SD) versus 93.9% +/- 5.7% in the normal control group (p < 0.0001). Villi from patients undergoing elective abortions and with pr egnancy losses that were not attributed to antiphospholipid antibodies also showed higher mean villous surface annexin-V levels (86.9% +/- 1 0.6% and 83.5% +/- 11.3%, respectively, p < 0.0001). Organ culture of normal placental villi with affinity-purified immunoglobulin G from pa tients with antiphospholipid antibodies showed a dose-dependent decrea se of villous surface annexin-V over a concentration range of 1.5 mu g /ml to 1.5 mg/ml. Annexin-V concentrations in conditioned media were s ignificantly lower in the presence of antiphospholipid antibodies immu noglobulin G compared with normal immunoglobulin G (49.4 +/- 8.9 ng/gm wet weight vs 57.2 + 11.5 ng/gm, respectively, p < 0.05). In contrast , the mean level of annexin-V in placental villi incubated with antiph ospholipid antibodies immunoglobulin G was greater than in villi incub ated with normal immunoglobulin G, 1328 +/- 130 ng/gm wet weight versu s 1183 +/- 165 ng/gm (p < 0.02). CONCLUSIONS: Patients with antiphosph olipid antibodies and a history of previous pregnancy losses have a si gnificant reduction in annexin-V immunostaining on placental villous s urfaces, and antiphospholipid antibodies immunoglobulin G can directly decrease levels of villous surface annexin-V on cultured placental vi lli. Assays of annexin-V in the conditioned media and cell pellets of cultured placental villi suggest that the mechanism for antiphospholip id antibodies-mediated reduced annexin-V surface staining is an inhibi tion of annexin-V transport to the villous surface rather than displac ement by antiphospholipid antibodies from the surface. This antiphosph olipid antibodies-induced deficiency of placental surface annexin-V ma y contribute to the placental thrombosis observed in these patients.