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A Review of the Literature
a Department of Obstetrics and Gynecology, Catholic University of Sacred Heart, Rome, Italy b Allergy, Clinical Immunology and Rheumatology Unit, IRCCS Istituto Auxologico Italiano, Department of Internal Medicine, University of Milan, Milan, Italy
Key Words: antiphospholipid syndrome • anti-  2-glycoprotein-I • trophoblast cells • heparin
Address for correspondence: Nicoletta Di Simone, M.D., Department of Obstetrics and Gynecology, Catholic University of Sacred Heart, Largo Gemelli 8, 00168 Rome, Italy. Voice: +390630154298; fax: +39063051160. nicolettadisimone{at}rm.unicatt.it
There are several possible mechanisms by which antiphospholipid antibodies (aPL) may have adverse effects on placental functions. Examination of placentas and first-trimester decidua from antiphospholipid syndrome–complicated pregnancies has found little evidence of specific thrombotic placental pathology. It is now generally accepted that the clinically relevant aPL bind to proteins with affinity for phospholipids. The most important epitope for antiphospholipid syndrome–related aPL resides on
2-glycoprotein-I (2GPI). aPL detected by anti-2GPI assays are associated with fetal loss. During differentiation to syncytium, trophoblasts express cell membrane anionic phospholipids that can bind 2GPI. Adhered 2GPI can be recognized by the antibodies that, once bound, interfere with trophoblast cell maturation, resulting in defective placentation. The improved outcome of pregnancies treated with heparin stimulated interest on the drug's mechanism of action. Several mechanisms could explain its beneficial effects in addition to a direct effect of heparin on the coagulation cascade. It might reduce the binding of aPL, inflammation by inhibiting complement activation, and might facilitate implantation. Further investigations are needed to better understand how aPL induce obstetric complications and to better clarify the functional role of heparin in the human placenta, leading to more successful therapeutic options.
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