Anti-endothelial cell antibodies: another cause for pregnancy loss?

Previous studies demonstrated that unique tissue-specific antigens expressed on vascular endothelial cells can serve as immunogens, and the apparent association between transplant rejection and antiendothelial cell (EC) antibodies is well established. A common feature of some placentas from women with recurrent pregnancy loss is the diffuse formation of microthrombi associated with changes in thromboresistant properties of endothelial cells, similar to the findings in rejected organs. Therefore, the prevalence of anti-EC antibodies in patients with recurrent pregnancy loss and the role of these antibodies in cultured human endothelial cells from umbilical cord vein were studied.

To evaluate the frequency of anti-EC antibodies, sera from 160 nonpregnant patients with recurrent pregnancy loss after absorption with pooled platelets and pooled leukocytes were tested using cultured human umbilical cord vein endothelial cells (HUVEC) by flow cytometry. To study the role of anti-EC antibodies, purified anti-EC IgGs were added to HUVEC cultures and hemostatic, fibrinolytic, and anticoagulation pathway markers (tissue factor, tissue plasminogen activator, palsminogen-activator inhibitor, thrombomodulin, heparan-sulfate proteoglican, antithrombin III, von Willebrand factor, CD54, human leukocyte antigens-DR, and transferin receptor) were detected by specific antibodies and flow cytometry. Immunoblotting analyses were done by using purified anti-EC IgGs against cell membrane proteins from endothelial cells and leukocytes extracted by detergent solubilization.

Thirty-nine (24%) of the patients were positive for EC antibodies. Antipaternal lymphocyte antibodies were tested as well and were found in 37 (23%) of the patients as 25 sera (15.6%) showed reactivity with both EC and lymphocytes. Certain patient sera were reactive with HUVEC lines from some but not other umbilical cords, which suggests allotypy. Sera from 70 normal healthy male and nonpregnant female controls did not react with any of the individual HUVEC lines used. The purified anti-EC immunoglobulin G (IgGs) recognized bands, from HUVEC surface membrane protein preparations, with molecular weights of 120 kDa. Both hemostatic and fibrinolytic pathway markers were found activated in the presence of anti-EC IgGs, suggesting an altered endothelial cell surface activation state.

The results indicate that anti-EC antibody is another marker for a subset of recurrent spontaneous aborters who may have activation of hemostasis and fibrinolysis as a mechanism involved in their losses.