ROLE OF KALLIKREIN-KININ SYSTEM IN MAINTENANCE OF PREGNANCY

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Coagulation factor XII, prekallikrein and high molecular weight kininogen are known as proteins of kallikrein-kinin system. Recently, surprisingly high prevalence of factor XII deficiency among patients with RPL have been reported. We have now tested plasma samples from RPL patients for the presence of autoantibodies to factor XII. One hundred ninety one patients with RPL were screened for factor XII activity. We found 34 (17.8%) patients with factor XII deficiency (activity <60%). Thirteen (38.2%) of these 34 patients were positive for antiphospholipid antibodies. We hypothesized that factor XII deficiency may be partly due to presence of antibodies to factor XII and tested plasma samples from patients with factor XII deficiency for the presence of antibodies to factor XII by immunoblot and ELISA. We found that 53.5% of factor XII deficient patients with RPL were positive for IgG anti-factor XII antibodies (p<0.001, OR36.8). Anti-factor XII antibodies recognized the amino-terminal heavy chain region of factor XII. Literatures have reported that human factor XII binding to the glycoprotein Ib-IX-V complex via the amino-terminal heavy chain region inhibits thorombin-induced platelet aggregation. We hypothesize that autoantibodies to factor XII may be associated with RPL.