Kininogen domain 3 contains regions recognized by antiphosphatidylethanolamine antibodies

Abstract

Summary. Antiphosphatidylethanolamine antibodies (APE) have been described in patients with thrombotic diseases and recurrent pregnancy loss (RPL). It has been reported that certain APE are not specific for phosphatidylethanolamine (PE) per se, but are directed to PE-binding plasma proteins, called kininogens. Our recent in vitro data suggest that APE may recognize the domain 3 (D3) region of kininogens. In this study, we have used synthetic peptides that span the D3 of kininogens in inhibition and direct binding studies to identify epitopes that are sites for binding APE. Our present data demonstrate that among 24 RPL patients who were positive for kininogendependent immunoglobulin (IgG) APE, 17 patients (70.8%) recognized the LDC27 peptide. We mapped the APE-binding region on D3 using plasma from a RPL patient (X) who had a high titer of IgG APE that recognized LDC27. APE of patient X recognized a 13-residue segment in LDC27, named CNA13. Leu331-Met357 (LDC27) and Cys333-Lys345 (CNA13) are located on the carboxyl-terminal portion of kininogen D3, which is known as the major kininogen heavy chain cell attachment site where it overlaps its cysteine protease inhibitory region. Because APE interferes with the balance of hemostasis in vitro, APE may therefore induce a similar condition in patients thereby causing thrombosis and RPL.

Autoantibodies to Factor XII and Kininogen‐Dependent Antiphosphatidylethanolamine Antibodies in Patients with Recurrent Pregnancy Loss Augment Platelet Aggregation

“…12 In other words, 63% of the patients who were positive for plasma proteindependent IgG aPE recognized the LDC27. However, a significant association was not observed between aPE and augmentation of SSPA (data not shown).…”

“…12 Among plasmas from 24 RPL patients who were positive for kininogen-dependent IgG aPE, 17 (70.8%) recognized the LDC27 peptide. 12 Among plasmas from 24 RPL patients who were positive for kininogen-dependent IgG aPE, 17 (70.8%) recognized the LDC27 peptide.…”

Antiphospholipid Antibody-Mediated Reproductive Failure in Antiphospholipid Syndrome

“…An additional subpopulation of anti-PL Abs associated with pregnancy failure on thrombotic background is the antiphosphatidylethanolamine (anti-PE) found mainly in plasma of patients with SLE and APS [52][53][54][55][56][57][58][59][60]. Since PE is a major component of both the outer and the inner leaflets of cell plasma membranes, autoantibodies to PE and/or PE binding proteins may exert an effect on both resting and activated cells or cell fragments.…”

“…Interestingly, the female reproductive tract is the second richest site for kininogen and its metabolic products in the body, which increase during pregnancy and is decreased in reproductive failure conditions [58,59]. Domain 3 of the kininogen is the target epitope for anti-PE binding [60].…”

Laboratory Evaluation of Antiphospholipid Antibodies in Patients With Venous Thromboembolism

“…As contact protein deficiencies might be associated with thrombosis, autoantibodies to contact proteins might have the same clinical association. [39][40][41] We detected IgM-anti-pE in 20 patients-in 9 of them as the sole APA of the tested antiphospholipid profile. Moreover, only 8 of the 20 patients also had criteria APA, so the remaining 12 cases are candidates for ''seronegative'' APS.…”