Autoantibodies to phosphatidylethanolamine (PE) recognize a kininogen- PE complex

Abstract

Demonstration of autoimmune antiphospholipid antibodies (aPA) to negatively charged phospholipids (PL) in an enzyme-linked immunosorbent assay (ELISA) requires the presence of certain phospholipid-binding plasma proteins, eg, beta 2-glycoprotein I. We found a requirement for plasma against the electrically neutral or zwitterionic phospholipid, phosphatidylethanolamine (PE). Two of these PE-binding plasma proteins were identified as high molecular weight kininogen (HMWK) and low molecular weight kininogen (LMWK). We studied anti-PE antibody (aPE) seropositive plasma from 13 patients with SLE and/or recurrent spontaneous abortions by using partially purified kininogens and kininogen binding proteins from adult bovine serum isolated by carboxymethyl (CM)-papain affinity chromatography. Eleven of 13 sera recognized a kininogen-PE complex and/or a kininogen-binding protein-kininogen-PE complex. Some aPE-positive patient sera were shown to recognize highly purified HMWK and LMWK by ELISA only when the kininogens were presented on a PE substrate. These aPE sera did not recognize PE, HMWK, or LMWK when they were presented independently as the sole antigens on the ELISA plates. Other aPE-positive sera that did not react with PE-bound HMWK or LMWK reacted with the CM-papain column eluate when it was bound to PE, which suggests that these aPE recognize factor XI or prekallikrein, which normally bind to HMWK. The aPE ELISA reactivity of two patient sera were inhibited by preincubation of the CM-papain column eluate in the ELISA plate. These data show that most aPE are not specific for PE but require the presence of certain PL-binding plasma proteins that are kininogens or proteins in complex with kininogens. Our studies indicate that aPE bind to different plasma proteins than those implicated in anionic PL, aPA ELISA reactivity.

A Unique Preliminary Study on Placental Apoptosis in Mice with Passive Immunization of Anti-Phosphatidylethanolamine Antibodies and Anti-Factor XII Antibodies

“…Sera from RPL women positive for aPE and/or aFXII antibodies or without any antibodies were used in the study. IgG was purified from sera by diethylaminoethyl (DEAE)–Sepharose followed by protein G‐Sepharose described elsewhere 13 . IgG fraction was used for the study, because our previous reports revealed that the IgG fraction is most persistent and pathogenic in patients with reproductive failure 3,4,37 …”

“…Sera from both patient A and patient B showed negative for all other aPA. All the aPA were measured as described elsewhere 13–15,19 …”

“…Although a few investigators have looked at aPE, aPE has been reported as sole aPA in several patients 3,6,11,12 . The target phospholipid of aPE is zwitterionic (neutral), and high‐ or low molecular weight kininogens (HK or LK) were confirmed to be cofactors for aPE 13,14 . Epitope mapping analysis revealed that the target antigen site for kininogen‐dependent aPE was LDC27 (a one‐letter code for amino acid residues used) in the third domain (D3) of kininogen 15 .…”

Expression of Apoptosis in Placenta of Experimental Antiphospholipid Syndrome Mouse

“…IgG was purified from sera by diethyl aminoethyl (DEAE)‐Sepharose followed by protein G‐Sepharose as described elsewhere . IgG fraction was used for the study, because our previous reports revealed that the IgG fraction is most frequent and pathogenic in patients with reproductive failure …”

Antiphospholipid Antibodies and Kininogens in Pathologic Pregnancies: A Review

“…Because PE is a major component of both the outer and inner leaflet of cell plasma membranes, production of aPE may interfere with normal cell functions. Sugi and McIntyre reported that certain aPE are not specific for PE per se, but are directed to PE‐binding plasma proteins, kininogens 10 . Kininogens are known as members of kallikrein–kinin system.…”