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

Area of Science:

• Immunology
• Clinical Chemistry
• Autoimmunity

Background:

• Antiphospholipid antibodies (aPA) are crucial in diagnosing antiphospholipid syndrome (APS).
• Detection of aPA typically requires specific phospholipid-binding plasma proteins, such as beta 2-glycoprotein I, for assay sensitivity.
• The reactivity of antibodies against neutral or zwitterionic phospholipids like phosphatidylethanolamine (PE) remains less understood.

Purpose of the Study:

• To investigate the specificity of anti-PE antibodies (aPE) found in patients with SLE and/or recurrent spontaneous abortions.
• To identify the plasma proteins that aPE recognize in the presence of PE.
• To differentiate the binding targets of aPE from those of antibodies against anionic phospholipids.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA) was used to detect aPE.
• Partially purified kininogens and kininogen-binding proteins were isolated using carboxymethyl (CM)-papain affinity chromatography.
• Patient sera were tested against PE, kininogens (high molecular weight kininogen - HMWK, and low molecular weight kininogen - LMWK), and their complexes with PE.

Main Results:

• Eleven out of 13 patient sera recognized a PE-kininogen complex or a complex involving kininogen-binding proteins.
• Highly purified HMWK and LMWK were recognized by some aPE-positive sera only when presented on a PE substrate.
• Antibodies did not react with PE, HMWK, or LMWK independently, suggesting aPE target complexes.
• Some sera reacted with CM-papain eluate bound to PE, indicating recognition of factor XI or prekallikrein.
• Reactivity was inhibited by preincubation, confirming antibody binding to specific components.

Conclusions:

• Most anti-PE antibodies (aPE) are not specific for PE but rather target certain phospholipid-binding plasma proteins, primarily kininogens or associated proteins.
• These aPE recognize different plasma protein targets compared to antibodies implicated in anionic phospholipid reactivity.
• The findings highlight the complexity of aPE recognition and suggest a distinct immunological mechanism in certain autoimmune conditions.