Lysophosphatidylethanolamine is the antigen to which apparent antibody to phosphatidylethanolamine binds.

Because binding of antiphospholipid antibody (aPL) to phosphatidylethanolamine (PE) is central to the definition of the antigenic epitope targeted by aPLs, we examined the binding of aPL-positive SLE sera to PE under various conditions. No serum bound to PE uncontaminated with lysophosphatidylethanolamine (1PE), but many aPL-positive sera bound to 1PE-contaminated PE and to 1PE coated onto an ELISA plate. Absorption studies indicated partial cross-reactivity between PE containing 1PE and cardiolipin. We conclude that clinical aPLs do not bind to PE. Prior reports to the contrary most likely represent binding of aPL to PE's degradation product, 1PE.