Detection of Antiphospholipid Autoantibody in Systemic Lupus Erythematosus is Temperature-Dependent

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Abstract
Non-reactive SLE sera in an ELISA for anticardiolipin antibody (aCL) retested positive in the immunoassay when the sera were first heat-inactivated at 56 C for 30 minutes. This was not a false positive phenomenon since the positive ELISA reactivity of the heated SLE sera was markedly reduced by inhibition with the cardiolipin antigen. Furthermore, the heat-potentiated ELISA reaction was abolished by prior IgG depletion of the SLE sera with Protein A preparation. The unmasked aCL in the heat-treated SLE sera also exhibited selective binding in ELISA to other negatively-charged phospholipids, namely phosphatidylserine and phosphatidic acid but not against either phosphatidylcholine or phosphatidylethanolamine. The data strongly indicate an interaction between antiphospholipid antibodies and heat-sensitive serum component(s), a reduction of the latter resulting in the ELISA detection of the autoantibody.