Anticardiolipin and Anti-β₂-GPI Are Two Distinct Populations of Autoantibodies

Summary

This study has been undertaken to assess whether anticardiolipin and anti-(32-GPI are two distinct populations of (auto)antibodies, and to clarify whether the β₂-GPI region critical for phospholipid binding is also crucial for anti-β₂-GPI reactivity.

Fourteen of the 62 anticardiolipin (aCL) ELISA positive sera (22.6%) were positive for anti-β₂-GPI by immunoblotting, 42 (67.7%) for aCL using TLC immunostaining.

IgG fractions from 5 sera gave the same anticardiolipin reactivity detected by TLC immunostaining in the corresponding sera.

All anti-β₂-GPI-positive sera were reactive with the phenylthio-carbamyl derivative of the protein, indicating that binding of phe-nylisothiocyanate with lysine residues does not modify the molecule antigenicity. In addition, incubation of IgG fractions with the phospholipid binding site did not modify reactivity with β₂-GPI.

These findings demonstrate that: a) “true” antiphospholipid antibodies are detectable in patients sera; b) aCL and anti-β₂-GPI have a different immunological profile; c) the β₂-GPI phospholipid-binding site is not the region recognized by the antibodies.

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