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.