Antibodies to Domain I of β2Glycoprotein I are in close relation to patients risk categories in Antiphospholipid Syndrome (APS)

IntroductionAntiphospholipid Syndrome (APS) is characterized by the presence of circulating antiphospholipid antibodies in patients with thrombosis or pregnancy morbidity. Antibodies involved in these disorders are mainly those directed against β2-Glycoprotein I (β2GPI) with the major epitope apparently located on discontinuous antigen with several parts of Domain I (DmI) involved. The relation between anti-DmI antibodies and patients’ risk categories is unknown.Materials and MethodsThe synthetic full-length and correctly-folded DmI (1–64) to set up a competitive inhibition enzyme-linked immunoadsorbent assays (ELISA) was used. Plasma of 22 patients with APS and triple positivity [Lupus Anticoagulant positive (LAC+), IgG anti-cardiolipin positive (aCL+), IgG anti-β2GPI positive (a β2GPI +)], 15 with double positivity (IgG aCL+, IgG aβ2GPI+), 9 with single positivity (IgG aβ2GPI+) and 20 controls were evaluated.ResultsMedian of percentage inhibition was 25.5% [interquartile range (IQR)17.2-33.0] in triple positive patients. Significantly lower inhibition was observed in patients with double positivity, median inhibition 5.0% (IQR 0.0-27.0) and in patients with single positivity median inhibition was 2.0% (IQR 0.5-8.0) (p < 0.0001). No inhibition was detected in control subjects or using β2GPI peptides (40–52 and 57–70), or when antithrombin, an insignificant control protein was used.ConclusionsHigh risk patients with APS and triple laboratory positivity as compared with double and single positivity patients have significantly higher titre of anti-DmI antibodies as evaluated by an inhibition test.