Summary
The aim of this study was to evaluate the heterogeneity of IgG-anti- β2 -glycoprotein I antibodies (IgG-aβ2 GPI) as regarding their reactivity pattern against different sources of human β2 GPI,their avidity and their association with clinical events of antiphospholipid syndrome (APS).Three thousand six hundred and eightyfour consecutive patient sera were routinely tested for IgG-a β2 GPI over 1 year using an in-house ELISA with 2 different commercial preparations of human purified β2GPI. Of the 340 sera found positive, all those clinically documented were included in this study; 61 were positive with only one preparation (S1) and 59 with both (S2).The results of ELISA were confirmed by Western blot. Heterogeneity was stressed by testing sera with a human recombinant protein and 3 β2 GPI-related peptides. No contribution of glycosylation in the binding to β2GPI was found.The avidity indices for each protein were significantly higher in S1 than in S2 (p = 0.0021). S2 were more associated with antiphospholipid antibodies than S1 (75% versus 21% ; p <0.0001).A similar frequency of the main clinical features of APS was found in S1 and S2 sera (69% and 71%, respectively). In conclusion, our data show a heterogeneity in the antigenic reactivity pattern of IgG- a β2 GPI and a relationship between a binding profile and antibody avidity.This heterogeneity could represent a crucial factor of variability in test results and underlines the difficulty of getting standardisation.
Keywords
β2-glycoprotein I - heterogeneity - avidity - antiphospholipid syndrome