Avidity of anticardiolipin antibodies-A factor that could be important for their detection by ELISA methods

Avidity is an important feature of antibodies associated with their pathogenic effects. Anticardiolipin antibodies (aCLs) are the most commonly examined antiphospholipid antibodies, however, their avidity has been investigated only marginally. The aim of the study was to compare the avidity of the antibodies specifically bound to the cardiolipin-coated microtitrate wells with those bound to the wells bearing no cardiolipin in various conditions. We analysed 22 serum samples with high, medium and low levels of aCL IgG. The avidity of aCL IgG was determined in serially diluted sera by the ELISA method in the presence of increasing urea concentrations (from 2 to 8 mol/L) as a chaotropic agent. The serum dilution 1:50 and 1:100 and the concentrations of urea 6 mol/L and 8 mol/L seemed to be suitable for the determination of aCL avidity. The avidity of antibodies specifically bound to the cardiolipin and those bound to the cardiolipin-free wells significantly differed in their avidity. The simultaneous determination of higher-avidity aCL and lower-avidity polyspecific antibodies, whose presence complicates the ELISA methods by an increase of the background signal, might limit the shortcomings of some ELISA methods.