IgG binding in the modified ACA ELISA of the patient sera, diluted 1:600 (no. 1) or 1:100 (others). The antibody binding step was performed in the presence of gelatin buffer (□), 10 μg/mL purified β₂GPI of human () or bovine (▩) origin, or 10% bovine plasma (⧇) or serum (). The means ± SD of specific absorbance values from three independent experiments are shown.