Analysis of antigen specificity of the monoclonal Ab preparations. (A) ELISA analysis of antigen specificity. IgG-APS (500 μg/mL), IgG-NHS (500 μg/mL), 4C5 (100 μg/mL), MuMoAbC (100 μg/mL), and anti-A2 MoAb (100 μg/mL) were diluted 1/50 for aCL and 1/100 for anti-β₂GPI and anti-A2 assays, and tested by ELISA, as described in “Preparation of immunoglobulin G” and “Western blotting to detect antigen specificity.” Results are expressed as means ± SD O.D. units. (B) Western blot analysis of antigen specificity. Proteins (25 μg/lane from HUVECs, A2^+/+, and A2^−/−) as well as 200 ng/lane purified β₂GPI were resolved on 10% sodium dodecyl sulfate–polyacrylamide gels and blotted with the respective IgGs (4C5 and MuMoAbC). To control for loading, the same blot was stripped and probed with monoclonal IgG directed against A2 and glyceraldehyde-3-phosphate dehydrogenase.