PL-binding and cofactor dependency of 3 selected monoclonal antibodies originated from patient 1. (A-B) The mAbs are tested with 2 anionic PLs (CL and PS) and with a neutral PL (PC) in the presence of FCS. (A) Results with the somatically mutated M9; (B) results with the germline M7 and the mutated (but apparently not antigen driven) M2. Protein A-purified human IgG (PC, CL, or PS Hu IgG) are used as negative controls. The results are expressed as OD at 492 nm minus background (mean ± SE of 2 experiments). (C) Competition experiments using biotin-labeled M9 and M7 mAbs and varying dilutions of the patient 1 serum to test the ability of the serum to inhibit the binding of the mAbs on solid phase cardiolipin. (D) The mAbs are tested for their reactivity with CL in the absence or the presence of FCS or purified human cofactors (β2GP1, PT, prot S, prot S, and AnV). The results are expressed as the percentage of OD increase in the presence of FCS or purified cofactors.