Inhibition of annexin 2 enhancement of plasmin generation by anti–annexin 2 IgG. (A) Plasminogen activation by tPA in a purified protein assay. Initial rates of plasmin generation were calculated as RFU/min² . Results are shown for 3 healthy controls (CON) and 2 SLE patients lacking anti-A2 antibodies (SLE). The effect of individual patient anti-A2–containing IgG on plasmin generation is depicted (A-G). Shown are mean values ± SE (n = 3-10). (B) Effect of anti-A2–depleted IgG on plasmin generation. Plasmin generation was recorded in the presence of A2 alone, patient anti-A2–containing IgG alone (Hu > A2 IgG), both A2 and Hu > A2 IgG, and A2 in the presence of IgG depleted of anti-A2 antibodies (Hu > A2 ID). (C) Effect of patient anti–A2 IgG on HUVEC-based plasmin generation. Human umbilical vein endothelial cells (HUVECs) were preincubated with IgG lacking reactivity against A2 from 2 APS patient samples containing anti-β₂GPI and anticardiolipin antibodies (CON), as well as with 6 patient IgG samples containing anti-A2 (C,E,G-J). Results are expressed in relation to the mean value for patient controls (± SEM, n = 3). (D) Effect of rabbit anti–human A2 on tPA-dependent plasmin generation. Initial rates of tPA-induced plasmin generation were recorded in the presence of HUVECs preincubated with medium alone or with rabbit polyclonal anti–human A2 (RAH-A2) or rabbit nonimmune IgG (RNI).