Failure of autoantibodies to dissociate the C1-inh-C1s complex. The concentrations of C1-inh and autoantibodies and 125I-labeled C1s were 2.1 µM, 0.9 µM, and 1.8 µM (75,000 cpm), respectively. In the case of C1s-C1-inh complex formation, C1-inh was preincubated with C1s for 2 hr before addition of autoantibody. The reaction volume was 40 Jul in PBS-1% Triton ×100. Lane 1: 125I-labeled C1s alone; lane 2: C1-inh and 125I-labeled C1s incubated 2 hr, 37°C; lanes 3–8: C1-inh and 125I-labeled C1s incubated 2 hr, 37°C, then autoantibody added and incubation continued for 1 hr (lane 3), 2 hr (lane 4), 4 hr (lane 5), 6 hr (lane 6), 8 hr (lane 7), and 16 hr (lane 8). Data shown are from Patient 1 autoantibody but an identical result was obtained with Patient 2 autoantibody.