Binding of the plasma protease C1 inhibitor (C1Inh, SERPING1) to the C1s and C1r subunits of the C1 complex leads to C1 disassembly, releasing inactive C1r:C1Inh and C1s:C1Inh complexes (Arlaud et al. 1979, Sim et al. 1979, Ziccardi & Cooper 1979). Thus C1Inh plays an important role in regulating nonspecific complement activation (Ziccardi et al. 1983).