FORMATION OF COMPLEXES COMPOSED OF Cr, Cs, AND C INACTIVATOR IN HUMAN SERUM ON ACTIVATION OF C1

CI subcomponent complexes in normal serum incubated with Clq binding substances or with proteolytic enzymes were studied by crossed Immunoelectrophoresis. Cr, Cs, trypsin. Heat aggregated IgG, immune complexes, cell‐bound antibody or complexes of C‐reactive protein with‐ protamine sulphate gave rise to dissociation of CI and the appearance of Cls protein in the 02 position. In contrast, plasmin, DNA and endotoxin did not affect the normal Cls protein pattern. Following incubation with Cr, Cs, trypsin, or complexes containing C‐reactive protein, the Cq in serum was found in a cathodal position similar to that of purified Cq. The Cs protein in the α2 position was shown to be part of a complex composed of Cr, Cs and C inactivator proteins. Cr in the complex was only detected immunochemically by using anti Cr and anti Cls in combination. The complex had a molecular weight of about 5 105 daltons. The results show that complexes of Cr, Cs and C inactivator proteins in serum are formed on C activation, implying that the complexes contain activated Cr and Cs (Cr‐Cs‐C IA). Cr‐Cs complexes with (Si mobility were not formed in vitro , β1 Clr‐Cls complexes in pathological sera could be converted to Cr‐Cs‐C IA by treatment with Cr and Cs and also, provided Clq was available in serum, by treatment with heat aggregated IgG. It was concluded that β 1 Cr‐Cs complexes in serum contain Cr and Cs in proenzyme form.