부산대학교 도서관

ABSTRACT. Hemolytic complement was found to be absent in the serum of an 11-yr-old girl (R.N.) with meningococcal septicemia. C1, C4, an C2 were slightly decreased, C3 was absent, C5-C9 within the normal range. B levels immunochemically and electrophoretic mobility of B were normal. C3d was >1000% of a pooled EDTA-plasma standard indicating hypercatabolism of C3. On incubation of the patient's serum with normal human serum activation of C3 occurred even in the presence of 0.04 M EDTA. The amount of C3b generated was, however, greater without any chelating agent or in Mg-EGTA. On gel filtration of the serum two protein containing peaks were found to be responsible for activation of C3: the IgG containing peak was able to activate C3 in normal human serum without chelating agents and in Mg-EGTA but not in the presence of EDTA. The IgM-containing peak activated the third component of complement even in the presence of EDTA. The factor responsible for this phenomenon was termed C3 converting factor (C3 CoF). The IgG fraction of the patients serum caused activation of C3 in Mg-EGTA. However, in the presence of EDTA no activation of C3 could be induced even if physiological concentrations of the patients IgG were added to normal human EDTA-plasma. Thus the activity of the patient's IgG did not differ from typical C3 nephritic factor. The decay of C2 in EAC42 intermediates in the presence of the patient's IgG was uninfluenced indicating that it did not carry autoantibody activity against the classical pathway convertase C4b,2a, an activity recently termed NFc. As the ability of the patient's serum to activate C3 in the presence of excess EDTA was still unexplained further analyses were performed. C3 CoF was found to be a β 2-euglobulin and could be separated from IgG by anion exchange chromatography following euglobulin precipitation. C3 conversion with this material was independent from Ca2+and Mg2+. It was partly heat resistant at 56° C and could not be inhibited by soy bean trypsin inhibitor at 5 mg/ml. In contrast, DFP at 5 mM concentration lead to approximately 50% inhibition indicating that C3 CoF might be a serine protease. Treatment of patient's EDTA plasma with anti-C3 or anti-B totally eliminated C3 CoF activity while antialbumin, anti-C2, anti-C4, or nonimmune rabbit-IgG did not. Precipitation with anti-IgG partly eliminated C3 CoF but absorption of serum with an anti-IgG affinity column totally eliminated C3 CoF; these observations suggest that C3 CoF may be a C3 NeF-stabilized alternative pathway C3 convertase.