Activation of the early components of the classical complement pathway under physiologic conditions
Ziccardi, R.J.
Journal of Immunology 126(5): 1769-1773
1981
ISSN/ISBN: 0022-1767 PMID: 7217665 Document Number: 178001
The early events in activation of the classical complement (C) pathway were studied by treating normal human serum (NHS) with different C activators and measuring the following parameters as a function of time: C1 or EAIgM were added to NHS. The nonimmune activator lipopolysaccharide R595 differed from these immune activators in that it induced the activation of 5 times less C2 per C.hivin.1. The Km (0.96 .times. 10-6 M) and turnover number (303 C4/C.hivin.1 per min) were calculated for the activation of purified C4 by purified C.hivin.1. These values are consistent with the observed turnover of C4 in NHS when the short half-life of C.hivin.1 is taken into account. The early classical pathway was reconstituted from purified C1q, C1r, C1s, C.hivin.1-In, C2 and C4, all at physiologic concentrations. When treated with aggIgG, this purified component mixture and NHS were indistinguishable with respect to consumption of C2 and C4. Thus, C.hivin.1-In is the only serum factor involved in the control of C.hivin.1 activities. Evidently the control protein C.hivin.1-In is extraordinarily efficient.