Activation of the early components of the classical complement pathway under physiologic conditions.

作者：Robert J. Ziccardi · 发表于：The Journal of Immunology · 年份：1981 · DOI：10.4049/jimmunol.126.5.1769 · 被引用次数：124 · 研究领域：Pharmacological Effects of Natural Compounds、Erythrocyte Function and Pathophysiology、Complement system in diseases

Abstract We studied the early events in activation of the classical complement (C) pathway by treating normal human serum (NHS) with different C activators and measuring the following parameters as a function of time: C1 activation, C2 consumption, C4 consumption, and C1 inactivation. C1 activation and inactivatidn were quantitated with SDS-PAGE radioassays, whereas C2 and C4 consumption were measured by hemolytic titration. In undiluted NHS at 37°C, C1 activation as well as C2 and C4 consumption were turned off within 3 min after the addition of limiting quantities of activator. The binding of C1-inactivator (C1-ln) to C1 was so rapid that no free C1 was detected at any time during the reaction. Direct binding studies with purified proteins revealed that, under physiologic conditions, 50% of the C1 bound to C1-In within 13 sec and 90% within 55 sec of activation. Thus, the activation of C1 is the rate limiting step for this 3-min reaction sequence. C1 turned over a surprisingly low number of C2 and C4 molecules in NHS. This was due to the fact that C1 was so rapidly inactivated by C1-ln. An average of only 4 C2 molecules and 35 C4 molecules Were activated per C1 molecule when soluble agglgG, tetanus-anti-tetanus precipitate, EAIgG, or EAIgM were added to NHS. The nonimmune activator LPS R595 differed from these immune activators in that it induced the activation of 5 times less C2 per C1. The Michaelis-Menten constant (0.96 × 10−6 M) and turnover number (303 C4/C1/min) were ...