Wolbink G J, Brouwer M C, Buysmann S, ten Berge I J, Hack C E
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam.
J Immunol. 1996 Jul 1;157(1):473-9.
The in vivo function of C-reactive protein (CRP) is unknown. Among the in vitro functions assigned to CRP is the ability to activate complement via the classical pathway. To date, there is no evidence supporting that CRP exerts this function in vivo. We here show a novel approach to assess CRP-mediated complement activation in vivo, which is based on the property that activated complement factors C3 and C4 fix to CRP during complement activation induced by this acute phase protein. We developed specific ELISAs for complexes between CRP and C4b, C4d, C3b, or C3d. We established that in vitro complement-CRP complexes were formed only during CRP-dependent activation, and not during activation by other activators, even in the presence of high CRP levels. Circulating levels of complement-CRP complexes were undetectable in normal donors, but significantly increased in nine patients following implantation of a renal allograft. Importantly, levels of complement-CRP complexes did not change in these patients upon a bolus infusion of mAb OKT3, which induces activation of the classical complement pathway, demonstrating in vivo that complement-CRP complexes are not formed during CRP-independent activation of complement, even when CRP is elevated. We conclude that measurement of complement-CRP complexes provides a suitable tool to study CRP-mediated activation of complement in vivo. Furthermore, increased levels of these complexes occur in clinical samples, indicating that CRP may induce activation of complement in vivo.
C反应蛋白（CRP）的体内功能尚不清楚。在赋予CRP的体外功能中，有一项是通过经典途径激活补体的能力。迄今为止，尚无证据支持CRP在体内发挥此功能。我们在此展示了一种评估体内CRP介导的补体激活的新方法，该方法基于在这种急性期蛋白诱导的补体激活过程中，活化的补体因子C3和C4会与CRP结合的特性。我们开发了针对CRP与C4b、C4d、C3b或C3d之间复合物的特异性酶联免疫吸附测定（ELISA）。我们确定，体外补体-CRP复合物仅在依赖CRP的激活过程中形成，而在其他激活剂激活过程中不形成，即使存在高CRP水平也是如此。正常供体中未检测到循环中的补体-CRP复合物水平，但在9例肾移植受者术后显著升高。重要的是，在这些患者中，静脉注射单克隆抗体OKT3（可诱导经典补体途径激活）后，补体-CRP复合物水平并未改变，这在体内证明了在补体非依赖CRP的激活过程中，即使CRP升高，也不会形成补体-CRP复合物。我们得出结论，补体-CRP复合物的检测为研究体内CRP介导的补体激活提供了一种合适的工具。此外，临床样本中这些复合物水平升高，表明CRP可能在体内诱导补体激活。
