Ziccardi R J
J Immunol. 1986 May 1;136(9):3378-83.
We have demonstrated that immune complexes turn over C1, i.e., limiting quantities of immune complexes activate an excess of C1. This was readily apparent in a system of purified C1 and C1-inhibitor (C1-In) but not in normal human serum (NHS). The following results indicate that C3 and C4 are the serum factors responsible for the inhibition of C1 turnover by immune complexes. 1) In a purified protein system composed of C1 and C1-In at pH 7.5, ionic strength 0.14 M, doses of immune complexes that activated all the C1 in 60 min at 37 degrees C yielded no detectable C1 activation when C2, C3, and C4 were also present. All proteins were at their physiologic concentrations. Activation was quantified by SDS-PAGE analysis and hemolytic titration 2) In order to inactivate C3 and C4, NHS was treated with 50 mM methylamine (MeAm) for 15 min at 37 degrees C, after which the MeAm was removed by dialysis. The activities of C1, C2, and C1-In were unaffected by this treatment. Doses of immune complexes that consumed no C1 in NHS, consumed all the C1 in MeAm-treated NHS (MeAm-NHS). 3) Reconstitution of MeAm-NHS with physiologic concentrations of C3 and C4 rendered the serum again resistant to excessive C1 consumption by immune complexes. Immune complexes used in these studies included EA-IgG, EA-IgM, tetanus-human anti-tetanus, and aggregated human IgG. There appeared to be specificity to the inhibition reaction since C4 by itself could inhibit C1 consumption by EA-IgM, whereas the presence of C3 was also required to control EA-IgG. Finally, N-acetyl-L-tyrosine was added to NHS at a final concentration of 30 mM. This nucleophile did not interact with native C3 or C4, nor did it directly activate C1. However, upon the addition of low doses of immune complexes, acetyl tyrosine did yield uncontrolled C1 activation, presumably by binding nascent C3b and C4b and thereby blocking their attachment to the immune complexes. We conclude that in NHS there is a mechanism of feedback inhibition by which nascent C3b and C4b inhibit C1 turnover by immune complexes. This mechanism of control might be physiologically important in that it prevents excessive complement activation by low concentrations of immune complexes.
我们已经证明免疫复合物可使C1周转，即有限量的免疫复合物能激活过量的C1。这在纯化的C1和C1抑制剂（C1-In）系统中很明显，但在正常人血清（NHS）中则不然。以下结果表明，C3和C4是血清中负责抑制免疫复合物引起的C1周转的因子。1）在pH 7.5、离子强度0.14 M的由C1和C1-In组成的纯化蛋白系统中，在37℃下60分钟内激活所有C1的免疫复合物剂量，当同时存在C2、C3和C4时未检测到C1激活。所有蛋白质均处于其生理浓度。通过SDS-PAGE分析和溶血滴定对激活进行定量。2）为了使C3和C4失活，将NHS在37℃下用50 mM甲胺（MeAm）处理15分钟，之后通过透析去除MeAm。C1、C2和C1-In的活性不受此处理的影响。在NHS中不消耗C1的免疫复合物剂量，在经MeAm处理的NHS（MeAm-NHS）中消耗了所有C1。3）用生理浓度的C3和C4重建MeAm-NHS，使血清再次对免疫复合物引起的过量C1消耗具有抗性。这些研究中使用的免疫复合物包括EA-IgG、EA-IgM、破伤风-人抗破伤风和聚集的人IgG。抑制反应似乎具有特异性，因为C4本身可抑制EA-IgM引起的C1消耗，而控制EA-IgG则还需要C3的存在。最后，以终浓度30 mM将N-乙酰-L-酪氨酸添加到NHS中。这种亲核试剂不与天然C3或C4相互作用，也不直接激活C1。然而，加入低剂量的免疫复合物后，乙酰酪氨酸确实导致了不受控制的C1激活，可能是通过结合新生的C3b和C4b，从而阻止它们附着于免疫复合物。我们得出结论，在NHS中存在一种反馈抑制机制，通过该机制新生的C3b和C4b抑制免疫复合物引起的C1周转。这种控制机制在生理上可能很重要，因为它可防止低浓度免疫复合物引起的补体过度激活。
