Hindmarsh E J, Marks R M
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, USA.
Eur J Immunol. 1998 Mar;28(3):1052-62. doi: 10.1002/(SICI)1521-4141(199803)28:03<1052::AID-IMMU1052>3.0.CO;2-W.
The vasculature is protected from complement activation by regulatory molecules expressed on endothelial cells. However, complement fixation also occurs on subendothelial extracellular matrix (ECM) in vitro, and is initiated simply by retraction or removal of overlying cells. To investigate mechanisms controlling vascular complement activation, we examined subendothelial ECM for the presence of complement regulatory proteins. Decay-accelerating factor (DAF) was found on both human umbilical vein endothelial cells (HUVEC) and in their ECM; in contrast, membrane cofactor protein was found only on cells. ECM and HUVEC DAF were distinguishable based on several properties. While HUVEC DAF is anchored to cell membranes by a phospholipase C-sensitive glycosylphosphatidylinositol linkage. DAF was removed from ECM only by proteolytic digestion. Cytokines (TNF-alpha, IL-1 beta, IL-4) increased HUVEC DAF expression, but had minimal effect on ECM DAF; in contrast, phorbol 12-myristate 13-acetate (PMA) and wheat germ agglutinin markedly increased DAF on both HUVEC and ECM. The effect of PMA was mediated by activation of protein kinase C. The complement regulatory potential of ECM DAF was assessed by evaluating the effect of DAF-neutralizing antibodies on C3 deposition on HUVEC ECM, as well as on HeLa cell ECM, which had a considerably higher DAF content. DAF blockade enhanced C3 deposition on HeLa ECM, but had no effect on HUVEC ECM. As ECM DAF is likely to be immobile, i.e. able to interact only with C3 convertases forming in the immediate vicinity, its ability to regulate complement activation may be particularly density dependent, and contingent on endothelial-dependent up-regulation.
血管系统通过内皮细胞表达的调节分子来避免补体激活。然而，体外补体固定也会发生在血管内皮细胞下的细胞外基质（ECM）上，并且仅仅通过覆盖细胞的回缩或去除就会引发。为了研究控制血管补体激活的机制，我们检测了血管内皮细胞下的细胞外基质中补体调节蛋白的存在情况。衰变加速因子（DAF）在人脐静脉内皮细胞（HUVEC）及其细胞外基质中均有发现；相比之下，膜辅因子蛋白仅在细胞上被发现。基于几个特性，细胞外基质和人脐静脉内皮细胞的衰变加速因子是可区分的。人脐静脉内皮细胞的衰变加速因子通过对磷脂酶C敏感的糖基磷脂酰肌醇连接锚定在细胞膜上。衰变加速因子仅通过蛋白水解消化才能从细胞外基质中去除。细胞因子（肿瘤坏死因子-α、白细胞介素-1β、白细胞介素-4）增加了人脐静脉内皮细胞衰变加速因子的表达，但对细胞外基质的衰变加速因子影响极小；相反，佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）和麦胚凝集素显著增加了人脐静脉内皮细胞和细胞外基质上的衰变加速因子。佛波醇12-肉豆蔻酸酯13-乙酸酯的作用是由蛋白激酶C的激活介导的。通过评估衰变加速因子中和抗体对C3沉积在人脐静脉内皮细胞细胞外基质以及对衰变加速因子含量高得多的HeLa细胞细胞外基质上的影响，来评估细胞外基质衰变加速因子的补体调节潜力。衰变加速因子的阻断增强了C3在HeLa细胞细胞外基质上的沉积，但对人脐静脉内皮细胞细胞外基质没有影响。由于细胞外基质衰变加速因子可能是固定不动的，即仅能与在紧邻区域形成的C3转化酶相互作用，其调节补体激活的能力可能特别依赖于密度，并取决于内皮细胞依赖性上调。
