Harboe Morten, Johnson Christina, Nymo Stig, Ekholt Karin, Schjalm Camilla, Lindstad Julie K, Pharo Anne, Hellerud Bernt Christian, Nilsson Ekdahl Kristina, Mollnes Tom Eirik, Nilsson Per H
Department of Immunology, Oslo University Hospital, Rikshospitalet, 0424 Oslo, Norway.
Research Laboratory, Nordland Hospital, 8092 Bodo, Norway.
Proc Natl Acad Sci U S A. 2017 Jan 24;114(4):E534-E539. doi: 10.1073/pnas.1612385114. Epub 2017 Jan 9.
Two functions have been assigned to properdin; stabilization of the alternative convertase, C3bBb, is well accepted, whereas the role of properdin as pattern recognition molecule is controversial. The presence of nonphysiological aggregates in purified properdin preparations and experimental models that do not allow discrimination between the initial binding of properdin and binding secondary to C3b deposition is a critical factor contributing to this controversy. In previous work, by inhibiting C3, we showed that properdin binding to zymosan and Escherichia coli is not a primary event, but rather is solely dependent on initial C3 deposition. In the present study, we found that properdin in human serum bound dose-dependently to solid-phase myeloperoxidase. This binding was dependent on C3 activation, as demonstrated by the lack of binding in human serum with the C3-inhibitor compstatin Cp40, in C3-depleted human serum, or when purified properdin is applied in buffer. Similarly, binding of properdin to the surface of human umbilical vein endothelial cells or Neisseria meningitidis after incubation with human serum was completely C3-dependent, as detected by flow cytometry. Properdin, which lacks the structural homology shared by other complement pattern recognition molecules and has its major function in stabilizing the C3bBb convertase, was found to bind both exogenous and endogenous molecular patterns in a completely C3-dependent manner. We therefore challenge the view of properdin as a pattern recognition molecule, and argue that the experimental conditions used to test this hypothesis should be carefully considered, with emphasis on controlling initial C3 activation under physiological conditions.
备解素具有两种功能；稳定替代途径转化酶C3bBb已被广泛接受，而备解素作为模式识别分子的作用则存在争议。纯化的备解素制剂中存在非生理性聚集体，以及实验模型无法区分备解素的初始结合和C3b沉积后的继发性结合，是导致这一争议的关键因素。在先前的研究中，通过抑制C3，我们发现备解素与酵母聚糖和大肠杆菌的结合不是一个原发性事件，而是完全依赖于初始C3沉积。在本研究中，我们发现人血清中的备解素与固相髓过氧化物酶呈剂量依赖性结合。这种结合依赖于C3激活，这在使用C3抑制剂compstatin Cp40的人血清、C3缺失的人血清中，或在缓冲液中应用纯化的备解素时均未观察到结合得以证明。同样，通过流式细胞术检测，人血清孵育后备解素与人脐静脉内皮细胞或脑膜炎奈瑟菌表面的结合完全依赖于C3。备解素缺乏其他补体模式识别分子共有的结构同源性，并主要在稳定C3bBb转化酶中发挥作用，但其被发现以完全依赖于C3的方式结合外源性和内源性分子模式。因此，我们对备解素作为模式识别分子的观点提出质疑，并认为在检验这一假设时所使用的实验条件应仔细考虑，重点是在生理条件下控制初始C3激活。
