Popadiak Katarzyna, Potempa Jan, Riesbeck Kristian, Blom Anna M
Lund University, Department of Laboratory Medicine, Section of Medical Protein Chemistry, University Hospital Malmö, Malmö, Sweden.
J Immunol. 2007 Jun 1;178(11):7242-50. doi: 10.4049/jimmunol.178.11.7242.
Periodontitis is an inflammatory disease of the supporting structures of the teeth and is caused by, among other agents, Porphyromonas gingivalis. P. gingivalis is very resistant to killing by human complement, which is present in a gingival fluid at 70% of the serum concentration. We found that the incubation of human serum with purified cysteine proteases of P. gingivalis (gingipains) or P. gingivalis wild-type strains W83 and W50 resulted in a drastic decrease of the bactericidal activity of the serum. In contrast, serum treated with P. gingivalis mutants lacking gingipains (particularly strains without HRgpA) maintained significant bactericidal activity. To understand in detail the mechanism by which gingipains destroy the serum bactericidal activity, we investigated the effects of gingipains on the human complement system. We found that all three proteases degraded multiple complement components, with arginine-specific gingipains (HRgpA and RgpB) being more efficient than lysine-specific gingipain (Kgp). Interestingly, all three proteases at certain concentrations were able to activate the C1 complex in serum, which resulted in the deposition of C1q on inert surfaces and on bacteria themselves. It is therefore plausible that P. gingivalis activates complement when present at low numbers, resulting in a local inflammatory reaction and providing the bacteria with a colonization opportunity and nutrients. At later stages of infection the concentration of proteases is high enough to destroy complement factors and thus render the bacteria resistant to the bactericidal activity of complement.
牙周炎是一种牙齿支持结构的炎症性疾病，除其他因素外，牙龈卟啉单胞菌是其病因之一。牙龈卟啉单胞菌对人类补体杀伤具有很强的抵抗力，牙龈液中补体的浓度为血清浓度的70%。我们发现，将人血清与牙龈卟啉单胞菌的纯化半胱氨酸蛋白酶（牙龈蛋白酶）或牙龈卟啉单胞菌野生型菌株W83和W50一起孵育，会导致血清杀菌活性急剧下降。相比之下，用缺乏牙龈蛋白酶的牙龈卟啉单胞菌突变体（特别是没有HRgpA的菌株）处理的血清保持了显著的杀菌活性。为了详细了解牙龈蛋白酶破坏血清杀菌活性的机制，我们研究了牙龈蛋白酶对人类补体系统的影响。我们发现，所有三种蛋白酶都能降解多种补体成分，精氨酸特异性牙龈蛋白酶（HRgpA和RgpB）比赖氨酸特异性牙龈蛋白酶（Kgp）更有效。有趣的是，所有三种蛋白酶在一定浓度下都能够激活血清中的C1复合物，这导致C1q沉积在惰性表面和细菌自身上。因此，当牙龈卟啉单胞菌数量较少时激活补体，从而引发局部炎症反应，并为细菌提供定植机会和营养物质，这似乎是合理的。在感染后期，蛋白酶的浓度足够高，足以破坏补体因子，从而使细菌对补体的杀菌活性产生抗性。
