Hajishengallis George, Ratti Pukar, Harokopakis Evlambia
Center of Excellence in Oral and Craniofacial Biology and Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70119, USA.
J Biol Chem. 2005 Nov 25;280(47):38902-13. doi: 10.1074/jbc.M507326200. Epub 2005 Aug 29.
The fimbriae of the oral pathogen Porphyromonas gingivalis induce Toll-like receptor 2 (TLR2)-dependent macrophage activation upon their recognition by CD14 and the beta(2) integrin CD11b/CD18. To map functional epitopes of fimbriae that interact with these pattern recognition receptors (PRRs), we examined 20 synthetic peptides covering the entire length of the 41-kDa fimbrillin subunit. Using direct or competitive inhibition assays for receptor binding or cell activation, the CD14 binding activity of fimbriae was localized to residues 69-90 and was essential for TLR2-dependent cytokine induction. The CD11b/CD18 binding activity of fimbriae was localized to two neighboring epitopes defined by residues 166-185 and 206-225. Unlike epitope 69-90 that constitutively bound CD14, the CD11b/CD18 binding activity of epitopes 166-185 and 206-225 was inducible by integrin activators. The CD11b/CD18 binding activity played a contributory role to TLR2-dependent induction of tumor necrosis factor-alpha by fimbriae but was involved in specific down-regulation of interleukin-12. Cell activation by a combination of fimbrillin peptides corresponding to the CD14 and CD11b/CD18 binding activities resulted in higher tumor necrosis factor-alpha responses than would be expected from a simply additive effect, attributable to CD14-dependent inside-out signaling leading to enhanced binding interactions with CD11b/CD18. These data suggest that P. gingivalis fimbriae display a modular structure that interacts through discrete epitopes and in a regulated mode with distinct PRRs, which in turn differentially modulate the state of cell activation. Elucidation of pathogen interactions with PRRs at the molecular level may glean insight into host defense mechanisms as well as into microbial strategies that subvert innate immunity.
口腔病原体牙龈卟啉单胞菌的菌毛在被CD14和β2整合素CD11b/CD18识别后，可诱导Toll样受体2（TLR2）依赖性巨噬细胞活化。为了绘制与这些模式识别受体（PRR）相互作用的菌毛功能表位，我们检测了覆盖41 kDa菌毛蛋白亚基全长的20种合成肽。通过受体结合或细胞活化的直接或竞争性抑制试验，菌毛的CD14结合活性定位于第69 - 90位氨基酸残基，这对于TLR2依赖性细胞因子诱导至关重要。菌毛的CD11b/CD18结合活性定位于由第166 - 185位和第206 - 225位氨基酸残基定义的两个相邻表位。与组成性结合CD14的69 - 90位表位不同，166 - 185位和206 - 225位表位的CD11b/CD18结合活性可被整合素激活剂诱导。CD11b/CD18结合活性对菌毛依赖性TLR2诱导肿瘤坏死因子-α起辅助作用，但参与白细胞介素-12的特异性下调。由对应于CD14和CD11b/CD18结合活性的菌毛蛋白肽组合引起的细胞活化导致的肿瘤坏死因子-α反应高于简单相加效应所预期的水平，这归因于CD14依赖性的由内向外信号传导导致与CD11b/CD18的结合相互作用增强。这些数据表明，牙龈卟啉单胞菌菌毛呈现出一种模块化结构，通过离散表位并以一种受调控的方式与不同的PRR相互作用，进而差异性地调节细胞活化状态。在分子水平上阐明病原体与PRR的相互作用可能有助于深入了解宿主防御机制以及颠覆先天免疫的微生物策略。
