Innate Immune Response via Intracellular Receptor NODs and Periodontal Diseases

在先天性免疫中，病原体相关分子模式(PAMPs)是微生物常见的和特殊的结构，由宿主细胞中以Toll样受体(TLRs)为代表的模式识别分子(PRM)识别。另一个细胞内PRM家族，NOD1和NOD2，识别细菌肽聚糖。我们通过不同细胞中的TLR和NODS来检测先天免疫反应，以阐明先天免疫在口腔粘膜中的作用。在这些实验中，只使用化学合成的配体来排除细菌制剂中的次要成分：细菌脂肽Pam3CSSNA(TLR2配体)、大肠杆菌型脂质A LA-15-PP(TLR4配体)、细菌CpG DNA(TLR9配体)、MDP(NOD2配体)和ie-DAP(NOD1配体)。我们证明了NOD1或NOD2激动剂与不同的TLR激动剂协同诱导人单核细胞THP-1细胞产生炎性细胞因子。同样的组合刺激也在人树突状细胞中诱导了Th1系反应。到目前为止，人类口腔上皮细胞也携带所有TLR和NOD分子。然而，不同配体的刺激并不能诱导炎症细胞因子的产生，但却能明显诱导抗菌因子，如肽聚糖识别蛋白(PgrP-L、I-α、I-β、S)和β-防御素2。考虑到所有这些发现，我们假设了一个工作假说：口腔上皮细胞与正常菌群中的各种细菌相互作用，积极地产生抗菌因子。然而，这些细胞是负控制的，以防止免疫和炎症反应的诱导。当负调控被关闭时，就会发生过度的炎症反应，进而引发组织破坏。一旦黏膜屏障被打破，聚集的巨噬细胞和树突状细胞就会启动Th1系获得性免疫反应，这是以牙周病为代表的口腔粘膜疾病的典型特征。

In innate immunity, common and peculiar structures of microbes, pathogen-associated molecular patterns (PAMPs), are recognized by pattern-recognition molecules (PRMs) represented by Toll-like receptors (TLRs) in host cells. Another intracellular PRM family, NOD1 and NOD2, recognizes bacterial peptidoglycans. We examined innate immune responses through TLRs and NODs in various cells to elucidate the roles of innate immunity in the oral mucosa. In these experiments, only chemically synthesized ligands were used to rule out the influences of minor components in bacterial preparations ; bacterial lipopeptide Pam3CSSNA (TLR2 ligand), E.coli-type lipid A LA-15-PP (TLR4 ligand), bacterial CpG DNA (TLR9 ligand), MDP (NOD2 ligand) and iE-DAP (NOD1 ligand). We demonstrated that NOD1- or NOD2-agonist in combination with various TLR-agonists synergistically induced inflammatory cytokines in human monocytic THP-1 cells in culture. The same combinatory stimulation also induced Th1-lineage responses in human dendritic cells. Human oral epithelial cells also carried all of the TLR and NOD molecules examined to date. However, stimulation by the respective ligands did not induce inflammatory cytokines, but definitely induced anti-bacterial factors such as peptidoglycan recognition proteins (PGRP-L,Iα,Iβ,S) and β-defensin 2. Taking all of these findings in consideration, we postulate a working hypothesis : Oral epithelial cells, which interact with various bacteria in normal flora, actively produce anti-bacterial factors. The cells, however, are negatively controlled to prevent the induction of immune and inflammatory responses. When the negative regulation is turned off, excessive inflammatory responses occur, which in turn initiate tissue destruction. Once the mucosal barrier was broken, accumulated macrophages and dendritic cells initiate Th1-lineage acquired immune responses, which are were typical of oral mucosal disease represented by periodontal diseases.