Hornef Mathias W, Bogdan Christian
Institute for Medical Microbiology and Hygiene, University of Freiburg, Germany.
J Endotoxin Res. 2005;11(2):124-8. doi: 10.1179/096805105X35224.
The recognition of microbial structures by Toll-like receptors (TLRs) on professional immune cells situated at sterile internal body sites occurs during invasive microbial infection. It indicates infectious non-self and thereby represents the adequate co-stimulatory signal to initiate activation of the adaptive immune system against the invading pathogen. In contrast, most epithelial body surfaces are permanently colonized by microbial organisms of the normal flora and thus TLR ligands are present under physiological conditions. In the following, we discuss the characteristics of TLR-mediated recognition by epithelial cells, the subsequent activation of the host immune system, and protective mechanisms that might help to avoid inadequate stimulation and allow differentiation between commensal or pathogenic micro-organisms. Recent findings suggest that the role of epithelial cells in the maintenance of stable microbial colonization of host surfaces and the immediate host response to infectious challenges might have to be revised.
位于无菌体内部位的专职免疫细胞上的Toll样受体（TLR）对微生物结构的识别发生在侵袭性微生物感染期间。它表明存在感染性非自身物质，从而代表启动针对入侵病原体的适应性免疫系统激活的适当共刺激信号。相比之下，大多数上皮体表被正常菌群的微生物永久定植，因此在生理条件下存在TLR配体。在本文中，我们将讨论上皮细胞介导的TLR识别的特征、宿主免疫系统的后续激活以及可能有助于避免不适当刺激并区分共生或致病微生物的保护机制。最近的研究结果表明，上皮细胞在维持宿主表面稳定的微生物定植以及宿主对感染性挑战的即时反应中的作用可能需要重新审视。
