The innate immune system relies on a vast array of non-clonally expressed pattern recognition receptors for the detection of pathogens. Pattern recognition receptors bind conserved molecular structures shared by large groups of pathogens, termed pathogen-associated molecular patterns. The Toll-like receptors (TLRs) are a recently discovered family of pattern recognition receptors which show homology with the Drosophila Toll protein and the human interleukin-1 receptor family. Engagement of different TLRs can induce overlapping yet distinct patterns of gene expression that contribute to an inflammatory response. The TLR family is characterized by the presence of leucine-rich repeats and a Toll/interleukin-1 receptor-like domain, which mediate ligand binding and interaction with intracellular signaling proteins, respectively. Most TLR ligands identified so far are conserved microbial products which signal the presence of an infection, but evidence for some endogenous ligands that might signal other danger conditions has also been obtained. Molecular mechanisms for pathogen-associated molecular pattern recognition still remain elusive but seem to be more complicated than initially anticipated. In most cases, direct binding of microbial ligands to TLRs still has to be demonstrated. Moreover, Drosophila TLRs bind endogenous ligands, generated through a proteolytic cascade in response to an infection. In the case of endotoxin, recognition involves a complex of TLR4 and a number of other proteins. Moreover, TLR heterodimerization further extends the spectrum of ligands and modulates the response towards specific ligands. The fact that TLR expression is regulated in both a cell type- and stimulus-dependent fashion further contributes to the complexity.

中文翻译：

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Toll样受体在病原体识别中的作用。

先天免疫系统依赖于大量非克隆表达的模式识别受体来检测病原体。模式识别受体结合由大量病原体共享的保守分子结构，称为病原体相关分子模式。Toll样受体（TLR）是最近发现的模式识别受体家族，与果蝇Toll蛋白和人类白介素1受体家族具有同源性。参与不同的TLR可以诱导重叠但截然不同的基因表达模式，从而导致炎症反应。TLR家族的特征是富含亮氨酸的重复序列和Toll / interleukin-1受体样结构域，分别介导配体结合和与细胞内信号蛋白的相互作用。迄今为止，大多数鉴定出的TLR配体都是保守的微生物产物，可发出感染信号，但也已获得一些内源性配体的信号，这些信号可能暗示了其他危险情况。病原体相关的分子模式识别的分子机制仍然难以捉摸，但似乎比最初预期的要复杂。在大多数情况下，仍然必须证明微生物配体与TLR的直接结合。此外，果蝇TLR结合通过蛋白水解级联反应产生的内源性配体。就内毒素而言，识别涉及TLR4和许多其他蛋白质的复合物。此外，TLR异二聚化进一步扩展了配体的范围，并调节了对特定配体的反应。