Adenosine Shapes Neonatal Toll-like Receptor Function

描述(由申请人提供)：新生儿感染的风险增加，但其易感性的机制尚未完全确定。Toll样受体(Toll-like Receptor，TLRs)在识别微生物成分中起着至关重要的作用，包括细菌脂肽(BLPs)，它们通过TLR1/2(三酰化BLPs)或TLR2/6(二酰化BLPs)的异源二聚体激活单核细胞，在多种细菌中表达。初步研究表明，尽管TLRs及其相关信号成分表达正常，但在BLP诱导的促炎和Th1极化细胞因子肿瘤坏死因子-α(TNF-α)的合成过程中，人类新生儿单核细胞表现出2-3对数的损伤，但保留了BLP诱导的IL-6的产生，IL-6具有抗炎和Th2极化活性。对表达BLPS的致病细菌E.ColiK1/r的反应中，新生儿肿瘤坏死因子-α的产生也明显受到类似的损害。我们发现，BLP和E.col1诱导的新生儿单核细胞产生的肿瘤坏死因子-α的减少是由于血浆腺苷的作用，腺苷是一种内源性嘌呤代谢产物，具有免疫调节特性，在应激或缺氧条件下从细胞中释放出来。新生儿单个核细胞对腺苷诱导的肿瘤坏死因子-α的产生抑制和腺苷诱导的环磷酸腺苷的产生特别敏感，环磷酸腺苷是一种细胞内代谢物，可以抑制肿瘤坏死因子-α的合成，同时保持IL-6的产生。该项目的总体目标是表征新生儿腺苷系统在调节TLR介导的新生儿单核细胞天然免疫反应中的作用。这一目标将通过三个具体目标来实现：(1)确定新生儿单核细胞对腺苷更敏感的机制，(2)确定腺苷受体亚型(S)，该亚型介导抑制BLP和大肠杆菌诱导的新生儿单核细胞产生肿瘤坏死因子-α，以及(3)表征腺苷受体结合导致BLP和E.Coli诱导的单核细胞产生减少的肿瘤坏死因子-α，同时保持IL-6产生的机制。机制分析将定义腺苷如何改变新生儿TLR介导的免疫反应。总体而言，这些研究将加深我们对人类新生儿独特的生理如何从根本上改变出生时的先天免疫的理解。

DESCRIPTION (provided by applicant): Newborns are at increased risk of infection yet the mechanisms underlying their susceptibility are incompletely defined. Toll-like receptors (TLRs) play crucial roles in the recognition of microbial components including bacterial lipopeptides (BLPs), expressed by a wide-range of bacteria, that activate monocytes via a heterodimer of TLR1/2 (triacylated BLPs) or TLR2/6 (diacylated BLPs). Preliminary studies indicate that despite normal expression of TLRs and associated signaling components, human newborn blood monocytes demonstrate a 2- to 3-log impairment in BLP-induced synthesis of pro-inflammatory and Th1-polarizing cytokine tumor necrosis factor-alpha (TNF-alpha) with preservation of BLP-induced production of IL-6, a cytokine with anti-inflammatory and Th2-polarizing activities. Similar impairment in neonatal TNF-alpha production is evident in response to E. coli K1/r, a pathogenic bacterium that expresses BLPs. We have discovered that impaired BLP- and E. col1- induced TNF-alpha production from neonatal blood monocytes is attributable to the action of plasma adenosine, an endogenous purine metabolite with immunomodulatory properties that is released from cells under conditions of stress or hypoxia. Neonatal mononuclear cells are especially sensitive to adenosine-induced inhibition of TNF-alpha production and to adenosine-induced production of cyclic AMP, an intracellular metabolite that inhibits TNF-alpha synthesis while preserving IL-6 production. The overall goal of this project is to characterize the role of the neonatal adenosine system in modulating TLR-mediated innate immune responses in neonatal blood monocytes. This goal will be accomplished through three specific aims: (1) to determine the mechanism for the greater adenosine sensitivity of neonatal mononuclear cells, (2) to define the adenosine receptor sub-type(s) that mediate inhibition of BLP- and E. coli-induced TNF-alpha production from neonatal blood monocytes; and (3) to characterize the mechanism by which engagement of adenosine receptors results in diminished BLP- and E. coli-induced monocyte TNF-alpha production while preserving IL-6 production. Mechanistic analysis will define how adenosine alters neonatal TLR-mediated immune responses. As a whole, these studies will deepen our understanding of how the unique physiology of the human newborn fundamentally alters innate immunity at birth.