Early Life Exposure to Microbial Products and Asthma

描述（由申请人提供）：在过去的二十年中，哮喘在工业化国家的患病率和严重程度有所增加;它是儿童最常见的慢性疾病，死亡率不断上升。“卫生假说”认为，减少早期生活暴露于微生物和微生物产品是这种流行病的原因。根据这一范式，微生物暴露抑制Th 2-歪斜的反应，环境过敏原，通过诱导的Th 1和/或调节型反应pupillin的发展。支持这一假设的流行病学数据是令人信服的，如果相关的：在农场环境中长大的儿童（特别是大量接触牲畜），年长的兄弟姐妹或早期日托的人数增加（因此在较早的年龄暴露于儿童感染），或早期接触宠物的儿童患哮喘和特应性疾病的风险降低。卫生假说很难在人类中直接测试;确定促进微生物暴露儿童免疫耐受的途径仍然很重要。了解这种耐受性的机制将有助于开发新的诱导耐受性的治疗方法，从而减轻哮喘和特应性的负担。诱导耐受性的一个候选者是内毒素;在一些研究中，环境灰尘中的内毒素水平与特应性的风险降低相关。然而，内毒素吸入并没有显示出对人类特应性疾病的保护作用;事实上，许多证据表明内毒素在哮喘中的有害作用。第二个候选者是细菌（富含CpG）DNA。我们以前已经证明，使用小鼠模型，含有CpG为中心的序列基序（CpG ODN）的寡核苷酸是非常有效的预防和逆转特应性气道疾病。这些化合物可抑制变应原特异性免疫（Th 2型）应答并诱导Th 1型以及调节性（IL-10）细胞因子应答。CpG-ODN模拟天然细菌DNA的免疫刺激作用。与内毒素一样，细菌DNA被Toll样受体（TLR-9）识别，并有效激活先天免疫系统。我们认为，暴露于细菌DNA可能介导对特应性的保护。因此，我们建议测试卫生假说，并比较内毒素和富含CpG的DNA的调节作用。驱动这些研究的总体假设是，早期生活中暴露于微生物产品会促进耐受性，并降低日后发生特应性疾病（如哮喘）的易感性。吸入内毒素和细菌DNA可能通过不同的介质和途径影响对吸入性过敏原的反应;这些作用可能是相加的、协同的，甚至是拮抗的。我们建议解决这些假设在以下目的：目的1：为了测试的假设，即早期生活中暴露于微生物产品（细菌DNA或内毒素）降低以后的易感性发展特应性疾病。问题1A：生命早期暴露于微生物制品是否会改变肺部炎症环境？问题1B：生命早期接触微生物制品是否会改变日后发生特应性哮喘的易感性？问题1C：早期暴露于抗原和微生物制品是否是抗原特异性耐受所必需的？目的2：检验生命早期暴露于微生物产品通过诱导调节细胞群促进免疫耐受的假设。 问题2A：什么介质促进早期暴露于微生物制品诱导的免疫耐受？问题2B：哪些细胞负责早期暴露于微生物制品诱导的免疫耐受？

DESCRIPTION (provided by applicant): Asthma has increased in prevalence and severity in the industrialized world for the past two decades; it is the most common chronic illness of children and has had a rising mortality rate. The "hygiene hypothesis" proposes that reduced early-life exposures to microbes and microbial products are responsible for this epidemic. According to this paradigm, microbial exposures inhibit the development of Th2-skewed responses to environmental allergens, putatively through the induction of Th1 and/or regulatory-type responses. The epidemiological data supporting this hypothesis are compelling, if correlative: children raised in a farm environment (especially with significant exposure to livestock), with increased numbers of older siblings or early daycare attendance (and thus exposed to childhood infections at an earlier age), or with early life exposure to pets have a reduced risk of developing asthma and atopic disorders. The hygiene hypothesis has been difficult to directly test in humans; it remains important to identify the pathways that promote immune tolerance among microbe-exposed children. Understanding the mechanisms of this tolerance will aid development of novel tolerance-inducing therapeutic approaches, and thus reduce the burden, of asthma and atopy. One candidate for inducing tolerance is endotoxin; endotoxin levels in environmental dust correlate with reduced risk of atopy in some studies. Nevertheless, endotoxin inhalation has not been shown to protect against atopic disease in humans; indeed, much evidence points to a deleterious effect of endotoxin in asthma. A second candidate is bacterial (CpG-rich) DNA. We have previously demonstrated, using murine models, that oligonucleotides containing CpG-centered sequence motifs (CpG ODN) are highly effective in both preventing and reversing atopic airway disease. These compounds can suppress allergen-specific immune (Th2-type) responses and induce Th1-type as well as regulatory (IL-10) cytokine responses. CpG-ODN mimics the immunostimulatory effects of native bacterial DNA. Like endotoxin, bacterial DNA is recognized by a toll-like receptor (TLR-9) and potently activates the innate immune system. We suggest that exposure to bacterial DNA may mediate protection against atopy. Thus, we propose to test the hygiene hypothesis, and to compare the modulatory effects of endotoxin and CpG-rich DNA. The overarching hypothesis driving these studies is that early-life exposure to microbial products promotes tolerance and reduces later susceptibility to developing atopic disorders such as asthma. Inhalation of endotoxin and bacterial DNA may influence response to inhaled allergens through different mediators and pathways; these effects may be additive, synergistic, or even antagonistic. We propose to address these hypotheses in the following Aims: Aim 1: To test the hypothesis that early-life exposure to microbial products (bacterial DNA or endotoxin) reduces later susceptibility to developing atopic disorders. Question 1A: Does early life exposure to microbial products alter the pulmonary inflammatory milieu? Question 1B: Does early life exposure to microbial products alter later susceptibility to developing atopic asthma? Question 1C: Is early-life exposure to antigen as well as microbial products required for antigen-specific tolerance? Aim 2: To test the hypothesis that early-life exposure to microbial products promotes immune tolerance by inducing a regulatory cell population. Question 2A: What mediators promote immune tolerance induced by early life exposure to microbial products? Question 2B: What cells are responsible for immune tolerance induced by early life exposure to microbial products?