Functional impact of IL33 polymorphisms on asthma & other Th2-mediated diseases

描述(由申请人提供)：哮喘是一种复杂的特征，具有既定的遗传基础，是主要的公共卫生负担。哮喘下呼吸道炎症的常见来源是由常见环境变应原引发的Th2介导的反应，涉及抗原特异性IgE抗体的产生。长期以来，人们一直观察到变态反应疾病和蠕虫感染之间的反向关系，这种关系的特征也是IgE升高，有哮喘史的人似乎对蠕虫寄生虫(即曼氏血吸虫)“有保护”。许多基因与哮喘有关，但到目前为止，复制的基因很少。最近，代表40,000多个DNA样本的三项独立的全基因组关联研究(GWAS)发现了白介素33(IL33)基因及其两侧的多态与哮喘之间的显著关联，使IL33成为迄今为止哮喘的最强有力的候选基因之一。我们观察到，在居住在巴西巴伊亚州流行地区的村民中，同样的IL33‘哮喘风险’变异与血吸虫病相关的结局之间存在显著的相关性。IL-33是诱导Th2细胞因子的IL-1家族的新成员。其受体类白介素1(ST2)以膜和循环中的可溶性蛋白形式存在，ST2基因多态性也与哮喘相关，但IL-33在粘膜水平上扭曲Th2反应，导致哮喘和对寄生虫免疫的机制(S)尚不清楚。我们正在进行的以哮喘风险和血吸虫病抵抗力为特征的大型队列的遗传流行病学研究提供了一个独特的机会来检验这一假设，即IL33基因多态通过改变IL-33的功能而导致这两种疾病。为了实现我们的目标，我们聚集了一个由6个机构组成的多学科研究团队：(I)使用基于质谱仪(MS)的方法(提供绝对定量的蛋白质)来定量500名哮喘患者和对照组血清中循环中的IL-33及其受体Sst2，并测试IL-33和Sst2浓度与IL33基因类型/单倍型之间的关联；(Ii)表征IL33基因变异对IL-33和Sst2产生的影响，以响应人类髓系细胞中Th2促进抗原(尘螨、血吸虫)；(Iii)测试扭曲哮喘Th2反应的IL33变异体/单倍型与代表对血吸虫病抵抗力的定量结果(曼氏血吸虫抗原特异性IgE：IgG4比率)以及居住在巴西巴伊亚州血吸虫病流行地区的500名村民样本中IL-33和ST2水平之间的相关性；以及(Iv)建立与哮喘/血吸虫病风险/抵抗力相关的IL33单倍型人源化小鼠模型，以阐明IL33基因在这些疾病中的功能作用。这项研究的结果将为IL-33在两种具有高度公共卫生意义的疾病的发病机制中的作用提供新的见解。

DESCRIPTION (provided by applicant): Asthma is a complex trait with an established genetic basis that represents a major public health burden. The usual source of the lower airway inflammation characteristic of asthma is a Th2-mediated reaction initiated by common environmental allergens which involves the production of antigen-specific IgE antibodies. An inverse relationship between allergic disease and helminthic infection, also characterized by elevated IgE, has long been observed, and individuals with a history of asthma appear to be 'protected' from helminthic parasites (i.e., Schistosoma mansoni). Many genes have been associated with asthma, but to date very few have replicated. Recently, three independent genome-wide association studies (GWAS) representing over 40,000 DNA samples have identified significant associations between polymorphisms in and flanking the Interleukin-33 (IL33) gene and asthma, rendering IL33 as one of the strongest candidate genes for asthma to date. We observed significant associations between the same IL33 'asthma risk' variants and outcomes associated with schistosomiasis in villagers living in an endemic region in Bahia, Brazil. IL-33 is a new member of the IL-1 family that induces Th2 cytokines. Its receptor, interleukin 1-like (or ST2) exists as membrane and circulating soluble proteins, and ST2 polymorphisms were also associated with asthma in one of the asthma GWAS's. The mechanism(s) by which IL-33 skews the Th2 response at the level of the mucosa, leading to asthma and immunity to parasites, is not known. Our ongoing genetic epidemiology studies in large cohorts characterized for risk of asthma and resistance to schistosomiasis provide a unique opportunity to test the hypothesis that IL33 polymorphisms contribute to both diseases by altering the function of IL-33. To accomplish our goals, we have amassed a multidisciplinary team of investigators from 6 institutions to: (i) quantify circulating IL-33 and its receptor, sST2, in serum from 500 asthma cases and controls using a mass spectrometry (MS)- based method called 'multiple reaction monitoring' (MRM) that provides absolute quantification of protein, and to test for association between IL-33 and sST2 concentrations and IL33 genotypes/haplotypes; (ii) characterize the effects of IL33 genetic variation on production of IL-33 and sST2, in response to Th2-promoting antigens (dust mite, schistosome) in human myeloid cells; (iii) test for co-associations between the IL33 variants/haplotypes that skew the Th2 response in asthma and a quantitative outcome representing resistance (S. mansoni antigen-specific IgE:IgG4 ratio) to schistosomiasis and serum levels of IL-33 and ST2 in samples from 500 villagers living in a region endemic for schistosomiasis in Bahia, Brazil; and (iv) develop a humanized murine model of IL33 haplotypes associated with risk/resistance to asthma/schistosomiasis to elucidate the functional role of the IL33 gene in these diseases. Results from this study will provide novel insights into the role of IL-33 in the pathogenesis of two diseases of high public health significance.