Viral Infection and Impairment of Immune Tolerance

描述(由申请人提供)：儿童早期反复感染呼吸道病毒，如呼吸道合胞病毒(RSV)，增加了在以后的生活中发展为哮喘的风险。在成年人中也是如此，RSV是一种重大的健康风险，会导致“流感样”疾病。早期呼吸道合胞病毒感染导致哮喘风险的免疫学基础还没有得到充分的研究。由于哮喘是一个重大的公共卫生问题，了解易患这种疾病的潜在因素是很重要的。我们先前对抑制过敏性呼吸道疾病的免疫调节机制的研究表明，表达膜结合转化生长因子-β(mTGF-β)的调节性T细胞(Treg)在维持小鼠呼吸道免疫耐受方面的重要性。重要的是，人类母乳中的转化生长因子水平与婴儿的喘息呈负相关。鉴于Tregs在抑制呼吸道中不必要的过敏反应中的关键作用，我们调查了RSV感染是否通过使Tregs失效而损害了早期生命的免疫耐受性。最近的研究表明，对抗原(Ag)卵清蛋白(OVA)耐受的母亲可以通过母乳将OVA和TGF-β转移到新生儿体内，这与人类的数据非常一致。这一机制被发现可以诱导新生小鼠的免疫耐受，并基于新生小鼠对活跃的转化生长因子-β信号的依赖，调用了诱导Tregs(ITregs)的作用。如果新生儿中的RSV感染会促进变态反应性疾病，我们询问RSV是否会损害新生儿的Treg表型和功能，这在我们正在进行的实验中是显而易见的。由于RSV，特别是其糖蛋白G，与感染宿主的Th2应答有关，我们将研究它在RSV介导的Treg功能损害中的作用。总之，我们有令人兴奋的数据表明，在RSV感染的肺中存在表达Foxp3和GATA-3的Tregs，这种Tregs由病毒诱导的Th2型细胞因子促进，并被全反式维甲酸(ATRA)减弱。体外和体内试验都显示，从感染小鼠的肺中分离出Treg细胞后，Treg抑制功能严重受损。这些观察结果使我们形成了这一建议的主要假设，即RSV感染通过损害Treg功能损害了新生儿的母体获得性耐受机制。为了解决这一假设，我们将：目的1.研究RSV诱导的Th2细胞因子在新生儿耐受性和Treg功能损害中的作用。目的2.研究RSV G蛋白及其受体CX3CR1在RSV感染新生儿Treg功能损害中的作用。目的3.检测雾化脂质体包裹全反式维甲酸对呼吸道合胞病毒感染肺的Treg功能和气道耐受性的恢复作用。

DESCRIPTION (provided by applicant): Recurrent infections in early childhood by respiratory viruses such as respiratory syncytial virus (RSV) increase the risk for developing asthma later in life. In adults too, RSV is a significant health risk inducing "flu-like" illnesses. The immunologi basis for why RSV infections in early life pose a risk for asthma has not been adequately investigated. Since asthma is a significant public health problem, it is important to understand the underlying factors that predispose to this disease. Our prior studies of immunoregulatory mechanisms that suppress allergic airways disease have shown the importance of regulatory T cells (Tregs) expressing membrane-bound TGF-¿ (mTGF-¿) in maintaining immune tolerance in the airways of mice. Importantly, the TGF-¿ level in the breast milk of humans has been inversely associated with wheezing in infants. Given the crucial role of Tregs in suppressing unwarranted allergic responses in the airways, we investigated whether RSV infection compromises immune tolerance in early life by disabling Tregs. Using the same model of airway tolerance previously used by us to demonstrate the importance of mTGF-¿ in airway tolerance, it was recently shown that mothers tolerized to the antigen (Ag) ovalbumin (OVA) can transfer OVA and TGF-¿ to their newborns via breast milk showing a close correspondence with human data. This mechanism was found to induce immune tolerance in the newborn mice and based on the dependence on active TGF-¿ signaling in the neonates, a role for induced Tregs (iTregs) was invoked. If RSV infection in newborns can promote allergic disease, we asked whether RSV compromises Treg phenotype and function in the newborns which is clearly evident in our ongoing experiments. Since RSV, in particular its glycoprotein G, has been associated with Th2 responses in infected hosts, we will study its role in the RSV-mediated impairment of Treg function. Collectively, we have exciting data that show the presence of Tregs expressing Foxp3 and GATA-3 in RSV infected lungs, which is promoted by Th2-type cytokines induced by the virus and attenuated by all trans retinoic acid (ATRA). Both in vitro and in vivo assays show severe impairment of Treg suppressive function when the cells are isolated from the lungs of infected mice. These observations lead us to formulate the major hypothesis of this proposal, which is that RSV infection impairs maternally-acquired tolerance mechanisms in newborns by compromising Treg function. To address this hypothesis we will: Aim 1. Investigate the role of RSV-induced Th2 cytokines in impairment of tolerance and Treg function in neonates. Aim 2. Study the contribution of the RSV G protein and its receptor CX3CR1 in impairment of Treg function in RSV-infected neonates. Aim 3. Examine the ability of aerosolized liposome-encapsulated ATRA to restore Treg function and airway tolerance in RSV-infected lungs.