A role of osteopontin in innate immunity against fungal infection

描述(由申请人提供)：机会性真菌感染是免疫受损患者严重发病和死亡的常见原因，包括艾滋病患者、接受化疗的癌症患者和免疫抑制的移植受者。机会性真菌感染的一个关键易感因素是适应性免疫受损。然而，在缺乏获得性免疫的情况下，我们发现骨桥蛋白(OPN)在防御一种引起肺孢子虫肺炎(PCP)的机会性真菌肺孢子虫方面发挥着关键作用。这一发现表明，仅靠先天免疫就能显著提高对真菌的抵抗力。先前的一些研究表明OPN参与了抗真菌免疫，但机制尚不清楚。虽然OPN已经被作为一种细胞外分子(分泌型OPN；sOPN)进行了研究，但我们的初步数据强烈表明，一种新的细胞内OPN异构体(IOPN)是OPN介导的抗真菌反应的主要参与者。这项拟议研究的目的是阐明OPN保护免疫受损宿主免受肺孢子虫感染的机制。为了实现这一目标，我们将检验这一提议中的以下中心假设：iOPN增强抗真菌天然免疫，它是通过参与形成真菌模式识别受体(PRR)簇并作为细胞质适配器蛋白从受体传递信号来实现的。在这里，我们将追求以下特定目标：(目的1)阐明iOPN参与真菌PRR簇形成的机制，(目的2)阐明iOPN在真菌PRR信号转导中的作用机制，以及(目的3)确定表达iOPN的DC和巨噬细胞是否促进真菌清除。在目标1和2中，我们将使用生化和细胞生物学方法来阐明iOPN是如何参与真菌检测到的细胞反应的。在目标3中，我们将使用体外和体内方法来测试iOPN介导的肺孢子虫的清除。本研究成功完成后，将对病原菌识别研究领域产生重要的积极影响。OPN是一种研究较多的蛋白质，但过去对OPN的研究几乎都集中在sOPN上。因此，了解iOPN这一新的OPN异构体的生物学特性对免疫学领域具有重要意义。此外，这项研究的结果将为更好地理解先天免疫检测真菌的分子机制提供帮助。

DESCRIPTION (provided by applicant): Opportunistic fungal infection is a common cause of serious morbidity and mortality in immunocompromised individuals, including AIDS patients, cancer patients under chemotherapy, and immunosuppressed transplant recipients. A key predisposing factor for opportunistic fungal infections is impaired adaptive immunity. However, in the absence of adaptive immunity, we found that osteopontin (OPN) plays a critical role in defense against an opportunistic fungus, Pneumocystis, which causes Pneumocystis pneumonia (PCP). The finding suggested that innate immunity alone can make a significant difference in resistance against fungi. Involvement of OPN in anti-fungal immunity was suggested by several previous studies, but the mechanism is not known. Although OPN has been studied as an extracellular molecule (secreted OPN; sOPN), our preliminary data strongly suggested that a novel intracellular OPN isoform (iOPN) is the main player in OPN-mediated anti-fungal responses. The goal of this proposed research is to elucidate the mechanism by which OPN protects immunocompromised hosts from Pneumocystis infection. To achieve the goal, we will test the following central hypothesis in this proposal: iOPN enhances anti-fungal innate immunity, and it does so by participating in forming fungal pattern recognition receptor (PRR) clusters and in transducing signals from the receptors as a cytoplasmic adaptor protein. Here, we will pursue the following specific aims: (Aim 1) Elucidate the mechanism by which iOPN participates in fungal PRR cluster formation, (Aim 2) Elucidate the mechanism by which iOPN plays a role in signal transduction of fungal PRRs, and (Aim 3) Determine whether fungal clearance is enhanced by DCs and macrophages that express iOPN. In Aim 1 and 2, we will use biochemical and cell biological approaches to elucidate how iOPN is involved in cellular responses upon fungal detection. In Aim 3, we will use in vitro and in vivo approaches to test the iOPN- mediated clearance of Pneumocystis. Upon successful completion, our study will have an important positive impact on the research field of pathogen recognition by hosts. OPN is a well-studied protein, but virtually all the studies of OPN in the past focused on sOPN. Thus, understanding the biology of iOPN, a novel OPN isoform, has a great impact on the field of immunology. Furthermore, results from this study will provide better understanding in molecular mechanisms of fungal detection by innate immunity.