Regulation of Innate Immune System Sensing of C. Albicans Infections

 描述（由申请人提供）：播散性C。白念珠菌感染对免疫系统较弱的病人是致命的。在医院中，40%的血液感染（念珠菌血症）是由念珠菌属引起的。尽管几种抗真菌药物的可用性，侵袭性念珠菌病仍然具有从45%至75%的高死亡率。与播散性念珠菌病相关的高发病率和死亡率主要是由于缺乏早期和准确的诊断工具，有限的抗真菌药物，以及耐药性的出现，从而突出了需要进一步了解宿主-病原体相互作用和真菌传播的免疫耐药机制，并开发基于免疫的替代策略来对抗念珠菌血症。在正常宿主中，C.在先天免疫细胞激活后，通过检测感染真菌的细胞表面模式识别受体（PRR）如TLR 2和C型凝集素受体（CLR）来控制感染白色念珠菌。CCLRDectin-1和Dectin-2/3识别C.白念珠菌酵母细胞和菌丝通过结合表面的β-葡聚糖和α-甘露聚糖的两种真菌形式。这些分子的识别导致从先天免疫细胞释放炎性细胞因子，这对于抗真菌免疫至关重要。控制这种CLR介导的对真菌感染的先天免疫应答的机制是完全未知的。我们的初步研究结果表明，Cblb-/-小鼠感染C.白色念珠菌酵母和菌丝比野生型（WT）小鼠的BMDM产生更多的炎症细胞因子。该反应涉及通过Dectin-1、-2和/或-3但不通过TLR的信号传导。这一发现表明Cbl-b通过Dectin CLR而不是巨噬细胞中的TLR起作用。与这一观点一致，来自Cblb-/-小鼠的BMDM在与C相互作用后具有受损的Dectin-1、-2和-3降解。白色念珠菌酵母菌和菌丝。为了支持这一发现，Dectin-1在巨噬细胞中感染C.白念珠菌酵母，而这种泛素化在缺乏Cbl-b的BMDM中废除。此外，Cblb-/-小鼠被保护免受致死剂量的C.白色念珠菌基于这些结果，我们假设，在C。在白色念珠菌感染时，Cbl-b被募集到Dectin CLR，并且这靶向Dectin用于泛素化，其抑制针对真菌的CLR介导的先天免疫应答。为了验证这一假设，我们建议确定（1）Cbl-b是否以及如何通过体外蛋白质遍在化来调节Dectin下调;以及（2）Cbl-b是否抑制宿主针对C的有效反应。由CLR的Dectin家族介导的白色念珠菌。该项目的成功完成将揭示一种以前未知的宿主防御机制，并提供对宿主防御机制的分子见解，最终促进识别候选靶点，以适当调节抗真菌反应和治疗方案。

 DESCRIPTION (provided by applicant): Disseminated C. albicans infection in patients who have a weakened immune system is life-threatening. In hospitals 40% of bloodstream infections (candidemia) are caused by Candida spp. Despite the availability of several anti-fungal drugs, invasive candidiasis still has a high mortality rate ranging from 45 to 75%. The high morbidity and mortality associated with disseminated candidiasis are mainly due to the lack of early and accurate diagnostic tools, the limited anti-fungal drugs, and the emergence of drug resistance, thus highlighting the need to further understand host-pathogen interactions and the mechanisms of immune resistance to fungal spread, and to develop alternative immune-based strategies to combat candidemia. In normal hosts, C. albicans is controlled after activation of innate immune cells via cell surface pattern recognition receptors (PRRs) such as TLR2 and C-type lectin receptors (CLRs) that detect the infecting fungi. The CLRs Dectin-1 and Dectin-2/3 recognize C. albicans yeast cells and hyphae by binding to the surface β-glucans and α- mannans of the two fungal forms, respectively. Recognition of these molecules results in release of inflammatory cytokines from innate immune cells, which is critical for anti-fungal immunity. The mechanisms that control this CLR-mediated innate immune response to fungal infection are completely unknown. Our preliminary results showed that bone marrow-derived macrophages (BMDMs) from Cblb-/- mice infected with C. albicans yeast and hyphae produce more inflammatory cytokines than do BMDMs from wild type (WT) mice. This response involves signaling via Dectin-1, -2, and/or -3 but not via the TLRs. This finding suggests that Cbl-b acts through the Dectin CLRs but not the TLRs in macrophages. Consistent with this notion, BMDMs from Cblb-/- mice have impaired Dectin-1, -2, and -3 degradation upon interaction with C. albicans yeast and hyphae. In support of this finding, Dectin-1 undergoes poly-ubiquitination in macrophages upon infection with C. albicans yeasts, whereas this ubiquitination is abrogated in BMDMs lacking Cbl-b. Furthermore, Cblb-/- mice are protected from infection with a lethal dose of C. albicans. Based on these results, we hypothesize that during C. albicans infection, Cbl-b is recruited to Dectin CLRs, and this targets Dectins for ubiquitination which dampens CLR-mediated innate immune responses against fungi. To test this hypothesis, we propose to determine (1) whether and how Cbl-b regulates Dectin down-modulation via protein ubiquitination in vitro; and (2) whether Cbl-b dampens host effective responses against C. albicans mediated by the Dectin family of CLRs. Successful completion of this project will reveal a previously unknown host defense mechanism and provide molecular insight into the host defense machinery and ultimately facilitate the identification of candidate targets for appropriate modulation of anti-fungal responses and therapeutic options.