Deciphering a novel lipid-based mechanism of innate immune modulation

我们对抗真菌免疫的理解仍然相对有限， 调节这些反应的人就更少了。C.白色念珠菌是哺乳动物肠道中普遍存在的真菌成分 微生物以及人类真菌感染的最常见原因。我们鉴定了lip 2-/-毒力 突变体在~1500 ℃筛选。在全身感染的小鼠模型中的白色念珠菌突变体（Basso等，Cell Host 和Microbe，in press）。而lip 2-/-菌株在感染的前6小时内表现出正常的毒力属性， 感染，包括通过血流传播、实体器官侵入和酵母菌到菌丝 在形态发生中，其滴度在随后的时间点逐渐下降，并且宿主通常存活。免疫 对受感染的肾脏（该感染模型中的主要靶器官）的分析显示， 与野生型C.白色念珠菌（WT）。 令人惊讶的是，当在IL 17 af-/-动物中进行感染时，lip 2-/-的毒力完全恢复， 产生IL-17。这些结果表明：1）IL-17是全身性抗真菌反应所必需的。 2）Lip 2在某种程度上反对这种反应。我们鉴定了肾βδ T细胞作为IL-10的主要来源。 17在lip 2-/-感染的肾脏和肾脏树突状细胞中作为IL-23（一种已知刺激IL-23的细胞因子）的主要来源。 IL-17由ILδ T细胞产生）。此外，在体外条件下，我们观察到lip 2-/-（但不是WT C.白色念珠菌） 通过共培养的骨髓来源的树突状细胞（BMDC）激活IL-23表达。使用制备的BMDC 从Tlr 2-/-、Tlr 4-/-、Tlr 2/Tlr 4-/-和Clec 7a-/-动物中，我们进一步表明，TLR 2和/或TLR 4而不是Dectin-1 这一反应需要。值得注意的是，当共培养实验是 在0.1μ M棕榈酸（Lip 2的水解产物）存在下进行。数据支持一个模型， 其中WT C.白色念珠菌在实体器官中分泌Lip 2，从而提高棕榈酸的局部浓度， 抑制组织驻留DC的TLR 2和TLR 4依赖性活化，从而抑制下游IL-17- 依赖性抗真菌免疫反应。除了揭示一种新的真菌毒力机制外，这项工作还揭示了 IL-17在系统性真菌感染中的作用，除了其先前在防御中的作用外， 对抗皮肤粘膜念珠菌病。为了了解这种新的脂质介导的先天性 回应C。白念珠菌，我们将使用正向遗传学方法来确定调节白念珠菌的 对C.白色念珠菌由其脂肪酶活性产生的游离脂肪酸。这些探索性的、高风险的 研究将提供见解脂质介导的免疫抑制，真菌发病机制的新机制， 免疫调节

Our understanding of antifungal immunity remains relatively limited, and examples of fungal mechanisms to modulate these responses are even rarer. C. albicans is a ubiquitous fungal component of mammalian gut microbiota as well as the most common cause of fungal infections in humans. We identified the lip2-/- virulence mutant in a screen of ~1500 C. albicans mutants in a mouse model of systemic infection (Basso et al., Cell Host and Microbe, in press). Whereas a lip2-/- strain exhibits normal virulence attributes during the first 6 hours of infection, including dissemination through the bloodstream, solid organ invasion, and yeast-to-hypha morphogenesis, its titers progressively decline at subsequent timepoints, and the host typically survives. Immune profiling of infected kidneys (the primary target organ in this infection model) revealed significant increases in levels of IL-17 mRNA and protein in organs infected with lip2-/- compared to wild-type C. albicans (WT). Strikingly, the virulence of lip2-/- was fully restored when infections were performed in Il17af-/- animals that fail to produce IL-17. These results suggested that 1) IL-17 is required for a potent antifungal response during systemic candidiasis and 2) Lip2 somehow opposes this response. We identified renal 𝛄δ T cells as a major source of IL- 17 in lip2-/--infected kidneys and renal dendritic cells as a major source of IL-23 (a cytokine known to stimulate IL-17 production by 𝛄δ T cells). Further, under in vitro conditions, we observed that lip2-/- (but not WT C. albicans) activates IL-23 expression by co-cultured bone marrow-derived dendritic cells (BMDCs). Using BMDCs prepared from Tlr2-/-, Tlr4-/-, Tlr2/Tlr4-/-, and Clec7a-/- animals, we further showed that TLR2 and/or TLR4 but not Dectin-1 are required for this response. Remarkably, immune activation was blocked when the coculture experiment is performed in the presence of 0.1 𝛍M palmitic acid, a hydrolysis product of Lip2. The data support a model in which WT C. albicans secretes Lip2 in solid organs, thereby raising local concentrations of palmitic acid, which suppresses TLR2- and TLR4-dependent activation of tissue-resident DCs and, thereby, a downstream IL-17- dependent antifungal immune response. Beyond unveiling a novel fungal virulence mechanism, this work unveils a role for IL-17 during systemic fungal infection, in addition to its previously well-documented role in defense against mucocutaneous candidiasis. To understanding this novel lipid-mediated modulation of the innate response to C. albicans, we will use a forward genetic approach to identify factors required for modulation of the innate responses to C. albicans by free fatty acids produced by its lipase activity. These exploratory, high-risk studies will provide insights lipid-mediated immunosuppression, a novel mechanism of fungal pathogenesis and immune modulation.