Cryptococcus neoformans is an encapsulated yeast that causes disease mainly in immunosuppressed hosts. It is considered a facultative intracellular pathogen because of its capacity to survive and replicate inside phagocytes, especially macrophages. This ability is heavily dependent on various virulence factors, particularly the glucuronoxylomannan (GXM) component of the polysaccharide capsule. Inflammasome activation in phagocytes is usually protective against fungal infections, including cryptococcosis. Nevertheless, recognition of C. neoformans by inflammasome receptors requires specific changes in morphology or the opsonization of the yeast, impairing proper inflammasome function. In this context, we analyzed the impact of molecules secreted by C. neoformans B3501 strain and its acapsular mutant Δcap67 in inflammasome activation in an in vitro model. Our results showed that conditioned media derived from B3501 was capable of inhibiting inflammasome-dependent events (i.e., IL-1β secretion and LDH release via pyroptosis) more strongly than conditioned media from Δcap67, regardless of GXM presence. We also demonstrated that macrophages treated with conditioned media were less responsive against infection with the virulent strain H99, exhibiting lower rates of phagocytosis, increased fungal burdens, and enhanced vomocytosis. Moreover, we showed that the aromatic metabolite DL-Indole-3-lactic acid (ILA) and DL-p-Hydroxyphenyllactic acid (HPLA) were present in B3501’s conditioned media and that ILA alone or with HPLA is involved in the regulation of inflammasome activation by C. neoformans. These results were confirmed by in vivo experiments, where exposure to conditioned media led to higher fungal burdens in Acanthamoeba castellanii culture as well as in higher fungal loads in the lungs of infected mice. Overall, the results presented show that conditioned media from a wild-type strain can inhibit a vital recognition pathway and subsequent fungicidal functions of macrophages, contributing to fungal survival in vitro and in vivo and suggesting that secretion of aromatic metabolites, such as ILA, during cryptococcal infections fundamentally impacts pathogenesis.

中文翻译：

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新型隐球菌分泌抑制 IL-1β 炎症小体依赖性分泌的小分子

新型隐球菌是一种包囊酵母，主要在免疫抑制宿主中引起疾病​​。它被认为是一种兼性细胞内病原体，因为它能够在吞噬细胞（尤其是巨噬细胞）内存活和复制。这种能力在很大程度上取决于各种毒力因子，尤其是多糖胶囊中的葡糖醛木甘露聚糖 (GXM) 成分。吞噬细胞中的炎性体激活通常可以防止真菌感染，包括隐球菌病。然而，炎症小体受体对新型隐球菌的识别需要特定的形态学变化或酵母的调理作用，从而损害炎症小体的正常功能。在此背景下，我们分析了新型隐球菌分泌的分子的影响B3501 菌株及其无囊突变体Δcap67在体外模型中的炎性小体激活。我们的结果表明，源自 B3501 的条件培养基能够比源自Δcap67的条件培养基更强烈地抑制炎性体依赖性事件（即，IL-1 β分泌和通过细胞焦亡释放 LDH），无论 GXM 是否存在。我们还证明，用条件培养基处理的巨噬细胞对强毒株 H99 感染的反应较弱，表现出较低的吞噬率、增加的真菌负荷和增强的呕吐细胞增多。此外，我们发现芳香族代谢物 DL-Indole-3-lactic acid (ILA) 和 DL-p-Hydroxyphenyllactic acid (HPLA) 存在于 B3501 的条件培养基中，ILA 单独或与 HPLA 一起参与炎症小体激活的调节由C. neoformans。这些结果得到了体内实验的证实，其中暴露于条件培养基会导致棘阿米巴卡斯特拉尼的真菌负荷增加培养以及受感染小鼠肺部的较高真菌负荷。总体而言，所呈现的结果表明，来自野生型菌株的条件培养基可以抑制重要的识别途径和随后的巨噬细胞杀真菌功能，有助于真菌在体外和体内的存活，并表明芳香代谢物（如 ILA）的分泌，在隐球菌感染从根本上影响发病机制。