Synthetic amorphous silica nanoparticles (SAS-NPs) are widely employed in pharmaceutics, cosmetics, food and concretes. Workers and the general population are exposed daily via diverse routes of exposure. SAS-NPs are generally recognized as safe (GRAS) by the Food and Drug Administration, but because of their nanoscale size and extensive uses, a better assessment of their immunotoxicity is required. In the presence of immune “danger signals”, dendritic cells (DCs) undergo a maturation process resulting in their migration to regional lymph nodes where they activate naive T-cells. We have previously shown that fumed silica pyrogenic SAS-NPs promote the two first steps of the adaptative immune response by triggering DC maturation and T-lymphocyte response, suggesting that SAS-NPs could behave as immune “danger signals”. The present work aims to identify the mechanism and the signalling pathways involved in DC phenotype modifications provoked by pyrogenic SAS-NPs. As a pivotal intracellular signalling molecule whose phosphorylation is associated with DC maturation, we hypothesized that Spleen tyrosine kinase (Syk) may play a central role in SAS-NPs-induced DC response. In human monocyte-derived dendritic cells (moDCs) exposed to SAS-NPs, Syk inhibition prevented the induction of CD83 and CD86 marker expression. A significant decrease in T-cell proliferation and IFN-γ, IL-17F and IL-9 production was found in an allogeneic moDC:T-cell co-culture model. These results suggested that the activation of Syk was necessary for optimal co-stimulation of T-cells. Moreover, Syk phosphorylation, observed 30 min after SAS-NP exposure, occurred upstream of the c-Jun N-terminal kinase (JNK) Mitogen-activated protein kinases (MAPK) and was elicited by the Src family of protein tyrosine kinases. Our results also showed for the first time that SAS-NPs provoked aggregation of lipid rafts in moDCs and that MβCD-mediated raft destabilisation altered Syk activation. We showed that SAS-NPs could act as an immune danger signal in DCs through a Syk-dependent pathway. Our findings revealed an original mechanism whereby the interaction of SAS-NPs with DC membranes promoted aggregation of lipid rafts, leading to a Src kinase-initiated activation loop triggering Syk activation and functional DC maturation.

中文翻译：

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无定形二氧化硅纳米粒子诱导的人树突状细胞成熟是 Syk 依赖性的，由脂筏聚集触发

合成无定形二氧化硅纳米粒子 (SAS-NPs) 广泛应用于制药、化妆品、食品和混凝土中。工人和一般人群每天都通过不同的接触途径接触。SAS-NPs 通常被美国食品和药物管理局认为是安全的 (GRAS)，但由于它们的纳米级尺寸和广泛的用途，需要对其免疫毒性进行更好的评估。在存在免疫“危险信号”的情况下，树突状细胞 (DC) 经历成熟过程，导致它们迁移到区域淋巴结，在那里它们激活幼稚 T 细胞。我们之前已经表明，气相二氧化硅热解 SAS-NPs 通过触发 DC 成熟和 T 淋巴细胞反应来促进适应性免疫反应的前两个步骤，这表明 SAS-NPs 可以作为免疫“危险信号”。目前的工作旨在确定由热原 SAS-NPs 引起的 DC 表型修饰所涉及的机制和信号通路。作为磷酸化与 DC 成熟相关的关键细胞内信号分子，我们假设脾脏酪氨酸激酶 (Syk) 可能在 SAS-NPs 诱导的 DC 反应中发挥核心作用。在暴露于 SAS-NP 的人单核细胞来源的树突状细胞 (moDC) 中，Syk 抑制阻止了 CD83 和 CD86 标记物表达的诱导。在同种异体 moDC:T 细胞共培养模型中发现 T 细胞增殖和 IFN-γ、IL-17F 和 IL-9 产生显着减少。这些结果表明，Syk 的激活对于 T 细胞的最佳共刺激是必需的。此外，在 SAS-NP 暴露后 30 分钟观察到 Syk 磷酸化，发生在 c-Jun N 末端激酶 (JNK) 丝裂原活化蛋白激酶 (MAPK) 的上游，并由蛋白酪氨酸激酶的 Src 家族引发。我们的结果还首次表明，SAS-NPs 引发了 moDC 中脂筏的聚集，并且 MβCD 介导的脂筏不稳定改变了 Syk 激活。我们发现 SAS-NPs 可以通过 Syk 依赖性途径在 DC 中充当免疫危险信号。我们的研究结果揭示了一种原始机制，即 SAS-NP 与 DC 膜的相互作用促进了脂筏的聚集，导致 Src 激酶启动的激活环触发 Syk 激活和功能性 DC 成熟。我们的结果还首次表明，SAS-NPs 引发了 moDC 中脂筏的聚集，并且 MβCD 介导的脂筏不稳定改变了 Syk 激活。我们发现 SAS-NPs 可以通过 Syk 依赖性途径在 DC 中充当免疫危险信号。我们的研究结果揭示了一种原始机制，即 SAS-NP 与 DC 膜的相互作用促进了脂筏的聚集，导致 Src 激酶启动的激活环触发 Syk 激活和功能性 DC 成熟。我们的结果还首次表明，SAS-NPs 引发了 moDC 中脂筏的聚集，并且 MβCD 介导的脂筏不稳定改变了 Syk 激活。我们发现 SAS-NPs 可以通过 Syk 依赖性途径在 DC 中充当免疫危险信号。我们的研究结果揭示了一种原始机制，即 SAS-NP 与 DC 膜的相互作用促进了脂筏的聚集，导致 Src 激酶启动的激活环触发 Syk 激活和功能性 DC 成熟。