BACKGROUND Multiple sclerosis (MS) is an immune-mediated, chronic inflammatory, and demyelinating disease of the central nervous system (CNS). Several cytokines are thought to be involved in the regulation of MS pathogenesis. We recently identified interleukin (IL)-9 as a cytokine reducing inflammation and protecting from neurodegeneration in relapsing-remitting MS patients. However, the expression of IL-9 in CNS, and the mechanisms underlying the effect of IL-9 on CNS infiltrating immune cells have never been investigated. METHODS To address this question, we first analyzed the expression levels of IL-9 in post-mortem cerebrospinal fluid of MS patients and the in situ expression of IL-9 in post-mortem MS brain samples by immunohistochemistry. A complementary investigation focused on identifying which immune cells express IL-9 receptor (IL-9R) by flow cytometry, western blot, and immunohistochemistry. Finally, we explored the effect of IL-9 on IL-9-responsive cells, analyzing the induced signaling pathways and functional properties. RESULTS We found that macrophages, microglia, and CD4 T lymphocytes were the cells expressing the highest levels of IL-9 in the MS brain. Of the immune cells circulating in the blood, monocytes/macrophages were the most responsive to IL-9. We validated the expression of IL-9R by macrophages/microglia in post-mortem brain sections of MS patients. IL-9 induced activation of signal transducer and activator of transcription (STAT)1, STAT3, and STAT5 and reduced the expression of activation markers, such as CD45, CD14, CD68, and CD11b in inflammatory macrophages stimulated in vitro with lipopolysaccharide and interferon (IFN)-γ. Similarly, in situ the number of activated CD68+ macrophages was significantly reduced in areas with high levels of IL-9. Moreover, in the same conditions, IL-9 increased the secretion of the anti-inflammatory cytokine, transforming growth factor (TGF)-β. CONCLUSIONS These results reveal a new cytokine expressed in the CNS, with a role in the context of MS. We have demonstrated that IL-9 and its receptor are both expressed in CNS. Moreover, we found that IL-9 decreases the activation state and promotes the anti-inflammatory properties of human macrophages. This mechanism may contribute to the beneficial effects of IL-9 that are observed in MS, and may be therapeutically potentiated by modulating IL-9 expression in MS.

中文翻译：

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白介素9调节进行性多发性硬化症大脑中的巨噬细胞活化。

背景技术多发性硬化症（MS）是免疫介导的中枢神经系统（CNS）的慢性炎症性和脱髓鞘性疾病。几种细胞因子被认为与MS发病机理有关。最近，我们确定白介素（IL）-9是一种减轻复发缓解型MS患者炎症并保护其免受神经退变的细胞因子。但是，从未研究过CNS中IL-9的表达以及IL-9对CNS浸润免疫细胞的影响的潜在机制。方法为了解决这个问题，我们首先通过免疫组织化学分析了MS患者死后脑脊液中IL-9的表达水平以及MS患者死后脑组织中IL-9的原位表达。补充研究的重点是通过流式细胞仪，免疫印迹和免疫组化鉴定哪些免疫细胞表达IL-9受体（IL-9R）。最后，我们探讨了IL-9对IL-9应答细胞的作用，分析了诱导的信号通路和功能特性。结果我们发现巨噬细胞，小胶质细胞和CD4 T淋巴细胞是MS脑中表达最高水平的IL-9的细胞。在血液中循环的免疫细胞中，单核细胞/巨噬细胞对IL-9的反应最强。我们通过巨噬细胞/小胶质细胞验证了MS患者的死后脑切片中IL-9R的表达。IL-9诱导信号转导子和转录激活子（STAT）1，STAT3和STAT5的激活，并降低了激活标记（如CD45，CD14，CD68，脂多糖和干扰素（γ）体外刺激的炎症巨噬细胞中的CD11b和CD11b。同样，在IL-9水平高的地区，活化的CD68 +巨噬细胞的数量也明显减少。此外，在相同条件下，IL-9会增加抗炎细胞因子的分泌，从而转化生长因子（TGF）-β。结论这些结果揭示了在CNS中表达的新的细胞因子，其在MS的背景下起作用。我们已经证明IL-9及其受体均在CNS中表达。而且，我们发现IL-9降低了活化状态并促进了人类巨噬细胞的抗炎特性。该机制可能有助于在MS中观察到的IL-9的有益作用，并且可以通过调节MS中的IL-9表达来增强治疗效果。