我们之前的研究表明S100A9在胶质瘤中过度表达并促进肿瘤生长。然而，S100A9也可以由肿瘤细胞分泌来调节肿瘤微环境（TME）。在本研究中，我们旨在探讨胶质瘤来源的S100A9在小胶质细胞M2极化中的功能，从而抑制CD8 T淋巴细胞并促进免疫抑制。我们首先证明神经胶质瘤比星形胶质细胞表现出更高的 S100A9 表达和分泌。在两种神经胶质瘤细胞系中敲除 S100A9 后，S100A9 的分泌受到抑制。然后，收集培养基并视为条件培养基（CM），与小胶质细胞一起孵育。我们发现胶质瘤来源的 S100A9 驱动小胶质细胞 M2 极化并增加 TGFβ1 分泌。这些分子机制与 S100A9 与 αvβ3 整合素的相互作用以及随后小胶质细胞中 AKT1 的激活有关。此外，我们证明 S100A9 诱导的 M2 小胶质细胞对细胞活力、IL-2 和 IFN-γ 分泌产生负面影响，并通过 TGFβ1 增加 CD8 T 淋巴细胞的早期凋亡。此外，将神经胶质瘤细胞植入小鼠大脑中，我们证实 S100A9 刺激原位移植肿瘤中的小胶质细胞 M2 极化，增强 TGFβ1 水平并抑制 CD8 T 淋巴细胞。在人胶质瘤样本中，S100A9 表达与 CD206 表达呈正相关，但与 TME 中 CD8 T 淋巴细胞积累呈负相关。我们的数据表明，胶质瘤来源的 S100A9 具有操纵非恶性细胞和促进 TME 中免疫逃避的良好能力，为了解 S100A9 参与胶质瘤进展的机制提供了宝贵的见解。版权所有 © 2023。由 Elsevier B.V. 出版。

Our previous studies showed that S100A9 was overexpressed in glioma and promoted tumor growth. However, S100A9 can also be secreted by tumor cells to regulate the tumor microenvironment (TME). In this study, we aimed to explore the functions of glioma derived-S100A9 in microglial M2 polarization, resulting in inhibition of CD8+ T lymphocytes and promotion of immunosuppression. We first showed that glioma exhibited higher expression and secretion of S100A9 than astrocytes. After knocking down S100A9 in two glioma cell lines, the secretion of S100A9 was repressed. Then, the medium was collected and considered as conditioned medium (CM), which was incubated with microglia. We found that glioma-derived S100A9 drove microglial M2 polarization and increased TGFβ1 secretion. These molecular mechanisms were related to the interaction of S100A9 with αvβ3 integrin and the subsequent activation of AKT1 in microglia. Furthermore, we demonstrated that S100A9-induced M2 microglia negatively affected cell viability, IL-2 and IFN-γ secretion, together with increased early apoptosis in CD8+T lymphocytes via TGFβ1. Additionally, glioma cells were implanted into mouse brains, and we confirmed that S100A9 stimulated microglial M2 polarization, enhanced TGFβ1 levels and repressed CD8+ T lymphocytes in orthotopically transplanted tumors. In human glioma samples, S100A9 expression was positively associated with CD206 expression, but negatively correlated with CD8+T lymphocyte accumulation in the TME. Our data indicated that glioma-derived S100A9 has a promising ability to manipulate non-malignant cells and promote immune evasion in the TME, providing valuable insight into the mechanism by which S100A9 participates in the progression of glioma.Copyright © 2023. Published by Elsevier B.V.