Meningiomas are the most common primary intracranial tumors and show extensive infiltration of macrophages. The mitochondrial membrane protein translocator protein (TSPO) has been used as an in vivo marker of microglia and macrophage activation to visualize neuroinflammation. However, it is unknown which cell types express TSPO in meningiomas. Immunohistochemistry of 38 WHO grade 1–3 meningiomas was subjected to segmentation and deep learning classification of TSPO expression to either Iba1-positive tumor-associated macrophages (TAMs) or all other (mainly neoplastic) cells. A possible association between clinical data and TSPO expression intensities was also investigated. TAMs accounted for 15.9%–26% of all cells in the meningioma tissue. Mean fluorescence intensity of TSPO was significantly higher in TAMs (p < 0.0001), but the mass of neoplastic cells in the tumors exceeded that of TAMs. Thus, the summed fluorescence intensity of TSPO in meningioma cells was 64.1% higher than in TAMs (p = 0.0003). We observed no correlation between TSPO expression intensity and WHO grade. These results indicate that both macrophage-lineage and neoplastic cells in meningiomas express TSPO and that the SPECT-TSPO signal in meningiomas mainly reflects the latter; TSPO is expressed equally in parenchymal activated and resting macrophage/microglia lineage cells.

中文翻译：

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脑膜瘤肿瘤细胞和肿瘤相关巨噬细胞中易位蛋白（TSPO）的表达

脑膜瘤是最常见的原发性颅内肿瘤，显示巨噬细胞广泛浸润。线粒体膜蛋白易位蛋白 (TSPO) 已被用作小胶质细胞和巨噬细胞激活的体内标记物，以可视化神经炎症。然而，尚不清楚脑膜瘤中哪些细胞类型表达 TSPO。对 38 个 WHO 1-3 级脑膜瘤进行免疫组织化学分析，对 Iba1 阳性肿瘤相关巨噬细胞 (TAM) 或所有其他（主要是肿瘤）细胞的 TSPO 表达进行深度学习分类。还研究了临床数据和 TSPO 表达强度之间可能的关联。TAM 占脑膜瘤组织中所有细胞的 15.9%–26%。TAM 中 TSPO 的平均荧光强度显着较高 (p < 0.0001)，但肿瘤中肿瘤细胞的质量超过了 TAM。因此，脑膜瘤细胞中 TSPO 的荧光强度总和比 TAM 中高 64.1% (p = 0.0003)。我们观察到 TSPO 表达强度和 WHO 等级之间没有相关性。这些结果表明，脑膜瘤中的巨噬细胞系和肿瘤细胞均表达TSPO，并且脑膜瘤中的SPECT-TSPO信号主要反映后者；TSPO 在实质激活和静息巨噬细胞/小胶质细胞谱系细胞中表达相同。