Department of Functional Anatomy and Neuroscience, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan.
Department of Oral and Maxillofacial Surgery, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan.
Glia. 2017 Dec;65(12):1927-1943. doi: 10.1002/glia.23204. Epub 2017 Aug 24.
Several types of myeloid cell are resident in the CNS. In the steady state, microglia are present in the CNS parenchyma, whereas macrophages reside in boundary regions of the CNS, such as perivascular spaces, the meninges and choroid plexus. In addition, monocytes infiltrate into the CNS parenchyma from circulation upon blood-brain barrier breakdown after CNS injury and inflammation. Although several markers, such as CD11b and ionized calcium-binding adapter molecule 1 (Iba1), are frequently used as microglial markers, they are also expressed by other types of myeloid cell and microglia-specific markers were not defined until recently. Previous transcriptome analyses of isolated microglia identified a transmembrane lectin, sialic acid-binding immunoglobulin-like lectin H (Siglec-H), as a molecular signature for microglia; however, this was not confirmed by histological studies in the nervous system and the reliability of Siglec-H as a microglial marker remained unclear. Here, we demonstrate that Siglec-H is an authentic marker for microglia in mice by immunohistochemistry using a Siglec-H-specific antibody. Siglec-H was expressed by parenchymal microglia from developmental stages to adulthood, and the expression was maintained in activated microglia under injury or inflammatory condition. However, Siglec-H expression was absent from CNS-associated macrophages and CNS-infiltrating monocytes, except for a minor subset of cells. We also show that the Siglech gene locus is a feasible site for specific targeting of microglia in the nervous system. In conclusion, Siglec-H is a reliable marker for microglia that will allow histological identification of microglia and microglia-specific gene manipulation in the nervous system.
几种类型的髓样细胞存在于中枢神经系统（CNS）中。在稳态下，小胶质细胞存在于 CNS 实质中，而巨噬细胞存在于 CNS 的边界区域，如血管周围间隙、脑膜和脉络丛。此外，单核细胞在 CNS 损伤和炎症后血脑屏障破裂时从循环中渗透到 CNS 实质中。尽管 CD11b 和离子钙结合适配器分子 1（Iba1）等几种标记物常被用作小胶质细胞标记物，但它们也存在于其他类型的髓样细胞中，直到最近才定义了小胶质细胞特异性标记物。先前对分离的小胶质细胞的转录组分析确定了一种跨膜凝集素，唾液酸结合免疫球蛋白样凝集素 H（Siglec-H），作为小胶质细胞的分子特征；然而，这一点并未通过神经系统的组织学研究得到证实，Siglec-H 作为小胶质细胞标记物的可靠性仍不清楚。在这里，我们通过使用 Siglec-H 特异性抗体的免疫组织化学证明 Siglec-H 是小鼠小胶质细胞的真实标记物。Siglec-H 在发育阶段到成年期的实质小胶质细胞中表达，并且在损伤或炎症条件下激活的小胶质细胞中表达得到维持。然而，Siglec-H 表达不存在于 CNS 相关巨噬细胞和 CNS 浸润的单核细胞中，除了一小部分细胞。我们还表明，Siglech 基因座是神经系统中小胶质细胞特异性靶向的可行部位。总之，Siglec-H 是小胶质细胞的可靠标记物，可允许对小胶质细胞进行组织学鉴定和对神经系统中小胶质细胞特异性基因操作。
