Siglec‐H is a microglia‐specific marker that discriminates microglia from CNS‐associated macrophages and CNS‐infiltrating monocytes

Abstract

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.

Differential transcriptional profiles identify microglial- and macrophage-specific gene markers expressed during virus-induced neuroinflammation

“…4b, c, red asterisk) [27,28,55]. Sialic acid-binding immunoglobulin-type lectin H (SiglecH), a specific microglia marker [56] that was suggested to be expressed when these cells are polarized toward the inflammatory phenotype, was also highly expressed by reactive microglia in our assay (Fig. 4c).…”

Exercise Reverses Behavioral and Synaptic Abnormalities after Maternal Inflammation

“…For this purpose, we per-formed a synapse engulfment assay (Schafer et al, 2012) in the mossy fiber pathway to detect the volume of synaptic elements engulfed by microglia in mice, in which microglia are selectively labeled with GFP (Zhan et al, 2014) ( Figure 3A). We confirmed that no GFP(+) cell in the hippocampal CA3 was immunopositive for CCR2 (Prinz and Priller., 2010), an infiltrating cell-specific marker ( Figure S3), while GFP(+) cells were stained with an antibody for Siglec-H (Zhang et al, 2006;Konishi et al, 2017) and P2Y12R (Sasaki et al, 2003;Haynes et al, 2006;Mildner et al, 2017), which were generally used as microglia-specific markers ( Figure S3). Furthermore, GFP(+) cells expressed interleukin-1b (IL-1b), one of the typical cytokines released from microglia (Figure S3).…”

Enforced microglial depletion and repopulation as a promising strategy for the treatment of neurological disorders

“…In addition, CSF‐1R inhibition can robustly decline the actions of nerve‐associated macrophages in the periphery (Klein et al, ). However, several studies have identified some potential markers that are exclusively expressed in microglia including Tmem119, P2RY12, Siglec‐H and Sal1, permitting distinction of resident microglia from other myeloid cells (Bennett et al, ; Butovsky et al, ; Buttgereit et al, ; Konishi et al, ). These markers, together with the Cre/loxP technology, may make it possible to deplete microglia with exquisite precision in the near future.…”