Table 2.

Summary of Siglecs in CNS.

Type	Ligands	Cell type/ Subcellular location		Functions	References
Siglec-1 (sialoadhesin, CD169)	α2–3, α2–6 sialic acid residues	Microglia	• Plasma membrane	• Cell-cell interaction	Macauley et al. (2014) and Groh et al. (2016)
Siglec-3 (CD33)	α2–6, α2–3 sialic acid residues	Microglia	• Plasma membrane	• Modulation of microglial phagocytosis activity	Griciuc et al. (2013) and Macauley et al. (2014)
Siglec-4 (MAG)	α2–3, α2–6 sialic acid residues	On myelin sheath, produced by oligodendrocytes	• Inner-most, myelin periaxonal membrane	• Myelin-axon interaction, maintaining long-term axon stability	Sun et al. (2004), Huang et al. (2012) and Macauley et al. (2014)
Siglec-E	α2–3, α2–6, α2–8 sialic acid residues	Microglia	• Plasma membrane	• Inhibition of inflammation, ROS production and phagocytosis	Claude et al. (2013) and Macauley et al. (2014)
Siglec-F	α2–3 sialic acid residues	Microglia	• Plasma membrane	• Inhibition of phagocytosis	Wielgat and Braszko (2012) and Macauley et al. (2014)
Siglec-H	Abnormal sialic acid residues in glioma	Microglia	• Plasma membrane	• Promotion of phagocytosis	Kopatz et al. (2013) and Macauley et al. (2014)
Siglec-11	α2–8 sialic acid residues	Microglia	• Plasma membrane	• Inhibition of inflammation and phagocytosis	Wang and Neumann (2010), Wang X. et al. (2012) and Macauley et al. (2014)
Siglec-16	α2–8 sialic acid residues	Microglia	• Plasma membrane	• No functional data	Wang X. et al. (2012) and Macauley et al. (2014)