CD170, also known as Siglec-5 or OBBP2, is a type I transmembrane glycoprotein and a member of the sialic acid-binding Ig-like lectin （Siglec） family. It is expressed on various immune cells, including monocytes, neutrophils, macrophages, and dendritic cells. This molecule is characterized by its ability to bind sialic acids, which are often found on the surface of cells. It contains an immunoreceptor tyrosine-based inhibitory motif （ITIM） in its cytoplasmic domain, which is involved in intracellular signaling and can inhibit the activation of immune cells. CD170 is involved in mediating sialic acid-dependent cell adhesion and plays a role in immune regulation. In addition, it has been implicated in immune evasion by certain pathogens, such as Group B Streptococcus.