ABSTRACT
Sialic acid-binding immunoglobulin-like lectins (Siglecs) are members of the immunoglobulin superfamily expressed in most white blood cells of the immune system. The Siglec is a kind of transmembrane proteins that can recognize sialic acid-containing ligands, and it is the most important subgroup of type I lectin. All Siglecs contain at least three domains, including the V-set Ig domain, C2-set Ig domain and transmembrane domain. Some Siglecs contain immune receptor tyrosine-based inhibitory motifs (ITIMs), which are used to transmit inhibitory signals and play an inhibitory role. There are also some Siglecs that do not contain intracellular domains, and they can transmit activation signals through basic amino acids in transmembrane domains to play an activation role. Siglecs not only participate in the regulation of activation, proliferation and apoptosis of immune cells, but also help the immune system to distinguish itself from non-itself by recognizing glycan ligands containing sialic acid. In recent years, studies have shown that Siglecs, as an immune checkpoint, play an important role in the immune regulation in human diseases such as cancer, asthma, allergy, Alzheimer’s disease and autoimmune diseases, and it has received extensive attention. Enhancing or blocking the interaction of sialic acid with Siglecs is an effective strategy for the treatment of cancer, infection, and other diseases. In this review, we describe the classification of Siglecs, their expression in different immune cells and their role in the regulation of immune cell signaling. Emphasis was placed on the role of Siglecs in disease and methods of targeting Siglecs for the treatment of human diseases.