CD169, also known as Siglec-1 or sialoadhesin, is a type I transmembrane glycoprotein of the sialic acid binding Ig-like lectin family. It binds to sialylated glycoproteins on various haematopoietic cells to mediate cell-cell interactions. CD169 is expressed on a subset of macrophages and dendritic cells. On CD14+ monocytes its expression can be induced by interferon alpha and gamma. High expression of CD169 is observed in the spleen, lymph nodes, bone marrow, and under inflammatory conditions rheumatoid arthritis and atherosclerosis, lower in the liver, lungs and gut. It has been shown to be involved in antigen presentation to invariant NKT cells, which play an important role in the innate arm of the immune system to modulate the subsequent acquired immune responses.