Sialoadhesin on Macrophages

Siaoloadhesin (Sn, Siglec-1) is a sialic acid binding cell surface receptor of as yet unknown function that is found on subsets of macrophages in the lymphoid system and the bone marrow. The sialic acid-binding preference of this receptor favors Neu5Ac, the type of sialic acid found in excess on human cell surfaces, because of the genetic loss of the great ape sialic acid Neu5Gc. Human cells therefore have an excess of binding sites for this receptor. Possibly in relation to this difference, the distribution of Sn in human macrophages appears different between humans and chimpanzees. The chimpanzee pattern is similar to that of the rat, with only a subset being positive, and with negative areas in the center of the splenic follicles. In contrast human spleen macrophages appear to be almost universally positive for Sn, including within the follicles.