CD43 (gene ID 6693), also known as GALGP, GPL115, LSN, encodes a highly sialylated glycoprotein that functions in antigen-specific activation of T cells and is found on the surface of thymocytes, T lymphocytes, monocytes, granulocytes, and some B lymphocytes. It contains a mucin-like extracellular domain, a transmembrane region, and a carboxy-terminal intracellular region. The extracellular domain has a high proportion of serine and threonine residues, allowing extensive O-glycosylation, and has one potential N-glycosylation site, while the carboxy-terminal region has potential phosphorylation sites that may mediate transduction of activation signals. Different glycoforms of this protein have been described. In stimulated immune cells, proteolytic cleavage of the extracellular domain occurs in some cell types, releasing a soluble extracellular fragment. Multiple ligands have been described for CD43: ICAM-1, MHC-I, galectin-1, seroalbumin, Siglec-1, cell surface nucleolin, and E-selectin.CD43 has also been shown to act as a receptor for microbes and microbe-derived proteins as well. Interacting with ICAM-1, CD43 may regulate the adhesion between T cells and antigen presenting cells (APCs). Human serumGalectin-1 binds to 130 KDa isoform of CD43, regulates the thymocytes selection and maturation. Albumin would control neutrophil spreading but not neutrophil adhesion.CD43, as secreted by a colon adenocarcinoma cell line, could interact with E-selectin, and that this soluble form of CD43 was able to inhibit leukocyte adhesion to cells expressing E-selectin, and protect the cells from the immune system attack. Defects in the expression of this gene are associated with Wiskott-Aldrich syndrome.