CD58, or LFA-3, is a membrane glycoprotein of 55-70kD. It occurs in two forms, one transmembrane with a cytoplasmic domain, the other form anchored in the membrane via a glycosylphosphatidylinositol tail. The complete amino acid sequence of both forms has been deduced from cDNA. It is heavily N-glycosylated. CD58 is a cell adhesion molecule which plays a critical role in facilitation of antigen specific recognition through interaction with CD2 on T lymphocytes. It is a member of the immunoglobulin superfamily of molecules.CD58 has a wide tissue distribution, being present on erythrocytes, platelets, monocytes, a subset of lymphocytes, bone marrow cells, epithelium and endothelial cells[2]. There are approximately 5,000 CD58 molecules on each erythrocyte. There is reduced expression of CD58 on haemopoietic cells in individuals with paroxysmal nocturnal haemoglobinuria.