The 5B4 antigen expressed on sprouting neurons contains alpha-2,8-linked polysialic acid.

Monoclonal antibody 5B4 recognizes a large (approximately 185,000-255,000 Da) developmentally regulated membrane glycoprotein, whose expression on fetal rat neurons is coincident with neuronal sprouting. By the use of two prokaryotic-derived probes specific for recognizing alpha-2,8-linked polysialosyl units, we demonstrate the presence of this unusual carbohydrate moiety (a characteristic of neural cell adhesion molecules, NCAMs) on the fetal form of the 5B4 antigen. The 5B4 antigens expressed in adult rat brain (approximately 140,000 and 180,000 Da) do not contain polysialic acid.