CD9 antigen is a 24 to 27 kDa glycoprotein expressed on the surface of developing B lymphocytes, platelets, monocytes, eosinophils, basophils, stimulated T lymphocytes and by neurons and glial cells in the peripheral nervous system. In pre-B cells and platelets, CD9 antigen regulates cell activation aggregation possibly through an association with the integrin CD41/CD61. It also regulates cell motility in a variety of cell lines, and appears to be an important regulator of Schwann cell behaviour in peripheral nerve Synonyms: CD9 antigen, p24, Leukocyte antigen MIC3, Motility-related protein, MRP-1, Tetraspanin-29, Tspan-29, 5H9 antigen, Cell growth-inhibiting gene 2 protein, CD9, 5H9, BA2, P24, GIG2, MIC3, BTCC-1, DRAP-27, TSPAN29