The CD9 (HI9a) antibody recognizes a 24-kDa type-III single-chain transmembrane protein spanning the membrane 4 times therefore called TM4. The CD9 antigen is mainly e, Xenopus/Amphibian,pressed on platelets (present in the alpha-granules),Porcinere-B cells,Mouse,onocytes, endothelia cells, epithelial cells and activated T cells. The CD9 antigen is a marker for 90% non T acute lymphoblastic leukemia cells and 50% acute myeloid leukemia. CD9 is not e, Xenopus/Amphibian,pressed by hematopoietic progenitor cells nor by resting mature T and B cells. CD9 antigen mediates platelet activation and aggregation playing an important role in cellular adhesion and migration.