CD52 is a widely distributed antigen belonging to a GPI anchored glycoprotein with only twelve amino acid residues (GQNDTSQTSSPS). CD52 can be found on the surface of lymphocytes, monocytes, eosophils and dendritic cells in hematopoietic system. with a density of up to 5×10⁵molecules on lymphocytes, CD52 antigens express on many lymphoid cell malignancies and certain acute myeloid leukemia cells. When CD52 molecules are crosslinked with mAb, it triggers a series of signaling within the target cells. The signaling caused by the activation of CD52 molecules is similar to that caused by anti-CD3 antibodies. When CD52 molecules are triggered, PMA (Phorbol Myristate acetate, acetylmyridrobol ester) can promote the proliferation and secretion of cytokines in normal human CD4⁺and CD8⁺Tlymphocytes in vitro.