CD48 is a glycosyl phophatidyl inositol (GPI) anchored cell surface protein also known as Blast1, HuLy m3, BCM1 (in mouse), and OX45 (in rat). CD48 is strongly expressed on lymphocytes and monocytes and weakly on granulocytes but is absent on platelets, fibrolasts, epithelium and endothelium. CD48 is one of the markers for detecting the defects of GPI anchoring structure on patients with paroxysmal nocturnal hemoglobulinuria (PNH) and serves as a low affinity ligand for CD2. The CD48 antigen is closely related to the activation antigen, Blast 1.