Sialic Acid Binding Ig Like Lectin 2 (CD22)

CD22 is expressed early in B-cell development in pro-B cells, as a cytoplasmic protein, and later in B-cell development, at the late pre-B-cell stage, as a cell surface protein. Once expressed as a membrane protein, CD22 persists on B cells until they differentiate into plasma cells. The presence of cytoplasmic CD22 is a useful marker for B-cell precursor acute lymphocytic leukemia. CD22 appears to be a heterodimer consisting of 130- and 140-kD glycoproteins with protein cores of 80 and 100 kD, respectively. The 2 subunits are thought to be independently transported to the surface and originate from 2 separate precursor molecules. The CD22 polypeptide is structurally related to myelin-associated glycoprotein (MAG), neural cell adhesion molecule (NCAM), and carcinoembryonic antigen (CEA).