CD22 is a heterodimer consisting out of 2 glycoproteins (130 and 140 kD). The molecule is involved in signal transduction in B-cells activated via surface immunoglobulines. CD22 is in principle a B lineage antigen, that is present in the cytoplasm of progenitor B-cells and on the membrane of the majority of mature peripheral B-lymphocytes. Fur-thermore, it is strongly expressed on Hairy Cell Leukemia cells and very weakly on some other leukemias.Synonyms: B-cell receptor CD22, B-lymphocyte cell adhesion molecule, BL-CAM, Leu-14, SIGLEC2, Sialic acid-binding Ig-like lectin 2, Siglec-2