Description
CD22β, also known as Siglec-2, is a type 1 integral membrane glycoprotein belonging to the Ig family. It is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases. CD22β specifically recognizes sialic acid-containing glycans and is expressed on B cells (1). Both biochemical analysis on various B cells and studies using CD22β-deficient mice have demonstrated that CD22β negatively regulates signaling through the B cell antigen receptor (BCR), which plays a crucial role in response of B cells to antigen stimulation (2). CD22β does this by recruitment and activation of SH2-containing phosphatase 1 (SHP-1), which counteracts the phospharylation-mediated activation of signaling molecules by dephosphorylation, and reduces Ca2+ signaling by regulating the activity of the Ca2+ pump PMCA (3). Unlike other B cell markers, CD22β membrane expression is limited to the late differentiation stages comprised between mature B cells (CD22+) and plasma cells (CD22-), and may thus prove useful in phenotyping mature leukemias (4). CD22β is also strongly expressed in hairy cell leukemia