Siglec-2 (sialic acid binding Ig-like lectin 2), also known as CD22, is a 130-140 kDa type I transmembrane glycoprotein with seven Ig-like domains in the extracellular region and three ITIM motifs in its cytoplasmic region. Alternate splicing generates an additional isoform that lacks the third and fourth Ig-like domains. Siglec-2 is expressed on B cells, preferentially binds alpha 2-6 linked sialic glycans including CD45 and mediates B cell - B cell interactions. Phosphorylation of Tyr822 within one of the ITIMs is important for Siglec-2 signal transduction through its association with the kinases Lyn, PI 3-Kinase p85 alpha, and SYK.