Fig. 1

CD22 structure and signaling pathway. CD22 molecule is a transmembrane protein from SIGLEC (Sialic acid-binding immunoglobulin-type lectins) family. It has three parts: (i) V-type Ig domain with sia-binding site, (ii) C1-type Ig domain, (iii) C2-type Ig domain. The CD22 intracellular region contains ITIMs (Immunoreceptor tyrosine-based inhibitory motifs). The tyrosine residues of the ITIMs become phosphorylated with the ligand binding, which leads to activation of SHP-1 (Src homology region 2 domain-containing phosphatase-1), SHP-2 (Src homology region 2 domain-containing phosphatase-2), SHIP-1 ((Src homology region 2 domain-containing inositol 5′ polyphosphatase-1). These phosphatases act as negative regulators for down-streaming signaling from B-cell receptors