Siglec-2 Protein

Quality Statement:
Siglecs (sialic acid binding Ig-like lectins) are I-type (Ig-type) lectins belonging to the Ig superfamily. They are characterized by an N-terminal Ig-like V-type domain which mediates sialic acid binding, followed by varying numbers of Ig-like C2-type domains. Siglec-2 (CD22) belongs to a family of immune inhibitory Siglecs, which bears ITIM to deliver immunosuppressive signals such as reduced phagocytosis, dampened inflammation, and inhibited danger-associated molecular pattern/ pathogen-associated molecular pattern (DAMP/PAMP)-mediated inflammation. Siglec-2 is a cell surface receptor expressed mostly on B cells that regulates B-cell proliferation, survival, signaling, and antibody production. The structure of Siglec-2 contains six tyrosines in its cytoplasmic tail, four of which are in ITIM motifs: Y783, Y843, Y863, and Y828. Following cross-linking of B-cell receptors (BCRs), these tyrosine residues are phosphorylated and recruit Src homology region 2 (SH2) domain-containing protein tyrosine phosphatase-1 (SHP-1), which dephosphorylates BCR-proximal signaling complexes. Siglec-2 is an attractive therapeutic target considering its unique presence in B lymphocytes. Currently, many ongoing trials evaluating CD22-directed chimeric antigen receptors (CARs), particularly in children with relapsed or refractory B-cell leukemia, are showing safety and efficacy. Some novel CARs, such as bispecific CD20/CD22 CARs and CD19/CD22 CARs, are also in development.

Reference:
1.\tTedder T F. et al. (2005) CD22: a multifunctional receptor that regulates B lymphocyte survival and signal transduction. Adv Immunol. 88: 1-50.2.\tFujimoto M. et al. (2007) B cell signaling and autoimmune diseases: CD19/CD22 loop as a B cell signaling device to regulate the balance of autoimmunity. J Dermatol Sci. 46(1): 1-9.3.\tWalker J A. et al. (2008) CD22: an inhibitory enigma. Immunology. 123(3): 314-325.4.\tNitschke L. (2009) CD22 and Siglec-G: B-cell inhibitory receptors with distinct functions. Immunol Rev. 230(1): 128-143.