B-cell receptor CD22; sialic acid-binding Ig-like lectin 2; siglec-2; Leu-14; B-lymphocyte cell adhesion molecule; BL-CAM (CD22, SIGLEC2)

Function

• mediates B-cell B-cell interactions
• may be involved in localization of B-cells in lymphoid tissues
• binds sialylated glycoproteins; one of which is CD45
• preferentially binds to alpha-2,6-linked sialic acid
• the sialic acid recognition site can be masked by cis interactions with sialic acids on the same cell surface
• ligand induced tyrosine phosphorylation seems to play a role regulation of B-cell antigen receptor signaling
• plays a role in positive regulation through interaction with Src family tyrosine kinases & may also act as an inhibitory receptor by recruiting cytoplasmic phosphatases via their SH2 domains that block signal transduction through dephosphorylation of signaling molecules
• phosphorylation of Tyr-762, Tyr-807 & Tyr-822 are involved in binding to SYK, GRB2 & SYK, respectively
• phosphorylation of Tyr-842 is involved in binding to SYK, PLCG2 & PIK3R1/PIK3R2
• phosphorylated on Tyr by LYN (putative)
• interacts with PTPN6/SHP-1, LYN, SYK, PIK3R1/PIK3R2 & PLCG1 upon phosphorylation
• interacts with GRB2, INPP5D & SHC1 upon phosphorylation (putative)
• may form a complex with INPP5D/SHIP, GRB2 & SHC1

Structure

• predominantly monomer of isoform CD22-beta
• also found as heterodimer of isoform CD22-beta & a shorter isoform
• contains 4 copies of an ITIM motif
• belongs to the immunoglobulin superfamily, SIGLEC (sialic acid binding Ig-like lectin) family
• contains 6 Ig-like C2-type domains (immunoglobulin-like)
• contains 1 Ig-like V-type domain (immunoglobulin-like)

Compartment

• cell membrane; single-pass type I membrane protein

Alternative splicing

named isoforms=2; CD22-beta; CD22-alpha

Expression

• resting B-cells
• plasma cells stain negatively with antibody

Pathology

• expressed in B cell ALL

Pharmacology

• moxetumomab, an anti-CD22 monoclonal Ab FDA-approved to treat refractory hairy cell leukemia

Laboratory

• CD22 cells in body fluid
  • CD22 cells in blood
• CD22 blasts in specimen
  • cytoplasmic CD22 blasts in specimen
• CD22 blasts in blood
  • cytoplasmic CD22 blasts in blood
• CD22 blasts in bone marrow
  • cytoplasmic CD22 blasts in bone marrow

More general terms

• CD antigen
• glycoprotein
• cell surface receptor
• phosphoprotein

Database

• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=933
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:933
• OMIM: https://mirror.omim.org/entry/107266
• UniProt: http://www.uniprot.org/uniprot/P20273.html