Activation-Induced Cytidine Deaminase
Activation-induced cytidine deaminase (AID) (EC 220.127.116.11) is a 198-amino acid polypeptide enzyme that is primarily expressed in germinal center (GC) B cells of the secondary lymphoid organs. Its physiological function is to introduce point mutations into the variable and switch regions of immunoglobulin (Ig) genes during the processes of somatic hypermutation (SHM) and class switch recombination (CSR) in GC B cells, respectively, leading to a highly diversified antibody affinity repertoire and alternative use of different constant regions of Ig. Patients with defective AID due to germline mutations develop type 2 hyper-IgM syndrome (HIGM2), a type of immunodeficiency resulting in high levels of serum IgM and lack of other post-switch Ig isotypes. Given its potent mutation-inducing property, deregulated expression of AID in the wrong place or at the wrong time is often associated with various cancers.
Identification of AID