Keeping track of AID

A DNA-mutating enzyme that fine-tunes B cell antibody specificity can become a dangerous liability if its activity is mistimed, misplaced, or left unchecked. Crouch et al. (page 1145) have now designed a mouse model to track the enzyme's activity in B cells during development and immunity. The model can now be used to determine how the enzyme's destructive force is controlled.

The enzyme in question is AID (activation-induced cytidine deaminase), which converts cytidines to uracils. AID activity within activated B cells allows them to better recognize a pathogen by creating mutations in the variable regions of their immunoglobulin (Ig) genes. AID-assisted recombination within Ig constant regions also allows B cells to generate different types of antibodies. Mismatch repair mechanisms then splice out the...