In the course of an immune response, antibodies undergo affinity maturation in order to increase their efficiency in neutralizing foreign invaders. Affinity maturation occurs by the introduction of multiple point mutations in the variable region gene that encodes the antigen binding site. This somatic hypermutation is restricted to immunoglobulin genes and occurs at very high rates. The precise molecular basis of this process remains obscure. However, recent studies using a variety of in vivo and in vitro systems have revealed important (...) regulatory regions, base motifs that are preferred targets of mutation and evidence that transcription may play an active role in hypermutation. BioEssays 20:227–234, 1998. © 1998 John Wiley & Sons, Inc. (shrink)