Somatic hypermutation (or SHM) is a
cellular mechanism by which the
immune system adapts to the new foreign elements that confront it (e.g.
microbes), as seen during
class switching. A major component of the process of
affinity maturation, SHM diversifies
B cell receptors used to recognize foreign elements (
antigens) and allows the immune system to adapt its response to new threats during the lifetime of an organism. Somatic hypermutation involves a programmed process of
mutation affecting the variable regions of
immunoglobulin genes. Unlike
germline mutation, SHM affects only an organism's individual
immune cells, and the mutations are not transmitted to the organism's
offspring.