Antigenic variation in bacterial pathogens

Antigenic variation is the process of genetic or epigenetic changes that occur more frequently than the basal mutation rate. This variation mostly occurs in genes that encode surface-exposed proteins and involves the sequential expression of multiple different forms of the antigenic regions of those surface-exposed proteins. Phase variation is related to antigenic variation and refers to a switch between two phenotypes (i.e., turning gene expression on or off and switching between production of two different gene products). Antigenic and phase variation are most often used by microorganisms to evade the host immune response and to adapt to new environments within the host. Several different genetic mechanisms to achieve antigenic or phase variation are well understood thanks to decades of experimental investigation, and are the focus of this article.