Antigenic Variation - Antigenic Variation in Bacteria

Antigenic Variation in Bacteria

To generate intra-population diversity, some bacteria can produce variation by various methods such as antigenic or phase variation. Antigenic variation is the expression of various alternative forms of antigen on the cell surface. Whereas phase variation is the phenotypic switch that is usually reversible and is referred to as an ON-OFF switch. The outcome of either method of variation has a beneficial effect that can result in increased fitness, evasion strategies or environmental adaptation.

Antigenic variation in bacteria is best demonstrated by species of the genus Neisseria (most notably, Neisseria meningitidis and Neisseria gonorrhoeae, the gonococcus); species of the genus Streptococcus and the Mycoplasma. The Neisseria species mentioned variate their pili (protein polymers made up of subunits called pilin which play a critical role in bacterial adhesion, they are antigens which stimulate a vigorous host immune response) and the Streptococci variate their M-protein.

Additionally, Lyme disease is caused by the bacterium Borrelia burgdorferi. The surface lipoprotein VlsE can undergo recombination which results in antigenic diversity. The bacterium carries a plasmid that contains fifteen silent vls cassettes and one functional copy of vlsE. Segments of the silent cassettes recombine with the vlsE gene. Variety generated of the surface lipoprotein antigen allows the bacterium to evade the host humoral immune system.