Mechanism of the Antigenic Variation June, 2014 | Page 2

Antigenic Variation
Introduction
Antigenic Variation is the mechanism wherein infectious organisms such as viruses and bacteria
alter their surface proteins to disguise and evade the immune reaction generated by the white
blood cells. Mostly the organisms that attack old-aged people often target the same people and
are easily transmittable. Antigenic Variation helps the pathogen dodge the immune system and
then assist re-infection by the microbes. This happens because the microbes’ antigens are no
longer identifiable by the immune system of the host.

Mechanism of the Immune system
Usually when an antigen is introduced into the human body, the immune system generates an
immune reaction and stimulates antibodies to attack that antigen. The body’s immune system
is then familiarized with the particular antigen and the immune system acquires the immune
response against it. In case the same pathogen attacks again, the antibodies will react faster to
destroy the pathogen.

Mechanism of the Antigenic Variation
Meanwhile, in case the pathogen is capable of antigenic variation it can dodge the host’s
immune defenses. The immune system has to regenerate new antibodies for the new pathogen
and hence, the antigen buys more time for the attack. In such cases, the antigens usually alter
their surface by interchanging the arrangement of the proteins and carbohydrate molecules on
their external membranes. There are other mechanisms to antigenic variations as well. These
include gene conversion, DNA inversions, hypermutation and the combination of cassette
sequences.
Antigenic Variation in Bacteria
To become diverse, bacteria can go through antigenic as well as phase variation. Bacteria often
variate their protein polymers which are also called Pilin. Pilin play an essential role in the
generation of an immune response.
Antigenic Variation in Protozoa
To discuss the antigenic variation in protozoa, let us consider the example of Trypanosoma
brucei. Trypanosoma brucei is a protozoan that makes the host sleep sick. It regenerates in the
bloodstreams of mammals. Because of its regeneration capability, it is instantly detected by the
host’s immune system. To protect itself therefore, it processes antigenic variation by decorating
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