Antigenic drift

Antigenic Drift is a mechanism for viral evolution that is seen in both the influenza virus and the HIV virus. This process involves the accumulation of mutations within the genes that code for antibody binding sites. This results in a new strain of virus that is not recognized by pre-existing immune system memory cells, thus enabling the virus to spread throughout a population that was previously immune because of vaccination or a past infection.

Mechanism

The mechanism of antigenic drift can be understood in the context of the immune response. When a virus infects a host, the immune system responds by producing antibodies that recognize and bind to specific sites on the virus's surface proteins. These sites are known as antigens. The binding of an antibody to an antigen neutralizes the virus and marks it for destruction by the immune system.

However, the genetic material of viruses is often prone to errors during replication. These errors, or mutations, can lead to changes in the amino acid sequence of the virus's surface proteins, altering the structure of the antigens. If these changes occur in the antibody binding sites, the existing antibodies may no longer recognize and bind to the virus effectively. This allows the virus to evade the immune response and continue to replicate within the host.

Consequences

The primary consequence of antigenic drift is the ability of the virus to evade the immune response, leading to continued infection and spread within a population. This is a major factor in the seasonal epidemics of influenza. Because the influenza virus undergoes antigenic drift, the vaccine composition must be reviewed and updated each year to match the circulating strains.

Antigenic drift also has implications for the treatment and prevention of HIV. The high mutation rate of the HIV virus leads to rapid antigenic drift, making it difficult to develop an effective vaccine.

See also

• Antigenic shift
• Viral evolution
• Influenza vaccine
• HIV vaccine

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