Overview
This lecture explains antigenic variation, focusing on how pathogens change their surface markers to evade the immune system, with special emphasis on the influenza virus and its implications for vaccination.
Immune System Basics
- Antibodies are produced by B cells to target antigens, which are cell surface markers on pathogens.
- The immune system uses memory to recognize and respond to previously encountered antigens.
Antigenic Variation Explained
- Antigenic variation refers to changes in a pathogen’s surface antigens to avoid immune detection.
- Pathogens can alter their surface proteins, making it harder for the immune system to recognize and attack them.
- Both viruses and bacteria can use antigenic variation.
Examples of Antigenic Variation
- Borrelia burgdorferi, which causes Lyme disease, varies surface markers, leading to recurring fevers and chronic infection.
- Neisseria gonorrhoeae changes its pili (surface structures) to avoid immune response.
- Influenza virus frequently changes its surface proteins, causing new outbreaks yearly.
Influenza Virus: Antigenic Drift and Shift
- Antigenic Drift: Slow, gradual changes in the virus’s surface proteins due to point mutations during replication.
- Antigenic Shift: Sudden, major changes when two different influenza viruses infect the same cell, mix genes, and produce a new strain.
- Most influenza pandemics arise from antigenic shift events.
Flu Vaccine Implications
- The flu vaccine is updated annually due to ongoing antigenic drift and occasional antigenic shift.
- Vaccine effectiveness varies (around 30-70%) because the virus's surface proteins change frequently.
- A universal flu vaccine would need to target unchanging parts of the virus, which is not yet available.
Key Terms & Definitions
- Antigen — cell surface marker recognized by antibodies.
- Antibody — protein produced by B cells that binds to antigens.
- Antigenic variation — process by which pathogens alter their surface antigens to evade immune detection.
- Antigenic drift — gradual changes in viral surface proteins due to mutations.
- Antigenic shift — abrupt, major genetic changes in a virus, creating new surface antigens.
Action Items / Next Steps
- Review differences between antigenic drift and shift.
- Understand why flu vaccines need to be administered yearly.