Antigenic structure of influenza virus, antigen drift and shift

Dive into the intricate antigenic structure of the influenza virus and explore the mechanisms of antigenic drift and shift in this insightful presentation. Learn about the composition of influenza viral antigens, including hemagglutinin (HA) and neuraminidase (NA), and how changes in these antigens contribute to viral evolution and immune evasion. Understand the subtle variations of antigenic drift and the dramatic shifts of antigenic shift, and their implications for influenza vaccine development, epidemic preparedness, and public health strategies

1. Antigenic Structure of Influenza virus, Antigen drift and shift By Sunidhi Singh IM 534

2. ANTIGENS IN INFLUENZA VIRUS: There are two primary antigens present on the surface of the virus: 1. Hemagglutinin (HA): This antigen helps the virus to attach to the cells of the respiratory mucosa, thereby entering the cells. Variability in HA defines different subtypes of influenza viruses (e.g., H1, H3) Also known as red blood cell agglutination factor

3. 2. Neuraminidase (NA) It helps in thinning the mucous in the respiratory tract due to enzymatic action, which makes it easier for the virus to Contact the cells of mucosa. It also facilitates the release of newly formed virus particles from the infected cells. It has subtypes Like N1, N2 There are 18 subtypes of HA and 11 subtypes of NA but only H 1, 2 and 3, and N 1 and 2 are commonly found in humans

4. The combination of specific subtypes of these antigens determines the overall type of the virus, examples H1N1, H3N2 In addition to HA and NA, influenza viruses also have internal antigens. These include proteins such as nucleoprotein (NP) and matrix protein (M) While these internal antigens are not as variable as HA and NA, they still play roles in the virus's replication and in triggering immune responses

5. Structure of influenza A virus

6. Significance of antigenic structure of influenza virus: The antigen structure of influenza viruses, particularly the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA), is significant for several reasons: Immune Response: The immune system recognizes these antigens as foreign and produces antibodies against them. Vaccine Development: Understanding antigenic variations helps in designing effective vaccines.

7. Virus Classification: The variability in HA and NA subtypes is used to classify influenza viruses into different types and subtypes (e.g., H1N1, H3N2). This classification is crucial for monitoring and responding to outbreaks. Pandemic Potential: Antigenic shifts, where there are major changes in HA or NA, can lead to pandemics.

8. It has two main components: HA and NA HA and NA proteins are also present but have different subtypes Influenza C has a different HA-esterase-fusion glycoprotein but lacks neuraminidase subtypes Variability in HA and NA subtypes determines different strains of the virus. Influenza B is divided into two main lineages: B/Yamagata and B/Victoria, based on differences in the HA protein It doesn't have the same variability as Influenza A and B. Has no subtypes Examples: H1N1, H3N2 High pandemic protential due to antigen shifts Lower pandemic potential Causes mild illnesses Influenza A Influenza B Influenza C

9. Antigen Drift and Shift: antigenic shift and antigenic drift are terms used to describe changes in the antigens of the influenza virus, particularly in the hemagglutinin (HA) and neuraminidase (NA) proteins.

10. Antigenic Drift: Antigenic drift is caused by point mutations and is defined as the minor gradual antigenic changes in the HA or NA protein. Nature: Gradual, incremental changes in the amino acid sequence of HA and NA. Frequency: Common and occurs regularly in seasonal influenza viruses. Cause: Results from point mutations during the virus's replication.

11. Impact: Leads to minor antigenic changes, causing the virus to be slightly different from previous strains. Consequence: Individuals previously exposed to similar strains may have partial immunity, but immunity may decrease over time. Vaccine: Seasonal flu vaccines need periodic updates to account for these drifts.

12. Antigenic Shift: Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. Nature: Sudden, major change in the antigenic makeup of the influenza virus. Frequency: Relatively rare but can have significant consequences.

13. Cause: Results from the reassortment of genetic material between different influenza A viruses, often from different host species. Impact: Creates a novel virus with new HA and/or NA subtypes, to which the population has little to no immunity. Consequence: Can lead to influenza pandemics with higher morbidity and mortality rates.

14. Examples: Historic pandemics like the 1918 Spanish flu and the 2009 H1N1 pandemic were caused by antigenic shift. Vaccine: Existing immunity may offer little protection, and development of a specific vaccine for the new subtype is necessary.