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
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
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.
