So let’s talk about the
pathogenesis of this virus.
The hemagglutinin spike is the spike
that is the attachment protein.
This is what’s going to attack a
target respiratory epithelial cell.
Now, coding all of our respiratory
epithelial cells is sialic acid,
and so, the hemagglutinin
spikes are able to attach
to sialic acid on respiratory
Once they are attached,
the virus then is
internalized into an endosome
and that’s where another
envelope protein kicks in,
known as the M2 protein.
The M2 protein acts as an ion channel.
So you had the virus
in an endosome,
and then the M2 protein activates
acting as an ion channel
and it allows hydrogen ions from
the cell to enter that endosome,
and that sparks the
uncoding of the virus.
So now the virus is loose
in the cell cytoplasm.
And of course, the viral gene segments,
they go to the cell nucleus,
and what the virus is trying to
do is direct our chromosomes
to make more copies
of influenza virus.
So they do that by synthesizing
their own messenger RNA
and that messenger RNA
is acted upon by our ribosomes
making new influenza virus particles
near the surface of the infected cell.
That’s when the neuraminidase
spikes start their activity.
Now, I didn’t tell you this, but
sialic acid is actually a derivative
of N-acetylneuraminic acid,
and so that’s what’s
on the cell surface.
Well, if you remember,
if a virus is trying to come out of a cell
and it’s got those hemagglutinin spikes
where they’re going to stick to the sialic
acid and the virus will never get out.
So somehow, as the virus emerges,
something’s got to be done about that sialic
acid to prevent the hemagglutinin spikes
from causing the virus to stick
there in the infected cell.
So the neuraminidase spikes
get rid of sialic acid on that
cell so that the virus can emerge.
Without the neuraminic acid spike, the
virus gets stuck inside the target cell.
And once it’s out,
it can go down the respiratory
tree and infect an adjacent cell.
So what influenza does to the
respiratory epithelial cells
is cause great damage to them.
I think you can see in
this particular image
that the outer surface of the respiratory
epithelial cell is being stripped away.
And if you think about what’s happening,
the respiratory tree in a
severe case of influenza
can be totally denuded of its epithelium.
Well, what gets denuded of course, are the
cells that have cilia and the mucous cells.
So can you imagine that the
respiratory tract is now defenseless?
And so if, for example, a
staphylococcal bacterium gets in there,
you could have staphylococcal pneumonia
and a very severe case of influenza
because you don’t have the
normal mucosal defenses,
so you just strip away large
portions of the epithelium.
Well, the patient is going to feel that
with initially a nonproductive cough
starts out without productivity,
a severe sore throat,
and maybe symptoms of a typical viral
infection with nasal obstruction.
Picture what’s going on in
the respiratory epithelium.