00:01
Welcome.
00:02
Previously, in this series about
acute inflammation,
we've talked about
the vascular changes that occur.
00:08
We've talked about
the cellular recruitment.
00:11
And we've talked a little bit
about eicosanoids,
arachidonic acid metabolites,
that mediate some of
the inflammatory effects.
00:19
We're going to conclude this part
of our discussion
of acute inflammation,
looking at effector cascades.
00:27
Inflammatory cells,
neutrophils
don't just do their job
by eating and killing,
they also elaborate
a variety of molecules
that will drive very important
downstream effects.
00:41
So acute inflammation
is also about the effectors.
00:45
And that's where we're going.
00:48
There are effector cascades.
00:49
Remember that we talked about
one of the truisms in biology
is that you start
with a little spark,
and you get a cascade
of ever expanding
and ever increasing response.
01:03
And that's very true,
the various protein effector
cascades.
01:07
The proteins that we're
going to be talking about
come from two major sources,
one is preformed and circulating
in the blood.
01:14
Those are generally synthesized
by the liver
and excrete it into the plasma.
01:19
So there are a lot of
acute phase reactants
that we will revisit in other talks
that are elaborated by the liver.
01:30
Then there are things that
are also synthesized de novo
just at the site of action.
01:36
So many of the cells
directly in the line of fire,
at a site of injury
will elaborate proteins
that also have an effector cascade.
01:49
The major cell
that's synthesizing them,
yet that site
are going to be the macrophages.
01:54
So we have
preformed circulating mediators
from the liver
macrophages synthesizing things
as we need them,
where we need them.
02:03
These proteins
from both sources include
complement, coagulation factors,
and kinins.
02:11
And those are
the three cascades
that we're going to be
talking about now.
02:16
Notably, they're
synthesized by the liver,
and by macrophages.
02:21
So we're talking about
the same thing
in different places.
02:26
Let's talk first about
complement-activation.
02:28
There are many
different ways to activate
the complement cascade.
02:33
In the next few slides,
we'll talk about how we do that
and then exactly
what that cascade involves.
02:38
There is a classical pathway,
where antibody indicated here
is the orange bivalent molecules
binding to an antigen on the surface
of the microbe
will undergo a conformational change
that will allow the activation
of complement
will start that cascade.
02:57
And complement activation
is basically a variety,
a sequence of proteases
proteolytic cleavages
to give us activated fragments.
03:06
The key linchpin is going to be
C3 fragmentation
C3 proteolysis,
to give a C3a and C3b.
03:17
And we'll come back to that.
03:18
So the classical pathway involves
antibody binding,
and then complement being activated
because of an antibody binding.
03:25
There's another pathway
called the alternative pathway
to be compared
with the classical pathway.
03:31
And this involves
additional proteins
called factor B, factor D,
and properdin.
03:39
That will also get us to that
C3b proteolysis,
but by a slightly
different set of factors.
03:46
And then there's the lectin pathway.
03:48
And this has to do with
mannose-binding lectin.
03:52
So recall that many
of the proteins,
glycoproteins
on the surface of pathogens,
and in a terminal mannose.
04:01
We know that, and our
liver and macrophages synthesize
a mannose-binding protein
or mannose-binding lectin
that will then act as a trigger
once it's bound to a pathogen
to activate the complement.
04:14
Again, a proteolytic cleavage
from C3 to C3b and C3a.
04:19
C3a and C3b are just fragments
of the original C3 molecule.
04:25
Okay, that's the way
that we got it activated.
04:27
Now what happens?
Well, so C3a and C3b so that
activated C3b on the surface
will drive the subsequent
breakdown proteolysis, and a cascade
of additional complement
fragments including C5.
04:45
C3a and C5a are very potent
chemotactic agents.
04:51
They will recruit and activate
neutrophils, leukocytes
that will lead to the destruction
by those leukocyte
destruction of the microbes
by those leukocytes.
05:01
So it's pro inflammatory
C3a and C5a.
05:05
C3b, once it gets generated
is very sticky,
and on the surface of a microbe
acts as an obstinate,
it makes it tasty.
05:17
So now, cells that have receptors
for C3b
such as neutrophils, and macrophages
can bind, and will ingest
will phagocytize the microbe
and kill it.
05:29
And finally, starting with C3b
cleavage of C3, to C3a and b.
05:35
Starting with that,
we will then cleave
C5, and C6, and C7, and C8
and that will form a
membrane attack complex.
05:44
So we get a pore and that MAC
or Membrane Attack Complex
will lead to lysis of microbes.
05:50
So complement does
a variety of things.
05:52
It's pro inflammatory by
recruiting inflammatory cells.
05:55
It makes microbes tasty,
so that we can ingest them.
05:59
And it will also
directly lyse microbes.
06:04
So very important.
06:07
So complement.
06:08
Promised that we will give
an overview of this.
06:10
It's a collection of circulating and
macrophage-synthesize proteins.
06:15
It's a cascade of activation
triggered by
Antigen-antibody complexes,
bacterial polysaccharides.
06:22
that's that mannose-binding protein,
and aggregated IGA.
06:26
A form of immunoglobulin.
06:28
So that involves the
properdin alternate pathway.
06:32
Okay.
06:33
Once they're activated,
they have a variety of effects.
06:36
They will cause vasodilation
increased permeability.
06:40
They will increase
leukocyte adhesion.
06:42
Promote chemotaxis
and activation of leukocytes.
06:45
And they will induce opsonization.
06:49
Okay, so complement
does a lot of stuff.