Hello, I'm Ashley Frazer-Abel from the Division of
Rheumatology at the University of Colorado, School of Medicine.
Today, we'll be talking about the complement system
as an introduction for undergraduates.
So we'll be talking about complement,
which is part of the humoral and immune system.
But we need to keep in mind that,
that part of the complement system does not work alone and is
connected with the whole rest of the acquired immunity and cellular immunity system.
So the complement pathway is represented here and is quite complex.
At this point, many people get confused or lost,
but it's really quite simple.
So we'll walk through it.
There are three activation pathways; the classical, lectin,
and alternative pathway that converge and share the terminal pathway.
While we go through the pathways,
it's important to keep in mind what will activate complement.
Across the top line here,
we have what is considered the most common or
classically known ways of activating pathways.
For the classical system, that's immunoglobulins.
For the alternative system, that's the tick-over.
For the lectin system, that's repeating sugars.
We will walk through all of these later,
but it's important to keep in mind
the other methods that will activate the compliment system.
In fact, this list is ever growing and I don't think we
even know now all the things that can activate the compliment system.
So for that activation,
we can see some very consistent types of structures
for both the classical and lectin pathway activation.
On your left, we have depicted C1,
which is made up of C1q, C1r and C1s.
For the lectin pathway,
we have mannose-binding lectin and the ficolins,
which you can see have a very similar structure to C1q,
with the globular heads being a recognition units.