Complement Activation: Part 1 Flashcards
A _________ is a system of proteins that are activated by the presence of a ________, that are made up of predominantly inert until activation.
Complement
Pathogen
A key site of activation of complements, is at the ______ of pathogens, which can proceed into 3 pathways.
Surface
What are the 3 pathways of the complement system?
Classical, Lectin, and Alternative
What are the possible outcomes of the complement system?
Opsonization, MACs, or recruitment of inflammatory and immunocompetent cells
True or False: Some complements are capable of acting as chemoattractants during chemotaxis for phagocytic cells.
True
How does the complement also capable of activating the adaptive immune response?
Opsonization by APC’s (dendritic cells, macrophages, and B cells)
What is the correct order of discovery for the complement proteins 1 - 9?
C1, C4, C2, C3, C5, C6, C7, C8, C9
While more often, the larger fragment of complement proteins will be given the “b,” the larger complement protein of C2 is _ and the smaller is _.
C2a = larger C2b = smaller
The alternative pathway employs complement proteins that begin with different capital letters. Will the a fragment be smaller, or will the b fragment be larger?
a = smaller b = larger
Describe the initiation of the classical pathway.
C1q proteins will bind to the surface of a pathogen (lipoteichoic acid, CRPs on phosphocholine, Ag:Ab complexes).
Describe the initiation of the lectin pathway.
MBL binds to pathogen surfaces or ficolins to N-acetylglucosamine
Describe the initiation of the alternative pathway.
C3b proteins binding to pathogen surfaces
All the pathways of the complement system lead to the production of what protein complex? Where will it bind to?
C3 convertase, which binds to pathogen surfaces
What is the role of C3 convertase?
The production of C3a (mediates inflammation) and C3b (main molecule)
C3b acts as an ______, which marks the pathogen as a target for phagocytosis.
Opsonin
In order to form C5 convertase, what molecules must bind together on the surface of the pathogen?
C3b and C3 convertase
What are the products of C5’s interaction with C5 convertase?
C5a (an inflammatory mediator) and C5b (main molecule)
C5b leads to the formation of the -?
Membrane attack complex
How many Ig’s of IgM and IgG are needed to bind to an antigen, so that its Fc region can bind to the complement protein __?
One IgM, several IgG
C1 or C1qr2s2
The C1q backbone has six domains, with two copies of the ____ and ____ domains.
C1r and C1s
Explain how C1 is activated.
C1q binds to 2 adjacent Fc regions of antibodies, which activates C1r that cleaves itself and then C1s, which activates it
What function does C1s have?
It cleaves C4, and this leads the C4b fragment to attach to the Ag:Ab complex or microbe
It cleaves C2, where C2a will bind to C4b
What molecular name does C4b2a have?
C3 convertase
C3 convertase will cleave C3, which will lead to C3b -?
Binding to C3 convertase, to form C5 convertase (C4b2a3b)
C5 convertase leads to the formation of the _________ ______ _______.
Membrane Attach Complex
