The Complement System Flashcards
Quiz 2
What is the complement system?
A series of proteins that are secreted mostly by the liver. When in inactive form, they circulate in the blood, interstitial fluid, and other fluids
What is Opsonization
Coating of pathogens with proteins (opsonin)
How do the Phagocytes recognize the opsonins during opsonization?
phagocytes have receptors and this increases phagocytosis
What are two examples of opsonins
antibodies and complement proteins
What are the three proteins that C1 is made of
C1q, C1r, and C1s
What is the function of C1q
Binds to the antigen: antibody complexes and pathogen surfaces
List the 8 complement proteins that are activating enzymes
C1r, C1s, C2a, Bb, D, MASP-1, MASP-2, MASP-3
Describe C1 from the Classical Pathway
-C1q recognizes microbial surface OR binds to antibodies
-C1r and C1s are inactive proteases bound to C1q
Describe the start of the complement system with the classical pathway
-First, the pathogen infects
-antibodies that are already present (from previous infection) will then bind to the pathogen
-when C1q binds to the antibody, it will activate C1r which will cleave C1s
-C1s is then activated and will cleave C4 and C2
-C4b binds C2
-C4b2a (classical C3 convertase) cleaves C3 and activates C3
-C3b opsonizes the pathogen surface
what is the function of C1r
cleaves C1s to active protease
What is the function of C1s
Cleaves C4 and C2
What is the function of C4b
covalently binds to pathogen and opsonizes it. Binds C2 for cleavage by C1s
What is the function of C4a
Peptide mediator of inflammation (weak activity)
What is the function of C2a
active enzyme of classical pathway C3/C5 convertase: cleaves C3 and C5
What is the function of C3b
Binds to the pathogen surface and acts as opsonin. Initiates amplification via the alternative pathway. Binds C5 for cleavage by C2a
What is the function of C3a
Peptide mediator of inflammation (intermediate activity)
What is the purpose of anaphylatoxins
-vasodilators: (increase vascular permeability) gets cells to site
-can act as chemokines (attract immune cells)
-induce mast cell degranulation (Histamine release)
-THE END GOAL: inflammation
What are the two complement proteins that are anaphylatoxins
C4a and C3a
what induces anaphylactic shock?
anaphylatoxins induce shock (the same as an allergic reaction)
How does C3b opsonization work?
-C3 contains 2 disulfides
-highly reactive thioester (ThioEster Domain TED)
-The TED domain is how C3b binds to the pathogen surface
What happens if the TED domain of C3b binds to water
It will become inactive as a way to protect the immune system
Give a classical pathway summary (very brief)
-Starts with C1
-Recognizes antibody or cell wall/lipids of bacteria
-lead to a protease cascade
-releases anaphylatoxins (induce inflammation)
Create C3 convertase (C4b2a)
What does the lectin pathway recognize to begin process
-senses unique carbs on the pathogen surface
How does the Lectin pathway sense unique carbs on pathogens?
Bacteria and yeast have terminal mannose while vertebrates do not and this allows them to distinguish between the species