Immunology Exam 2: The Complement System
how is the MAC formed
- compliment proteins - proteins become amphipathic - allows them to intert into plasma membrane of target cell - C9 molecules then polymerize together to form a ring, creating a large pore/hole in membrane of target cell
Lectin Pathway Activation
- innate - lectins - MBL (mannose binding lectin) binds mannose found on some bacteria and fungi
Alternative Pathway Activation
- part of innate system - C3 directly recognizes certain microbial surface structures - these surface structures contain things that can activate the alternative pathway - C3 then fragments into active components
complement system proteins: step 1 inhibitor
- responsible for initation of complement cascade - interaction with initiator protein - once initator protein finds something to bind to, the protein goes through a conformational change that will then make it active
Classical Pathway Activation
-part of adaptive immunity -initator proteins interacting with antibody bound to antigen - only IgM and IgG antibodies can activate - the 3D structure of the antibody is changed when bound to antigen which exposes the binding site for C1q complex - proteases then go and cleave compliment proteins to their active forms
complement system proteins
C3a, C3b, C5a, and C5b
Complex of compliment proteins will not form without
C5b fragment
describe the glycoproteins of the compliment system
about 30 involved - made by liver hepatocytes - only cause immune response upon activation - highly conserved
overview comparing the different pathways
alternative: cleave directly on interface classical: interact with antibodies lectin: interact with sugar groups on pathogen * cleaved fragments: now activated * these cleaved fragments can now be used as C3/C5 convertases * these convertases cleave proteins into their active form = C3a, C3b, C5a, and C5b --> important for downstream complement cascades
antibody antigen complex clearance
antibody binding to antigen causes complement activation (classical pathway) -C3b bound to the antibody/antigen complex can bind to CR1 receptors on RBCs - RBCs take complex to liver and spleen so phagocytes can phagocytize
3 ways to activate complement system
classical alternative lectin
MAC
membrane attack complex - formed by complement proteins - MAC proteins insert into cell membranes of invading microbes - punch holes and result in cell death - C5b, C6,C7,C8,C9
what is the complement system
set of serum proteins that work with both the innate and adaptive systems to eliminate pathogens - interact with signaling cascades
