CHAPTER 2 by RH
Microbiology 4402 with Reilly at Texas Tech University
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complement
plasma proteins that coat the outside of pathogens and make them easier to phagocytize
complement activation
a cascade of proteases that activate complement (called zymogens when inactive)
C3 (C3a and C3b)
The most important component of compliment.
C3b fragment undergoes complement fixation and binds to a bacteria and tags it for destruction or starts a MAC.
C3a acts as a chemoattractant and recruits effectors.
iC3 or CB(H2O) involves no cleavage just the association of one water molecule .
Factor B
cleaved by factor D into Bb and Ba
Bb has protease properties and binds to iC3 to for iC3Bb
C3 convertase
iC3Bb binds to other C3s and cleaves into C3a and C3b. iC3Bb is soluble
Alternative C3 Convertase
C3bBb - works/binds to the surface of the pathogen and does not diffuse away like C3 convertase, so a larger portion of the C3b affix to the cell surface for marking. This positive feedback amplifies C3 cleavage.
CCPs
Complement Control Proteins
regulare C3b rxns
they stabilize or breakdown C3b at cell surfaces
Factor P
Properdin increases the effectiveness of compliment by binding to C3bBb (C3 convertase alternative) and preventing its degradation by proteases
Factor H
opposite of factor P, binds to alternative C3 convertase and facilitates its cleavage to iC3b by serine proteases factor I
Factor I
a serine protease, people deficient in factor I are more susceptible to encapsulated bacterial infections. They Do not adhere many C3b phagocytosis markers on pathogens.
DAF
decay accelerating factors - binds to the C3b of C3 convertase inactivating it by dissociating it.
also controls complement proteins
MCP
membrane co-factor protein - similiar to DAF, but its binding to C3b makes it susceptible to cleavage by factor I
similiar to function of factor H
CCP Modules
complement control modules - DAF, MCP, and Factor H are all built from these modules each module has 60 amino acids and 2 beta-pleated sheets
RCAs
regulators of complement activation - proteins made up of CCP modules
helps with self and non self ID
Complement Receptor 1
CR1s are located outside macrophages they facilitate by making macrophages more specific by recognizing C3b attached to pathogens this process is called opsonization.
CR1s, like MCP and factor H, protect the cells they're attached to by disrupting C3 convertase
CR3 and CR4
both binds to iC3b fragments on pathogen's surface. iC3b has no convertase ability but acts as a ligand for CR3 and CR4.
CR1, CR3, and CR4s work best together rather than separably
alternative C5 Convertase
C3b + alternative C3 convertase similar to C3 but lacks thioester.
C5a - larger
C5b - smaller; initiates MAC
Membrane-Attack Complex
MAC - C6 & C7 bind to C5b, they expose a hydrophobic spot for C7 which inserts into the membrane. Then C8 binds to C5b and exposes its hydrophobic side and initiates a polymerization of C9 unites to form a spore.
MAC Regulation
MAC Regulation - S protein, clusterin and Factor J prevent C5b, C6, and C7 from binding to the membrane along with CD59.
CD59
prevents C9 recruitment and blocks pore formation.
impaired CD59 tails causes paroxysmal nocturnal hemoglobina
anaphylatoxins
C3a and C5b (C5b is more potent) can induce acute inflammatory response throughout the body's tissues called anaphaletic shock. They contract smooth muscles, and cause mast cells and basophils to degranulate.
They make it easier for plasma protiens and cells to leave the blood and go to the site of infection. C5a also chemoattracts neutrophils and monocytes while increasing CR1 and CR3 expression.
defensins
35-40 amino acids, richly positive in arginine residues and have intra disulfide bonds.
amphipathic, penetrate and disrupt pathogen's membranes.
alpha- neutrophils, mostly intestines, released by paneth cells
beta - skin, respiratory, urogenital tracts.
work best with lower ionic strength like in sweat, tears, or gut lumen.
Lectins
look for differences in carbohydrates on the outside of cells
like mannose and glucagon receptors.
Scavenger Receptors
NOT A LECTIN. binds to the negatively charged ligands found on gram-positive bacteria.
Bacterial LPSs
bacterial lipopolysaccharides recognized by CR3 and CR4 bacterial LPSs are on gram-negative bacteria and many parasites either yeasts or protozoan.
Receptor Mediated Endocytosis
a receptor bound pathogen is engulfed by a macrophage which then enters and endosome or a phagosome. They then combine with a lysozome to form a phagoloysosomes.
Toll-like Receptors
TLRs signal receptors that vary innate immune responses for specific pathogens. They are transmembrane proteins composed of an extracellular domain that signals to the inside of the cell.
example - macrophages have TLR4 which looks for LPSs on gram-negative bacteria.
inflammatory cytokines
cytokines that induce innate immune responses and inflammation at the site of infection. like TLR4.
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