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What Ab isotypes are good at neutralization?
IgG1, IgG2, IgG3, IgG4, IgA
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What Ab isotypes are good at opsonization?
IgG1, IgG3
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What Ab isotypes are good at activation of a complement system?
IgM, IgG1, IgG3
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IgM characteristics
- pentamers, confined to blood (complementation)
- low affinity (due to no somatic hypermutations)
- multivalency
- high avidity
- rapidly clears organisms from bloodstream
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IgG characteristics
- principal Ab in blood and extracellular fluid
- sm, so diffuses out of blood into tissues (opsonize and complement)
- maternal IgG across placenta
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What facilitates movement of maternal IgG to fetus?
FcRB protein carries IgG from endothelium to extracellular and maternal to fetal; looks like MHC-1; 2 FcRB/IgG
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IgA characteristics
- principal isotype in secretions; dimer
- in blood as a monomer
- protects epithelial surfaces from infectious agents
- neutralizes toxins at mucosal sites
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What is the structure of IgA?
dimer; uses J chain to hold dimer together in secretions
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IgE characteristics
w/ mast cells below skin and mucosa and along blood vessels in epithelial and CT
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Mast cells
- bound to IgE via high aff rec for Fc portion of IgE
- activated when Fc receptor bound IgE is cross-linked by binding of multivalent Ag
- IgE-mast act important in local inflammatory responses (causes granules to release contents to extracellular env to cause expelling of path..cough, sneeze, etc)
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J chain
- made by B cells
- initiates polymerization
- covalently linked to Ab
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Neutralization
- done by IgA and IgG
- Ab binds to toxin so that the toxin cannot bind to a cell receptor; Ab +toxin binds to macrophage instead
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Opsonization
Ab coat surface of pathogen and facilitates ingestion of pathogen by neutrophils and macrophages
receptors for Fc region of Ab expressed on surface of phagocytes
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Fc receptors
on certain phagocytes to bind Fc part of Ab w/ pathogen attached
include Ab L chain domains
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Complement activation
system of plasma prot that interact w/ components of innate and adaptive immune system to aid in elimination of pathogens
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FDCs and Fc receptors
FDCs have Fc and complement receptors but DO NOT participate in phagoctytosis; only regular dendritic cells do
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What are the main functional consequences of complement activation?
- 1. opsonization of pathogens
- 2. recruitment of inflammatory cells
- 3. direct killing of pathogens
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What are the "early" events of the complement pathway?
proteolytic steps that generate C3 convertase that binds to pathogen surface via C1 protein
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What does C3 convertase do?
- C3 convertase + pathogen= lg amts of C3b
- generates several sm fragments that serve as inflammatory mediators and C5b prot
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What does C3b do?
binds to complement receptors on phagocytes (opsonization)
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What does C5b prot do?
initiates "late" events of complement cascade
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What are the "late" events of the complement cascade?
seq of polym rxns that result in formation of membrane attack complex (MAC) that directly damages membranes of certain pathogenes
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How is the host cell protected from MAC?
- prot CD59 disrupts formation of pores in host
- DAF prot disrupts C3 convertase in host
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