Lecture 6C - How Antibodies Work Flashcards
How do antibodies eliminate an antigen?
opsonisation
neutralisation
complement activation
What is opsonisation?
the promotion of phagocytosis
What does the coating of bacteria, viruses etc by antibodies cause?
them to be targeted for destruction by macrophages and other cytotoxic cells
What is an opsonin?
a protein which promotes opsonisation and subsequent phagocytosis
What is an example of cytotoxic cells?
natural killer (NK) cells
What does the Fc fragment of the antibody do?
binds to receptors on the surface of cytotoxic cells and thereby target the pathogen for destruction
The variable region of the antibody bind to…?
the target protein, which leaves the stem of the antibody exposed and sticking away from the target cell
What is neutralisation?
bacterial toxins may be specifically neutralised by antibodies e.g. diptheria toxin, tetanus, botulinum toxin
What is the complement system?
the formation of antigen-antibody complexes, or the presence of polysaccharides in a bacterial cell wall promotes binding on the first complement proteins which are then activated
What does each compliment protein do?
each complement protein in the cascade cleaves the successor
What happens to the products of each cleavage?
either become embedded in the membrane or go off to activate other systems
What do the late components do?
assemble together to form a pore
What does the formation of a pore cause?
high concentrations of Ca2+ to accumulate in the cells and destroy them
What does the complement system consist of?
about 20 interacting proteins
What are the reacting components?
C1-C9, factor B and factor D
What is the C1 protein subdivided into?
C1a, C1r, C1s
What can the peptides produced during the enzymatic chain of reactions cause?
inflammatory response due to the infection being strengthened
What is the classical pathway?
involving C1, C2, C4
activated by antigen antibody complexes, could be antibody binding to the surface of a bacterial cell
What is the alternative pathway?
using factors B and D
activated by microbial lipopolysaccharides
What happens after binding of the first component to its target molecule?
the enzymatic activity of the complement protein is activated
What does the smaller peptide product often produce?
Eg C3a, C5a
an inflammatory response
What does the C3a fragment cause?
the release of histamine by binding to basophils and mast cells
Where are basophils present?
in the blood
What else do basophils release?
serotonin
Where are mast cells present?
in tissues
What can mast cells release?
histamine and other inflammatory mediators in large quantities when triggered by binding C3a
How else can basophils and mast cells be activated?
by the binding of the Fc fragment of IgE molecules to their surfaces
When is binding of IgE to Fc important?
in allergy, where a strong IgE response to a harmless antigen can cause inappropriate inflammatory response
What does the larger fragment C3b bind to?
covalently binds to the target cell membrane, where it binds C5
What happens when C5 binds?
it is cleaved and spontaneously assembles the late components around it
What do the late components form?
the membrane attack complex
What does the membrane attack complex do?
forms transmembrane pores across cellular membranes
the pathogenic cells then rapidly swell and burst due to osmotic shock
What can each of the complement peptides do?
enhance the immune system reaction promoting phagocytosis, setting up a chemotactic gradient for the macrophages to follow or cause the activation of other cels to release chemical mediators
What does the complement system cause?
cytotoxicity
enhanced phagocytosis
chemotaxis
histamine release
What does histamine release cause?
increased vascular permeability
vasodilation
Examples of chemical mediators of inflammation?
complement
platelet activating factor
lysosomal enzymes, proteases
kinins
histamine
superoxide
leukotrienes
thromboxane
prostaglandins
NO
cytokines (TNF alpha)
What are receptors for chemical mediators often targets for?
drugs
What can the production of chemical mediators be encouraged to do?
influence the immune response
