Lecture 6C - How Antibodies Work Flashcards

1
Q

How do antibodies eliminate an antigen?

A

opsonisation
neutralisation
complement activation

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2
Q

What is opsonisation?

A

the promotion of phagocytosis

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3
Q

What does the coating of bacteria, viruses etc by antibodies cause?

A

them to be targeted for destruction by macrophages and other cytotoxic cells

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4
Q

What is an opsonin?

A

a protein which promotes opsonisation and subsequent phagocytosis

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5
Q

What is an example of cytotoxic cells?

A

natural killer (NK) cells

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6
Q

What does the Fc fragment of the antibody do?

A

binds to receptors on the surface of cytotoxic cells and thereby target the pathogen for destruction

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7
Q

The variable region of the antibody bind to…?

A

the target protein, which leaves the stem of the antibody exposed and sticking away from the target cell

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8
Q

What is neutralisation?

A

bacterial toxins may be specifically neutralised by antibodies e.g. diptheria toxin, tetanus, botulinum toxin

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9
Q

What is the complement system?

A

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

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10
Q

What does each compliment protein do?

A

each complement protein in the cascade cleaves the successor

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11
Q

What happens to the products of each cleavage?

A

either become embedded in the membrane or go off to activate other systems

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12
Q

What do the late components do?

A

assemble together to form a pore

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13
Q

What does the formation of a pore cause?

A

high concentrations of Ca2+ to accumulate in the cells and destroy them

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14
Q

What does the complement system consist of?

A

about 20 interacting proteins

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15
Q

What are the reacting components?

A

C1-C9, factor B and factor D

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16
Q

What is the C1 protein subdivided into?

A

C1a, C1r, C1s

17
Q

What can the peptides produced during the enzymatic chain of reactions cause?

A

inflammatory response due to the infection being strengthened

18
Q

What is the classical pathway?

A

involving C1, C2, C4

activated by antigen antibody complexes, could be antibody binding to the surface of a bacterial cell

19
Q

What is the alternative pathway?

A

using factors B and D

activated by microbial lipopolysaccharides

20
Q

What happens after binding of the first component to its target molecule?

A

the enzymatic activity of the complement protein is activated

21
Q

What does the smaller peptide product often produce?

A

Eg C3a, C5a

an inflammatory response

22
Q

What does the C3a fragment cause?

A

the release of histamine by binding to basophils and mast cells

23
Q

Where are basophils present?

A

in the blood

24
Q

What else do basophils release?

25
Where are mast cells present?
in tissues
26
What can mast cells release?
histamine and other inflammatory mediators in large quantities when triggered by binding C3a
27
How else can basophils and mast cells be activated?
by the binding of the Fc fragment of IgE molecules to their surfaces
28
When is binding of IgE to Fc important?
in allergy, where a strong IgE response to a harmless antigen can cause inappropriate inflammatory response
29
What does the larger fragment C3b bind to?
covalently binds to the target cell membrane, where it binds C5
30
What happens when C5 binds?
it is cleaved and spontaneously assembles the late components around it
31
What do the late components form?
the membrane attack complex
32
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
33
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
34
What does the complement system cause?
cytotoxicity enhanced phagocytosis chemotaxis histamine release
35
What does histamine release cause?
increased vascular permeability vasodilation
36
Examples of chemical mediators of inflammation?
complement platelet activating factor lysosomal enzymes, proteases kinins histamine superoxide leukotrienes thromboxane prostaglandins NO cytokines (TNF alpha)
37
What are receptors for chemical mediators often targets for?
drugs
38
What can the production of chemical mediators be encouraged to do?
influence the immune response