Lecture 6C - How Antibodies Work

Question 1

How do antibodies eliminate an antigen?

Answer 1

opsonisation
neutralisation
complement activation

Question 2

What is opsonisation?

Answer 2

the promotion of phagocytosis

Question 3

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

Answer 3

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

Question 4

What is an opsonin?

Answer 4

a protein which promotes opsonisation and subsequent phagocytosis

Question 5

What is an example of cytotoxic cells?

Answer 5

natural killer (NK) cells

Question 6

What does the Fc fragment of the antibody do?

Answer 6

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

Question 7

The variable region of the antibody bind to…?

Answer 7

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

Question 8

What is neutralisation?

Answer 8

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

Question 9

What is the complement system?

Answer 9

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

Question 10

What does each compliment protein do?

Answer 10

each complement protein in the cascade cleaves the successor

Question 11

What happens to the products of each cleavage?

Answer 11

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

Question 12

What do the late components do?

Answer 12

assemble together to form a pore

Question 13

What does the formation of a pore cause?

Answer 13

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

Question 14

What does the complement system consist of?

Answer 14

about 20 interacting proteins

Question 15

What are the reacting components?

Answer 15

C1-C9, factor B and factor D

Question 16

What is the C1 protein subdivided into?

Answer 16

C1a, C1r, C1s

Question 17

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

Answer 17

inflammatory response due to the infection being strengthened

Question 18

What is the classical pathway?

Answer 18

involving C1, C2, C4

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

Question 19

What is the alternative pathway?

Answer 19

using factors B and D

activated by microbial lipopolysaccharides

Question 20

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

Answer 20

the enzymatic activity of the complement protein is activated

Question 21

What does the smaller peptide product often produce?

Answer 21

Eg C3a, C5a

an inflammatory response

Question 22

What does the C3a fragment cause?

Answer 22

the release of histamine by binding to basophils and mast cells

Question 23

Where are basophils present?

Answer 23

in the blood

Question 24

What else do basophils release?

Answer 24

serotonin

Question 25

Where are mast cells present?

Answer 25

in tissues

Question 26

What can mast cells release?

Answer 26

histamine and other inflammatory mediators in large quantities when triggered by binding C3a

Question 27

How else can basophils and mast cells be activated?

Answer 27

by the binding of the Fc fragment of IgE molecules to their surfaces

Question 28

When is binding of IgE to Fc important?

Answer 28

in allergy, where a strong IgE response to a harmless antigen can cause inappropriate inflammatory response

Question 29

What does the larger fragment C3b bind to?

Answer 29

covalently binds to the target cell membrane, where it binds C5

Question 30

What happens when C5 binds?

Answer 30

it is cleaved and spontaneously assembles the late components around it

Question 31

What do the late components form?

Answer 31

the membrane attack complex

Question 32

What does the membrane attack complex do?

Answer 32

forms transmembrane pores across cellular membranes

the pathogenic cells then rapidly swell and burst due to osmotic shock

Question 33

What can each of the complement peptides do?

Answer 33

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

Question 34

What does the complement system cause?

Answer 34

cytotoxicity

enhanced phagocytosis

chemotaxis

histamine release

Question 35

What does histamine release cause?

Answer 35

increased vascular permeability

vasodilation

Question 36

Examples of chemical mediators of inflammation?

Answer 36

complement

platelet activating factor

lysosomal enzymes, proteases

kinins

histamine

superoxide

leukotrienes

thromboxane

prostaglandins

NO

cytokines (TNF alpha)

Question 37

What are receptors for chemical mediators often targets for?

Answer 37

drugs

Question 38

What can the production of chemical mediators be encouraged to do?

Answer 38

influence the immune response