Lecture 6 - Antibody Effector Function

Question 1

Direct and indirect antibody effector functions

Answer 1

Direct - Function of Fab, neutralisation

Indirect - Involves Fc, targets bound antigen for phagocytosis, etc

Question 2

Example of antibody direct mechanism

Answer 2

Antibody binds to influenza haemagglutinin

Influenza is now unable to enter host cell

Question 3

Example of antibody indirect mechanism

Answer 3

Antibody binds to target antigen

If IgE, stimulates mast cell degranulation

Question 4

Opsonisation
1)
2)
3)

Answer 4

1) Antibody binds to taret antigen
2) Bind to phagocyte by FcR
3) Phagocytosis

Question 5

What does ADCC stand for?

Answer 5

Antibody-dependent cell-mediated cytotoxicity

Question 6

Which receptor on a natural killer cell binds to antibody opsonising antigen?

Answer 6

FcgRIII (CD16)

Question 7

Another name for FcgRIII

Answer 7

CD16

Question 8

What is CD16?

Answer 8

IgG receptor on the surface of NK cells

Question 9

What triggers NK cell killing?

Answer 9

Crosslinking of CD16/FcgRIII receptors

Question 10

Mast cell degranulation
1)
2)
3)

Answer 10

1) Mast cell is ‘sensitised’ - IgE coats mast cell, binds to FceR
2) IgE Fab region comes into contact with allergen
3) Crosslinking of FceR leads to degranulation

Question 11

Does a mast cell have a monoclonal or polyclonal antibody coating?

Answer 11

Polyclonal.
Can respond to several different allergens
Probably clumps o fmonoclonal antibodies in different places to allow crosslinking, clumping of antibodies

Question 12

FcgRI affinity

Answer 12

High

Question 13

FcgRIIA affinity

Answer 13

Low

Question 14

FcgRIIB affinity

Answer 14

Low

Question 15

FcgRIIIA affinity

Answer 15

Low

Question 16

FcgRIIIB affinity

Answer 16

Low

Question 17

FcgRI cell distribution

Answer 17

Macrophages, neutrophils

Question 18

FcgRIIA cell distribution

Answer 18

Macrophages, neutrophils

Question 19

FcgRI function

Answer 19

Cell activation, phagocytosis

Question 20

FcgRIIA function

Answer 20

Cell activation, phagocytosis

Question 21

FcgRIIB cell distribution

Answer 21

B cells

Question 22

FcgRIIB function

Answer 22

B cell inhibition

Question 23

FcgRIIIA cell distribution

Answer 23

NK cells

Question 24

FcgRIIIA function

Answer 24

NK cell antibody-dependent cell-mediated cytotoxicity

Question 25

FcgRIIIB cell distribution

Answer 25

Neutrophils

Question 26

FcgRIIIB function

Answer 26

Neutrophil phagocytosis

Question 27

FceRI cell distribution

Answer 27

Mast cells

Question 28

FceRI function

Answer 28

Mast cell degranulation

Question 29

FceRI affinity

Answer 29

High

Question 30

Why are many Fcg receptors low affinity?

Answer 30

To keep serum IgG levels high. | If they were high affinity, IgG would be sequestered on cells, like IgE is.

Question 31

High avidity antibodies

Answer 31

Multimeric IgM, IgA

Question 32

Which FcgR can stably bind monomeric IgG

Answer 32

FcgRI (high affinity). | Can bind a single IgG bound to an antigen

Question 33

Which FcgR need multiple antibodies bound to a pathogen in order for stable binding?

Answer 33

FcgRIIA, fcgRIIB, FcgRIIIA, FcgRIIIB

Question 34

What kind of cells do NK cells kill?

Answer 34

Virus-infected cells | Not really extracellular bacteria

Question 35

What is the secretory component?

Answer 35

Part of the polymeric-Ig receptor on secretory IgA

Question 36

Is IgA dimeric in the blood?

Answer 36

Yes

Question 37

How is the classical complement cascade initiated?

Answer 37

C1q component of C1 binds to exposed region of IgM or IgG bound to antigen

Question 38

What is C1q?

Answer 38

Part of the C1 complex. | C1 is made up of three components, one of which is C1q

Question 39

Which antibody is best at activating complement?

Answer 39

IgM. IgG1, 2 and 3 are capable of activating complement, but need several antibodies bound to antigen to activate it, whereas pentameric IgM only needs one

Question 40

Can free antibodies activate complement?

Answer 40

No. Only IgG and IgM complexes can activate complement

Question 41

Which antibodies neutralise?

Answer 41

IgG, IgA

Question 42

Which antibodies opsonise?

Answer 42

IgG1 > IgG3 > IgG4, IgA

Question 43

Which antibodies induce antibody-dependend cell-mediated cytotoxicity?

Answer 43

IgG1, IgG3

Question 44

Which antibodies activate the complement cascade?

Answer 44

IgM >> IgG1, IgG3 > IgG2, IgA

Question 45

Which antibody degranulates mast cells?

Answer 45

IgE

Question 46

Antibody variability types 1) 2) 3)

Answer 46

1) Isotype 2) Allotype 3) Idiotype

Question 47

What is allotype?

Answer 47

Differences in antibody gene genetic code. Heritable Results in different Ig alleles Doesn't encode any noticeable difference in function

Question 48

What is idiotype?

Answer 48

Diversity in antibody binding sites | ~10^7 different binding sites in each individual

Question 49

An equation to quantify proteinomic variability

Answer 49

Number of different amino acids at a given position/Frequency of most common amino acid at a given position

Question 50

What are complement proteins very good at killing?

Answer 50

Extracellular bacteria

Question 51

What is the most variable region of an antibody?

Answer 51

CDR3