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

Another name for FcgRIII

Answer 6

CD16

Question 7

What is CD16?

Answer 7

IgG receptor on the surface of NK cells

Question 8

What triggers NK cell killing?

Answer 8

Crosslinking of CD16/FcgRIII receptors

Question 9

Mast cell degranulation
1)
2)
3)

Answer 9

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 10

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

Answer 10

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

Question 11

FcgRI affinity

Answer 11

High

Question 12

FcgRIIA affinity

Answer 12

Low

Question 13

FcgRIIB affinity

Answer 13

Low

Question 14

FcgRIIIA affinity

Answer 14

Low

Question 15

FcgRIIIB affinity

Answer 15

Low

Question 16

FcgRI cell distribution

Answer 16

Macrophages, neutrophils

Question 17

FcgRIIA cell distribution

Answer 17

Macrophages, neutrophils

Question 18

FcgRI function

Answer 18

Cell activation, phagocytosis

Question 19

FcgRIIA function

Answer 19

Cell activation, phagocytosis

Question 20

FcgRIIB cell distribution

Answer 20

B cells

Question 21

FcgRIIB function

Answer 21

B cell inhibition

Question 22

FcgRIIIA cell distribution

Answer 22

NK cells

Question 23

FcgRIIIA function

Answer 23

NK cell antibody-dependent cell-mediated cytotoxicity

Question 24

FcgRIIIB cell distribution

Answer 24

Neutrophils

Question 25

FcgRIIIB function

Answer 25

Neutrophil phagocytosis

Question 26

FceRI cell distribution

Answer 26

Mast cells

Question 27

FceRI function

Answer 27

Mast cell degranulation

Question 28

FceRI affinity

Answer 28

High

Question 29

Why are many Fcg receptors low affinity?

Answer 29

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

Question 30

High avidity antibodies

Answer 30

Multimeric IgM, IgA

Question 31

Which FcgR can stably bind monomeric IgG

Answer 31

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

Question 32

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

Answer 32

FcgRIIA, fcgRIIB, FcgRIIIA, FcgRIIIB

Question 33

What kind of cells do NK cells kill?

Answer 33

Virus-infected cells | Not really extracellular bacteria

Question 34

What is the secretory component?

Answer 34

Part of the polymeric-Ig receptor on secretory IgA

Question 35

Is IgA dimeric in the blood?

Answer 35

Yes

Question 36

How is the classical complement cascade initiated?

Answer 36

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

Question 37

What is C1q?

Answer 37

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

Question 38

Which antibody is best at activating complement?

Answer 38

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 39

Can free antibodies activate complement?

Answer 39

No. Only IgG and IgM complexes can activate complement

Question 40

Which antibodies neutralise?

Answer 40

IgG, IgA

Question 41

Which antibodies opsonise?

Answer 41

IgG1 > IgG3 > IgG4, IgA

Question 42

Which antibodies induce antibody-dependend cell-mediated cytotoxicity?

Answer 42

IgG1, IgG3

Question 43

Which antibodies activate the complement cascade?

Answer 43

IgM >> IgG1, IgG3 > IgG2, IgA

Question 44

Which antibody degranulates mast cells?

Answer 44

IgE

Question 45

Antibody variability types 1) 2) 3)

Answer 45

1) Isotype 2) Allotype 3) Idiotype

Question 46

What is allotype?

Answer 46

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

Question 47

What is idiotype?

Answer 47

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

Question 48

An equation to quantify proteinomic variability

Answer 48

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

Question 49

What are complement proteins very good at killing?

Answer 49

Extracellular bacteria

Question 50

What is the most variable region of an antibody?

Answer 50

CDR3