Antibody functions

Question 1

Describe isotype switching

Answer 1

All B cells begin making IgM, class switching means memory cells produce IgG, IgA, IgE with the same variable region/specificity.

Retain same V-D-J but change the constant region following after J region via non-homologous DNA recombination where AID enzyme acts on switch region to open dsDNA.

Two switch regions that are acted on come together and inbetween DNA is looped out.

Question 2

Describe isotype switching

Answer 2

All B cells begin making IgM, class switching means memory cells produce IgG, IgA, IgE with the same variable region/specificity.

Retain same V-D-J but change the constant region following after J region via non-homologous DNA recombination

Question 3

Describe isotype switching

Answer 3

All B cells begin making IgM, class swiching means memory cells produce IgG, IgA, IgE with the same variable region

Question 4

What are switch regions?

Answer 4

They are stretches of repetitive DNA upstream of the constant heavy gene segments

Question 5

What are switch regions?

Answer 5

They are stretches of repetitive DNA upstream of the constant heavy gene segments.

AID acts on switch regions

Question 6

Where in the body can you find each Ig be found?

Answer 6

Brain has no Ig: they are too large to cross the blood/brain barrier.

IgM/IgA/IgG in blood

IgA in secretions: dimeric

IgG/IgA in extracellular fluid/in tissues (where IgM is too large to diffuse)

IgE in connective tissue under skin, GI/respiratory tracts

Question 7

Which Ig protect the internal tissues of the body?

Answer 7

IgM, IgG and monomeric IgA

Question 8

Which Ig protect the mucosal surfaces of the body?

Answer 8

dimeric IgA

Question 9

Which Ig protect the Body from pathogens?

Answer 9

IgE

Question 10

Which Ig are important in pregancy and after birth?

Answer 10

IgG is delivered directly to foetal circuation

Question 11

Which Ig are important in pregancy and after birth?

Answer 11

IgG is delivered directly to foetal circuation so baby is born with high level of IgG until it can make its own.

IgM produced soon after birth, but IgG is produced until 6 months

dimeric IgA protects baby GI tract via breast milk passive transfer which helps when IgG is low.

Question 12

What is colostrum?

Answer 12

First breast-feeding milk which high concentrations of IgA

Question 13

What are high affinity neutralizing antibodies?

Answer 13

Where pathogen is neutralised simply by Ab binding and pathogen (virus and bacteria) cannot cause disease.

Question 14

What are high affinity neutralizing antibodies?

Answer 14

Where pathogen is neutralised simply by Ab binding and pathogen (virus and bacteria or pathogen produced toxins) cannot cause disease.

Example Abs coast bacteria at mucosal surface to prevent their attachment to fibronectin in extracellular matrix.

Question 15

Which antibodies are efficient at binding to soluble toxins

Answer 15

IgG, and IgA; prebents binding, internalisation, intracellular dissociation of poisonous toxin which disrupt cell function

Question 16

Which antibodies are efficient at binding to soluble toxins/exotoxins

Answer 16

IgG, and IgA; prebents binding, internalisation, intracellular dissociation of poisonous toxin which disrupt cell function

Question 17

What are high affinity neutralizing antibodies?

Answer 17

Where pathogen is neutralised simply by Ab binding to FAB recognition arms and so pathogen (virus and bacteria or pathogen produced toxins) cannot cause disease.

Example Abs coast bacteria at mucosal surface to prevent their attachment to fibronectin in extracellular matrix.

Question 18

Which antibodies are efficient at binding to soluble toxins/exotoxins

Answer 18

IgG, and IgA; prebents binding, internalisation, intracellular dissociation of poisonous toxin which disrupt cell function

For example Tetanus, Cholera.

Question 19

What is the general effector function

Answer 19

Clearance mechanisms mediated by interaction of Fc region with effector molecules

Question 20

Describe IgG

Answer 20

It is the most abundant
-Four genes/subclasses: G1-G4 which differ in the structure of the hinge region involving alterations in the disulphide bridges and differences throughout the constant regions.

Question 21

Describe IgG

Answer 21

It is the most abundant

• Four genes/subclasses: G1-G4 which differ in the structure of the hinge region involving alterations in the disulphide bridges and differences throughout the constant regions.
• It is the only Ig able to cross placenta via Fc receptors

Question 22

What is unique about IgG4?

Answer 22

They can undergo Fab arm exchange where the whole half of Ig can spit; no disulphide brige means one heavy chain and one light chain half can dissociate from the other half.

One half can bind with a different half (H and L chains) to make a new combinations; 2 different antigens can be recognised via the different halves variable domains.

Question 23

What are the terms used to describe the flexible movements of IgG molecule? Why is this important for the function?

Answer 23

• waves arms
• rotates Fab arms
• wags Fc tail
• bends Fab elbow (in the middle of arms)

They bind to adjacent antigens a various spacings and simultaneously Fc region engage with an effector molecule likr Fc receptor/complement.

Question 24

What are the terms used to describe the flexible movements of IgG molecule? Why is this important for the function?

Answer 24

• waves arms
• rotates Fab arms
• wags Fc tail
• bends Fab elbow (in the middle of arms)

They bind to adjacent antigens a various spacings and simultaneously Fc region engage with an effector molecule like Fc receptor/complement.

Question 25

Are antibodies long lived?

Answer 25

Yes, they have a long half life relative to other proteins. IgG1,2,4 can live up to 21 days

Question 26

Describe IgM

Answer 26

It is a pentamer; made of 5 subunits and therefoer 10 binding sites so it is good at binding/agglutinating to lots of antigen. They are joined by J chain and disulphide bridges. This is present only in secretions as it is too large to enter tissues

Question 27

Describe IgM

Answer 27

It is a pentamer; made of 5 subunits and therefore 10 binding sites so it is good at binding/agglutinating to lots of antigen. They are joined by J chain and disulphide bridges. This is present only in secretions as it is too large to enter tissues

Question 28

Which Igs begins the classical pathway of complement?

Answer 28

pentamer IgM binds to antigen on pathogen surface from a planar structure to a staple structure on antigen where C1q heads molecules fit with. monomer IgG also activates as at least 2 heads of C1q binds to 2 IgG molecules.

Question 29

What is Cyro-AFM?

Answer 29

A technique called atomic force microscopy where molecules are frozen and imaged.

Question 30

Describe Fc receptors.

Answer 30

There are receptors that bind IgG with gamma chains There are receptors that bind to IgE with beta chains.

Question 31

Describe FcRn

Answer 31

This binds IgG: it has 3 alpha domains and a B2 microglobulin

Question 32

Describe FcRn.

Answer 32

This binds IgG: it has 3 alpha domains and a B2 microglobulin. a1 and a2 domains form the binding site for Fc region of IgG.

Question 33

What are the functions/purpose of FcRn?

Answer 33

1) it maintains high levels of IgG in fluids 2) Selectiviely protects IgG from degradation 3) This means IgG have a longer half life 4) FcRn means IgG can cross placenta

Question 34

Describe Fc receptors.

Answer 34

There are receptors that bind IgG with gamma chains There are receptors that bind to IgE with beta chains. There are receptors that bind to IgA with alpha chains.

Question 35

What are the functions/purpose of FcRn?

Answer 35

1) it maintains high levels of IgG in fluids by transporting IgG from blood in low pH, through endothelial cells into extracellular space where there is high pH via endocytosis. 2) Selectiviely protects IgG from degradation; it is carried away from lysosomes in endocytic vesicles 3) This means IgG have a longer half life 4) FcRn means IgG can cross placenta

Question 36

Where doe FcRn interact with the IgG

Answer 36

The Fc interdomain region

Question 37

Describe Fc receptors.

Answer 37

There are receptors that bind IgG with gamma chains There are receptors that bind to IgE with beta chains. There are receptors that bind to IgA with alpha chains.

Question 38

What are the three classes of IgG receptors?

Answer 38

1) Fc-gamma-R1/CD64 with the highest affinity for IgG 2) Fc-gamma-R2/CD32 3) Fc-gamma-R3/CD16 They are transmembrane, with ITAM (activating) signalling motifs or ITIMs (inhibitory)

Question 39

What are the three classes of IgG receptors?

Answer 39

1) Fc-gamma-R1/CD64 with the highest affinity for IgG1 and IgG3 2) Fc-gamma-R2/CD32 3) Fc-gamma-R3/CD16 They are transmembrane, with ITAM (activating) signalling motifs or ITIMs (inhibitory) They bind to lower hinge region of Ch2 on constant heavy chain. Different IgG subclasses G1-G4 vary in the binding between each receptor type.

Question 40

What happens when Fc receptor binds to Ig

Answer 40

1) Increases efficiency of phagocytosis; coated bacterium allows activation signals that trigger engulfment ect. 2) The receptors can trigger ACC- antibody cell mediated cytotoxicity

Question 41

What is ACC- antibody cell mediated cytotoxicity ?

Answer 41

Fc receptors on NK cell recognise the Ab bound to target cells. This leads to cross-linking of Fc receptors trigger NK to kill target cell via apoptosis.

Question 42

Describe IgD

Answer 42

- Not present in high concentrations in blood; it is mainly found on B cell surface - produced in upper respiratory tract, where it can bind bacteria as well as a specific receptor on basophils which caused 1) release of cytokines 2) release of microbial factors to inhibit bacterial growth.

Question 43

What happens when Fc receptor binds to Ig

Answer 43

It mediate elimination of antibody coated targets 1) Increases efficiency of phagocytosis; coated bacterium allows activation signals that trigger engulfment ect. 2) The receptors can trigger ACC- antibody cell mediated cytotoxicity

Question 44

Describe IgD

Answer 44

- Not present in high concentrations in blood; it is mainly found on B cell surface - produced/protects in upper respiratory tract, where it can bind bacteria as well as a specific receptor on basophils which caused 1) release of cytokines 2) release of microbial factors to inhibit bacterial growth.