Antibody structure And Function

Question 1

B cell receptor structure

Answer 1

Memrane-bound immunoglobulin molecules with short cytoplasmic tails unable to interact with intracellular signal molecules.

Question 2

Antigen-binding region of the B cell receptor

Answer 2

mIg and the disulfide-liked Ig-α/Ig-β heterodimer, cytoplasmic tails of these regions can interact with signalling molecules such as tyrosine kinases.

Question 3

Immunoglobulin (antibody) is held together by what bonds

Answer 3

2 heavy, 2 light chains, held together by disulfide bonds and noncovalent interactions

Question 4

What are the classes of the immunoglobulin heavy chains

Answer 4

α, δ, ε, γ, μ

Question 5

What are the 2 classes of the immunoglobulin light chains

Answer 5

κ and λ

Question 6

What are globular domains?

Answer 6

Structures formed by about 110 amino acids held together by intrachain disulfide bonds

Question 7

What can affect antibody stability and its interactions

Answer 7

Glycosylation

Question 8

What does the light chain consist of?

Answer 8

1 variable, 1 constant domain

Question 9

What does the heavy chain consist of?

Answer 9

1 variable and 3 or 4 constant domains (denoted 1-4)

Question 10

What determines antigen binding?

Answer 10

Three hypervariable regions within the V region that have great amino acid sequence variability, the amino terminal of the heavy and light chains.

Question 11

What is the hinge region and how is it formed

Answer 11

Proline-rich amino acid sequences between the CH1 and CH2 domains, held together by a variable number of disulfide bonds (variable length and flexibility), found in IgA, IgD, IgG.

Question 12

Which antibodies have no hinge, what do they have instead?

Answer 12

IgM and IgE - they have a CH2 domain with hinge-region-like properties.

Question 13

What is the function of the constant regions

Answer 13

Carboxyl-terminal portion mediates biological effector function.

Question 14

Differences in the heavy chain determine

Answer 14

Anti-body half-life, distribution, complement-fixing ability, and Fc receptor binding.

Question 15

Carboxyl terminal in membrane bound and secreted immunoglobulins is:

Answer 15

Different in both structure and function.

Question 16

Ig Fab

Answer 16

The heavy and light chains that constitute the antigen binding arms, consisting of both variable and constant chains

Question 17

Ig Fc

Answer 17

The heavy chains that constitute the base of antibody that binds the cell when membrane bound, cytoplasmic tails, constant only.

Question 18

3 methods of IgG proteolysis

Answer 18

1. Papain digestion
2. Pepsin digestion
3. Mercaptoethanol reduction

Question 19

Papain mediated IgG digestion

Answer 19

2 identical Fab fragments (antigen binding) and 1 Fc fragment (crystalisable(

Question 20

Pesin mediated IgG digestion

Answer 20

Divalent F(ab’)2 fragment (above the hinge region, held together) and a pFc’ fragment

Question 21

Mercaptoethanol reduction of IgG

Answer 21

Yields 4 pieces, 2 heavy chains and 2 light chains by breaking the disulfide bonds by hydrogen reduction.

Question 22

Immunoglobulin epitopes

Answer 22

The portion of the antigen that the immunoglobulin binds to, antibodies also produce an immunogenic response when injected into other species as they contain their own epitopes.

Question 23

Isotypic epitopes

Answer 23

Epitopes present in the constant regions of the Ig that define heavy chain class/subclass and light chain types/subtypes within a species, ie - mouse IgM vs mouse IgE.

Question 24

Allotypic epitopes

Answer 24

Located in the constant regions, may vary from individual, ie - mouse IgG1 vs mouse IgG2.

Question 25

Idiotypic epitopes

Answer 25

Epitopes located within the heavy and light chain variable regions are are defined by the unique amino acid sequence that determine specificity, against different antigens, ie - mouse IgG1 against a, mouse IgG1 against b

Question 26

Antibody opsonisation

Answer 26

Interaction of antibodies with Fc receptors on phagocytes promotes phagocytosis

Question 27

Complementation via antibodies

Answer 27

Anti-body mediated activation of the complement is responsible for the inactivation/removal/killing of pathogens

Question 28

Antibody-dependent cell-mediated cytotoxicity (ADCC)

Answer 28

Antibody (IgG) acts as a receptor to enable the recognition and killing of target cells by NK cells with Fc receptors CD16

Question 29

Transcytosis

Answer 29

Passage antibodies across epithelial layers delivers certain classes of antibody (primarily IgA) to mucosal surfaces

Question 30

Induction of mast cell degranulation by antibodies

Answer 30

This function is initiated by Fc receptors for IgE.

Question 31

Five immunoglobulin effector functions

Answer 31

Opsonisation Complement activation Antibody-dependent cell-mediated cytotoxicity Transcytosis Induction of mast cell degranulation

Question 32

IgG structure

Answer 32

2 identical 50 kDa γ chains and 2 identical 25 kDa κ or λ chains. 4 subclasses with unique biological properties.

Question 33

Abundance of immmunoglobulins from highest to lowest

Answer 33

IgG, IgA, IgM, IgD, IgE IgG - 1, 3, 2, 4 IgA - 1, 2

Question 34

IgG function

Answer 34

Neutralises toxins/viruses, opsonises microbes, activates classical complement pathway, mediated ADCC reactions, and crosses the placenta during pregnancy.

Question 35

Four subclasses of IgG

Answer 35

IgG1 - 2 DB - complement activation and response to proteins IgG2 - 4 DB - response to carbohydrates IgG3 - 11 DB - complement activation and response to proteins IgG4 - 2 DB - responds to allergens IgG3 has the shortest halflife at 7 days as it has the longest hinge region, lowest proportion as it is so labile.

Question 36

IgM structure

Answer 36

Monomer - 2 μ chains and 2 κ or λ chains, found on the surface of B cells. Secreted as a pentamer by plasma cells, containing a J chain, (only 5 out of 10 antigen-binding sites are able to interact with large antigens)

Question 37

IgM function

Answer 37

First antibody made by newborns and in a primary immune response. Agglutination of particulate antigens, activation of the classical complement, transcytosis.

Question 38

IgA structure

Answer 38

Present as a monomer in serum, 2 α chains and 2 κ or λ chains. Forms a dimer, mucosal secretions, contains a J chain and a secretory component.

Question 39

Process of IgA dimerisation

Answer 39

Dimeric form occurs in plasma cells by J chain addition, then the secretory component is added as the IgA passes through glandular epithelial cells.

Question 40

Function of the IgA secretory component

Answer 40

Protects the secreted IgA molecule from proteolysis

Question 41

Function of IgA

Answer 41

Defends mucosal surfaces from microbial attack by inhibiting pathogen adherence, complexes with antigen to trap them in the mucus and be eliminated by mechanical action.

Question 42

IgE structure

Answer 42

Exists as a monomer of 2 ε and 2 κ or λ chains.

Question 43

IgE function

Answer 43

Sensitisation of mast cells - binds high affinity Fcε receptors on mast cells and basophils, crosslinking causes mast cell degranulation - acute inflammation and an atopic (type 1) allergic reaction, host defence against certain species of parasitic worms.

Question 44

IgD structure

Answer 44

Monomer consisting of 2 δ and 2 κ or λ chains.

Question 45

IgD function

Answer 45

Sensitisation of basophils - Most found on B cell surface, mucosal Ig present in the airways, saliva, and tear fluid. Initiates basophil and mast cell degranulation.

Question 46

Immunoglobulin superfamily

Answer 46

Many molecules in the immune system have the Ig fold domain structure - they are members of the immunoglobulin superfamily. This family of genes is thought to have originated through mutation and duplication from a single primordial gene encoding a polypeptide containing 110 amino acids.

Question 47

Monoclonal antibodies

Answer 47

Derived from a single B cell clone, specific for a single epitope.

Question 48

Polyclonal antibodies

Answer 48

Produced by many different B cell clones and binding many different epitopes.

Question 49

Monoclonal antibodies as treatment for disease

Answer 49

Muromonab - targets CD3 and treats organ transplant rejection Rituximab - targets CD20 and treats B-cell non-hodgkins lymphoma Adalimumab - targets TNF and treats rheumatoid arthritis.

Question 50

How are monoclonal antibodies produced

Answer 50

Mouse B cells immunised to an antigen are fused with transformed myeloma cells. These new cells are then grown in a drug containing media such that only the hybrid cells will live. These new cells are hybridomas and the antigen-specific cell can be cloned to produce that one antigen at greater rates…