L1 Antibody structure & function

Question 1

What is the primary function of an antibody?

Answer 1

Detect and neutralise foreign substances/invaders.

Question 2

Which three cells interact to imitate an antibody response?

Answer 2

Macrophages, T cells and B cells.

Question 3

Which cells are the APCs?

Answer 3

Macrophages, monocytes, langerhan cells, dendritic cells & B cells themselves are all antigen presenting cells.

Question 4

Briefly how are B cells activated?

Answer 4

B-cell binding with Ag induces signal to increase expression of MHC-II & B7.
Th cell recognises same antigen on MHC-II.
Th cell then expressed CD40-L & B7-CD28 interaction is co-stimulation. B cell beings to express cytokine receptors and binding of cytokines causes up regulation of DNA synthesis in B cell = proliferation.

Question 5

Immunoglobulins (antibodies) are expressed in two forms, what are they?

Answer 5

Secreted form = produced by plasma B-cells as antibodies.

Membrane bound = present on B-cell surface as antigen specific receptor.

Question 6

What four polypeptide chains come together to form an antibody?

Answer 6

2 Heavy chains & 2 Light chains.

Question 7

What three fragments of an antibody were discovered when mercaptoethanol (reducing agent) disrupted the disulphide bonds?

Answer 7

Fragment antigen binding region 2x (Fab region).

Fragment crystallisable (Fc, constant region).

Question 8

How many amino acids are found at tip of antigen binding site?

Answer 8

100-130

Question 9

In the constant domain of the antibody, which chain gives rise to the class?

Answer 9

The heavy chain

Question 10

What is the role of the hinge part of the antibody?

Answer 10

The Hinge connects the Fab and Fc regions of the antibody, via disulphide bonds.

Question 11

What are two classifications of light chain?

Answer 11

kappa or lambda (but not useful for class/subclass definition)

Question 12

Describe characteristics of IgG

Answer 12

Most common antibody, 80%. Major Ig in blood. Can cross placental barrier.
Standard 2H and 2L chains.
Key player in humour immune response, able activate complement, opsonise, activate phagocytes and neutralise toxins.

Question 13

Describe characteristics of IgA

Answer 13

Found as monomer in circulation but dimerises (active) at mucosal surfaces. Requires secretory component to dimerise and give resistance to enzymatic cleavage.
Good neutralising, provides defence at mucosal surfaces (saliva, tears, mucus, sweat, gastric fluid)

Question 14

Is IgA good at activating complement?

Answer 14

No, very weak, its involved in clearance, and preventing pathogens invading epithelial surfaces. Does not induce bacterial cell lysis via complement as this is very inflammatory. As its targets are not found ‘within’ body, no great need for large inflammatory response.

Question 15

Describe characteristics of IgM

Answer 15

IgM forms a pentamer via linking of J chains between 5 monomers.
Largest antibody and cannot enter tissues. Expressed on B cell surface as monomer as B cell antigen receptor.

Indicated primary response, good for removal of bacteria, good at activating complement and good for agglutination.

Question 16

Which antibody is first to be produced during immune response?

Answer 16

IgM, indicates primary response to antigen.

Question 17

Describe the chraracteristics of IgE?

Answer 17

Involved in hypersensitive reactions (allergies) Fc binds to mast cells and basophils causing release of amines (histamines).

Protects against parasites via releasing mediators that attract eosinophils.

Question 18

Describe IgD characteristics

Answer 18

The only known function is as the B-cell receptor. Found on naive B-cells. Once mature, replaced by other antibodies.
May play a protective role in severe infection.

Question 19

What part of the antibody dictates the effector functions, upon interaction with what receptor on which groups of cells?

Answer 19

Fc region interaction with cognate 
Fc receptors (FcR) which are found on macrophage/neutrophil/monocytes
/mastcells/basophils/etc

Class of antibody dictates its effect via binding to target specific cells, e.g. IgE binding to FcR’s specific only to mast cells/basophils

Question 20

Protein A and G are important in antibody technology for what reasons?

Answer 20

Important in binding IgG in beads. Able to pull antibodies out of a mixture as they bind to the Fc region.

Question 21

What is the difference between polyclonal and monoclonal antibodies?

Answer 21

Polyclonal antibodies are a pool of antibodies that recognise multiple epitopes (usually on one antigen).
Monoclonal antibodies are a pool that only recognise one specific epitope.

Question 22

Which three genes are rearranged during gene rearrangement of antibody?

Answer 22

Variable (V) diversity (D) and joining (J). Form the blueprint for the variable region of the antibody.

Question 23

What is isotope class switching?

Answer 23

The switching of the class of an antibody (e.g. IgM-IgG)

Question 24

What is the paratope?

Answer 24

Binding site on the antibody.

Question 25

What is the epitope?

Answer 25

Binding site on the antigen.

Question 26

What are the hyper variable region?

Answer 26

The HVR are regions of aa’s 10 in length. There are three of them on each chain (6 per binding site) complenentarity-determining regions (CDR) CDR1, CDR2 and CDR3.
They line the antibody binding site and make up the paratope. ~15% of variable region involved in binding. 4/6 minimum involved in binding.

Question 27

Which chains CDR’s make more contact with epitope?

Answer 27

Heavy chain CDRs make more contact than those on light chain (HDCR3 always involved)

Question 28

What four foreign substances can bind to the Fab region?

Answer 28

Protein, Carbohydrate, Nucleic Acid, Peptide.

Question 29

Is paratope-epitope binding covalent?

Answer 29

Binding is non-covalent, meaning that it is reversible and means antibodies can be used to extract and purify their targets from solutions. Basis for antibody technology.

Question 30

What bonds are involved in antibody-antigen binding?

Answer 30

Hydrophobic bonds drive molecules together.

Direct contact ionic bonds, hydrogen bonds and Van der Waals forces.