Immunoglobin Structure

Question 1

Is the immunoglobin isotype (class) determined by the heavy chain or the light chain?

Answer 1

Heavy chain

Question 2

Differentiate the functionality of the constant region from the functionality of the variable region

Answer 2

Constant Region (Fc): important for biological activity
Variable region (Fab): important for antigen binding

Question 3

How are the different parts of the antibody held together?

Answer 3

Disulfide bonds

Question 4

What are the two alleles from which the light chains are derived? What it the ratio between the two in a normal individual?

Answer 4

Kappa and lambda in a ratio of 3:1

Question 5

What are the hypervariable regions of an antibody?

Answer 5

The hypervariable regions are the regions within the variable region of both the light and heavy chain responsible for the specificity of the antibody binding (the residues directly responsible for Ag binding- located in the loops)

They are called CDRs, or complementarity determining regions

Question 6

Describe the polymeric structure of IgM in the blood.

Answer 6

IgM is a pentamer in the blood (connected with a J-chain)

Question 7

How many epitopes can an IgM polymer bind?

Answer 7

10- (2x5)

Question 8

What is the structure of IgA in the blood?

Answer 8

Dimer

Question 9

What is the concentration of IgD in the blood?

Answer 9

Almost zero- IgD is primarily bound to the surface of B-cells

Question 10

Which Ig is found in the highest levels in the blood?

Answer 10

IgG1

Question 11

Which Ig is responsible for allergies?

Answer 11

IgE

Cross-linking of IgE on mast cells leads to degranulation, release of histamine and other substances that mediate allergic reactions

Question 12

What is the first Ig made in response to an infection?

Answer 12

IgM

Question 13

Following IgM, which is the next antibody found in the blood following an infection?

Answer 13

IgG

Question 14

What are three ways by which antibodies mediate humoral immunity/

Answer 14

1) Neutralization
2) Opsonization (promotes phagocytosis)
3) Compliment activation (enhances opsonization)

Question 15

What is Fc receptor-mediated killing?

Answer 15

Fc receptors on the surface of certain cells (B-cells, follicular dendritic cells, natural killer cells, macrophages, neutrophils, …etc etc) bind to the Fc region of antibodies bound infected cells or extracellular pathogens. This activates the immune to kill the pathogen or infected cell by phagocytosis or antibody-dependent cell-mediated cytotoxicity.

Question 16

Will an effector cell be activated through binding of just one Fc-receptor an antibody?

Answer 16

No- activation through Fc-receptors requires aggregated Ig.

Cross-linking required!

Question 17

How long does maternal IgG protect a newborn?

Answer 17

Fully for 3 months, with transient low levels of IgG for up to 1 year

Question 18

Describe the half-life of serum antibody titers of someone who received a tetanus shot and someone who had measles as a child

Answer 18

Tetanus: half life is 11 years
Measles: Essentially forever

Question 19

What is IVIG?

Answer 19

A polyclonal antibody used to treat many immune deficiencies and autoimmune diseases

Question 20

Describe the use of tumor-specific monoclonal antibodies for the treatment of cancer

Answer 20

1) identify a tumor-specific antibody
2) Clone the antibody and clone it
3) Inject the antibody into someone with that tumor, and allow it to bind and activate effector cells to launch an immune response against tumor cells