Lecture 11: Immunoglobulin Structure and Function

Question 1

Recall the two forms of immunoglobulin.

Answer 1

Question 2

Recall the regions of an Ig molecule.

Answer 2

Question 3

Describe the features of the Ig structure.

Answer 3

• Consists of 2 heavy and light chains
  
  • light chains consist of 2 ‘Ig-domains’
  • Heavy chains have 4-5 ‘Ig-domains’ (depending on the class of antibody)
  • Note: chains are held together by disulphide bonds
• Chains have V and C regions
  
  • Variable - antigen binding
    
    • hypervariable
  • Constant - effector function
    
    • 1 to 5 forms (depends on isotype)
• Antigen-binding arms linked by a hinge; allow flexibility in binding to multiple antigens

Question 4

Recall the features of the ‘Ig-domain’ structure.

Answer 4

Question 5

Recall the concept of proteolysis of an Ig molecule and the enzymes responsible for it.

Answer 5

• Ig molecule can readily be cleaved into the functionally distinct fragments by specific enzymes
  
  • Papain releases individual Fab and Fc fragments
  • Pepsin separates both Fab regions from digested Fc region

Question 6

What are CDRs?

Answer 6

• Most of the variability between different immunoglobulins is within three regions of V_H and V_L
• These localised regions of hypervariable sequence form the antigen-binding site
  
  • Called hypervariable regions or Complementarity Determining Regions (CDRs) and are ~10 amino acids in length

Question 7

The most variability is found in which CDR?

Answer 7

in the CDR3 region

Question 8

Recall the variation of Ig in the aspect of their chains.

Answer 8

Question 9

Recall the isotypes of Ig.

Answer 9

Question 10

Recall the properties of IgG.

Answer 10

Question 11

Recall the properties of IgM.

Answer 11

Question 12

Distinguish between affinity and avidity.

Answer 12

• Affinity: The strength of binding of one molecule to another at a single site
• Avidity: Sum total of the strength of binding between two molecules or cells to one another (where multiple binding sites are involved)

Question 13

Recall the properties of IgA.

Answer 13

Question 14

Recall the properties of IgD.

Answer 14

Question 15

Recall the properties of IgE.

Answer 15

Question 16

Recall the distribution of the Ig isotypes.

Answer 16

Question 17

Recall the features of the constant regions of the Ig isotypes and how they might correlate with their respective function.

Answer 17

Question 18

Recall two mechanisms of antibody effector function and which part is involved.

Answer 18

Question 19

Recall the mechanism of neutralisation by an antibody. Is it a direct or indirect mechanism.

Answer 19

Question 20

Recall the mechanism of opsonisation by an antibody. Is it a direct or indirect mechanism?

Answer 20

Question 21

Recall the mechanism of ADCC by an antibody. Is it a direct or indirect mechanism?

Answer 21

Question 22

Recall the mechanism of degranulation by an antibody. Is it a direct or indirect mechanism?

Answer 22

Question 23

Recall the mechanism of complement activation by an antibody. Is it a direct or indirect mechanism?

Answer 23

Question 24

Recall the antibody effector functions.

Answer 24