Antibody structure

Question 1

5 components of immunoglobin molecule

Answer 1

1. Heavy chain
2. Light chain: either 2 lambda OR kappa
3. Constant regions: on light & heavy chains are same for each class/isotype
4. Variable regions: on identical antigen-binding sites (but vary per Ig molecule) of light & heavy chains
5. di-sulphide bonds: near hinge

Question 2

Which part of the immunoglobulin molecule is responsible for antigen recognition?

Answer 2

ends of Fab portion (the ends of the Y) that recognises a particular epitope on antigen

Question 3

Name two cell types that express immunoglobulin on their surface?

Answer 3

1. memory B cells

2. naive B cells

Question 4

five classes of human immunoglobulin?

Answer 4

1. IgM: 5x Ab star = 10 ab site (w/ Mu heavy chain)
2. IgA: monomer or dimer w/ alpha heavy chain
3. IgG: monomer w/ gamma heavy chain
4. IgE: monomer w/ eplipson heavy chain
5. IgD: monomer w/ delta heavy chain

Question 5

Which cell type is responsible for actively secreting immunoglobulin? Which of the human immunoglobulin isotypes in not produced by this cell?

Answer 5

a. Plasma cells
b. IgD not produced
- IgM produced w/out T cells
- IgA, G, E produced w/ help of T cells

Question 6

What must happen for a memory B cell to transform into a ________ cell and begin producing antibody? Which isotype of antibody will be produced if there is no T cell help?

Answer 6

a. B cell turns into plasma cell when exposed to particular antigen on 2º exposure
b. IgM produced w/out T cell (but short-lived)

Question 7

Which two human immunoglobulins have an extra fold domain in their heavy chains?

Answer 7

IgM & IgE

Question 8

*Which part of the immunoglobulin molecule is responsible for biological activity (once antigen has been bound to the Aby molecule)?

Answer 8

*

Question 9

Using diagrams, explain the fragments that are produced when an immunoglobulin molecule is treated with a) pepsin, b) papain and c) mercaptoethanol

Answer 9

a) \V/ = F(ab)2 = Fab fragments joined to each other
b) . \ + // + || = 2x Fab (separate) + Fc
c) 2x light chains + 2x heavy chains bc S-S in b/w chains are broken

Question 10

Which human immunoglobulin is the most prevalent in serum and which is able to cross the placenta?

Answer 10

IgG

Question 11

Which human immunoglobulin can best activate complement?

Answer 11

IgM

Question 12

Which human immunoglobulin (only one) can bind to the Fc receptors on PMN, Mϕ, NK cells?

Answer 12

IgG

Question 13

What is the main structural difference between the human subclasses of IgG?

Answer 13

vary due to no. of S-S bond in heavy chains

• IgG1: 2x
• IgG2: 4x
• IgG3: 11x
• IgG4: 2x

Question 14

During a humoral immune response, which immunoglobulin isotype is produced first? Which is produced second?

Answer 14

1. IgM (short lived, no memory & doesn’t require T helper cells)
2. IgG (long lived, memory & requires T helper cells)

Question 15

Affinity vs Avidity

Answer 15

• Affinity: strength of binding b/w one binding site & epitope
• Avidity: OVERALL strength of binding b/w Ag & Ab molecule

Question 16

3 types of epitopes on Ab molecules & describe

Answer 16

1. Isotypic: each Ig class has different epitopes on constant regions (CH & CL)
2. Allotypic: epitopes on CH & CL vary b/w individuals of same sp.
3. Idiotypic: antigen variation on variable regions (VH & VL)