A11 Immunoglobulins: IgG and IgM + A12. Immunoglobulins: IgA, IgE and IgD

Question 1

IgG

Answer 1

65-80% of serum Ig-s 
Molecular weight (Mw): 160000 Da
Monomeric, 
Structure: bivalent γ heavy chain, y-shaped with 4 peptide chains (2 heavy and 2 light) and disulphide bridges, 
t1/2: 10-20 days 
Can cross the endothelium

Functions 
• Agglutination 
• Precipitation 
• Complement activation 
• Neutralisation 
• Opsonosation 
• Cytotoxic (CT) reactions 
• protection from bacteria and viruses

Question 2

IgM

Answer 2

5-15% of serum Ab-s 
Mw: 900000 Da
Structure: Pentameric, -S-S-, J chain, Light (γ) and heavy (μ) chains.  
t1/2: 5 days 
Normaly not cross endothelium

Functions
Primary immune response 
BCR (as monomer) 
Agglutination Neutralisation 
Complement activation CT rarely, through complement

Question 3

IgA

Answer 3

• Makes up 5-10% of serum Igs, on body surfaces, cell membrane.
• T1/2 = 7 days in serum and 2 days on surface.
• Dimeric, mostly monomer in blood.
• Structure: alpha heavy chain, J chain, secretory component.
• MW: 360,000Da.
• Function: Local immune response, agglutination and neutralisation of pathogens,
• tetravalent, very important in the immune function of mucous membranes.

Question 4

IgE

Answer 4

• Makes up ≤0.5% of serum Igs, on cell membrane.
• T1/2 = 1-2 days.
• Structure: 2 epsilon heavy chains, 2 light chains.
• MW = 200,000 Da
• Functions: Type 1 hypersensitivity (allergy), protozoal and parasite infections, bivalent.

Question 5

IgD

Answer 5

• Present on B cells
• Monomer, not stable.
• Structure: Delta heavy chain.
• MW: 180,000
• Function: B-cell receptor – signals B cells to become activated.

Question 6

Memory B-cells

Answer 6

Do not produce antibodies, but transform easily to plasma cells

Question 7

Immunoglobulin supergene family

Answer 7

= A large protein superfamily that are responsible for relations among cells of the immune system, recognition and specific antigen binding (globular structure, domains)
• B-cell receptor
• T-cell receptor • Antibody • MHC (Major Histocompatibility Complex) • Fc receptors • Hormone receptors • Differentiation markers (clusters), CD4, CD8 etc.) • Others • Sera of animals recovered from infection o In vitro destroy the microorganism o In vivo protect the animal (passive immunity)

Immunoglobulins can be characterised using Electrophoresis (Agarose Gel/SDS) which separates them on the basis of their size. Amino Acid structure, DNA sequencing, Xray crystallography and electron microscope can also be used.