A12 Immunoglobulins: IgA, IgE and IgD

Question 1

IgG

Answer 1

65-80% of serum Ig-s Molecular weight (Mw): 160000 Monomeric, bivalent γ heavy chain, subclasses Serum 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 Pentameric, -S-S-, J chain (Mw 15000) μ heavy chain Pentavalent Serum 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

5-10 % of serum Igs, on body surfaces! Mw: 360000 Dimeric (trimer, tetramer), mostly monomer in blood α heavy chain, J chain, secretory component t1/2 in serum: 7 days, on surfaces: 2 days Tetravalent

-Functions
Local immune response
Agglutination, neutralisation

Question 4

IgE

Answer 4

<0.05% of serum Igs Mw: 200000 ε heavy chain t1/2: 1-2 days Bivalent
Functions
• Type I. hypersensitivity (anaphylaxis, allergy)
• Protozoa, parasite infections

Question 5

IgD

Answer 5

BCR, unstable Monomer, bivalent Mw: 180000 δ heavy chain t1/2: 3 days Always on cell membranes