Immunology 4

Question 1

Functions of different Ig classes - what are they and what are they determined by?

Answer 1

• Neutralization
• Opsonization
• Activation of Complement
• Intracellularly, targeting of virus to proteosome via TRIM21

Question 2

Different Ig classes?

Answer 2

There are 5 different classes determined by heavy chain,

• IgM (μ),
• IgD (δ),
• IgG (γ),
• IgE (ε),
• IgA (α).

Question 3

IgM

Answer 3

IgM.
First produced = prior to class switch.
Secreted form is a pentamer, increases avidity.
It is present in the blood stream but not in tissues.
Effective in rapid control of infections in bloodstream.
Strong activator of the classical pathway of complement.
Structure, 3 C domains but no hinge.
Has some functions with neutralisation and opsonisation.

Question 4

IgD

Answer 4

Co-expressed with IgM on B cells

Question 5

Feature of IgG, IgE and IgA?

Answer 5

IgG, IgE and IgA can diffuse more readily from blood into tissues.

Question 6

IgG

Answer 6

principal antibody in the blood
Different forms/subclasses found in the blood stream and tissues-
involved in neutralisation, opsonisation, binds to phagocyte FcRs to trigger engulfment, sensitisation for killing by NK cells and activation of compliment system

Question 7

IgE

Answer 7

IgE defence against multicellular parasites,
functions in allergy.
Binds mast cells which can induce pathogen expulsion by coughing, sneezing, vomiting.

Question 8

IgA

Answer 8

Principal antibody in secretions
Secreted at mucosal surfaces, in gut and respiratory tract.  
Major function as neutralising antibody.
Secreted in breastmilk
Monomeric or dimeric.

Question 9

IgG and maternal protection?

Answer 9

IgGs can cross placental barrier via binding to neonatal FcR (FcRn) and give passive maternal derived protection to newborns.
Possibly can cross epithelial layer in gut to be taken up from breast milk.