Immunoglobulin

Question 1

IgG

Answer 1

Highest concentration in serum.
Four subclasses: IgG1 - 4
Complement activation (IgG3 > IgG1 > IgG2). IgG4 does not activate complement.
Binding to Fcg -receptors on neutrophils, macrophages and NK cells (opsonization)
IgG3 is the most susceptible due to increased hinge region

Question 2

IgM

Answer 2

Membrane-bound monomer and secreted pentamer.
First immunoglobulin to be synthesized during ontogeny and in the immune response.
Activates complement pathway; agglutination.
Can be transported into mucosal secretions.

Question 3

IgA

Answer 3

Secretory IgA is a dimer with a secretory component.
Two subclasses: IgA1 and IgA2
IgA1 predominates in serum as monomer
Major immunoglobulin in mucosal secretions (dimer)
Neutralization; Prevents binding of micro-organisms to receptors
IgA-proteases produced by Streptococcus pneumoniae, Haemophilus influenzae, Meningococcus meningitidis.
Not effective activator of complement

Question 4

IgE

Answer 4

Very low serum concentration in healthy individuals.
Concentration is higher in patients with helminth infections and often in patients with allergies.
Lacks hinge region; extra CH domain
Binds to Fce receptor on mast cells and basophils. Cross-linking results in degranulation and release of pro-inflammatory mediators.

Question 5

IgD

Answer 5

Very low concentration in serum
Present with IgM on naïve mature B cells
IgD-secreting plasma cells in upper respiratory tract

Question 6

Isotype switching: IFN-y

Answer 6

IgG2a, IgG3

also involved in Th1

Question 7

Isotype switching: TGF-B or IL-5

Answer 7

IgA, IgG2b

Question 8

Isotype switching: IL-4

Answer 8

IgE, IgG1

Question 9

Centrocytes exposed to IL-4 become…

Answer 9

memory B cells

Question 10

Centrocytes exposed to IL-10 become….

Answer 10

Plasma cells