Types of Antibodies

Question 2

IgG – The Versatile Defender

Answer 2

Monomeric, most abundant in serum & body fluids

Longest half-life (21–30 days)

Main antibody in secondary immune response

Opsonization: Enhances phagocytosis (binds Fcγ receptors on phagocytes)

Activates complement (IgG1 & IgG3 strongest activators)

Crosses placenta to protect newborn

Question 3

IgA – The Mucosal Shield

Answer 3

Secreted at mucosal surfaces (respiratory, GI, urogenital tracts)

Major antibody in secretions (milk, saliva, tears)

Exists in 2 forms:

Serum IgA = Monomer (80% of IgA)

Secretory IgA (sIgA) = Dimer (joined by J chain)

Prevents microbial attachment to mucosal surfaces

Reduces uptake of bacterial toxins

Question 4

IgE – The Allergy Trigger & Parasite Fighter

Answer 4

Binds to Fc receptors on mast cells & basophils

Mediates allergic reactions (triggers histamine release → anaphylaxis)

Main antibody against parasites (helminths)

Found in very low levels in serum (<0.05%) but very potent

Question 5

IgD – The Mysterious One

Answer 5

Monomeric

Found on naïve B cells (before antigen exposure)

Low serum levels (~0.2%)

Exact immune function not well understood