🌞 B Cell Function and Antibodies

Question 1

What kind of antigens do B cell receptors recognise?

Answer 1

Intact, unprocessed ags (proteins, polysaccharides, lipids, nucleic acids)
→ can bind soluble or surface-bound ags directly w/out MHC

Question 2

What is the difference between linear and conformational epitopes?

Answer 2

Linear epitope → cont AA seq (recog in denatured or native form)
Conformational epitope → formed by 3D folding; non-contiguous AAs brought together (lost if protein denatured)

Question 3

What is the structure of an antibody?

Answer 3

• 2 Fab regions: Bind antigen
• 1 Fc region: Effector functions (e.g., complement)
• Fab: Hypervariable VH + VL, unique heavy + light chains
• Fc: Constant, 5 isotypes, CH2 + CH3 domains
• Key features: Flexible hinge, complement activation site on Fc

Question 4

What are the Fab and Fc regions?

Answer 4

• Fab region: Antigen-binding (VH + VL domains), binds antigen, one light & one heavy chain
• Fc region: Constant, determines isotype, mediates effector functions (complement, Fc receptor binding)

Question 5

How do antibodies neutralise pathogens?

Answer 5

• Block binding: Antibodies bind to pathogen, prevent host cell attachment.
• Toxin neutralization: Bind toxins, prevent interaction with cells.
• Opsonization: Antibodies mark pathogen for phagocytosis.
• Agglutination: Crosslink pathogens into clumps for easier clearance.
• Complement activation: IgM/IgG trigger complement → pathogen lysis.

Question 6

How do antibodies promote opsonisation?

Question 7

How do antibodies activate complement?

Question 8

How do antibodies mediate ADCC (antibody-dependent cellular cytotoxicity)?

Question 9

What are the five major antibody isotypes?

Question 10

What are the functions of IgM?

Question 11

What are the functions of IgG?

Question 12

What are the functions of IgA?

Question 13

What are the functions of IgE?

Question 14

What are the functions of IgD?

Question 15

What is isotype switching and when does it occur?

Question 16

What enzyme is required for class-switch recombination?

Question 17

How does antibody isotype determine effector function?

Question 18

What is the difference between the two forms of antibodies?

Answer 18

• Membrane-bound: On B cell surface, antigen recognition.
• Secreted: Released into blood, neutralize pathogens.