Antibody Biology 1

Question 1

B cells originate and mature in the BLANK

Answer 1

B cells originate and mature in the BONE MARROW

Question 2

Adaptive immunity has humoral and cellular components

TRUE OR FALSE

Answer 2

TRUE

Question 3

B cells are responsible for the killing of cells

TRUE OR FALSE

Answer 3

FALSE

B cells are responsible for production of antibodies

Question 4

What happens to B cells upon activation by an antigen?

Answer 4

On activation with antigen:
B cells -> antibody-secreting cells (plasma cells)
-> memory B cells

Plasma cells secrete antibodies of the same specificity as the membrane-bound immunoglobulin expressed by their B cell precursor.

Question 5

Immunoglobulin (Ig) Structure:

Answer 5

All immunoglobulins are structurally similar.
Y-shaped
VL, CL, VH, CH, CH2, CH3 (N terminal at variable region)
Hinge domain (Flexible hinge of IgG allows both arms to bind to many arrangements of antigens on pathogen surfaces)
Heavy chains = 50kDa
Light chains = 25kDa
Fab = Fragment antigen binding: Responsible for binding antigen. Top “half” of structure (above hinge).
Fc = Fragment crystallisable: Responsible for effector function. Bottom “half” of structure (below hinge).
2 types of light chain: Lambda and Kappa. In any individual antibody, both light chains are the same type.
Heavy chain determines antibody class:
IgG: gamma
IgA: alpha
IgM: mu
IgE: epsilon
IgD: delta

Question 6

Immunoglobulin Fold:

Answer 6

Antibodies fold into globular domains with a distinctive 3D structure.
Each domain comprises 2 beta sheets with a total of 7 or 8 anti-parallel beta strands which are linked by a disulphide bridge to form a beta barrel.
Folded structure is known as the ‘immunoglobulin fold’

Question 7

Hypervariable regions:

Answer 7

• Variable domains in both light and heavy chains have hypervariable loops which vary extensively between different antibodies
• Hypervariable loops form the antigen binding site
• Hypervariable loops are more commonly termed the complementarity-determining regions (CDRs)
• CDRs form close-lying loops at one end of the Variable domain
• When VH and VL domains are paired their 6 CDRs create the antigen-binding site
• Antigen binding site has complementary 3D structure to that of antigenic epitope providing high specificity and high affinity

Question 8

Epitopes:

Answer 8

Epitopes in protein antigens:

• May comprise a single stretch of polypeptide chain (linear or continuous epitope)
• Or may depend on 3D folded structure (conformational or discontinuous epitope)

Antibody recognises structural ‘epitopes’ or ‘antigenic determinants’ on the antigen.
Epitopes can bind to pockets, grooves, extended surfaces or projections in antigen binding sites.
Epitopes for antibodies are exposed on pathogen surfaces.