B cells

Question 1

Innate immune system (3)

Answer 1

• Rapid response
• Non-specific (generic anti-bacterial or anti-viral mechanisms)
• Most often fails to completely eliminate the infection.

Question 2

Adaptive immune system

Answer 2

Delayed response
•	Highly specific
•	Usually eliminates infection
•	Rapid response to a repeated infection
•	Gives long term immunity
•	Memory
o	Long term immunity, but specific to that particular pathogen

Question 3

Types of immunity (3)

Answer 3

1) Humoral immunity – Mediated by B-lymphocytes.
2) Cellular immunity – Mediated by CD8+ cytotoxic T-lymphocytes.
Both branches regulated by CD4+ helper T-lymphocytes (T-helper cells).

Question 4

What is an antibody? (8)

Answer 4

Glycoprotein - carb added in GA.
Immunoglobin (Ig).
Tetrameric.
2 light/heavy chains.
Light chain two forms lambda/kappa , never both - "light-chain restriction".
Variable regions - varies per antigen.
Constant region - effector functions/ binds to phagocytes.
Flexible hinge region.
S-S / Non-covalent bonds.

Question 5

Fab and Fc Antibody fragments (3)

Answer 5

• Ig treated briefly with protease. Cuts molecule with nuclease at hinge region.
• Fc fragment has an effector function- activate complement, bind to Fc receptors on phagocytes.
• Fab: fragment antigen binding.

Question 6

How does antibody fight infection? (3)

Answer 6

1) By coating and neutralising a pathogen
e.g. if a virus is coated with Ab it cannot bind to its receptors on the cell surface.
2) By activating complement
Which can then blow holes in a bacterial cell membrane.
3) By opsonisation
Phagocytes have Fc receptors on their cell membrane.
Bind to pathogens coated with Ab and phagocytose them.

Question 7

How does an Ab bind to antigen? (4)

Answer 7

Non-covalent interactions.
Body CAN NOT DESIGN SPECIFIC antibodies to antigens.
Specific binding site is called EPITOPE.
Once specific Ab found. body undergoes clonal selection with B cells (which make Ab).

Question 8

B - cell activation (4)

Answer 8

ON FC

Question 9

Classes (isotypes) of Ig (3)

Answer 9

Classes (isotypes) of Ig:
• The body can make different classes of Ig.
• IgG, IgM, IgA, IgD, IgE
• Differ slightly in heavy chain constant region amino acid sequence and have different functions.

Question 10

IgM (4)

Answer 10

First class of Igs made by b cells during primary response.
Activates signal transduction/complements.
Acts as an opsonin.
Single Ig tertramer bind to 4 other to make a pentamer,

Question 11

IgG (4)

Answer 11

• Main circulating Ig.
• Very good at activating complement system.
• Good as an opsonin.
• Formed of a single Ig tetramer.

Question 12

IgA (4,4,2)

Answer 12

• Most abundant class in external secretions.
• Main secreted Ig.
o Milk, sweat, tears, gut secretions
o Protects mucosal surfaces
o Does not activate complement
o Does bind Fc receptors triggering
 Phagocytosis
 Inflammatory reactions
• In serum, occurs as a single Ig molecule.
• In secretions, most IgA is present as a dimer of two whole Ig molecules (+ accessory proteins).

Question 13

IgE (5)

Answer 13

• Involved in anti-parasite response and in allergy.
• Physiological role in protection against parasitic worms.
o Binds to Fc receptors on mast cells and basophils.
o Triggers release of histamine, this causes symptoms of allergies.
o Over response can cause anaphylactic shock.

Question 14

IgD (3)

Answer 14

• Extremely low concentration in circulation.
• Also found on B-cell membrane.
• Role is unknown.