Immunology

Question 1

What is the immune system and what is the immune response?

Answer 1

The immune system is a network of cells, tissues and organs that function to defend the body against pathogens. The immune response is a coordination reaction of the immune system against a trigger.

Question 2

What are the stages of an immune response?

Answer 2

• Adherence of pathogen (innate immunity)
• Penetrance of epithelium (innate immunity)
• Local infection of tissues (innate immunity)
• Lymphatic spread (adaptive immunity)
• Adaptive immunity

Question 3

What are the different isotypes of the Fc (heavy chain) region of an antibody? Why is the Fc region important?

Answer 3

IgA, IgE, IgM, IgG and IgD

• The effector function of the antibody is largely derived from the constant region
• Interacts with other components such as complement

Question 4

What is the Fab region?

Answer 4

Antigen binding, hypervariable - our antibody repertoire can bind an infinite array of antigens

Question 5

How does antibody diversity come about?

Answer 5

• Gene recombination of the B cell receptor
• V, D and J segments of the heavy chain
• V and J segment of the light chain
• Only one of the V, D and J heavy chain genes and one of the V and J light chain genes are selected
• Deletion and insertions of nucleotides boosts number of antibodies

Question 6

What is IgM?

Answer 6

• Expressed on naïve B cells
• Secreted form is a pentamer
• Linked by the J chain (not J gene segment)
• Very efficient at activating complement
  * Pore forming protein complex that lyses bacteria and mammalian cells
• First antibody that you find
• 10 different binding sites - weak affinity

Question 7

What is IgG?

Answer 7

• Major immunoglobulin class in serum
• Major class in secondary response
• Binds receptors (Fc receptors) expressed by monocytes, macrophages and NK cells
• Can activate complement
Can cross the placenta

Question 8

What is IgE?

Answer 8

• Important in responses to parasites
• Can cause allergic reactions
Mast cells and basophils -> involved in the allergic response

Question 9

What is IgA?

Answer 9

• Expressed on the cell surface as a monomer
• Secreted form is a dimer = held together by a J chain that binds to the secretory component
Secreted IgA is prominent in mucosal secretions = airways, gut, breast milk

Question 10

What is IgD?

Answer 10

IgD
• Expressed on naïve B cells (coexpressed with IgM)
• Similar to IgG but cannot cross placenta
Does not activate complement

Question 11

What are the two events that a B cell undergoes?

Answer 11

1. Isotype (class) switching -> switching out constant regions to change antibody type
2. Affinity maturations -> point mutations which allow for a tighter fit of the antigen

Isotype switching, affinity maturation -> memory cells, plasma cells