The Immune Response to Infection - A wrap up

Question 1

Describe the combination of cell mediated immunity and antibody production that provides us with immunity to pathogens

Answer 1

Adaptive immunity:
- Antigen presentation triggers an immune response which leads to cell mediated immunity and antibody-mediated immunity

Cell Mediated immunity:
- Phagocytes and T cell activated
- Direct physical and chemical attack: activated T cells find the pathogens and attack then through phagocytosis or the release of chemical toxins

Antibody-mediated immunity:
- Activated B cells give rise to cells that produce antibodies
- Attack by circulating antibodies

Question 2

Describe memory B cells and their formation

Answer 2

• Activated B ells divide and differentiate into plasma cells that secrete antibody, as well as forming a separate population of memory B cells.
• At the second encounter with antigen, Memory B cells are more numerous and are rapidly stimulated by antigen to become plasma cells
• Secondary immune responses are characterised by the predominance of class-switched antibodies; IgG, IgA and IgE

Question 3

What is clonal selection?

Answer 3

Clonal selection is the selective expansion of lymphocytes that interact with antigen.

• If a B cell that is specific for a native antigen is activated then it will undergo extensive cell division (also requires CD4 to help). A mass of antibody will also be produced in this process. The other B cells that aren’t activated will just keep existing as normal.
• Same thing happens with T cells. If a T cell that is specific for the peptide is activated, it undergoes extensive cell division.

Question 4

Describe the rearrangements of different parts of the B cells

Answer 4

• Antigen binding sites (light chains) are produced in the bone marrow. The genes there are rearranged for diversity between the B cells. It is a randomised system with random light chains and heavy chains grouped together.
• Isotope (class switching) occurs in the lymph nodes and spleen in the immune response. The entire constant region of the heavy chain can get switched to another one which will result in different functions (ie. if it is switched to IgE then it will now be able to activate mast cells). In this process the antigen binding sites stay the same.

This does not change antibody-specificity, but does change the function of the antibody.

Question 5

Primary vs secondary responses

Answer 5

Primary immune response to antigen A occurs after a delay.

Secondary immune response to antigen A is faster and larger; primary immune response to antigen B is similar to that for antigen A.

It is not a yes or a no as to specific antibodies being present, it is just that there are different amounts.

You form a whole lot more memory cells from the secondary immune response. This is how vaccines work, and is the reason for booster vaccines

Question 6

Describe what ‘Adjuvants’, which are usually required for sub-unit vaccines are

Answer 6

• Adjuvants are immune stimulants added the vaccines that enhance the activation of antigen presenting cells (APC)
• For example, the mRNA SARS-2 vaccine is intrinsically adjuvants: the lipid-encapsulated mRNA is immunostimulatory
• RNA can stimulate Toll-like receptors

Question 7

What are the four different vaccine types?

Answer 7

Live attenuated, Killed, Sub-unit protein, Sub-unit mRNA