Adaptive Immune Recognition

Question 1

What are the key adaptive immune cells?

Answer 1

B and T lymphocytes.

Question 2

List 2 functional differences between B and T lymphocytes.

Answer 2

1 - B lymphocytes are responsible for the humoral response via antibodies, whereas T lymphocytes are responsible for the cellular response.

2 - B cell receptors are able to be secreted by the cell, whereas T cell receptors are not able to escape the cell surface.

Question 3

What is a B cell receptor?

How does it differ from a T cell receptor?

Answer 3

• A B cell receptor is a surface immunoglobulin (antibody) that has not been secreted.
• A T cell receptor is similar in structure, however consists only of one alpha chain (analogous to a light chain) and one beta chain (analogous to a heavy chain).

Question 4

Which gene segments are contained within light chains only?

Answer 4

Only variable (V) and joining (J) - not diversity (D), which is only present in heavy chains.

Question 5

Which chains of a T cell receptor rearrange first?

Which gene segments rearrange during the formation of T cell receptors?

Answer 5

Beta chains rearrange first (like heavy chains in B cell receptors).

• Variable (V), diversity (D) and joining (J) chains all rearrange.

Question 6

Describe the roles of 2 enzymes involved in gene rearrangement.

Answer 6

• Rearrangement is coordinated by RAG (an enzyme which is able to excise and repair DNA).
• Further diversity is created by TdT (an enzyme which produces point mutations).

Question 7

How is the way in which B cell receptors recognise antigens different to the way in which T cell receptors recognise antigens?

Answer 7

• B cell receptors can recognise whole antigens through surface patterns.
• T cell receptors can only recognise short amino acid sequences, and antigens must be processed by antigen presenting cells using the major histocompatibility complex (MHC).

Question 8

What is the human leukocyte antigen (HLA)?

Answer 8

A gene complex encoding the major histocompatibility complex.

Question 9

What is the functional difference between MHC Class I and II proteins?

Answer 9

• MHC class I proteins mainly present peptides derived from proteins within the cell. This is a way of dealing with pathogens that have already invaded the cell.
• MHC class II proteins mainly present peptides derived from extracellular pathogens.

Question 10

Which T cells bind to MHC class I proteins (via T cell receptors)?

Answer 10

CD8 (cytotoxic) T cells.

Question 11

Which T cells bind to MHC class II proteins (via T cell receptors)?

Answer 11

CD4 (helper) T cells.

Question 12

To which domain of the MHC class I proteins do T cells bind?

Answer 12

The alpha 3 domain.

Question 13

To which domain of the MHC class II proteins do T cells bind?

Answer 13

The beta 2 domain.

Question 14

List 2 responses of T cells binding to MHC class I proteins via T cell receptors.

Answer 14

1 - Proliferation.

2 - Lysis of the target cell (the cell expressing the MHC).

Question 15

List 2 responses of T cells binding to MHC class II proteins via T cell receptors

Answer 15

1 - Proliferation.

2 - Secretion of cytokines by the CD4 cell.

Question 16

What is the function of costimulatory molecules?

Why is this function important?

Answer 16

• To enhance or inhibit the MHC binding response of the T cell receptor.
• This function is important for determining tolerance.

Question 17

List 6 cells that express MHC proteins.

Answer 17

1 - Langerhans cells

2 - B cells.

3 - T cells

4 - Macrophages

5 - Thymic epithelial cells.

6 - Neutrophils.

Question 18

What type of inheritance pattern is shown by MHC genes?

Answer 18

Codominance.

Question 19

Why is it important that MHC proteins are polymorphic?

Answer 19

Because MHCs must bind to a wide range of peptides.

Question 20

What is the risk / benefit associated with the HLA-B8 gene (a human leukocyte antigen gene)?

Answer 20

It is associated with more rapid progression of HIV.

Question 21

What is the risk / benefit associated with the HLA-B53 gene (a human leukocyte antigen gene)?

Answer 21

It is associated with a reduced risk of malaria.

Question 22

What is the risk / benefit associated with the HLA-DR2 gene (a human leukocyte antigen gene)?

Answer 22

It is associated with increased risk of leprosy.

Question 23

What is the risk / benefit associated with the HLA-B27 gene (a human leukocyte antigen gene)?

Answer 23

It is associated with ankylosing spondylitis (an autoimmune condition).

Question 24

What is the risk / benefit associated with the HLA-DR4 gene (a human leukocyte antigen gene)?

Answer 24

It is associated with rheumatoid arthritis (an autoimmune condition).

Question 25

What is the risk / benefit associated with the HLA-B57:01 gene (a human leukocyte antigen gene)?

Answer 25

it is associated with abacavir (an antiretroviral drug) hypersensitivity.