Cell mediated immunity

Question 1

… changes from one t-cell to the next and it recognises the antigen

Answer 1

Variable region

Question 2

What is the function of transmembrane tails of T-cell recpetors?

Answer 2

Where signals are generated once an antigen is bound in the variable region
T-cell turns on and is activated

Question 3

What are the two forms of T-cell receptors?

Answer 3

α/β (95%) heterodimers

γ/δ (5%) heterodimers

Question 4

What are the two types of α/β heterodimers?

Answer 4

Classic MHC I

Or MHC II restricted

Question 5

How is diversity related to disease?

Answer 5

An absence of diversity increases susceptibility of disease

Question 6

How does diversity occur in a developing lymphocyte?

Answer 6

By somatic DNA recombination of different gene segments of the variable region

Question 7

Compare the structures of a B-cell receptor and an antibody

Answer 7

• Both have variable and constant regions
• Both have a light chain and a heavy chain
• Both have an antigen binding site
• B-cell receptors have a transmembrane domain

Question 8

What is the thymus responsible for?

Answer 8

T-cell selection

Question 9

What are the 2 questions immature T-cells are asked on arrival at the thymus?

Answer 9

• Can you see MHC? (can the T-cell recognise the complex in which antigen is normally presented)
• Can you see self-proteins?

Question 10

What occurs if immature T-lymphocytes can’t answer the two questions?

Answer 10

Cell death

Question 11

What does MHC stand for?

Answer 11

Major histocompatibility complex

Question 12

What is the role of MHC?

Answer 12

It is a complex glycoprotein and is the final step in antigen presentation.
It sits on the surface of mammalian host cells and it has antigens bound to it, this enables it to engage with T or B cells.
Processed antigenic protein is presented to the T cell as a peptide in the groove of the MHC molecule

Question 13

Explain class I and II MHC

Answer 13

• MHC can be divided into MHC class I or class II
• Some t-cells will only recognise class I and some class II
• Thus the T cell is MHC class I or II restricted, depending on the presenting molecule

Question 14

Describe class I and II MHC expression patterns

Answer 14

Class I = expressed on all nucleated cells in the body except RBCs, platelets and nerve cells
Class II = Expressed only on the surface of professional antigen presenting cells

Question 15

What are the 4 antigen presenting cells?

Answer 15

• Dendritic cells
• Macrophages
• B-cells
• Basophils
• Express MHC class II on their surface

Question 16

What is the function of MHC class I and II?

Answer 16

To transport peptides of intracellular proteins to the cell surface

Question 17

How is the expressed MHC protein different/recognised if the cell is normal and abnormal?

Answer 17

Normal: ‘self’ peptides are expressed on the cell surface within the groove of the MHC molecule. Circulating T-cells do not respond to the normal ‘self’ peptides
Abnormal: The peptides which are expressed alter, these are recognised by T-cells

Question 18

Why do CD4 and CD8 molecules bind to MHC molecules?

Answer 18

• Bind at sites distal to the peptide cleft
• This stabilizes the APC/lymphocyte interaction
• Reinforcing MHC restriction

Question 19

What are the routes of antigen entry into cells?

Answer 19

• Phagocytosis
• Endocytosis
• Direct entry into the cytosol

Question 20

What type of antigen processing occurs for the MHC class 1 pathway and the MHC class 2 pathway?

Answer 20

MHC class I = Endogenous
MHC class II = Exogenous

Question 21

Describe endogenous antigen processing

Answer 21

• Intracellular pathogens (viruses)
• Proteins are processed via the cytosol & proteasome
• Resultant peptides are presented by MHC class I molecules on the surface of the APC
• Recognised by T cell receptor of CD8+ T cytotoxic lymphocytes
• Cytokines are secreted

Question 22

Describe exogenous antigen presenting

Answer 22

• Extracellular pathogens
• Proteins are processed via the endocytic pathway
• Resultant peptides are presented by MHC class II molecules on surface of APC
• Recognised by T cell receptor of CD4+ T helper lymphocytes
• Cytokines are secreted

Question 23

To which cells do MHC class I and II present antigens to?

Answer 23

MHC class I - CD8 T-cells
MHC class II - CD4 T-cells

Question 24

What is a germinal centre called in the spleen?

Answer 24

A follicular aggregation

Question 25

CD8 T-cells produce what response?

Answer 25

A cytotoxic response

Question 26

What is the role of CD4 T-cells in the immune response?

Answer 26

Become T-helper cells and give 3 types of effectors and 3 types of regulatory cells which help control the immune response

Question 27

Compare the Th1 and Th2 immune responses

Answer 27

• Both MHC II restricted
• Th1 = proinflammatory. Activate effectors to kill intracellular pathogens e.g. bacteria and viruses
• Th2 = Stimulate antibody production and switching

Question 28

What is Th0?

Answer 28

An unactivated T-cell

Question 29

What is an intracellular infection?

Answer 29

Antibodies cannot function - not able to penetrate the cell membrane
Need to kill infected cell
Cytotoxic T-cells

Question 30

What is an extracellular infection?

Answer 30

Antibodies best defence – hence B cells secrete antibodies to bind pathogen

Question 31

What are cytokines?

Answer 31

Soluble protein messengers of the immune system

Question 32

How do cytokines work in the following:

• Autocrine
• Paracrine
• Endocrine

Answer 32

• Able to work on the cell that produced it
• Able to work on the cell that didnt produce it but is neighbouring
• Able to work on a systemic level

Question 33

Describe the 3 signals in a cellular immune response

Answer 33

1 = antigen, involves MHC, peptide epitope, T-cell receptors
2 = other molecules that bind to reinforce the interaction e.g. CD4
3 = cytokine that is produced by either the antigen presenting cell or another near-by cell

Question 34

What occurs upon antigenic and co-stimulation?

Answer 34

You get clonal expansion:

• Cell enlarges
• Stops migrating
• Chromatin becomes less dense – mRNA and protein synthesis
• Within hrs cell looks different and now referred to as lymphoblast
• Lymphoblasts divide until there are 1000 effector cells

Question 35

What happens to the cells in the absence of antigen?

Answer 35

• Effector cells can no longer be activated so they die
• Memory cells do not require activation and persist in the absence of antigen – provides protection if the antigen is encountered again