Session 3: Adaptive Immune Response: Recognition Phase

Question 1

What are Naive T cells?

Answer 1

They are inactivated T-cells the needs to be presented by antigen presenting cells.

Question 2

Give some features of antigen presenting cells.

Answer 2

They have a strategic location. They can capture pathogens There’s a diversity in pathogen sensors called Pathogen Recognition Receptor

Question 3

What are the strategic locations of antigen presenting cells?

Answer 3

• Mucosa associated lymphoid tissue (MALT): Skin (SALT Mucous membranes (GALT, NALT, BALT, GUALT) Tonsils or Peyer’s patches • Lymphoid organs (Lymph nodes, spleen) • Blood circulation

Question 4

How do antigen presenting cells capture pathogens?

Answer 4

Phagocytosis Macropinocytosis

Question 5

What are the different pathogen recognition receptors (PRRs)? (Two main groups)

Answer 5

Extracellular pathogens (bacteria) Intracellular pathogens (viruses) Most are toll-like receptors and some NOD receptors.

Question 6

What are the sensors of Adenovirus?

Answer 6

TLR9

Question 7

Where are the sensors of Staphylococcus aureus?

Answer 7

TL2/4/9

Question 8

Give examples of different types of antigen-presenting cells.

Answer 8

Dendritic cells Langerhans cells Macrophages B cells (BCR)

Question 9

Location and presentation to of: Dendritic cells.

Answer 9

Lymph nodes, mucous membranes and blood. Present to Naive T cells

Question 10

Location and presentation to of: Langerhans cells

Answer 10

Skin Naive T cells

Question 11

Location and presentation to of: Macrophages

Answer 11

Various tissues throughout the body. They present to effect T cells which will produce cytokines to attract more macrophages for enhanced phagocytosis. Effector T cells are already activated.

Question 12

Location and presentation to of: B cells (BCR)

Answer 12

Lymphoid tissue. Present to both effector T cells and Naive T cells

Question 13

Role of MHC (Major Histocompatibility complex).

Answer 13

To present peptides from pathogens to CD4+ T cells or CD8+ T cell.

Question 14

On which cells can you find MHC class I molecules?

Answer 14

They are expressed on all nucleated cells.

Question 15

On which cells can you find MHC class II molecules?

Answer 15

They are expressed on dendritic cells, macrophages and B cells.

Question 16

So which MHCs can you find on macrophages?

Answer 16

Both MHC class I and MHC class II because macrophages are nucleated.

Question 17

Give the key features of MHC class I and class II molecules.

Answer 17

They have co-dominant expression so the number of different MHC molecules is high. They have polymorphic genes with different alleles so the number of microbial antigens being presented will be high as well.

Question 18

Functions of antigen-presenting cells.

Answer 18

They process microbes via exogenous pathways or endogenous pathways. They present microbial peptides to T cells.

Question 19

Explain the endogenous pathway of processing of intracellular microbes.

Answer 19

There is a microbial protein present in the cytoplasm. In the form of a virus or tumour antigen.

It is then marked for destruction by proteasome.

A proteasome-generated peptide is then transported to ER by TAP proteins.

There is then a formation of peptide-MHC class I complex if there is a right match.

The peptide is then presented to CD8+ T cells.

Question 20

Explain the exogenous pathway of processing intracellular microbes.

Answer 20

The microbe is captured by phagocytosis or micropinocytosis.

Degradation into small peptides in endosomes.

Peptide-rich vesicles fuse with vescile containing MHC-class II molecules.

Formation of peptide-MHC class II complex if right match.

This only occurs in antigen presenting cells including dendritic cells, B cells and macrophages.

The peptide is then present to CD4+ T cells.

Question 21

What T cell recognises MHC class I?

Answer 21

CD8+ T cells

Question 22

What T cells recognises MHC class II?

Answer 22

CD4+ T cells

Question 23

What type of pathogen is common for the exogenous pathway?

What type of immunity is common?

Answer 23

Bacteria

Humoral immunity (antibodies, complement and phagocytosis)

Question 24

What type of pathogen is common for the endogenous pathway?

What type of immune response is common?

Answer 24

Viruses

Cell-dependent immunity (Cytotoxic T lymphocytes, antibodies and macrophages)

Question 25

What is the clinical importance of MHC molecules?

Answer 25

Host can deal with a variety of microbes No two individuals have the same set of MHC molecules Different susceptibility to infections

Question 26

Why might some HIV-infected individuals progress slower than others?

Answer 26

Depending on their set of MHC molecules. There are slow progressors and rapid progressors. Depending on what MHC molecules they have they will fall ill quicker than others. Slow progressors will show an effective T cell response against infected cells because their MHCs can recognise key peptides for the survival of the virus. Rapid progressors will show a poor T cell response because of poor recognition of infected cells. This is because their MHCs may only recognise less critical peptides for the survival of the virus.

Question 27

What are some clinical problems with MHC molecules?

Answer 27

It's a major cause of why organs might be rejected by the new host in an organ transplant. If the HLA molecules mismatch the new host might not accept it. HLA molecuels are associated with autoimmune disease like ankylosing spondylitis and insulin-dependent diabetes mellitus.

Question 28

Case of cellulitis. Give causative organism. Antigen presenting cells Sensor Mode of capture and pathway of processing antigen.

Answer 28

Staph aureus Langerhans Cell in skin Toll-like receptors (PRRs) Phagocytosis and proceeding onto exogenous pathway.

Question 29

Cellulitis. Lymphoid tissue involved Antigen presentation Which T cells? T cells to what cells? Which adapted immune response?

Answer 29

SALT (Skin associated lymphoid tissue) MHC class II CD4+ T cells To B cells Humoral immune response

Question 30

Respiratory infection due to adenovirus. Give antigen presenting cells. Sensors Capture Antigen processing pathway.

Answer 30

Dendritic cells Toll-like receptors The infection of the virus itself Endogenous pathway

Question 31

Adenovirus Lymphoid tissue Antigen presentation T cells T cells to what cells? Adapted immune response.

Answer 31

BALT MHC class I CD8+ T cells Cytotoxic T lymphocytes Cell mediated response