T-cell immunity - part 2

Question 1

Where do immature dendritic cells reside?

Answer 1

Tissues and blood - this includes peripheral tissues and secondary lymphoid tissues

Question 2

How does a naive T cell encounter a dendritic cell?

Answer 2

Dendritic cell localizes in the secondary lymphoid tissues. A naive T cell enters the secondary lymphoid tissue and encouters the dendritic cell

Question 3

If there is an extracellular pathogen in the bloodstream, what happens?

Answer 3

Dendritic cell will encouter it and present it to a T-cell in the spleen.

Question 4

If there is an extracellular pathogen in the lymph, what happens?

Answer 4

Dendritic cell will encouter it and present it to a naive T cell in a lymph node.

Question 5

If there is an extracellular pathogen in the mucosal area, what happens?

Answer 5

Dendritic cell will be in mucosal tissues, ready to present to T cells.

Question 6

Describe what happens when an immature dendritic cell in the peripheral tissues encounters a pathogen.

Answer 6

Immature dendritic cell either phagocytoses or gets infected by pathogen.
Some of the dendritic cells leave the tissue and enter the lymphatic systems, and localize to a lymph note.
Dendritic cell presents peptide on MHC1 (if infected) or MHC2 (if phagocytosed) to a naive T cell.

Question 7

Whereas dendritic cells can leave peripheral tissues, which inflammatory cell cannot?

Answer 7

Macrophages

Question 8

Primary immune response:

• Must have a ______ ______ presenting peptide on _____ to a _____ _ cell. This always occurs in the _________ ________ ________.
• Naive T cell responds and undergoes ______ _______ to form ________ T cells

Answer 8

dendritic cell
MHC
naive T
secondary lymphoid tissues
clonal expansion
effector

Question 9

The DC that presents peptides to the naive T cells can be from what locations? How does it make it to the secondary lymphoid tissues?

Answer 9

Either tissues or blood (peripheral tissues or secondary lymphoid).
If in the peripheral tissues, migrates to the secondary lymphoid tissues.

Question 10

Only _____ _ cells can enter into infected peripheral tissues. Through what process?

Answer 10

effector T cells

inflammation

Question 11

Do naive T cells enter into your tissues?

Answer 11

NO! Only effector T cells can enter into your tissues via inflammation

Question 12

What is the reason that naive T cells cannot enter the tissues but effector T cells can?

Answer 12

Naive T cells cannot respond to chemokines; Effector cells can.

Question 13

How to CTLs kill their target cells?

Answer 13

By initiating apoptosis in infected cells.

Question 14

What are the targets of CTLs?

Answer 14

Intracellular viruses and intracellular bacteria that are replicating in the cytoplasm of infected cells.

Question 15

What do CTLs use to destroy infected nucleated cells?

Answer 15

Cytotoxic granules in the cytoplasm which they release into the infected cell, inducing apoptosis

Question 16

Are CTLs or NKs destroyed after killing a cell?

Answer 16

No, they can kill lots of cells in the infected tissue.

Question 17

How do some viruses evade the CTL response?

Answer 17

Some viruses block peptide presentation by MHC class I molecules to evade the CTL response.

Question 18

What are the different ways in which some viruses can evade the CTL response?

Answer 18

Block proteins from entering the proteasome
Block peptide from binding to MHC class I molecule
Inhibit transport of MHC 1:peptide to surface of virus-infected cell

Question 19

Why are cells that evade the CTL response very dangerous?

Answer 19

They basically remove cytotoxic T cells from contributing in immunity, as they do not get activated.
We only have NK cells to kill these infected cells

Question 20

What to effector T helper cells do?

Answer 20

Help other cells by “telling” them how to eliminate pathogens.

Question 21

How do effector T helper cells tell cells what to do?

Answer 21

by secreting cytokines

Question 22

What are the two roles of effector T helper cells?

Answer 22

Th1 cytokines activate infected macrophages –> increases the fusion of lysosomes to phagosomes

Form a granuloma to “wall off” infected macrophages and suffocate the pathogen

Question 23

Effector T helper 1 cells:

- Enhance the destruction of ________ _________ replicating in _________ or ___________ of macrophages.

Answer 23

intracellular bacteria
phagosome
phagolysosome

Question 24

What is the idea behind a granuloma?

Answer 24

Forms an area of necrosis, particularly of macrophages. They essentially wall off nutrients and oxygen from getting to these macrophages and intracellular bacteria

Question 25

How can TB survive granulomas?

Answer 25

Can survive hypoxic environment

Question 26

After a Th cell gets activated by a DC, what does it do to help macrophages fight off intracellular bacteria?

Answer 26

Leaves the secondary lymphoid tissue and enters the infected tissue, where, it secretes cytokines to increase the production of acids and enzymes in the lysosomes, and induces more fusion of lysosomes with phagosomes.

Question 27

The memory T cell respons is more _________ since circulating memory (Effector) CTLs and TH1 cells respond faster upon re-infection.

Answer 27

protective

Question 28

After a pathogen has been destroyed, what happens to the effector T cells?

Answer 28

Vast majority undergo apoptosis and some are left as memory cells, which remain in circulation for a long time.

Question 29

What is the purpose of a booster?

Answer 29

A booster vaccination is given when you don’t retain your memory population.