T cell response immunity

Question 1

Structure of TCR

Answer 1

alpha and beta chains (versus BCR light and heavy chains)

Question 2

What co-receptor do all naive T cells express

Answer 2

CD3

Question 3

2 signals involved in T cell activation

Answer 3

1. TCR + CD4/8 + MHC + Ag
2. CD28 + B7.1 (CD80) or B7.2 (CD81)

• Activated T cells only need 1st signal
• Lack of 2nd signal leads to anergy (unresponsiveness to further stimulation by Ag)

Question 4

Explain how CTLA-4 blocks co-stimulation of T cells

Answer 4

CTLA-4 has higher affinity than CD28 for B7

Binds to B7.1 and B7.2, inhibits T cell activation

(initially resides on intracellular membranes but moves to cell surface after TCR signalling)

Question 5

What cells are CD28 and CTLA-4 expressed in

Answer 5

CD28: resting and activated cells

CTLA-4: only in activated cells. Inhibits excessive expansion of activated T cells

Question 6

Function of CD8 T cells

Answer 6

Targets viruses

Kill viral infected cells

Question 7

Function of CD4 Th1 cells

Answer 7

Targets extracellular bacteria, microbes in macrophages (mycobacteria, listeria, leishmania, pneumocytis)

Activated infected macrophages.

Helps B cells in antibody production

Question 8

Function of CD4 Th2 cells

Answer 8

Targets helminths

Helps B cells in antibody production (especially switching to IgE)

Activates eosinophils, basophils, mast cells

Question 9

Function of CD4 Th17 cells

Answer 9

Targets fungi (candida), Klebsiella pneumoniae

Enhances neutrophil response, promotes barrier integrity (skin, intestines)

Question 10

Function of Tfh

Answer 10

B cell help

Isotype switching

Antibody production

Question 11

Function of CD4 regulatory

Answer 11

Suppress T cell responses

Question 12

Function of the following cytotoxic granules:

• Perforin
• Granzymes
• Granulysin
• TFN-alpha
• TFN-beta
• IFN-gamma

Answer 12

• Perforin: forms pore in target membrane
• Granzymes: proteases, activate apoptosis once in cytoplasm
• Granulysin: induces apoptosis
• TFN-alpha: activate macrophages, directly cytotoxic
• TFN-beta: activates and induces NO production
• IFN-gamma: blocks viral replication. Can lead to viral death without cell death

Question 13

What signal by APC induces differentiation into Treg cell

What cytokines does the Treg cell then produce

Answer 13

TGF-beta

Treg produces TGF-beta, IL-10

Question 14

What signal by APC induces differentiation into Tfh cell

What cytokines does the Tfh cell then produce

Answer 14

IL-6

Tfh produces IL-21, ICOS

Question 15

What signal by APC induces differentiation into Th17 cell

What cytokines does the Treg cell then produce

Answer 15

TGF-beta, IL-6

Th17 produces IL-6, 17

Question 16

What signal by APC induces differentiation into Th1 cell

What cytokines does the Treg cell then produce

Answer 16

IL-12, IFN-gamma

Th1 produces IL-2, IFN-gamma

Question 17

What signal by APC induces differentiation into Th2 cell

What cytokines does the Treg cell then produce

Answer 17

IL-4

Th2 produces IL-4, IL-5

Question 18

What sort of T cells are made in the following situations:

• No infection
• Early infection
• Viruses + bacteria
• Helminths

Answer 18

• No infection: Treg
• Early infection: Th17
• Viruses + bacteria: Th1
• Helminths: Th2

Th1 involves cell-mediated immunity, opsonises Ab
Th2

Question 19

Difference between Th1 and Th2 response to Ab

Answer 19

Th1 involves cell-mediated immunity, opsonises Ab

Th2 neutralises Ab

Question 20

How do CD8 cells destroy infected cells

Answer 20

Via release of perforin followed by granzymes, via Fas ligand interactions