T-Cell Mediated Immunity

Question 1

How do naive T-cells encounter antigen?

Answer 1

Travel in the lymphatics around the secondary lymphoid tissues - leaving at High Endothelial Venules (HEVs) into lymph nodes to communicate with dendritic cells

Question 2

Receptors

How do naive T-cells recognise antigen?

Answer 2

Express T-cell receptors that can recognise antigen fragments on the surface of interdigitating dendritic cells in the lymph node paracortex

Question 3

What is the Third Law of Immunology?

Answer 3

• CD8 T-cells only recognise MCH Class I
• CD4 T-cells only recognise MHC Class II

Question 4

What signal is required for naive T-cell activation?

Answer 4

Inate and adaptive immune system communicate - if pathogen dangerous dendritic clls signal via CD80 and CD86 which activate naive T-cells
Activation of t-cells requires two signals - signal 1 = antigen bound to TCR (dangerous) CD80 and CD86 and signal 2 = CD28 binding to CD80 and CD86

Question 5

What is clonal expansion?

Answer 5

Activation of t-cells first results in proliferation (autocrine) via IL-2 signalling

Question 6

What are cytokines?

Answer 6

T-cells produce cytokines:
Immunological hormones that influence the function of other cells for immune defence primarily via a local paracrine effect but some endocrine

Question 7

Give some examples of cytokines

Answer 7

Interleukins:
- IL-2: Clonal expansion of T-cells
- IL-4: B-cell growth factor
- IL-10: immunosuppression

Interferons:
IFN-gamma: macrophage activating factor

TNF Family:
-TNF-alpha: cell killing

Question 8

How do CD8 T-cells work?

Answer 8

• Leave secondary lymphoid tissues and re-enter circulation looking for infected tissues
• Alter their homing receptors to target inflamed endothelium
• Seek and destroy virus infected cells in tissues (by use of cytokines, cytotoxic granules or death receptors)

Question 9

What are the two types of T-cells?

Answer 9

T-helper cells and T-regulatory cells

Question 10

What influence does the innate immune system have on T-cell responses?

Answer 10

• Pattern recognition receptors on dendritic cells induces the expression of CD80/CD86 for signal 2
• PRRs also induce expresion of cytokines from dendritic cells and other cells of innate immunity
• Different PRRs induce different cytokine patterns, that influence CD4 T cell differentiation (Signal 3)

Question 11

What are the two main types of CD4 T-helper cells?

Answer 11

TH1 - bind with macrophages
TH2 - bind with B-cells
T-cells then induce enhanced activity of these cells by realesing cytokines

Question 12

How do TH1 cells activate macrophages?

Answer 12

• Release IFN-gamma superactivates macrophage which causes:
• Respiratory burst: Increased oxygen free-radicals, nitric oxide, anti-microbial peptides and proteases
• Increased lysosomal digestion
• TH1 cells are important for vesicular infections where pathogens deliberatley infect macrophages - lots of TH1 = superativated macrophages via IFN-gamma

Question 13

Why are TH2 cells important?

Answer 13

Produce cytokines to tell B-cells which anto=ibody to secrete (without this only IgM secreted)

Question 14

In regards to TH1 and TH2 what is a biased response?

Answer 14

When one (either TH1 or TH2) is needed more such as in the case of tuberculosis where macrophages are infected, TH1 is needed more in order to realease IFN-gamma for superactivation of macrophages