T cells

Question 1

Describe Cell Mediated Immunity

Answer 1

• can be transferred to other inbred animals by cells
• involves T cells
• provides protection against intracellular microbes
• provides help for development of humour immunity

Question 2

Describe Humoral Immunity

Answer 2

• immunity can be transported to other inbred animals by antibody
• involves B cells
• provides protection against extracellular microbes

Question 3

Describe T cells

Answer 3

• can identify & remove intracellular pathogens & altered self cells
• also promote development & maintenance of Ab producing cells
• 2 distinct T cell populations - helper & cytotoxic

Question 4

Describe T helper cells

Answer 4

• Th cells
• MHC class 2
• Co-receptor = CD4
• assists B cells
• macrophage activation
• cytokine secretion
• help for CD8 cells

Question 5

Describe Cytotoxic T cells

Answer 5

• Tc cells
• Co-receptor = CD8
• MHC class 1
• Kills virus infected cells & tumour cells

Question 6

Describe T Lymphocytes

Answer 6

• leave the bone marrow & move to thymus to mature
• have membrane receptors for antigen called T cell receptors
• Receptor recognises antigen only when associated with MHC molecules

Question 7

Describe T cell receptors

Answer 7

• sometimes called CD3
• each T cell has 2 (alpha & beta) surface two-chain molecule that interact with antigen
• receptor is clonal distributed
• belongs to the immunoglobulin superfamily

Question 8

What does MHC stand for ?

Answer 8

Major Histocompatibility Complex

Question 9

What are the 2 classes of the Major Histocompatibility Complex ?

Answer 9

• MHC Class 1 - found on all nucleated cells
• MHC Class 2 - found on all specialised antigen presenting cells

Question 10

Describe the mechanism of Cytotoxic T cells

Answer 10

• express CD8
• peptides from the intracellular microbe are presented on the infected cell surface in MHC class 1 molecules
• this marks the cell as infected and enables Tc cells to target it
• Tc cells kill infected cells 2 ways

Question 11

What are the 2 ways Tc cells can kill infected cells ?

Answer 11

1. Release of lytic granules containing perforin & granzymes
2. interaction of FasL on the target cell with Fas on the Tc cell

Question 12

Describe the mechanism of T helper cells

Answer 12

• express CD4
• Interact with cells expressing MHC class 2
• produce cytokines which activate or modulate the function of other cells of the immune system

Question 13

What are the two subcategories of T helper cells ?

Answer 13

TH1
TH2

Question 14

Describe TH1 cells

Answer 14

• particularly involved in stimulation inflammatory responses
• activation of macrophages
• produce IFN gamma & TNF alpha

Question 15

Describe TH2 cells

Answer 15

• supporting the development of B cells & humour immune responses
• IL-4, IL-5, IL-6
  (IL = Interleukin)

Question 16

Define Interleukin

Answer 16

messenger between white cells - molecules involved in control of immune response and fine tuning them

Question 17

What are some other ways to active T cells ?

Answer 17

• Superantigens can activate T cells irrespective of the TCR specificity
• superantigen may be produced in Staphylococcal & Streptococcal infections leading to Toxic Shock Syndrome

Question 18

How do superantigens activate T cells ?

Answer 18

• in a non-antigen specific manner
• large number of T cells can be activated at once - can be as many as 20% of total body T cells
• results in massive stimulation of the immune system

Question 19

What are some symptoms of Toxic Shock Syndrome ?

Answer 19

• vomiting
• high fever
• watery diarrhoea
• headache
• muscle aches
• sunburn type rash within 24 hrs

Question 20

Describe the mechanism that causes organ failure in severe cases of Toxic shock syndrome ?

Answer 20

• clinical manifestations of TSS are a consequence of massive cytokine production
• IL-1 & TNF alpha are involved in acute-phase response & fever
• TNF alpha activates vascular endothelium & permeability
• fluid leaks from the vascular space leading to hypotension, shock & multiple organ failure