T cells Flashcards
Describe Cell Mediated Immunity
- can be transferred to other inbred animals by cells
- involves T cells
- provides protection against intracellular microbes
- provides help for development of humour immunity
Describe Humoral Immunity
- immunity can be transported to other inbred animals by antibody
- involves B cells
- provides protection against extracellular microbes
Describe T cells
- can identify & remove intracellular pathogens & altered self cells
- also promote development & maintenance of Ab producing cells
- 2 distinct T cell populations - helper & cytotoxic
Describe T helper cells
- Th cells
- MHC class 2
- Co-receptor = CD4
- assists B cells
- macrophage activation
- cytokine secretion
- help for CD8 cells
Describe Cytotoxic T cells
- Tc cells
- Co-receptor = CD8
- MHC class 1
- Kills virus infected cells & tumour cells
Describe T Lymphocytes
- 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
Describe T cell receptors
- 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
What does MHC stand for ?
Major Histocompatibility Complex
What are the 2 classes of the Major Histocompatibility Complex ?
- MHC Class 1 - found on all nucleated cells
- MHC Class 2 - found on all specialised antigen presenting cells
Describe the mechanism of Cytotoxic T cells
- 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
What are the 2 ways Tc cells can kill infected cells ?
- Release of lytic granules containing perforin & granzymes
- interaction of FasL on the target cell with Fas on the Tc cell
Describe the mechanism of T helper cells
- express CD4
- Interact with cells expressing MHC class 2
- produce cytokines which activate or modulate the function of other cells of the immune system
What are the two subcategories of T helper cells ?
TH1
TH2
Describe TH1 cells
- particularly involved in stimulation inflammatory responses
- activation of macrophages
- produce IFN gamma & TNF alpha
Describe TH2 cells
- supporting the development of B cells & humour immune responses
- IL-4, IL-5, IL-6
(IL = Interleukin)
Define Interleukin
messenger between white cells - molecules involved in control of immune response and fine tuning them
What are some other ways to active T cells ?
- Superantigens can activate T cells irrespective of the TCR specificity
- superantigen may be produced in Staphylococcal & Streptococcal infections leading to Toxic Shock Syndrome
How do superantigens activate T cells ?
- 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
What are some symptoms of Toxic Shock Syndrome ?
- vomiting
- high fever
- watery diarrhoea
- headache
- muscle aches
- sunburn type rash within 24 hrs
Describe the mechanism that causes organ failure in severe cases of Toxic shock syndrome ?
- 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
