7 Effector T-Lymphocytes Flashcards
Q: When can antibody responses be insufficient? What is required to deal with this?
A: Some pathogens are intracellular and hide in the cell
Some organisms evolve to avoid antigen recognition
To deal with these pathogens, T cell mediated immunity is required
Q: What does an antigen presenting cell do in essence? What is its main subset?
A: chew up a pathogen, put it up onto an MHC and show it to a T cell
Dendritic Cell - MAIN subset of APCs
Q: Name the two families of MHC molecule and state which types of T cell gets activated by them
A: MHC I - presents intracellular antigen to CD8+ T cells
MHC II - presents extracellular derived antigen to CD4+ T cells
This is important in terms of disease susceptibility
Q: What is the only way that TCR recognises a peptide?
A: in the context of MHC - the antigen must be presented on the MHC molecules
Q: How do T cells migrate? Where to and from?
A: T cells start in the bone marrow, they mature in the thymus and they move to the lymph nodes
Once they have encountered the dendritic cell bearing the antigen that they recognise - they can migrate back into the circulation (go to site of infection)
There is a molecular address system that is used:
- Chemokine gradient - so if the cells express the right chemokine receptors they can follow these gradients
- Adressins and Integrins - allows the cells to move out of the vessels
So in summary…DC recognises the antigen - moves to the lymph node - meets the T cell - T cell migrates to the source of infection
Q: What do memory cells start as?
A: start as naïve, you then become activated (effector cells), they fulfil their roles and then they become memory cells
Q: Summarise the effector functions of CD8+ T cells. Alternative name? Main role? How do they function?
A: = Cytotoxic T Lymphocytes
Their main role is to target and kill infected cells
When a virus peptide is presented on the MHC Class I of a cell, the effector CTL identifies the MHC I with a foreign peptide and kills it.
Specific recognition of target cells by cytotoxic effectors causes polarisation of cytotoxic vesicles within the cell.
This causes release of granules by T cells
This induces apoptosis in targets
Q: What is necrosis?
A: inflammatory cell death (this is a classic danger signal)
Q: What is apoptosis?
A: programmed cell death (instead of exploding outwards, it collapses in on itself)
Q: How many cells can CD8 kill? What does CD8 drive?
A: CD8 cells don’t just kill one cell. They can induce apoptosis in a target cell then move on and induce apoptosis in the next target cell - it can control an area
Regulation is important to make sure you don’t cause too much damage.
CD8 is important because it drives viral evolution
Q: What are the 2 mechanisms of inducing apoptosis?
A: Perforin + Granzyme - CD8 injects perforin into the membrane of the target cell. This makes a pore in the membrane and allows granzyme to enter the cell.
Fas-fas Ligand where the Fas ligand (FasL) = on the CD8 cell -> Fas Receptor = on the target cell ->
When Fas has been engaged - it releases caspases
Both of these pathways upregulate CASPASE within the target cell which drives apoptosis
Q: Describe the function of CD4+ T cells / T helper cells.
A: Critical in host defence
A naïve T cell can differentiate into different subsets which produce restricted cytokine patterns
They have a range of effector functions: Macrophage activation Delayed Type Hypersensitivity Response B cell activation Regulation
CD4 are helper cells and their role is to turn off or turn on the response of other cells by producing cytokines
Q: How are macrophages activated? What happens as a result? Communication.
A: They get activated by CD4 T cells which enable them to engulf and kill pathogens better
Once activated, they increase the levels of pro-inflammatory molecules: TNF-a and CD40
T cells and macrophages cross-talk - via cytokines
Q: What is delayed type hypersensitivity associated with? Why is it described as delayed?
A: Tend to be associated with ALLERGY
It is delayed because it takes a couple of days to develop
Q: Describe the function of the delayed type hypersensitivity response. What’s its main role?
A: Seems pathological but it is protective as well
MAIN ROLE: defence against intracellular pathogens
If the antigen is NOT A MICROBE, delayed type hypersensitivity produces tissue injury without protection = ‘hypersensitivity’
