T cells Block A Flashcards
what do the T cell progenitors develop from ?
the bone marrow which then migrates to the thymus to mature
what then occurs in the thymus ?
there is positive and negative selection , the immature T cell that recognises self MHC and binds moderately will receive signals for survival. Those who interact strongly with MHC self peptides are deleted by apoptosis as they have the potential to be self reactive..
when does a T cell become activated ?
the mature T cells encounter foreign antigens in the peripheral lymphoid they are then activated.
what occurs when the T cell is activated ?
it migrates to the site of infection
whats normally the 2 chains of .a T cell receptor ?
normally a and B
what is the main 2 chains in receptor of gut T cells ?
y and 8 chains
what region of the TCR recognises diversity ?
the variable region
what is the cytoplasmic tail used for ?
signalling upon recognition
why does each T cell recognise a different antigen ?
as each TCR is different
why are the TCR different?
due to random recombination of germ line DNA for both TCR chains.
are all the TCR produced useful ?
no as some may not recognise MHC or self recognition may occur to selection is needed.
in the thymus selection occurs to make sure it doesn’t recognise self , how is this done?
based on affinity , strength of binding
what does strong affinity mean ?
recognises self MHC to tightky and therefore deleted
CD8+ cells ?
T killer cells surface proteins , MHC I
what do the T cells recognise ?
the antigens from the pathogen that the phagocyte has chewed up and produced lots of short peptides for.
what type of cell does MHC class II present an antigen too and what type of antigen?
CD4+ and extracellular pathogens such as worms.
what type of cell does the MHC class I present an antigen too and what type of antigen ?
CD8 cell killer cells and intracellular pathogen such as a virus.
what do naive antigen specific T cells do ?
recirculate looking for phagocytes that are presenting their cognate antigen
what occurs upon recognition ?
T cell and antigen presenting cell form an interaction. The TCR transmits signals and the T cell becomes activated
what happens once the T cell is activated ?
- Proliferates
- Turns on effector functions
- Polarisation
why does proliferation occur ?
Huge diversity means that antigen-specific T cells are rare , activated T cells are ‘useful’ so need to proliferate to generate effective immune response.
what is the effector function?
the CD4+ T cells are helper while the CD8+ cells are the killer function.
why is polarisation done ?
This is done to ensure the immune system has the correct type of helper cell.
The polarisation of the CD4+ T cell can be a Th1 or Th2 cell.
if the CD4+ cell is TH1 what will it secreate and functions ?
secrete IFNg or TNF and activate the macrophage and delayed type hypersensitivity .
if the CD4+ cell is Th2 then what is secreated and function ?
secrete IL-4 and helps antibody production and allergy response.
advantages of adaptive immune system ?
There is random generation of specificity which allows the lymphocyte population to recognize antigenic peptides from many potential pathogens and this stops pathogens evading immune system.
disadvantages ?
Not all antigens are harmful and autoimmunity, allergy to food may occur. There need’s to be cross-talk between innate and adaptive immune system to control this “Danger” signal and alarm signals from injured or stressed cells. If there is no danger signal then this could be self antigen and no response is needed.
