T cells Block A

Question 1

what do the T cell progenitors develop from ?

Answer 1

the bone marrow which then migrates to the thymus to mature

Question 2

what then occurs in the thymus ?

Answer 2

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..

Question 3

when does a T cell become activated ?

Answer 3

the mature T cells encounter foreign antigens in the peripheral lymphoid they are then activated.

Question 4

what occurs when the T cell is activated ?

Answer 4

it migrates to the site of infection

Question 5

whats normally the 2 chains of .a T cell receptor ?

Answer 5

normally a and B

Question 6

what is the main 2 chains in receptor of gut T cells ?

Answer 6

y and 8 chains

Question 7

what region of the TCR recognises diversity ?

Answer 7

the variable region

Question 8

what is the cytoplasmic tail used for ?

Answer 8

signalling upon recognition

Question 9

why does each T cell recognise a different antigen ?

Answer 9

as each TCR is different

Question 10

why are the TCR different?

Answer 10

due to random recombination of germ line DNA for both TCR chains.

Question 11

are all the TCR produced useful ?

Answer 11

no as some may not recognise MHC or self recognition may occur to selection is needed.

Question 12

in the thymus selection occurs to make sure it doesn’t recognise self , how is this done?

Answer 12

based on affinity , strength of binding

Question 13

what does strong affinity mean ?

Answer 13

recognises self MHC to tightky and therefore deleted

Question 14

CD8+ cells ?

Answer 14

T killer cells surface proteins , MHC I

Question 15

what do the T cells recognise ?

Answer 15

the antigens from the pathogen that the phagocyte has chewed up and produced lots of short peptides for.

Question 16

what type of cell does MHC class II present an antigen too and what type of antigen?

Answer 16

CD4+ and extracellular pathogens such as worms.

Question 17

what type of cell does the MHC class I present an antigen too and what type of antigen ?

Answer 17

CD8 cell killer cells and intracellular pathogen such as a virus.

Question 18

what do naive antigen specific T cells do ?

Answer 18

recirculate looking for phagocytes that are presenting their cognate antigen

Question 19

what occurs upon recognition ?

Answer 19

T cell and antigen presenting cell form an interaction. The TCR transmits signals and the T cell becomes activated

Question 20

what happens once the T cell is activated ?

Answer 20

• Proliferates
• Turns on effector functions
• Polarisation

Question 21

why does proliferation occur ?

Answer 21

Huge diversity means that antigen-specific T cells are rare , activated T cells are ‘useful’ so need to proliferate to generate effective immune response.

Question 22

what is the effector function?

Answer 22

the CD4+ T cells are helper while the CD8+ cells are the killer function.

Question 23

why is polarisation done ?

Answer 23

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.

Question 24

if the CD4+ cell is TH1 what will it secreate and functions ?

Answer 24

secrete IFNg or TNF and activate the macrophage and delayed type hypersensitivity .

Question 25

if the CD4+ cell is Th2 then what is secreated and function ?

Answer 25

secrete IL-4 and helps antibody production and allergy response.

Question 26

advantages of adaptive immune system ?

Answer 26

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.

Question 27

disadvantages ?

Answer 27

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.