Lecture 19 Flashcards
where does central tolerance occur
primary lymphoid tissue
what does central tolerance do
eliminate clones that recognise self
what are the 3 mechanisms for lymphocytes that recognise self
apoptosis, helper cells become Treg cells and B cells may ingest their receptor and undergo receptor editing
what are T cell populations based on
1) TCR has right sequence and shape so it can bind MHC
2) Can recognise a foreign peptide in grove of MHC and not self peptide
what happens to majority of thymocytes
80% die via neglect as most thymocytes that dont bind self dont get provided a signal during maturation
what happens to the thymocytes that bind strongly to self
20% of T cells die via apoptosis as they bind too strongly
where do Treg cells come from
small amount of thymocytes that bind strongly to self peptide turn into Treg cells
what thymocytes are positively selected
the 1-2% of thymocytes that dont react with self peptides
how are Treg cells formed
small subset of negatively selected are presented with a self peptide however they dont receive signals to die
What do Treg cells do
provide peripheral tolerance mechanisms and if deleted provides autoimmunity
what are the mechanisms for periphreal tolerance
Normal T cell response, Anergy, Suppression, Deletion, Ignorance
what is normal T cell response
produces effector and memory T cells
what is suppression
when there is a block in activation so Tregs control self reactive cells
what is deletion
apoptosis
what is anergy
functional unresponsiveness
Where does central tolerance in B cells occur
Bone marrow
what happens if they dont receive signals
die via apoptosis
What are B cells able to do if they bind self
B cells can ingest their receptor and edit it. It is then redisplayed as a different receptor.
what happens if the B cells arent able to edit their receptor
it dies via apoptosis
What happens if the B cell escapes out into the periphery
it becomes anergic (unresponsive) due to its low binding affinity
what is periphreal tolerance
a back up mechanism that silences any lymphocytes that recognise self
what is clonal anergy
self reactive lymphocytes that are not activated properly and become resistant to stimulation
what does T cell tolerance lead to
B cell tolerance
what is the breakdown of tolerance
failure of an organism to recognize its own parts as self due to loss of tolerance
