Ch. 9 Tolerance And MHC Restriction Flashcards
(35 cards)
Does the thymus express CD4, CD8 or TCR
Nope
Does the thymus contain HEV’s or afferent lymphatics
Nope
How do T cells enter the thymus
The blood
T cell express lots of what that is a protein that protects against apoptosis
Lots of Bcl-2
Where do T cells mature
Into double positive (DP) cells in the thymus
What type of co-receptor molecules do DP cells contain
Both CD4 and CD8
What are DP cells very vulnerable to?
Death
What two tests must a DP cell pass to live
1) MHC restriction
2) Tolerance to self
What do DP cells express a lot of and very little of
Lots of Fas protein on the surface, little Bcl-2
What type of selection is MHC restriction
Positive selection
What is positive selection for MHC restriction
Maturing T cell must recognize peptides presented on self MHC’s, this takes place in the cortex
What type of selection is tolerance to self in DP testing
Negative selection
What is negative selection in the tolerance to self DP test
Maturing T cell must not recognize peptides presented on self MHC’s, takes place in medulla
What do cortical epithelial cells ask t cells
They see if they have receptors that recognize on of the MHC molecules on the surface. If not then the cell dies
What do cortical epithelial cells do
Display peptides MHC 1 molecules made in cell, MHC2 molecules made in cell and sampled from the area
What happens if mature T cells don’t recognize MHC antigen presented molecules
They are eliminated
After positive selection T cells choose what
Either CD4 or CD8 becoming a single positive cell or SP cell
What cells give the tolerance to self or negative selection test?
Thymic dendritic cells, medullary thymic epithelial cells
What do thymic dendritic cells do
Display self peptides on MHC molecules, if unrecognizable the death to the T cell
What 2 features make the medullary thymic epithelial cells good at testing self tolerance
They break MHC peptide expression rules (displaying endogenous AG on MHC 2, like cortical cells) and express several thousand tissue specific proteins
Medullary thymic epithelial cells make sure we what
Create T cells that don’t recognize our tissue specific proteins that thymic dendritic cells missed
What happens when t cells do recognize MHC peptide complexes
This is a positive selection, presented on cortical thymic epithelial cells
What happens when t cells do not recognize self antigens on MHC
This is negative selection, presented on thymic dendritic cells and medullary thymic epithelial cells
Naive t cells primarily traffic though where
Secondary lymphoid tissues (express same antigen found in thymus)
