Flashcards in Tolerance Induction/MHC Restriction Deck (87)
Are HEVs present in the thymus?
What two organs lack afferent lymphatics?
Spleen and thymus
What hormones are produced by the thymus?
Thymulin, thymosin alpha-1, thymopoietin
Thymulin produced by the thymus is dependent on what mineral?
What happened when the thymus was removed from neonatal mice?
Degeneration of the anterior pituitary within 30 days
What is the function of thymulin that is produced by the thymus?
Involved with T cell maturation and differentiation (can also affect the neuroendocrine system
In what organ do T cells mature?
What does it mean when T cells become mature?
Learn tolerance of self aka "central tolerance induction"
What does it mean when a T cell is "nude"?
Doesn't express CD4, CD8, or TCR
Nude T cells enter the thymus from what location?
Where in the thymus do nude T cells proliferate?
Nude T cells are resistant to what process?
Why are nude T cells resistant to apoptosis?
They express little or no Fas protein
What is expressed heavily on nude T cells that help protect them against apoptosis?
What does it mean when a T cell becomes a double positive (DP) cell?
Possesses both CD4 and CD8 co-receptor molecules, lots of Fas protein on surface, and very little Bcl-2
What is the most common lymphocyte in the thymus (80%)?
Double positive (DP) cells
What two tests must a DP cell pass to avoid death?
Tolerance to self
What is CD44?
Receptor for hyaluronic acid
Associated with thymocyte migration events
Considered a marker for T-cell activation
What is CD25?
Alpha chain of IL-2 receptor
Favors IL-2 thymocyte proliferation
Which DP test is considered "positive selection"?
Which DP test is considered "negative selection"?
Tolerance to self
What occurs in the positive selection DP test?
T cell must only recognize peptides presented on MHCs
What occurs in the negative selection DP test?
T cell must not recognize self peptides
During which DP test does 95% of the maturing T cell deaths occur?
Positive selection (MHC restriction)
What cells check to see that T cells have receptors (TCR) that recognize one of the "self MHC" molecules (both I and II) during positive selection?
Cortical epithelial cells (CEC)
Where does the MHC restriction (positive selection) DP test occur?
Cortex of thymus
What happens to a T cell that recognizes peptides not presented by MHC molecules during positive selection?
Eliminated by apoptosis
When is a T cell referred to as a single positive cell (SP)?
After positive selection when it chooses either CD4 or CD8
What cells give the negative selection test?
Thymic dendritic cells and medullary thymic epithelial cells