Chapter 7 Part 3 - Development of T lymphocytes Flashcards
T cells that pass the positive selection process by cortical epithelial cells are subjected to…..
negative selection
WHERE is negative selection occuring?
in the MEDULLARY region of the thymus
explain the process of negative selection
Single-positive thymocytes (either expressing CD4 or CD8 NOT both) are presented antigen by antigen presenting cells (APC’s) – most important ones are dendritic cells and macrophages.
the single-positive thymocytes encounter self-peptides from these cells (dendritic and macrophages) and material that they have engulfed.
for tissue-specific antigens, AIRE (autoimmune regulator) is a transcription factor that induces the expression of tissue-specific antigens in a subpopulation of epithelial cells
what are the “rules” for negative selection
the opposite of positive selection
moderate binding - survival signal
tight bonding = death by apoptosis
this produces CENTRAL TOLERANCE. circulating T cells will not react to self antigens
if the TCR encounters self antigen in the PERIPHERY…..
the cell receives a negative survival signal (Activation-induced cell death)
true or false
a large fraction of a:B T cells pass through positive and negative selection
FALSE – only a small fraction pass through positive and negative selection
IF the T cell passes through both positive and negative selection, what happens?
they leave the thymus and travel to secondary lymphoid tissue as mature, naive T cells.
true or false
naive T cells can recirculate for many years
true
what initiates the FINAL phase of T cell development?
encounter with antigen in lymph tissue
upon encounter with antigen in secondary lymphoid tissue, the final phase of T cell development is initiated.
They differentiate into effector T cells. name them
cytotoxic T cells
Treg (regulatory T cells)
various helper (CD4+) T cells
encounter with antigen in secondary lymphoid tissue initiates the final phase of T cell development where they differentiate into effector T cells (cytotoxic, helper, Treg)
name 2 fates of these effector T cells
-stay in secondary lymphoid tissue
-migrate to the site of infection
The selection process produces either ___ or ___ T cells
CD4 or CD8
CD4 T cells differentiate into……
helper T cells or Regulatory T cells
explain the function of regulatory T cells
-Treg have TCRs specific for self antigen.
-suppress the CD4 T cells in response to self antigens
this suppressive effect requires contact of naive T cell and Treg on the same antigen presenting cell (APC). Also requires the release of cytokines by Treg that inhibits the activation and differentiation of the effector T cell
What is the main mechanism for protection against autoreactivity AFTER the selection processes have occurred?
regulatory T cells
