T cells Flashcards
Name the 2 effector T cell classes and what they do:
- CD4 T cells: help other cells (B cells) to respond to extracellular sources of infx.
- CD8 T cells: kill cells that are infected w virus or other intracellular pathogens (CYTOTOXIC).
What interaction determines whether a T cell and B cell of the same Ag specificity will result in B cell activation (via CD40 expression + cytokines)?
Cognate interaction.
T cells activate infected macrophages to kill intravesicular bacteria/pathogens. What 2 signals are required for this?
- IFN-gamma (produced by TH1)
- CD40 ligand on T cell must bind CD40 receptor on macrophage
What to classes of T cell receptors (TCR) are there?
- a:B (alpha: beta)–> CD4 and CD8, common circulating T cell
- y:d (gamma: delta): funx not understood
Where does TCR rearrangement and selection occur?
Thymus. (precursor T cells travel here from the BM)
Epitopes are presented to TCR in the context of what?
An MHC (self) molecule.
This is a specialized Ag-presenting glycoprotein.
What does MHC restriction mean?
TCRs can only bing to a particular peptide bound to a particular MHC molecule.
What are the two classes of MHC molecules and where are they found?
- MHC class I: HLA A,B,C; found on most NUCLEATED cells
- MHC class II: HLA DP, DQ, DR; found only on APCs.
What MHC do CD8 and CD4 T cells recognize?
CD8: MHC I (intracellular infx ex. viruses)
CD4: MHC II (extracellular infx ex. bacteria)
How are do antigens get processed and presented by MHC I and MHC II?
intracellular antigen–> proteosome–> ER–> peptide binds MHCI–> presented on cell surface (to CD8 cells)
extracellular antigen–> endocytosed in vesicle–> phagolysozome–> peptide binds MHC II–> presented on cell surface ( to CD4 cells)
Where are each of the following found within the thymus:
cortical epithelial cell dendritic cell thymocyte macrophage medullary epithelial cell Hassall's corpuscle
cortical epithelial cell (thymic origin): cortex
thymocyte (BM origin): throughout the thymus as it develops
medullary epithelial cell (thymic origin): cortico-medullary jnx/medullar
dendritic cell (BM origin): medulla
macrophage (BM origin): medullar
Hassall’s corpuscle: medullar
Where does gene rearrangement of T cells (thymocytes) occur?
cortex of thymus.
What is:
Positive selection
Negative selection
- positive selection: selecting for T cells that are restricted by ‘self’ MHC
- negative selection: eliminating T cells that recognize Ags of self tissue (autoreactive)
Where does positive selection take place?
cortex of the thymus (cortical epithelial cells present MHC+peptide to TCR)
During positive selection, what happens to the co-receptor that is not involved in the epithelial APC-TCR interaction?
The co-receptor (either CD8 or CD4) not involved in the interaction ceases being expressed.
Self-restrcited CD4 or CD8 cells are tested for their reactivity to self-peptide in what process?
negative selection
What cells present self-peptide to CD4/CD8 cells during negative selection?
dendritic cells and macrophages
What TF extends negative selection to proteins that are specific to one or a few cell types (self)?
AIRE: autoimmune regulator
ex. transcription of insulin which is usually made only by beta cells in the pancreas
Where is AIRE active?
AIRE is active in a sub-population of epithelial cells in the thymic medulla.
Where does central T cell tolerance happen?
thymic medulla
Where are naive T lymphocytes activated by their specific Ag?
secondary lymphoid tissue
What chemokines do CCR7 receptors expressed by T cells bind to? Where are these secreted?
CCL21
CCL19
secreted in the lymph node cortex.
What happens when T cells interact with their specific Ag in the lymph node?
They complete differentiation and proliferate (become effector cells).
What ‘professional’ APCs are required to provide the necessary ‘co-stimulation’ to activate T cells?
dendritic cells
macrophages
B cells
