Exam 1-- Ch.5 T Cells Flashcards
What are T cells? Where are they produced? Where do they mature?
- WBCs from bone marrow that mature in the thymus
Where are T cells found? How many?
circulate in blood and lymph (can enter tissue)
–billions!
What type of receptors to T-cells have? What do they recognize?
T Cell Receptors (TCRs)
- “antibody like receptors” (are NOT Ab, like how B-cells have)
- recognize protein antigens presented by MHCs
What are the two types of T cells?
Killer T cells (aka Cytotoxic T Cells – CTLs)
Helper T cells
What activates Killer T cells (CTLs)?
by MHC I and abnormal peptide presented on cells
T/F. Very few cells in body can present antigen to CTLs (T Killer Cell) via MHC class I molecules.
False– most cells can
What occurs after the Killer Cell connects to the target cell?
triggers apoptosis, for it to commit suicide
What activated Helper T cells?
MHC II and abnormal Antigen Presenting Cells (B-cells, macrophages, or dendritic cells)
What will a T Helper Cell do after it is activated?
secrete cytokines
- interleukin 2 (IL-2)
- interferon gamma (IFN-gamma)
Recall: Which cells are presenting MHC I? What about MHC II? What does the peptide look like they are presenting? What T cell are they stimulating?
MHC I – infected cell presenting endogenous; peptide enclosed; T Killer Cell
MHC II – APC; peptide sticks out; T Helper Cell
What are the three “primary” signals a T cell needs to be activated?
- T Cell Receptor
- Co-Receptor
- Co-stimulation
What do these “primary” signals entail for a T-cell to be activated?
- T Cell Receptor
- Co-Receptor
- Co-stimulation
- TCR must recognize its cognate antigen
- co-receptor must recognize the MC (I or II)
- other receptor(s) must recognize other molecules
What is the difference b/w a Co-Receptor and Co-Stimulation?
Co-receptor is recognizing the MHC (I or II)
Co-stimulation means recognizing other molecules
What occurs if the T cell’s TCR recognizes MHC plus self peptides?
the T-cell commits suicide (apoptosis)
– (T cells created that would kill self need to go away)
What occurs if the T-cell’s TCR recognizes cognate antigen(non-self) on MHC with no co-stimulation?
T cell is anergized (inactivated)
What occurs if the T-cell’s TCR recognizes cognate antigen on MHC plus there is co-stimulation?
T cell is activated
T/F All T-cell TCRs only recognize peptides presented by MHC I and MHC II molecules.
True
What are the two types of TCRs?
- alpha-beta (95%) –traditional
2. gamma-delta –non-traditional
T/F. All TCrs on a given mature T cell are usually different.
False– they are usually ALL identical!!!
What is the name given to the group of signaling proteins ass. with TCR?
CD3
What are the elements needed for a T-cell to be activated?
- Recognition (TCR–alpha-beta; and Co-receptor–CD4 or CD8)
- Co-stimulation (B7 on APC; and CD28 on T-cell)
- Signaling (CD3; and CD28 on T-cell)
What is the TCR proteins (alpha-beta) needed for?
antigen recognition
What is the co-receptor needed for?
the co-receptor = CD4 or CD8–(on T-cell); are for MHC recognition
What are the co-stimulatory molecules?
B7 proteins on APC
What is CD3 needed for?
signaling
or those other 4 proteins– weird symbols
What type of T-cell expresses CD4? What MHC is then involved? What type of signal is created?
Helper T cells; attaches TCR to MHC II molecules
HELP signal
What type of T-cell expresses CD8? What MHC is involved? What type of signal is created
Killer T Cells (CTLs); attaches TCR to MHC I molecules
KILL signal
What are the two kinds of Co-receptors of T-cells?
CD8 —> is MHC I restricted (peptides in cell)
CD4–> implies MHC II (peptides from outside cell)
What do the co-receptors do for T-cells? Why are they important?
Co-receptors bind T cells to MHCs (Type I or II)
w/o them the T-cell would not know if an APC is presenting protein fragments and need help (helper T) or if an APC is infected and needs to be killed (killer T)
What can created the Co-stimulation of T-cells?
many moelcules!
- B7 proteins (CD80, CD86) from APC’s, connect with CD28 receptor on T-cell
What is B7? What is CD28? What occurs when CD28 is activated?
B7–> is a co-stimulatory molecule expressed on surface of APCs
CD28–> is a receptor molecule on T-cell; when activated it amplifies signal and lowers number of TCR crosslinks needed for activation
What are Helper T cells constantly doing in the lymph nodes?
scanning dendritic cells; if find cognate antigen it will:
- TCR engages antigen/MHC
- CD4 co-receptor on Helper T cell attaches to MHC II on dendritic cell
- CD40L proteins attach to CD40 on dendritic cell
- dendritic cell makes co-stimulatory molecules (B7)
- adhesion molecules bind two cell together (immunological synpase)
Once the Helper T cells are fully activated and bound to the dendritic cells, what happens next?
Helper T cell and APC part ways
- Helper T proliferates and makes more IL-2
- APCs goes on to activate other Helper T cells
What does IL-2 serve as for Helper T cells?
a positive feedback for division
Do naive T cells have IL-2 receptors on their surface? What does this results in?
No, therefore only T cells replicating are specific ones needed to combat the particular antigen
How are Killer T cells activated?
only need an activated dendritic cell for activation
What is the process of a Killer T cell becoming activated?
- Naive CTL meets activated DC presenting cognate antigen on a MHC I
- Co-receptors and co-stimulation occur (CD8 on Killer T cells binds to MHC I)
(same concept as helper T cells)
How long to dendritic cells and Helper T cells bind for? What occurs during this time?
for hours
- emit cytokines which attract CTLs
Which cell is in charge of supplying IL-2 for CTL proliferation? What cell regulates magnitude of CTL response?
Helper T cells!!
What are non-traditional T cells?
- T cells that express gamma-delta receptors
- are Natural Killer T cells (somewhat b/w T cells and NK cells)
- have traditional alpha-beta receptors
Where are Non-Traditional T cells most abundant?
- intestine
- uterus
- tongue
What do non-Traditional T cells recognize?
lipid antigens presented by non-traditional MHC- called CD1
