T Cells 6 Flashcards
(46 cards)
what happens after T cell activity?
contraction and negative regulation of T cells
and restoration of epithelial activity
when does the immune response contract?
within 10-14 days of infection –> at the end of the primary immune response, once Ag is cleared
how do Treg cells help with contraction?
by releasing inhibitory cytokines
how are lymphocytes lost for clonal contraction?
via apoptosis
which types of lymphocytes remain after clonal contraction? what type of response will they be needed for?
memory cells –> for secondary response when antigen is encountered again
what are the 2 unknown aspects of clonal contraction?
- is clonal contraction triggered by a lack of Ag or an active switch?
- how are memory cells selected for survival instead of death induction
what are the 2 apoptosis pathways?
- intrinsic pathway
- extrinsic pathway
what is another name for the intrinsic apoptosis pathway? how does the intrinsic pathway work?
“death by neglect”
lack of IL2Ralpha expression = absence of IL-2 survival signal = apoptosis
what property of IL-2Ralpha allows the intrinsic pathway to occur? what type of molecules have this common property?
IL-2Ralpha has transient expression, so it is impermanent and can therefore be reduced when needed
common for all cytokine receptor expression
what are the 2 types of inhibitory/regulatory receptors?
- CTLA-4
- PD-1
what is the function of CTLA-4?
downregulates T cell activation
how does CTLA-4 downregulate T cell activation?
binds B7 molecules with higher affinity than CD28, so it sequesters B7 and prevents CD28 binding
ultimately shuts down signaling pathways
when is CTLA-4 induced?
after signal 1,2,3 about 24h after T cell activation
when does CTLA-4 activity peak?
2-3 days post-stimulation
how does CTLA-4 get expressed on cell membrane?
CTLA-4 is fully translated intracellularly but undergoes PHOSPHORYLATION (post-translational regulation)
how many B7 molecules does CD28 bind vs how many B7 molecules does CTLA-4 bind?
1 CD28 binds 1 B7
1 CTLA-4 binds 2 B7
describe what happens when effector T cell binds APC (describe without vs with CTLA-4)
WITHOUT:
- Effector T cell binds APC
- CD28 can bind B7 and allow proliferation
WITH CTLA-4:
- Effector T cell binds APC
- CTLA-4 binds B7, blocking CD28 and blocking proliferation
ultimately, how does CTLA-4 affect sensitivity of T cells to APCs and how does affect proliferation?
CTLA-4 makes activated T cells less sensitive than naive T cells to stimulation by APCs
reduces IL-2 production which reduces proliferation and prevents lymphocyte overgrowth
what happens in mice that don’t have CTLA-4?
too many lymphocytes –> disease
what cells express PD-1?
activated T cells express PD-1
What does PD-1 bind? (2)
- PDL-1
- PDL-2
what type of cells express PDL-1?
constitutively express on many cells
what type of cells express PDL-2?
on APCs during inflammation
what is the function of PD-1?
downregulates T cell activation/function
