Cell Mediated Cytotoxicity Flashcards
What’s the major antigen NON-specific effector cell in the cell-mediated immunity world? Antigen specific?
natural killer cells
cytotoxic T cells
What are the three types ot cytotoxic lymphocytes?
natrual killes
natural killer T cells
CTLs
What are the three sequential signals required for CTL activation?
- antigen-specific signal delivered by the TCR upon recognition of proper peptide on MHC 1 (from APC or tissue cell)
- co-stimulatory signal transmitted by CD28:B7 interaction
- SIgnal induced by IL-2 secreted from a Th1 (or Th17) CD4+ cell
What are the two ways an APC can become licensed?
through engagement with an activated CD40l+ help T cell or thorugh engagement with pathogens via TLRs
Which is more efficient: when the licensing of the APC and the activation of the CD8 cell occurs sequentially or simultaneously? Why?
It’s more efficient when it’s simultaneous because the CD4 cell that helped license the APC will secrete huge amounts of IL-2, which is necessary for the CD8 cell to fully differentiate - so it happens simultaneously, there’s already a pool of IL-2 for the CD8 cell to enjoy
CTL-P cells lack expression of what cytokine and it’s receptor compared to mature CTLs?
IL-2 and the IL-2R
Why don’t CTL-Ps have cytotoxic activity?
They don’t have the appropriate granules yet
How can CD45 be used to differentiate between a naive CTL-P and a mature CTL?
CTL-Ps express CD45RA and mature CTLs express CD45RO
Why don’t memory CTLs require Th1 CD4+ T cell help to reactivate?
Because memory CTLs only need low levels of IL-2 to reactivate, and they can produce that themselves
What are the steps involved to CTL-mediated killing of target cells?
- the TCR/CD3 complex recognizes the peptide on MHC1 on the target cell and binds
- LFA-1 (an adhesion molecule) binds to ICAMs on the target cell to help the adjesion junction so you can transfer granules
- Perforin molecules form a pore on the target cell membrane
- Granzyme molecules activate apoptosis by cleavage of caspases
- Fas ligand protein binds to Fas on the membrane of target cells and also initiates apoptosis
- CTL produces TNF which also feeds into apoptosis pathway
- CTL lets go and target cell dies
How is the CTL able to bind tightly and then let go before the cell is even killed?
When you get antigen activation, the LFA-1 converts from a low affinity state to a high affinity state for strong binding
this is transient though
5-10 minutes later, the LFA-1 returns to a low-affinity state, resulting in the dissotiation of the CTL from the target cell
So…what were those three ways CTLs initiate apoptosis again?
- secrete perforin and granzymes
- Fas/FasL binding
- TNF secretion
What sort of molecule is a granzyme? WHat does it do specifically?
a serine protease - so it cleaves at serine residues specific for proteins along the apoptosis pathway
for example, granzyme B bill cleave Bid which gives a pro-apoprotic signal to the mitochondria to release cytochrome C and will also cleave procaspase 3 to lead to apoptosis as well
How does Fas’Fas-L binding lead to apoptosis?
It will actiate death domains (FADD) which will cleave caspase-8 to initiate apoptosis
What cytokines will stimulate NK activity?
IFN alpha, beta and gamma
TNF alpha
IL-15
What cytokine is released by NK cells and what’s the purpose of it in that context?
IFN-gamma
It will tilt the immune response toward Th1 cells by inhibiting Th2 cells and inducing IL-12 production by macropahges and dendritic cells (specifically M1-angry macrophages)
Which start working first in a viral infection: NKs or CTLs?
NKs - remember they’re not antigen-specific, so they just need the Type 1 IFNs from the viral infected cells
What do NK cells use to bind to the constant portion of antibody stuck on target cells?
Fc gamma RIII
True or false: NK cells undergo rearrangement of receptor genes?
false - they don’t
True or false: NK cells are not MHC restricted.
True - remember it doesn’t even need antigen
Is NK cell killing different from CTL killing?
Nope - pretty much identical
What are the two categories of NK cell receptors?
- lectin-like receptors
2. immunoglobulin-like receptors (KIR = killer cell immunoglobulin-like receptors)
What do the lectin-like receptors bind? THe KIRs?
lectin - bind proteins KIR - bind to most MHC class 1 molecules
Which have stronger affinity for their ligands: NK activation receptors or inhibition receptors?
inhibition receptors
If a receptor is associated with an ITIM, is it inhibiting or activating? With an ITAM?
ITIM = inhibiting ITAM = activating
FOr the KIRs - which are the ones that have the long cytoplasmic tails - the activating or the inhibiting?
The long cytoplasmic tails contain the ITIMs (inhibiting0
The ones with ITAMs just have a short tail with a charged lysine residue
If an NK cell has an activating receptor bind it’s ligand, but there’s lots of MHC1 on the target cell, will the NK kill it?
no - MHC1 bind to inhibitory receptors with greater affinity than the activating receptor iwll bind its ligand, so there will be no killing
Why then are NK cells so great for killing virally infected cells?
Viruses often down-regulate MHC1 expression in an attempt to evade the CTL killing, but this triggers death from NK cells
What makes HLA-E special and what effect does it have?
It’s similar to MHC1, but not quite
It doesn’t really present peptides that were synthesized in the cell - it just presents a single “leader peptide” that it picks up as it’s synthesized in the RER
The leader peptide is the target for a c-type lectin-like receptor which is an INHIBITORY SIGNAL
So even if a healthy cell is having an issue with antigen presentation, it won’t necessarily be killed needlessly because the HLA-E doesn’t do antigen presentation per se
Activation of an ITIM will inhibit any activating signals present through interaction with which molecule?
SHP-1
Although NK T cell express a TCR and CD3, how are they different from CTLs?
The TCR is INVARIANT and they do NOT recognize MHC-bound peptides
also don’t have memory (probaby)
If NK T cells don’t recognize MHC-bound peptides, what do they recognize?
they recognize glycolipids presented by a molecule called CD1d
Antibody-dependent Cell mediated cytotoxicity entails what?
effector cells binding to antigen via the antibody through the Fc receptor and then killing occurs thorugh cytolytic enzymes released by the effector cells
