Lecture 5 Flashcards
what type of receptors do cytokines signal thru?
signal via HETERODIMERIC receptors
describe the activation of cytokine receptors (4 steps)
- cytokine binding allows for dimerization
- each subunit has kinase domain that phosphorylates opposite subunit
- more phosphorylation allows for more STAT phosphorylation
- STATs dimerize and go to nucleus to drive transcription
how is cytokine receptor signaling different than PRR signaling?
PRRs usually monomers, cytokine receptors are heterodimers
what is the common gamma chain?
common subunit for many cytokine receptors
describe the 2 subunits of cytokine receptors
1 is common gamma chain, 1 is subunit specific to cytokine
2 ways that specificity is achieved with cytokine signaling
- unique subunit
- heterodimerization of diff STATs
describe how heterodimerization of STATs allows for specificity with cytokine signaling
many cytokines can signal through the same STAT protein but diff combinations of STAT dimers allows specific downstream signaling
explain IL-2 signaling vs IL-7 signaling
both signal via receptor via common gamma chain + IL-2 or IL-7 specific subunit
both signal thru same JAK kinases
both use STAT5 but heterodimerize with diff STATs
why is it important that cytokine signaling has specificity? use IL2 vs IL7 as example
for example, IL2 and IL7 are important for lymphocyte growth but at different times so receptors are expressed at different times
to identify the unknown lineage negative cells from last lecture, why is it helpful to see if they respond to common gamma chain cytokines?
lymphocytes respond to cytokines bc their cytokine receptors have the common gamma chain –> so interesting to see if these unknown cells can also respond like T cells
what happens if you put T cells in a dish with IL-2?
IL-2 is lymphocyte development cytokine –> will proliferate and differentiate
what happens if you put the unknown cells in a dish with IL-2?
cells are responding to the cytokine –> PROLIFERATING but not differentiating into lineage and maintaining stem cell-like markers
explain these results, one column at a time
IL-2
- growing but not making cytokines
IL-2 + IL-25
- making IL5 and IL13, not IFNy
IL-33
- making IL5 and IL13, not IFNy
Th1 and Th2 are positive controls
what is the significance of these unknown cells being able to produce IL5 and IL13? how do we know?
must be INNATE-LIKE LYMPHOID cells bc they are making Type 2 cytokines, IL5 and IL13
but they are NOT T cells bc T cells require APC and antigen to activate, but these cells could activate with only cytokines (a property of innate cells)
what do these data show? conclusion?
(Rag KO = cant make TCR/BCR)
Stimulating cells with IL33:
- In Rag KO: lots of IL5 and IL13
- In Rag and gamma chain KO: no IL5 or IL13 produced
therefore, when stimulated must respond via gamma chain to produce IL5 and IL13
what do these images show? significance?
injecting with IL33 allows for production of goblet cells in rag KO but not rag and gamma chain KO mice
significant bc goblet cells can only be made when IL13 is produced
what is the INDIRECT evidence that these unknown cells are the cells that produce IL13? why is this only indirect evidence?
stimulating Rag KO mice with IL33 allows production of IL13 and goblet cells (stimulated by IL13)
this is INDIRECT bc maybe other cells that make IL13 are also being knocked out, we’re not directly looking at the cells of interest
what do these data show?
instead of injecting IL33, infect mouse with Nippo worm
WT and Rag KO similarly produce IL5 and IL13 (therefore Rag not necessary for function, therefore not lymphocyte)
Gamma chain and Rag KO has no IL5 or IL13 production
how can we show direct evidence of ILC2 function?
instead of using IL33 alarmin cytokine to stimulate cells, actually infect the mouse with Nippo worm bc more physiologically relevant
what did they do after showing that Nippo worm infection stimulates cytokine production in WT and Rag KO mice but not in gamma chain and Rag KO mice? what did they find?
transfer the ILC2s to infected gamma chain and Rag KO mice
infected mice who received the ILC2s produced IL13 and more goblet cells
what is the direct evidence of these unknown cells producing IL13?
when there is a worm infection, the unknown cells are sufficient to drive the response and make IL13 and therefore goblet cells
describe the ILC lineage (4 stages)
- common lymphoid progenitor
- diff signals allow for diff cells to be produced but all require GATA3
- Become ILC precursor in bone marrow
- diff cytokine signals promote differentiation
describe the common lymphoid progenitor
lives in bone marrow and gives rise to all lymphoid cells and ILCs
are ILCs tissue-resident?
yes, they are tissue-resident cells of lymphoid origin
since ILCs are tissue resident what does this mean about the signals they receive?
they are responsive to epithelial-derived cytokines and alarmins
describe the level of ILC activity vs lymphocyte activity
ILCs are more potent than T cells so they have a large effect very quickly at the barrier site
how are ILCs grouped?
based on function –> i.e. the type of response and pathogen
grouped similarly to Th1, Th2, and Th17
what adaptive cell does ILC2 correspond to?
corresponds to Th2 cell
what is similar about the ILC2 and Th2 counterparts?
both come from same progenitor and make similar cytokines
what cytokines do Th2 cells make? what cytokines do ILC2 cells make?
Th2 cells make IL4, IL5, and IL13
ILC2 cells make IL5 and IL13
what transcription factor regulates expression of Th2 and ILC2 cytokines?
GATA3
If GATA3 is required for ILC2 and Th2 development, why does ILC2 not make IL4?
IL4, IL5, and IL13 genes are all next to each other so making one usually means you will make the other
but the way that GATA3 is stimulated in each cell type is different, allowing IL4 gene to be silenced for ILC2s
explain the differing pathways to activate Th2 and ILC2
T cells are stimulated by TCRs with NFk and IL4R activation allowing for GATA3 to activate IL4, IL5, and IL13 production
but ILC doesn’t receive TCR signal so drives different pathway for GATA3 to activate IL5 and IL13 production
what could be another reason that IL4 is not expressed in ILCs?
IL4 may selectively silenced in ILCs thru epigenetics
what are pioneer TFs? how are they different from other TFs?
pioneer TFs access DNA regardless of their state
other TFs require DNA to have certain accessibility
how does pioneer TF function affect function of other TFs?
pioneer TFs can alter DNA accessibility so other TFs can access the DNA
Describe how memory T cells are produced
- T cell activated by antigen, costimulatory molecules, and polarizing cytokines
- after responding to infection, some cells remain at site of infection
- cells can just see antigen without costimulatory molecules or polarizing cytokines which is sufficient to activate the memory cell
what allows for the memory of memory T cells?
epigenetic imprinting!
what is the actual “memory” of memory T cells?
at the site of infection they can respond to antigen ONLY without the need for costimulatory molecules or polarizing cytokines
describe the experiment looking at innate immune memory: what were the 2 stimulating experiments?
stimulated macrophages with:
- LPS –> makes lots of pro-inflammatory cytokines
- B-glucan –> makes lots of pro-inflammatory cytokines
- no stimulus –> no cytokines
then wash and stimulate with TLR2 agonist:
- cells previously stimulated with LPS –> makes very little pro-inflammatory cytokines
- cells previously stimulated with B-glucan –> makes lots of pro-inflammatory cytokines
- cells without previous stimulus –> make some pro-inflammatory cytokines
what can be concluded from the fact that cells previously stimulated with LPS produced no cytokines from TLR2 agonist?
cells gained LPS tolerance
when is it important for cells to gain tolerance to antigens?
important in the gut where there’s lots of bacteria bc we don’t want to respond under normal conditions
- immune cells extend dendrites thru epithelium to sample gut lumen and gain tolerance
what can be concluded from the fact that cells previously stimulated with B-glucan produced lots of cytokines from TLR2 agonist?
the cells had TRAINED immunity
what is trained immunity?
cells can have innate immune memory and maintain a response even if TLR2 is being stimulated with diff stimulus
what makes innate memory different than adaptive memory?
innate memory is NOT specific –> don’t need to see the same thing twice to get memory
what is the issue with innate memory not being specific?
could lead to inappropriate response
how do the findings of Kariko and Weissman “fine-tune” Janeway’s self vs non-self concept of host defense?
modifications of RNA are what allow the host to distinguish btwn microbial and host RNA
if unmodified RNA is a PAMP, why do we modify it to hide it from the immune system?
allows us to make RNA vaccines –> don’t want the RNA to be immediately destroyed or trigger an immune response
starting from intestinal epithelial cells and ending at worm expulsion, how do ILCs contribute to parasitic worm expulsion?
when there’s a worm, epithelial cells activate stress response and make alarmins, IL25 and IL33, which activate ILCs to make cytokines that act on the epithelium
3 reasons why ILCs are well-suited to be an innate counterpart to CD4+ Th cells?
- involve same TFs and cytokines
- both are tissue-resident
- don’t require antigen-presentation so they are innate
2 factors that explain why CD4+ T cell and ILC cytokine production differs?
- epigenetic differences
- convergence of multi-signaling pathways –> ex. T cells have TCR signaling that doesn’t happen in ILCs
