Lecture 3: Innate Sensing by the Immune System Flashcards
Why do we have response against virus with spike protein but not spike protein alone?
Virus has PAMPs along with spike protein antigen –> virus serves as adjuvant
do we mount immune response against an adjuvant? why?
yes –> adjuvant acts as PAMP or DAMP to trigger immune response
difference btwn PAMP/DAMP and epitope that T cells recognize
T cells recognize PEPTIDES that have been processed by DCs
PAMP is usually not a peptide
role of epigenetics in innate immunity?
epigenetics allows for trained immunity by altering gene expression in a way that is long-lasting
what is trained innate immunity?
due to epigenetic changes, the cell can react differently than the first exposure
difference btwn trained innate immunity and adaptive memory
trained innate immunity is NOT specific
what is sterile inflammation? example?
sterile inflammation = inflammation that occurs in the absence of microbial stimuli
ex. lesion on internal organ
does sterile inflammation support Janeway’s hypothesis or Matzinger’s theory?
Matzinger’s theory (DAMPs)
advantage of having lots of non-lymphoid tissue-resident cells?
centralized location
disadvantage of having lots of non-lymphoid tissue-resident cells?
can have non-specific hyperinflammatory response leading to unnecessary tissue damage
2 examples of how our immune system could have evolved from pre-existing program to ensure tissue development and/or proper tissue physiology
- macrophages initially undergoing efferocytosis to clean up dead cells during development
- type 2 immune response evolved for tissue repair, rather than immunity
3 ways in which “form follows function” impacts the activation of our immune system
- DC has dendrites to reach out into environment
- PRRs on outside vs inside of cell depending on pathogen
- MHC interacting with TCR for specificity
describe the cells of gut villi
bottom of crypts has proliferating stem cells that migrate up villi to make the rest of the differentiated epithelial cells with specialized functions
how do proliferation and differentiation change further up the villi?
proliferation decreases, differentiation increases
describe “form follows function” in the context of gut villi
- stem cells are protected in the crypt
- easier to dispose of dead cells in lumen rather than crypt
describe our skin cells
proliferating basal cells at the bottom rise up to differentiate
top cells are superficial skin layer –> cells die and lose everything except lipids to create a seal and make us waterproof
what do we see when looking at the gut microscopically?
can see villi projections covered in dead cells, mucous, food, bacteria, fungi, viruses
what do we see when looking at the gut histologically?
villi acts as sieve
what does DAPI stain?
nuclei
what does UEA1 label?
mucous
what does DCLK label?
subset of cells that produce IL-25 to activate innate immune response
all PRR signaling pathways converge at:
MyD88 and NFkB conserved signaling pathway
describe the MyD88 and NFkB signaling pathway
MyD88 adaptor protein recruits other proteins to activate NFkB pro-inflammatory TF
if all PRR pathways converge at MyD88 and NFkB, how can we differentiate btwn diff pathogens and allow specificity? (4)
- location
- Magnitude of response
- Certain cell types mount response against certain PAMPs due to epigenetics
- Other adaptor proteins involved that activate and recruit other TFs
why doesn’t bacteria colonizing our gut just pierce thru and stimulate the immune system?
TLR signaling promotes a physical separation (“DMZ”) of the microbiota and the small intestinal surface
how did they find the DMZ?
used 16S rDNA probe to stain all bacteria –> no bacteria found at DMZ
What happened to villi in cells without MyD88 expression? Why?
no more DMZ –> bacteria directly interacting with villi
without MyD88, the signaling pathway cannot function so the cells cannot respond to bacteria
What type of cells express MyD88?
most cells but mainly innate immune cells
what did the experiment with cells lacking MyD88 indicate?
epithelial cells aren’t just a physical barrier but play a role in sensing and mounting a response
describe the CreLox mouse model used
Mouse 1: MyD88 gene flanked by loxP on either side
Mouse 2: Villin promoter driving Cre expression
Cross the mice:
- intestinal epithelial cells will activate villin promoter and therefore activate Cre expression
- Cre recombinase will cleave at loxP sites and delete MyD88
what happened to the DMZ in the mice with deleted MyD88 from CreLox system?
no more DMZ
How did they look at MyD88 gain of function?
constitutively overexpress MyD88 in Villin-expressing/intestinal epithelium cells with MyD88 deleted in all other cells
results of MyD88 gain of function experiment
DMZ is present
therefore, what is the role of MyD88
MyD88 is necessary and sufficient to limit bacterial association with the small intestine surface, i.e. create DMZ
RegIIIy in context of:
- Control, WT mice
- MyD88 KO
- MyD88 overexpression
- WT: RegIIIy expressed
- KO: no RegIIIy expression
- Overexpression: lots of RegIIIy expressed
what does RegIIIy do?
bactericidal –> pokes holes in bacteria to kill it
what happens in RegIIIy KO?
No more DMZ
what cells produce RegIIIy?
less differentiated cells make RegIIIy to protect stem cells
after all these experiments, what do we know about how the DMZ works?
DMZ is full of mucous, acting as a barrier and also holds RegIIIy bc the mucous is sticky
therefore, bacteria physically cannot reach epithelium and will be killed by RegIIIy
what is the epithelial escalator?
increased differentiation of cells as they move out of intestinal crypts / rise to outer skin layers
difference btwn gain of function and loss of function experiment –> why are they used?
use CreLox system to block gene
use transgene to induce gene
used to test if molecule or cell type is necessary and sufficient for a specific function
in addition to RegIIIy in intestinal epithelial cells, how can you test whether TLR2 in CD4+ T cells is important for gut barrier integrity?
KO TLR in CD4+ T cells to see how this changes gut barrier
are DAMPs and PAMPs sensed differently?
no –> both recognized by PRRs
how do anti-microbial proteins like RegIIIy and goblet cells work together for host defense at the intestinal barrier?
mucous forms physical barrier as viscous substance that traps RegIIIy to prevent bacterial infiltration into the gut
