Cell Signalling in Health and Disease Flashcards
Toll-Like Receptor Signalling
what is needed for a foreign protein to induce an immune response
an adjuvant
what is the immune system dogma
only responds to foreign molecules
what is toll-like receptor 4 activated by
lipopolysaccharides
function and description of LPS-binding protein (LBP)
is an acute-phase protein released by the liver
binds to LPS
what is the function of the LPS-LBP
transfers LPS onto CD14 on the surface of phagocytes
what occurs once LPS is bound to CD14 on phagocytes
CD14 interacts with TLR4
leads to activation of NFkappaB in the nucleus
what binds to the LPS bound TLR4
the adapter protein - Myd88
binds to the TIR domain of TLR4
what does TIR bound Myd88 accomplish
activates IRAK
IRAK phosphorylates TRAF6
what is the function of phosphorylated TRAF6
activates MAPKKK and TAK1 which become a complex
function of activated MAPKKK-TAK1
degrades IkB
leads to NFkB entry into nucleus
what are the 2 TLR4 signalling pathways
Myd88 dependent
Myd88 independent, TRIF dependent
what does TLR4 siganlling via the TRIF dependent pathway lead to
IFN-beta response
what are the general features of TLR Myd88 - dependent pathway
activated by most TLR’s
leads to activation of MAP kinases and NFkB
expression of inflammatory cytokines
up-regulation of co-stimulatory molecules and MHC on cell surface
what are the general features of the TLR Myd88-independent pathway
activated by TLR4/3
leads to activation of IRF-3 and production of type I interferon
increased co-stimulation and MHC on cell surface
expression of inflammatory cytokines
maturation of dendritic cells
what is NFkB
it is an inducible transcription factor expressed in all mammalian cells
why is NFkB usually inactive
because inhibitory transcription factors are usually bound
how is NFkB liberated and activated
phosphorylation of IkB leads to its ubiquitination
leads to release of active NFkB
what is the NFkB family composed of
5 related transcription factors:
p50
p52
RelA
c-Rel
RelB
what is required for NFkB mediated transcription
formation of heterodimers with activation domains
macrophages have stimulant-dependent responses, what is the difference in response to a LPS and glucan-beta
LPS - leads to tolerant macrophage
- desensitized/immune tolerance
-decrease in IL6/TNFalpha
glucan-beta - leads to trained macrophage
- sensitized/trained immunity
- increase in IL6/TNFalpha
how does the dose of LPS affect the macrophage response
high dose of LPS - results in tolerant macrophage
low dose - doesn’t result in tolerant macrophage
how does an LPS stimulus affect chromatin formation
leads to acetylation - subsequent loosening of chromatin for gene transcription
how does a second LPS stimulus affect chromatin formation
leads to deacetylation - no transcription
the cell has become tolerant
how can nucleic acids be a PAMP, when our own cells contain them in RNA/DNA
toll-like receptors bind to features of nucleic acid specific to microbes absent in mammalian cells
what is TLR9 specific for and why
an unmethylated CpG DNA
bacterial CpGs are unmethylated whereas mammalian CpGs are usually methylated
what does TLR3 recognise
long double stranded RNA - common in microbes, rare in mammals
what is the NOD protein structure composed of
CARD - Caspase activating and recruitment domain
NBD - nucleotide binding domain
LRR’s - leucine rich repeats
what is the difference between NOD - 1/2
NOD-1 - one CARD domain
NOD-2 - two CARD domains
what are the ligands of the NOD receptors and where are they found
peptidoglycans
found in gram+ bacteria in cell wall
also found in thin layer of periplasmic space in gram - bacteria
what do NOD1/2 receptors bind to
NOD1 - Meso-DAP domain of peptidoglycan
NOD2 - MDP domain of a peptidoglycan
how does NOD1/2 activation leads to activation of NFkB
NOD1/2 signal via serine/threonine RIP2 kinase (RICK)
RICK mediates ubiquitination of NEMO/IKKgamma
leads to activation of NFkB
besides NFkB what else does NOD signalling activate
activation of MAPK
what does LPS-TL4 signalling increased expression of NFkB lead to the increased expression of what
leads to the increased expression of NLR3P and IL-1b
what does the increased expression of NLR3P/IL-1b lead to
forms a complex with ASC - preventing the ubiquitination of ASC
what does ASC/NLR3P/IL-1b form
forms an inflammasome
NLR3P forms a star shape around stacks of ASC
what does an inflammasome form
the caspase activity
how do phagocytes sabotage TLR signalling
1 - camouflaging or changing the molecules that interact TLR
2 - interference with downstream TLR signalling
3 - hijacking lymphocytes to hide
function of the glycoprotein hemagglutinin (HA)
it is a lectin that mediates binding of the virus to target cells and entry of the viral genome
function of the glycoprotein neuraminidase (NA)
involved in the release of progeny virus from infected cells
how does neuraminidase achieve its function
cleaves the sugars that bind the mature viral particle
what is the RNA that is largely responsible for a viruses’ virulence
NS1
what do virus infected cells release to halt viral infection
IFN-alpha
IFN-beta
what is the function of IFN-alpha/beta
induces resistance to viral replication in all cells
increases MHC class I and increases antigen presentation
activate dendritic/macrophages
activate NK-cells to kill infected cells
what must be done to the CARD domain of RIG-1 for IFN induction
it must be ubiquitinated
what is responsible for ubiquitinating RIG-1
TRIM25
what is the difference between normal cells and cells infected with influenza in terms of RIG-1
in influenza infected cells the CARD domain of RIG-1 is not ubiquitinated
prevents IFN response
function of TRIM19
inhibits replication of many DNA/RNA viruses
function of TRIM5alpha
blocks replication of HIV
what is the function of TRIM21
key in initiating antibody response to influenza
outline the difference between autocrine/endocrine/paracrine function
autocrine - cell signals are expressed that effect the cell that released them
paracrine - cell signals released affect nearby cells
endocrine - cell signals released into bloodstream to effect distant cells
what does the release of IL-4 from T helper cells effect
B-cells - activation/proliferation/differentiation
thymocyte - proliferation
mast cells - proliferation
how do activated T helper cells effect macrophages
via release of IFN-gamma
what interleukins induce proliferation in B cells and what are the released from
IL-2
IL-4
IL-5
T helper cells
what does the release of IL-4 and IL-5 from Th cells to B cells cause
causes a class switch to IgE antibodies
how does IFN-gamma released from Th cells affect B-cells
inhibits class switch to IgE
how are Th cells activated
IL-12 released by macrophages
why do cytokines only effect cells in close proximity
most cytokines have a very short half-life
what is needed for cytokines to induce an effect on cells
high concentration of cytokines
may require cell-cell interaction