3. Innate Immunity and Inflamm II Flashcards
do PRRs sense extracellular or intracellular pathogens?
both
what happens (specifically) when a TLR binds a PAMP?
TLRs interact with microbial ligand (PAMPs) through N-terminal ectodomain.
This results in TLR dimerization, recruitment of adapter proteins and other signaling molecs, leading to NK-kB translocation to the nucleus (and other impt TFs)
thus txn of proinflammatory genes, release of cytokines, and INFLAMMATION
(some TLRs also initiate phagocytosis)
what are the receptors of the innate immune response? What do they do?
PRRs:
- detect “danger” and transduce signals, eg TLRs (in cell membrane or intracellular), NODs, NLRs, RLRs (intracellular) - multiply structurally related receptors in each group that allow for detection of multiple pathogens
- phagocytic Prrs (eg mannose receptor)
- secreted PRRs activates C’ (MBL); opsonize bacteria to facilitate phagocytosis (eg acute phase reactants like MBL/mannose binding lectin, or CRP)
they can’t discriminate b/w pathogenic and non-pathogenic PAMPs
PAMPs
pathogen-associated molecular patterns
egs: LPS, lipopeptides from bacterial cell wall proteins, mycobacterial lipoarabinomannan, viral dsRNA or ssRNA, beta-glucans and mannans found in fungi, viral proteins (molecular signatures not made by mammalian cells)
alarmins
human or microbial in origin, alarm the body that something bad is going on
eg defensins, chemokines
endogenous TLR agonists: 2 examples
uric acid crystals and gout, Beta-amyloid aggregates in brain and alzheimer’s
what is the principle PAMP for gram+ bacteria?
thick peptidoglycan layer
what PRR is activated by gram+ organisms?
TLR2 (thanks to thick Peptidoglycan layer = PAMP)
what PRR is activated by gram- organisms?
TLR4 (thanks to LPS)
what is the principle PAMP for gram- bacteria?
LPS (lipopolysaccharide)
how many PAMPS are there per pathogen?
many coexisting, but usually one predominates
_____ is the only TLR that uses both the MyD88-dependent and the MyD8-independent (TRIF) signaling pathways
TLR4
how does CD14 interact with TLR4?
- LPS binding protein (LBP) extracts monomer of LPS from a micelle (PAMP from gram- bacteria) and transfers it to CD14 (a PRR)
- high affinity binding b/w CD14 and LBP causes transfer of LPS (the PAMP) to a second PRR, MD2
- MD2 binds non-covalently to TLR4, causes TLR4 dimerization
- thus induction of inflammatory mediators and uptake of organisms that contain LPS
generic model of PRR-mediated signal transduction
In general, signaling is induced as follows: the PRR is activated by its cognate ligand. Often, the receptor then recruits an “adapter” protein that facilitates the binding of a kinase. Kinase-induced phosphorylation of downstream proteins can lead to their ability to move into the nucleus and activate transcriptional events, either by acting on inactive transcriptional proteins associated with promoters (e.g. MAP kinase example) or by binding directly to the promoter region (in the case of NF-kappaB)
The outcome of an inflammatory response is mediated by the different genes that are activated transcriptionally. These reflect the specific transcription factor(s) that are activated by ligand-receptor interaction (i.e., not all ligand-receptor interactions recruit the same downstream kinases, etc. and therefore different transcriptional activators are associated with different receptor signaling pathways).
physiological consequences of LPS-macrophage interactions?
- lipid metabolites (PAF, TXA2, PGE2) regulate ability of vessel to become more porous and allow edema
- reduced oxygen species (superoxide anion, OH radical, nitric oxide) are super antibacterial
- cytokines/chemokines (TNF a, IL1B, IFN-a/B, CSFs, MCPs, MIPs) are txn regulated and induce inflammation (IFN-gamma amplifies the response)
it is critical to have a balance between pro- and anti-inflammatory mediators to achieve homeostasis. What are the physiological effects of LPS-macrophage interactions? pathological?
physiological: host immunity, adjuvant effect
pathological: circulatory collapse, multiple organ failure, shock/death (why septic people have high incidence of lethality)
____ mediate the outcome of the inflammatory process by interacting with cytokine/chemokine specific receptors that lead to intracellular signaling also.
cytokines/chemokines
local and systemic effects of IL-1B (produced strongly by classically activated macrophages)?
local: activates vascular endothelium, activates lymphocytes, local tissue destruction, increases access of effector cells
systemic: fever, production of IL-6
local and systemic effects of TNF-a (produced strongly by classically activated macrophages)?
local: activates vascular endothelium and increases vascular permeability, which leads to increased entry of IgG, complement, and cells to tissues and increased fluid drainage to lymph nodes
systemic: fever, mobilization of metabolites, shock
local and systemic effects of IL-6 (produced strongly by classically activated macrophages)?
local: lymphocyte activation, increased Ab production
systemic: fever, induces acute-phase protein production
local and systemic effects of CXCL8 (produced strongly by classically activated macrophages)?
local: chemotactic factor recruits neutrophils, basophils, and T cells to site of infection
local and systemic effects of IL-12 (produced strongly by classically activated macrophages)?
local: activates NK cells, induces the differentiation of CD4 T cells into Th1 cells
what are acute phase reactants?
APR, produced to help resolve inflammation (need a way to turn it off)
IL-6 action, induced by LPS, on liver cells
bacteria induce macrophages to produce IL-6 which acts on hepatocytes to induce the synthesis of acute-phase proteins (like CRP or mannan binding lectin)
C reactive protein
(CRP, an acute phase reactant) is used clinically as a surrogate measurement of inflammation in people - can bind to bacteria and facilitate uptake by phagocytes (OPSONIZATION), and activates C’
mannan-binding lectin
(an acute phase reactant) activates C’ after binding to mannose on the surface of microbes or facilitates phagocytosis
are TLRs extracellular or intracellular?
both
how many PAMPS does each TLR recognize?
multiple
what follows interaction of TLR with PAMP and results in signaling?
dimerization
the ectodomain of TLRs is rich in which aa?
leucine
which TLR is the only TLR that only activates the endosome TRIF pathway?
TLR3
how do TLRs diversify their signaling?
by using different adapter molecs that activate distinct signaling pathways
dsRNA is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: replicating viruses
PRR: TLR3
response: Type I IFN production by infected cells
LPS is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: gram - bacterial outer membrane
pRR: CD14/TLR4 + MD-2
prinicpal innate immune response: macrophage activation (MyD88-dependent and independent pathways); cytokines
Flagellin is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: bacterial flagella
PRR: TLR5
response: epithelial cell activation, cytokines
unmethylated CpG DNA is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: bacterial DNA
PRR: TLR9
response: macrophage activation, cytokines
N-formylmethionyl peptides is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: bacterial proteins
PRR: N-formylmethionyl peptide receptors
response: neutrophil and macrophage activation, chemotaxis
mannose-rich glycans is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: microbial glycoproteins/glycolipids
PRR: mannose receptor, plasma mannose-binding lectin
response: phagocytosis, opsonization, C’ activation
phosphorylcholine is a PAMP…
source?
pRR?
prinicpal innate immune response?
source: microbial membranes
PRR: plasma C-reactive protein
response: opsonization, C’ activation
lipoproteins and peptidoglycans are PAMPs…
source?
pRR?
prinicpal innate immune response?
source: gram + bacteria
PRR: TLR2 heterodimerizes with TLR1 or TLR6
response: macrophage activation (MyD88-pathway only), cytokines
phagocytosis is accompanied by the uptake of what molecule?
oxygen
____ converts oxygen taken up by phagocytosis to superoxide anion (microbicidal). this can be converted to H2O2 by _____.
NADPH oxidase; superoxide dismutase
H2O2 is also microbicidal
what breaks down H2O2 to water?
catalase (** many pathogens make catalase to evade killing)
what does myeloperoxidase do?
in the presence of halide ions and H2O2 leads to insertion of halide ions into the bacterial cell wall and killing of the microbe by osmolar disruption
what disease is caused by NADPH-oxidase deficiency?
chronic granulomatous disease
induction of iNOS (inducible nitric oxide synthase) by classically activated macrophages leads to conversion of what?
arginine to NO - both microbicidal and tumoricidal (induced thanks to synergistic signals from IFN-gamma and LPS)
chediak-higashi syndrome
abnormal fusion of phagosomes with lysosomes; failure to kill ingested microbes; impaired MPO
LAD
leukocyte adhesion deficiency:
group of disorders where interaction of leukocytes with vascular endothelium is disrupted; due to AR mutation that results in faulty expression of CD18 are present on neutrophils and monocytes and are pivotal to attachment to endothelium for diapedesis into tissues
complement system abnormalities - C8 defic
increased frequency neisseria infection (no formation of MAC)
IRAK4 defic?
defect in a key enzyme in TLR signaling, resulting in recurrent bacterial infections (mostly Gram+)
TLR polymorphisms
increase sensitivity to certain infections
how does neisseria gonorrhoeae evade immune response?
prevents cell sloughing (increase adhesion molecs on vaginal epithelial cells)
