mediators of inflammation Flashcards
what is inflammation?
tissue-based startle reaction to trauma
go/no-go decisions are constantly re-assessed
based on integration of molecular clues indicating tissue penetration by microbes
what is the purpose of inflammation?
molecular and cellular response to traumatic infection
recruit cells, give them instructions, send them out
liquefy the surrounding tissue to prevent microbial metastasis
induce healing of tissues damaged by trauma, pathogens, or the host’s response
what can be the consequence of unresolved inflammatory response?
mediator-induced tissue damage
aggregates of lymphocytes/macrophages = granuloma
distortion of the repair mechanisms - too much collagen => fibrosis
persistent inflammation can lead to increased proliferation of cells and production of substances that are damaging to DNA => neoplasia
describe the steps in the process of inflammation
trauma => release of mediators (neuropeptides and Hsps, HMGB1, formyl-peptides)
bacterial substances themselves are also potent triggers of inflammatory response
triggers antigen-specific immunity
what is the importance of the dendritic cell?
link between the innate and adaptive immune systems
picks up antigens but not great at presenting them until it migrates to the lymph nodes or is exposed to certain signals - matures - down-regulates phagocytic activity and up-regulates presenting functions
activates antigen-specific T-cells or T-reg cells
what are the different possible sources of inflammatory mediators? what is the speed with which these can act
1: pre-stored in cells - active when released - available within minutes - stored in granules
2: present in plasma - circulates as zymogen (needs activation = proteolytic cleavage usually)
3: needs synthesis de novo (ie gene activation) - slower to act (minutes-hours)
what are the mechanisms of action of inflammatory mediators?
1: bind to receptors on target cells (cytokine or growth factor)
2: direct enzymatic activity (eg lysosomal proteases)
3: oxidative damage (oxygen metabolites)
most short-lived and can do damage if not adequately controlled
what is diapedesis?
passage or blood or any of its formed elements (such as leukocytes) through the intact walls of the blood vessels
what are the steps of diapedesis of leukocytes? what types of signalling factors are involved in each step?
1: initial interaction: transinet adhesion ‘rolling”
2: subsequent interaction: firm adhesion
3: trans-endothelial migration - diapadesis
selectins during steps 1 and 2
integrins during steps 2 and 3
chemokines from other cells guide during steps 2 and 2
what is the typical structure of integrins? what changes when its activated?
alpha and beta segemnts
have leg, thigh, cap/head - bent over = inactive
activation by chemokines or other signals changes it from bent form to extended form - head group comes up, legs separate = activated
movement also changes - can move around more when activated
what are some important preformed mediators?
histamine
seratonin
where is histamine found?
synthesized and stored in mast cells in CT, adjacent to blood vessels
also in circulating basophils and platelets
what causes histamine to be released?
physical stimuli
immune reactions - cross-liking of surface bound IgE
C3a and C5a (anaphylatoxins)
cytokines (IL-1, IL-8)
what is the consequence of histamine release?
dilation of arterioles
increased vascular permeability of the venules (principle mediator of immediate vascular permeability)
what receptors does histamine act on?
H1 receptors
where is serotonin stored?
platelets
what causes serotonin to be released?
platelet aggregation induced by contact with collagen, thrombin, ADP (from cells lysing/dying), Ag/Ab complexes
what does serotonin do (in terms of immune response)?
similar to histamine
increased vascular permeability
what is complement?
system of proteins taht interact with one another in a highly regulated manner to provide many of the effector functions of humoral immunity and of inflammation
what does complement do?
cytolysis by formation of the MAC opsonization of foreign organisms inflammatory manifestations chemotaxis anaphylatoxins solubilization and clearance of Ab-Ag complexes
what activates compliment?
ab-ag complexes (classical pathway)
surfaces of pathogens (alternative pathway)
alternative is actually probably evolutionarily older and more commonly used
what are the steps in activation of complement cascade?
central component is C3
activation of pathways generates C3 convertase complements that activate C3 => coverts C3 into C3a and C3b (a is smaller)
C3b proteolytically cleaves C5 into C5a and C5b
C5b+C6, C7, C8, C9 => C5-9 = MAC
what are the histamine dependent actions of anaphylatoxins?
bind to mast cells and release histamine
dilation of arterioles
increased vascular permeability of the venules - histamine is the principal mediator of immediate vascular permeability
what are teh histamine-independent actions of C5a?
activates lipoxygenase pathway in PMN => leukotrines => increased permeability
potent chemoattractant for and activator of PMNs
increases leukocyte adhesion to endothelium
what are the histamine-independent actions of C3b?
opsonizes bacteria
what is the mechanism of action of decay-accelerating factor (DAF)? what is the resulting complement activation abnormality? what is the associated disease of pathology?
competitively inhibitis binding of factor B to cell-associated C3B
deregulated alternative pathway C3 convertase activity
compelment-mediated intravascular hemolysis - PNH
what is the mechanism of action of membran inhibitor of reactive lysis (MIRL)? what is the resulting complement activation abnormality? what is the associated disease of pathology?
blocks MAC formation by blocking C7, C8 binding
deregulated MAC formation
complement-mediated intravascular hemolysis - PNH
what is the mechanism of action of C1 inhibitor? what is the resulting complement activation abnormality? what is the associated disease of pathology?
SERPIN: binds to active forms of C1 (C1r, C1s)
deregulated classical pathway C3 convertase activity
=> acute, intermittent attacks of skin and mucosal edema = HANE (hereditary angioneurotic edema)
what is the arachidonic acid cascade?
1: cell membrane phospholipids converted by phospholipases to arachidonic acid
=> eicosanoids
how do steroids inhibit inflammation?
block phospholipidases in arachidonic acid cascades
glucocorticoid receptor directly binds to NF(kappa)B
glucocorticoid receptor also drives formation of I(kappa)B(alpha)
how are prostaglandins named?
letter = structural features numbers = number of double bonds
what enzymes are tissue restricted?
platelets need TxA2 synthease
endothelium requires prostacyclin synthase to make PGI2
TxA2 - vasoconstriction
PGI2 - vasodilation
what are chemokines?
superfamily of small proteins that activate and chemoattract leukocytes
what are the four classes of chemokines?
1: CXC (alpha) - have one AA separating first two conserved Cys residues
2: C-C (beta) - two Cys are adjacent
3: C (gamma)
4: CxxxC
note: x’s indicate AA that are not cystine
C = cysteine
each has its own specific receptor group based on the cysteine order on the end
how do chemokines form a gradient?
released and bind to cell surface proteoglycans - immobilized - allows formation of gradient
what type of receptors do chemokines bind to?
7 TM receptors - GPCR
where is NO released from?
endothelial cells
what does NO do?
potent vasodilator
acts as local paracrine factor
extremely short-lived
forms adducts with thiol groups on proteins (s-nitrosoproteins)
may be important in function of hemoglobin
how is NO synthesized?
produced from L-argenine by enzyme NO synthase (NOS)
what are the three forms of NO?
constitutive: eNOS, n-NOS - low levels, Ca activated
inducible: iNOS - requires de novo synthesis - no Ca needed
important for host defense: reactive species have potent anti-microbial activity, particularly for killing of intracellular bacteria
what is the NF(kappa)B signaling pathway?
heterodimer of P50 and P65
bound to I(kappa)b(alpha) is bound to this heterodimer and sits in cytoplasm
activation of I(kappa)b kinase phosphorylates I(kappa)b(alpha) => Ikappab alapha releases, is ubiquinated, degraded
NF(kappa)B can now move to the nucleus and act as a transcription factor
what activates NF(kappa)B?
viruses cytokines lipopolysacchardes chemokines adhesion molecules
how do TLRs act?
through NF(kappa)b via NyD88 ==> phos of NF(kappa)B
what do the different TLRs recognize?
3 and 9 recognize unmethylated CpG islands - because humans are normally methylated
………….
what does aspirin do?
inhibits I(kappa)B kinases
