mediators of inflammation

Question 1

what is inflammation?

Answer 1

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

Question 2

what is the purpose of inflammation?

Answer 2

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

Question 3

what can be the consequence of unresolved inflammatory response?

Answer 3

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

Question 4

describe the steps in the process of inflammation

Answer 4

trauma => release of mediators (neuropeptides and Hsps, HMGB1, formyl-peptides)
bacterial substances themselves are also potent triggers of inflammatory response

triggers antigen-specific immunity

Question 5

what is the importance of the dendritic cell?

Answer 5

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

Question 6

what are the different possible sources of inflammatory mediators? what is the speed with which these can act

Answer 6

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)

Question 7

what are the mechanisms of action of inflammatory mediators?

Answer 7

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

Question 8

what is diapedesis?

Answer 8

passage or blood or any of its formed elements (such as leukocytes) through the intact walls of the blood vessels

Question 9

what are the steps of diapedesis of leukocytes? what types of signalling factors are involved in each step?

Answer 9

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

Question 10

what is the typical structure of integrins? what changes when its activated?

Answer 10

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

Question 11

what are some important preformed mediators?

Answer 11

histamine

seratonin

Question 12

where is histamine found?

Answer 12

synthesized and stored in mast cells in CT, adjacent to blood vessels
also in circulating basophils and platelets

Question 13

what causes histamine to be released?

Answer 13

physical stimuli
immune reactions - cross-liking of surface bound IgE
C3a and C5a (anaphylatoxins)
cytokines (IL-1, IL-8)

Question 14

what is the consequence of histamine release?

Answer 14

dilation of arterioles

increased vascular permeability of the venules (principle mediator of immediate vascular permeability)

Question 15

what receptors does histamine act on?

Answer 15

H1 receptors

Question 16

where is serotonin stored?

Answer 16

platelets

Question 17

what causes serotonin to be released?

Answer 17

platelet aggregation induced by contact with collagen, thrombin, ADP (from cells lysing/dying), Ag/Ab complexes

Question 18

what does serotonin do (in terms of immune response)?

Answer 18

similar to histamine

increased vascular permeability

Question 19

what is complement?

Answer 19

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

Question 20

what does complement do?

Answer 20

cytolysis by formation of the MAC
opsonization of foreign organisms
inflammatory manifestations
chemotaxis
anaphylatoxins
solubilization and clearance of Ab-Ag complexes

Question 21

what activates compliment?

Answer 21

ab-ag complexes (classical pathway)
surfaces of pathogens (alternative pathway)

alternative is actually probably evolutionarily older and more commonly used

Question 22

what are the steps in activation of complement cascade?

Answer 22

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

Question 23

what are the histamine dependent actions of anaphylatoxins?

Answer 23

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

Question 24

what are teh histamine-independent actions of C5a?

Answer 24

activates lipoxygenase pathway in PMN => leukotrines => increased permeability

potent chemoattractant for and activator of PMNs

increases leukocyte adhesion to endothelium

Question 25

what are the histamine-independent actions of C3b?

Answer 25

opsonizes bacteria

Question 26

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?

Answer 26

competitively inhibitis binding of factor B to cell-associated C3B

deregulated alternative pathway C3 convertase activity

compelment-mediated intravascular hemolysis - PNH

Question 27

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?

Answer 27

blocks MAC formation by blocking C7, C8 binding

deregulated MAC formation

complement-mediated intravascular hemolysis - PNH

Question 28

what is the mechanism of action of C1 inhibitor? what is the resulting complement activation abnormality? what is the associated disease of pathology?

Answer 28

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)

Question 29

what is the arachidonic acid cascade?

Answer 29

1: cell membrane phospholipids converted by phospholipases to arachidonic acid

=> eicosanoids

Question 30

how do steroids inhibit inflammation?

Answer 30

block phospholipidases in arachidonic acid cascades
glucocorticoid receptor directly binds to NF(kappa)B
glucocorticoid receptor also drives formation of I(kappa)B(alpha)

Question 31

how are prostaglandins named?

Answer 31

letter = structural features
numbers = number of double bonds

Question 32

what enzymes are tissue restricted?

Answer 32

platelets need TxA2 synthease
endothelium requires prostacyclin synthase to make PGI2
TxA2 - vasoconstriction
PGI2 - vasodilation

Question 33

what are chemokines?

Answer 33

superfamily of small proteins that activate and chemoattract leukocytes

Question 34

what are the four classes of chemokines?

Answer 34

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

Question 35

how do chemokines form a gradient?

Answer 35

released and bind to cell surface proteoglycans - immobilized - allows formation of gradient

Question 36

what type of receptors do chemokines bind to?

Answer 36

7 TM receptors - GPCR

Question 37

where is NO released from?

Answer 37

endothelial cells

Question 38

what does NO do?

Answer 38

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

Question 39

how is NO synthesized?

Answer 39

produced from L-argenine by enzyme NO synthase (NOS)

Question 40

what are the three forms of NO?

Answer 40

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

Question 41

what is the NF(kappa)B signaling pathway?

Answer 41

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

Question 42

what activates NF(kappa)B?

Answer 42

viruses
cytokines
lipopolysacchardes
chemokines
adhesion molecules

Question 43

how do TLRs act?

Answer 43

through NF(kappa)b
via NyD88 ==> phos of NF(kappa)B

Question 44

what do the different TLRs recognize?

Answer 44

3 and 9 recognize unmethylated CpG islands - because humans are normally methylated
………….

Question 45

what does aspirin do?

Answer 45

inhibits I(kappa)B kinases