Acute Inflammation

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Acute Inflammation

• WWAMI lecture
• Nicole Meissner-Pearson

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Inflammation

• provoked response to tissue injury
• chemical agents
• cold, heat
• trauma
• invasion of microbes
• serves to destroy, dilute or wall off the
  injurious agent
• induces repair
• protective response
• can be potentially harmful

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Cardinal signs of (acute) inflammation

• Rubor redness
• Tumor swelling
• Calor heat
• Dolor pain
• (described by Celsus 1st. Century AD)
• Functio laesa loss of function
• (added by R. Virchow)

Cellulits acute skin infection commonly caused
by Streptococcus pyogenes or Staphylococcus aureus
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The inflammatory response consists of two main
componentsa vascular and a cellular reaction
Intensive Care Med. (2004) 30 1702-1714
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Acute inflammation involves alteration of
vascular caliber (vasodilation leads to
increased blood flow) changes of
microvasculature (increased permeability for
plasma proteins and cells) emigration of
leukocytes from microcirculation(leukocyte
activation leads to elimination of offending
agent)
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Vascular changes and fluid leakage during acute
inflammation lead to Edema in a process called
Exudation
Exudate result of inflammation high protein
and cell debris - content specific gravity
gt1.020 Transudate result of hydrostatic or
osmotic imbalance (ultrafiltrate of plasma, no
increased vascular permeability) low
protein content specific gravity lt
1.015 Pus inflammatory exudate rich in
neutrophils, debris of dead cells microbes
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Different morphological patterns of acute
inflammation can be found depending on the cause
and extend of injury and site of inflammation
Serous inflammation
Purulent inflammation
ulcers
Fibrinous inflammation
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Vascular changes play an important role during
acute inflammation

• Vasodilation, leads to increased blood flow
  causing redness and swelling
• Increased Permeability, leads to exudation of
  protein rich fluid into the extravascular space
• Concentration of red cells due to fluid loss in
  small vessels leads to increased velocity and
  stasis of the blood flow
• Leukocyte rolling, adhesion and migration leads
  to the accumulation of inflammatory cells

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Increased vascular permeability and edema a
hallmark of acute inflammation

• Leakage is restricted to venules of 20-60mm in
  diameter
• caused by endothelial gaps
• usually an immediate and transient response (30
  min.)
• Gaps occur due to contraction of e.g myosin and
  shortening of the individual endothelia cell
• loss of protein from plasma leads to edema
• due to reduces osmotic pressure in the
  vasculature
• and increases osmotic pressure in the interstitium

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• direct endothelial injury causing necrotic cell
  death will result in leakage from all levels of
  microcirculation (venules, capillaries and
  arterioles)
• This reaction is immediate and sustained
• Delayed prolonged leakage begins after 2-12 hours
  and can last several days due to thermal-, x-ray
  radiation or ultraviolet radiation (sunburn) and
  involves venules and capillaries
• Leakage from new blood vessels during tissue
  repair (angiogenesis) due to immature endothelial
  layer

All these described mechanisms may occur in one
wound
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A critical function of the vascular inflammatory
response (stasis and vascular permeability) is to
deliver leukocytes to the site of injury in order
to clear injurious agents
Neutrophils are commonly the first inflammatory
cells (first 6-24 hours) recruited to a site of
inflammation. Extravasation of leukocytes is a
coordinated event of margination rolling,
adhesion, transmigration (diapedesis) migration.
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In order for leukocytes to leave the vessel
lumen, endothelial cells need to be activated and
upregulate adhesion molecules that can interact
with complementary adhesion molecules on
leukocytes
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Four families of adhesion molecules are involved
in leukocyte migration
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Chemokines and their receptors
Chemokines are a family of low molecular weight
proteins involved in leukocyte activation and
migration. Chemokines are classified in four
distinct groups Two main groups are CXC
primarlily act on neutrophils (IL-8) CC
primarily act on macrophages, lymph., basophil
and eosinophil Chemokines signal via G-protein
coupled 7-transmembrane receptors
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Multiple chemokines may signal via the same
receptor
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Induction of adhesion molecules on endothelial
cells is induced by an array of inflammatory
mediators like TNF, IL-1, histamine and others
Chemokines produced at the site of injury (e.g
IL-8) are released and bind to heparan sulfate on
vessel wall, facilitating activation of rolling
leukocyte and firm adhesion via integrin mediated
actions
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Leukocytes follow towards the site of injury in
the tissue along a chemical gradient of
chemo-attractants in a process called
chemotaxis. Exogenous and endogenous stimuli can
act as chemoattractants Exogenous bacterial
product (e.g N-formyl- methionyl
peptides Endogenous anaphylatoxins (C5a),
leukotrienes (LTB4), chemokines (e.g IL-8)
This is not a leukocyte, however they form very
similar shapes
Most chemotactic agents signal via G-protein
coupled 7 transmembrane receptors leading to the
activation of phospholipase C resulting in
intracellular Ca2 release and activation of
small GTPases (Rac,Rho, cdc42). This leads to
actin/myosin polymerization and a morphological
response with directional filopodia formation
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Rac, Rho and cdc42 and the morphological response
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Wiskott-Aldrich Syndromea Trafficking defect of
antigen presenting cells
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While signaling of chemo-attractants induces a
morphological response and locomotion of
neuotrophils, pattern recognition receptors or
opsonin receptors induce neutrophil and
macrophage effector functions
Pattern recognition receptors recognize CD14
LPS Toll-like receptor endotoxins, CpG, dsRNA,
bacterial proteoglycans Mannose
receptor bacterial carbohydrates Scavenger
receptors lipids Opsonin-receptors recognize
CR1 complement product C3b Fcg
receptor IgG coated pathogens
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Neutrophil and macrophage effector functions
serve to eliminate pathogens and noxious
substances

• Phagocytosis of pathogens and noxious agents
• Release of bactericidal and cytoxic molecules

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Neutrophils are commonly the first effector cell
to arrive at a site of inflammation
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Neutrophils have oxidative and non-oxidative
mechanisms of killing
NADPH oxidase system, a membrane bound enzyme
complex, reduces O2 to superoxide anion (02-),
hydrogen peroxide (H2O2), and hydroxyl radical
(OH) Oxidative burst Bacteriocidal and cell
degrading enzyme contents of lysosomal granules
(azurophil- and specific granules) fuse with
phagosome to form phago-lysosome H2O-MPO-halide
system is the most efficient bactericidal system
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Phagocytosis and its outcome involves three
distinct steps

• Recognition and attachment
• Engulfment and fusion of phagosome and lysosome
• Killing and degradation mainly through the
  generation of oxygen radicals and their
  halogneation

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Phagocytosis and Oxidative burst
Inflammatory products may be released into the
extracellular space causing tissue damage and
additional disease. Release occurs transiently
during engulfing regurgitation during feeding
If material is deposited on flat membranes and
can not be removed (e.g immune complexes on
basement membrane) frustrated
phagocytosis Ingestion of membranolytic material
(urate crystals)
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Immunodeficiency Diseases caused by defects in
phagocytes (neutrophils and macrophages)
Lack of neutrophil/macrophage numbers or defect
of their function can lead to live threatening
infectious diseases, particularly with bacterial
and fungal pathogens Clinically most common
bone marrow suppression with decreased cell
numbers (leukopenia) due to tumor infiltrate or
chemotherapy resulting in myelosuppression (gt500
neutrophils /ml is considered very
severe) However, inherited defects of adhesion,
phago-lysosome- and microbicidal functions have
been found

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Leukocyte adhesion deficiency 1 and 2(LAD1/2)

• LAD 1 is a result of a lack of b2 intergrin
  expression due to defect of CD18 (LFA-1 and
  MAC-1). Interaction with ICAM and VCAM on
  endothelium is impaired
• LAD 2 results from a lack of sialyl LewisX
  (defect of carbohydrate fucosylation).
  Interaction with endothelial E-and P-selectins is
  impaired

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Leukocyte adhesion deficiencies (LAD 1 and 2)
Neutrophils are unable to aggregate Leukocytes
are unable to leave the circulatory system to
sites of inflammation Neutrophil counts are
commonly twice the normal level even without an
ongoing infection Clinical findings History of
delayed separation of umbilical cord Severe
peridonitis Recurrent bacterial and fungal
infections of oral and genital mucosa (enteric
bacteria, staph, candida, aspergillus) Infected
foci contain few neutrophils (no pus) and heal
poorly
NEJM Vol. 343 No 23, pp1703-1714
LAD 2 immunodeficiency is less severe, however
the defect is associated with growth retardation,
dysmorphy and neurological deficits
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Chronic granulomatous disease (a defect of NADPH
oxidase system)

• CGD is a heterogeneous disorder caused by defects
  of any of the four subunits of NADPH oxidase.
• 70 are due to X-linked defect of gp91 phox (more
  severe form)
• Second most due to autosomal recessive defect of
  p47 phox

NEJM Vol. 343 No 23, pp1703-1714
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Chronic granulomatous disease defect of NADPH
oxidase system
Clinical findings Recurrent infections with
catalse-positve microorganisms (S. aureus,
Burgholderia cepacia, aspergillus spec., nocardia
spec., and Serratia marrcescens) Recurrent
infections of lungs, soft tissue and other organs
(typical is infection of nares, and
gingivitis) Appearance of fever and clinical
signs of infection may be delaye Excessive
formation of granuloma in all tissues
NEJM Vol. 343 No 23, pp1703-1714
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Chediak-Higashi SyndromeDefect of the
formation and function of neutrophil granules

• CHS is an autosomal recessive disorder of all
  lysosomal granule containing cells with clinical
  features invoving the hematologic and neurologic
  system
• All cells containing lysosomes have giant
  granules.
• In neutrophils large granules result from
  abnormal fusion of azurophilic and specific
  granules and delayed fusion with phagosomes.
• Mutated gene LYST protein involved in vacuolar
  formation and transport of proteins

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Defect of the formation and function of
neutrophil granules Chediak-Higashi Syndrome
Clinical features recurrent bacterial
infections with S. aureus and beta hemolytic
streptoc. Peripheral nerve defects (nystagmus
and neuropathy) Mild mental retardation and
partial ocular and cutaneus albinism Platelet
dysfunction and severe peridonatal disease Mild
neutropenia and normal immunoglobulins
NEJM Vol. 343 No 23, pp1703-1714
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Acute Inflammation 2chemical mediators, outcome
and termination

• Nicole Meissner-Pearson

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The inflammatory response consists of two main
componentsa vascular and a cellular reaction
Intensive Care Med. (2004) 30 1702-1714
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Mediators of acute inflammation
Cellular derived factorspreformed in secretory
granules
Newly synthesized
ProstaglandinsLeukotrienesPlatelet activating
factorOxygen radicalsNOcytokines
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Mediators of acute inflammation
Plasma factors synthesized mainly in liver
Kinin system
Factor XII coagulation system (Hageman factor)
activation
Coagulation system
Plasma proteins
C3a C5a C3b C5b-C9
anaphylatoxins
Complementactivation
opsonin
MAC
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Histamine and Serotonininduce vasodilation and
increased permeability

• Mast cell
• richest source of histamine
• located in connective tissue
• adjacent to blood vessels
• Degranulation through receptors for IgE-, IgG,
  histamine, bacterial products and anaphylatoxin
  C5a, physical injury, cold, heat
• release of PAF (platelet activating factor)
  leads to serotonin release from activated
  platelets
• Mastcells are very important effector cells in
  hypersensitivity reactions (anaphylactic
  reactions)

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Further mediator release by mast cells
perpetuates acute inflammation at the site of
release
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Histamine receptors
H2 blockers more relevant in gastric ulcer
treatment
H1 blockers are used to treat allergic and
inflammatory reactions
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Metabolites of Arachidonic Acid (eicosanoids)
Membrane lipids of activated cells can be
transformed into biological active lipid
mediators. They are autocoids short-range
hormones (very short range and half-life).
Arachidonic acid is derived from conversion of
linoleic acid
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-1 , COX-2
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Distinct Prostaglandins and Leukotrienes are
derived by the action of specific enzymes on an
intermediate in the pathway and some of these
enzymes have restricted tissue distribution

5-hydroxyperoxyeicosatetraenoic acids
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Eicosanoids can mediate virtually every step of
inflammation
Action Metabolite Vasoconstriction Throm
boxane A2, Leukotrien C4, D4,
E4 Vasodilation PGI2, PGE1, PGE2,
PGD2 Increased vascul. permeab. LTC4, LTD4,
LTE4 Chemotaxis, leuko. adhesion LTB4, 5-HETE,
lipoxins Bronchospasm Leukotrien C4, D4, E4
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Therapeutic intervention in arachidonic acid
metabolism and mediator action
steroids
X
Lipoxigenase inhibitors
X
Leukotriene receptor antagonists
X
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Nitric Oxide (NO) a pleitropic mediator of
inflammation
NO was initally discovered as endothelium derived
relaxing factor NO is produce by endothelial
cells,some neurons phagocytes synthesized from
L-arginine by nitric oxide synthase (NOS) Three
different NOS Endothelial eNOSneuronal
nNOSinducible iNOS(phagocytes)
Constitutive expression
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NO modulates the inflammatory response

• No is a potent vasodilator
• Reduces platelet aggregation
• Reduces leukocyte recruitment
• Is antimicrobial

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Kinin-Bradykinin System
Bradykinin increases vascular permeability,
contraction of smooth muscles, vasodilation and
pain Kallikrein is a potent activator of factor
XII, is chemotactic and can directly convert C5
to C5a
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Coagulation systema cascade of serine proteases
Thrombin provides the main link between
coagulation and inflammation by binding to
protease activated receptors (PARs) on platelets,
endothelium and smooth muscle
PAR-signaling induces Chemokines Endothelial
adhesion molecules (ICAM, VCAM) P selectin
mobilisation from Weibel Palade
bodies COX-2 PAF NO
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Complement System
B,D,P
MBL
C1, C2, C4
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Interaction of Kinin-, Coagulation- and
Complement system during acute inflammation
Factor XII (Hageman)
Collagen, basement membrane, platelets
XIIa
Kinin cascade
Clotting cascade
Intrinsic pathway
Prekallikrein
Kallikrein
PAR
Acute Inflammation
Prothrombin
Thrombin
Bradykinin
HMWK
Fibrinolysis
Plasminogen
Plasmin
Fibrin
Fibrinogen
Complement
C3a
C3
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TNF and IL-1 two macrophage derived cytokines
mediating inflammation

• Action
• Activation of endothelium
• Priming of neutrophils
• Stimulation of inflammatory mediator release
• Induction of systemic acute phase response

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Mediators that directly or indirectly induce
vasodilation and increased permeability during
acute inflammation

• Plasmaproteins that are metabolized and activated
• Complement metabolites C3a and C5a
  (anaphylatoxins)
• Kinin system (Bradykinin)
• Coagulation factor XII (Hageman factor, activates
  Kinin system and plasmin)
• Cell derived factor that are released
• Histamine
• Serotonin
• Substance P
• PAF (Platelet-activating factor)
• Archachidonic Acid metabolites (prostaglandins,
  leukotriens)
• Nitric oxide

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Mediators that induce leukocyte activation,
adhesion and chemotaxis

• Complement factors
• C5a is a powerful chemotactic factor for all
  granulocytes and monocytes
• Kinin System
• Kallikrein has potent has chemotactic activity
  and can directly convert C5 into C5a
• Coagulation system
• Thrombin (Factor IIa) binds PAR I (protease
  activated receptor)expression adhesion
  molecules, release of chemokines, NO,
  prostaglandins
• Factor XIIa activates plasmin, which can cleave
  C3
• Cell derived factors (neutrophils, and
  macrophages)
• LTB4, 5-HETE strong neutrophil chemo- attractants
  
• TNF and IL-1 (macrophages)adhesion molecules,
  neutrophil-priming,Chemokines

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Mediators that induce opsonization and
phagocytosis

• Complement split products
• mainly C3b and iC3B and subsequent binding to CR1
• Immunoglobulins
• IgM via activation of complement cascade and
  uptake via CR1-4
• IgG and IgA via binding to antigen and uptake via
  Fcg and FcaR

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Mediators that are bacterio-/cytocidal

• Complement membrane attack complex
• Lysosomal enzymes
• NO
• Oxygen derived free radicals

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Systemic effects of acute inflammationacute
phase response

• Fever (temperature gt 37.8oC or gt100 F)
• Increased pulse, blood pressure
• Chills
• Anorexia
• Leukocytosis
• neutrophilia and left shift of neutrophils points
  to bacterial infection
• Lymphocytosis points to viral infection
• Eosinophilia point to allergy or parasitic
  infection
• Acute phase protein production in liver
• fibrinogen, CRP,SAA leads to increased ESR

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Increased Erythrocyte Sedimentation Rate as a
result of the presence of acute phase reactants
ESR rate at which erythrocytes settle out of
unclotted blood in one hour Normally,
Erythrocytes are very buoyant and settle
slowly Erythrocytes are negatively charged and
repel each other (no aggregation occurs) In
presence of acute phase reactants (fibrinogen)
erythrocytes aggregate due to loss of their
negative charge resulting in increased
sedimentation
ESR is a widely performed test to detect occult
processes and monitor inflammatory conditions
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Granulocytosis with left shift of neutrophil
population are a good indicator for a severe
bacterial infection
Leukocyte release result from a direct effect of
IL-1 and IL-6 on bone marrow neutrophil stores.
Exaggeration of this can result in a Leukemoid
reaction release of very immature precursors and
cell counts gt25-30 x 106/ml
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Termination of acute inflammation

• Eradication of an offending agent should lead to
  discontinuation of the inflammatory response
• Neutrophils have only a short life span (few
  hours -1 day)
• Most mediators are very short lived and are
  degraded immediately
• Anti-inflammatory cytokines (TGF-beta, and IL-10)
  can inhibit the production of pro-inflammatory
  cytokines (TNF)
• In Arachidonic acid metabolism, lipoxin and
  resolvins are generated that have
  anti-inflammatory activity

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Outcome of acute inflammation

• Complete restitution
• Abscess formation (encapsulation and pus)
• Chronic inflammation
• Healing with scar formation

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Examples of acute inflammatory diseases of
different origin

• Allergic reaction
• Peptic ulcer
• Bacterial pneumonia
• Sepsis

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Allergic Reaction with swelling of the larynx
www.nature.com/.../ images/nature01324-f1.2.jpg
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Bacterial pneumonia
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Peptic ulcer
An ulcer is a local defect of mucosal lining
produced by shedding of necrotic tissue Peptic
ulcers are produced by an imbalance between
gastro-duodenal defense mechanisms and the
damaging force 70 of all ulcers are due to H.
pyolri infection which initiates a strong
inflammatory response
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Septicemia with disseminated intravascular
coagulation due to Meningococcal Infection
Invasion of the bloodstream by Neisseria
meningitides leads to widespread vascular injury
with endothelial necrosis, thrombosis and
peri-vascular hemorrhage. Hemorrhage as it is
seen in the skin can occur in all organs
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