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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Acute versus chronic inflammation are
distinguished by the duration and the type of
infiltrating inflammatory cells
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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 nomenclature used to describe inflammation in
different tissues employs the tissue name and the
suffix -itis e.g pancreatitis meningitis pericar
ditis arthritis
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The inflammatory response consists of a vascular
and a cellular reaction
Intensive Care Med. (2004) 30 1702-1714
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Acute inflammation involves alteration of
vascular caliber following very brief
vasoconstriction (seconds), vasodilation leads to
increased blood flow and blood pooling creating
redness and warmth (rubor and calor) changes of
microvasculature increased permeability for
plasma proteins and cells creating swelling
(tumor). Fluid loss leads to concentration of red
blood cells and slowed blood flow
(stasis) emigration of leukocytes from
microcirculationdue to stasis and activation
leads migration towards offending agent
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Vascular changes and fluid leakage during acute
inflammation lead to Edema in a process called
Exudation

• Transudate
• result of hydrostatic
• or osmotic imbalance
• ultrafiltrate of plasma
• Low protein content
• specific gravity lt 1.015
• Exudate
• result of inflammation
• vascular permeability
• high protein content
• specific gravity gt1.020

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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 reduced osmotic pressure in the
  vasculature
• and increased 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 (e.g burns) and can be life threatening
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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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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
Integrins
Selectins
Up-regulation of adhesion molecules on
endothelial cells is induced by an array of
inflammatory mediators such as TNF, IL-1,
histamine and others produced by tissue resident
inflammatory cells.
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Four families of adhesion molecules are involved
in leukocyte migration
Selectins E-selectin (on endothelium) P-selectin
(on endothelium platelets is preformed and
stored in Weible Palade bodies) L-selectin
(leukocytes) Ligands for E-and P-Selectins are
sialylated glycoproteins (e.g Sialylated Lewis
X) Ligands for L-Selectin are Glycan-bearing
molecules such as GlyCam-1, CD34, MadCam-1
Integrins (a b chain) Heterodimeric
molecules VLA-4 (b1 integrin) binds to
VCAM-1 LFA1 and MAC1 (CD11/CD18) b2 integrin
bind to ICAM Expressed on leukocytes
Immunoglobulin family ICAM-1 (intercellular
adhesion molecule 1) VCAM-1 (vascular adhesion
molecule 1) Are expressed on activated
endothelium Ligands are integrins on leukocytes
Mucin-like glycoproteins Heparan sulfate
(endothelium) Ligands for CD44 on leukocytes Bind
chemokines
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Specific targeting of adhesion molecules may be a
promising tool in drug development against some
chronic inflammatory diseases

• e.g Natalizumab, a monoclonal antibody to a4
  integrin chain, blocks the binding of VLA-4 to
  VCAM-1 on brain-infiltrating TH-1 cells and the
  binding of a4b7 integrin to MadCAM on
  gut-infiltrating TH-1 cells and has been
  successfully used in the treatment of MS and
  Crohns disease.
• ( the drug was transiently taken off the market
  because of safety concerns, but has recently been
  re-approved)
• Odulimomab and Efaluzimab are antibodies
  inhibiting LFA-1 and have shown promising results
  in the treatment of Psoriasis and Graft versus
  Host disease

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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)
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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Wiskott-Aldrich Syndromea defect in the
morphological response and trafficking defect of
antigen presenting cells
WAS patient leukocyte unable to respond to
chemoattractant
Normal leukocytes responding to chemoattractant
WAS Syndrome Recurrent infections Eczema
Thrombocytopenia
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While signaling of chemo-attractants induces a
morphological response and locomotion of
neutrophils, 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 C1q
collectins
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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 highly motile cells that
constitute the first line of defense of the
innate immune system
They are characterized by a high content of
granules in their cytoplasm which gave them the
name granulocytes
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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 of ingested material
  

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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 H2O-MPO-halide system is
thought to be the most efficient bactericidal
system (in vitro!!) by catalyzing the formation
of bleach (hypochlorous radical HOCL.) from
H2O2 and Cl- which kills bacteria by halogenation
or protein and lipid peroxidation Bacteriocidal
and cell degrading enzyme contents of lysosomal
granules (azurophil- and specific granules) fuse
with phagosome to form phago-lysosome
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Oxidative burst and co-lateral damage
The NADPH oxidase system is only active when the
cytosolic subunits are assembled with the
membrane bound subunits in response to leukocyte
activation. 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 deficiencies
or 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 unable to aggregate Leukocytes
unable to leave the circulatory system
Neutrophil counts are commonly twice the
normal level even without an ongoing infection
(Leukocytosis) Clinical findings History of
delayed separation of umbilical cord Severe
peridontitis 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 and therefore inability to undergo
oxidative burst and production of hydrogen
peroxide)

• 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) Fever and other clinical signs of
infection may be delayed 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 involving the hematological and
  neurological 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.
• Neutrophils of CHS patients fail to orient
  themselves during chemotaxis resulting in delayed
  diapedesis
• 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 cutaneous albinism Platelet
dysfunction and severe periodontal disease Mild
neutropenia and normal immunoglobulins
Normal PMN Abnormal PMN
NEJM Vol. 343 No 23, pp1703-1714
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Myeloperoxidase deficiency

• Most common inherited disorder of neutrophils
• Catalyzes the generation of hypochlorous acid
  (HOCL)
• A deficiency is not generally associated with
  disease(!!!!)
• Except in patients with diabetes mellitus, who
  are susceptible to disseminated Candidiasis

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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
Effector-cell-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 vascular 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 and histamine 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
H1 receptors are found on smooth muscles of
intestines, blood vessels and bronchi H2
receptors are found in gastric parietal cells,
vasculature and central nervous system H3
receptors are found in brain
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Metabolites of Arachidonic Acid (eicosanoids)

• Membrane lipids of activated cells can be
  transformed into biological active lipid
  mediators
• All mammalian cells except erythrocytes can
  produce eicosanoids
• 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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Numerous stimuli (e.g. thrombin, bradykinin,
epinephrine) activate phospoholipase A2
Cox-1 constitutively expressed Cox-2 inducible
-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 () refers
to vasoconstriction, (-) refers to vasodilation
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Eicosanoids can mediate virtually every step of
inflammation
Action Metabolite Vasoconstriction Thromb
oxane A2, Leukotrien C4, D4,
E4 Vasodilation PGI2, PGE1, PGE2,
PGD2 Increased vascul. permeab. LTC4,
LTD4, LTE4 Chemotaxis, Leuko. adhesion LTB4,
5-HETE Bronchospasm Leukotrien C4, D4,
E4 Platelet aggregation Thromboxane A2 Pain
mediation, Fever induction PGE2
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Therapeutic intervention in arachidonic acid
metabolism and mediator action
Steroids
X
Aspirin suppresses Cox-1 10-100 X more than Cox-2
Lipoxigenase inhibitors
Coxibs selective Cox-2 inhibitors
X
Leukotriene receptor antagonists
X
Predominantly Cox-1
Predominantly Cox-2
5-hydroxyperoxyeicosatetraenoic acids () refers
to vasoconstriction, (-) refers to vasodilation
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Nitric Oxide (NO) a pleitropic mediator of
inflammation

• NO was initially discovered as endothelium
  derived relaxing factor
• NO is a soluble gas
• NO is produce by many cells including
• endothelial cells
• some neurons
• phagocytes
• synthesized from L-arginine by nitric oxide
  synthase (NOS)
• Three different NOS
• endothelial eNOS neuronal nNOS
  inducible iNOS(phagocytes)

Constitutive expression
peroxynitrate
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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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Inhaled Nitric Oxide in the treatment of
Persistent Pulmonary Hypertension of the Newborn
(PPHN)
PPHN is caused by the persistence of fetal
circulation after birth with right to left
shunting of blood through fetal channels (foramen
ovale and ductus ateriosus) secondary to elevated
pulmonary vascular resistance and consequently
reduction of pulmonary blood flow
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Inhaled Nitric Oxide in the treatment of
Persistent Pulmonary Hypertension of the Newborn

• Inhaled NO relaxes pulmonary vessels and thereby
  decreases pulmonary vascular resistance
• This selectivity is the result of rapid
  hemoglobin-mediated inactivation
• Pulmonary blood flow is increased and right
  ventricular afterload is reduced

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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 and leukocytes
PAR-signaling induces Chemokines Endothelial
adhesion molecules (ICAM, VCAM) P selectin
mobilization from Weibel Palade
bodies COX-2 PAF NO
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Bi-directional relationship between coagulation
and Inflammation
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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 and
microbial surfaces
XIIa
Kinin cascade
Clotting cascade
Intrinsic pathway
Prekallikrein
Kallikrein
Acute Inflammation
PAR
Prothrombin
Thrombin
Bradykinin
HMWK
Fibrinolysis
Plasminogen
Plasmin
Fibrin
Fibrinogen
Complement
Protease activated receptors
C3a
C3
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Acute Inflammation 3Systemic effects, outcome
and termination

• Nicole Meissner Pearson

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TNF and IL-1 (and IL-6)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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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 results 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
• However, the exact mechanisms by which acute
  inflammation resolves remain still somewhat
  elusive

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Nature Immunology 2005
Lipoxins are generated from Arachidonic acid
(AA)-metabolites Resolvins are generated from
Omega-3 poly unsaturated fatty acids
Once leukocytes enter tissue they gradually
Switch their lipoxygenase-derived
AA-mediators from proinflammatory to
anti-inflammatory mediators
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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
• Bacterial pneumonia
• Peptic ulcer
• Sepsis

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Allergic Reaction with swelling of the larynx
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Pneumonia infection of the lung

• Most community acquired Pneumonias are bacterial
  of origin
• Often the infection follows a viral upper
  respiratory tract infection
• Acute bacterial pneumonias present as two
  anatomical patterns
• Bronchopneumonia
• Lobar pneumonia

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What causes the white consolidation of the
Chest-X-ray?
Normal lung histology
Pneumonia
red hepatization
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Pathological Stages of Lobar Pneumonia

• Congestion
• Lung is heavy and red due to vascular engorgement
  and intra-alveolar fluid with few neutrophils
• Red Hepatization
• Massive confluent exudation with red cells,
  neutrophils and fibrin into alveolar spaces
• Lobes are distinctly red, firm and airless, with
  liver-like consistency
• Gray Hepatization
• Follows with progressive disintegration of red
  cells and persistence of a fibrino-suppurative
  exudate resulting in grayish dry appearance
• Resolution or scarring
• Resolution due to clearance of the infection and
  enzymatic digest of exudate which can be
  reabosrbed, ingested by macrophages cleared via
  muco-cilliary escalator
• Scarring due to organization of exudate,
  infiltration of fibroblasts and deposition of
  collagen

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Gray hepatization
Red hepatization
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• Abscess formation
• is the result of a suppurative (purulent)
  necrosis of the parechyma resulting in the
  formation of one or more cavities
• it has a central necrosis, rimmed by neutrophils
  and surrounded by fibroblasts
• Occurs in the lung due to
• Aspiration of infective material
• Aspiration of gastric content
• Complication of necrotizing bacterial pneumonia
  (e.g Staphylococcus)
• Septic embolism

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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