Acute inflammation Chemical mediators and outcome

1. Possible outcomes of acute
inflammation
• Complete resolution
– Little tissue damage
– Capable of regeneration
• Scarring (fibrosis)
– In tissues unable to regenerate
– Excessive fibrin deposition organized into
fibrous tissue

2. Outcomes (cont’d)
• Abscess formation occurs with some
bacterial or fungal infections
• Progression to chronic inflammation
(next)

3. Morphology of acute inflammation
• Pseudomembranous infla.-due to toxins of
diphtheria or irritant gases.
• Ulcer- in stomach, duodenum, inte.
• E.g. typhoid, inte. Tb, bacillary & amoebic
dysentry
• Suppuration(abscess) e.g.- boil, carbuncle
• Cellulitis- diffuse inflammation of soft tissue.
• Bacterial infection of blood- bacteremia,
septicemia, pyemia

4. Different morphological patterns of acute inflammation can be found
depending on the cause and extend of injury and site of inflammation
Serous inflammation
Fibrinous inflammation
Purulent inflammation
ulcers

5. Chemical mediators
Cell derived
• Vasoactive amines
• Arachidonic acid metabolites ( Eicosanoids)
• Via cyclo-oxygenase pathway- PG, thromboxane A2, prostacyclins,
resolvins
• Via lipo-oxygenase pathway- 5-HETE, leucotrines,lipoxins
• Lysosomal components
• PAF
• Cytokines- IL1,TNF- α, TNF-β, IFN-‫ץ‬, chemokines
• Free radicals-Oxygen metabolites, NO
Plasma derived
• Kinin system
• Clotting system
• Fibrinolytic system
• Complement system

6. general principles of production and actions.
• Mediators are generated either from cells or from plasma
proteins.
1.Cell-derived mediators are normally sequestered in
intracellular granules and can be rapidly secreted by
granule exocytosis (e.g., histamine in mast cell granules) or
are synthesized de novo (e.g., prostaglandins, cytokines) in
response to a stimulus.
2.The major cell types are platelets, neutrophils,
monocytes/macrophages, and mast cells, mesenchymal
cells (endothelium, smooth muscle, fibroblasts) and most
epithelia can also be induced to elaborate some of the
mediators.

7. 3. Plasma-derived mediators (e.g., complement
proteins, kinins) are produced mainly in the liver
and present in the circulation as inactive
precursors that must be activated, usually by a
series of proteolytic cleavages, to acquire their
biologic properties.
• One mediator can stimulate the release of other
mediators.e.g. the cytokine TNF acts on
endothelial cells to stimulate the production of
another cytokine, IL-1, and many chemokines.
• The secondary mediators may have the same
actions as the initial mediators but may also
have different and even opposing activities

8. • Active mediators are produced in
response to various stimuli. like microbial
products, substances released from
necrotic cells, and the proteins of the
complement, kinin, and coagulation
systems, which are themselves activated
by microbes and damaged tissues.

9. • Mediators vary in their range of cellular targets.
They can act on one or a few target cell types,
can have diverse targets, or may even have
differing effects on different types of cells.

10. • Once activated and released from the cell, most
of these mediators are short-lived.
a.They quickly decay (e.g., arachidonic acid
metabolites) or
b. are inactivated by enzymes (e.g., kininase
inactivates bradykinin), or
c. they are otherwise scavenged (e.g., antioxidants
scavenge toxic oxygen metabolites) or inhibited
(e.g., complement regulatory proteins break up
and degrade activated complement
components).

12. Cell derived
• Vasoactive amines
 Histamine
 Serotonin
• Lysosomal
components
• Platelet activating
factor
• Cytokines
• Chemokines
• Neuropeptides
• Neuropeptides
• Free radicals
• AA metabolites
• NO

13. Histamine and Serotonin
induce 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
• Mast cells are very important effector cells in hypersensitivity reactions
(anaphylactic reactions)

15. Histamine
• Histamine is present in mast cell granules and is
released by mast cell degranulation in response to a
variety of stimuli,
(1) physical injury such as trauma, cold, or heat;
(2) binding of antibodies to mast cells, which underlies
allergic reactions
(3) fragments of complement called anaphylatoxins (C3a
and C5a);
(4) histamine-releasing proteins derived from leukocytes;
(5) neuropeptides (e.g., substance P); and
(6) cytokines (IL-1, IL-8).

16. Histamine
• Histamine causes dilation of arterioles and
increases the permeability of venules.
• the principal mediator of the immediate
transient phase of increased vascular
permeability, producing interendothelial gaps in
venules.

17. serotonin
• release of PAF (platelet activating factor) leads to
serotonin and histamine release from activated platelets
• Serotonin (5-hydroxytryptamine) is a preformed
vasoactive mediator
• It is present in platelets and certain neuroendocrine
cells, e.g. in the gastrointestinal tract,
• Release of serotonin (and histamine) from platelets is
stimulated when platelets aggregate after contact with
collagen, thrombin, adenosine diphosphate, and antigen
antibody complexes.
• Thus, the platelet release reaction, which is a key
component of coagulation, also results in increased
vascular permeability. This is one of several links
between clotting and inflammation.

18. Lysosomal components
• Neutrophils have two main types of granules.
• The smaller specific ( secondary) granules
contain lysozyme, collagenase, gelatinase,
lactoferrin, plasminogen activator, histaminase,
and alkaline phosphatase.
• The larger azurophil ( primary) granules
contain myeloperoxidase, bactericidal factors
(lysozyme, defensins), acid hydrolases, and a
variety of neutral proteases (elastase, cathepsin
G, nonspecific collagenases, proteinase 3)

19. Lysosomal components
Granules of monocytes& tissue macrophage-
• more active in chronic inflammation ,
• release of acid proteases, collagenase, elastase,
phospholipase, and plasminogen activator etc.

20. • Acid proteases degrade bacteria and debris within the
phagolysosomes, in which an acid pH is readily reached.
• Neutral proteases are capable of degrading various
extracellular components, such as collagen, basement
membrane, fibrin, elastin, and cartilage, resulting in the
tissue destruction
• Neutral proteases can also cleave C3 and C5
complement proteins directly, releasing anaphylatoxins,
and release a kinin-like peptide from kininogen.
• Neutrophil elastase degrade virulence factors of
bacteria and thus combat bacterial infections.

21. • Because of the destructive effects of lysosomal
enzymes, the initial leukocytic infiltration, if unchecked,
can potentiate further inflammation and tissue damage.
• These harmful proteases are held in check by a system
of antiproteases in the serum and tissue fluids.
• E.g. α1-antitrypsin, which is the major inhibitor of
neutrophil elastase
• α2-Macroglobulin is another antiprotease found in serum
and various secretions.

22. Platelet activating factor
• released from IgE sensitised basophils or mast cells ,
neutrophils,other leucocytes, endothelium, platelets
• Actions-
 platelet aggregation, release reaction
 Vasodilatation in low conc., vasoconstriction otherwise
 Increased vascular permeability,
 adhesion of leucocytes to endothelium.
 Chemotaxis
 Bronchoconstriction
 Increase O2 production (oxidative burst) & degranulation
in macrophage.
 boosts the synthesis of other mediators, particularly
eicosanoids, by leukocytes and other cells

23. Cytokines
• Cytokines are proteins produced by many cell
types (activated lymphocytes and macrophages,
endothelial, epithelial, and connective tissue
cells) that modulate the functions of other cell
types
• TABLE

25. TNF & IL1
• In endothelium they induce a spectrum of changes
referred to as endothelial activation
a) they induce the expression of endothelial adhesion
molecules;
b) synthesis of chemical mediators, including other
cytokines, chemokines, growth factors, eicosanoids, and
NO;
c) production of enzymes associated with matrix
remodeling; and
d) increases in the surface thrombogenicity of the
endothelium
e) TNF also augments responses of neutrophils to other
stimuli such as bacterial endotoxin.

26. • TNF also regulates energy balance by
promoting lipid and protein mobilization and by
suppressing appetite.
• sustained production of TNF leads to cachexia,
a pathologic state characterized by weight loss
and anorexia that accompanies some chronic
infections and neoplastic diseases

27. Chemokines
• Chemokines are a family of small (8 to 10 kD)
proteins that act primarily as chemoattractants for
specific types of leukocytes
• classified into four major groups
1. C-X-C chemokines (α chemokines)-
• e.g. IL-8 -secreted by activated macrophages,
endothelial cells, and other cell types by microbial
products and other cytokines, mainly IL-1 and
TNF.
• causes activation and chemotaxis of neutrophils,
with limited activity on monocytes and eosinophils.

28. 2. The C-C chemokines, (β chemokines) -e.g.
a.monocyte chemoattractant protein (MCP-1),
b. eotaxin,
c.macrophage inflammatory protein-1α (MIP-1α),
d.RANTES (regulated and normal T-cell expressed
and secreted),
•generally attract monocytes, eosinophils,
basophils, and lymphocytes but not neutrophils.
•eotaxin selectively recruits eosinophils.

29. 3. C chemokines (γ chemokines)-
• e.g., lymphotactin- are relatively specific for
lymphocytes
4. CX3C chemokines –
• E.g. fractalkine-exists in two forms:
• the cell surface-bound protein can be induced on
endothelial cells by inflammatory cytokines and
promotes strong adhesion of monocytes and T cells,
• a soluble form, derived by proteolysis of the membrane-
bound protein, has potent chemoattractant activity for the
same cells.

30. Chemokines have two main functions:
1. they stimulate leukocyte recruitment in
inflammation and
2.control the normal migration of cells
through various tissues

31. Other Cytokines in Acute Inflammation.
• IL-6, made by macrophages and other
cells, is involved in local and systemic
reactions
• IL-17, produced mainly by T lymphocytes,
promotes neutrophil recruitment

32. Neuropeptides
• Neuropeptides are secreted by sensory nerves
and various leukocytes, and play a role in the
initiation and propagation of an inflammatory
response
• The small peptides, such as substance P and
neurokinin A, produced in the central and
peripheral nervous systems
• Substance P has many biologic functions, like
the transmission of pain signals, regulation of
blood pressure, stimulation of secretion by
endocrine cells, and increasing vascular
permeability

33. Free radicals
• Oxygen metabolites- superoxide oxygen, H2O2,
OH & toxic NO products
• Actions-
• endo. cell damage & thereby increased vascular
permeability
• Activation of protease & inactivation of anti-
protease causing tissue matrix damage
• Damage to other cells
• These actions are counteracted by antioxidants
present in tissue & serum.

34. • the physiologic function of these ROS in leukocytes is to
destroy phagocytosed microbes, but release of these
potent mediators can be damaging to the host .
• They are implicated in the following responses in
inflammation:
• Endothelial cell damage, with resultant increased
vascular permeability. Adherent neutrophils, when
activated, not only produce their own toxic species but also
stimulate production of ROS in the endothelial cells.
• Injury to other cell types (parenchymal cells, red
blood cells).
• Inactivation of antiproteases, such as α1-antitrypsin.
This leads to unopposed protease activity, with
increased destruction of extracellular matrix. In the lung,
such inhibition of anti-proteases contributes to
destruction of elastic tissues, as in emphysema

35. • Serum, tissue fluids, and host cells possess antioxidant
mechanisms that protect against these potentially
harmful oxygen-derived radicals.
(1) the enzyme superoxide dismutase, which is found in or
can be activated in a variety of cell types;
(2) the enzyme catalase, which detoxifies H2O2;
(3) glutathione peroxidase, another powerful H2O2
detoxifier;
(4) the copper-containing serum protein ceruloplasmin;
(5) the iron-free fraction of serum transferrin.
• Thus, the influence of oxygen-derived free radicals in
any given inflammatory reaction depends on the balance
between production and inactivation of these metabolites
by cells and tissues.

36. 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

37. Arachidonic Acid (eicosanoids)
• AA is a 20-carbon polyunsaturated fatty acid (5,8,11,14-
eicosatetraenoic acid) derived from dietary sources or by conversion
from the essential fatty acid linoleic acid.
• It does not occur free in the cell but is normally esterified in
membrane phospholipids.
• Mechanical, chemical, and physical stimuli or other mediators (e.g.,
C5a) release AA from membrane phospholipids through the action
of cellular phospholipases, mainly phospholipase A2.
• AA-derived mediators, (eicosanoids,) are synthesized by two major
classes of enzymes: cyclooxygenases (which generate
prostaglandins) and lipoxygenases (which produce leukotrienes and
lipoxins)
• Eicosanoids bind to G protein–coupled receptors on many cell types
and can mediate virtually every step of inflammation

40. • Prostaglandins (PGs) are produced by mast
cells, macrophages, endothelial cells, and many
other cell types, and are involved in the vascular
and systemic reactions of inflammation
• They are produced by the actions of two
cyclooxygenases COX1 & COX2.
• TxA2 -platelets contain the enzyme
thromboxane synthetase, TxA2 is the major
product in these cells. TxA2, a potent platelet-
aggregating agent and vasoconstrictor,
• is itself unstable and rapidly converted to its
inactive form TxB2

41. • prostacyclin (PGI2)-Vascular endothelium possesses
prostacyclin synthetase, which leads to the formation of
prostacyclin (PGI2) and its stable end product PGF1α.
• Prostacyclin is a vasodilator, a potent inhibitor of platelet
aggregation and markedly potentiates the permeability-
increasing and chemotactic effects of other mediators
• PGD2 is the major prostaglandin made by mast cells;
along with PGE2 , it causes vasodilation and increases
the permeability of post-capillary venules, thus
potentiating edema formation.
• PGD2 is a chemoattractant for neutrophils.
• PGF2α stimulates the contraction of uterine and
bronchial smooth muscle and small arterioles

42. • Leukotrienes-The lipoxygenase enzymes are
responsible for the production of leukotrienes,
which are secreted mainly by leukocytes,
• are chemoattractants for leukocytes, and also
have vascular effects.
• There are three different lipoxygenases, 5-
lipoxygenase being the predominant one in
neutrophils.
• This enzyme converts AA to 5-
hydroxyeicosatetraenoic acid, which is
chemotactic for neutrophils, and is the precursor
of the leukotrienes

43. • LTB4 is a potent chemotactic agent and
activator of neutrophils, causing aggregation and
adhesion of the cells to venular endothelium,
generation of ROS, and release of lysosomal
enzymes.
• The leukotrienes C4, D4, and E4 (LTC4, LTD4,
LTE4) cause intense vasoconstriction,
bronchospasm (important in asthma), and
increased vascular permeability.
• Leukotrienes are much more potent than is
histamine in increasing vascular permeability
and causing bronchospasm.

44. • Lipoxins are generated from AA by the lipoxygenase
pathway,
• the lipoxins are inhibitors of inflammation.
• Leukocytes, (particularly neutrophils), produce
intermediates in lipoxin synthesis, and these are
converted to lipoxins by platelets interacting with the
leukocytes.
• The principal actions of lipoxins are
a. to inhibit leukocyte recruitment and the cellular
components of inflammation.
b. inhibit neutrophil chemotaxis and adhesion to
endothelium

45. • There is an inverse relationship between
the production of lipoxin and leukotrienes,
• the lipoxins may be endogenous negative
regulators of leukotrienes and may thus
play a role in the resolution of
inflammation.

46. Eicosanoids can mediate virtually every step of
inflammation
Action Metabolite
Vasoconstriction Thromboxane 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

47. Mediator
• PGD2,PGE2
• PGF2α
• TXA2
• PGI2
• Resolvin
• LTB4
• LTC4,LTD4,
LTE4,lipoxins
Action
• Brochodilator, vasodilator,increased permeability
• Vasodilator, bronchoconstrictor
• Vasoconstrictor,bronchoconstrictor,plt.
Aggregation
• Vasodilator,bronchodilator,antiaggregating agent
• Inhibitor of pro-inflammatory cytokines
• Chemotactic, cell adherence
• Smooth muscle
constrictor,vasoconstrictor,bronchoconstrictor,
increased vas. permeability

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

49. • eNOS and nNOS are constitutively expressed at
low levels and can be activated rapidly by an
increase in cytoplasmic Ca2+.
• iNOS,, is induced when macrophages and other
cells are activated by cytokines (e.g., TNF, IFN-
γ) or microbial products.
•

52. NO has dual actions in inflammation:
• it relaxes vascular smooth muscle and promotes
vasodilation, thus contributing to the vascular reaction,
• an inhibitor of the cellular component of inflammatory
responses
• reduces platelet aggregation and adhesion
• inhibits several features of mast cell–induced
inflammation,
• inhibits leukocyte recruitment.
• NO is thought to be an endogenous mechanism for
controlling inflammatory responses.
• NO and its derivatives are microbicidal, and thus NO is a
mediator of host defense against infection

53. Plasma derived mediators of acute
inflammation
Plasma factors synthesized mainly in liver
Plasma proteins
Factor XII =
coagulation system
(Hageman factor)
activation
Kinin system
Coagulation
system
Complement
activation
C3a
C5a
C3b
C5b-C9
anaphylatoxins
opsonin
MAC

54. Complement system
• functions in both innate and adaptive immunity
for defense against microbial pathogens.
• In the process of complement activation several
cleavage products of complement proteins are
elaborated that cause increased vascular
permeability, chemotaxis, and opsonisation
• C3 and C5 can be cleaved by several proteolytic
enzymes present within the inflammatory
exudate(plasmin and lysosomal enzymes
released from neutrophils)

56. • The biologic functions of the complement system fall into
three general categories
• Inflammation. C3a, C5a, and C4a are cleavage
products of the corresponding complement components
that stimulate histamine release from mast cells and
thereby increase vascular permeability and cause
vasodilation.
• They are called anaphylatoxins because they have
effects similar to those of mast cell mediators that are
involved in the reaction called anaphylaxis
• C5a is also a powerful chemotactic agent for neutrophils,
monocytes, eosinophils, and basophils.
• C5a activates the lipoxygenase pathway of AA
metabolism in neutrophils and monocytes, causing
further release of inflammatory mediators.
•

57. • Phagocytosis- C3b and its cleavage product
iC3b (inactive C3b), when fixed to a microbial
cell wall, act as opsonins and promote
phagocytosis by neutrophils and macrophages,
which bear cell surface receptors for the
complement fragments.
• Cell lysis-The deposition of the MAC on cells
makes these cells permeable to water and ions
and results in death (lysis) of the cells.

58. Kinin-Bradykinin System
(HMWK)
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

59. Coagulation system
a 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

62. Complement System
Immune complex Mannose on microbe Microbes

64. Interaction of Kinin-, Coagulation- and
Complement system during acute inflammation
Kallikrein
HMWK
Plasminogen
Prekallikrein
Factor XII (Hageman)
XIIa
Collagen, basement membrane,
platelets and microbial surfaces
Kinin cascade Clotting cascade
Fibrinolysis
Plasmin
Complement
Bradykinin
Acute
Inflammation
Fibrin Fibrinogen
C3 C3a
Prothrombin Thrombin
PAR*
* Protease activated receptors

65. Outcome of acute inflammation
• Complete resolution
• Abscess formation (encapsulation and pus)-
• Chronic inflammation-
• Healing with scar formation- when tissue
destruction is extensive so that there is no
tissue regeneration but healing by fibrosis
occurs.
• Suppuration- pyogenic bacteria causing acute
infla. results in severe tissue necrosis, the
process progress to suppuration .

66. Fate of acute inflammation
• Resolution
• Healing
• Suppuration
• Chronic inflammation

67. Factors determining infla. responce
Involving organisms-
• Type of injury & infection
• Virulence
• Dose
• Portal of entry
• Product of organisms
Involving host
• Systemic disease
• Immune status of host
• Cong. Neutrophil defect
• Leukopenia
• Site or type of tissue involved
• Local host factors

68. • Type of exudation
• Serous
• Fibrinous
• Purulent or suppurative
• Hemorrhagic
• catarrhal

69. • Acute infla.etiologic agents removed
• if no tissue lossresolution or with tissue
loss healing by fibrosis or regeneration.
• If etiologic agent persists  chronic infla.
or discharge of pus suppuration

70. Systemic effects of acute inflammation
acute phase response
• Fever (temperature > 37.8oC or >100 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
• Lymphangitis & lymphadenitis
• Shock in severe cases

71. 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

72. 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 >25-30 x 106/ml

73. Examples of acute inflammatory diseases of
different origin
• Allergic reaction
• Bacterial pneumonia
• Peptic ulcer
• Sepsis

74. Allergic Reaction with swelling of the larynx
Or mucosa
Asthma symptoms
when affecting the lung

75. 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

76. 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

77. 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

78. 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