Mediators are either derived from plasma or locally produced by cells. Plasma mediators require activation to function, while cell-derived mediators are stored in granules or synthesized de novo. Most mediators bind to specific receptors on target cells and can stimulate the release of secondary mediators that amplify or counteract the initial response. Mediators have varying levels of specificity and regulation to prevent harmful effects.

2.  Mediators are derived from plasma or by local
production of cells.
 plasma derived mediators (complement
kinins,coagulation factors) are present as circulating
precursors that must be activated,usually by proteolytic
cleavage,to acquire their biological properties.
 cell-derived mediators are normally
sequestered in intracellular granules (e.g.,histamine in
mast cells) that are subsequently secreted,or are
synthesized de novo(e.g.,prostaglandins)in response to a
stimulus.

4.  Most mediators perform their biologic activity by
initially binding to specific receptors on target
cells.
 However some have direct enzymatic or toxic
activities(e.g., lysosomal proteases or reactive
oxygen species)
 Mediators may stimulate target cells to release
secondary effector molecules.These secondary
mediators may have activities similar to the initial
effector molecule,in which case they may amplify a
particular response.
 On the other hand they may have opposing
activities, and thereby function to counter-regulate
the initial stimulus.

5.  Mediators may act on only one or a very few
targets,or may have widespread activity,, and may
have widely differing outcomes depending on
which cell type they affect.
 Mediator function is generally tightly
regulated.once activated and released from the
cell,most mediators quickly decay(e.g.,AA
metabolites),are inactivated by
enzymes(e.g.,kininase inactivates bradykinin),or
are eliminated(e.g.,antioxidants scavenge toxic
oxygen metabolites).
 A major reason for the checks and balances is that
most mediators have the potential to cause harmful
effects.

6. VASOACTIVE AMINES
The two amines,
Histamine &
Serotonin
are the first mediators to be released during inflammation.
Histamine is widely distributed in tissues,
particularly in mast cells adjacent to vessels,as well as
in circulating basophils and platelets.
 Preformed histamine is present in mast cell granules
that are released in response to a variety of stimuli:

7. 1. Physical injury such as trauma and heat
2. Immune reactions involving binding of IgE
antibodies to Fc receptors on mast cells
3. C3a and C5a fragments of complement,the so called
anaphylotoxins
4. Leukocyte-derived histamine-releasing proteins

8. 5.Neuropeptides (e.g.,substance p)and
6.Certain cytokines(e.g.,IL-1andIL-8)
In humans ,histamine causes arteriolar dilation &
is the principal mediator of the immediate phase of
increased vascular permeability, causing venular
endothelial contraction and widening of the
interendothelial cell junctions.
 soon after its release, histamine is inactivated by
histaminase.

9.  Serotonin (5-hydroxytryptamine)
 - is also a preformed vasoactive mediator,with
effects similar to histamine .
 it is found primarily within platelet-dense
body granules (along with histamine,adenosine
diphosphate and calcium) and release is stimulated
by platelet aggregation.

10. PLASMA PROTEASES
Many of the effects of inflammation are mediated
by three interrelated plasma derived factors-
1. The clotting system,
2. Complement,and
3. The kinins , all linked by the initial activation of
hageman factor.

11. THE CLOTTING SYSTEM
 Is a cascade of plasma proteases,which can be
triggered by proteoytic action of activated
Hageman factor.
 Hageman factor (factor XII of the intrinsic
coagulation cascade) is a protein synthesized by
liver that circulates in an inactive form untill it
encounters collagen,basement membrane,or
activated platelets(as at a site of endothelial injury).
 Factor XII then undergoes a conformational
change(becoming factor XIIa)

12.  In the clotting system,the resultant proteolytic cascade
results in activation of thrombin (factor IIa) from
precursor prothrombin(factor II) which in turn cleaves
circulating soluble fibrinogen to generate an insoluble
fibrin clot.
 Thrombin also enhances leukocyte adhesion to
endothelium,and fibrinopeptides resulting from
fibrinogen cleavage increase vascular permeability and
are chemotactic for leukocytes.

13.  At the same time,when it is inducing clotting , it
can activate the fibrinolytic system.
 This mechanism is to counterregulate clotting
by causing further cleavage of the fibrin
molecule to fibrin split products.

14.  Without fibrinolysis, initiation of the coagulation
cascade ,even by trivial injury, would result in
continuous and irrevocable clotting of the
entire vasculature
 In addition it contributes to the vascular
phenomenon of inflammation
 Plasminogen activator (released from
endothelium, leukocytes, and other tissues)
cleaves plasminogen, a plasma protein bound
up in the evolving fibrin clot.

15.  This generates plasmin, a protease that
degrades fibrin to fibrin split products and is
therefore important in lysing fibrin clots.
 Fibrin split products also increase vascular
permeability,while plasmin cleaves the
complement C3 component to C3a,resulting in
vasodilation and increased vascular
permeability.

16.  Kinin system activation leads ultimately to the
formation of bradykinin from its circulating
precursor,high molecular weight kininogen(HMWK).
 Like histamine ,bradykinin causes increased vascular
permeability,arteriolar dilation, and extravascular
smooth muscle contraction(e.g.,in bronchial smooth
muscle )
 It also causes pain when injected into the skin.
 It is short lived because it is rapidly inactivated by
kininases.

18. COMPLEMENT SYSTEM
 Consists of a cascade of plasma proteins that play an
important role in both immunity and inflammation .
 They function in immunity by ultimately generating a
porelike membrane attack complex(MAC).
 In the process of generating the MAC ,a number of
complement fragments are produced e.g. C3b opsonins.

19.  Complement components (C1 to C9) are present in
plasma.
 The most critical step in the elaboration of the biologic
functions of complement is the activation of the third
component,C3.
 C3 cleavage can occur
1. via the classic pathway,triggered by fixation of C1 to
antigen-antibody complexes.
2. Through the alternative pathway,triggered by bacterial
polysaccharides, or aggregated IgA.The alternative
pathway involves a distinct set of serum components,
including properdin and factors B and D.

20. 3.C3 convertase cleaves C3 to C3a and C3b.
4.C3b then binds to the C3 convertase complex to form C5
convertase.
5.This complex cleaves C5 to generate C5a and initiate the
final stages of assembly of the C5a to C9MAC

21. The various effects of the complement
derived mediators in acute inflammation :
 Vascular effects: C3a and C5a (anphylotoxins) increase
vascular permeability and cause vasodilation by
inducing mast cells to release their histamine.C5a also
activates the lipoxygenase pathway of AA metabolism
in neutrophils and monocytes

22.  Leukocyte activation,adhesion and chemotaxis:C5a
activates leukocytes and increases the avidity of
their integrins ,thereby increasing adhesion to
endothelium
 Phagocytosis when fixed to to a microbial
surface,C3b and C3bi act as opsonins,augmenting
phagocytosis by cell bearing C3b receptors.
 The significance of C3 and C5 is further increased
by the fact that they can also be activated by the fact
that they can also be activated by proteolytic
enzymes present within the inflammatory exudate.

24. ARACHIDONIC ACID METABOLITES
(EICOSANOIDS):PROSTAGLANDINS AND
LEUKOTRIENES
 Arachidonic acid is a 20 C polyunsaturated fatty acid
derived primarily from linoleic acid present in the body in
the cell membrane phospholipids.
 It is released from these phospholipids via cellular
phospholipases that have been activated by
mechanical,chemical or physical stimuli or by
inflammatory mediators such as C5a.

25.  AA metabolism proceeds along one of two major
pathways
 Are named for the enzymes that initiate the
reactions
1. Cycloxygenase pathway
2. Lipoxygenase pathway

26. CYCLOXYGENASE PATHWAY
 Include PGE2,PGD2,PGF2α,PGI2
(PROSTACYCLIN) each of which is derived by
the action of specific enzyme
 Some of these enzymes have a restricted tissue
distribution.
 E.g. platelets contain the enzyme thromboxane
synthetase, and hence TXA2,a potent platelet
aggregating agent and vasoconstrictor, is the major
prostaglandin product in these cells.

27.  Endothelium,on the other hand, lacks thromboxane
synthetase but possess prostacyclin synthetase,which
leads to the formation of PGI2,a vasodilator and a potent
inhibitor of platelet aggregation.
 PGD2 is the major metabolite of the cycloxygenase
pathway in mast cells;along with PGE2 and
PGF2α(which are most widely distributed), it causes
vasodilatation and causes edema formation.
 Recent studies revealed that there are two forms of
cycloxygenases(COX), called COX1 and COX2 .

28.  COX1 is expressed in gastric mucosa.
 At this site the mucosal prostaglandins generated by the
actions of COX1 are protective because they prevent the
acid induced damage.
 While inhibition of cycloxygenases by aspirin and
NSAID reduces inflammation by blocking prostaglandin
synthesis,these drugs also predispose to gastric
ulceration.
 To preserve the anti-inflammatory effects and prevent
the harmful effects on the gastric mucosa,several highly
selective COX2 inhibitors are being developed.

29. LIPOXYGENASE PATHWAY
 5 Lipoxygenase is the predominant AA
metabolizing enzyme in neutrophils, and the
products of its actions are the best characterized.
 The 5-hydroxyperoxy derivative of AA,5-HPETE,
is quite unstable and is either reduced to 5-HETE
or converted to leukotrienes.
 The first leukotriene generated from 5-HPETE is
called leukotriene A4(LTA4),which in turn gives rise
to LTB4 or LTC4

30.  LTB4 is a chemotactic agent and causes aggregation
of neutrophils.
 LTC4 and its subsequent metabolites LTD4 and
LTE4,cause vasoconstriction, bronchospasm, and
increased vascular permeability.

31. CLINICAL UTILITY
 The fact that eicosanoids hold a central role in
inflammatory processes is borne out by the clinical
anti-inflammatory utility of agents that suppress
cycloxygenase activity (e.g.,aspirin and NSAIDs).
 Glucocorticoids, which are powerful anti-
inflammatory agents,may act in part by inhibiting
the activity of phospholipase A2.

33. PLATELET ACTIVATING FACTOR
 Originally named for its ability to aggregate
platelets and cause degranulation.
 PAF is phospholipid derived mediator.
 Formally PAF is acetyl glycerol ether
phosphocholine.
 It is derived from the membrane phospholipids of
neutrophils, monocytes, basophils, endothelium,
and platelets by the action of phospholipids A2.

34.  Besides platelet stimulation PAF causes
vasoconstriction and bronchoconstriction.
 It is 100-10,000 times more potent than histamine
in inducing vasodilation and increased vascular
permeability.
 PAF also causes enhanced leukocyte adhesion (via
integrin conformational changes),
chemotaxis,leukocyte degranulation, and the
oxidative burst.

35.  PAF also stimulates the synthesis of other
mediators,particularly eicosanoids.

36. CYTOKINES
 Cytokines are polypeptide products of many cell
types(but principally activated lymphocytes and
macrophages) that modulate the function of other
cell types.
 Cytokines can act
 On the same cell (autocrine effect),
 On other cells in the immediate vicinity(paracrine
effect), or
 Systemically (endocrine effect)

37.  Historically associated with cellular immune
responses,various cytokines, in particular (IL-1),
(TNF-α and –β), (INF-ᵧ), and the chemokines,have
additional effects that are important in the
inflammatory response
 These cytokines can exert local effects on
endothelium, leukocytes, and fibroblasts, as well as
induce systemic acute-phase reactions.

39. NITRIC OXIDE AND OXYGEN DERIVED
FREE RADICALS
 NO is a short acting, soluble free radical gas
produced by a variety of cells.
 In the CNS, it regulates neurotransmitter release, as
well as blood flow.
 Macrophages use it as a cytotoxic metabolite for
microbes and tumor cells.
 When produced by endothelium(EDRF or
endothelium-derived relaxation factor),it activates
guanylyl cyclase in vascular smooth
muscle,resulting in increased cGMP and ultimately
smooth muscle relaxation(vasodilation).

40.  Since the half life of NO is measured in seconds, it
can affect only those cells in near proximity to the
source where it is generated.
 Moreover, the short half life of NO dictates that its
effects are regulated primarily by the rate of
synthesis.

42. NO plays multiple roles inflammation,including
1. Vascular smooth muscle relaxation(vasodialation)
2. Antagonism of all stages of platelet
activation(adhesion,aggregation,and degranulation), and
3. Acting as a microbicidal agent(with or without
superoxide radicals) in activated macrophages

43.  OXYGEN DERIVED FREE RADICALS are
synthesized via the NADPH oxidase pathway
and are released from neutrophils and
macrophages after stimulation by chemotactic
agents, immune complexes, or phagocytic
activity
 Superoxide is subsequently converted to H2O2,
OH- And toxic NO derivatives.
 These shortlived mediators have been
implicated in a variety of tissue
injuries,including

44. 1. Endothelial damage, with thrombosis and
increased permeability;
2. Protease activation and antiprotease inactivation,
with a net increase in breakdown of the
extracellular matrix;and
3. Direct injury to other cell types(e.g.,tumor
cells,erythrocytes,parenchymal cells).
4. Fortunately, a variety of antioxidant protective
mechanisms (e.g, catalase, superoxide dismutase,
and glutathione) are present in tissues and serun to
minimize the toxicity of the oxygen metabolites.

45. LYSOSOMAL CONSTITUENTS
 The lysosomal granules of neutrophils and
monocytes contain a number of molecules that can
potentially act as mediators of acute inflammation.
 They may be released after cell death , by leakage
during the formation of the phagocytic vacuole, or
by frustrated phagocytosis against large surfaces.
 While acid proteases have acidic pH optima and are
generally active only within phagolysosomes,
neutral proteases, including enzymes such as
elastase,collegenase, and cathepsin,are active in the
extracellular matrix and cause
destructive,deforming tissue injury by degrading
elastin,collagen,basement membrane, and other
matrix proteins.

46.  Neutral proteases can also cleave C3 and C5
directly to generate the C3a and C5a
anaphylotoxins, and can promote the generation
of bradykinin like peptides from kininogen.
 Thus if the initial leukocyte infiltration is left
unrestrined,substantial vascular permeability
and tissue damage may result .
 These effects are checked, however,by a series
of antiproteases present in the serum and
extracellular matrix

47. MOST LIKELY MEDIATORS IN
INFLAMMATION
Vasodilation
 Prostaglandins
 Nitric oxide
Increased vascular permeability
 Vasoactive amines
 C3a and C5a
 Bradykinin
 Leukotrienes C4,D4,E4
 PAF

48. Chemotaxis and leukocyte activation
 C5a
 Leukotriene B4
 Bacterial products
 Chemokines (e.g:IL8)
Fever
 IL-1,IL-6,TNF-α
 PG
Pain
 PG’s
 bradykinin

49.  Tissue damage
 Neutrophil and macrophage lysosomal enzymes
 Oxygen metabolites
 Nitric oxide

50. OUTCOMES OF ACUTE INFLAMMATION
 Complete resolution
 Scarring or fibrosis
 Abscess formation
 Progression to chronic inflammation

51. CHRONIC INFLAMMATION
 Chronic inflammation is characterized by:
 Infiltration with mononuclear cells including
macrophages, lymphocytes, and plasma cells.
 Tissue destruction
 Repair involving new vessel
proliferation(angiogenesis) and fibrosis.

52.  Chronic inflammation can be considered to be
inflammation of prolonged duration(weeks to
months to years) in which active inflammation
,tissue injury , and healing proceed simultaneously
 Chronic inflammation may follow acute
inflammation.
 This transition occurs when the acute response
cannot be resolved,either because of the persistence
of the injurious agent or because of interference in
the normal process of healing

53.  For e.g., a peptic ulcer of the duodenum initially
shows acute inflammation followed by the
beginning stages of resolution.
 However recurrent bouts of duodenal epithelial
injury interrupt this process and result in a lesion
characterized by both acute and chronic
inflammation.
 Alternatively, some forms of injury (e.g.,viral
infections) engender a response that involves a
chronic inflammation esentially from the
beginning.
 Although the injurious agents mediating chronic
inflammation may be less noxious than those that
cause acute inflammation, the overall failure to
resolve the process may lead to substantially more
long term injury.

54.  Fibrosis –the proliferation of fibroblasts and
accumulation of excess extracellular matrix-is also a
common feature of many chronic inflammatory diseases
and is an important cause of organ dysfunction.
 Chronic inflammation arises in the following settings.
1. Persistent infections,most characteristically by a set of
microorganisms including mycobacteria,treponema
pallidum and certain fungi.
These organisms are of low direct pathogenicity ,
but typically evoke an immune response called
DELAYED HYPERSENSITIVITY that may culminate
in a granulomatous reaction.

55. 2. Prolonged exposure to potentially toxic agents.e.g.
nondegradable exogenous material such as inhaled
particulate silica, which can induce a chronic
inflammatory response in the lungs(silicosis)
3.Autoimmune diseases, in which individual develops
an immune response to self antigens and tissues.

56.  CHRONIC INFLAMMATORY CELLS
1. Macrophages, are but one component of the
mononuclear phagocyte system, consisting of
closely related cells of bone marrow origin,
including the circulating blood monocytes, and
tissue macrophages.
2. Macrophages are diffusely scattered in connective
tissues, or clustered in organs such as the
liver(kupffer cells),spleen and lymph nodes (sinus
histiocytes),central nervous system(microglia),
and lungs (alveolar macrophages).

57. The half life of circulating monocytes is about 1 day
Under the influence of adhesion molecules and chemotactic
factors, they begin to emigrate at a site of injury within
the first 24 to 48 hours after onset of acute inflammation.
When monocytes reach the extravascular tissue, they
undergo transformation into larger phagocytic cells
called macrophages.
Macrophages may also become activated, a process
resulting in increased cell size, increased content of
lysosomal enzymes, more active metabolism, and
greater ability to kill ingested microorganisms.

58.  Activation signals include cytokines secreted by
sensitized T lymphocytes, bacterial endotoxins,
various mediators produced during acute
inflammation, and extracellular matrix proteins
such as fibronectin.

59. After activation, macrophages produce a wide
variety of biologically active products-
1. Acid and neutral proteases
2. Complement components and coagulation factors
3. Reactive oxygen species and NO
4. Eicosanoids
5. Cytokines such as IL-1 and TNF

61.  At the site of acute inflammation, where the irritant
is removed and the process is resolved,
macrophages eventually die or wander off into
lympatics.
 In chronic inflammatory sites, however
macrophage accumulation persists.
 Other types of cells present in chronic
inflammation are lymphocytes, plasma cells, and
eosinophils.

62.  Both T and B lymphocytes migrate into
inflammatory sites via adhesion molecules.
 T lymphocytes are activated by macrophages.
 The activated lymphocytes produce cytokines like
IFN-ᵧ, a stimulant for monocytes and macrophages.
 Activated macrophages release cytokines,
including IL-1 and TNF.
 The end result is an inflammatory focus where
macrophages and T cells can persistently stimulate
one another until the triggering antigen is removed.
 Plasma cells are the end product of B-cell
activation.
 They can produce antibodies directed against
antigens in the inflammatory site.

63. GRANULOMATOUS INFLAMMATION
 Is a distinctive pattern of chronic inflammation
characterized by aggregations of activated
macrophages, that have acquired an enlarged,
squamous cell-like (called epitheloid) appearance.
 Examples
Bacterial
1. Tuberculosis (Mycobacterium tuberculosis)
2. Leprosy (M. Leprae)
Parasitic
1. schistosomiasis

64. Fungal
 Histoplasma Capsulatum
 Blastomycosis
Inorganic metals or dusts
 Silicosis
 Berylliosis
Foreign bodies
 Suture, vascular graft
Unknown
 sarcoidosis

65. Morphologic patterns in acute and chronic
inflammation
SEROUS INFLAMMATION
 Is characterized by the outpouring of a watery ,
relatively protein poor fluid that ,depending on the
site of injury,derives either from the serum or from
the secretions of mesothelial cells lining the
peritoneal, pleural and pericardial cavities.
 The skin blister resulting from a burn or a viral
infection is a good example.

66. FIBRINOUS INFLAMMATION
 This occurs as a consequence of more severe
injuries,with the resultant greater vascular
permeability allowing larger molecules(fibrinogen)
to pass the endothelial barrier.
 Fibrinous exudates may be degraded by fibrinolysis
and the accumulated debris may be removed by
macrophages

67.  resulting in restoration of the normal tissue
structure(resolution).however ,failure to completely
remove the fibrin results in the ingrowth of
fibroblasts and blood vessels, leading ultimately to
scarring(organization)

68.  example:organization of a fibrinous pericardial
exudate to form scar tissue can lead to the
development of fibrous strands that bridge the
pericardial space and restrict myocardial function.

69. SUPPURATIVE INFLAMMATION
(PURULENT)
 This is manifested by the presence of large
amounts of purulent exudate (pus) consisting
of neutrophils,necrotic cells, and edema fluid.
 Staphylococci are more likely to induce this
localized suppuration and are therefore
referred to as pyogenic.
 Abscesses are focal collections of pus that
may be caused by deep seeding of pyogenic
organisms into a tissue or by secondary
infections of necrotic foci.

70.  Abscesses typically have a central, largely necrotic
region rimmed by a layer of preserved
neutrophils,with a surrounding zone of dilated
vessels and fibroblastic proliferation .
 In time ,the abscess may become completely walled
off and eventually replaced by connective tissue.

71. ULCERATION
 This refers to a site of inflammation where an
epithelial surface has become necrotic and
eroded,often with associated subepithelial acute
and chronic inflammation.
 Can occur as a consequence of toxic or
traumatic injury to the epithelial surface E.g.
peptic ulcers or
 May be due to vascular compromise (as in the
foot ulcers associated with the vasculopathy of
diabetes)

72.  There is usually an early intense neutrophilic
infiltrate with associated vascular dilation.
 In chronic lesions where there has been repeated
insult ,the area surrounding the ulcer develops
fibroblastic proliferation, scarring, and the
accumulation of chronic inflammatory cells.

73. SYSTEMIC EFFECTS OF INFLAMMATION
1. Fever
2. Higher erythrocyte sedimentation rate
3. Leukocytosis
4. Neutrophilia
5. Lymphocytosis
6. leukopenia

74.  Fever is one of the most obvious of the systemic
effects of inflammation,collectively identified as
acute phase reactions.
 Acute phase reactions includes
 Increased slow wave sleep
 Anorexia
 Accelerated degradation of skeletal muscle proteins
 Hypotension

75.  Hepatic synthesis of a variety of acute phase
proteins
 Alterations in the circulating white blood cell pool.

76.  The cytokines IL-1,IL-6 and TNF are the most
important mediators of the acute phase reactions.
 These cytokines are released by leukocytes in
response to infection, or to immune and toxic
injury, and are released systemically, frequently in a
sort of cytokine cascade.

77.  TNF can induce the production of IL-1,which
inturn induces the production of IL-6.
 IL-6 stimulates the hepatic synthesis of several
plasma proteins,most notably fibrinogen,
 Elevated fibrinogen levels cause erythrocytes to
agglutinate more readily,which explains for the
higher erythrocyte sedimentation rate.

78.  Although IL-1 and TNF induce other consequences
,their effects are similar to one another.
 For example they both act on the thermoregulatory
centre of the hypothalamus, most likely via local
prostaglandin E production, to induce fever(hence
the efficacy of aspirin and NSAIDs in reducing
fever)

79.  Leukocytosis (increased white blood cell count) is
a common feature of inflammatory reactions,
especially those induced by bacterial infection.
 The leukocyte count usually increases to 15000 or
20000 cells/µl.
 It may exceptionally may climb as high as 40000 to
100000 cells/µl , a so called leukemoid reaction.

80.  Leukocytosis initially results from the release of
cells from the bone marrow(caused by IL-1 and
TNF) and is associated with an increased number
of relatively immature neutrophils in the blood
 Most bacterial infections induce a relatively
selective increase in polymorphonuclear cells
(neutrophilia)

81.  Parasitic infections as well as allergic responses
characteristically induce eosinophilia.
 Certain viruses, such as infectious
mononucleosis,mumps, rubella, engender
selective increase in
lymphocytes(lymphocytosis)
 However most viral infections as well as
rickettsial ,protozoal and certain types of
bacterial infections (typhoid fever) are
associated with a decreased number of
circulating white cells.(leukopenia)

82. THANK YOU