Biology of Disease CH0576
The Inflammatory Response II
Dr Stephen Todryk
Endothelial cells
Oedema
Plasma derived mediators
Bradykinin
C3 of complement
Plasminogen
Hageman Factor
(factor XII)
Thrombin
Cell derived mediators
Histamine
Leukotriene B4
Prostaglandin
Nitric Oxide
TNFa
IL-8
Situations / Diseases involving inflammation
Situations / Diseases involving inflammation
Wounds, burns, infections
Situations / Diseases involving inflammation
Wounds, burns, infections
Arthritis, Inflammatory Bowel Disease
Allergy / hypersensitivity, dermatitis
Atherosclerosis
Inflammatory Response
Body's rapid reaction to trauma
- Increase of blood flow to the affected area
(vessel dilation and increased permeability)
- Release of chemical mediators to attract
white blood cells (neutrophils)
- Increase flow of plasma
- Recruitment of monocytes to remove
damaged tissue / clean up the debris /
microbes.
This macrophage is ingesting chains of coccoid bacteria.
Dr Gordon Beakes © University of Newcastle upon Tyne
Inflammatory Response
Acute / Chronic
Signs : swelling, redness, heat, pain, loss of function
Causes
Functions / Results (beneficial and harmful)
containment
Components / steps
Mediators
e.g. Oedema – swelling due to fluid
Chemical mediators
Cellular effectors
Physical effects
CHEMICAL MEDIATORS OF INFLAMMATION
Definition: Any messenger molecule that acts
on blood vessels, inflammatory cells, or other
cells to contribute to an inflammatory response
• Exogenous - Endotoxins e.g. LPS from gram -ve
trigger complement activation and
other inflammatory response mediators
• Endogenous - Plasma
Leukocytes
Endothelial cells
Fibroblasts
Acute Inflammation - Chemical Mediators
The spread of an acute inflammatory response
following injury to a small area of tissue suggests
chemical substances are released from injured
tissues and disseminate towards uninjured areas
• These chemicals are:
ENDOGENOUS CHEMICAL MEDIATORS
• Chemical mediators can be split into two groups
CELLULAR OR PLASMA DERIVED
Acute Inflammation – Chemical Mediators
• Endogenous mediators can be derived from molecules
normally present in plasma in inactive form
OR
• Are released at injury site by various cell types that
may store preformed mediator molecules in granules e.g.
histamine or can rapidly switch on mediator synthesis
machinery to produce e.g. metabolites of arachidonic acid
• Their activities result in vasodilation, increased vascular
permeability, emigration of neutrophils and chemotaxis
Acute Inflammation - Chemical Mediators
Acute Inflammation - Cellular Mediators
HISTAMINE
• Histamine is the major pre-formed
chemical mediator in acute inflammation.
• It is stored in and released from MAST CELLS,
BASOPHILS, EOSINOPHILS and PLATLETS.
• The pharmacologic effects of histamine are
a) Transient dilation of arterioles.
b) Increased vascular permeability in venules.
c) Primary cause of early increase in vascular
permeability in the first hour after injury.
HISTAMINE
• Mast cells and Basophils can be made to
degranulate their contents by a range
of different mechanisms including:
a) Physical agents such as cold or trauma
to the tissue
b) Exposure to cationic proteins derived
from platelets and lysosomal granules
c) Immune mechanisms mediated by IgE
d) Complement components C3a and C5a.
Histamine
• Mast Cell degranulation of histamine and other preformed mediators (heparin and tryptase)
- triggered most often by cross-linking of IgE
receptors on cell surface (e.g. pollens; foods)
- fusion of the granule membranes with the cell
membrane
- granules are released and are rapidly solubilised
in the surrounding aqueous environment
Acute Inflammation - Cellular Mediators
Arachidonic Acid Derivatives
• PROSTAGLANDINS (PG) THROMBOXANES (Tx)
and LEUKOTRIENES are all metabolites of the long
chain unsaturated fatty acid ARACHIDONIC ACID,
a molecule stored in membranes of many cell types
• Release of Arachidonic acid can be initiated by a
variety of stimuli including histamine and interaction
of Neutrophils and monocytes with damaged tissues
or cells.
• Arachidonic acid is metabolised via two pathways:
Arachidonic Acid Derivatives
1.CYCLO-OXYGENASE PATHWAY
• This pathway of arachidonic acid metabolism produces
the PROSTAGLANDINS and THROMBOXANES
There are two cyclo-oxygenase enzymes:
COX-1
COX-2
that generate three important chemical mediators
Arachidonic Acid metabolites
via COX Pathway
• Prostacyclin (PGI2) inhibits platelet
aggregation and causes vasodilation
• Stable prostaglandins (PGE2, PGF2 and
PGD2) all act on vascular tone and
increase permeability; PGE2 also
causes pain
• Thromboxane A2 aggregates platelets
and causes vasoconstriction
Arachidonic Acid Derivatives
2.LIPOXYGENASE PATHWAY
This pathway produces all the LEUKOTRIENES (LT)
• Occurs mainly in neutrophils
• LTC4, LTD4 and LTE4 are potent vasoconstrictors,
cause smooth muscle contraction and an increase
in venule specific vascular permeability and are
1000x more potent than histamine at ↑ permeability
• LTB4 stimulates the adhesion of neutrophils to
endothelial cells and is a potent chemotactic agent
Arachidonic Acid Derivatives
The important role that the various metabolites of
Arachidonic acid play in inflammation is well
illustrated by the fact that many of non-steroidal
anti-inflammatory drugs act by inhibiting various
points in the two pathways discussed
E.g. aspirin, ibuprofen, indomethacin
Aspirin exerts it powerful anti-inflammatory effect by
inhibiting the first step in prostoglandin synthesis
Pharmaceutical companies are very keen to have
successful COX-2 inhibitors in the marketplace
Arachidonic Acid Derivatives
NSAIDS;
Ibuprofen
To summarise:
Some anti-inflammatory properties interfere with arachidonic acid metabolism
– Corticosteroids interfere with phospholipase
– Aspirin interferes with cyclooxygenase
Acute Inflammation - Cellular Mediators
Platelet Activating Factor (PAF)
• PAF is a phospholipid synthesised by mast cells
and basophils and also by platelets, neutrophils,
monocytes and endothelial cells.
• PAF is a mixture of molecular species.
• PAF dilates blood vessels, increases
platelet aggregation, induces phagocytosis,
triggers arachidonic acid metabolism and
promotes leukocyte chemotaxis.
Acute Inflammation - Cellular Mediators
Cytokine Network
• Cytokines have multiple physiological roles and
act to mediate communication between organs
including those that are generated during inflammation
• Cytokines are small protein products of activated
leukocytes, particularly lymphocytes and monocytes
and interact with specific receptors on target cells
• Cytokines may form a concentration gradient and are
therefore thought to be important controllers of directed
cell migration (CHEMOTAXIS ; chemokines)
Acute Inflammation - Cellular Mediators
• Cytokines with a role
in inflammatory
response include:
• IL-1b, IL-8,
TNFa, IL-6
Acute Inflammation - Cellular Mediators
Nitric Oxide (NO)
• NITRIC OXIDE - a small molecule locally
synthesised by the endothelium and macrophages
from L-Arginine by the action of the enzyme
NITRIC OXIDE SYNTHASE (NOS)
• Nitric oxide diffuses into smooth muscle and is a
potent vasodilator and increases vascular permeability
• Nitric oxide has a very short half life (3-4 seconds)
• NO•, the nitric oxide radical is the active compound
produced from several vasodilator drugs employed
commercially.
Nitric Oxide
• Nitric oxide can be highly toxic and used
by the body to kill invading cells (bacteria)
or used by the body as an intracellular signal.
• Thus it may have both a protective and damaging effect.
• Nitric oxide is sometimes referred to ENDOTHELIUM
DERIVED RELAXING FACTOR (EDRF).
• Endothelial cells also produce PGI2 and ENDOTHELIN.
• Endothelin is a low MW peptide that induces prolonged
constriction of vascular smooth muscle.
Nitric Oxide
Acute Inflammation
Plasma Derived Mediators
• Plasma contains four enzymatic cascade systems
which produce various inflammatory mediators
• Each cascade occurs as a series of inactive precursor
molecules which, when triggered, react as a series of
sequential proteases
• The four cascade systems are :
1. The complement system.
2. Coagulation factors.
3. The kinin system.
4. The fibrinolytic system.
Plasma Derived Mediators
The Alternative Pathway of Complement Activation
• The complement system is a cascade of
enzymatic proteins. It can be activated
during acute inflammation in a number of ways:
a) Tissue necrosis
b) During infection - A variety of viral, bacterial, fungal
and parasite material can activate complement
e.g. Yeast cell walls (Zymosan), endotoxins from
gram -ve bacteria and polysaccharides
c) Products of the kinin, coagulation and fibronolytic
systems.
Alternative Pathway of Complement Activation
• Complement can be activated via 3 pathwaysClassical, lectin and Alternative pathway
Antibodies do not have role in the Alternative pathway
The first three components of the classical pathway
are bypassed
• Six proteins perform the functions of initiation,
recognition and amplification of the pathway
These are : C3, B, D, H, I and P
• This results in the formation of the activator bound
C3/C5 convertase
Alternative Pathway of Complement Activation
Proteins: C3, B, D, H, I and P
1. C3 undergoes spontaneous cleavage to
C3a and C3b in plasma
2. Unless it binds to a cell surface, C3b is
rapidly inactivated
3. C3b forms a complex with Bb and factor P.
This is a C3 convertase which deposits many
more molecules of C3b on the pathogen.
4. Some molecules of C3b bind to the existing C3b,
Bb complex to form C3b2,Bb which is a
C5 convertase
5. C5 is split into C5a and C5b
Alternative Pathway of Complement Activation
• C3a and C5a are ANAPHYLATOXINS • cause smooth muscle contraction and
increased vascular permeablity.
• This effect is amplified by the release of
further histamine from mast cells and
basophils.
• C3a and C5a are also powerful
chemotactic agents.
Acute Inflammation Plasma Derived Mediators
COAGULATION FACTORS
THE HAGEMAN FACTOR (coagulation factor XII)
• Factor XII is activated by:
1. contact with a variety of negatively charged surfaces
e.g. basal lamina, enzymes of bacterial origin
2. Platelets
3. Proteases from inflammatory cells
Plasma Derived Mediators
• COAGULATION FACTORS
• Activated Factor XII can activate a number of
systems – it converts PLASMINOGEN to PLASMIN,
PREKALLIKREIN to KALLIKREIN and activates the
KININ system
• Products from this sequence can themselves activate
Factor XII by a feedback mechanism resulting in
amplification
Plasma Derived Mediators
Acute Inflammation Plasma Derived Mediators
THE KININ SYSTEM
• Kinins are small peptides, 9-11 amino acids long,
including BRADYKININ and LYSYL BRADYKININ.
Both are powerful vasodilators, increase vascular
permeability and mediate pain
THE FIBRINOLYTIC SYSTEM
Plasmin is responsible for the lysis of fibrin into fibrin
degradation products which have local effects on
vascular permeability.
Acute Inflammation
Cellular/Plasma Derived Mediators
• These complex interactions bring about increased
vascular permeability at the LOCAL site of damage.
• After this the next phase of the acute inflammatory
response occurs. This is cellular recruitment into
the inflammatory site.
• The cells which are recruited at the site vary with time.
This has led to the classification of the inflammatory
cells into acute and chronic categories.
Acute Inflammation - Cellular Recruitment
•
The main cellular events in acute inflammation,
all brought about by chemical mediators are :1. Normally inactive endothelial cells are activated to
allow the adhesion of neutrophils.
2. Normally inactive circulating neutrophils are
activated to enhance their capacity for phagocytosis
and killing.
3. Neutrophils develop the ability to move actively in a
directional fashion from the vessels towards the site
of tissue damage.
Acute Inflammation - Cellular Recruitment
• During the first 24 hours following injury the main
cells to accumulate are neutrophils due to the
production of high concentrations of chemotactic
factors at the site of injury
• The main cell to mediate the effects of acute
inflammation is the NEUTROPHIL
• If tissue damage is slight there will be adequate
neutrophils in the peripheral circulation
Acute Inflammation - Cellular Recruitment
• If tissue damage is extensive stores of
neutrophils,including some immature
forms, are released from the bone marrow
to increase number of neutrophils in blood
• To maintain a supply of short lived neutrophils,
growth factors derived from the inflammatory
process, stimulate the division of myeloid precursors
in the bone marrow.