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‘The Holy Grail’ - mediators of inflammation. Lecture 3 Rod Flower, WHRI, London. The components of inflammation. Cells.. - Fixed cells such as vascular cells. - Migratory cells such as PMNs. Mediators.. - many chemicals released into the body. Immune system.. -Innate. -Acquired.

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the holy grail mediators of inflammation

‘The Holy Grail’-mediators of inflammation.

Lecture 3

Rod Flower, WHRI, London.

the components of inflammation
The components of inflammation.
  • Cells..- Fixed cells such as vascular cells. - Migratory cells such as PMNs.
  • Mediators..- many chemicals released into the body.
  • Immune system..-Innate. -Acquired.
the chemical theory
The ‘chemical theory’.
  • Chemical substances, called mediators, released from injured or activated cells co-ordinate the development of the inflammatory response.
a chemical mediator should
A ‘chemical mediator' should….
  • .. be found in tissues in concentrations that can explain the observed symptoms or effects.
  • .. be released by the endogenous trigger which produces the response.
  • .. have the same action in all species where the phenomenon occurs.
  • .. be destroyed locally or systemically to avoid undue accumulation.
  • .. be blocked (directly or indirectly) by inhibitors of inflammation. - Rocha E Silva, 1978.
the mediators of inflammation
The mediators of inflammation.
  • Plasma proteins such as complement and antibodies.
  • Other proteins such as sPLA2 and acute phase reactants.
  • Cytokines and chemokines.
  • Lipids such as prostaglandins and PAF.
  • Amines such as histamine.
  • ‘Gasses’ such as NO and O2-.
  • Kinins such as bradykinin.
  • Neuropeptides such as substance P.
mediators which suppress inflammation
Mediators which suppress inflammation.
  • ACTH, GCs and products of the HPA axis.
  • Some cytokines such as IL-10.
  • Some induced proteins such as anti-proteases and lipocortin 1(annexin 1).
two types of immunity
Innate. Includes…- phagocytosis.- complement activation.- natural killer cells.

Aquired. Includes…- secondary antibody mediated response.-secondary cell mediated response.

Two types of ‘immunity’.
antibody mediated effects
Antibody mediated effects.
  • IgG, IgA, IgM, IgD, IgE subtypes.
  • Fab region recognises antigen.
  • Fc region important for host defence functions
  • Responsible for antibody mediated immunity and some ‘innate’ immunity.
immunoglobulins
IgG

Major bloodborne immunoglobulin.

75% total Igs.

150 kda mw.

Four subtypes.

Main antibody of the secondary immune response.

Immunoglobulins.
immunoglobulins10
IgA

Predominant form in mucous secretions.

Occurs as a dimer (especially in secreted form) and also in the plasma of some animals.

Has a secretory component associated with it.

Two subclasses A1 & A2.

Immunoglobulins
immunoglobulins11
IgM.

A pentameric molecule.

Confined to the blood.

Important in the primary immune response.

Immunoglobulins.
immunoglobulins12
IgD.

A minority (1%) immunoglobulin present on B-cells.

Short half life.

Immunoglobulins
immunoglobulins13
IgE.

Pentameric heavy chain.

Low concentrations in serum.

High concentrations on surface of mast cells which posses a IgE Fc receptor.

When bound to antigen, histamine is released from mast cells.

Immunoglobulins.
auto immunity
Auto-immunity.
  • A case of ‘mistaken identity’.
  • Responsible for a range of disorders, both trivial and serious.
t cell mediated immunity
T-cell mediated immunity.
  • The primary immune response.
  • Immunological ‘memory’.
  • Some effector functions.
t cell mediated immunity16
T-cell mediated immunity.
  • T-cell receptor is a heterodimer (a,b,g,d chains).
  • Recognises MHC complexes.
  • Detects antigenic fragments presented by APC thus priming the ab response
  • Unique to each lymphocyte.
phagocytes
Phagocytes.
  • Uptake of foreign organisms.
  • Destruction of micro-organisms etc.
  • Many microbiocidal weapons e.g. lytic enzymes, active oxygen etc.
natural killer nk cells
Natural killer (NK) cells.
  • A type of lymphocyte.
  • Cytotoxic potential.
  • Attacks invading, infected or transformed cells.
  • Differs from T-cells in the way in which they ‘recognise’ their targets.
  • Secrete toxic proteins.
  • Sometimes involved in acute rejection.
complement

Ab-ag, Gm neg bacteria, subcellular particles

Yeasts, parasites, ab-ag.

Classical (C1,4,2 & 2)

Alternate (C3)

C3

C5

Complement.
  • A complex series of about 20 proteolytic enzymes in the blood.
  • ‘Classical’ and ‘alternate’ pathways act in a cascade fashion.
  • Accelerated in the presence of IgGs
  • Lytic to many micro-organisms.
  • ‘Opsonise’ others.
some actions of complement fragments
Some actions of complement fragments.

C5a chemotaxis, phagocyte degranulation, stimulation of O2-.

C5a, C3a mast cell and platelet degranulation.

C5a, C5b-9 enhancement of cytokine release,

induction of eicosanoid synthesis.

C3b potentiation of Ab response, opsonisation of cells and lysis.

C5b-9 cell lysis.

non immune mediators
Non-immune mediators.
  • Soluble chemicals released by injured, activated or dying cells.
  • Regulate, activate and terminate the inflammatory response.
  • Some are fairly ‘insult specific’, others more generally found in lesions.
histamine

CH2CH2NH2

N

HN

Histamine.
  • Formed from histidine.
  • Stored in high concentrations in mast cells and basophils together with heparin and ATP.
  • Three main receptor subtypes (H1 etc).
  • Inmportant in allergies, itch, inflammatory response. Causes ‘triple response’.
histamine23
Histamine.
  • Synthesised as a curiosity by Windaus and Vogt, 1907.
  • Extracted from putrefying mixtures by Ackerman 1910.
  • Assumed to be responsible for anaphylaxis by Dale and Laidlaw (1911, 1960) as synthetic material had the same effects.
  • Eppinger (1913) demonstrated that histamine produced a reaction in human skin similar to that seen with insect bites.
histamine24
Histamine.
  • Lewis (1927) proposed that histamine was released by a variety of injurious stimuli.
  • Best (1927) unequivocally demonstrated the presence off histamine in the mammalian body.
  • The development of anti-histamine in the 1940’s led to the realisation that histamine was not the only inflammatory mediator.
5ht serotonin

HO

CH2CH2NH2

NH

5HT; serotonin.
  • Found in platelets, neurones and in CNS. Often stored with other transmitters.
  • Inactivated by MAO.
serotonin 5ht
Serotonin (5HT).
  • Very potent at increasing vascular permeability in rodents but not guinea pigs or rabbits (various groups, 1950’s)
  • A histamine releaser in man?
  • Many inflammatory effects but species specific.
  • Multiple receptors.
neuropeptides
Neuropeptides.
  • Tachykinins- substance P- neurokinin A- neurokinin B- CGRP
  • Kinins:- bradykinin- kallidin
tachykinins
Substance P.

Neurokins A & B.

Mainly located in sensory neurones.

Released on nerve stimulation.

Act on 7TM ‘NK’ receptors (3 subtypes; NK1 etc).

Cause vasodilatation, vascular permeability, smooth muscle contraction, mucus secretion, pain.

Tachykinins.
tachykinins29
CGRP.

A product of the calcitonin gene generated through differential splicing.

Found in sensory neurones.

Induces neurogenic inflammation.

Tachykinins.
kinins
Bradykinin (9 aa)

Kallidin (10 aa).

Formed from kininogens (2 forms) by kallikreins (also 2 forms).

Inactivated by kininases (2 forms).

Two receptors B1 (inducible) and B2 (constitutive).

Produce; vasodilation, smooth muscle contraction, pain and inflammation.

Anti-proteases and receptor antagonists are occasionally useful.

Kinins.
the kinin system
The kinin system.
  • Kallikrein strongly increases vascular permeability in rabbits. Rocha E Silva 1940.
  • A biologically active agent, named bradykinin was generated by the action of trypsin on plasma. Rocha E Silva 1949.
  • BK has strong vascular permeability effects (several groups; 1950’s).
  • BK causes pain. Armstrong et al 1954.
eicosanoids

Arachidonic acid

PG G2

LTA4

TxA2PGs LT B4LTs

E,I,F,D C,D,E

Eicosanoids.
  • Arachidonic acid from cellular phospholipids.
  • At least 2 different pathways:- cycloxygenase forms prostaglandins and thromboxanes.- lipoxygenase forms leukotrienes.
the prostaglandin pg system
The prostaglandin (PG) system.
  • PGs discovered in seminal vesicles and in human plasma (1930s).
  • Synthesis from essential fatty acids demonstrated (1960s).
  • Aspirin like drugs prevent PG synthesis and this explains mechanism of action (1970s).
  • Multiple forms of cyclo-oxygenase discovered (1990s).
synthesis of paf

C12-C18 fatty acid.

Acetyl group

Phoshatidylcholine

Synthesis of PAF.
  • PAF formed from phoshatidyl choline by and acetylase.
  • Key role of phospholipase A2

(1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine.)

paf platelet activating factor
PAF (platelet activating factor).
  • Modified phospholipid.
  • Synthesised by many cells including PMN, monocytes, mast cells and eosinophils.
  • Acts through specific G-protein linked receptors.
  • Sometimes acts intracellularly.
  • Causes increased vascular permeability, PMN migration, brochoconstriction and many other signs and symptoms of inflammation.
  • PAF receptor antagonists useful treatment in experimental models.
nitric oxide no edrf

H2N-CH.COOH

(CH2)3

NH

C

HN NH2

Nitric oxide (NO; EDRF).
  • Formed in many tissues from arginine.
  • Three enzymes (NOS) described; iNOS, ncNOS & ecNOS.
  • Resonsible for NANC transmission.
  • Potent vasodilator and microbiocidal.
  • Physiological effects dependent of guanylate cyclase activation.
slide37
iNOS.
  • Induced in cells by cytokines, TNFa, IL1b or LPS.
  • iNOS does not require Ca2+ for activation, only a supply of arginine.
  • GCs, IL10 and some other factors can inhibit iNOS or its induction.
  • With active oxygen, NO can form peroxynitrite which is a potent cytotoxic agent.
  • Can be blocked in (e.g.septic shock) by arginine analogues such as L-NMMA.
  • NO is scavenged by haemoglobin and reacts with thiols.
cytokines
Cytokines.
  • All are proteins.
  • Mainly synthesised by immune cells.
  • Regulate differentiation and activation of immune cells.
  • Partly responsible for coordination of the inflammatory response.
  • Act through high affinity receptors on target cells.
key cytokines which activate the inflammatory response
IL1

Two forms found IL1a & IL1 b.

17Kd mw.

Soluble IL1 receptor regulates activity.

Produced by monocytes and many other cells.

Activate lymphocytes and many inflammatory cells.

Key cytokines which activate the inflammatory response.
key cytokines which activate the inflammatory response40
IL6

26Kd mw.

Produced by T-cells but also by many other cells too.

Activates B & T-cells and other cell types.

Key cytokines which activate the inflammatory response.
key cytokines which activate the inflammatory response41
IL2

15Kd mw.

Produced by T-cells.

Activates T-cells, monocytes and NK cells.

Key cytokines which activate the inflammatory response.
key cytokines which regulate the inflammatory response
IL10.

17-21Kd mw.

Produced by T-cells.

Stimulation of mast cell replication.

Inhibits cellular immune reactions.

Key cytokines which regulate the inflammatory response.
key cytokines which activate the inflammatory response43
IL5

45-60Kd mw.

Produced by T-cells.

Increases B-cell proliferation.

Promotes eosinophil maturation and inhibits macrophage activation.

Key cytokines which activate the inflammatory response.
key cytokines which activate the inflammatory response44
TNF

Two forms found, TNFa and TNFb.

17Kd mw.

Produced by many cells including monocytes (TNFa ) .

Produced by T-cells (TNFb).

Widespread activation of cells; apoptosis, shock, cachexia etc.

Key cytokines which activate the inflammatory response.
key cytokines which activate the inflammatory response45
Interferons (IFNs).

3 forms found a,b & g.

Many different subtypes.

Generally 19-26 Kd mw.

Produced by monocytes (a), fibroblasts (b) and T-cells (g).

Antiviral, cell activating and tumour suppressant effects.

Key cytokines which activate the inflammatory response.
strategies for inhibiting cytokines
Strategies for inhibiting cytokines.
  • Reduce cytokine producing cells (e.g. with cytostatics).
  • Inhibitory cytokines (e.g. IL 10).
  • Inhibitors of signal transduction (e.g.cyclosporin).
  • Regulation of gene expression (e.g. glucocorticoids)
  • Inhibitors of release (e.g. ICE inhibitors)
  • Reduction in circulating cytokines(e.g. monoclonals, soluble receptors)
  • Receptor blockade (e.g. antagonists or monoclonals).
chemokines
Chemokines.
  • At least 3 families of small proteins mw usually 7-15Kd.
  • Relative position of Cys residue determines nomenclature e.g. CXC, CC or C.
  • Act through 7TM receptors which also function as co-receptors for HIV entry into immune cells.
chemokines48
CXC chemokines.

IL8.

Platelet factor IV.

Granulocyte chemotactic protein 2.

Platelet basic protein and related species.

Utilise CXCR 1-5.

Main target PMN.

Chemokines.
chemokines49
C-C chemokines.

MCP 1,2,3,&4.

RANTES

MIP 1a & b.

Eotaxin.

Utilise CCR 1-5 receptors.

Main targets eosinophils and monocytes.

Chemokines
the plurality of mediators
The plurality of mediators.
  • “..it would be very unfortunate if any of the above mentioned mediators might constitute the final answer to the problem, because that would mean to shut our laboratories., or do something else!”. Rocha E Silva, 1973.
how can we understand the plurality of mediators
How can we understand the plurality of mediators?
  • Different mediators are required to produce different aspects of the inflammatory response.
  • Sequential release is necessary throughout to co-ordinate the process.
  • Synergism between mediators is required to produce the full response.
the holy grail hypothesis
The ‘Holy Grail’ hypothesis.
  • “One mediator, or family of mediators, is responsible for the majority of inflammatory signs and symptoms. By inhibiting the formation or antagonising the action of this mediator(s), a resolution of most types of inflammatory disease would be possible”. - Flower, 1986.
summary of lecture 3
Summary of lecture 3.
  • Inflammation is regulated by a great many factors including immune and non-immune chemical mediators.
  • There is considerable redundancy.
  • There is a degree of ‘insult specificity’.
picture credits
Picture credits.
  • Life Art.
  • Austrian Rheumatology Teaching slides.
  • ‘Mediators of Inflammation’, GP Lewis .
  • ‘Cellular and Molecular Immunology’, Abbas et al.
  • N Goulding.
  • St Barts Hospital Medical Illustration service.
  • A du Vivier.
  • Leo & Astra.
  • ‘Atlas of Clinical Endocrinology’, Besser et al.