Biology of Disease CH0576

The Inflammatory Response III

Dr Stephen Todryk

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

Physical effects

Cellular effectors

Destroyed overlying epithelium

Mouth Ulcer

INFLAMMATION

Acute Chronic(diseases)Blood flow

Plasma, oedema (permeability)Chemical mediatorsRecruitment of cells (Neutrophils Die in 48 hours– PUS, staphs)Neutrophil deficiency - infections

Offense persists

Insidious(low grade irritant, microbe)

Cellular (mononuclear)

Acute

Non-specific

Innate

Complete resolutionScaringAbscess Chronic inflammation

Granuloma

Chronic

Specific

Adaptive(mononuclear cells:Monocytes/macrophages,T cells, B cells)

Stop bleeding

Keep bugs out

Abscess- walled off

Granuloma

repair

Acute Inflammation - Cellular Recruitment

• The physiological response of circulating neutrophils to chemotactic factors include the following four steps:

1. MARGINATION2. ADHERENCE3. EMIGRATION

• A key mechanism in acute inflammation is the activation of the local endothelium by cytokines and other soluble mediators

4. CHEMOTAXIS

Cellular Recruitment - MARGINATION

• Normally blood flows in the centre of the lumen of the vessel (AXIAL FLOW) whilst the area near the vessel wall carries only plasma (PLASMATIC ZONE)

• Following vasodilation the blood flow slows and leukocytes start to appear in the periphery of the stream

• The result is an increase in the concentration of white cells adjacent to the endothelial cells in the vessel walls

Cellular Recruitment - ADHERENCE

• Normally the endothelial surface prevents platelet aggregation and cellular migration

• In acute inflammation the balance of many mediators is changed e.g. increase in PAF and NO•

• The result is an alteration in the surface features and characteristics of both endothelial cells and circulating leukocytes

• Cellular adhesion molecules are expressed on both surfaces in response to inflammatory mediators e.g. SELECTINS, INTEGRINS and ICAMs(intercellular adhesion molecules)

Acute Inflammation - EXTRAVASATION

• The migration of leukocytes out of the blood vessel into the tissue is known as EXTRAVASATION - The act of forcing or letting out of its proper vessels or ducts, as a fluid (effusion), as in an extravasation of blood after a rupture of the vessels

• Extravasation occurs in four steps 1. Rolling Adhesion. 2. Tight Binding. 3. Diapedesis- passage of cells through capillary wall 4. Migration (by chemotaxis).

Acute Inflammation – Cellular Adhesion

• Steps of cellular adhesion in acute inflammation are: 1. The adhesive molecule P-selectin appears on the endothelial cell surface within a few minutes of exposure to histamine, C5a or LTB4

2. E-selectin appears a few hours after exposure to lipopolysaccharide or TNF

3. These selectins recognise a carbohydrate structure called sialyl Lewis-X (S-Lex or CD15) displayed on cell surface of neutrophils, monocytes and eosinophils

4. Interaction of P-selectin and E-selectin with S-LeX

allows leukocytes to adhere and roll along the endothelium

Acute Inflammation – Cellular Adhesion

5. The adhesive interaction allows the second step of stronger interactions to occur

6. PAF and C5a induce an increased expression of integrins LFA-1 (Lymphocyte Function Antigen) and

CR3 on leukocytes

7. The cytokine TNF induces the expression of the intercellular adhesion molecules (ICAM -1, -2 and -3) on endothelial cells 8. LFA-1 and CR3 interact with the ICAM molecules leading to firm attachment of the leukocyte to the endothelium and the rolling stops

Leukocyte Extravasation

Acute Inflammation - Cellular Migration

• Once the leukocyte has undergone margination and stopped at the site of injury the cell moves out of the blood vessel into the damaged tissue. This is the process of EXTRAVASATION

• The main chemotactic factors for neutrophils are C5a (initial recruitment) and IL-8 (6-48 hours)

• The chemotactic factors attach to specific receptors on neutrophil surface and activate secondary messenger systems within the cell

EXTRAVASATION

• Intracellular calcium levels are increased within the neutrophil

• Contraction of cytoplasmic microtubules induced and gel changes in cytoplasmic fluidity bringing about amoeboid movement of the neutrophil

• The movement shows a directed response (chemotaxis) to various chemicals

• Tertiary granules containing proteolytic enzymes, gelatinase and cathepsins, are released at the leading edge of the migrating cell

• These aid in the digestion of the basement membrane

Acute Inflammation - PHAGOCYTOSIS

• Phagocytosis is a process of engulfment and destruction of extracellularly derived materials (and microbes) by phagocytic cells is one of the key roles of acute inflammatory cells

• The process of phagocytosis is dependent upon the following organised sequence of events. 1. Recognition and attachment. 2. Internalisation. 3. Fusion (to form phagolysosome) 4. Digestion of internalised material. 5. Release of digested products from the cell.• Both Neutrophils and Macrophages are phagocytic cells.

Neutrophil most common leukocyte (40-75%). Notelobulated nucleus of neutrophil. Stain = Giemsa

Dr Michelle Peckham © University of Leeds licensed for use through the Centre for Bioscience ImageBank

Monocyte. The third most common leucocyte; about 2-10% and the largest at ~20m. Involved in inflammatory responses and are precursors to tissue macrophages. Stain =

May Grunwald-Giemsa

Dr. Michelle Peckham © University of Leeds  image courtesy Centre for Bioscience, the Higher Education Academy, ImageBank

• Recognition - Neutrophils recognise and phagocytose bacteria and foreign material in the absence of antibody

• Phagocytosis is greatly enhanced by coating ‘foreign’ material with plasma components - Opsonins e.g. C3b or antibody because neutrophils have specific complement and Fc receptors

• Internalisation - Invagination of the plasma membrane, enclosing the foreign material, in a membrane bound cytoplasmic vacuole - the PHAGOSOME

• Fusion - The phagosome fuses with the cytoplasmic lysosomes to form PHAGOLYSOSOMES

PHAGOCYTOSIS

PHAGOCYTOSIS

• Ingestion of foreign material via the phagosome triggers the production or release of many bactericidal agents including:

hydrolytic enzymes, competitors and antimicrobial peptides from neutrophil granules, toxic oxygen derived products and nitrogen oxides

• The phagolysosome has an acid pH thus it may be bacteriostatic (inhibit reproduction) or bactericidal

PHAGOCYTOSIS• Neutrophil cytoplasmic granules are of three

major types:

AZUROPHIL, SPECIFIC or STORAGE

• The contents of the granules vary:

• Azurophil - LYSOZYME, ELASTASE, CATHEPSIN B and D

• Specific - LYSOZYME, COLLAGENASE, LACTOFERRIN

• Storage - GELATINASE, CATHEPSIN B

PHAGOCYTOSIS

• In addition to the release of powerful hydrolytic enzymes there is the generation of highly toxic free radicals

• These include REACTIVE OXYGEN INTERMEDIATES (ROI) and include the superoxide anion O2

¯ and hydrogen peroxide H2O2 which is produced through the activity of NADPH-oxidase and superoxide dismutase

PHAGOCYTOSIS

• H2O2 interacts with myeloperoxidase to produce HYPOCHLORUS ACID

• ROI are highly toxic for the producing cells, therefore, neutrophils have to contain large reserves of endogenous antioxidants such as glutathione and ascorbate for neutralisation

• REACTIVE NITROGEN INTERMEDIATES (RNI) include nitric oxide (NO•) which may react with

superoxide to form the highly toxic PEROXYNITRITE anion

Acute Inflammation - Tissue Damage

• Inflammatory cells have evolved as a means of combating foreign material and infectious agents.

• They are also capable of causing appreciable tissue damage to normal surrounding tissue.

• Tissue injury caused by inflammatory cells plays an important role in the pathogenesis of many diseases including - Rheumatoid Arthritis, Tuberculosis, Gout, Emphysema, Silicosis, Inflammatory Bowel Disease and Immune Complex Diseases.

CHRONIC INFLAMMATION

• Chronic inflammation is an inflammatory response of prolonged duration e.g. weeks, months or indefinitely.

• The extended time course is provoked by the persistence of the causative stimulus for the initial inflammation.

• The process causes tissue damage and is accompanied by simultaneous attempts at healing and repair.

• Chronic inflammation will continue until the damaging agent is removed; may have an inherited / genetic component.

CHRONIC INFLAMMATION

• The histological appearance of sites of chronic inflammation vary considerably however the general features are:- 1. A mixed cellular infiltrate which consists mainly of macrophages, lymphocytes and plasma cells (there are very few neutrophils and eosinophils).

2. Tissue necrosis - caused by the causative agent of the inflammatory process.

• The macrophage is the key cell type in chronic inflammation and it functions as a source of pro-inflammatory mediators.

Chronic Inflammation - The Macrophage

• The accumulation of macrophages at sites of chronic inflammation occurs in at least three ways:

1. Continued recruitment of monocytes from the circulation in response to chemotactic stimuli followed by their differentiation into macrophages in the tissue

2. Local proliferation of tissue macrophages

3. Prolonged survival and immobilisation in the inflammed area

• Macrophages also regulate the lymphocyte response to antigens and they secrete other mediators which control the proliferation and function of endothelial cells and fibroblasts.

MACROPHAGES - M• The macrophage is the main effector cell in chronic inflammation.• They are converted from inactive monocytes by signals from gamma interferon (IFN-), a product of activated CD4+ and CD8+ T cells, NK cells.• The activated macrophage has a much larger cytoplasm and a much increased capacity for protein synthesis. It is known as an EPITHELIOD cell.• Activated macrophages commonly fuse together to form multinucleate histiocytic GIANT cells.• Once activated, macrophages have both a major secretory and phagocytic role in the defence against the injuring agent.• M are also Professional Antigen Presenting Cells.

Granulomatous Inflammation• Granulomatous inflammation is a histologically distinctive form of chronic inflammation

• A range of damaging agents can lead to the generation of GRANULOMA e.g. specific infections (e.g. Mtb, foreign bodies, specific chemicals and drugs

• Granulomas are aggregates of chronic inflammatory cells which form small nodules, < 2mm

• Granuloma may be confluent, forming very large areas

• Granuloma are collections of modified M s, EPITHELIOD cells, usually with a surrounding zone of lymphocytes

Granulomatous Inflammation

• Epitheliod cells are less phagocytic than normal Ms and appear to be modified for secretory functions

• Ms in granulomas are further modified to form multinucleate giant cells

• These arise by fusion of epithelial Ms without nuclear or cell division

• In some cases nuclei are arranged around the periphery of the cell, Langerhans-type giant cell

• In other cases nuclei may be randomly scattered throughout the cytoplasm, Foreign-body giant cell.

http://www.usc.edu/hsc/dental/PTHL312abc/312a/03/IMGs/26bb.html

Chronic Inflammation

• The Inflammatory Response is necessary to combat sudden trauma however inappropriate chronic inflammation has been linked to many diseases including cardiovascular disease, neurodegenerative disease, autoimmune disorders and cancers

• Sunburn (UV) – melanoma• Smoking, asbestos – lung cancer

Resolution: Repair / Healing

• Growth factors• New vessels• Fibroblasts• Collagen deposition (SCAR)• Resolution of response

Further info

• The Cytokine Network: Fran Balkwill, 2000

• Immunology. 6th Edition. Roitt, Brostoff and Male

• Jokiranta Research Group, Helsinki, Finland: www.hi.helsinki.fi/jokiranta/intro.html

•http://library.med.utah.edu/WebPath/GENERAL.html#2

•http://multimedia.mcb.harvard.edu/flash/extravasation.swf