Lecture 4 - Kapila - Ac Infl I - 6 Sep 2006

Acute Inflammation-I

Kusum Kapila September,2006

Lectures Inflammation – generalities Classification of inflammation Acute inflammation - Vascular events/permeability - Inflammatory Cell Types - Sequence of events - Chemical Mediators Chronic Inflammation and Granulomatous Inflammation Repair Wound Healing Healing in Specific Tissues

Inflammation "Inflammation is one of the most important and most useful of our host defense mechanisms, and without an adequate inflammatory response none of us or our patients would be living. It is not a disease but a manifestation of a disease Ironically it is also one of the most common means whereby our own tissues are injured."

GENERALITIES REGARDING THE INFLAMMATORY RESPONSE: process involving multiple participants. Inflammation is the reaction of vascularized living tissues to local injury fairly stereotypical It is a series of events which overlap and form a continuum in the terminal vascular bed, in blood and in connective tissues It is a response to an initiating event a defense mechanism. purpose is to eliminate the offending irritant and to repair the damaged tissue. It can be harmful.

Roles of Inflammation: Protection -Contain and isolate the injury -Destroy invading organisms and inactive toxins Achieve healing and repair -ideally tissue should return to normal -abscess formation may occur -persistent infection -chronic infection -scar formation-may distort tissue and alter their function

Outcome of Acute Inflammation

Resolution INJURY

Mediators

Acute inflammation

Abscess formation Healing

Mediators

Chronic inflammation

Persistent infection Persistent toxins Autoimmune diseases

Regeneration Scarring

CLASSIFICATION OF INFLAMMATION Extent Mild Moderate Severe Duration Peracute Acute Subacute Chronic Chronic-active Distribution Focal Multifocal Coalescent Locally Extensive Diffuse

Exudate Suppurative Fibrinous Serofibrinous Fibrino-purulent Necrotizing Granulomatous, Anatomic Modifiers Interstitial Broncho-interstital Glomerulonephritis Submandibular Organ Nephritis Hepatitis Enteritis Etc

Extent – how severe? Mild

not too bad Minimal tissue damage few inflammatory cells - small edema and/or congestion Moderate – pretty bad Some obvious tissue damage Some inflammatory cells Vascular involvement edema/haemorrhage + Severe – really bad Lots of tissue damage Lots of inflammatory cells Lots of edema and haemorrhage

Duration – how long has the processes been underway? Peracute Acute Subacute Chronic Chronic -active

PERACUTE INFLAMMATION: Usually caused by a potent stimulus Eg: Bee Sting Time: 0-4 hours Vascular Involvement: Hyperaemia, Slight edema, Haemorrhage Inflammatory cells: Not usually numerous, Few leucocytes Clinical Signs: Shock, sudden death

Inflammation “Is a reaction of a tissue and its microcirculation to a pathogenic insult” It is characterized by the generation of inflammatory mediators and movement of fluid & leukocytes from the blood into extravascular tissues.

Causes of Inflammation

microbial Infections – pyogenic bacteria, virus hypersesitivity reactions – parasites, TB physical agents – trauma, radiation, heat, cold Chemicals – corrosives,bacterial toxins Tissue necrosis - infarction

ACUTE INFLAMMATION Cardinal Signs (Celsus, 2 AD) Redness (rubor) Swelling (tumor) Heat (calor) Pain (dolor) Loss of function (functio laesa) (added by Virchow)

Phases of Acute Inflammation 1- Initiation: 1- Stimulation (injury) with changes in microvasculature 2- Structural changes leading to fluid extra-vasation 3- Emigration of WBCs to the site of injury 2- Amplification: Both soluble mediators and cellular inflammatory systems are activated and amplified 3- Termination: Specific inhibition or dissipation of the mediators

Acute Inflammation Acute inflammation involves several processes: Vascular component- Alterations in vascular caliber leading to increased blood flow Exudative component- Changes in the microvasculature causing protein rich fluid to leave circulation Cellular component- recruitment and emigration of the leukocytes outside circulation and accumulation in the focus of injury Proliferative component- resulting in tissue regeneration,granulation tissue and healing

Acute InflammationVascular events

Triple response to injury The white line - momentary -arteriolar vasoconstriction The flush - dull red line - cap.dilatationrelaxed precapillary sphincters The flare – red irregular surrounding zone – arteriolar dilatation The wheal – edema – fluid extravasation

Components of the vascular response Vascular Changes - Vasodilation (change in caliber and flow) - increased vascular permeability - acute local active hyperemia Cellular Events - Movement from capillaries and post capillary venules - emigration -Accumulation of leukocytes at sites of injury - migration -Activation of inflammatory cells

Sequence of Events

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  



 

Arteries dilate Volume of blood flow increases Capillary beds open Congestion of veins Increase permeability of microvasculature RBC’s become concentrated Blood flow slows down Margination, Pavementing and Emigration of WBC’s

What happens? Simply speaking 

Increase vascular permeability

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Exudation of plasma proteins

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Leukocytes enter the tissue

Sequence of events Increased Vascular permeability Escape of protein rich fluid into extravascular space -immunoglobulins -coagulation factors -fibrinogen Results in edema

Inflammation Pathogenesis of Edema Inflammatory edema: 1. Direct, irreversible injury - all vessels (burns) 2. Transient increase in vascular permeability, i.e., the effect of mediators on post-capillary venules 3- Increased hydrostatic pressure

Inflammation Increased Hydrostatic Pressure

EDEMA -TRANSUDATE (protein content low - specific gravity <1.012)

Hydrostatic

Oncotic

pressure

pressure

Inflammation Increased Vascular Permeability

EDEMA -EXUDATE (protein content high: specific gravity >1.015)

Hydrostatic

Oncotic

pressure

pressure

Diapedesis

Increased Vascular permeability Escape of protein rich fluid into extravascular space -immunoglobulins -coagulation factors -fibrinogen Results in edema

Here is an example of the fibrin mesh in fluid with PMN's that has formed in the area of acute inflammation. It is this fluid collection that produces the "tumor" or swelling aspect of acute inflammation

Mechanisms of increased vascular permeability

Mechanisms of increased vascular permeability 1- Formation of endothelial gaps in post capillary venules 2- Direct injury to endothelial cell 3-Leukocyte Dependent Endothelial Injury 4-Increased Transcytosis 5- Leakage from

Vascular Permeability Although mechanisms are separable All may participate at same time example: Thermal burn 

Chemically mediated endothelial contraction

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Direct injury

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Leukocyte mediated

COMPONENTS OF THE INFLAMMATORY RESPONSE Vascular Changes - Vasodilation (change in caliber and flow) -Increased Vascular Permeability – Acute Local Active Hyperemia Cellular Events - Movement from capillaries and post capillary venules - emigration -Accumulation of leukocytes at sites of injury - migration -Activation of inflammatory cells

Cellular component Accumulation of neutrophil polymorphs in the extracellular space is the diagnostic histologic feature of acute inflammation

Increased Permeability 

Post capillary venules Concentration of RBC’s increases as fluid decreases Blood flow decreases ( slows-stasis) Leucocytes interact with endothelium

Margination Slowing and stagnation of blood flow WBC’s fall out of the central column Tumble slowly and roll along the endothelium of venules

PAVEMENTING endothelium appears to be essentially lined by white cells

Adhesion and Emigration Prerequisite for cells to get to site of inflammation through endothelium. Leukocyte-Endothelial interaction –important Leukocyte aggregation – WBC stick to endothelium and to each other. Adhesion molecules -

molecular surface of WBC’s and endothelium. Bind together to allow WBC’s to adhere.

Sequential involvement of adhesion molecules Rolling  Adhesion  Transmigration

Central Axial Stream

SELECTINS (E&P)

INTEGRINS & Ig-LIKE MOLECULES (ICAM, VCAM)

Qualitative and Quantitative Endothelial and PMN Changes

EMIGRATION Process by which leukocytes escape from their location in the blood to reach the perivascular tissues, (sometimes referred to as Diapedesis…)

Emigration - Process 1. After adhesion - leukocytes move along the endothelial surface 2. Insert large cytoplasmic extension pseudopodia into endothelial gaps 3. Gaps created by actions of histamine and other chemical mediators as well as by the leukocytes themselves 4. PECAM – adhesion molecule is important in this process 5. Entire cell passes through once pseudopodia are through 6. Collagenase excreted breakdown basement membrane

Transmigration Location: postcapillary venule because: -Adequate number of interendothelial gaps -Adequate number of histamine receptors Time: with Mild Inflam -Neutrophils peak 4-6 hours -Mononuclear cells peak 1824 hours-emigration begins when PMN’s decrease and lasts longer

SEQUENCE OF LEUKOCYTE EVENTS Margination Pavementing Emigration Chemotaxis Phagocytosis and Synthesis of biochemical Mediators Intracellular Degradation Extracellular Release of Leukocyte Products

Regulation of Leucocyte Recruitment Binding of chemical agents to specific receptors of leukocyte cell membranes stimulates a variety of events including chemotaxis

Chemotaxis Chemotaxis: Directional migration in response to a chemical gradient of chemoattractant.It is a dynamic and energy dependent activity – -process is receptor mediated. -implies directed locomotion Chemotaxins and Chemokines: - mediators which make leukocytes travel - chemoattractants

Mechanisms of Chemotaxis Leukocytes crawl - require adhesive surface Undergo morphological shape changes - Release of calcium Migrate towards the highest concentration of chemoattractant (Adherence, secretion and locomotion)

Inflammation Chemotaxis Exogenous mediators, e.g.: a- N-formyl methionine terminal amino acids from bacteria b- Lipids from destroyed or damaged membranes (including LPS)

Endogenous mediators, e.g.: a- Complement proteins (C5a) b- Chemokines, particularly IL-8 c-Arachidonic acid products (LTB4)

LEUKOCYTES - CHEMOATTRACTANTS Plasma-derived - C5a, C5a des-Arg - Fibrin degradation products Inflammatory Cell derived - LTB4, HETE’s - from arachidonic acid metabolism - PAF, cytokines – IL-8 Others - Bacterial - fMLP-like peptides, lipid products - Dead cells – necrotaxis Chemokines -Small proteins divided into families. - A form of cytokine.

Inflammation Inflammatory Cell Activation PMNs are activated by many substances: The Fc portion of IgM and IgG molecules C5a, C3b, and iC3b Leukotriene B4 Cytokines (TNF-α) Formylated chemotactic peptides derived from bacteria

Inflammation Activation of Inflammatory Cells Macrophages are activated by many substances: Lipopolysaccharide (LPS), found in Gram-negative bacteria Platelet activating factor (PAF) Cytokines produced by T-cells, particularly interferon gamma (IFN-γ) Fibronectin, a component of extracellular matrix

PHAGOCYTOSIS AND INTRACELLULAR DEGRADATION Purpose- engulf, kill and degrade bacteria Recognise the enemy Engulf it Fuse with enzymes

Recognition and attachment of bacteria Best when coated with opsonins - bind to specific receptors - phagocytosis Important Opsonins i. Antibody (Fc fragment) ii. Fibronectin iii. C3b

Engulfment - Small cytoplasmic extensions or pseudopods extended by cell - Flow around the attached particle until it is engulfed - Cytoplasmic processes pinch together, meet, and fuse - Form a phagosome

Phagolysosome formation Fusion of lysosomal granules with phagosome Degranulation of lysosomes into phagosome Cellular mechanisms similar to that of chemotaxis

Intracellular killing and degradation

Two categories of bactericidal mechanisms are recognized 1) Oxygen-dependent 2) Oxygen-independent

Oxygen-dependent mechanism Respiratory burst of phagocytosis 1.

2-3 x

O2 consumption

2.

superoxide anion generation (02-)

3. H202 production 4.

Glucose metabolism via hexose monophosphate shunt

The Killers H2O2 – Myeloperoxidase-Halide system Myeloperoxidase-dependent killing H2O2 + Cl HOCL

Myeloperoxidase Haber-Weiss reaction O2 + H2O2

iron

- Hydroxyl ion

Nitric Oxide - Peroxynitrite

HO + OH + O2

Fe++

Oxygen Independent Mechanisms Substances within granules Lysozyme - attacks bacterial cell walls - especially gram + bacteria Bacterial permeability increasing protein (BPI) - activates phospholipase degrades cell membranes Lactoferrin - Iron binding glycoprotein Defensins - Cytotoxic to microbes and certain mammalian

Oxygen Independent Mechanisms others Nramp1 protein - (natural resistance-associated macrophage protein one) Major basic protein - Cationic protein of eosinophils - Limited bactericidal activity - Cytotoxic to many parasites Cathepsin G - Antimicrobial properties Lysosomal enzymes

Degradation: pH of the phagolysosome drops (ph 4-5) after phagocytosis This is the optimal pH for the action of degradative enzymes within lysosomes.

Tissue Damage Resulting During Phagocytosis 3 basic mechanisms whereby phagocytic cells release their potent chemical and release tissue at sites of inflammation and thereby contribute to inflammation: - Lysosomal Suicide -Regurgitation during feeding -Reverse endocytosis (frustrated phagocytosis) Important Tissue Toxins 1. Lysosomal enzymes 2. Oxygen-derived active metabolites 3. Products of arachidonic acid metabolism (prostaglandins and leukotrienes)

Lysosomal Suicide - Cytotoxic release 1. Pathogenic bacteria overwhelms the leukocyte -Phagolysosome may rupture into the cytoplasm thus releasing lysosomal enzymes -Kill cell 2. Leukocyte dies • -Releases lysosomal enzymes into local environment • -Producing exudate seen in inflammatory conditions

Regurgitation during feeding -Fusion of lysosome occurs before phagosome is closed -Lysosomal contents released to environment -Producing enzymatic damage to host tissues

Reverse endocytosis (frustrated phagocytosis) Phagocytic stimuli too large to be internalized -eg: bacteria on a fibrin meshwork -eg: complexes of antigen antibody fixed against a basement membrane -eg; immune complexes on joint surface Can not form a phagosome Discharge of lysosomal contents (In frustration!)

Termination of the acute inflammatory response · Mediators have short half lives · Mediators are degraded after release · Produced in short bursts when stimulus persists · Switch to anti-inflammatory lipoxins from arachidonic acid · Production of anti-inflammatory cytokines (TGF-•) · Inhibit the production of TNF in macrophages

Survival of Phagocytosed Microorganisms Most bacteria are killed following phagocytosis.

some survive - either due to a disorder of the

host’s defense system – or due to their own specialized protective mechanisms. Organisms survive within phagolysosome - eg. Coxiella burnetti, some Mycobacterium Some escape phagolysosome and grow in cytoplasm - Eg. Listeria, Rickettsiae Some don’t allow lysosome to fuse with phagosome - Eg. Toxoplasma gondii - Mycobacterium tuberculosis

Inflammation Defects in Phagocytosis Congenital: 1. Chediak-Higashi Syndrome (autosomal recessive) Defective intracellular transport protein, inability to lyse bacteria

2. Job Syndrome (Hyper IgE) 3. Chronic granulomatous disease (x-linked) Neutrophils incapable of producing H2O2 during phagocytosis - No oxidative burst - Results in recurrent infections.

4. Myeloperoxidase deficiency

Inflammation Defects in Phagocytosis Acquired: • • • • •

Iatrogenic immunosuppression (most common) Overwhelming infections Severe trauma or burn Diabetes mellitus Chronic debilitating disease

Acute inflammation

Time 4-6 hours to 3-5 days Vascular involvement Active hyperemia Edema, occ.fibrin thrombi

Neutrophils Cardinal signs of inflammation Lymphatics Role to remove exudate Can lead to inflammation.

Lymphangitis

The series of events in the process of inflammation in organs are: Vasodilation: leads to greater blood flow to the area of inflammation, resulting in redness and heat. Vascular permeability: endothelial cells become "leaky" from either direct endothelial cell injury or via chemical mediators.

Exudation: fluid, proteins, red blood cells, and white blood cells escape from the intravascular space as a result of increased osmotic pressure extravascularly and increased hydrostatic pressure intravascularly here PMN's that are marginated along the dilated venule wall (arrow) by process of diapedesis spill out into extravascular space.

FUNCTION OF THE LOCAL EVENTS OF INFLAMMATION Move defense mechanisms from vascular system out to tissues Results in several basic mechanisms activated at once 1. Increased vascular permeability 2. Leukocyte production 3. Chemotaxis and phagocytosis 4. Coagulation 5. Neovascularization 6. Fibrinolysis 7. Fibroplasia and repair