ACUTE AND CHRONIC INFLAMMATIONMila Amor V. Reyes, MD, FPSPAnatomic and Clinical Pathologist #vlbdatud

INFLAMMATION is the reaction of vascularized living tissue to local injury- evoked by microbial infections, physical agents, chemicals, necrotic tissue, and

immunologic reactions- roles are to contain and isolate injury, to destroy invading microorganisms and

inactive toxins, and to prepare the tissue or organ for healing and repair- maybe potentially harmful causing life threatening hypersensitivity

reactions and progressive organ damage with chronic inflammation may lead to permanent scarring

ACUTE INFLAMMATION: MAJOR EVENTS3 major components:

a. Alterations in vascular caliber that lead to an increase in blood flowb. Structural changes in the microvasculature that permit plasma proteins and

leukocytes to leave the circulation and to produce inflammatory exudate.c. Emigration of the leukocytes from the microcirculation and their accumulation

in the focus of injury

5 cardinal signs of inflammation:Heat (calor) Redness (rubor)Edema (tumor) Pain (dolor)Loss of function (functio laesa)

Definitions Exudation — the escape of fluid, proteins, and blood cells from the vascular

system into the insterstitial tissue or body cavities. Exudate — inflammatory extravascular fluid that has a high protein

concentration, much cellular debris- specific gravity above 1.020

Transudate—fluid with low protein content- SG < 1.012- ultrafiltrate of blood plasma and results from hydrostatic imbalance

across the vascular endothelium. Edema—excess of fluid in the interstitial tissue or serous cavities;

- can be an exudate or a transudate. Pus—purulent inflammatory exudate rich in leukocytes and parenchymal cell

debris

I. CHANGES IN VASCULAR FLOW AND CALIBER- Begin immediately after injury - develop at various rate depending on the severity of the injury- Initially, transient vasoconstriction of arterioles occur vasodilation follows

causing increased flow heat and redness- Eventually slowing of the circulation occurs as a result of increased vascular

permeability lead to stasis. The increased permeability is the cause of edema

- With slowing, the larger white cells fall out of the axial stream, and leukocytic margination appears, a prelude to the cellular events

II. INCREASED VASCULAR PERMEABILITY- Leads to the escape of protein rich fluid into the interstitium- Normal fluid exchange depends on Starling’s law and an intact endothelium

*Starling’s law – maintains normal fluid balance , modulated mainly by two opposing forces:

a. Hydrostatic pressure – cause fluid to move out of the circulationb. Plasma colloid osmotic pressure – cause fluid to move into capillaries

In inflammation: increased hydrostatic pressure – caused by vasodilation decreased osmotic pressure – caused by leakage of high protein fluid across a

hyperpermeable endothelium- marked net outflow of fluid and edema

6 mechanisms of increase endothelial permeability

1. Endothelial cell contraction in venules—formation of widened intercellular junctions, or intercellular gaps, most common form- elicited by chemical mediators (e.g., histamine)- occurs immediately after injection of the mediator- is short lived (immediate transient response)- classically involves venules 20 to 60 µm in diameter, leaving capillaries

and arterioles unaffected

2. Endothelial retraction—due to cystoskeletal and junctional reorganization resulting in widened interendothelial junctions results in delayed response that can be long-lived- induce by cytokine mediators, such as IL-1 & TNF

3. Direct endothelial injury—resulting in endothelial cell necrosis and detachment- caused by severe necrotizing injuries and affects all levels of the

microcirculation- damage usually evokes an immediate and sustained endothelial leakage

4. Leukocyte-mediated endothelial injury—resulting from leukocyte aggregation, adhesion, and emigration across the endothelium- leukocytes release toxic oxygen species and proteolytic enzymes

endothelial injury or detachment increased permeability

5. Increased transcytosis—across the endothelial cytoplasm via vesicles and vacuoles of the vesiculvacuolar organelle- growth factors (e.g., VEGF) may cause vascular leakage by increasing the

number and size of these channels

6. Leakage from regenerating capillaries—during healing- occurs when new capillaries sprouts are leaky

III. CELLULAR EVENTS: LEUKOCYTE EXTRAVASATION AND PHAGOCYTOSIS

A critical function of inflammation is the delivery of leukocytes to the site of injury. The following are the sequence of events in this journey, called EXTRAVASATION:

1. Margination, rolling, and adhesion of leukocytes in the lumen2. Diapedesis – transmigration across the endothelium3. Chemotaxis – migration in the interstitial tissue toward a chemotactic stimulus

ADHESION AND TRANSMIGRATION- Occur largely as a result of interactions between complementary adhesion

molecules on the leukocytes and on the endothelium- Chemoattactants and some cytokines affect these process by modulating the

surface expression or avidity of the adhesion molecules

Major ligand-receptor pairs include:a. selectins (E,P, and L) – bind through their lectin (sugar binding) domains to

oligosaccharides (e.g., sialylated Lewis X), which themselves are covalently bound to cell surface glycoproteins

b. The immunoglobulin family – includes the endothelial ICAM-1 and VCAM-1c. The integrins – functions as receptors for some of the immunoglobulin family

and the extracellular matrix- principal integrin receptors for ICAM-1 are the β2 integrins, LFA-1 and

MAC-1- those for VCAM-1 are the integrins α4β1 and α4β7

These molecules induce leukocyte adhesion in inflammation by 3 mechanisms:a. Redistribution of preformed adhesion molecules to the cell surfaceb. Induction of adhesion molecules on endotheliumc. Increased avidity of binding

Sequence of Leukocyte events in inflammation, shown here for neutrophils. The leukocytes first roll, then become activated and adhere to endothelium transmigrate across and pierce basement membrane migrate toward chemoattractants emanating from the source of injury

ENDOTHELIAL LEUKOCYTE ADHESION MOLECULESPMN adhesion and transmigration in acute inflammation occur only by a

series of overlapping steps:

1. Endothelial activation—mediators present at the inflammatory sites increased the expression of E-selectin and P-selectin by endothelial cells

2. Leukocyte rolling—initial rapid and relatively loose adhesion, resulting from interactions between the selectins and their carbohydrate ligands

3. Firm adhesion—leukocytes are then activated by chemokines or other agents to increased the avidity of their integrins

4. Transmigration—mediated by interactions between PECAM-1 on leukocytes and endothelial cells

Leukocyte adhesion deficiency type-I—defect in the synthesis of β2 integrins Leukocyte adhesion deficiency type-II—defect in fucose metabolism in the absence

of sialyl Lewis X, the ligand for E-selectin and P-selectin - Both deficiencies result in impaired leukocyte adhesion and recurrent

bacterial infections.

CHEMOTAXIS AND LEUKOCYTE ACTIVATION Adherent leukocytes emigrate through interendothelial junctions traverse

the basement membrane move toward the site of injury along a gradient of chemotactic agents

Neutrophils emigrate first, monocytes and lymphocytes follow

Chemotactic agents for neutrophils include- bacterial products- complements fragments (e.g., C5a)- arachidonic acid metabolites (e.g., leukotriene B4)- chemokines (e.g., IL-8)

Chemotaxis involves binding of chemotactic agents to specific receptors on leukocytes production of second messengers

Signal transduction process results In:- activation of phospholipase C and protein kinase C- increased intracellular calcium - assembly of the contractile elements responsible for cell movement

leukocyte moves by extending a pseudopod pulls the remainder of the cell in the direction of extension

Locomotion is controlled by the effects of Ca++ and phosphoinositols on actin regulatory proteins, such as gelsolin, filanin and calmodulin

Chemotactic agents also cause leukocyte activation, characterized by:- Degranulation and secretion of enzymes- Activation of an oxidative burst- Production of arachidonic acid metabolites- Modulation of the leukocyte adhesion molecule

Biochemical events in leukocyte activation. (1) receptor-ligand binding (2) Phospholipase C activation (3) intracellular calcium and (4) activation of Protein Kinase C. The biologic activities (5) resulting include chemotaxis, modulation of adhesion molecules, elaboration of arachidonic acid metabolites, secretion/degranulation, and oxidative burst. PIP2 – phosphatidylinositol biphosphate

PHAGOCYTOSIS Release of enzymes by neutrophils and macrophages constitute two of the

major benefits derived from the accumulation of leukocytes at the inflammatory focus

Phagocytosis involves three steps:1. Recognition and attachment of the particles to be injected by the leukocyte—

microorganisms are coated with specific factors, called OPSONINS, which enhance the efficiency of phagocytosis because they are recognized by the receptors on the leukocytes- two major opsonins:a. the Fc fragments of the immunoglobulin G b. a product of complement C3b

2. Engulfment by pseudopods encircling the phagocytosed particle—> subsequent formation of a phagocytic vacuole or PHAGOSOME membrane of the phagosome fuses with the membrane of a lysosomal granule discharge of the granules content into the PHAGOLYSOSOME

3. Killing and degradation of bacteria—phagocytosis stimulates a burst of oxygen consumption and production of reactive oxygen metabolites

There are two types of bactericidal mechanisms:a. Oxygen dependent mechanisms—triggered by activation of NADPH oxidase

reduce O2 to O2- and hence to H2O2;

- MPO from lysosomal granules then converts H2O2, in the presence of a halide such as Cl-, to a highly bactericidal HOCl - ;

- H2O2-MPO-halide system is the most efficient bactericidal mechanism, the reactive O2 species produced during an oxidative burst can kill bacteria directly

b. Oxygen independent mechanisms—includes bactericidal permeability increasing protein, lysozyme, lactoferrin, MBP of eosinophils, and arginine rich defensins- killed organisms are then degraded by hydrolases and other enzymes in

lysosomes

RELEASE OF LEUKOCYTE PRODUCTS AND LEUKOCYTE-INDUCED TISSUE INJURY During phagocytosis, leukocytes release products not only within the

phagolysosome but also potentially into the extracellular space:a. From regurgitation during feeding, reverse endocytosis, or cytotoxic

release Lysosomal enzymesb. Oxygen derived active metabolitesc. Arachidonic acid metabolism products prostaglandins and leukotrienes

- These products are powerful mediators of tissue damage amplify the effects of the initial inflammatoy stimulus ff persistent leukocyte dependent tissue can cause chronic inflammation

DEFECTS IN LEUKOCYTES FUNCTION- Interfere with inflammation - increase susceptibility to infections- Include both genetic and acquired defects, such as deficiency in the number of

circulating cells (neutropenia)- Clinical genetic deficiencies have been identified in most phases of leukocyte

function, from adherence to vascular endothelium to microbicidal activity, and include the following:a. Defects in leukocyte adhesion – leukocyte adhesion deficiency type I and

type II

b. Defects in phagocytosis – Chediak-Higashi syndrome—PMNs have a giant granules because of abberant organelle fusion and reduced transfer of lysosomal enzymes to phagocytic vacuoles (causing susceptibility to infections)

c. Defects in microbial activity such as CGD—inherited defects in NADPH oxidase, leading to a defect in the respiratory burst, H2O2-MPO-halide bactericidal mechanism

(A) Phagocytosis of a particle (e.g. bacterium) involves attachment and binding of Fe and C3b receptors on the leukocyte membrane. Engulfment and fusion of granules (in red) with phagocytic vacuoles, followed by degranulation. Note that during phagocytosis, granule contents may be released extracellularly

(B) Summary of oxygen-dependent bactericidal mechanisms within the phagocytic vacuole

Clinical Examples Of Leukocyte-Induced Injury

Defects In Leukocyte Functions

Acute

Acute respiratory distress syndromeAcute transplant rejectionAsthmaGlomerulonephritisReperfusion injurySeptic shockVasculitis

Chronic

ArthritisAsthmaAtherosclerosisChronic lung diseaseChronic rejectionOthers

SUMMARY

The vascular phenomena in acute inflammation are characterized by increased blood flow to the injured area, resulting mainly from arteriolar dilation and opening of capillary beds.

Increased vascular permeability results in the accumulation of protein-rich extavascular fluid, which forms the exudate.

Plasma proteins leave the vessels most commonly through widened interendothelial cell junctions of the venules or by direct endothelial cell injury.

The leukocytes, initially predominantly neutrophils, adhere to the endothelium via adhesion molecules, transmigrate across the endothelium, and migrate to the site of injury under the influence of chemotactic agents.

Phagocytosis of the offending agent follows, which may lead to the death of the microorganism.

During chemotaxis and phagocytosis, activated leukocytes may release toxic metabolites and proteases extracellularly, potentially causing tissue damage.

CHEMICAL MEDIATORS OF INFLAMMATION The vascular and white cell events described previously are brought about by

the variety of chemical mediators, derived either from plasma or from cells. Most perform their biologic activity by binding initially to a specific receptors

on target cells, although some have direct enzymatic activity (e.g., proteases), and others mediate oxidative damage (e.g., oxygen metabolites).

One mediator can stimulate the release of other mediators by the target cells themselves, providing a mechanism for amplification or in certain instances counteracting the initial mediator action.

Once the activated and released, most mediators are short lived, either quickly decaying or becoming inactivated by enzymes or inhibited by inhibitors. Thus, a system of checks and balances exist in the regulation of mediators also have potentially harmful effects.

VASOACTIVE AMINES

Histamine and serotonin—available from preformed cellular stores- among the first mediators to be release during inflammation- found in mast cells, basophils, and platelets- cause vasodilation and increase vascular permeability

Released from mast cells is caused by:- Physical agents (e.g., trauma, heat)- Immunologic reactions involving binding of IgE antibodies to mast cells- Complement fragments C3a and C5a (anaphylatoxins)- Neuropeptides (substance P)- Cytokines (IL-1 and IL-8)- Histamine releasing factors derived from leukocytes

Released from platelets is stimulated by: contact with collagen, thrombin, ADP, antigen-antibody complexes, and by PAF

PLASMA PROTEASESThere are interrelated plasma derived mediators that play key roles in inflammatory responses:

1. Complement system2. Kinin sytem 3. Clotting factor system

Complement system:- Activation of complement functions in host defense against microbial agents,

culminating in the assembly of the MAC and lysis of the offending agent- complement components are generated that caused increased vascular

permeability, chemotaxis and opsonization - Activation of complement occurs via two general mechanisms:

a. The classic pathway—initiated by antigen-antibody complexesb. The alternate pathway—activated by endotoxin, complex

polysaccharides, and aggregated globulins

Complement components with inflammatory activity include: C3a—which increases vascular permeability C5a—which increases vascular permeability and is highly chemotactic to

WBCs C3b and C3bi—the opsonins important in phagocytosis C5b-9—MAC that lyses cells and stimulates arachidonic acid metabolism and

production of reactive oxygen metabolites by a leukocytes

Protein inhibitors:1. decay accelerating factor – regulation of C3 and C5 convertases

Paroxysmal nocturnal hemoglobinuria—cells lack the ability to express phosphatidylinositol-linked membrane proteins, including decay accelerating factor- characterized by recurrent bouts of intravascular hemolysis

resulting from complement-mediated lysis of red blood cells, leading to chronic hemolytic anemia

2. Binding of active complement components by specific proteins in the plasma, such as by C1 inhibitor

Deficiency of C1 inhibitor associated with the syndrome of hereditary angioneurotic edema—episodic edema accumulation in the skin and extremities as well as in the laryngeal and intestinal mucosa, provoked by emotional stress or trauma

Kinin System Generates vasoactive peptides from plasma proteins called kininogens by

specific proteases called kallikreins, ultimately resulting in the production of bradykinin

Surface activation of Hageman factor (factor XII) produces CF XIIa converts plasma prekallikrein into Kallikrein latter cleaves HMWK to produce Bradykinin—a potent stimulator of increase vascular permeability

Kallikrein in an autocatalytic loop is a potent activator of Hageman factor, has chemotactic activity, and causes neutrophil aggregation; resulting in profound amplification of the effects of the initial contact

Clotting System divided into two interrelated that converges to activate a primary hemostatic

mechanism:1. Intrinsic pathway – consists of plasma proenzymes that can be activated by

Hageman factor activation of thrombin cleavage of fibrinogen, and generation of a fibrin clot - During this process, fibrinopeptides are formed that induce vascular

permeability and are chemotactic for leukocytes.- Thrombin also has inflammatory properties causing increased leukocyte

adhesion to endothelium.

2. At the same time that factor XIIa is inducing clotting, it can also activate the fibrinolytic system produces plasmin and degrades fibrin solubilize the clot.Plasmin can contribute to inflammation in several ways:- Cleave C3 to produce C3 fragment- Form fibrin split products – may increase vascular permeability- Activate Hageman factor – ampliying the response

ARACHINDONIC ACID METABOLITES: Eicosanoids- are synthesized from arachidonic acids by two major classes of enzymes:

a. Cyclooxygenases—generate prostaglandins and thromboxanesb. Lipoxygenases—produce leukotriene and lipoxins

Inflammatory prostaglandins and leukotrienes: Prostaglandin I2 (prostacyclin) and prostaglandin E2 cause vasodilation Prostaglandin E2 is hyperalgesic—makes the skin hypersensitive to painful

stimuli Thromboxane A2 causes vasoconstriction Leukotrienes C4, D4, and E4—cause increased vascular permeability and

vasoconstriction Leukotriene B4 is a powerful chemotactic agent Lipoxins may be endogenous negative regulators of leukotriene action

*Cell-cell interactions are important in the biosynthesis of both the leukotrienes and lipoxins. Arachidonic acid products can pass from one cell to another to generate these classes of eicosanoids. *This transcellular biosynthesis allows cells that are not capable of generating specific eicosanoids to produce these mediators from intermediate generated in other cells.

PLATELET-ACTIVATING FACTOR- PAF is a bioactive phospholipids-derived mediator.- Produced by mast cells and other leukocytes- Causes platelet aggregation and release, bonchoconstriction, vasodilation,

increased vascular permeability, increased leukocyte adhesion, and leukocyte chemotaxis

- Can elicit most of the cardinal features of inflammation

CYTOKINES- Cytokines are proteins produced principally by activated lymphocytes and

macrophages that modulate the function of other cell types. - Many classic growth factors act as cytokines, and conversely many cytokines

have growth-promoting properties.

MONOKINES—cytokines generated by mononuclear phagocytes LYMPHOKINES—cytokines generated by active lymphocytes Colony Stimulating Factors (CSF) – cytokines that are produced by monocytes and

macrophages that stimulate the growth of immature leukocytes in the bone marrow

INTERLEUKINS (IL)—broad family of cytokines that are made by the hematopoietic cells and act primarily on leukocytes

CHEMOKINES—cytokines that share the ability to stimulate leukocyte movement (chemokinesis) and directed movement (chemotaxis), particularly important in inflammation

General Properties and Classes of Cytokines1. Cytokines are produced during immune and inflammatory responses, and

secretion of these mediators is transient and closely regulated.2. Many cell types produce multiple cytokines.3. The proteins are pleiotropic in that they can act on different cell types.4. Cytokine effects are often redundant, and these proteins can influence the

synthesis or action of other cytokines.5. Cytokines are multifunctional in that an individual cytokine may have both

positive and negative regulatory actions.6. Cytokines mediate their effects by binding to specific receptors on target cells,

and the expression of cytokine receptors can be regulated by a variety of exogenous and endogenous signals.

Functions of Cytokines1. Cytokines that regulate lymphocyte function

- Regulate lymphocyte activation, growth, and differentiation (e.g., IL-2 and IL-4, which favor lymphocyte growth; IL-10 and TGF-β, which are negative regulators of immune responses)

2. Cytokines involved with natural immunity- Includes the inflammatory cytokines (e.g., TNF-α and IL-1β), type I IFN

(IFN- α and IFN- β), and IL-63. Cytokines that activate inflammatory cells

- Activate macrophages during cell mediated immune responses (e.g., IFN-γ, TNF- α, IL-5, IL-10, and IL-12)

4. Chemokines - Cytokines characterized by chemotactic activity for various leukocytes

(e.g., IL-8)5. Cytokines that stimulate hematopoiesis

- Mediate immature leukocyte growth and differentiation (e.g., IL-3, IL-7, c-kit ligand, GM-CSF, M-CSF, G-CSF, and stem cell factor)

*IL-1 and TNF-α - major cytokines that mediate inflammation and are produced by activated macrophages. Their most important actions in inflammation are their effects on endothelium, leukocytes and induction of the systemic acute-phase reactions.

- Secretion in stimulated by endotoxin, immune complexes, toxins, physical injury and a variety of inflammatory products

- Induce endothelial activation, which includes induction of endothelial adhesion molecules and chemical mediators (e.g., other cytokines [IL-6], chemokines [IL-8], growth factors, eicosanoids [PGI2 and PAF], and nitric oxide) production of enzymes associated with matrix remodeling, and increases in the surface thrombogenicity of the endothelium

- Induce the systemic acute-phase responses associated with infection or injury, including fever, loss of appetite, production of sleep, release of neutrophils into the circulation, release of ACTH and corticosteroids; and particularly with

regard to TNF, hemodynamic effects of septic shock – hypotension, decreased vascular resistance, increased heart rate, and decreased blood pH

*TNF-α has a key role in the normal control of body mass- In obesity—physiologic actions of TNF- α as a signal to control food intake are

impaired- In cachexia—pathologic state characterized by weight loss and anorexia that

accompanies some infections and neoplastic diseases, there is an overproduction of TNF-α

CHEMOKINES - Chemokines act primarily as activators and chemoreactants for specific types

of leukocytes. - Chemokines are classified into four major classes, which have relatively

distinct biologic activities, according to the arrangement of the conserved cysteine (C) residues:

1. C-X-C or α-chemokines—have one amino acid residue separating the first two conserved cysteine residues act primarily on neutrophils; IL-8 is typical of this group

2. C-C or β-chemokines—have the two first conserved cysteine residues adjacent: e.g., monocyte chemoattractant protein (MCP-1), generally attract

monocytes, eosinophils, basophils, and lymphocytes but not neutrophils: eotoxin selectively recruits eosinophils

3. C or γ-chemokines—lack two (the first and third) of the four conserved cysteines: relatively specific for lymphocytes (e.g., lymphotactin)

4. CX3C chemokines—include fractalkine, exist in two forms:a. Cell surface-bound protein—can be induced in endothelial cells that

promote adhesion of the leukocytesb. hSoluble form—derived from proteolysis of membrane-bound protein,

has chemoattractant activity

- Chemokines mediate their activities by binding to G-protein-linked receptors:a. CXCR (1-4) for the C-X-C chemokinesb. CCR (1-5) for the C-C chemokines.

NITRIC OXIDE – endothelium-derived relaxation factor- Acts in paracrine manner and causes vasodilation; inhibits platelet

aggregation and adhesion; and may act as a free radical, becoming cytotoxic to certain microbes, tumor cells and also possibly other tissue cells

- Synthesized from arginine, molecular O2, NADPH, and other cofactors by the enzyme nitric oxide synthase (NOS)

3 types of NOS:a. Endothelial (eNOSb. neuronal (nNOS)c. cytokine inducible [iNOS]

Exhibits two patterns of expression:1. eNOS and nNOS are present constitutively and are rapidly activated by an

increased in cytoplasmic Ca++

2. iNOS is present in macrophages and is induced by cytokines, such as IFN-γ, without an increase in intracellular Ca++

Properties:- Plays an important role in vascular function during an inflammatory response- eNOS is important in maintaining vascular tone- Increased production of NO from iNOS is an endogenous compensatory

mechanism that reduces leukocyte recruitment in inflammatory responses- iNOS production of NO by activated macrophages is also important in the

pathogenesis of septic shock- Acts in the host response to infection- Interactions occur between NO and reactive O2 species, leading to the

formation of multiple antimicrobial metabolites (e.g., peroxynitrite [OONO], S-nitrosothiols [RSNO], and nitrogen dioxide [NO2])

- Each reactive form is distinct, but they share the ability to damage microbes, at the potential cost of inflammatory damage to host cells and tissue

Two types of NO synthesis in endothelium (left) and macrophages (right). NOS = NO synthase

LYSOSOMAL CONSTITUENTS OF LEUKOCYTES- can potentiate further increases in vascular permeability and chemotaxis and

cause tissue damage- harmful proteases are held in check by a system of antiproteases in the serum

and the tissue fluidex.: α1-antitrypsin – major inhibitor of neutrophilic elastase

If (+) deficiency sustained action of leukocyte proteasesex: patients with α1-antitrypsin deficiency

1. Lysosomal granules – found in neutrophils and monocytes which when released may contribute to the inflammatory response and to tissue injury.Neutrophils have two main types of granulesa. Smaller specific (or secondary) granules—contain lysozyme, type IV

collagenase, gelatinase, lactoferrin, plasminogen activator, istaminases, alkaline phosphatase, leukocyte adhesion molecules, and phospholipase A2

b. Large azurophil (or primary) granules—contain myeloperoxidase, bactericidal factors (lysozyme defensins), acid hydrolases, cationic proteins, phospholipase A2, and a variety of neutral proteases (elastase, cathepsin G, non-specific collagenases, proteinase 3)

- Both can empty into phagocytic vacuoles that form around engulfed material, or the contents can be secreted extracellulary, as well as released after cell death

2. Acid proteases – degrade proteins, bacteria, and debris within the acidic environment of the phagolysosome

3. Neutral proteases – degrade extracellular components4. Hydrolases (collagenase, elastase, phospholipase, and plasminogen activator) –

found in monocytes and macrophages bb, which maybe particularly active in chronic inflammatory reactions

Oxygen-Derived Free Radicals Maybe released extracellularly from leukocytes after exposure to chemotactic

agents, immune complexes, or a phagocytic challenge Include O2

.-,H2O2, and OH., these metabolites can combine with NO to form other reactive nitrogen intermediates, which cause:- Endothelial cell damage with resultant increased vascular permeability- Inactivation of antiproteases, thus leading to unopposed protease activity- Injury to a variety of cell types (e.g., tumor cells, red cells, parenchymal

cells) Oxygen metabolites are detoxified by: ANTIOXIDANTS—serum proteins

(ceruloplasmin and transferrin), enzymes (superoxide dismutase, catalase, and glutathione peroxidase)

Net effects on tissue injury of oxygen metabolites depend on the balance between their production and activation

NEUROPEPTIDES – play a role in the initiation of an inflammatory response Substance P—belong to a family of tachykinin neuropeptides in the central

and peripheral nervous system- Biologic functions: transmission of pain signals, regulation of blood

pressure, and stimulation of secretion by immune and endocrine cells- Powerful mediator of vascular permeability- Released of substance P alters vascular permeability leading to influx of

plasma components at the site of injury and amplification of the initial inflammatory stimulus

SUMMARY OF MEDIATORS OF ACUTE INFLAMMATION

Mediator SourceVascula

r Leakage

Chemotaxis Other

Histamine and serotonin

Mast cells and platelets

+ -

Bradykinin Plasma substrate

+ - Pain

C3a Plasma protein + - Opsonic fragment

via liver (C3b)

C5a Macrophages + +Leukocyte adhesion,

activation

Prosta-glandins

Mast cells, from membrane

phospholipids

Potentiate other

mediators-

Vasodilation, pain, fever

Leukotriene B4 Leukocytes - +Leukocyte adhesion,

activationLeukotriene

C4, D4, E4

Leukocytes, mast cells

+ -Bronchoconstriction,

vasoconstrictionOxygen

metabolitesLeukocytes + -

Endothelial damage, tissue

PAF Leukocytes, mast cells

+ +Bronchoconstriction,

leukocyte priming

IL-1 and TNF Macrophages, other

- +Acute phase

reactions, endothelial activation

Chemokines Leukocytes, other

- + Leukocyte activation

Nitric oxide Macrophages, endothelium

+ +Vasodilation, cytotoxicity

Early course of inflammation increased vascular permeability is medicated by histamine; the anaphylatoxins (C3a and C5a); the kinins; leukotrienes C, D, and E; PAF; and substance P

For chemotaxis, complement fragment C5a, lipoxygenase products (leukotriene B4), other chemotactic lipids, and chemokines are the most likely protagonist

prostaglandins – role in vasodilation, pain, and fever and in potentiating edema.

IL-1 and TNF – involved with endothelial-leukocyte interactions and with acute phase reactions.

Lysosomal products and oxygen-derived radicals – most likely candidates as causes of the ensuing tissue destruction.

Nitric oxide is involved in vasodilation and cytotoxicity

OUTCOME OF ACUTE INFLAMMATION process of acute inflammation can be altered by the nature and intensity of

the injury, the site and the tissue affected, and the responsiveness of the host, but generally the process has one of the 4 outcomes:

1. Complete resolution—regeneration of native cells and restoration of the site to normal

2. Abscess formation—infections by pyogenic organisms

3. Healing by connective tissue replacement (fibrosis) and scarring— occurs after substantial tissue destruction, when the inflammation occurs in tissues that do not regenerate, or when there is abundant fibrin exudation

4. Progression to chronic inflammation

Events in resolution of inflammation: (1) return to normal vascular permeability, (2) drainage of edema fluids and proteins into lymphatics, or (3) by pinocytosis in macrophages; (4) phagocytosis of apoptotic neutrophils; (5) necrotic debris by macrophages; and (6) disposal of macrophages. Note the central role of macrophages in resolution.

CHRONIC INFLAMMATION Inflammation of prolonged duration (weeks or months) in which active

inflammation, tissue destruction, and attempts at healing may be all proceeding simultaneously

Arises in several ways:- May follow acute inflammation, because of the inciting stimulus or

because of some interference in some process of healing- May results from repeated bouts of acute inflammation

Begins insidiously as a low grade, smoldering response that does not follow classic acute inflammation in one of the following settings:a. Persistent infections by intracellular microbes which are of low toxicity

but evoked an immunologic reaction b. Prolonged exposure to potentially toxic exogenous or endogenous

substancesc. Immune reactions, perpetuated against the individual’s own tissues

Characteristic of Chronic Inflammation: Infiltration with mononuclear cells (macrophages, lymphocytes, and plasma

cells)—a reflection of a persistent reaction to injury Tissue destruction, largely induced by the inflammatory cells Attempts at repair by connective tissue replacement, proliferation of small

blood vessels (angiogenesis) and fibrosis

MONONUCLEAR INFILTRATION: CELLS AND MECHANISMS

Macrophages the major cellular players in chronic inflammation Derived from peripheral blood monocytes that have been induced to emigrate

across the endothelium by chemokines as well as well as other chemotactic agents; when the monocytes reaches the extravascular tissue; it transform into a large phagocytic cell, the macrophage

Central figures in chronic inflammation- great number of biologically active products they can secrete- can be activated by cytokines produced by immune activated T-cells or

by nonimmune factors (e.g., endotoxin) to secrete numerous factors including:

a. Neutral proteasesb. Chemotactic factorsc. Arachidonic acid metabolitesd. Reactive oxygen & nitrogen speciese. Complement componentsf. Coagulation factorsg. Growth factors

h. Cytokines (eg, IL-1 & TNF)i. Other factors (eg, PAF & α- IFN)

important host defense – some of these mediators induce the tissue damage characteristic of chronic inflammation - Secretory products can be toxic to cells (reactive oxygen and nitric oxide

metabolites) or extracellular matrix (protease)- Other products cause fibroblast proliferation, connective tissue

production, and angiogenesis (cytokines and growth factors) Macrophage accumulation persists primarily through continued recruitment

of monocytes from circulation—results from the steady expression of adhesion molecules and chemotactic factors

Maturation of Macrophage:

Macrophage Activation:

Products released By Macrophages - Enzymes- Neutral proteases- Elastase - Collagenase - Plasminogen activator- Acid hydrolases - Phosphates - Nitric oxide

- Lipases- Plasma proteins- Complement components (e.g., C1 to C5, properdin)- Coagulation factors (e.g., factors V, VIII, tissue factor)- Reactive metabolites of oxygen- Eicosanoids - Cytokinesis, chemokines (IL-1, TNF, IL-8)- Growth factors (PDGF, EGF, FGF TGF-β)

Other Cells of Chronic InflammationLYMPHOCYTES—mobilized by antibody and cell-mediated immune reactions and by nonimmunologic reactions

Have a unique reciprocal relationship to macrophages in chronic inflammation activated by contact with antigen and nonspecifically by bacterial endotoxin Activated lymphocytes produce lymphokines, and these (particularly IFN-γ)

are major stimulators of monocytes and macrophages

ACTIVATED MACROPHAGES – produces monokines B-cell and T-cell function (particularly IL—1, TNF)

PLASMA CELLS – produce antibodies directed against either foreign antigen or altered tissue components

MAST CELLS—widely distributed in connective tissues and participate in both acute and persistent inflammatory reactions

Express on their surface the receptor that binds the Fc portion of the IgE antibody In acute reactions, IgE antibodies specifically recognize antigen cells degranulate and release mediators, such as histamine

response occurs during anaphylactic reactions to food, insect venom, or drugs, frequently with catastrophic results

Specific types of parasite infections are also associated with increased levels of IgE and activation of mast cells

EOSINOPHILS—characteristic of immune reactions mediated by IgE and of parasitic infections

Recruitment depends on eotoxin, a member of the C-C family of chemokines Have granules that contain MBP – a highly cationic protein that is toxic to

parasites but also causes lysis of mammalian epithelial cells May be of benefit in parasitic infection but contribute to tissue damage in

immune reactions

GRANULOMATOUS INFLAMMATION Distinctive chronic inflammatory reaction in which the predominant cell type

is an activated macrophage with a modified epithelial-like (epithelioid cell) appearance

Encountered in a relatively few but widespread chronic immune and infectious diseases, such as tuberculosis, sarcoidosis, and syphilis

Characterized by GRANULOMAS—focal collections epithelioid macrophages that are surrounded by a collar of mononuclear leukocytes, principally lymphocytes and occasionally plasma cell- epithelioid cells may coalesce to form multinucleated giant cells- central necrosis may also be present in some granulomas - two types of granulomas:a. Foreign body granulomas—incited by relatively inert foreign bodiesb. Immune granulomas—formed by immune T-cell-mediated reactions to

poorly degradable antigens- lymphokines, principally IFN-γ from activated T-cells cause

transformation of macrophages to epitheloid cells and multinucleated giant cells

- Ex: TUBERCLE – immune granuloma caused by the M. tuberculosis, characterized by the presence of central caseous necrosis

Examples Of Granulomatous Infections DISEASE CAUSE TISSUE REACTION

Tuberculosis

• M. tuberculosis

a. Noncaseating tubercle (granuloma prototype) – focus of epithelioid cell, rimmed by fibroblast, lymphocytes, histiocytes, occasional Langhans giant cell

b. caseating tubercle – central amorphous granular debris, loss of all cellular detail; acid-fast bacilli

Leprosy • M. lepraeAcid-fast bacilli in macrophages; granulomas and epithelioid types

Syphillis• Treponema

pallidum

GUMMA – microscopic to grossly visible lesion, enclosing wall of histiocytes; plasma cell infiltrate; center cells are necrotic without loss of cellular outline

Cat-scratch disease

Gram-negative bacillus

Rounded or stellate granuloma containing central granular debris and recognizable neutrophils; giant cells uncommon

Morphologic Patterns in Acute and Chronic InflammationInflammatory responses often have certain features that point to their possible cause and create a distinctive morphologic patterns:

a. Serous inflammation—implies a modest increase in vascular permeability; marked by an accumulation of fluid (e.g., skin burn blisters)

- when it occurs in the peritoneal, pleural, and pericardial cavities, is called an effusion

- ascitis – peritoneal effusionb. Fibrinous inflammation—occurs when the injury causes a more marked

increased in vascular permeability- exudate contains large amounts of fibrinogen, which is converted to fibrin as a

result of the coagulation system - when a serosal surface is involved, such as the pericardium, pleura, or

peitoneum, it is referred to as fibrinous pericarditis, pleuritis, or peritonitis, respectively

c. Suppurative or purulent inflammation—characterized by the production of purulent exudates or pus consisting of white cells and necrotic cells- ABSCESS refers to a localized collection of purulent inflammatory tissue

that is accompanied by liquefactive necrosis; there is a wall to separate it from environment

d. Ulcers—local defects, or excavation, of the surface of an organ or tissue that are produced by the sloughing (shedding) of inflammatory necrotic tissue

e. Granulomatous inflammation

major systemic manifestations: Endocrine and metabolic—secretion of acute-phase proteins by the liver

(including CRP, serum amyloid A, complement and coagulation proteins)

Autonomic—redirection in blood flow from cutaneous to deep vascular beds, to minimize heat loss through the skin; increased pulse and blood pressure; and decrease sweating

Behavioral—rigors (shivering), chills (search for warmth), anorexia, somnolence, and malaise

Other major systemic manifestations: Fever is an elevation of body temperature, usually by 1 to 4oC.

- Cytokines play a key role in signaling a fever—IL-1, IL-6, and TNF-α, produced by leukocytes in response to infectious agents or immunologic reactions, are released into the circulation

- IL-1 acts directly and also by inducing IL-6, which has essentially similar effects in producing the acute-phase responses

- IL-1 and TNF interact with vascular receptors in the thermoregulatory centers of the hypothalamus, inducing local prostaglandin E2 production, resulting in a sympathetic nerve stimulation, vasoconstriction of skin vessels, and fever

Leukocytosis—a common feature of inflammatory reactions, especially those induced by bacterial infection- Extreme elevations are referred to as leukemoid reactions- occurs because of the proliferation of precursors in the bone marrow and

the accelerated released of cells from the bone marrow, induced by CSF Neutrophilia – induced by most bacterial infections Lymphocytosis – induced by some viral infections Eosinophilia— bronchial asthma, hay fever, and parasitic infestations Leukopenia – caused by certain infections (e.g., typhoid fever and infections

caused by viruses, rickettsiae, and certain protozoa)- also encountered in infections that overwhelm patients debilitated by

disseminated cancerThus the major systemic effects of a significant inflammatory reaction are fever, leukocytosis (most often owing to an increased number of circulating neutrophils, sometimes lymphocytes) and chills, well known to all who have had a respiratory infection.