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BASICS OF INFLAMMATION AND HYPERSENSITIVITY REACTIONS

BY

Dr. Bhuvan Nagpal B.D.S. (Hons.), M.D.S. (Oral Pathology)

(Gold Medalist) Consulting Oral & Maxillofacial Pathologist

Ex. Post Graduate Resident, Dept. of Oral Pathology & Microbiology,

JSS Dental College & Hospital, JSS University,

Mysuru, Karnataka, India

Dr. Anuradha Nagpal M.B.B.S. (Hons.) House Surgeon

Teerthanker Mahaveer Medical College & Research Centre, Teerthanker Mahaveer University, Moradabad, Uttar Pradesh, India

Dr. Anupam Nagpal B.D.S. (Hons.) (Gold Medalist) House Surgeon

Teerthanker Mahaveer Dental College & Research Centre, Teerthanker Mahaveer University, Moradabad, Uttar Pradesh, India

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S. No CONTENTS Page No.

1. INTRODUCTION 3

2. TYPES OF INFLAMMATION 4

3. ACUTE INFLAMMATION 5

4. CHEMICAL MEDIATORS OF INFLAMMATION 11

5. INFLAMMATORY CELLS 16

6. MORPHOLOGY OF ACUTE INFLAMMATION 18

7. APPLIED ASPECTS OF INFLAMMATION IN DENTISTRY 19

CHRONIC INFLAMMATION 20

GRANULOMATOUS INFLAMMATION 26

SYSTEMIC EFFECTS OF INFLAMMATION 29

11. INTRODUCTION TO HYPERSENSITIVITY 34

12. CLASSIFICATION 34

13. MECHANISM 35

14. OVERVIEW OF TYPES OF HYPERSENSITIVITY 35

15. TYPE I ANAPHYLAXIS 36

16. TYPE II CYTOTOXIC TYPE 41

17. TYPE III IMMUNE COMPLEX MEDIATED TYPE 44

18. TYPE IV DELAYED TYPE HYPERSENSITIVITY 45

19. TYPE V STIMULATORY HYPERSENSITIVITY 57

20. SUMMARY OF HYPERSENSITIVITY 58

21. REFERENCES 59

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INTRODUCTION

Inflammation is defined as a local response of living mammalian tissue to

injury due to any agent. It is a body defense mechanism in order to eliminate the

spread of injurious agent as well as to remove the consequent necrosed cells and

tissues.

The agents causing inflammation may be as under :

Physical agents like heat, cold, radiation, mechanical trauma.

Chemical agents like organic and inorganic poisons

Infective agents like bacteria, viruses and their toxins.

Immunological agents like cell mediated and antigen antibody reactions.

Signs of inflammation

Rubour (redness)

Tumor (swelling)

Calor (heat)

Dolor (pain)

Functio laesa (loss of function)

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Functions of inflammation

1. Destroy and remove pathogens

2. If destruction is not possible, to limit effects by confining the pathogen and its

products.

3. Repair and replace tissue damaged by pathogen and its products.

Types of inflammation

Depending upon the defense capacity of the host and duration of response,

inflammation can be classified as acute and chronic.

1. Acute inflammation

It is of short duration and represents the early body reaction and is usually

followed by repair.

The main features of acute inflammation are :

1. Accumulation of fluid and plasma at the affected site.

2. Intravascular activation of platelets.

3. Polymorphonuclear neutrophils as inflammatory cells.

2. Chronic inflammation

It is of longer duration and occurs either after the causative agent of acute

inflammation persists for a long time, or the stimulus is such that it induces chronic

inflammation from the beginning.

The characteristic of chronic inflammation is presence of chronic inflammatory

cells such as lymphocytes, plasma cells and macrophages.

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ACUTE INFLAMMATION

The changes in acute inflammation can be described under the following 2

headings

1. Vascular events

2. Cellular events

I. Vascular events

Alteration in the microvasculature (arterioles, capillaries and venules) is the

earliest response to tissue injury. These alterations include hemodynamic changes and

changes in vascular permeability.

Hemodynamic Changes

1. Transient vasoconstriction : Irrespective of the type of injury, immediate

vascular response is of transient vasoconstriction of arterioles. With mild form

of injury, the blood flow may be reestablished in 3 5 seconds while with more

severe injury the vasoconstriction may last for about 5 minutes.

2. Persistent progressive vasodilatation : It involves mainly the arterioles, but to a

lesser extent, affects other components of the microcirculation like venules and

capillaries. This change is obvious within half an hour of injury.

3. Increase in local hydrostatic pressure : Progressive vasodilatation, in turn, may

elevate the local hydrostatic pressure resulting in transudation of fluid into the

extracellular space.

4. Slowing or Stasis : It occurs next. It is attributed to increased permeability of

micro vasculature that results in increased concentration of red cells, and thus

raised blood viscosity.

5. Leucocyte margination : It is the peripheral orientation of leucocytes (mainly

neutrophils) along the vascular endothelium. The leucocytes stick to the

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vascular endothelium briefly, and then move and migrate through the gaps

between the endothelial cells into the extravascular space.

Pathogenesis of increased vascular permeability

There is a loss of fluid balance which is normally maintained by two opposing

sets of forces i.e.

1. Forces that cause outward movement of fluid

Intravascular hydrostatic pressure

Interstitial osmotic pressure

2. Forces that cause inward movement of fluid

Intravascular osmotic pressure

Interstitial hydrostatic pressure

Mechanisms of increased vascular permeability

In acute inflammation, normally permeable endothelial layer of

microvasculature becomes leaky. This is explained by one or more of the following

mechanisms.

1. Contraction of endothelial cells

This is the most common mechanism of increased leakiness that affects venules

exclusively while capillaries and arterioles remain unaffected. The endothelial cells

develop temporary gaps between them due to their contraction resulting in vascular

leakiness. It is mediated by the release of histamine, bradykinin and other chemical

mediators. It is reversible and of short duration (15 30 mins).

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2. Retraction of endothelial cells

Here, there is structural re-organization of the cytoskeleton of endothelial cells

that causes reversible retraction at the intercellular junctions. This change too affects

venules and is mediated by cytokines such as IL1 and TNF. The onset of response

takes 4 6 hours after injury and lasts for 24 hours or more.

3. Direct injury to endothelial cells

It causes cell necrosis and appearance of physical gaps at the site of detached

endothelial cells. This change affects all levels of microvasculature. The increased

permeability may either appear immediately after injury and lasts for several hours or

days, or may occur after a delay of 2 12

4. Endothelial injury mediated by leucocytes

Adherence of leucocytes to the endothelium at the site of inflammation may

result in activation of leucocytes. The activated leucocytes release proteolytic

enzymes and toxic oxygen species which may cause endothelial injury and increased

vascular leakiness. This form of increased vascular leakiness is al late response.

5. Other Mechanisms

Also the newly formed capillaries during the process of repair are excessively

leaky. Vesicles and vacuoles within the cytoplasm of endothelial cells of blood vessels

in tymours may account for leakage of fluid across the cytoplasm.

II. Cellular events

The cellular phase of inflammation consists of two phases

1. Exudation of leukocytes

2. Phagocytes

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Exudation of leukocytes

The escape of leucocytes from the lumen of microvasculature to the interstitial

tissue is the most important feature of inflammatory response.

The changes leading to migration of leucocytes are as follows:

1. Changes in the formed elements of blood

The normal axial flow of blood consists of central stream of cells comprised by

cell free layer of plasma close to vessel wall.

Due to slowing and stasis, the central stream of cells widens and peripheral plasma

zone becomes narrower because of loss of plasma by exudation. This phenomenon is

known as margination. Now the neutrophils of the central column come close to the

vessel wall and this phenomenon is known as pavementing.

2. Adhesion and rolling

Peripherally marginated and pavemented neutrophils stick briefly to the

endothelial cells lining the vessel wall or roll over it. Injury leads to nertralisation of

the normal negative charge on leucocytes and endothelial cells so as to cause

adhesion. This mechanism is brought about by 4 types of adhesion molecules. They

are :

a. Selectins mainly P selectin, E selectin, and L selectin.

b. Addressins

c. Integrins and

d. Immunoglobulin superfamily adhesion molecule (ICAM 1,2)

3. Emigration

After sticking of neutrophils to endothelium, the former move along the

endothelial surface till a suitable site between the endothelial cells is found where the

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neutrophils throw out cytoplasimc pseudopods. Subsequently, the neutrophils lodged

between the endothelial cells and basement membrane cross the basement membrane

by damaging it locally with secreted collagenases and escape out into the

extravascular space. This is known as emigration. Simultaneous to emigration of

leucocytes, escape of red cells through gaps between the endothelial cells, diapedesis

takes place. It is a passive phenomenon

hydrostatic pressure or may escape through the endothelial defects left after

emigration of leucocytes.

4. Chemotaxis

The chemotactic factor mediated transmigration of leucocytes after crossing

several barriers (endothelium, basement membrane, perivascular myofibroblasts and

matrix) to reach the interstitial tissues is called chemotaxis.

The agents acting as potent chemotactic substances for different leucocytes

called chemokines are as follows:

i. Leukotriene B4 (LTB4)

ii. Platelet factor 4 (PF4)

iii. Components of complement system (C5a in particular)

iv. Cytokines (particularly IL8)

v. Soluble bacterial products (such as formylated peptides)

vi. Monocyte chemoattractant protein (MCP 1)

vii. Chem9otactic factor for CD4 + T cells

viii. Eotaxin chemotactic for eosinophils

There are specific receptors for each of the chemoattractants listed above. In

addition, chemotactic agents also induce leucocyte activation that includes: the

production of arachidonic acid metabolites, degranulation and secretion of lysosomal

enzymes, generation of oxygen metabolites, increased intracellular calcium, and

increase in the leucocyte surface adhesion molecules.

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5. Phagocytosis

It is defined as the process of engulfment of solid particulate material by the

cells (cell eating). The cells performing this function are called phagocytes. There

are two main types of phagocytic cells. Viz Microphages (Neutrophils) and

Macrophages.

The process of phagocytosis involves the following 4 steps:

1. Attachment stage (Opsonisation)

2. Engulfment

3. Secretion (Degranulation)

4. Killing or degradation

1. Attachment stage

The phagocytic cells as well as micro organisms to be injested have usually

negatively charged surface and, thus, they repel each other. In order to establish a

bond between bacteria and the cell membrane of phagocytic cell, the micro

organism get coated with opsonins which are naturally occurring factors in the serum.

The two main opsonins present in the serum and their corresponding receptors on the

surface of phagocytic cells are as under:

a. IgG Opsonin and its corresponding receptor on the surface of polymorphs is

Fc fragment of immunoglobulin.

b. C3b Opsonin fragment of complement and corresponding receptor for C3b on

the surface of phagocytic cells

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2. Engulfment stage

Here pseudopods are formed around the particle, enveloping it in a phagocytic

vacuole. Eventually, the plasma membrane enclosing the phagovytic vacuole breaks

from the cell surface so that the membrane lined phagocytic vacuole lies free in the

cell cytoplasm. The lysosome of the cell fuse with the phagocytic vacuole and form

phagolysosome or phagosome.

3. Secretion stage

During this process, the preformed granule

discharged or secreted into the phagosome and the extracellular environment.

4. Killing or Degradation stage

Here, killing and digestion of micro organisms takes place. After being killed

by antibacterial substances, the micro organisms are degraded by hydrolytic enzymes.

Chemical mediators of inflammation

They are of two types:

I. Cell derived mediators

1. Vasoactive amines (Histamine, 5 hydroxyl tryptamine)

2. Arachidonic acid metabolites

a. Via cyclo oxygenase pathway

b. Via lipo oxygenase pathway

3. Lysosomal components

4. Platelet activating factor

5. Cytokines

6. Nitric oxide and oxygen metabolites

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II. Plasma derived mediators

These are the products of

1. The Kinin system

2. The Clotting system

3. The Fibrinolytic system

4. The Complement system

I. Cell derived mediators

1. Vasoactive amines

i. Histamine : It is stored in the granules of mast cells, basophils and

platelets. The main actions of histamine are : Vasodilation, increased

vascular permeability, itching and pain.

ii. 5 Hydroxytryptamine (serotonin): It is present in tissues like chromaffin

cells of GIT, spleen, nervous tissue, mast cells and platelets. The actions

are similar to histamine but it is a less potent mediator of increased

permeability and vasodilatation than histamine.

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2. Arachidonic Acid Metabolities

i. Via cyclo oxygenase pathway

Activated arachidonic acid

Cyclooxygenase

PGG2 PGH2 + Free oxygen radical

PGD2, PGE2 PGF2 TXA2 PGI2

Vasodialator Vasodialator Vasoconstrictor Vasodialator

Bronchodialator Bronchoconstrictor Bronchoconstrictor

Bronchodialator

Permeability Platelet aggregation Anti aggr agent

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ii. Via lipooxygenase pathway

Activated Arachidonic acid

Lipo oxygenase

5 HPETE 5 - HETE

Chemotactic

LTA4

LTB4 LTC4 LTD4 LTE4

Chemotactic Smooth muscle constrictor

Cell adherence Vasoconstrictor

Bronchoconstrictor

3. Lysosomal Components

i. Granules of neutrophils: They are of two types: specific granules and

azurophil granules. The specific granules contain lactoferrin, lysozyme,

alkaline phosphatase and collagenase while the large azurophil granules

have myeloperoxidase, acid hydrolases and neutral proteases such as

elastase, collagenase and proteinase.

ii. Granules of monocytes and tissue macrophages : These cells on

degranulation also release mediators of inflammation lke acid proteases,

collagenase, elastase and plasminogen activator.

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4. Platelet Activating Factor (PAF)

It is released from IgE sensitized basophils or mast cells, other leucocytes,

endothelium and platelets. Its fuctions are Platelet aggregation, increased vascular

permeability, vasodilatation in low concentration and vasoconstriction,

bronchoconstriction, adhesion of leucocytes to endothelium and chemotaxis.

5. Cytokines

They are polypeptide substances produced by activated lymphocytes and

monocytes. The actions of various cytokines are as under

i. IL1 and TNF - - induce endothelial effects in the form of

increased leucocyte adherence, thrombogenicity, elaboration of other

cytokines, fibroblastic proliferation and acute phase reactions

ii. IF

with synthesis of nitric acid synthase.

iii. Chemokines are a family of chemoattractants for inflammatory cells and

include IL8, PF4, MCP1 and eotaxin.

6. Nitric Oxide and Oxygen Metabolites

NO plays the following role in inflammation:

i. Vasodilatation

ii. Anti Platelet activating agent

iii. Possibly microbicidal action.

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II. Plasma derived mediators

These include the various products derived from activation and interaction of 4

interlinked systems.

1. The Kinin System : Bradykinin is the end product of this system. Its effects

include smooth muscle contraction, vasodilatation, increased permeability and

pain.

2. The Clotting System : The action of fibrinopeptides in inflammation are

increased permeability, chemotaxis for leukocyte and anticoagulant activity.

3. The Fibrinolytic System : The action of plasmin in inflammation are activation

of factor XII to form prekallikrein activator, split off complement C3 to C3a

and degrades fibrin to form fibrin split products.

4. The Complement System : It can occur by Classical or Alternate pathway. It

yields anaphylatoxins. Its action in inflammation are to release histamine from

mast cells and basophils, increase permeability, C3b augments phagocytosis and

C5a is chemotactic for leukocytes.

The inflammatory cells

The cells participating in acute and chronic inflammation are circulating

leucocytes, plasma cells and tissue macrophages. They are described as follows :

1. Polymorphonuclear Neutrophils (PMN )

The functions of neutrophils in inflammation are initial phagocytosis of micro

organisms, engulfment of antigen antibody complexes and non microbial

material.

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2. Eosinophils

Eosinophils share many structural and functional similarities with

neutrophils like their production in the bone marrow, locomotion, phagocytosis,

lobed nucleus and presence of granules in the cytoplasm containing a variety of

enzymes, of which major basic protein and eosinophil cationic protein are the

most important which have bactericidal and toxic action against helminthic

parasites.

3. Basophils

They comprise about 1% of circulating leukocytes and are

morphologically and pharmacologically similar to mast cells of tissue. The role

of these cells in acute inflammation is in immediate and delayed type of

hypersensitivity reactions and release of histamine by IgE sensitized basophils.

4. Lymphocytes

Besides their role in antibody formation and in cell mediated immunity,

these cells participate in chronic inflammation as these are the dominant cells in

the tissues and also their number is increased in chronic infections like

tuberculosis.

5. Plasma Cells

Their number is increased in prolonged infection with immunological

responses e.g. syphilis, RA, tuberculosis, hypersensitivity states and in multiple

myeloma.

6. Mononuclear Phagocyte System

This cell system includes cells derived form 2 sources namely Blood monocytes

and Tissue macrophages. Their functions in inflammation are Phagocytosis and

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elaboration of a variety of biologically active substances like proteases,

plasminogen activator, products of complement, some coagulation factors,

chemotactic agents, metabolites of arachidonic acid, growth promoting factors for

fibroblasts, blood vessels and granulocytes, cytoines and oxygen derived free

radicals.

Morphology of Acute Inflammation

1. Pseudomembranous Inflammation : It is an inflammatory response of mucous

surface to toxins of diphtheria or irritant gases. As a result of denudation of

epithelium, plasma exudes on the surface where it coagulates, and together

with necrosed epithelium, forms false membrane that gives this type of

inflammation its name.

2. Ulcer : Ulcers are local defects on the surface of an organ produced by

inflammation. Common sites for ulcerations are the stomach, duodenum,

intestinal ulcers in typhoid fever, intestinal tuberculosis, bacillary and amoebic

dysentery, ulcers of legs due to varicose veins etc.

3. Suppuration : When acute bacterial infection is accompanied by intense

neutrophilic infiltrate in the inflamed tissue, it results in tissue necrosis. A

cavity is formed which is called an abscess and contains purulent exudates or

pus and the process of abscess formation is known as suppuration.

4. Cellulitis : It is a diffuse inflammation of the soft tissues resulting from

spreading effects of substances like hyaluronidase released by some bacteria.

5. Bacterial infection of the blood : This includes the following 3 conditions.

a. Bacterimia : It is defined as the presence of small number of bacteria in

the blood which do not multiply significantly.

b. Septicemia : means presence of rapidly multiplying pathologic bacteria

in blood.

c. Pyaemia : It is the dissemination of small septic thrombi in blood which

cause their effect at the site where it is lodged.

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APPLIED ASPECTS IN DENTISTRY

DRY SOCKET It is called as alveolitis sicca dolorasa. This is most common and

painful complication in the healing of human extraction wounds. Basically this is a

focal osteomyelitis in which the blood clot has disintegrated or been lost, with the

production of a foul odor and severe pain of the throbbing type, but no suppuration.

More common in women and tobacco users and most frequently related with difficult

or traumatic extraction.

Destruction of clot is caused by the action of proteolytic enzymes produced by

bacteria or fibrinolytic activity.

Safe and skilled procedure of extraction is the prevention from this condition.

Treatment includes sulfanilamide, aureomycin, trypsin and iodoform gauze packing.

OSTEOMYELITIS This is defined as inflammation of bone and its marrow

contents. Changes in the calcified tissue are secondary to inflammation of the soft

tissue component of the bone. Dental infection through periapical infection is the most

frequent cause of inflammation of jaw. Clinical features include pain, swelling,

paresthesia, leukocytosis,elevated temperature. Types of osteomyelitis are acute and

chronic osteomyelitis. Difference between these two is the duration of the

inflammation and severity of the condition. Antibiotics are effective to reduce the

effects of the disease. In advanced stages of osteomyelitis sequestromy is the

treatment of choice.

Gingivitis, periodontitis, pulpitis are the other main inflammatory conditions of the

oral cavity.

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CONCLUSION

Inflammation is basically a protective response intended to eliminate initial cause of

cell injury as well as necrotic cells and tissues resulting from original insult.

Inflammation is also intimately interwoven with repair process whereby damaged

tissue is replaced by regeneration of parenchymal cells or by filling of any residual

defect with fibrous scar tissue.

CHRONIC INFLAMMATION

This is considered to be inflammation of prolonged duration (weeks or

months) in which active inflammation, tissue destruction and attempts at

repair are proceeding simultaneously.

It may follow either an acute inflammation or even may begin insidiously as

a low grade smouldering , often asymptomatic response. This latter type

causes tissue damage in some of the most common and disabling human

diseases like rheumatoid arthritis, TB etc.

CAUSES OF CHRONIC INFLAMMATION:

It usually arises in the following settings :

Persistent Infection which is usually of low toxicity and thus evokes an

immune reaction called the Delayed Type of Hypersensitivity. This form of

inflammation sometimes takes on a specific pattern called

GRANULOMATOUS REACTION. The organisms involved are like

Tubercle bacilli, Treponema Pallidum and other viruses, fungi or parasites.

Prolonged Exposure to potentially toxic agents (exogenous / endogenous).

Exogenous agents like SILICA when inhaled over prolonged exposure

causes an inflammatory lung disease called SILICOSIS.

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ATHEROSCLEROSIS is said to be a chronic inflammatory process of the

arterial wall induced in part by endogenous toxic plasma lipid components.

Autoimmunity: Sometimes in certain conditions immune reactions develop

perpetuating immune reaction resulting in chronic tissue damage and

inflammation. Eg : SLE, rheumatoid arthritis etc.

MORPHOLOGIC FEATURES

Infilteration with mononuclear cells which include macrophages, lymphocytes

and plasma cells.

Tissue destruction induced by the persistent offending agent or by the

inflammatory cells.

Healing attempts by replacement of the damaged tissue with connective tissue

done by angiogenesis and fibrosis.

MONONUCLEAR CELL INFILTERATION:

The mononuclear phagocyte system (RE system) consists of closely related

cells of bone marrow origin, incl blood monocytes and tissue macrophages. Of

this the most dominant cellular component is the macrophage which is diffusely

scattered in the connective tissue or located in the organs like liver (kupffer

cells), spleen and lymph nodes (sinus histiocytes) and lungs( alveolar

macrophages).

Mononuclear phagocytes arise from a common precursor in the bone marrow

which initially gives rise to blood monocytes which further migrate into various

tissues and differentiates into macrophages. The half life of a blood monocyte is

1 day but that of the macrophages is several months to years.

In acute inflammation, the monocytes begin to emigrate quite early and within

the first 48 hrs they constitute the predominant cell type. Once they reach the

site of inflammation they transform into a bigger cell type called the

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macrophage. These are then activated by various factors like cytokines,

bacterial endotoxins and other chemical mediators. Activation results in

increased cell size, increased levels of lysosomal enzymes leading to more

active metabolism thus greater ability to phagocytose and kill ingested

microbes. To do this they secrete a wide variety of biologically active products

which if left in a longer situation also causes tissue injury and fibrosis

characteristics of chronic inflammation.

In short lived inflammation the macrophages eventually disappear but in

chronic inflammation, macrophage accumulation persists and is mediated by

different mechanisms :

Recruitment of monocytes from the circulation results from the expression of

adhesion molecules and chemotactic factors.

Local proliferation of macrophages after their emigration from the bloodstream

and this is found to be very prominent in chronic inflammatory lesions like

atheromatous plaques.

Immobilization of macrophages is done within the site of inflammation. This

maybe caused by certain cytokines and oxidized lipids.

The products of activated macrophages serve to eliminate injurious agents such

as microbes and to initiate the process of repair and are also responsible for

much of the tissue destruction occurring in chronic inflammation. Thus the

macrophages are powerful allies in the body defense against unwanted invaders,

but at the same time the same weaponry can also induce considerable tissue

destruction when the macrophages are inappropriately inactivated and thus

making TISSUE DESTRUCTION as one of the hallmarks of chronic

inflammation.

Other substances also are capable of tissue damage like---

Necrotic tissue itself can perpetuate an inflammatory cascade.

In cellular immune reactions, T lymphocytes may directly kill cells.Thus as we

see sometimes the features of both acute and chronic inflammation may co-exist

in certain circumstances.

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OTHER CELL TYPES IN CHRONIC INFLAMMATION

LYMPHOCYTES

Mobilized in both Ab mediated and cell mediated immune reactions and even in

non-immune inflammation.

Ag stimulated lymphocytes (T & B) use various adhesion molecule pairs

(integrins and ligands) and chemokines to migrate into inflammatory sites.

Lymphocytes and macrophages interact in a bidirectional way, which helps in

chronic inflammation.

Macrophages display Ag to T cells stimulate the T cells.

Activated T lymphocyte--- produces cytokines of which one particular one is a

macrophage activator.

Activated B lymphocytes form plasma cells.

Plasma cells produce Ab directed either against a persistent Ag in the

inflammatory site or against altered tissue components.

Sometimes in strong chronic inflammatory reactions like long standing

rheumatoid arthritis the accumulation of lymphocytes, Ag presenting cells and

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plasma cells may end up assuming the morphologic features of lymphoid

organs called lymphoid organogenesis.

EOSINOPHILS

They are abundant in immune reactions mediated by IgE and in parasitic

infections.

The important chemokine for their extravasation is eotaxin.

They possess granules that contain major basic protein, a highly cationic is

toxic to parasites but also causes lysis of mammalian epithelial cells.

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So they are good for control of parasitic infection but in long standing immune

reactions it also has a tendency to cause tissue damage.

MAST CELLS widely distributed in connective tissue and participate in both acute

and chronic inflammation. They express on their surface the receptor that binds the Fc

portion of IgE Ab . basically found in acute inflammation but in chronic inflammation

they may produce cytokines which contribute to fibrosis.

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NEUTROPHILS they are predominantly the cells found in acute inflammation but

in long standing chronic inflammation, lasting for months, continue to show large

numbers of neutrophils induced either by persistent microbes or by mediators

produced by macrophages and T lymphocytes. In chronic bacterial infection of bone

(osteomyelitis) a neutrophilic exudate can persist for months. They are also found in

the chronic damage induced in lungs by smoking and irritant stimuli.

GRANULOMATOUS INFLAMMATION

This is a distinctive pattern of chronic inflammatory reactions characterized by

focal accumulations of activated macrophages, which often develop an

epithelial - like (epithelioid) appearance.

It is encountered in a limited number of immunologically mediated, infectious

and noninfectious conditions.

- scratch disease,

lymphogranuloma inguinale, leprosy, brucellosis, syphilis, some mycotic

infections, berylliosis and reactions of irritant lipids are also included.

A granuloma is a focus of chronic inflammation consisting of a microscopic

aggregation of macrophages that are transformed into epithelium-like cells

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The prototype here is the bacillus of TB. Here the granuloma is referred to as a

tubercle and is classically characterized by the presence of central caseous

necrosis. This type of necrosis is rare in other granulomatous diseases

thoughtheir morphologic pattern maybe sufficiently different to allow a

reasonably accurate diagnosis.

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LYMPHATICS IN INFLAMMATION

The system of lymph nodes and lymphatics filter and polices the extravascular

fluid and along with the mononuclear phagocytic system it forms the 2nd line of

defense that is called into play whenever a local inflammatory reaction fails to

contain and neutralize an external agent like a microbe.

Lymphatics are delicate channels that are not readily visualized in normal tissue

sections as they collapse. They are lined by continuous, thin endothelium with

loose , overlapping cell junctions, scant basement membrane and no muscular

support except in the larger ducts.

In inflammation there is an increase in the lymph flow and it helps to drain the

edema fluid from the extravascular space. As they have loose overlapping

junctions, the lymphatic fluid eventually equilibrates with extravascular fluid.

Valves are present in the collecting lymphatics, allowing the lymph content to

flow only in one direction proximally. The vessel patency is maintained by

delicate fibrils which are attatched at right angles to the walls of the vessels.

In severe injuries the lymph may transport the offending organism or toxin

which may lead to secondary inflammation of the lymphatics (lymphangitis) or

of the draining nodes (lymphadenitis). Enlargements of the lymph nodes is

caused by the hyperplasia of the lymphoid follicles as well as by hyperplasia of

the phagocytic cells lining the sinuses of the lymph nodes. This constellation of

nodal histologic changes is called reactive, or inflammatory lymphadenitis.

Basically the lymph functions to contain the spread of the infection though in

severe infections it becomes difficult to contain thus leading to bacteremia.

SYSTEMIC EFFECTS OF INFLAMMATION

The systemic changes associated with inflammation, especially in patients who have

infections are called the Acute phase response or the systemic inflammatory response

syndrome SIRS. These changes are reactions to cytokines whose productions is

stimulated by bacterial products and other inflammatory stimuli.

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This acute phase response consists of several clinical and pathological changes

FEVER

usually characterized by the elevation of body temperature by 1 4 C

especially when inflammation is associated with infection. Fever is produced in

response to substances called Pyrogens act by stimulating prostaglandin

synthesis in the vascular and perivascular cells of the hypothalamus.

In amphibians the raise of temperature is meant to ward off any microbial attack

which even though the mechanism is unknown it is thought to be a reaction to

the same as the fever may induce shock proteins that enhance lymphocyte

responses to microbial agents.

ACUTE-PHASE PROTEINS

These are plasma proteins, mostly synthesized in the liver, whose plasma

concentrations may increase several hundred fold as part of the response to

inflammatory stimuli. The best known examples being C- reactive protein

(CRP), fibrinogen and serum Amyloid A (SAA) protein.

CRP and SAA bind to the microbial cell walls and may act as opsonins and fix

complement. They also bind the chromatin, possibly aiding in the clearing of

necrotic cell nuclei.

SAA protein replaces apolipoprotein A which is a high density lipoprotein

particle and this changes the target of the high density protein from the liver

cells to the macrophages, which further can utilize these particles as a source of

energy producing lipids.

The rise in fibrinogen causes the erythrocytes to form stacks or go into rouleaux

formation which causes them to sediment thus making the ESR test important

for information of inflammation.

These proteins do have a beneficial effect on inflammation but prolonged

production of these proteins causes secondary amyloidosis in cases of chronic

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inflammation. Thus, the CRP elevated levels in a patient with coronary artery

disease, are used as a marker for risk to MI.

LEUKOCYTOSIS

This is a common feature of inflammatory reactions especially ones associated

with bacterial infection. The count may usually be raised to 15,000 20,000

of 40,000

they are similar to the WBC count obtained in leukemia. This leukocytosis

occurs mainly due to initially an accelerated release of cells from the bone

marrow postmitotic pool and is therefore, associated with a rise of more

immature cells mainly neutrophils.

Prolonged infection also induces proliferation of precursors in the bone marrow,

caused by increased production of colony stimulating factors (CSFs). Thus, the

bone marrow output of leukocytes is increased to compensate for the loss of

these cells in the inflammatory reaction.

Bacterial infections Neutrophilia

Viral infections Lymphocytosis

Parasitic infection and allergic reactions Eosinophilia

Certain infection ( typhoid fever and infections caused by viruses, rickettsiae,

and certain protozoa) Leukopenia

Debilitating infection due to disseminated cancer or rampant TB.

Other manifestation of the acute phase responses:

Increased pulse and blood pressure

Decreased sweating

Rigors, chills, anorexia, somnolence and malaise

Because of redirection of blood flow from cutaneous to deep vascular beds and

to minimize heat loss through the skin.

32

SEPSIS

Due to severe bacterial infections there is the presence of a large no. of

organisms which stimulate to produce cytokines ( TNF and IL-1). High levels

of TNF cause DIC.

Thrombosis is due to two main simultaneous reactions

LPS and TNF induce tissue factor on the endothelial cells initiates

coagulation and these same agents will inhibit the natural anticoagulation

mechanisms by decreasing the expression of tissue factor pathway inhibitor

(TFPI) and endothelial cell thrombo- modulin.

Cytokines cause liver injury and thus impaired liver function which results in

the failure to maintain normal blood glucose levels due to lack of

gluconeogenesis from stored glycogen.

Overproduction of NO by the cytokine activated cardiac myocytes and vascular

smooth muscle cells leads to heart failure and loss of perfusion pressure

consequently resulting in hemodynamic shock.

Septic shock = DIC + Hypoglycemia +Cardiovascular Failure (Triad)

Multiple organs show inflammation and intravascular thrombosis resulting in

multi organ failure.

Tissue injury in response to LPS can also result from the activation of

neutrophils before they are extravasated thus causing damage to the endothelial

cells and resulting in reduced blood flow.

Lungs and liver are more susceptible to injury by the neutrophils. This lung

damage in the systemic inflammatory response , commonly called ARDS and

results from neutrophil mediated endothelial injury which allows the fluid to

escape from the blood into the airspace. The kidney and the bowel are also

injured largely due to reduced perfusion. This condition is fatal.

33

DEFECTIVE / EXCESSIVE INFLAMMATION

Defective Inflammation ---

This results in increased susceptibility to infections and delayed healing of the

wounds and tissue damage. Thus the innate immunity of the person is

compromised.

Delayed repair is because the inflammatory response is essential for clearing

damaged tissue debris and provides the necessary stimulus to get the repair

process started.

Excessive Inflammation ---

It is the basis of many categories of human disease. Allergies in individuals

have a tendency to mount unregulated immune responses against commonly

encountered environmental antigens; in cases of autoimmune diseases the

immune responses develop against normally tolerated self antigens and here the

fundamental cause of tissue damage is inflammation.

Also, prolonged inflammation and the fibrosis that accompanies it are

responsible for much of the pathology in many chronic infectious, metabolic

and other diseases. As these are the major scourges of mankind this normally

protective inflammatory response is being called the SILENT KILLER.

34

HYPERSENSITIVITY

Definition

manner resulting in tissue damage.

It does not manifest on first contact, which is sensitizing / premising dose

and appears on subsequent contact, known as shocking dose.

Allergy altered state, coined by von Pirquest.

Allergen any foreign substance capable of inducing allergy is an allergen.

Types I Natural

Synthetic

II Specific

Nonspecific

Routes of entry

1) Inhalation

2) Ingestion

3) Injection

4) Skin contact

Classification of Hypersensitivity

By Philip Gell and Robin Coombs in 1963

1) Type I: Anaphylactic /Ig E dependent Hypersensitivity

2) Type II: Cytotoxic/ cell stimulating Hypersensitivity

3) Type III: Immune complex Hypersensitivity

4) Type IV: Delayed/ cell mediated Hypersensitivity

5) Type V: Stimulatory Hypersensitivity

35

Type I, II, III and V are immediate hypersensitivity and are Ag-Ab reactions.

Type IV is delayed hypersensitivity and involves T- lymphocyte response to antigen

via inflammation mediation and lymphokines.

Mechanisms of Hypersensitivity

1) Ig E/mast cell mediator pathway.

2) IgG/IgM immune complex/ complement/ neutrophil pathway.

3) T- lymphocyte/ Lymphokine pathway.

Overview of types of Hypersensitivity

1) Type I Mast cell + IgE/ Ag Fc

Mast cell + mediators

Inflammation

2)Type II hypersensitivity

a) K cell + IgG/Ag (cell surface)

LYSIS OF TARGET CELL

b) IgG/IgH+ target cell (Antigen) complement

LYSIS OF TARGET CELL

Complement PMN

3)Type III Ag+ Ig immune complex deposition

Tissue damage by FRUSTRATED PHAGOCYTOSIS

Lymphokines

4) Type IV: Ag+ T cells macrophage

inflammation+ mediators

36

Type I Hypersensitivity

It is characterized by immediate reactions following the contact with

Ag/allergen in sensitized host. It takes few minutes.

It depends on presence of IgE Ab to the antigen.

IgE+ mast cell /Basophil

Via Fc gragement of IgE and FcER1 on the cell.

FcER1 for mast cell or Basophils Allergies

FcER1 for eosinophils or platelets parasitic infections

Anaphylaxis classical immediate type I hypersensitivity reaction.

Anaphylaxis Ana without, phylaxis- Protection

Coined by Richet (1902)

Tissues/organs involved in anaphylactic reaction

organs.

Species variation to Anaphylaxis.

1) Highly susceptible Guinea pigs

2) Inter mediate Rabbit, Dog and Human beings.

3) Very resistant Rats.

Clinical effects

a) Vascular permeability

b) Edema, coagulation of blood.

c) B.P or temperature.

d) Smooth muscle contraction.

e) Thrombocytopenia.

f) Fusing of skin.

g) Difficulty in breathing due to bronchospasm.

h) Nausea, vomiting, abdominal pain.

i) Acute hypotension, unconsciousness and death in severe cases.

37

Uriticaria, eczema, allergic Rhinitis (Hay fever)

Allergens for Anaphylaxis

1) Foods pear, peanuts, fish, egg white, crab, cotton seeds, mustard seed,

berries, milk and milk products, wheat etc.

2) Drugs Penicillin, St.mycin, cephalosporin, tetracyclin, insulin, Barbiturates,

diazepams phenytoin, salicylic acid, parathormone, dextran, thiamine, folic

acid, etc.

3) Insect Honey bee, wasp, fire ants, deer flies, bed bug, snake venome rarely.

4) Others Latex, pollen, animal dandruff, house dust mites etc.,

Mechanism of Anaphylaxis

very complex gp

D2 Vasodilatation or vascular permeability

E1 and E2 smooth muscle relaxation or vasodilatation

I2 and F2x promote mast cell mediator release

Regulation of mast cell degranulation

Regulated by cyclic nucleotides. c AMP/ c GMP inhibit mast cell

degranulation finally on c AMP- c GMP ratio.

2 Types of receptor on mast cell and for adreno receptors.

Stimulation of receptor c AMP c GMP mast cell degranulation

Stimulation of adreno receptor vice versa

-adreno receptor stimulators Nor adrenaline, phenylephrine

- Adrenoreceptor stimulators adrenoline, salbutamol

In Atopy impairment in adrenoreceptor by B. pertusis, H. influenza, auto

antibodies.

38

Role of mediators in Anaphylaxis

I Preformed mediators: (Primary mediators)

1) Histamine smooth muscle contraction, vascular permeability sections.

2) Serotonin vasospasm, smooth muscle contraction.

3) ECF-A Eosinophil chemotaxis

4) PAF platelet aggregation and secretion..

5) NCF-A Neutrophil chemotaxis.

II Newly generated mediators: (Sec mediators)

1) Prostaglandins influence vascular and smooth muscle tone, platelet

aggregation, and immune reactivity.

2) Leukotrienes smooth muscle contraction, V. Permeability, neutrophils

and eosinophil chemotaxis.

3) Bradykinin Smooth muscle contraction or vasospasm.

4) Serotonin

Histamine: Preformed in granules of mast cells, basophils & platelets.

In skin: stimulates sensory nerves burning and itching sensation, vasodilation,

cap permeability (wheal effect)

Smooth muscle: smooth: Smooth muscle contraction in B.V. intestine, branchioles,

uterus, uri. Bladder.

Mucosal surfaces: secretions bronchus, stomach, and lacrimal gland, mouth

Chemotoxis: eosinophils or basophils for C5a

Serotonin (5-HT)

Derivative of tryptophan.

From mast cells and platelets, preformed.

Heart: Causes vasoconstriction, wheal or flare effect B.P.

Leukotrienes

4 types, synthesized by mast cells after stimulation by Ag.

LTB4 Neutrophil or eosinophil chemotaxis

40

Clinical tests for Anaphylaxis

1) PK list: It is a skin test. Serum from allergic individuals is injected Idly, into a

normal individual, after 24-48 hours the Ag is injected again. In the reaction,

wheal and flare reaction is seen at the same site with in 2-3 minutes.

2) PLA list: Several separate injections of different dilutions of serum are used.

They are administered Intravenously. If +ve, at each site an immediate

inflammation response is seen.

3) Schultz- Dale technique: In vitro experiment. A strip of smooth muscle is

removed from is sensitized animal, kept in saline. The tissue is cyposed to Ag,

degranulation of mast cell will louse contraction of muscle. Modification:

Incubate muscle from normal person in serum from sensitized individual.

Muscle contracts when exposed to Ag.

4) RAST: (Radio allegren Sorbent test) done for IgE detection for specific Ag.

Atopy

Means- out of place / strangeness.

By Coca and Cooke in 1923.

Refers to naturally occurring familial hypersensitivity of human beings typed

by hay fever asthma.

Ag involved are pollen, house dust, egg, milk.

5-10% have this type.

Difficult to induce artificially.

Strong hereditary association.

50% chance in children

If one parent is allergic 30% chance

Not allergic to specific Ag, but tendency to produce IgE Ab in large quantities.

41

Anaphylactoid reactions

Reaction clinically and pathologically identical anaphylaxis but without IgE

antibody and corresponding allergen.

Same chemical mediators and is a non-specific mechanism involving activation

of complement and anaphylatoxins.

Types

a) Exercise- induced during exercise, familial tendency.

b) Cholinergic during emotions, allergies, body temp.

c) Aggregate in globulin prophylaxis for immunodeficiency diseases.

d) Non IgE IgE anti IgA anaphylaxis in plasma transfusions.

e) From ionic compounds

f) Others Dextrans, gum, resins, tooth pastes, mouth washes.

g) Idiopathic

Anaphylatoxins: Peptides with mediate inflammation by release of histamine. Seen

in complement during cleavage of C4, C3 and C5.

Type II Hypersensitivity (Antibody dependant cytotoxicity)

Involve combination of IgG/IgM Ab against cell surface molecules/ tissue

components with complement and other variety of effector cell, causing damage

to target cells.

A) Ab (IgG/ IgM) link target cells to effector cell by Fc receptor on effector

cells.

B) Ab+ complement cell lysis.

C5b

1) Ab+ target cell lysis.

C3b

2) Ab + target cell lysis.

42

Normally, neutrophils + target cell+ complement phagocytosis by fusion of

lysosomes (phagolysome).

In this, target cell self or large, Type II neutrophil + IgG + complement +

target cell

contents outside the cell.

Lysosomal content + free oxygen radicals, arachidonic acid

Examples of Type II Hypersensitivity

1) Transfusion reaction.

2) Rh incompatibility.

3) Organ transplantation.

4) Autoimmune reactions Autoimmune Hemolytic Anemia

SLE.

Type I DM

Myasthenia gravis.

5) Pemphigus vulgaris.

6) Drugs penicillin, chlorpromazine, sulfonamides guanidine.

44

Triggered by deposition of circulating immune complexes in tissues causing

inflammation.

vaccines self-antigens. Complement is activated with results in inflammation.

Type III is similar to Type II, both by IgG/ IgM. The distinction is in

Type II Type III

1) Ag Specific Widely distributed

2) Ag site Specific target cells In serum

3) Nature of Ag Membranes bound Soluble

4) Damage Only target cell/tissue Involved organ

5) Quantity Ag Ab Small Large

The area of vascular permeability (blood flow) and turbulence B.P (Hemo-

dynamics) are the predilection for this complex deposition.

The bifurcation of heart value and renal glomeruli frequently involved organ

sites.

Types localized

Generalized serum sickness glomerulonephritis.

These immune complexes damage tissue, occlude b.v damage joints and

produce necrosis by blood supply.

I Microbial agents:

1) Leprosy (LL)

2) Bacterial endocarditic

3) Malaria.

4) Hepatitis-B

II Autoimmune

1) Rheumatoid arthritic.

2) SLE

45

3) Polyarteritis.

4) Fibrosing alveolitis.

Examples

1) SLE.

2)

3) Steven- Johnson syndrome.

4)

5)

Type IV Hypersensitivity (DTH)

FEATURES

1. Appears slowly & lasts longer.

2. Induced by infection, injection of antigen intradermally or by skin contact with

chemicals or with Freund`s adjuvant.

3. Circulating antibodies may be absent, not responsible for reaction. It is

CMI reaction.

4. Transfer - Serum - not possible.

- Lymphocytes or transfer factor- possible.

5. Desensitization - Difficult, long lasting.

6. Sensitization- Sensitising or priming dose required.

Elicitation- Shocking or second dose required

7. Tissue induration & Monocyte accumulation seen.

INDUCING AGENTS OF DHS :

BACTERIAL : Tuberculosis, Leprosy, Salmonella infection etc.

FUNGAL:Candidiasis,Dermatomycosis, Histoplasmosis, Coccidioidomycosis,

Blastomycosis.

46

PARASITIC : Leishmaniasis, Schistosomiasis.

VIRAL : Herpes simplex, Measles.

CHEMICAL : Contact dermatitis. Metals - Nickel, Chromium etc. Chemicals - dye

stuffs, potassium dichromate, poison ivy, paraphenylene diamine(from hair dyes).

Topical drugs - sulfonamides, neomycin, cosmetics & soaps.

SENSITIZATION & ELICITATION :

Sensitization of an individual refers to the exposure of the antigen to an

individual for the first time. It is liable to occur when the antigen contacts an area of

inflamed skin (contact type) or due to intrdermal injection of the antigen (tuberculin).

For the contact type the antigen should be applied in an oily base. Antigenicity is

acquired on combining with skin proteins. Sensitization requires percutaneous

absorption. Since most of the antigens are fat soluble, the passage is thought to be via

the sebaceous glands.

Factor for sensitization :The antigen dose / unit area, than the total dose or total

area is important in determining the sensitization potential.

The T- cell has specific recognition for the hapten-carrier complex & not for

hapten or carrier individually.

Elicitation occurs when the individual is exposed to the same or similar antigen

for the second time.

LIST OF LYMPHOKINES & MONOKINES

I . FACTORS THAT AFFECT MACROPHAGE FUNCTION :

1. Gamma interferon - Migratory inhibitory factor(MIF)

- Macrophage activating factor(MAF)

- Macrophage aggregating factor

- Factor that causes disappearence of

macrophages from the peritoneal cavity

47

2. Macrophage chemotactic factor(MCF)

3. Factors that alter surface tension

4. Antigen dependent MIF

II . FACTORS THAT AFFECT NEUTROPHIL FUNCTION :

1. Chemotactic factor

2. Leucocyte inhibitory factor(LIF)

III . FACTORS THAT AFFECT LYMPHOCYTE FUNCTION :

1. IL-1 (lymphocyte activating factor)

2. IL-2 (T-Cell growth factor)

3. IL-3

4. B-Cell growth factor

5. Chemotactic factor

6. Antigen dependent helper factor

7. Antigen dependent suppresor factor

8. Antigen independent helper factor

9. Antigen independent suppresor factor

10. E-Rosette augmenting factor (E-RAF)

11. Transfer factor

NOTE : Through these lymphokines, lymphocytes cause accumulation of

inflammatory cells & injury to tissues.

IMPORTANT CYTOKINE MEDIATED EFFECTS IN DTH :

1. IL-2 : Proliferation of activated T-Cells.

Increased concentration of IL-2 stimulates bystander T-Cells not specific for antigen

& augments synthesis of cytokines by CD4 + T-Cells, specially IFN-gamma, TNF. T-

Cells have receptors for IL-2, so IL-2 causes T-Cell proliferation

48

2. INF-gamma : Acts on antigen presenting cells & increases class II MHC molecule

expression, thus the efficiency of the antigen presentation to CD4 + T-Cells at local

site is increased. It also acts on Keratinocytes & Endothelial cells of dermal

capillaries to express ICAM-1 within 24 hours & HLA-DR around 48 hours, which

are the intercellular adhesion molecules.

ICAM-1 on the keratinocyte binds with Integrin LFA-1 present on the cells of

lymphoid & myeloid lineage. Expression of ICAM-1 is important in localization of

lymphocytes & macrohages to skin.

Activated keratinocytes release IL-1, IL-6 & GM-CSF, which promote activation &

proliferation of T-Cells. GM-CSF also stimulates langerhan`s cells. It also releases

PGE which inhibit lymphocyte.

IFN-gamma activates monocytes to macrophages, hence important in DTH.

3. TNF : It acts on venular endothelial cells to augment their capacities to bind &

activate WBCs leading to inflammation. IFN-gamma & IL-4 have similar functions &

thus specific mononuclear cells are recruited.

4. PGE : From keratinocytes & macrophages. It has inhibitory effect on IL-1 & IL-2

production. Thus PGE prodution & it`s binding to activated T-Cells, to keratinocytes

& the enzymatic & cellular degradation of hapten-carrier complex, all act in down

regulation of the DTH reaction.

ROLE OF VENULAR ENDOTHELIAL CELLS :

1. They act as APCs during elicitation phase.

2. They regulate infiltration of WBCs into the inflammatory reaction & contribute to

inflammation.

49

a) The production of prostacyclin & nitric oxide(vasodialators) causes increase in

the blood flow & delivery of WBCs at the site of inflammation.

b) TNF causes increased expression of enzymes in endothelial cells that synthesise

prostacyclin & along with IFN-gamma increases production of nitric oxide.

c) The expression of the adhesion molecule(E-Selectin, VCAM-1, ICAM-1) on

endothelial cells. This binds the WBCs, first the neutrophils & then the

lymphocytes & monocytes.

d) TNF causes synthesis & expression of chemokines, IL-8, MCP-1 etc. These

activate WBCs, increase their integrin affinity & cell motility. (MCP-

Monocyte chemotactic protein)

e) TNF & IFN-gamma causes the change in shape of the endothelial cells &

basement membrane remodelling. This favours the leakage of macromolecules

& extravasation of cells.

The leakage of fibrinogen is the basis of induration. Deposition of fibrinogen, fibrin &

plasma fibronectin in tissue sccafold facilitates WBC migration & extravasation &

retention in extravascular tissues. Leakage of plasma reduces the shear forces of

flowing blood which favours WBC attachment to endothelium.

MACROPHAGE DIFFERENTIATION :

MACROPHAGE ACTIVATION - causes an increase in the gene transcription for

certain enzymes. Eg : The cytochrome enzymes help in generating the reactive oxygen

species such as the superoxide, which has a microbicidal action by increasing the

oxidative burst. The increase in this enzyme is an example of macrophage activation.

The factors which help in macrophage activation are - Cytokines ( INF-gamma, IL - 2,

etc.) .

- Lipopolysaccharides

- Extracellular matrix molecules.

50

THE ROLE OF ACTIVATED MACROPHAGES IN DTH

1. ACTIVATED MACROPHAGES KILL MICRO-ORGANISMS :

IFN-gamma induces transcription of gene encoding the enzyme that generates

active oxygen.Thus macrophage are activated and the mi crorganisms are killed.

2. ACTIVATED MACROPHAGES STIMULATE ACUTE INFLAMMATI-

ON THROUGH SECRETION OF SHORT LIVED INFLAMMATORY

MEDIATORS :

MACROPHAGES ----------- Tissue factor (Protein). IFN-gamma increases

it`s synthesis.

Prostaglandins Leukotrienes - Initiates extrinsic cascade

- Thrombin & Blood protease

activation causes

- PMN & Endothelial cells

to secrete PAF.

Infectious organism is destroyed & the injured tissue is rid off.

3. ACTIVATED MACROPHAGES BECOME MORE EFFECTIVE ANTI-

GEN PRESENTING CELLS :

GM-CSF & IFN-gamma causes increase in Class II MHC genes.Activated

macrophages increase expression of ICAM-1 & LFA-3.

4. ACTIVATED MACROPHAGE PRODUCTS - CYTOKINES & GROW-

TH FACTORS MODIFY LOCAL TISSUE ENVIRONMENT :

Initially there is tissue destruction & later there is replacement by connective

tissue.

52

CHARACTERISTICS OF THE TYPES OF DTH :

DTH TYPE REACTION TIME

CLINICAL APPEARANCE

CHARECTERSTIC HISTOLOGICAL APPEARANCE

ANTIGEN

CONTACT (DERMATITIS or STOMATITIS)

48-72 hrs

Eczema,erythema, itching, vesication, skin necrosis.

Infiltration of lympho- cytes & later macrop-ges, intracellular ede- ma of epidermis. Few basophils may be seen.

Epidermal : Chemicals -nickel, chromium. Plant product -poison ivy, poison oak. Topical drugs - Neomycin, sulpo namides. Cosmetics & soaps.

TUBERC-ULIN

48-72 hrs Local hardening & swelling with fever(+ or -), necrosis(+ or -).

Infiltration of lympho- cytes, monocytes & macrophages. Subepidermal edema(?).

Intradermal injection of tuberculin, mycobacteria &leishmanial antigens.

GRANUL- OMATOUS

4 wks Hardening. Eg:in skin or lung.

Granuloma containing epitheloid cells, giant cells & macrophages. Fibrosis, + or - necrosis.

Persistent antigen or antigen-antibody complexes in macrophages or non-immunological. Eg : Cotton, gauze etc.

53

FEW IMPORTANT DISEASES MANIFESTING DTH :

1. TUBERCULOSIS :

Granulomatous kind of DTH.

Tuberculin test done in order to

- diagnose active infection in infants & young children.

- measure the prevalence of infection in a community.

- select suceptibles for BCG vaccination or as an indication of

successful vaccination.

2. LEPROSY :

FEATURES TUBERCULOID BORDERLINE LEPROMATOUS DHS(Granulomatous)

+++ +++

Either due to drug treatment or

naturally.

+ or -

LEPROMIN SKIN TEST(MITSUDA REACTION).Indicate- the prognosis.

+++ ++ _

MICRO-ORGANISM - + +++ ANTIGEN-ANTIBODY COMPLEX

- + + or -

3. SARCOIDOSIS :

Unknown etiology. Kveim test is done to confirm this diagnosis. It is a positive

granulomatous reaction. In this test unknown splenic antigens derived from other

Sarcoid patients is used as the antigen.

54

4. SCHISTOSOMIASIS :

Typical granulomatous type of DTH seen in the parasitized tissue. The antigens

are known as the schistosomes.

ORAL ASPECTS OF DELAYED HYPERSENSITIVITY :

Contact Stomatitis, also known as Stomatitis Venenata is the DTH reaction seen

to occur in the oral cavity. The causative agents are

I) DENTAL or COSMETIC PREPARATIONS :

- Dentifrices

- Mouth washes

- Denture powders

- Lipstick, Candy, Cough drops & Chewing gum.

II) DENTAL MATERIALS :

- Vulcanite

- Acrylic

- Metal alloy bases

III) DENTAL THERAPEUTIC AGENTS :

- Alcohol

- Antibiotics

- Chloroform

- Iodides

- Phenol

- Procaine

- Volatile oils

55

However the contact stomatitis is less compared to the cotact dermatitis because - the

saliva dilutes the allergens.

the saliva washes the allergens from the surface of the mucosa.

the saliva digests the allergens with it`s enzymes.

the keratin layer which has a rich source of the proteins (haptens) is absent

or limited in the oral mucosa.

JONES - MOTE HYPERSENSITIVITY :

It is also known as CUTANEOUS BASOPHIL HYPERSENSITIVITY.

A transient DTH develops on immunisation with protein antigens, in absence of the

adjuvants, antibody response develops.

DIFFERENCE FROM CLASSICAL DTH :

- Rapid appearance (12-24 hrs)

- Transitory in nature

- Basophils & mononuclear cells present in the infiltrate

- Transfer by serum antibodies, T or B cells.

- In humans it is seen in Renal allograft rejection & allergic contact

dermatitis.

TESTS TO DETERMINE DTH REACTIONS :

I) PATCH TEST TO DETERMINE CONTACT DERMATITIS :

The suspected allergen is placed on normal non-hairy skin, (upper portion of the

back being the most suited place) with the help of an adhesive plaster & is allowed to

remain in contact with the skin for 48hrs. A control of plain adhesive plaster is also

placed to rule out allergy to it. Once the patch is removed the development of

erythema within 2-4hrs indicates a positive test.

56

II) PATCH TEST TO DETERMINE CONTACT STOMATITIS :

The test is similar to contact dermatitis, but the suspected allergen is placed

directly in contact with the oral mucosa. This is done by incorporating the test

substance in Orabase & it is held in place by use of a prosthetic appliance or rubber

cup attached to the teeth.

III) TUBERCULIN TEST TO DETERMINE TUBERCULIN TYPE OF DTH

The test substance to be used is either the dead tubercle bacilli or sterile

infiltrate of the broth in which they have been grown ( old tuberculin OT ) or purified

protein derivative (PPD) extracted from the bacilli. 0.1ml of 1 in 1000 dilution of the

allergen is injected intradermally. After 24-48hrs of the injection of the allergen a red

zone of at least 5mm in diameter develops. The skin in this area is firm, swollen &

indurated. The red zone fades in a day or so, but the induration remains palpable for a

few days.

Similar tests can be done for Histoplasmosis (using Histoplasmin antigen) & for

Coccidioidmycosis (using Coccidioidin antigen).

TREATMENT OF DTH :

- Removal of the offending agent.

- Application of topical steriods.

DESENSITIZATION :

It was established by administering an antigen to a sensitized individual. Partial

desensitization is possible when an individual with DTH is tested simultaneously at

many skin sites with the same antigen reaction at each site. It is less intense than when

a single test is applied because the number of antigen specific sensitized T cells is

limited. Similarly in overwhelming infections like Miliary Tuberculosis, Disseminated

fungal & protozoan infections the DTH skin reactions are not usually elicited, because

large number of disseminated antigen bearing cells saturates the sensitized T cells.

57

Comparable events sometimes develop in the industrial workers who exhibit

loss of skin sensitivity during prolonged & intense exposure to the sensitizer.

The deliberate desensitization of CMI responses is difficult to acheive.

LATEST ADVANCES :

The experimental animal studies have shown that the DTH can be induced &

used in the treatment of tumours. When certain skin tumours were painted with a

simple chemical antigen & thus a DTH reaction being induced, healing with the

disappearance of the tumour was noted. This has been implied to be due to the

lymphokines-lymphotoxins released during DTH, which destroys the tumour cells.

It has also been noted that the injection of BCG vaccine a week before the

injection of the tumour cells (to induce the tumour experimentally) the tumour is

destroyed more readily. Hence it is thought that the tumour mass has to be reduced by

drug or X-ray therapy before treatment with BCG. An additional finding with the

BCG vaccine is that, when injected directly into the tumours they suppress the tumour

growth.

However further studies need to be done to arrive at any conclusions.

Type V stimulatory Hypersensitivity

Cells receive instructions by hormones activate interior cell signaled.

Ab + surface component (hormone receptor) Activate the messenger in an

organ for functioning.

EX: 1) TSH from pituitary Thyroid cell receptor Activation of cAMP second

messanger stimulates thyroid cell

58

Summary of Hypersensitivity Reactions

Hypersensitivi

ty

Effector

cells

Immuno-

globulin

Compleme

nt

activation

Duratio

n

Example

Type I

Anaphylactic

Basophils

mast cells

Eosinophils

platelets

IgE

(Hemocytotraphi

n)

No <30min Atopic

allergy insect

bite

Type II

cytotoxicosis

- IgG/IgM Yes - Rh incomp-

atibility

pemphigus

vulgaris

Type III

immune

complex

- IgG/IgM Yes 3-8hrs SLE,

Rheumatoid

arthritis

Type IV cell

mediated

T-cells

macrophag

es

- No 24-48

hrs and

3-4

weeks

Tuberculosis

, syphilis

diseases

Type V

stimulatory

- IgM/IgG No - Thyrotoxicos

is

Histology of types of Hypersensitivity

1) Type I Wheal and flare reaction degranulation of mast cells, vasodilation

edema, and eosinophilic infiltration.

2) Type III

3) Type IV Granuloma formation Erythema, induration, and perivascular

inflammation mononuclear cells predominance.

59

References

1. Immunology ---- D. M. Weir, 5th eds.

2. Fundamentals of Immunology & Allergy ---- Lockey & Bukantz.

3. Text Book of Microbiology ---- Ananthanarayan R and Jayaram Panicker C.

K., 4th eds.

4. Essentials of Medical Microbiology ---- Rajesh Bhatia and Rattan Lal

Ichhpujani.

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