Defense mechanism of Periodontium

CONTENTS

Introduction.

Classification.Innate Defense systems.Adaptive Defense systems.

Conclusion.References.

INTRODUCTIONThe Periodontal tissue is constantly subjected

to mechanical and bacterial aggressions.

Defense mechanism factors provide resistance to these actions.

Clinically the gingival tissue is able to deal with external challenges without progressing to a diseased state due to several defensive factors.

Effective defense mechanism is necessary within the oral cavity to safeguard it from these attacks.

A number of mechanisms operate to protect the

body from attack by foreign bodies and toxins, and these defense mechanisms can be broadly classified as follows : - (Jan Linde) Vol.1

Defense Mechanism NON-SPECIFIC(INNATE)INFLAMMATORY

SPECIFIC(ADAPTIVE)IMMUNOLOGICAL

1. Bacterial Balance2. Surface integrity3. Surface fluid and

enzymes4. Phagocytosis5. Inflammatory

reaction

1. Cell mediated Immunity

(T lymphocytes)2. Humoral

Immunity (B lymphocytes)

1.Bacterial balanceThe mouth as a whole and various zones in the

mouth , including what has been called the ‘crevicular domain’,can be viewed as ecosystem in which a balance exists between the different species of microorganisms and between flora and the tissues.

Upset in this balance is most commonly seen after prolonged use of antibiotics which suppress some types of bacteria and allow others to flourish to the detriment of the tissues.

2.Surface integrity Surface integrity of skin and mucous membrane

barriers,including the gingiva,is maintained by the continuing renewal of the epithelium from its base and desquamation of the surface layers.These two activities balance so that the thickness of the epithelium remains constant.

The efficiency of the surface barrier is enhanced by keratinization and parakeratinization.

‘’Junctional epithelium ‘’exhibits several unique structural and functional features that contribute to preventing pathogenic bacterial flora from colonizing the subgingival tooth surface.

J.E is firmly attached to the tooth surface,forming an epithelial barrier against plaque bacteria.

It allows access of gingival fluid,inflammatory cells,and components of the immunologic host defense to the gingival margin.

Junctional epithelium exhibits rapid turnover and shedding rate compared to oral gingival epithelium,which contributes the host-parasite equilibrium and rapid repair of damaged tissue,also may explain why gingivitis can be reversible condition,which is considered a defensive mechanism of this tissue.

The Junctional epithelium is permeable membrane.

Molecules injected I.V. can be detected in sulcus.

Also bacteria in sulcus releaselarge quantities of metaboliteswhich diffuse through junctional epithelium.

Some investigators indicate that the cells of the junctional epithelium have an ‘endocytic capacity’ to that of macrophages and neutrophils, and that this activity might be protective in nature.

Junctional epithelium has impressive antimicrobial systems and is a part of immune system of defense mechanism.

ANTIMICROBIAL PEPTIDES

It also has sensory function detecting chemical excreted from bacteria.

BACTERIA

Below the Junctional epithelium is a vascular network which supplies the epithelium with nutrients and defense cells.

Therefore,Junctional epithelium in antimicrobial defense has the role of the epithelial barrier, and the combination of the epithelial cells themselves can produce effective anti-bacterial substances, including defensins and liposomal enzymes.

Epithelial cells can be activated by microbial products chemokines such as interleukins, cytokines and tumor necrosis factor alpha.

Cytokines are soluble proteins secreted by cells involved in both the innate and adaptive host response act by maintenance of immune and inflammatory responses.

Cytokines - important role in cell mediated immune responses.

Interleukins are important members of the cytokine group and are primarily involved in communication between leukocytes and other cells.

3.Surface fluid and enzymesGCF• Tissue fluid that seeps through the crevicular

epithelium is known as gingival crevicular fluid.• The composition and possible role in oral defense

mechanisms were elucidated by Waerhaug and Brill and Krasse.

• METHOD OF COLLECTION Absorbing paper strips Preweighed twisted threads Micropippetes Crevicular washings

COMPOSITION OF GCFENZYMES• Acid

phospatase• Alkaline

phosphatase• Alpha1-

Antitrypsin• Arylsulfatase• Aspartase

aminotransferase

• Chondroitin sulfatase

• Cystatins• Cytokines• Endopeptidase

s• Exopepetidase

s• Hyaluronidase• Immunoglobuli

ns• Lactate

dehydrogenase

• Lactoferrin• Lactic acid• Lysozyme etc.

CELLULAR ELEMENTS• Bacteria• Desquamat

ed epithelial cells

• Leukocytes

ELECTROLYTES• Potassium• Sodium• Calcium

ORGANIC COMPOUNDS• Carbohydrates• Lipids• Proteins-

Ig,Complement components.

METABOLLIC AND BACTERIAL PRODUCTS• Urea• Endotoxins• Lactic acid• Prostaglandins• Hydroxyprolin

e• Antibacterial

factors• Cytotoxic

substances.

CLINICAL SIGNIFICANCE GCF is an inflammatory exudate. The amount of GCF is greater when inflammation is present.

• Circadian periodicity: There is a gradual increase in GCF amount from 6AM to 10PM and a decrease afterward.

• Sex hormones:Female sex hormones,Pregnancy,ovulation • and hormonal contraceptives increase gingival fluid production.

• Mechanical Stimulation: Chewing and vigorous gingival brushing stimulate the flow of GCF.

• Smoking: Immediate transient but marked increase in GCF flow.

• Periodontal therapy: There is increase in GCF production during the healing period after periodontal surgery.

• DRUGS IN GCFDrugs that are excreted through the GCF may be used advantageously in periodontal therapy(Bader and Goldhaber)• Tetrayclines• Metronidazole

LEUKOCYTES IN THE DENTOGINGIVAL AREA. The main port of entry of leukocytes into oral cavity is

the gingival sulcus. Leukocytes found are predominantly PMNs. The majority of these cells are viable and have

phagocytic and killing capacity. Therefore, leukocytes constitute a major protective

mechanism against the extension of plaque ito the gingival sulcus.

SALIVA Salivary secretions are protective in nature because

they maintain the oral tissues in a physiologic state.

Saliva exerts a major influence on plaque by mechanically cleansing the exposed oral surfaces,by buffering acids produced by bacteria,and by controlling bacterial activity.

COMPOSITION OF SALIVAElectrolytes Sodium Calcium Potassium Magnesium

ORGANIC CONSTITUENTS OF SALIVA Proteins Mucin Amylase Cystatins Peroxidases Carbonic anhydrases Histatins and Statherins Proline rich proteins and glycoproteins.

ANTIBACTERIAL FACTORS IN SALIVAImmunoglobulin proteins• Secretory IgA• IgG• IgMNon-immunoglobulin proteins• Lysozyme• Lactoferrin• Proline rich proteins• Histidine rich proteins• Salivary peroxidase systemAgglutinins• Mucins• Fibronectin• Alpha2- Macroglobulins

ROLE OF GCF COMPONENTS IN DEFENSE MECHANISMGCF COMPONENT

DEFENSE MECHANISM

Leucocytes Phagocytosis and killing of microorganisms

ImmunoglobulinsIgG more prevalent

Control of inflammatory action preparation of microbes and foreign bodies for phagocytosis

Salivary antibacterial factors

Prevents growth of bacteria

Acid phosphatase Attacks techoic acid ,one of the components of the bacterial cell wall

Lysozyme Bactericidal properties

Streptokinase Plays a role in inflammation.

ROLE OF SALIVARY COMPONENTS IN DEFENSE MECHANISM

COMPONENTS MODE OF ACTION

Lysozyme Lysis of bacterial cell wall.

Lactoferrin Binds to iron leading to inhibition of bacterial cell growth.

Lactoperoxidase Catalyses hypothiocynate ion which disrupts bacterial proteins.

Secretary IgA Interfere with bacterial attachment to the host tissues by agglutinating specific bacteria.

Salivary glycoproteins

Can act as special bacterial agglutinins.

Bicarbonates Can buffer organic acids produced during sugar fermentation.

4.PHAGOCYTOSISCertain cells in the blood stream and in the

tissues are capable of engulfing and digesting foreign material.

The two most important phagocytic cells are the Polymorphonuclear leucocyteMacrophage

Polymorphonuclear leucocyteProvide the first cellular host mechanism to

control periodontopathic bacteria.Produced in the bone marrow ,they are the

most important blood cell for protecting the body against acute invasion by bacteria.

As they possess an amoeba like ability to change shape and move rapidly they can pass through the tissue.

• The direction in which they move is determined by chemical substances,mainly derived from bacteria or the complement cascade.

• These attract PMNs to the site of damage where foreign particles are engulfed and digested.

• While their role is primarily defensive, PMNs can also produce proteolytic enzymes which can destroy the surrounding tissue.

MacrophagesThe macrophage is an indiscriminate scavenger

of foreign material.

It starts life as a monocyte which moves into the tissues and matures to become the extremely efficient phagocyte,the macrophage, which is capable of digesting large foreign particles.

If a bacterial disease lasts more than a few days the number of monocytes in the tissues increase until there may be as many monocytes as PMNs.

• Unlike PMNs, monocytes are capable of several divisions within the tissues which progressively increase the number of macrophages.

• While PMNs are the main line of defense in acute infection the monocytes are more important in long-term chronic infection.

• The macrophages also take up antigens from the circulating fluid for processing and presentation to the lymphocytes.

Phagocytosis is aided by a battery of nine related proteins known as ‘complement’.

The complement cascade is initiated by the combination of immunoglobulin and the C1 component.

The final product of the cascade is an esterase which damages cell membranes and leads to bacteriolysis.

Complement Pathway :The functions of complement are:• Chemotaxis cellular activation:Complements

products released in this reaction attracts phagocytes to the site of infection.e.g.C3a and C5a

• Opsonization:once they arrive at the site of infection the complement coat the bacterial surface and allow the phagocytes to recognize the bacteria and there by facilitating the bacterial phagocytosis.e.g.C3b

• Cytolysis:Damage to the plasma membranes of the cells can lead to lysis of the cell,e.g.C5-C9

5.THE INFLAMMATORY REACTION

Inflammation may be defined as the reation of living tissues to the injury in essence,it is a defense mechanism in itself.This reaction is a beneficial one.

5.THE INFLAMMATORY REACTIONTissue Injury and infection stimulates inflammatory reaction.

Changes in the local microcirculation

Hyperaemia, increased vascular permeability

Formation of a fluid and cellular exudate

In this way serum proteins and phagocytic cells accumulate around the irritant.

ADAPTIVE IMMUNE SYSTEM

The unique surveillence and attack system developed has three following main characteristics:

1. It can distinguish between itself and the enemy,i.e. between ‘self’ and ‘non-self’ so that it does not attack parts of itself.

2.The defenses contain elements specific against any given antigen.This is possible because each antigen contains specific amino acid sequences or ‘flags’ which the immune system uses to recognize ‘non- self’.

3.The system has memory .The first contact with the antigen produces a

primary response in which the uneducated lymphocytes proliferate and mature,and the antigen is memorized so that the further contact provokes a ready secondary response.

Adaptive immune system is brought about by actions of an array of cells which take up , process ,present and react to foreign proteins known as antigens.

APCs such as macrophages roam the body ingesting the antigen they find and fragmenting it into antigenic peptides.

Within the cell these species of peptide are joined to the major histocompatibility complex(MHC) molecules and displayed on the surface of the cell.

The T-Lymphocytes are activated by the process and divide to produce memory and effector cells.

B lymphocytes which also have specific receptor molecules on their surface respond to these signals.

When activated they differentiate into plasma cells that secrete specific antibodies.

By binding to antigen the antibodies can neutralize them or precipitate their destruction by activating the complement cascade or enabling phagocytic cells to destroy them.

CONCLUSION

The defense mechanisms of GCF,leukocytes,saliva and the epithelial barrier of the gingival sulcus are generally effective in controlling the deleterious effects of the heavy concentration of bacteria found in dental plaque.

If this balance between host and parasite is slightly changed,the result can be progressive periodontal breakdown.

Small clinical alterations,such as an over-contoured restoration or an open subgingival margin,can allow the bacteria to gain a small advantage over the host defenses,resulting in increased gingival inflammation and eventual loss of attachment.

• In summary, the closed role of the epithelial attachment, combined with rapid epithelial cell renewal and repair, saliva rinse,gingival crevicular fluid washing,complement of immune function, and granulocyte cells and monocyte / macrophage phagocytosis and bactericidal effect, etc., constitute a multiple defense mechanisms of the periodontal tissues.

• This defense mechanism against bacterial invasion and destruction play a vital role to resist the plaque to the gingival sulcus extension and protection periodontal tissue.

REFERENCES:Host defense processes, Clinical periodontology

and Implant dentistry(5th Edition) Jan Lindhe Vol 1.

Carranza’s Clinical Periodontology Tenth edition.Outline of periodontics,J.D.Manson,B.M.Eley.Essentials Of Periodontology,Sahitya Reddy S. Basic defense mechanisms in periodontal

diseaseMed Oral Patol Oral Cir Bucal. 2009 Dec 1;14 (12):e680-5.

Polymicrobial Diseases ,Janet M. Guthmiller and Karen F. Novak.

Journal of Dental Research,The Junctional Epithelium: from Health to Disease,D.D. Bosshardt and N.P. Lang, J dent res, 2005 84: 9