Defense mechanisms of gingiva

Defense mechanisms of gingiva

1. DEFENSE MECHANISMS OF GINGIVA Dr Jaffar Raza Syed

2. INTRODUCTION  Defense Mechanisms The mechanisms by which health is preserved in the face of potential disease.  The innate immunity system : Acts as a first line of defense against infections, Present since birth. Resistance to infection, which an individual possesses by virtue of his genetic and constitutional make up.  The adaptive immune system: Activated when innate fails to protect the host. Produces a specific reaction to each infectious agent Also remembers the infectious agent and can prevent it from causing disease later.

3. What’s the need for defense mechanisms?

4. Gingiva is constantly subjected to a PLETHORA of mechanical, chemical and antigenic challenges from bacteria and other foreign bodies. During mastication of food the bolus passes over the gingival surface with force. Gingiva is also exposed to extreme variations in temperature and pH. Over 300 bacterial species, some of them pathogenic, have been recognized as commensals of the oral cavity. Inspite of all these adverse environmental conditions, periodontal tissues remain in a state of health, normally. & This is because of these host defense systems.. The gingiva is able to withstand all of these adverse environmental conditions, with the help of certain defense mechanisms.

5. Defense mechanisms Nonspecific Specific Host- microbial symbiosis Adaptive immunity Tissue Resistance Local inflammatory response Anatomical factors Mucous barrier Epithelial barrier Ging crevi Saliva fluid Eshan V, Apurv J. Defense Mechanisms of Gingiva. Journal of Orofacial Research .2014 April-June;4(2):111-114 CLASSIFICATION

6. Host-Microbial Symbiosis Close, prolonged association between two or more organisms of different species, regardless of the benefit to the members. • Presence commensal habitats essential for host immune system protects periodontium from pathogenic microbes. • Bacteria associated with periodontal health include: various facultative gram-positive bacteria Streptococcus sanguis , Streptococcus mitis, Actinomyces naeslundii and Actinomyces viscosus .

7. Proposed mechanisms for commensal bacteria in maintaining health of host tissue • Commensals promote host tolerance to pathogenic bacteria by:  Suppressing inflammatory cytokine production.  Inducing generation of suppressive T-lymphocytes  Favoring secretion of Th2 cytokine • Certain commensals are capable of inducing release of antimicrobial peptides from epithelial cells.  F. nucleatum protects oral ep. From P.gingivalis invasion by inducing release of antimicrobial peptides • They also prevent over colonization of pathogenic/exogenous bacteria and compete with them for resources. Zhimin Feng & Aaron Weinberg . Role Of Bacteria In Health And Disease Of Periodontal Tissues Periodontology 2000, Vol. 40, 2006, 50 – 76.

8. Tissue Resistance  Tissue resistance consists of four barriers:

9. Anatomical Factors: • Anatomy of gingival tissues is designed for effective mastication and clearance of food debris. • Any poor functional tissue relations lead to plaque accumulation. • Stippling: functional adaptation resistance to mechanical trauma. • Attached gingiva: contoured to allow for proper deflection of food.

10. • Gingival fibers:  braces marginal gingiva firmly against tooth surface,  provides rigidity to combat forces of mastication and  tends to throw out any foreign material into the sulcus.  This expulsion is aided by the movement of teeth and gingival tissues during function of dentition and pulse beats.

11. Mucus barrier: • Mucus barrier is formed by Saliva washing the gingival surface and Gingival crevicular fluid flowing through junctional epithelium (JE) into the gingival sulcus.

12. Saliva • Saliva has been defined as “the fluid secreted by the salivary glands that begins the digestion of foods”. • Salivary secretions protective maintain the oral tissues in a physiologic state. • Saliva exerts a major influence on  plaque by mechanically cleansing the exposed oral surfaces,  by buffering, the acids produced by bacteria,  by controlling bacterial activity.

13. Composition of Saliva

14. Schematic presentation of the main functions of saliva in relation to its constituents

15. Antibacterial Factors • Saliva contains numerous inorganic and organic factors that influence bacteria and their products in the oral environment, aiding in the defense of the host. • They are:  Salivary antibodies  Enzymes  Glycoproteins  Buffer system  Saliva pH

16. Salivary Antibodies: • First line of defense in saliva, mucous layer of epithelium & acquired pellicle. • Salivary Ab: o Secretory IgA – gland derived o IgG – Serum/ local plasma cells o Non- secretory IgA- serum/local plasma cells o Traces of other Ig like: IgM,D,E • Functions:  Antibacterial, fungal, viral  Helps in phagocytosis, Ag presentation, degranulation, cytokine production.

17. • Many bacteria coated with IgA, • bacterial deposits contain both IgA and IgG • IgA antibodies present in parotid saliva can inhibit the attachment of oral Streptococcus species to epithelial cells . • Gibbons and colleagues suggested that antibodies in secretions may impair the ability of bacteria to attach to mucosal or dental surfaces.

18. Enzymes: Derived from the salivary glands, bacteria, leukocytes, oral tissues, and ingested substances; Major enzyme parotid amylase. Certain salivary enzymes have been reported in increased concentrations in periodontal disease: ↑ hyaluronidase and lipase, ↑ β-glucuronidase and chondroitin sulfatase, ↑ aspartate aminotransferase and alkaline phosphatase, ↑ amino acid decarboxylases, catalase, peroxidase, and collagenase.

19. • Proteolytic enzymes in the saliva are generated by both the host and oral bacteria. • These enzymes have been recognized as contributors to the initiation and progression of periodontal disease. • To combat these enzymes, saliva contains:  Antiproteases cysteine proteases such as cathepsins  Antileukoproteases elastase.  Tissue inhibitor of matrix metalloproteinase , activity of collagen-degrading enzymes.

20.  Lysozyme: • Hydrolytic enzyme • cleaves the linkage between structural components of the glycopeptide muramic acid–containing region of the cell wall of certain bacteria in vitro. • It works on both gram-negative and gram-positive organisms ; its targets include Veillonella species and Actinobacillus actinomycetemcomitans. • It probably repels certain transient bacterial invaders of the mouth.

21.  Lactoperoxidase–thiocyanate system: Bactericidal to some strains of Lactobacillus and Streptococcus by preventing the accumulation of lysine and glutamic acid, which are essential for bacterial growth.  Lactoferrin: Effective against Actinobacillus species.  Myeloperoxidase: • similar to salivary peroxidase, • released by leukocytes; • bactericidal for Actinobacillus, • inhibits the attachment of Actinomyces strains to hydroxyapatite.

22. Glycoproteins: • Bind specifically to many plaque-forming bacteria. • Facilitate bacterial accumulation on the exposed tooth surface. • selectively adsorb to the hydroxyapatite to make  acquired pellicle. • Glycoproteins with blood group reactivity inhibit the sorption of some bacteria to the tooth surface and to epithelial cells. • Glycoproteins and a glycolipid, serve as receptors for the attachment of some viruses and bacteria.

23. Salivary Buffers and Coagulation Factors: • The maintenance of the pH  important function of salivary buffers. • The primary effect of these buffers is on dental caries. • the bicarbonate–carbonic acid system  important buffer system. • Saliva also contains coagulation factors (i.e., factors VIII, IX, and X; plasma thromboplastin antecedent; and Hageman factor) that hasten blood coagulation and that protect wounds from bacterial invasion. • An active fibrinolytic enzyme may also be present.

24. Saliva buffer system protects oral cavity in 2 ways: 1 many bacteria requires specific pH for their growth, & altering optimal environment conditions prevents colonization. 2 plaque organisms produce acids which if not rapidly buffered can cause demineralization of tooth. Salivary pH: • Normally mixed saliva has a pH of 5.6-7.0, average 6.7 . • pH increases with flow due to increased bicarbonate concentration. • Low ph favors survival of bacilli, yeasts and streptococci. • High ph favors proteolytic bacteria.

25. Leukocytes: • Saliva contains all forms of leukocytes, principal cells are PMNs. • The number of PMNs varies from person to person at different times of the day, and it is increased in the presence of gingivitis. • PMNs reach the oral cavity by migrating through the lining of the gingival sulcus. Orogranulocytes:  Living PMNs in saliva  Their rate of migration into the oral cavity is termed the orogranulocytic migratory rate.  Rate of migration correlates with the severity of gingival inflammation and is therefore a reliable index for the assessment of gingivitis

26. Role in Periodontal Pathology: • Influences:  plaque initiation & maturation  calculus formation,  periodontal disease and caries. ↓ SALIVA SECRETION: ↑ inflammatory gingival diseases, dental caries, → rapid tooth destruction (cemental and cervical caries).

27. The generation of crevicular fluid Squier & Johnson (1973) • Intercellular movement of molecules and ions along intercellular spaces • Three routes have been described:  Passage From CT Into The Sulcus  Passage From The Sulcus Into The CT  Passage of Substances through pathological or experimentally modified gingival sulcus.

28. Permeability of junctional & sulcular epithelium • Brill and krasse confirmed the permeability by using fluorescein. • Substances that have been shown to penetrate the sulcular epithelium:  Albumin  Endotoxin Indicate that its  Thymidine permeable to  Histamine molecules upto 1000kd wt.  Phenytoin  Horseradish peroxidase

29. Clinical Significance • Amount of GCF is greater when inflammation is present. • Sometimes proportional to the severity of inflammation. GCF production is:  Not Increased by trauma from occlusion  Increased by :  mastication of coarse foods  Toothbrushing  Gingival massage  Ovulation  Hormonal contraceptives  Prosthetic appliances  Smoking • Other factors affecting amount of gcf : circadian periodicity & periodontal therapy

30. Gingival fluid flow and sex hormones : Lindhe & Lundgren, 1972 ( 3 groups of females are studied ) • During mensturation: ↑ in GCF because sex hormones cause ↑ in the gingival vascular permeability. • Females on birth control pills : significant ↑ GCF • Females during pregnancy : gingival exudates reached max values during the last trimester and ↓ to min after delivery. Loe,1965: During pregnancy ↑ levels of gcf due to exacerbation of gingivitis. Muhlemann,1948: menstrual cycle Sutcliffe,1972: at puberty

31. Circadian periodicity: ↑ in GCF from 6:00AM -10:00PM and ↓ afterward. • Bisada et al. 1967: Average flow was greater in the evening and minimal early in the morning .

32. Influence of Mechanical Stimuli Mechanical stimulation of the marginal gingiva, such as massage by means of a round instrument, causes a significant increase in the permeability of the blood vessels located below the junctional and sulcular epithelia. Brill in 1959: The amount of gingival fluid was shown to increase significantly under the influence of chewing . Mcluaghlin WS et al 1993 Smoking produces an immediate but transient increase in GCF flow.

33. Periodontal Therapy and Gingival Fluid • Oral prophylaxis : Gwinnett et al 1978: GCF flow decreases 1 week after oral prophylaxis and slowly returned to pretreatment values. • After surgical procedure : Suppipat et al 1978: inc rease in GCF flow during the first 2 weeks during healing period after surgery, followed by a gradual decrease Tsuchida & Hara 1981 . decrease in GCF flow 4 weeks following root planing & Curettage Arnold et al., 1966: One week after gingivectomy there was a striking increase in GCF flow .

34. The Epithelial Barrier • Continuous epithelial sheath consisting of gingival, sulcular and junctional epithelium. • Continuity of the epithelium protective barrier to foreign agents, including bacteria, their toxic products and antigenic substances. • The ability of an epithelial surface to resist penetration of bacterial toxins is related to:  Thickness of the epithelium.  Degree of keratinization  Rate of turnover of the cell population

35. Thickness of the epithelium: • oral mucosa respond to irritation hyperplasia and downgrowth of basal layers. • The sulcular epithelium (non- keratinised , thin ) easily damaged and less effective barrier to penetration of the connective tissue by bacterial products than is the oral mucosa in the other areas.

36. Degree of keratinization • Protection afforded by the epithelium is dependent keratinization and its ability to desquamate or shed epithelial cells. • Desquamation: process wherein dehydrated and flattened cells of superficial layers are lost and and replaced by cells of underlying layers. • This limits colonization of bacteria and also removes the already colonized bacteria from the epithelial surfaces.

37. Rate of turn over of the cell population: • Constant process of shedding and cell renewal in the oral epithelium. • The following have been the reported turn over times time for different areas in the oral epithelium of experimental animals Palate, tongue, cheek - 5 - 6 days. Gingiva J.E. - - 10 – 12 days 1 – 6 days. (Skougaard et al 1962). • The high turn over rate of epithelium as well as the connective tissue of the periodontium, are important aspects of the defense mechanism.

38. Components that contribute to various aspects of the epithelial barrier Early responders of innate immunity Toughened mechanically resistant surface Wound healing Tissue turnover

39. These include cell–cell attachments and the overall integrity of the tissue as well as the process of differentiation (keratinization) of the tissue leading to the toughened, mechanically resistant surface. Desmosomes mediate keratinocyte cell–cell attachment, and hemidesmosomes mediate keratinocyte–basal lamina attachment. Langerhans cells (purple dendritic cells) within the epithelium do not have desmosom al attachments. Constant cell renewal is critical to tissue turnover and continual differentiation. Cell migration is critical to wound healing and re- epithelialization. Constitutively expressed antimicrobial peptides contribute to the barrier to microbial invasion.

40. Antimicrobial defense of junctional epithelium 1) Rapid turnover  cell exfoliation 2) Funneling of JE towards sulcus  hinders bacterial colonization 3) Basement membrane forms an effective barrier against microbes 4) Release of antimicrobial substances 5) Release of cytokines from ep. Cells 6) Cytokines & chemokines released attract LC & PMN

41. Gingival Connective Tissue The gingival turgor, • The resilience and pliability of the attached gingiva withstand frictional forces and pressures that result from mastication. The fiber apparatus • Controls the positioning of teeth within the dental arch • Biostability of the gingival tissue. • Protects the cellular defenses located at the dentogingival interface. • Maintenance of this fibrous complex connective tissue turnover rate. • Consequently, post inflammatory repair of the fiber apparatus is completed within 40 to 60 days . Gingival connective tissue protect the root surface and alveolar bone from the external oral environment.

42. Cells of gingiva involved in defense mechanism Immune cells Neutrophils Monocytes Macrophages Lymphocytes Basophils Non-immune cells Keratinocytes Langerhans cells Fibroblasts Eosinophils Mast cells Plasma cells

43. Neutrophils • the most predominant inflammatory cells in gingiva. Adhere to the host substrate, migrate to the site of infection recognize the bacteria, Extend Cytoplasmic processes or pseudopodia Engulf bacteria & bring about phagocytosis. integrate the pathogen forming a phagosome Phagosomes fuse with lysosymes  phagolysosome digestion and destruction of pathogen takes place.

44. • PMNs also undergo degranulation and allow extracellular killing of pathogens which is considered a principle mode of reducing bacterial count in the gingival crevice. • The granules found in PMN consist of primary (azurophilic) and secondary (specific) granules. • These can bring about oxygen dependent or independent killing.

45. Keratinocytes: • Keratinocytes, no longer considered as passive by-standers • play an active role in the activation of inflammation within the gingival tissues. • They synthesize number of cytokines , adhesin molecules, growth factors and enzymes . • They also produce Interleukin 1, TNF, prostaglandin E2, matrix metalloproteinases , that diffuse through JE, enter the gingival connective tissue and initiate the cellular immune reaction. • Recruitment of neutrophils into the JE is mediated by antigen presenting cells (Langerhans cells), and adhesion molecules secreted by keratinocytes, promoting diapedesis of neutrophils along the chemical gradient.

46. Langerhans cells • Dendritics cells - Modified monocytes • Reside chiefly in suprabasal layers. • Act as antigen -presenting cells for lymphocytes. • Specific elongated g-specific granules called as Birbecks Granules. • Have marked adenosine triphosphatase activity. • Only epidermal cells which express receptors for C3 and Fc portion of IgG. • Found in oral ep. of normal gingiva. • Smaller amounts in sulcular ep. • Absent in healthy junctional ep.

47. Odland Body / Keratinosome / Membrane – coating granules: • The upper most cells of the stratum spinosum contain numerous dense granules, keratinosomes , which are modified lysosomes. • They contain a large amount of acid phosphatase, an enzyme involved in the destruction of organelle membranes, which occurs suddenly between the granulosum and corneum strata and during the intercellular cementation of cornified cells.

48. Fibroblasts: • Principal cell type of connective tissue. • Provide structural framework , maintains CT integrity. • Many studies shown that, fibroblasts senses pathogens & PAMPs’ inflammatory mediators regulate inflammatory response • Express functional TLR’s

49. PRR • Cells of epithelium and connective tissue express Pattern Recognition Receptors (PRRs) that bind Pathogen- Associated Molecular Patterns (PAMPs ), found in a broad type of organisms. • These receptor types include:  toll-like receptors (TLR),  nucleotide-binding oligomerization domain (NOD) proteins,  cluster of differentiation 14 (CD14),  complement receptor-3,  lectins and scavenger receptors.

50. Local inflammatory response most significant and final barrier to penetration of connective tissue by bacteria and their toxins. • This response is stimulated by tissue injury and infection. • A series of reactions brings about local changes like increased vascularization leading to increased fluid collection and cellular exudation that eventually causes accumulation of serum proteins and phagocytic cells in the affected area.

51. Conclusion • The oral cavity is well equipped to counterattack any adverse condition that may harm the gingiva. • While the innate immunity acts primarily against any foreign invader, the specific immunity takes a more complex targeted approach to protect the gingiva. • Right from its superficial epithelial layer to the innermost connective tissue, there is a line of defense that acts in harmony with other oral structures to maintain homeostasis.