This document provides an overview of the microbiological and immunological aspects of the microbial-host interaction in periodontal disease. It discusses the various bacterial species involved, including the "red complex" bacteria Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. It describes the virulence factors of these bacteria and how they evade host defenses. It also summarizes the innate and adaptive immune response phases, focusing on the acute inflammatory response and roles of neutrophils in controlling bacterial challenge through opsonization and phagocytosis.

2. CONTENTS
 Introduction
 Definitions
 Historical background
 Microbiologic aspects of the
microbial-host interaction
 Actinobacillus Actinomycete
comitans
 Treponema Denticola
 T. Forsythia
 P. gingivilis
 Capnocytophaga species
 Immunologic aspects of the
microbial host interaction
 Connective tissue alterations:
tissue destruction in
periodontitis
 Connective tissue alterations: Healing
processes in periodontitis.
 Microbiology and immunology in
gingival health.
 Microbiology and immunology in
periodontal diseases.
 Gingivitis.
 Chronic periodontitis.
 Necrotizing periodontal diseases.
 Aggressive periodontitis.
 Periodontal abscess.
 Conclusion.
 References

3. Introduction
• The mouth, like all external surfaces of the body and the gut, has a
substantial microflora living in symbiosis with a healthy host.
• The microflora of the mouth contains hundreds of species of aerobic
and anaerobic bacteria.
• Cultural studies indicate that more than 500 distinct microbial species
can be found in dental plaque.
 Although bacteria are necessary for periodontal disease to take place, a
susceptible host is also needed.
 The immune-inflammatory response that develops in the gingival and
periodontal tissues in response to the chronic presence of plaque
bacteria results in destruction of structural components of the
periodontium leading, ultimately, to clinical signs of periodontitis.

4.  The host response is essentially protective, but both hypo- responsiveness
and hyper-responsiveness of certain pathways can result in enhanced tissue
destruction (Bruce l Pihlstrom 2005 ).
 Closer investigations of the destructive pathway of periodontal disease
began to focus on the relation-ship between bacteria and the host response
in the initiation and progression of periodontal disease..
4
 This shift in etiological theory produced a paradigm that called attention to
the fact that although microorganisms are the cause of periodontitis, the
clinical expression of the disease depends on how the host responds to the
extent and virulence of the microbial burden.
 It was found that degradation of host tissue results from this bacterial-host
interaction. (Casey Hein 2004)
A dynamic equilibrium exists between dental plaque bacterium and innate
host defense system. Dental plaque bacteria have adapted survival
strategies favoring growth, while the host limits growth by combination of
innate and adaptive immune responses. This interaction represents a highly
evolved interaction between bacteria and host.

5. What is host ?
An organism which harbors
the parasite .
5
What is bacteria?
Extremely small—usually 0.3 to 2.0
micrometers in diameter—and
relatively simple microorganisms
possessing the prokaryotic type of
cell construction.
Interaction
The combined effect of two or more independent variables
acting simultaneously on a dependent variable.

6.  Symbiosis: It is an association in which both host and
parasite are so dependent upon each other that cannot live
without the help of other and none of them suffers any harm
from the association.
 Commensal: Is a non disease forming organism; part of the
resident flora.
 Commensalisms: is an association in which parasite is
deriving benefits without causing injury to its host.
6
 Parasitism: is an association where parasites gets benefits
and the host gets harmful effects.
 Mutualism: is an association where parasite and host both
are benefited.

7.  Pathogen :is an organism that causes disease.
 Opportunistic pathogens: are normally not pathogenic , but are able
to become so if their local environment is changed, they can
overgrow and the microbial load can cause disease.
7
 Virulence : ability of a microorganisms to cause the disease
 Toxins : Anything that is injurious, destructive, or fatal
or
A poisonous substance, especially a protein, that is produced by
living cells or organisms and is capable of causing disease when
introduced into the body tissues but is often also capable of inducing
neutralizing antibodies or antitoxins.

8. Etiology of periodontal disease past
to present
1960 Calculus Theory
1965 -1975 Nonspecific Plaque Theory
1975-1985 Specific Plaque Theory
1985- Today Ecological Plaque Hypothesis
8
The host-bacterial interaction theory and the risk continuum: casey hein contemporary
oral hygiene december 2004

9. Microbiological Aspects Of The Microbial-host
Interaction

10. VIRULENT ABILITY OF THE MICROBIAL SPECIES
1) It must be a virulent clonal type.
2) It must possess the chromosomal and extra-chromosomal genetic factors to
initiate disease.
3) The host must be susceptible to this pathogen.
4) The pathogen must be in numbers sufficient to exceed the threshold for
that host.
5) It must be located at the right place with ideal environment to proceed.
6) Other bacterial species must foster, or at least not inhibit, the process.
7) The local environment must be one which is conducive to the expression
of the species' virulence properties.
(The Bacterial Etiology of Destructive Periodontal
Disease: Current Concepts. J Periodontol 1992; 63:322-
331.)

11. Predominant bacterial species
• Porphyromonas gingivalis,
• A. actinomycetemcomitans,
• Treponema denticola,
• Bacteroides forsythus,
• Fusobacterium nucleatum,
• Prevotella intermedia,
• Campylobacter rectus,
• Peptostreptococcus micros,
• Eikenella corrodens.
Formation of
plaque
Host tissue
invasion
Bacterial
evasion of
host defense
mechanism
Virulence
factors of
different
micro-
organisms

12. 12
Acquisition
Adherence or
retention
Initial survival
Longer term
survival
Avoidance of
elimination
Multiplication
Elaboration of
virulence
factor
Formation of plaque

13. Host tissue invasion
Mode of entry of bacteria:
• Through the ulceration in the epithelium
• Through gingival sulcus
• Through periodontal pockets
• Direct penetration of microorganisms
Organisms capable of invading tissues directly:(AAP 1996)
• Actinobacillus actinomycetemcomitans
• P. gingivilis
• Fusobacterium nucleatum
• Trepanoma denticola

14. Bacterial evasion of host defense mechanism
Direct damage to polymorph
nuclear leucocytes and
macrophages
Reduced PMN chemotaxis
Degradation of
immunoglobulins
Degradation of fibrin
Altered lymphocyte
function
Damage to sulcular
epithelium
Production of
volatile sulphur
compounds
Degradation of
periodontal tissues
by bacterial enzyme.

15. VIRULENCE FACTORS OF MICRORGANISMS
AGGREGATIBACTER
ACTINOMYCETEMCOMITANS
 Actinobacillus actinomycetemcomitans.
 Klinger (1912) first isolated from cervicofacial
actinomycosis lesions.
 Henrich and Pulverer(1959) were the first to demonstrate
that A. a was part of the normal oral flora and indicated that
it could colonize teeth, mucosa and the oropharynx.
 With respect to periodontal disease, A. a was first
implicated as the cause of juvenile periodontitis in 1976 by
Newman et al. and by Slots .

16.  The primary oral ecological
niche for Aa is dental plaque.
 High levels- in pockets
 Low levels- in other oral
surfaces, tongue, saliva
 It has not been cultured from
edentulous mouths
 It does not belong to
indigenous microbiota of any
other body site.
 Can cause non oral infections
such as endocarditis, abscess
in lungs, head & neck and
abdominal areas.
 Distribution pattern-
generally isolated areas, as
IgG response to Aa is
protective and limit infection.

17.  Are classified as_
i. Factors that assist in colonizing the dental plaque and
gingival sulcus-bacterial capsule and fimbriae
ii. Factors helping it to evade host defense mechanism-
leukotoxin
iii. Factors causing tissue destruction-LPS endotoxin(bone
resorption), Collagenase( connective tissue breakdown)
reduction in collagen density.

18. Red complex bacteria
T . denticola
T. forsythia
P.gingivalis

19. Porphyromonas gingivalis
 Gram-negative, anaerobic, non-motile, asaccharolytic rods - member of the
much investigated "black-pigmented Bacteroides" group.
 Initially grouped into a single species, B. melaninogenicus.
 At present only known Porphyromonas spp. isolated from humans that
produce phenylacetic acid as metabolic end product.
 Non-oral infections- endocarditis
Habitat
 Mouth with poor oral hygiene prefered over clean tooth surface, need
G+ve bacteria.
 Not seen in edentulous mouth
 Levels increase with age so infrequent in children, acquired in later life

20. Association:
 Commonly encountered in sites with destructive periodontal
disease
 Refractory sites (haffajee et al, 1988)
 Advanced periodontal disease (Slots 1977)
 Highly inflamed gingivitis lesions (mayrand 1981)
 Acute periodontal abscess (newman and sims 1979)

21. Virulence factors
1. Capsule: polysaccharide capsule helps in protection against phagocytosis.
2. Fimbriae: helps in binding to host cells and saliva coated tooth
3. Proteinases: a large no. of hemolytic, proteolytic and lipolytic substances are
produced.
 4 proteolytic substances are recognized.
 Serine
 Aspartate
 Thiol
 Metalloprotienases
 Out of these collagenase, aminopeptidase, trypsin like protease are critical.
Cysteine proteinases (gingipains)
 Cleave polypeptides after arginine and lysine residue and classified as
 Arginine (Arg-) specific proteinases
 Lysine (Lys-) specific proteinases
Effects:
 ↑ vascular permeability ---↑ GCF
 Chemotactic for PMNL so ↑ conc. of PMNL at sites of tissue destruction
 Arg- gingipain distrupts oxidative burst mechanism of PMNLs.
 Only known prokaryote to inhibit this PMN function.

22. Tanerella forsythus
Previously known as B. forsythus
First described in 1979 (Tanner et al.
1979) as a "fusiform" Bacteroides at The
Forsyth Institute.
Gram-negative, anaerobic, spindle-
shaped, highly pleomorphic rod.
Difficult to grow, often requiring 7–14
days for minute colonies to develop.
The growth of the organism was shown
to be enhanced by co-cultivation with F.
nucleatum and commonly occurs with
this species in subgingival sites
(Socransky et al. 1988).
The species was shown to have an
unusual requirement for N-
acetylmuramic acid (Wyss 1989).

23. TREPONEMA DENTICOLA
ADHESINS
 Coaggregation b/w P.g & T.d is mediated by fimbriae binding
protein-DENTILYSIN
 Helps transport of Pg to deeper regions
 Binds to ECM proteins like laminin fibronetin /heparin
 And host cells like gingival fibroblast
 Collagen binding proteins of T.d binds Type I,IV,V adherence
/colonozation (Li et al)

24.  Produces major outer
sheath proteins
host cells
lectin like proteins
 Binding activity (-)
mannose/galactose
residues
 This protein might have
porin activity –enables
transportation of molecules
into /out of host cells
SUSTENINS
 Possess peptidases associated
with its outer sheath
 Chymotripsin like protease (
Uilto et al )
 T.denticola + erythrocyte---
resulting in cell lysis &
competing with host for
available hemin derived iron
 Synthesize 2 low iron induced
outer membrane proteins :
HbpA & HbpB—binds hemin

25. EVASINS
 Chymotrypsin like
protease + proteins on
outer sheath
 Chymotrypsin like
protease complex
 Adhesion
 Degradation of humoral
proteins ( basement
membrane components)
 Activates MMPs
 Forms vesicles with
hyaluronidase
Effects on host innate & immune
mechanism
T.denticola on fibroblast
Cell rounding
Formation of surface blebs
Detachment from cell surface
(Weinberg & Holt)

26. IMMUNOLOGICAL ASPECTS OF MICROBIAL-HOST
INTERACTION
 Innate factors such as complement, resident leukocytes and especially mast
cells play an important role in signaling endothelium, thus initiating
inflammation.
 Acute inflammatory cells (i.e. Neutrophils) protect local tissues by
controlling the periodontal microbiota within the gingival crevice and
junctional epithelium .
 Chronic inflammatory cells, macrophages and lymphocytes protect the
entire host from within the subjacent connective tissue and do all that is
necessary to prevent a local infection from becoming systemic and life
threatening.
Immune
response
phase
ACUTE
INFLAMMAT
ORY
RESPONSE
ACUTE
BACTERIA
L
CHALLENG
E PHASE

27. Acute bacterial challenge phase
There is a very high turnover of epithelium -that permits rapid replacement of cells and tissue
components damaged by microbial challenge.
The gingival crevicular fluid flushes the sulcus or pocket and delivers complement proteins and
specific antibodies.
Salivary secretions provides continuous flushing and supply of agglutinins and specific antibodies.
The intact epithelial barrier of the gingival, sulcular and junctional epithelium prevents bacterial
invasion.
The epithelial and vascular elements response to bacterial challenge
27

28. Acute inflammatory response
Vascular leakage enhances the localized response:
Leukocytes selectively emigrate from the vessels to alter the immuno-inflammatory
cell populations in the gingival tissues
Neutrophil migration into the gingival sulcus:
The inflammatory infiltrate within the tissues:
• Opsonization
• Phagocytosis
28

29. OPSONIZATION AND PHAGOCYTOSIS

30. Vascular leakage enhances the localized response
 In the presence of lipopolysaccharide or cytokines, the endothelial cells of
the microcirculation become activated. The vessels of the microcirculation
become inflamed, dilated and engorged with blood, and the blood flow
slows.
 The endothelial cell junctions open and protein-rich fluid leaves the vessels
at the site of the post-capillary venules /and accumulates in the extra cellular
matrix.
 Leukocytes selectively emigrate from the vessels to alter the immune
inflammatory cell populations in the gingival tissues.
 Neutrophils are believed to play an important role in controlling the
periodontal microbiota. They are the first leukocytes to arrive at the site of
inflammation and are always the dominant cell type within the junctional
epithelium and the gingival crevice.
 Neutrophils exit the inflamed vessel of the' microcirculation and migrate
through the connective tissues and junctional epithelium, to form a barrier
between the subgingval microbial plaque and the gingival tissue
 There is specific interactions among vascular cell adhesion molecules and
leukocyte integrins and thus the chance of inducing leukocyte extravasation
by diapedesis into the extravascular spaces.

32. Controlling Bacterial Challenge: Primary Role for
Neutrophils
Neutrophils are believed to play an important role in controlling
the periodontal microbiota. They are the first leukocytes to
arrive at the site of inflammation and are always the dominant
cell type within the junctional epithelium and the gingival
crevice.
For neutrophils to control bacterial infections effectively, their
functions, including transendothelial migration, chemotaxis,
transepithelial migration, opsonization, phagocytosis, and
intraphagolysosomal killing, must be intact.
About 1% to 2% of all neutrophils migrate across the junctional
epithelium daily. This transepithelial migration requires a
chemotaxin gradient . The junctional epithelium expresses the
chemotactic cytokine (chemokine) IL-8 and intercellular
adhesion molecule-1 (ICAM-1).

34. A gradient of the membrane-bound ICAM-1 and the soluble IL-8
molecules is formed, with increased expression toward the
outer surface of the tissue. This distribution is ideal for the
migration of neutrophils into the gingival sulcus.
Neutrophils may use their adhesins leukocyte function associated
antigen-1 (LFA-1), Mac-1, or both to bind ICAM-1 on the
epithelial cell in the process of epithelial transmigration.
In vitro studies have shown that P. gingivalis impedes
transepithelial migration of neutrophils and prevents epithelial
cells from secreting IL-8 in response to bacterial challenge.
P. gingivalis also has a potential virulence factor through
production of periodontain, an α1-proteinase inhibitor of
human neutrophil elastase. These properties may contribute to
the virulence of P. gingivalis by interfering with the host
immune response.

35. Neutrophil migration into the gingival sulcus
Following extravasation, neutrophils seem to gain access to the
more coronal portion of the junctional epithelium and to
selectively migrate through this multilayered epithelium to gain
access to the bacterial flora.
Two mechanisms of possible importance in the regulation of
neutrophil migration towards the gingival sulcus or the
periodontal pocket following neutrophil extravasation:
The expression of leukocyte adhesion molecules such as the
intercellular adhesion molecule I, in epithelial cells.
Cytokines with potent and cell type-specific leukocyte
chemotactic properties: the chemokines and the neutrophil-
selective interleukin 8, in particular.

36. Immune response phase
 The bacterial products and epithelial derived cytokines activate the
local tissue mononuclear cells that shape the local immune response.
 Macrophages have been reported to be few in healthy gingiva.
Although increased in gingivitis, periodontitis, macrophage density
remain in low proportions relative to other cell types.
36

37. 37
Connective tissue alterations: tissue destruction
in periodontitis
Factors causing tissue destruction
Bacterial
products
Proteinases
Cytokines
Prostagland-
ins
Reactive
oxygen
species

38. Bacterial products
 Degrade basement membrane and extracellular matrix proteins
including collagen, proteoglycans, and glycoproteins. This would
destroy periodontal connective tissue and facilitates bacterial
invasion.
 Interferes with tissue repair by inhibiting clot formation or
lysing the fibrin matrix in periodontal lesions.
 Activates latent host tissue collagenase which would
enhance host-tissue enzyme mediated tissue
destruction.
 Inactivates proteins important in host defense.

39. PROTEINASES
 Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that
degrade extracellular matrix molecules, such as collagen, gelatin, and elastin.
 MMP-8 and MMP-1:- MMP-8 and MMP-l both collagenase are elevated in
tissues and GCF associated with periodontitis.
 MMP-8 is released by infiltrating new fibroblasts, monocytes/macrophages,
and epithelial cells.
 MMPs are secreted in an inactive (latent) form. One mechanism of MMP
activation involves the proteolytic cleavage of a portion of the latent enzyme.
 Proteases capable of activation of MMPs include bacterial enzymes such as the
chymotrypsin-like protease produced by T. denticola, as well as host cell
enzymes such as neutrophil cathepsin G.

41. Arg-gingipain have been found potently to enhance vascular permeability.
These enzymes increase gingival crevicular fluid production and thus provide a
continuous supply of nutrients for the bacterium, enhancing its growth and
virulence.
Arg-gingipain has also been found to be a very efficient enzyme for the
production of the potent chemotactic factor c5a by directly cleaving the C5
component of complement.
These enzyme also degrades c3,and in this way eliminates the creation of c3-
derived opsonins. This render sp. gingivalis more resistant to phagocytosis by
neutrophils
41
Role of gingipain
Pick et al. (1994) separated the trypsin-like activity in P. Gingivalis culture
supernatants called' gingipain' and found that there were two separate cysteine
proteinase activities, one with arginine and one with lysine specificity.

42. Fibrinogen is a major target for lys-gingipain and it thus increases
the local clotting time, leading to gingival bleeding.
The bleeding of periodontal sites is of primary importance for the
growth of P. gingivalis, since it ensures the rich source of haem and
iron that it requires for survival.
Gingipains act as adhesins and have a strong binding affinity for
fibrinogen , fibronectin and laminin. It inhibits haemagglutination.
Since these complexes are present on the surfaces of both the
vesicles and membranes of P. gingivalis , they may play an
important role in the attachment of this bacterium to host cells.
42

43. CYTOKINES
 Two proinflammatory cytokines, IL-1 and tumor necrosis factor (TNF).
 IL- 1 is found in two active forms, IL-lα and IL-1ß. Both are potent
proinflammatory molecules and are the main constituents of what was once called
"osteoclast activating factor." The IL-1 family also includes the IL-1 receptor
antagonist (IL-la), which will bind the IL-1 receptor without stimulation of the host
cell.
 TNF also is found in two forms, TNF-α and TNF-β. TNF-α shares many of the
same biologic activities as IL-1, including the stimulation of bone resorption.
 IL-1 is produced primarily by activated macrophages or lymphocytes but also may
be released by other cells, including mast cells, fibroblasts, keratinocytes, and
endothelial cells.

44.  Bacterial LPS is a potent activator of
macrophage IL-1 production, whereas TNF-a
and IL-1 itself also can activate macrophage
IL-1 production.
 TNF-alpha also is produced by activated
macrophages, particularly in response to
bacterial LPS.
 TNF-ß is primarily produced by the Th l
subset of CD4+ T-cells that have been
activated by antigen or mitogen.
 The proinflammatory effects of IL-1 and TNF-
a include stimulation of endothelial cells to
express selectins that facilitate recruitment of
leukocytes, activation of macrophage IL-1
production, and induction of prostaglandin E2
(PGE2 ) by macrophages and gingival
fibroblasts.

45. PROSTAGLANDINS
The prostaglandins (PGs) are a group of lipid compounds derived
from arachidonic acid, a polyunsaturated fatty acid found in the
plasma membrane of most cells.
Arachidonic acid is metabolized by cyclooxygenase-1 and -2 (COX-
1 and COX-2) to generate a series of related compounds called the
prostanoids, which includes the PGs, thromboxanes, and
prostacyclins.
 PGs are important mediators of inflammation, particularly
prostaglandin E2 (PGE2), which results in vasodilatation and induces
cytokine production by a variety of cell types. COX-2 is up-regulated
by IL-1β,
TNF-α, and bacterial LPS, resulting in increased production of PGE2
in inflamed tissues.
PGE2 is produced by various types of cells and most significantly in
the periodontium by macrophages and fibroblasts.
PGE2 results in induction of MMPs and osteoclastic bone resorption
and has a major role in contributing to the tissue damage that
characterizes periodontitis.

46. CONNECTIVE TISSUE ALTERATIONS: HEALING PROCESSES IN
PERIODONTITIS
The chronic immune system plays an important role in healing
processes, which consist of regeneration and repair.
Regeneration involves the replacement of tissues with new,
identical tissues that function the same as the original tissues.
Repair involves replacement of one tissue with another tissue,
such as fibrous connective tissue, which may not function the
same as the tissue replaced. After traumatic or surgical injury,
healing is initiated as part of the immediate and acute
inflammatory responses.
A clot that usually provides homeostasis almost immediately after
injury also forms a matrix rich in platelet-derived cytokines
that stimulates and facilitates healing.

47.  In contrast, periodontal infections do not normally produce the
massive, platelet-rich clot observed in traumatic injury. Thus the
periodontal “healing” cycle during the pathogenesis of periodontal
disease is primarily post-inflammatory, and cellular elements other
than platelets provide important signals in this process.
 Periodontal repair occurs in overlapping phases of inflammation
shutdown, angiogenesis, and fibrogenesis.
 In the post-inflammatory healing process, the shutdown of
inflammatory processes and initiation of post-inflammatory healing
is orchestrated by leukocytes. Some of the important anti-
inflammatory signals generated by leukocytes include IL-1 receptor
antagonist(IL-1ra) and transforming growth factor beta (TGF-β).
 Other cytokines that depress an inflammatory response include IL-4,
IL-10, and IL-11.112 In inflamed periodontal tissues, macrophages
are a source of IL-1ra,whereas neutrophils, macrophages, and mast
cells and lymphocytes produce TGF-β.

48.  Angiogenesis and fibrogenesis, as well as cytokines such as IL-
1β and TNF-β that help to induce these processes, participate in
both inflammation and healing. IL-1β and IL-1α are indirectly
involved in inducing fibro-blast proliferation and collagen
synthesis by stimulating the production of PGE2 or the release
of “secondary” cytokines such as platelet-derived growth
factor (PDGF) and TGF-β.
 TGF-β is a multifunctional peptide that stimulates osteoblasts
and fibroblasts and inhibits osteoclasts, epithelial cells, and
most immune cells.
 Receptors for TGF-β are found in almost all cells. TGF-β is
produced as a pro-peptide, and activation requires acidic
conditions.
 TGF-β is known for its ability to promote the elaboration of
fibroblast extracellular matrix adhesion.

49. MICROBIOLOGY & IMMUNOLOGY IN HEALTH
The gingival crevice harbors bacteria in both health and
disease. In a clinically healthy periodontium, the microbial
flora is largely composed of gram-positive facultative
microorganisms, predominately species such as
Actinomyces and Streptococcus spp.
Gram-negative species and spirochete forms also may be
found, but they are considerably less prevalent and occur
in much smaller numbers.
Serum antibodies to microorganisms are usually in low
titers, suggesting the minimal systemic antigenic
stimulation by plaque during gingival health. The gingival
tissues typically demonstrate some evidence of
inflammation.

50.  Tissues are usually infiltrated with chronic inflammatory cells,
generally lymphocytes. Neutrophils also are common within
the junctional epithelium and in the gingival crevice. The
infiltration of inflammatory cells is thought to be a response to
bacterial plaque, and host defense mechanisms in a healthy
individual are effective in managing the bacterial challenge.

51. MICROBIOLOGY AND IMMUNOLOGY IN
PERIODONTAL DISEASES
Gingivitis
 The most common form of gingivitis is plaque-induced gingivitis. Common clinical
findings in gingivitis include erythema, edema, tissue enlargement, and bleeding.
 Page and Schroeder reviewed the histopathology of human and animal
experimental gingivitis in a classic article that delineated three temporal
stages of gingivitis: the initial, early, and established lesions .
 Central to the histopathologic changes are the vascular inflamation and
infiltration of neutrophils and then lymphocytes in the early stages. The
early lymphocytic infiltrate is dominated by T cells, but eventually B cells
become dominant.
 The established lesion is characterized by a predominance of B cells that
have transformed into plasma cells in the connective tissues. Neutrophils
continue to dominate the junctional epithelium and gingival crevice with a
marked increase in GCF flow.
 It is noteworthy that collagen loss in the involved tissues is evident in the
earliest stages of gingivitis.
 Page and Schroeder report a predominance of plasma cells in the
established lesion.

52. Chronic Periodontitis
 Chronic periodontitis is characterized primarily as involving
alternative pathway activation of complement, with C3 and
C3B cleavage in gingival fluids observed.
 This suggests that even though pathogen-specific antibodies are
formed in chronic periodontitis, activation of the classical
complement pathway by processes involving antibody-antigen
binding does not predominate.
 It also is possible that specific cleavage products in GCF result
from the action of bacterial enzymes. P. gingivalis, for
example, produces an enzyme that can cleave C5 to its active
metabolite, C5a.

53.  Collagenase activity is associated with active periodontal
destruction.100 MMP-8 is elevated inchronic
periodontitis, whereas the levels of TIMP (TIMP-1) are
not.
 The ability of the chymotrypsin-like enzyme of T.
denticola to activate MMPs may contribute to MMP-
mediated tissue destruction at periodontitis sites with high
levels of this microorganism.
 In addition, studies of GCF in chronic periodontitis reveal
that collagenase activity is as much as six-fold greater
than that of gingivitis. Most of the collagenase activity
associated with chronic periodontitis is caused by the
neutrophil collagenase MMP-8.

55.  Toll gene products were first
discovered in 1985 and were
described as being critical for the
embryonic development of
dorsal–ventral polarity in the fruit
fly, drosophILa.
 They contain common
extracellular leucine-rich domain
and a conserved intracellular
domain.

56.  They are critical for
recognition of microbes
by the innate immune
system and for bridging
the innate and acquired
immune system.
 Toll-like receptors are
predominantly expressed on
cells of the innate immune
system, including neutrophils,
dendritic cells and
monocytes/macrophages.
 These cells express different
toll-like receptors, allowing
them to induce a wide variety
of immune responses to
specific pathogens.

58. TLR
 The gate keepers of
innate immunity
 These are a class of
prrs that recognises
MAMPS and that
signals cytokine
secretion in innate
cells.

60. Pathogen
invasion
Activation of
MyD88 and
IRAK 4
Recognition by
TLR-4
Activation of
Kinase
Release of
NFκβ

61. Production of
cytokines and
CD80
Pathogen
invasion
Phagocytosis
MHC-II
moleculeMHC- II
complex

62. Activation of
CD20 and TCR
Activation of
T-cells

63. Molecular Biology of the Host-Microbe
Interaction in Periodontal Diseases
INNATE IMMUNITY IN PERIODONTAL DISEASES
Nucleotide-oligomerization domain (NOD) protein-like receptors
represent cytoplasmic PRRs and are characterized by C-terminal
leucine-rich repeats (LRR domain, similar to the TLRs), an N-terminal
caspase-activating recruitment domain (CARD), and a nucleotide-
binding domain (NBD). These were initially described as cytosolic
TLRs, analogous to the R proteins
NOD proteins are capable of recognizing different peptidoglycan
molecules: Nod1 recognizes peptidoglycan containing meso-
diaminopimelic acid (meso-DAP) fragments present in most gram-
negative and some gram-positive bacteria, whereas Nod2 recognizes
muramyl dipeptide (MDP), which is found in peptidoglycan from both
gram-negative and gram-positive bacteria.

64. All of these different PRRs represent the necessary armamentaria for recognition of
MAMPs by the host and are expressed by a variety of cells that play a role in innate
immunity. Importantly, understanding of the roles of PRRs in inflammation and
immune responses has been expanded, so it is now appreciated that these receptors
not only recognize various MAMPs to activate innate immune response, but they can
also bind to endogenous molecules derived from damaged tissue and have a role in
inflammation and adaptive immune responses.
The cells involved in innate immunity include macrophages and
polymorphonuclear cells as professional phagocytes with the primary function of
engulfing and destroying microbes; dendritic cells as professional antigen-presenting
cells and activators of adaptive immunity; and natural killer (NK) cells, the innate
cytotoxic lymphocytes that recognize and kill host cells that are altered (e.g., tumor
cells) or infected with viruses.

66. However, other cell types can also play important roles in innate immunity,
since they are able to recognize MAMPs through their PRRs and respond by
expressing biologically-active molecules, such as cytokines and matrix
metalloproteases (MMPs),that will have an effect on homeostasis of the host
tissues in the periodontal microenvironment. Resident, “non-professional” cells
such as fibroblasts and osteoblasts are also capable of producing a variety of
cytokines, such as interleukin-6 (IL-6), prostaglandin E2 (PGE2), MMPs, and
receptor activator of NF-κB ligand (RANKL).
Because of the sheer proportion of fibroblasts in the periodontal tissues and also
to the proximity and relevance of both fibroblasts and osteoblasts to non-
mineralized and mineralized tissue turnover, respectively, these cells an play
important roles in innate immunity during periodontal
diseases.

67. Cell Signalling Pathways and the Expression of
Biologically-Active Mediators in the Innate
Immune Response

68. The molecular biology of adaptive
immunity
 Its a antigen-specific immune response.
 Is more complex than the innate.
 The antigen first must be processed and recognized.
Once an antigen has been recognized, the adaptive
immune system creates an army of immune cells
specifically designed to attack that antigen.

69. T-CELL SUB-POPULATION
1) CD4 T helper lymphocytes (TH)
- TH lymphocytes recognize antigen on the surface of antigen
presenting cells in association with class II MHC molecules
- They are activated and secrete several cytokines
- There are two main subsets of the cells (TH1 and TH2)
- the two subsets are differentiated on basis of the cytokine they produce
TH1 produce mainly :
- cytokines of CMI and inflammation
e.g. IFN-γ, TNF- β, IL-3 and IL-2
TH2 produce mainly:
- Cytokines that stimulate b-cells
- suppressor cytokines
e.g. IL-4, IL-5, IL-6 and IL-10

70. CD8 Cytotoxic T-lymphocytes
They constitute 35% 0o peripheral t-cells
* CTLS recognize antigen on surface of target cells
(infected APC or other infected nucleotid cell) in
association with MHC-i
* they are activated and kill the virus infected cell or
tumor cell

71. T-Cell Differentiation

72. Conclusion
 The host-bacterial interaction theory may explain why
otherwise healthy individuals with moderate levels of
plaque do not exhibit loss of periodontal support. In these
individuals, PMNS are effective in blocking invading
pathogens without destroying the collagen content of the
periodontium in the process.

73.  If these same pathogens attempted to invade the
periodontium of people predisposed to periodontal disease,
it appears that impaired chemotaxis and phagocytosis of
defense cells may put these individuals at significantly
greater risk for progressive periodontal destruction.