Microbial interactions with the host in periodontal disease

1. Microbial Interactions with the
Host in Periodontal Diseases
HEENA SHARMA

2. INTRODUCTION
 The interaction of microorganism with the host
determines the course and extent of resulting disease.
 Microorganism may exert pathogenic effects directly by
causing tissue destruction or indirectly by stimulating the
modulating host responses.
 The host response is mediated by microbial interaction
and inherent characteristics of the host, including genetic
factors.

3. MICROBIOLOGIC ASPECTS OF THE MICROBIAL-
HOST INTERACTION
 Predominant microorganisms associated with disease
appear to be gram-ve facultative or anaerobic bacteria.
e.g. P. gingivalis, A.a, T. Forsythia, F nucleatum, P
intermedia, C rectus, E corrodens.
 The properties of microorganism that enable it to cause
disease are reffered as virulence factors.

4.  Thus, virulence properties can be broadly classified into 2
groups:
I. Factors that enable bacterial species to colonize and
invade host tissues.
II. Factors that enable a bacterial species to cause host
tissue damage directly or indirectly.

5. Bacterial colonization and survival in the
periodontal region

6. BACTERIAL ADHERENCE IN THE PERIODONTAL
ENVIRONMENT
 Surfaces available for attachment include:
 Tooth or root
 Tissues
 Pre-existing plaque
 Bacteria that initially colonize the periodontal
environment , most likely to attach to the pellicle or saliva
coated tooth surface.
e.g. P. gingivalis, actinomyces viscosus with its surface
fimbrae attach to the proline rich receptor present on the
saliva coated tooth surface.

7.  P. ginivalis through its surface fimbrae attach to the
galactosyl residues on the epithelial cells and fibroblasts.
 Bacterial attachment with the pre-existing plaque is
studied by examining the adherence between different
bacterial strains.
e.g. 1. A. viscosus with its surface fimbrae attach to the
polysaccharide receptors on the cells of streptococcus
sanguis.
2. F. nucleatum interact with its heat and protease
sensitive protein with the galactosyl residues on the p.
Gingivalis.

8. HOST TISSUE INVASION
 Bacteria may enter host tissues through :
I. Ulcerations in the epithelium of gingival sulcus or
pocket.
II. Through the intercellular spaces in the gingival tissues.
III. Direct penetration of bacteria into the host epithelial or
connective tissue cells.
 A. actinomycetumcomitans, P. gingivalis, F. nucleatum,
T. denticola invade host tissue cells directly.

9.  Bacterial species that have identified as capable of tissue
invasion are strongly associated with disease.
 The ability to invade has been proposed as a key factor
that distinguishes pathogenic from non-pathogenic gram
–ve species or strains.
 Localization of bacteria to the tissues provides an ideal
position from where the organism can effectively deliver
toxic molecules and enzymes to the host tissue cells.

10.  Sageli FR et al in1988, stated that the ‘bursts of disease
activity’ observed in periodontitis may be releated to
phases of bacterial invasion of the tissues.
 An additional possibility is that bacteria in the tissues may
enable persistence of that species in the periodontal
pocket by providing a reservoir for colonization.

11. BACTERIAL EVASION OF HOST DEFENCE
MECHANISMS
 To survive in the periodontal environment, bacteria must
neutralize or evade the host mechanisms involved in
bacterial clearence and killing.
 Periodontal bacteria neutralize or evade the host defense
through numerous other mechanisms
e.g.1. P. gingivalis, P. intermedia, P. melanogenica produce
immunoglobulin degrading protease may counteract the
host defense, as immunoglobulins might function to
facilitate phagocytosis of bacteria by opsonization or by
may block adherence by binding to the bacterial cell
surface.

12. 2. Bacteria may produce substance that supress the activity
of or kill polymorphonuclear leukocytes and
lymphocytes.
Host Defence
Mechanism
Bacterial Species Bacterial property Biologic Effect
PMN A.
actinomycetumcom
itans
leukotoxin Inhibition of PMN
function
F. nucleatum Heat-sensitive
protein
Apoptosis of PMN
Lymphocytes A.
actinomycetumcom
itans
leukotoxin Killing of mature B
and T cells
Cytolethal
distending toxin
Impairment of
function by
arresting
lymphocyte cell
cycle

13. Host Defence
Mechanism
Bacterial
Species
Bacterial
property
Biologic Effect
macrophages F. nucleatum Heat sensitive
protein
Apoptosis of
mononuclear cells
lymphocytes T. denticola cytotoxin Apoptosis of
lymphocytes

14. 3. P. gingivalis is able to inhibit the production of IL-8 by
epithelial cells, which may provide the micro-organisms
with an advantage in evading PMN- mediating killing.

15. MICROBIAL MECHANISMS OF HOST TISSUE
DAMAGE
 The properties of bacteria releated to tissue destruction
can be broadly classified as:
I. Those resulting directly in degradation of host tissues.
II. Those causing the release of biologic mediators from the
host tissue cells that leads to tissue destruction.

16.  Some bacterial products that inhibit the growth or alter
the metabolism of host tissue cells includes:
 Sulfur compounds
 Indole
 Fatty acids
 Ammonia
 peptides

17.  some enzymes produced by periodontal pathogen that
are capable of degrading the all host tissue cells and
intercellular matrix molecules includes:
Enzymes Bacterial species
collagenase P. ginigvalis
A. actinomycetumcomitans
Trypsin like enzyme P. gingivalis
A. actinomycetumcomitans
T. denticola
Fibronectin-degrading enzyme P. gingivalis
P. intermedia

18. Enzymes Bacterial species
Arylphosphatase neuroaminodase P. gingivalis
P. melanogenica
T. forsythus
C. rectus
Phospholipase A P. intermedia
P. melanogenica

19.  one another mechanism by which bacteria may
indirectly cause tissue damage is by induction of host
tissue proteinases such as elastase and matrix
metalloproteinases.
 Host immune system involves a complex interaction
network among cells and regulatory molecules.
 Well characterized interaction involves the release of IL-
1, TNF, prostaglandins from monocytes, macrophages,
PMNs exposed to bacterial endotoxins.
 Host-dervied mediators have potential to stimulate bone
resorption and activate/ inhibit other immune cells.

20. Immunological aspects of microbial
interaction
with the Host

21. PARADIGM FOR THE ROLE OF IMMUNE SYSTEM
IN PERIODONTAL PATHOGENESIS
 Innate factors such as complement , resident leukocytes
play a very important role in signaling the endothelium
thus initiating inflammation.
 Acute inflammatory cells, neutrophils protect local
tissues by controllig periodontal microbiota in gingival
cervice and junctional epithelium.

22.  Chronic inflammatory cells (macrophages, lymphocytes)
protect the entire host from within subjacent connective
tissue and do all that which is necessary to prevent local
infection from becoming systemic and life threatening
such as sacrifice of local tissues.

23. INNATE FACTORS
 Onset of inflammation involves the development of
edema, errythma.
 Complement activation in response to bacterial infection
leads to generation of complement derived anaphylatoxins
C3a, C5b, causing degradation of resident leukocytes and
mast cells.
 Degranulated mast cells increases with in gingival
connective tissue as gingival inflammation increases.

24.  Mast cells transcribes TNF-α, TGF-β, IL-4, IL-6.
 Stimulation of endothelial cells by C3a, IL-1β, TNF-α ,
bacterial LPS results in expression of selectin on the
lumen surface of endothelial cells and release of
chemokines from endothelial cells.
 These processes are central in tranendothelial migration
of leukocytes.

25. CONTROLLING THE BACTERIAL CHALLENGE:
PRIMARY ROLE OF NEUTROPHILS
 They are the first to arrive at the site of inflammation and
are always dominant cell type within the junctional
epithelium and gingival cervice.
 To effectively control the bacterial infections,
neutrophils functions such as transendothelial migration,
chemotaxis, transepithelial migration , opsonization,
phagocytosis , intraphagolysosomal killing need to be
intact.

26.  Transepithelial migration of neutrophils requires
chemotaxin gradient.
 Junctional epithelium express chemotactic cytokine IL-8,
intercellular cell adhesion molecule-1 (ICAM-1).
 Neutrophils moves along the gradient towards the outer
surface of tissues.

27.  Neutrophils may use their adhesions ( LFA-1, MAC-1) to
bind ICAM-1 on the epithelial cell in process of epithelial
transmigration.
 P. Gingivalis impedes transepithelial migration of
neutrophils by preventing epithelial cells from secreting
IL-8 in response to bacterial challange.

28.  Opsonization refers to the coating of a particle, such as
bacterial cell by host proteins that facilitate the
phagocytosis.
e.g. Bacteril cell coated with molecule derived complement
compounds (iC3b) , for which neutrophils have
receptors.
 Specific antibody of IgG facilitates phagocytosis directly
b binding with the neutrophil Fc receptor.

29.  Patients with periodontitis have high level of serum titers
of IgG to specific periodontal pathogens.
 These antibodies also neutralize bacterial component
important in colonization.

30.  Once the bacteria bound to the neutrophils, phagocytosis
results.
 There is enterapment of bacterial cell into membrane
delimited structure known as phagosome.
 Bacteria within phagosome and phagolysosome killed by
oxidative or non-oxidative mechanisms.

31.  Some periodontal pathogen evade phagocytic cells as
virulence mechanism.
e.g. Leukotoxin of A. actinomycetumcomitans kills
phagocytes by binding with LFA-1 adhesins and
subsequently lysing the eukaryotic cells.

32. CONNECTIVE TISSUE ALTERATIONS: TISSUE
DESTRUCTION IN PERIODONTITIS
 Mediators produced as a part of host response that
contribute to tissue destruction includes:
 Prostagladins
 Proteinases
 Cytokines

33. PROTEINASES
 MMPs are the primary proteinases involved in
periodontal tissue destruction by degradation of
extracellular matrix molecules.
 MMPs are the family of proteolytic enzymes found in
neutrophils, fibroblasts, macrophages, osteoblasts and
osteoclasts that degrade extracellular matrix molecules
such as:
 Collagen
 Gelatin
 Elastin

34.  MMP-8, MMP-1 are both collagenases.
 MMP-8 is released by neutrophils and MMP-1 is released
by residual cells ( fibroblasts, monocytes, epithelial cells).
 MMPs are secreted in inactive form.
 Enzyme activity in the tissues is partly controlled by:
 Activation of latent enzyme.
 Level of enzymatic inhibitors present.

35.  1 mechanism of MMP activation involves proteolytic
cleavage of a portion of latent enzyme.
 Proteases capable of activation of MMPs includes:
• Bacterial enzymes such as chymotrypsin like protease
produced by T. denticola, host cell enzyme ( neutrophil
cathepsin G).
 MMPs are inactivated by macroglobulins that are found
in the serum and GCF.

36.  Other proteinases associatd with periodontitis include
elastase and cathepsin G.
 Elastse is capable of degrading wide range of molecules
including elastin, collagen, fibronectin.
 Cathepsin G is a bactericidal proteinase that involved in
the activation of MMP-8.

37. CYTOKINES
 3 proinflammatory cytokines, IL-1,IL-6 and tumor
necrosis factor (TNF) appear to have a central role in
periodontal tissue destruction.
 IL-1 is found in 2 active forms, IL-1α, IL-1β encoded by
separate genes. They are the major constituents of
osteocleast-activating factor.
 IL-1 family also contain IL-1 receptor antagonist (IL-1ra)
that binds to IL-1 receptor without stimulation of host
cells.
 IL-1 is produced by macrophages and lymphocytes but
also may produced by other cells like:

38.  Mast cells
 Keratinocytes
 Fibroblasts
 Endothelial cells
 Potent activator of IL-1 production is bacterial LPS, IL-1
can also itself activate its production.
 IL-6 leads to bone remodelling.
 TNF can also found in 2 active forms TNF-α and TNF-β.

39.  TNF-α is produced by activated macrophages in response
to bacterial LPS.
 TNF-β is produced by TH1 subset of CD4+T cells, that
have been activated by antigen/mitogen.
 Proinflammatory effects of IL-1 and TNF-α :
 Stimulation of endothelial cells to express selectin that
facilitate the requirement of leukocyte.
 Activation of macrophage IL-1 production.
 Induction of PGE2 by macrphage and gingival fibroblast.

40.  Properties of cytokine releated to tissue destruction
involves:
 Stimulation of bone resorption.
 Induction of tissue degrading proteinases.
 IL-1 is a potent stimulant of osteoclasts proliferation,
differentiation, activation.
 TNF-α also has same effect, but less potent than IL-1.
 Both IL-1 and TNF-α induce the production of
proteinases in mesenchymal cells including MMPs, that
contribute connective tissue destruction.

41. PROSTAGLANDINS
 Are the arachidonic acid metabolites, generated by
cycloxygenases.
 COX-2 is upregulated by IL-1β, TNF-α and bacterial LPS
and appaear to be responsible for generating PGE2 which
is associated with inflammation.
 Primary cells responsible for PGE2 production are:
 Macrophages
 fibroblasts

42.  PGE2 is increased in periodontal sites demonstrating
inflammation and attachment loss.
 PGE2 induce MMP and osteoclastic bone resorption.
 PGE2 levels are elevated in gingivitis and periodontitis.
 Assays in GCF may considered as diagnostic marker for
future bone loss.

43. 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 the replacement of one tissue with
another tissue such as fibrous connective tissue, which
may not function the same as the tissue replaced.

44.  Periodontal repair occurs in overlapping phases of
inflammation shutdown, angiogenesis and fibrogenesis.
 In postinflammatory healing process, the shutdown of
inflammatory processes and initiation of
postinflammatory healing is orchestrated by leukocytes.
 Some of the important antinflammatory signals generated
by leukocytes including IL-1ra, TGF-β.
 Other cytokines that depress an inflammatory response
includes IL-4, IL-10, IL-11.

45.  Angioenesis and fibrogenesis as well as cytokine as (IL-
1β, IL1-α, TNF-α) that help to induce these processes,
participate in both inflammation and healing.
 IL-1β, IL1-α are indirectly involved in inducing fibroblast
proliferation and collagen synthesis by stimulating the
production of PGE2 or release of PDGF and TGF-β.

46.  PDGF activates fibroblasts and osteoblasts resulting in the
induction of protein synthesis.
 TGF-β is a multifunctional peptide that stimulates
osteoblasts, fibroblasts and inhibits osteoclats, epithelial
cells and most immune cells.