Host Microbial Interactions in Periodontal diseases

1. HEENA SHARMA
Host Microbial Interactions in
Periodontal Diseases

2. Initiation of host response by junctional
epithelium
 The junctional epithelium is constantly exposed to
microbial flora which can initiate the inflammatory
response.
 Inflammatory response is primarily mediated by
neutrophils.
 Phagocytic macrophages then play an important role of
recognition of invading microorganism and to initiate
the adapative immune response.

3.  Host response against periodontal pathogens can be
divided into 2 parts:
 Innate Immune response
 Adaptive Immune response
 Innate immune response primarily consists of :
 Neutrophil’s response
Complement system
Toll-like receptors

4.  Adaptive immune response consists of:
Antigen presentation by antigen presenting cells(APC’s)
Generation of T-cell and B-cell response.

5. Innate Immune Response
 Gingival epithelium provides a physical barrier to infection
and has an active role in innate host defense as, these
epithelial cells are in constant contact with the bacterial
products.
 It is now well recognized that epithelium produces a diverse
range of antimicrobial peptides, that belongs to 4 families:
 α-defensins
 Β-defensins
 Cathelicidins
 saposins

6.  α and β defensins have an important role in host immune
response.
 Oral, sulcular, pocket and junction epithelium are associated
associated with the expression of β-defensins.
 The primary role of β- defensins is to signal other innate and
and aquired immune responses.
 While the α-defensins and LL37( proteolytic peptide) are
important for their antimicrobial properties in the gingival
sulcus.

7.  These peptides are capable of activating the classical
complement pathway and in upregulating the production
of IL-8 by epithelial cells.
 The antimicrobial factors of saliva such as histatins,
lysozymes and salivary immunoglobulins also have a
specific role in innate host defense.

8. 1. Neutrophil Response
 Neutrophils are the primary cells involved in the initial
immune response against invading microorganisms.
 It is well established that neutrophils are the most
abundant type of leukocytes within periodontal tissues in
acute and chronic periodontal lesions.
 The neutrophil recruitment is along the gradient which is
created by the pro-inflammatory cytokines, secreted in
response to bacterial products.

9.  The most potent and abundant chemoattractants for
neutrophils are CXC chemokines that participate in the
regulation of angiogenesis.
 IL-8 is the most potent human CXC chemokine,
secreted by leukocytes, fibroblasts, endothelial cells,
keratinocytes, in response to both endogenous and
exogenous stimuli.
 In response to IL-8 secreted by cells of junctional
epithelium, neutrophils migrate along the
chemoattractant gradient towards the surface of
junctional epithelium.

10.  The density of neurophils within the junctional
epithelium has been found to be increased towards
more superficial layers of the epithelium, which are in
close relationship with the subgingival plaque bacteria
as compared to the deeper layers.

11. Complement System
 It is a very important component of the innate immune
response.
 It causes the destruction of the microorganisms by the
formation of membrane attack complex.
 Components of complement system are pro-enzymes
that get cleaved and form active enzymes.
 Complement system get activated by 3 mechanisms:
I. Classical pathway
II. Alternative pathway
III. Lectin pathway

13. Classical pathway
 The binding of antibody to the antigen triggers the
complement system through classical pathway.
 Only IgM, IgG can activate the complement cascade.
 1 molecule of IgM activate the complement, but the
activation of IgG is with the help of cross linking of 2
molecules.

14. C1 activation
 C1 binds to Fc region of IgM/ IgG antibody that have
interacted with antigen.
 The binding of c1 to antibody occurs via c1q that leads
to the activation of c1r, which further activates c1s that
results in the formation of c1qrs complex.
 C1qrs complex cleaves c4 into c4a and c4b.

15. C4 and C2 activation
 C4b fragment binds with the membrane, where as C4a
is releaased into the microenvironment.
 Activated C1qrs complex also cleaves C2 into C2a and
C2b, out of which C2b releases into microenvironment
and C2a binds with membrane associated C4b and
form C4bC2a complex.
 C4bC2a complex acts as C3 convertase and cleaves
C3 into C3a and C3b.

16. C3 activation
 C3a releases into the microenvironment, C3b binds
with membrane in association with C4bC2a and forms
C4bC2aC3b complex.
 This complex acts as C5 convertase and generation of
C5 is the end of classical pathway.
 It results in formation of C5a and C5b that participates
in the formation of membrane attack complex (MAC)
which is responsible for lysis of bacteria by C5b,
C6,C7,C8,C9.

17. Alternate Pathway
 It get activated by immunogenic bacterial, viral, fungal
cell surfaces substances.
 There is no antibody present.
 The cell wall polysaccharides and endotoxins possess
binding with C3 and factor B.
 This complex is cleaved by factor D to produce C3bBb,
which act as C3 convertase and produces more C3b
that results in formation of C3bBb3b complex, which
further act as C5 convertase.

18. Lectin pathway
 It is similar to classical pathway, it is initiated by the
binding of mannose binding lectin (MBL) to the bacterial
surface with mannose containing polysacchride.
 This leads to the association of 2 serine proteases:
 MASP-1 (mannose binding lectin associated serine
protease1)
 MASP-2 (mannose binding lectin associated serine
protease2 )
 MASP-1 , MASP-2 are to Cr and Cs. Where as MBL is
similar to C1q.

19.  Formation of MBL/MASP-1/MASP-2 complex results in
activation of MASP.
 MASP cleaves C4 and C2 into C4a, C4b and C2a,
C2b respectively.
 C4a and C2b releases into the microenvironment and
C4b and C2a bind with membrane and form C4bC2a
complex.
 C4bC2a complex acts as C3 convertase and cleaves
C3 into C3a, C3b, C3a releases into microenvironment
and C3b bind with membrane associated C4b, C2a

20. Role of Toll-Like Receptors in Host-
microbial interaction
 When microorganisms enter the tissue after penetrating
the epithelial barrier, they are encountered by tissue
macrophages, mast cells, and immature dendritic cells.
 TLRs help these cells to distinguish between apoptotic
particles generated by normal tissue turnover and
particles indicative of infection.

21.  TLRs are transmembrane proteins expressed by cells of
the innate immune system, which are involved in
recognition of invading microorganisms and initiation of
immune and inflammatory response.
 TLRs help in regonition of pathogen-associated
molecular patterns (PAMPs) expressed by a wide
spectrum of infectious agents.
 The main effect of stimulation of TLRs is the synthesis
and secretion of pro-inflammatory cytokines and lipid
mediators, thereby initiating the inflammatory response.

22.  In mammals, the TLR family includes 11 proteins
(TLR1-TLR11), recently TLR12 and TLR 13 have also
been discovered in murine cells.

23. Structure of TLRs
 TLRs are characterized by an amino-terminal extracellular
domain composed of repeated motifs, high in leucine and
known as leucine-rich repeats(LPRs).
 Followed by a single transmembrane domain and a globular
cytoplasmic domain, called the Toll/IL-1 receptor (TIR)
domain or TIR domain.
 Despite this similarity, the extracellular portions of both types
of receptors are structurally unreleated. IL-1 receptor
possess immunoglobulin like domain, whereas TLRs bear

24. Signaling Pathways
 MyD88-dependent pathway (common to all TLRs)
 MyD88-independent pathway (peculiar to TLR3 and
TLR4)

25. MyD88-dependent pathway
 Upon stimulation , MyD88 recruits IL-1 receptor-associated
kinase (IRAK) to TLRs.
 IRAK is activated by phosphorylation, then associates with
TRAF6.
 TRAF6 interacts with TAK1,TAB1 and TAB2 that further forms
a larger complex with Ubc13 and Uev1A, that activates TAKI.
 Activated TAK1 phosphorylates the IKK complex, consisting
of IKKα, IKKβ, NEMO/IKKγ and MAP kinases and thereby
induces the activation of the transcription factors NF-Κb and

27. MyD88-independent pathway
 ILR3 signaling occurs mainly via MyD88-independent
pathway.
 In TLR3 and TLR4 mediated signaling pathways, a
MyD88-independent pathway exists that leads to the
activation of IRF-3 via TBK1 and IKKε / IKKi.
 The domain-containing adaptor TRIF mediates this
MyD88-independent pathway.

29. Result of TLR activation
 TLR activation results in the production of various pro-
inflammatory cytokines and chemokines.
 Interaction of TLR4 on dendritic cell and LPS results in
the production of pro-inflammatory cytokines such as IL-
12.
 Interaction of TLR3 with LPS results in the production of
type-1 interferon.
 TLR response may vary depending upon the intracellular

30.  e.g. After binding LPS with TLR4, if the intercellular
pathway is mediated by MyD88, that leads to the
formation of TNFα, IL-6, IL-12. on the other hand, if the
intercellular pathway is mediated by TRIF related
adapter molecule that leads to release of interferon-α/β
and activation of interferon regulatory factor 3.
 It has been shown that TLR 1,2,4,5,6 recognize
the products of bacterial origin and not those derived
host.
 Thus, it can be concluded that TLR’s play a crucial role
innate immune response.

31. Adaptive Immune Response
 The adaptive / acquired immune response is activated when
the epithelial barrier, with its antimicrobial peptides and other
components of innate systems, is breached.
 The pathogenic species present in the subgingival biofilm
evade the antibacterial host defense mechanisms by
releasing an array of virulence factors that causes damage
to the host tissue by immune/inflammatory interactions,
consisting of neutrophils, monocytes/macrophages, dendritic

32.  The T-cell adaptive immune response is activated by
processing and presentation of bacterial antigens by
lymphocytes ,macrophages and dendritic cells

33. Antigen presenting cells (APC’s)
 The APC’s have antigenic peptides with a major
histocompatibility complex (MHC) molecule located at their
surface.
 Cytotoxin T-lymphocytes expressing the CD-8 co- receptor
recognize the peptide associated with MHC Class-I
molecules ,whereas T-cells expressing the CD-4 co-receptor
do so with a eptide associated with MHC II molecules.
 Adhesion molecules such a ICAM-I present on APC’s are
involved in the formation of strong immunological synapses
to facilitate the proper activation of T-cells.

34. Interaction between APC’s and T-
cells
 There is a series of intercellular signalling cascade
that is activated when a receptor is activated, which
ultimately leads to synthesis and secreation of
biochemical mediators like cytokines.

35. T-cell receptors (TCR)
 One of the intial steps in the generation of the immune
response is the recognition by T- lymphocytes of
peptide fragments (antigens) derived from foreign
pathogens that are presented on the surface of APC’s.
 The event is mediated by TCR, which transduces these
extracellualr signals by initiating a wide array of
intercellular signaling pathways

36.  MHC molecules on APC’s trigger TCR and induce a
series of intracellular signaling cascades, initiating
positive (signal enhancing ) and negative (signal
attenuating ) cascade that ultimately result in cellular
proliferation, differentiation, cytokine production and/or
activation induced cell death.

37. Signaling cascade stimulated by
TCR

38.  TCR is composed of six different chains that form the
TCR heterodimer responsible for ligand recognition.
 TCR activation is the activation of Src family tyrosine
kinase (p561ck), that in turn, phosphorylate
phospholipase Cg1 (PLC g1).
 Activation of PLCg1 leads to hydrolysis of
phosphatidylinositol 4,5-bisphosphate (PIP2) generting,
diacylglycerol (DAG) and inositol triphosphate (IP3).

39.  Dag activates protien kinase( PKC) that in turn
phosphorylates Ras, a GTPase that activates Raf
leading to the recruitment of MAP kinase cascade.
 The calcium binds to the calmodium, that ,in turn
activates calcineurin, a Ca2+ calmodulin dependent
protien.
 Calcineurin dephosphrylates the cytosolic component
of NFAT, NFATc which migrates to the nucleus and
induces transcription of the IL- 2 gene

40.  To mount an immunological response, the T-cell
needs to receive a second signal from an antigen-
presenting cell in he form of a co-stimulatory
molecule.
 Co stimulatory molecules act through different TCR’s
such as the CD28 and TFNR families, producing a
second signal that induces T-cell activation and
proliferaion.

41. Steps in activation of T-cells
1. Antigen which is phagocytosed by a macrophage is
cleaved into polypeptides which are then transported to
the surface for presenting to T-cells
2. The APC complex consists of both antigen and MHC. If
MHC Class-II is associated with presenting cells, CD4 or
helper T-cells are activated.
3. Macrophage which is attached to the antigen, produces
IL-! Which activates CD4 cells.

42. 4. CD4 interacts with MHC Class-II on APC surface. This
union is stabilized by other protiens LFA On T-cells
and ICAM 1 on APC.
5. A co-stimulatory signal is formed by B7 protein on
APC and CD28 on CD4 cells which results in the
secretion of IL-2 by the helper T cells and thus it is
helpful in the execution of all the function i.e
 regulator
 effector and
 memory functions.

43. Th1 an Th2 helper T-cells
 Th1 and Th2 cells are produced by differentiation from
the non-antigen exposed precursor cell type, Thn
(native T-cells).
 When Thn cells are exposed to antigen by APC’s , it
results in the differentiation of THn cells into Th0 cells.
 IL-12 causes Th1 differntaiation and blocks Th2 cell
production while IL-4 causes Th2 differntiation and

45. Role of regulatory T cells in
periodontal diseases
 Naturally occurirng treg cells, CD4 and Cd25 T-cells,
originate directly from the thymus during the early
stages of fetal and neonatal T-cell development.
 These cells make up approx 5-10% of peripheral T cell
pool.
 Studies showed an increased percentage of Treg cells
in the gingival connective tissue in periodontitis patients
as compared with gingivitis

46.  Another study showed Treg cells downregulate RANKL
expression in periodontal disease.
 One study suggested that Treg cells may not have a
regulatory function due to the lack of CTLA-4 expession
that is required for cell-cell contact inhibiting T-cell
proliferation.

47. Role of Th17 cells in periodontal
disease
 A distinctive type of helper T-cell lineage, The Th17 has
been recently identified.
 This population secretes several pro-inflammatory
cytokines, including the novel cytokine IL-17 and hence,
has been term“Th17”.
 It expands in the presence of IL-23 and exerts both pro-
inflammatory and anti-inflammatory functions.

48. B cell activation in adaptive immune
response
 B cells express a unique B cell receptor(BCR) on their
surface that recognizes and binds to one and only one
particular antigen.
 After b cell recognizes the antigen and receives appropriate
signals from the helper Tcells, it further differentiates into an
effector cell, i.e the palsma cell.
 These cells are short lived but about 10% cells become long
lived and are reffered to as antigen specific memory B-cells.

49.  Then the antibodies thus produced, which binds with the
antigen that make them easier target for phagocytosis.

50. Humoral immune response in the
periodontal diseases
 It is suggested that the humoral immune response has a
protective role in the pathogenesis of periodontal diseases.
 B- lymphocytes contribute in multiple ways such as
production of antibodies, presentation of antigens,
organogenesis of secondary lymphoid organs and secretion
of cytokines.
 The local production of IgG is protective in nature and is
found to be increased in inflamed gingival and periodontal

51.  Antibodies prevent bacterial colonization by 2
mechanisms:
1. By directly binding with the bacterial surface antigen
and blocking its adherence, colonization and
aggregation of bacteria.
2. Opsonization of bacteria by constant release of
antibodies that makes the bacteria more suseptible for
phagocytosis and enables activation of complement
cascade.