HOST MICROBIAL INTERACTIONS CONTENTS  MICROBIAL ASPECTS OF HOST MICROBIAL INTERACTIONS 1. Bacterial Colonization and Survival in the Periodontal Region 2. Microbial Mechanisms of Host Tissue Damage  MOLECULAR ASPECTS OF HOST MICROBIAL INTERACTIONS 1. Microbe-Associated Molecular Patterns (MAMPs) 2. Pattern Recognition Receptors (PRRs)  Toll-Like Receptors (TLRs)  NOD-Like Receptors (NLRs) 3. Complement System Antimicrobial peptides MICROBIAL ASPECTS OF HOST MICROBIAL INTERACTIONS Gingivitis and periodontitis are chronic infectious diseases. The interaction of the microorganism with the host determines the course and extent of the resulting disease. Microorganisms may exert pathogenic effects directly by causing tissue destruction or indirectly by stimulating and modulating host responses. The host response is mediated by the microbial interaction and inherent characteristics of the host, including genetic factors that vary among individuals. In general, the host response functions in a protective capacity by preventing the local infection from progressing to a systemic, life-threatening infection. However, local alteration and destruction of host tissues as a result of the microbial-host interactions may manifest as periodontal disease. The varying balance between locally harmful and beneficial effects of the pathogenic microorganisms and the host accounts for the wide variety of patterns of tissue changes observed among patients. In periodontitis, the initial step in the disease process is the colonization of the periodontal tissues by pathogenic species. Entry of the bacterium itself (invasion) or of bacterial products into the periodontal tissues may be important in the disease process. Furthermore, inherent in successful colonization of host tissues is the ability of the bacterium to evade host defense mechanisms aimed at eliminating the bacterium from the periodontal environment. BACTERIAL COLONIZATION AND SURVIVAL IN THE PERIODONTAL REGION Bacterial Adherence in the Periodontal Environment The gingival sulcus and periodontal pocket are bathed in gingival crevicular fluid, which flows outward from the base of the pocket. Bacterial species that colonize this region must attach to available surfaces to avoid displacement by the fluid flow. Therefore, adherence represents a virulence factor for periodontal pathogens. Bacteria may enter host tissues through ulcerations in the epithelium of the gingival sulcus or pocket and/ or direct penetration of bacteria into host epithelial or connective tissue cells. Laboratory investigations have demonstrated the ability of A. actinomycetemcomitans, P. gingivalis, F. nucleatum, and Treponema denticola to invade host tissue cells directly. COMPLEMENT SYSTEM The periodontal host immune response is dependent on a functional complement system, which notably coordinates the recruitment and activation of immune cells, bacterial opsonization, phagocytosis, and lysis.

1. HOST MICROBIAL
INTERACTIONS
DR. SUBHRADIP KAYAL (PGT-MDS)
DEPT. OF PERIODONTICS
GURU NANAK INSTITUTE OF DENTAL SCIENCES & RESEARCH

2. CONTENTS
 MICROBIAL ASPECTS OF HOST MICROBIAL INTERACTIONS
1. Bacterial Colonization and Survival in the Periodontal Region
2. Microbial Mechanisms of Host Tissue Damage
 MOLECULAR ASPECTS OF HOST MICROBIAL INTERACTIONS
1. Microbe-Associated Molecular Patterns (MAMPs)
2. Pattern Recognition Receptors (PRRs)
 Toll-Like Receptors (TLRs)
 NOD-Like Receptors (NLRs)
3. Complement System
4. Antimicrobial peptides

3. MICROBIAL ASPECTS OF HOST
MICROBIAL INTERACTIONS
Gingivitis and periodontitis are chronic infectious diseases.
The interaction of the microorganism with the host determines the course and extent of the resulting
disease.
Microorganisms may exert pathogenic effects directly by causing tissue destruction or indirectly by
stimulating and modulating host responses.
The host response is mediated by the microbial interaction and inherent characteristics of the host,
including genetic factors that vary among individuals.
In general, the host response functions in a protective capacity by preventing the local infection from
progressing to a systemic, life-threatening infection. However, local alteration and destruction of host
tissues as a result of the microbial-host interactions may manifest as periodontal disease.

4. The varying balance between locally harmful and beneficial effects of the pathogenic microorganisms
and the host accounts for the wide variety of patterns of tissue changes observed among patients.
In periodontitis, the initial step in the disease process is the colonization of the periodontal tissues by
pathogenic species.
Entry of the bacterium itself (invasion) or of bacterial products into the periodontal tissues may be
important in the disease process.
Furthermore, inherent in successful colonization of host tissues is the ability of the bacterium to evade
host defense mechanisms aimed at eliminating the bacterium from the periodontal environment.

5. BACTERIAL COLONIZATION AND
SURVIVAL IN THE PERIODONTAL
REGION
Bacterial Adherence in the Periodontal Environment
The gingival sulcus and periodontal pocket are bathed in gingival crevicular fluid, which flows outward
from the base of the pocket.
Bacterial species that colonize this region must attach to available surfaces to avoid displacement by
the fluid flow. Therefore, adherence represents a virulence factor for periodontal pathogens.

6. SURFACE EXAMPLE
TOOTH: pellicle, saliva coated A. viscosus via FIMBRIAE
TISSUES: epithelial cells. Fibroblasts, connective
tissue components
P. gingivalis via FIMBRIAE with epithelial cells &
fibroblasts
P. gingivalis via MEMBRANE PROTEINS
with connective tissue components
PRE-EXISTING PLAQUE MASS: mechanism
of co-aggregation
Co-aggregation between:
 A. viscosus & S. sanguis
 P. gingivalis & F. nucleatum

7. Host Tissue Invasion
Bacteria may enter host tissues through ulcerations in the epithelium of the gingival sulcus or pocket
and/ or direct penetration of bacteria into host epithelial or connective tissue cells.
Laboratory investigations have demonstrated the ability of A. actinomycetemcomitans, P. gingivalis, F.
nucleatum, and Treponema denticola to invade host tissue cells directly.
The clinical significance of bacterial invasion is:
Bacterial species that have been identified as capable of tissue invasion are strongly associated
with disease, and the ability to invade has been proposed as a key factor that distinguishes
pathogenic from nonpathogenic gram negative species or strains.
Certainly, localization of bacteria to the tissues provides an ideal position from which the organism
can effectively deliver toxic molecules and enzymes to the host tissue cells, and this may be the
significance of invasion as a virulence factor.
An additional possibility is that bacteria in the tissues may enable persistence of that species in the
periodontal pocket by providing a reservoir for recolonization.

8. Bacterial Evasion of Host Defense Mechanisms
To survive in the periodontal environment, bacteria must neutralize or evade the host mechanisms
involved in bacterial clearance and killing.
Bacterial adherence and invasion are representative strategies by which microorganisms accomplish
this task.
The ability to adhere allows bacteria to avoid displacement by host secretions, and its invasion
disrupts the natural barriers formed by host tissue cells.
Periodontal bacteria neutralize or evade host defenses through numerous other mechanisms

9. Host
defense
mechanism
Bacterial species Bacterial property Effect
Specific
antibody such as
Ig
P. gingivalis Proteases Degradation of antibody
PMNL A. actinomycetemco
mitans
Leukotoxin Inhibition of PMNLfunction
Lymphocytes A. actinomycetemco
mitans
 Leukotoxin
 Cytolethal distending toxin
 Killing of mature B & T cells
 Impairment of function
IL-8 P.gingivalis Serine phosphatase Inhibit IL-8 synthesis
thereby impairing PMN
response and
evade PMN mediated
killing

10. MICROBIAL MECHANISMS OF HOST
TISSUE DAMAGE
Research on virulence factors has focused on the properties of bacteria related to the destruction of
host tissues.
These bacterial properties can be broadly categorized as:
o those resulting directly in degradation of host tissues
o those causing the release of biologic mediators from host tissue cells that lead to host tissue
destruction.
Some bacterial products inhibit the growth or alter the metabolism of host tissue cells; these include a
number of metabolic byproducts such as ammonia, volatile sulfur compounds and fatty acids,
peptides, and indoles.
An important class of molecules in tissue destruction is the variety of enzymes produced by
periodontal microorganisms. These enzymes appear to be capable of degrading essentially all host
tissue and intercellular matrix molecules.

11. In particular, a wide range of proteolytic enzymes have been identified from P.gingivalis including a
trypsin like enzyme and those that degrade collagen, fibronectin, and immunoglobulins.
Bacterial enzymes may facilitate tissue destruction and invasion of bacteria into host tissues.
However, the exact role of bacterially derived proteases in the disease process has not been
determined because similar enzymes (e.g., collagenases) in the periodontal environment originate
from host tissue cells.
Indeed, one mechanism by which bacteria may indirectly cause tissue damage is by induction of host
tissue proteinases such as elastase and matrix metalloproteinases (MMPs).

12. MOLECULAR ASPECTS OF HOST
MICROBIAL INTERACTIONS
Considering the oral microbiome as a diverse microbial community and knowing that classically defined
periopathogenic bacteria are present in both health and disease implies that the vigilance and the tolerance
mechanisms are used by the host to mount an appropriate immune defense response.
Tolerance mechanisms modulate the host response to commensal (nonpathogenic) bacteria to establish a
balanced or homeostatic relationship, whereas vigilance mechanisms protect against periopathogenic bacteria–
associated opportunistic infections.
The host is capable of discerning among commensal and pathogenic bacteria, and appropriately modulating the
immune response, by the direct recognition of MAMPs at PRRs.

13. MICROBE-ASSOCIATED MOLECULAR
PATTERNS (MAMPS)
MAMPs, which are evolutionary-conserved molecular motifs present in microorganisms.
MAMPs include microbial cell wall macromolecules, nucleic acids, and flagellin, which function as
ligands having specificity for corresponding PRRs, expressed by host cells. lipopolysaccharide (LPS) is
unique to the outer membrane of gram-negative bacteria, lipoteichoic acid (LTA) and peptidoglycan are
distinct to the outer membrane of gram-positive bacteria. Importantly, lipoproteins are common
constituents of the outer membranes of both gram-negative and gram-positive bacteria.

14. The host immune system discriminates between self and the pathogenic bacteria by direct recognition
of MAMPs at PRRs.
MAMP recognition by the corresponding PRR induces host cell signaling, leading to the expression of
cytokines and enzymes that drives the immune response.
MAMP signaling immunomodulation plays a critical role in the homeostatic regulation of colonizing
commensal microbes in health, and it also contributes to pathophysiologic tissue destruction in
chronic inflammatory disease states such as periodontitis.

15. PATTERN RECOGNITION RECEPTORS
(PRRs)
The periodontal innate immune response functions as the first line of defense against the colonizing oral
microbiota. Recognition of MAMPs by innate immune cells stimulates the secretion of proinflammatory
cytokines (e.g., interleukin-1 beta [IL-1β], IL-6, and tumor necrosis factor [TNF]) and type I interferons
(IFN-α, IFN-β), critical for mounting an appropriate innate immune response to colonizing or invading
microorganisms.
Furthermore, MAMP signaling at innate immune cells up-regulates the production of co-stimulatory
molecules that are critical for the activation of adaptive immunity.
For this reason, PRRs are considered the bridge between the innate and adaptive immune systems.

16. In addition to innate immune cells (neutrophils, monocytes, macrophages, dendritic cells, natural
killer cells), investigators have realized that PRRs are also expressed by epithelial cells,
extracellular matrix cells (fibroblasts, cementoblasts, osteoblasts), and adaptive immune cells
(T lymphocytes, B lymphocytes).
The two major families of PRRs that have been most extensively studied in the periodontium are the
TLRs and the NLRs.
TLRs are transmembrane receptors, and NLRs are cytosolic receptors, which recognize a broad range of
MAMPs derived from the oral microbiota.
In addition to recognizing MAMPs, more recently it has been realized that PRRs also recognize
immunostimulatory by-products derived from damaged host tissues, known as damage-associated molecular
patterns (DAMPs).

17. TOLL-LIKE RECEPTORS (TLRS)
The TLR family currently consists of 10 known functional TLRs in humans, of
which TLR-10 is the only member having an unclear biologic role.
TLR-1 through TLR-9 has been reported to be expressed in the periodontium, in
both health and disease. 2 groups based on their location; Notably, TLR-4 is unique
in that it has the ability to localize to both the plasma membrane and the
endolysosomal membrane.
The TLRs are single-pass transmembrane proteins characterized by an N-terminal
leucine-rich recognition domain and an intracellular C-terminal Toll/IL-1 receptor
signaling domain (TIR).

19. NOD-LIKE RECEPTORS (NLRs)
Currently, 22 family members comprise the intracellularly expressed NLRs in humans.
NLRs are localized to the cytosol, and they play a critical role in sensing invading microorganisms
and prompting the immune response.
NLRs are characterized by C-terminal leucine-rich repeats that act as a sensing domain, a central
nucleotide-binding and oligomerization domain (i.e., a NOD), and an N-terminal effector domain that
mediates downstream signaling.

20. TLRs NLRs
10 members.
2 groups based on their location:
22 members
plasma membrane endolysosomal
membrane
Cytosol
TLR: 1,2,4,5,6,10 TLR: 3,4,7,8,9 22
Induces
expression of
proinflammatory
cytokines
Induces
expression of
interferons
Induces expression of proinflammatory
cytokines
Recognize
extracellular
microbial cell wall
components
or flagellin
recognize
microbial nucleic
acids
a broad range of MAMPs such
as peptidoglycans, exogenous
& endogenous MAMPs

21. In periodontal health, pattern-recognition receptor (PRR) signaling is effectively modulated to regulate the
oral commensal microbiota (tolerance) and protect against periopathogenic bacteria (vigilance), thus
supporting periodontal tissues homeostasis.
Conversely, failed tolerance and vigilance mechanisms in periodontal disease states lead to shifts in the oral
microbiota that drive PRR signaling–induced proinflammatory periodontal tissue destruction.

22. LPS is the major macromolecule composing the outer surface envelope of gram-negative bacteria, critical
to the bacterium for maintaining structural integrity, selective permeability, and proper folding and
insertion of outer membrane proteins.
LPS is typically made up of three domains (lipid A, a short core oligosaccharide, and an O-antigen), and it
induces a host immune response through recognition of lipid A.
Mammalian cells recognize LPS through a TLR-4 homodimer protein complex consisting of TLR-4, the
coreceptor myeloid differentiation factor 2 (MD2), and accessory proteins CD14 and lipopolysaccharide-
binding protein (LBP).
LBP processes and delivers LPS to CD14, which sensitizes cells for LPS binding by the MD2-TLR-4
receptor.
SIGNALING PATHWAYS

24. On MAMP ligand recognition at the N-terminal domain
and subsequent formation of a sustainable homodimer
or heterodimer, TIR (i.e. Toll/IL-1 receptor signaling
domain) domains of TLRs act as a scaffold to recruit
various TIR domain-containing adaptor proteins:
myeloid differentiation primary response protein 88
(MYD88) and MYD88-adaptor-like protein (MAL), or TIR
domain containing adaptor protein inducing IFN-β
(TRIF) and TRIF-related adaptor molecule (TRAM).
With the exception of TLR-3, all TLRs engage the
MyD88 adapter protein.

25. TLR-3 and endosomal TLR-4 uniquely interact with the TRIF adapter protein.
Engagement of the adapter proteins at the TIR domain of TLRs initiates signal transduction that
involves interactions between the adaptor molecules, IL-1 receptor–associated kinases (IRAKs)
and TNF receptor–associated factors (TRAFs).
In the case of TLR-2 and TLR-4 localized to the plasma membrane, MyD88-dependent
downstream activation of transforming growth factor-beta (TGF-β)–activated kinase 1(TAK-1)
simultaneously induces mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB)
signaling. NF-κB translocates to the nucleus, and MAPK cascades activate activator protein 1
(AP-1), ultimately resulting in the expression of proinflammatory cytokine genes.

27. When TLR-4 translocates to endosomes, TRIF-dependent signaling leads to the activation of NF-κB
and IFN-regulatory factor (IRF)-3, resulting in the expression of proinflammatory cytokine and type I
IFN genes.
Concerning TLR-9 localized to the endolysosomal membrane, MyD88-dependendent signaling leads
to the activation of IRF-7, which up-regulates the expression of type I IFN genes.

28. Nucleotide-Binding Oligomerization Domain–Like Receptors
NLRs are characterized by C-terminal leucine-rich repeats that act as a sensing domain, a central
nucleotide-binding and oligomerization domain (i.e., a NOD), and an N-terminal effector domain that
mediates downstream signaling.
NOD1/NOD2–Peptidoglycan Recognition
NOD1 recognizes gamma-d-glutamyl-mesodiaminopimelic acid (iE-DAP), a component of peptidoglycan
present in most gram-negative and some gram-positive bacteria, whereas NOD2 recognizes muramyl
dipeptide (MDP), which is found in peptidoglycan from all gram-negative and gram-positive bacteria.
Peptidoglycan binding at NOD1 and NOD2 receptors causes their oligomerization, which results in
recruitment of a serine/threonine kinase adapter protein, RIP-2/RICK, to a caspase activation and
recruitment domain (CARD) at the N-terminus.
RIP-2/RICK recruitment at the N-terminus activates NF-κB and MAPK-dependent upregulation of
proinflammatory cytokine genes.
NOD-LIKE RECEPTORS (NLRs)

30. NLRP3–Inflammasome Complex
Inflammasomes are multiprotein complexes that recognize diverse inflammation inducing stimuli, including
exogenous MAMPs and endogenous DAMPs, to control the production of proinflammatory cytokines and
regulate pyroptosis (an inflammatory form of cell death).
Several PRR families act as components in the inflammasome complex, including the cytosolic NLRs. The
NLR proteins represent the “core” of the multiprotein inflammasome complex and are reflected in the name
of the inflammasome.
NLRP3, the most extensively investigated inflammasome complex which plays a critical role in the terminal
processing and secretion of the proinflammatory cytokines IL-1β and IL-18.
Guo H, Callaway JB, Ting JP: Inlammasomes: mechanism of action, role in disease, and therapeutics, Nat Med. 2015; 21(7):677–687.
Strowig T, Henao-Mejia J, Elinav E, et al: Inlammasomes in health and disease, Nature. 2012; 481(7381):278–286.

31. Recognition of cytosolic MAMPs and DAMPs induces NLRP3 to act as a recruiting scaffold for the
inactive zymogen pro-caspase-1. Pro-caspase-1 (which has a CARD) is recruited to the
inflammasome complex through homotypic binding of CARD via a pyrin domain (PYD) and the adaptor
apoptosis-associated speck like protein containing a CARD (ASC).
Oligomerization of pro-caspase-1 proteins in the inflammasome leads to their autoproteolytic cleavage
into active caspase-1. Activated caspase-1 subsequently functions to cleave pro–IL-1β and pro–IL-18
into their biologically active forms.
Guo H, Callaway JB, Ting JP: Inlammasomes: mechanism of action, role in disease, and therapeutics, Nat Med. 2015; 21(7):677–687.
Strowig T, Henao-Mejia J, Elinav E, et al: Inlammasomes in health and disease, Nature. 2012; 481(7381):278–286.

32. The periodontal host immune response is dependent on a functional complement system, which notably
coordinates the recruitment and activation of immune cells, bacterial opsonization, phagocytosis, and
lysis.
Complement–Pattern-Recognition Receptor Signaling
In addition to PRR localization in plasma membranes (TLRs) and the cytoplasmic compartment (NLRs),
some soluble PRR families are also secreted into the plasma as humoral proteins. Soluble PRRs include
pentraxins, mannose-binding lectin (MBL), ficolins, and properdin, which represent the functional
ancestors of antibodies.
Soluble PRRs interact with circulating MAMPs and DAMPS to activate the complement system, ultimately
resulting in the opsonization, phagocytosis, and lysis of microbes.
Notably, complement interactions can amplify the host immune response through synergy with TLRs,
another example of crosstalk among diverse PRR signaling pathways.
COMPLEMENT SYSTEM

33. Classical/Lectin/Alternative Pathways
The activation of the complement cascade involves the sequential activation and proteolytic cleavage
of a series of serum proteins by three distinct mechanisms, namely, the classical, lectin, and alternative
pathways.
Classical pathway activation occurs in response to antigen–antibody complexes that are recognized by
the C1q subunit of C1.
C1q activates complement by functioning as a PRR to recognize distinct MAMPs and DAMPs, or
alternatively through other soluble PRRs such as pentraxins (i.e., C-reactive protein).
The lectin pathway is similarly triggered through soluble PRRs, including MBL and ficolins, which
predominantly recognize carbohydrate groups.
Both the classical and the lectin pathways then proceed through C4 and C2 cleavage for the
generation of the classical/lectin C3 convertase (C4bC2b).

34. Activation and therapeutic blockade of the complement system.

35. The alternative pathway is initiated by the hydrolysis of C3 to C3(H2O), which is a C3b analogue that forms
the initial alternative pathway for C3 convertase.
The alternative pathway also possesses a PRR-based initiation mechanism via properdin, which recognizes
MAMPs and DAMPs.
The alternative pathway also serves as a positive feedback loop for the classical and lectin pathways.
All three pathways converge at the third component of complement (C3), which on activation by pathway-
specific C3 convertases leads to the generation of key effector molecules.
These include the C3a and C5a anaphylatoxins, which activate specific G-protein– coupled receptors and
mediate the mobilization and activation of leukocytes.
Also important are the C3b opsonins, which promote phagocytosis through complement receptors, and the
C5b-9 membrane attack complex, which can lyse targeted pathogens.

36. Role of Complement in Periodontitis
In the context of periodontal inflammation, complement subversion appears to play a major role in
periodontal pathogenesis.
The dysregulation of complement activities may lead to a failure to protect the host against pathogens and
amplify inflammatory tissue damage.
Local complement activation may promote periodontal inflammation predominantly via C5a-induced
vasodilation, increased vascular permeability and flow of inflammatory exudate, and chemotactic
recruitment of inflammatory cells, especially neutrophils.

37. Antimicrobial peptides are components of the innate immune
response, thus providing defense against a wide spectrum of
gram-positive and gram-negative bacteria, viruses, and fungi.
In the oral cavity, at least 45 different antimicrobial peptides
belonging to different biochemical classes are found in the saliva
and the gingival crevicular fluid.
ANTIMICROBIAL PEPTIDES

38. STRUCTURE OF ANTIMICROBIAL PEPTIDES
AMPs are commonly classified by variation in structural characteristics, there are some structural
features that AMPs share, including a length of less than 60 amino acids, broad spectrum
antimicrobial activity at physiological conditions, and an overall positive charge.
Antimicrobial Peptides
Primary (1°)
Seconday (2°)
AMPs (2°) can be divided into five sub-categories on the basis of their amino acid composition and
structure

40. THE MECHANISM OF ACTION OF THE AMPS INVOLVES A SERIES OF STEPS DESCRIBED AS
FOLLOWS
1. Attraction – the electrostatic interaction between the cationic peptides and the anionic moieties on
bacterial membrane (Gram-negative bacteria: lipopolysaccharide [LPS] phosphate group and anionic lipids;
Gram-positive bacteria: teichoic acids) is presumed to cause attraction.
Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J Indian Soc Periodontol 2017;21:434-8.

41. 2. Attachment – after getting bound to the bacterial membrane surface the AMPs get transformed into a
secondary structure which causes them to orient either parallel or perpendicular to the membrane. The initial
low and later high peptide/lipid ratios allow the bacterial membrane to stretch causing it to thin down. This is
followed by subsequent pore formation with the peptides getting oriented in a perpendicular fashion to insert
into the bilayer
Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J Indian Soc Periodontol 2017;21:434-8.

42. 3. Models of insertion – the penetration of the AMPs across the bacterial membrane takes place by either
the carpet model, the barrel-stave model, or the toroidal pore model causing the ultimate bacterial cell death.
Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J Indian Soc Periodontol 2017;21:434-8.

43. Barrel-stave model
Carpet model
Toroidal pore model
Antimicrobial peptide

44. Antimicrobial Peptides has broad bactericidal effect. It causes cell death by two mechanism.
By forming transmembrane pores Through intracellular killing
Bacteria Bacteria

45. Defensins and Cathelicidin LL-37
• Defensins and cathelicidin LL-37, the most thoroughly studied antimicrobial peptides in humans.
• They are cationic peptides that bind to negatively charged molecules on the microbial cell
surface (e.g., LPS in gram-negative bacteria and lipoteichoic acid in gram-positive bacteria) that
ultimately depolarize the cell membrane and render it permeable, with resulting bacterial cell
death.
In human two major Antimicrobial peptides are
Defensins Cathelicidins
β-defensins
α-defensins
LL-37

46. Defensins can be classified into α-defensins and β-defensins, based on structural distinctions.
Alpha- and β-defensins are peptides with six disulphide-linked cysteines. Structurally, the difference between the
two defensins lies within the length of peptide segments between the six cysteines and pairing of the cysteines.
Structure of β-defensins
Structure of α-defensins

47. Six human α-defensins and four human β-defensins have been extensively characterized.
α-Defensins 1 to 4, known as human neutrophil peptides due to their expression in neutrophils,
are present in the oral cavity, whereas α-defensins 5 and 6 are localized to the mucosal Paneth
cells of the small intestine.
β-Defensins 1 to 4, which are produced by a variety of epithelial cells throughout the body, are
abundantly produced by epithelial tissues within the oral cavity and are found in the gingival
crevicular fluid and saliva.

48. Cathelicidin AMPs are heterogeneous and share similar characteristics with other AMPs, such as a basic
residue, overall amphipathic nature, and a net positive charge at neutral pH.
LL-37, the only member in human cathelicidin family, is transcribed by CAMP (cathelicidin antimicrobial
peptide) gene, which translates to an 18 kDa proprotein. This AMP is detected and expressed in higher
amounts within neutrophils that migrate through the junctional epithelium to the gingival sulcus.
Structure of Cathelicidin Family - LL-37

49. β-defensins 1 and 2 (hBD-1 and hBD-2) are
found in normal, uninflamed gingival tissues
as part of the innate host defense mechanism.
They are localized at the gingival margin
where there is the most exposure to oral
bacteria of the plaque on the tooth surface,
but not in the junctional epithelium.
Thus, the junctional epithelium is protected
by α-defensins and LL-37 released from
neutrophils, while the differentiated, stratified
epithelia are protected by β-defensins.
Various sites in the oral cavity where different AMPs
are predominantly expressed.
(Dale and Fredericks 2005)

50. ROLE OF ANTIMICROBIAL PEPTIDES IN PERIODONTITICS
• A protective role.
• β-defensins 1 and 2 are observed in the upper layers of the gingival and sulcular epithelium,
adjacent to the microbial biofilm and external environment, consistent with the innate immune
“barrier” function of the epithelium.
• The expression of defensins induced by whole periopathogenic bacteria such as Fusobacterium
nucleatum, P. gingivalis, A. actinomycetemcomitans, and T. denticola.

51. • Protection in the junctional epithelium may be provided by the higher concentration of α-defensins and
LL-37 produced by granulocytes migrating toward the gingival sulcus.
• GCF analysis for the content of LL-37 was carried out by Puklo et al. in 2008. They concluded that
LL-37 was chiefly produced by neutrophils in the healthy periodontium and helped maintain it in a
steady state.
Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J Indian Soc Periodontol. 2017;21:434-8.

52. • LL-37 possesses a broad spectrum of activity against both Gram-positive and Gram-negative bacteria
including periodontopathogens such as Porphyromonas gingivalis, Prevotella intermedia, and
Aggregatibacter actinomycetemcomitans alongside fungi and viruses.
• LL-37 has also emerged as having novel antibiofilm properties at low concentration as well helping fight
the biofilm bacteria such as Pseudomonas aeruginosa, Burkholderia pseudomallei, Streptococcus
mutans, and Staphylococcus epidermidis.
• AMPs are considered as biomarkers. They give an idea of healthy/disease state of an individual. So if
AMPs are increased, it indicates periodontitis and if AMPs are decreased, it indicates healthy state of an
individual.
Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J Indian Soc Periodontol. 2017;21:434-8.

53. REFERENCES
1. Newman and Caranza’s Clinical Periodontology 13th Edition by Newman, Takei, Klokkevold, Carranza
2. Clinical Periodontology and Implant Dentistry 6th Edition by Niklaus P. Lang and Jan Lindhe
3. Divya et. al. Host bacterial interactions in periodontal disease:Review article. International Journal of
Applied Dental Sciences. 2018; 4(3): 109-112
4. Sujeetha et.al. Host bacterial interactions in periodontal disease - an overview. International Journal of
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5. Mallapragada S, Wadhwa A, Agrawal P. Antimicrobial peptides: The miraculous biological molecules. J
Indian Soc Periodontol. 2017;21:434-8.
6. Mounika B et. al. Epithelial Antimicrobial Peptides in Defensive Mechanism of Gingiva. Indian J Dent
Adv. 2014; 6(4): 1686-1695.