Pathogenesis of Periodontal Disease & Host Response

periodontal disease pathogenesis

periodontal disease results from a complex interplay btwn subgingival biofilm (bacteria) and the host immune-inflammatory response... which ultimately causes tissue destruction

cardinal signs of inflammation

redness

heat

swelling

pain

loss of function

what initiates inflammation in periodontal disease

tissue injury or bacterial infection

what is arachidonic acid

polyunsaturated fatty acid in phospholipids of cell membranes & released during cell injury

abundant in brain, muscles, and liver

what does arachidonic acid produce

prostaglandins

leukotrienes

thromboxanes

prostacyclin

role of COX-2

converts arachidonic acid into prostaglandins → inflammation + vasodilation

what is clinical significicance

pathway drives inflammation, edema, and bone resorption

tissue injury or infection initiates activation of the ____ system and the ____ ____ pathway

kinin, arachidonic acid

what is the kinin system

blood protein system involved in (hormonal):

- inflammation

- pain

- blood pressure

- coagulation

key mediators of kinin system

bradykinin & kallidin

roles of bradykinin & kallidin

vasodilation

increase vascular permeability

promote pain

*vasodilation = slow down blood flow = when you want things to come out of vessels*

periodontal disease results from a complex interplay between _____ biofilm and the host ____-_____ response

subgingival, immune-inflammatory

*need control of inflam response to decrease colateral damage*

what is dysbiosis

imbalance in the microbial community → pathogenic bacteria dominate

how fast does biofilm form

within minutes after bruhsing (~30 seconds)

how many bacteria exist in oral biofilm

~500 species, but only a few cause disease

what determines disease severity

host response, not just bacteria

direct recognition of pathogenic bacteria is mediated by ____ ____ ___ ___ (MAMPs) or pattern recognition receptors on cell surfaces

microbial-associated molecular patterns

what is the red complex

group of highly pathogenic bacteria strongly associated with periodontitis

includes:

- P. gingivalis

- T. forsythia

- T. denticola

orange complex

bridge between gingivitis and more severe periodontitis

proliferate as plaque accumulates, leading to increased gum inflammation

Fusobacterium, Prevotella, and Campylobacter species

visual of pathogenesis of periodontal disease

microbial virulence factors

- lipopolysaccharide (LPS)

- bacterial enzymes

- microbial invasion

host derived inflammatory mediators

- cytokines

- prostaglandins

- matrix metalloproteinases (MMPs)

host responses = mainly protective

mainly responsible for tissue damage in peridontal disease

what is LPS

lipopolysaccharide (endotoxin) from gram - bacteria

effect of LPS

- strong immune activation

- cytokine release

- tissue destruction ( indirect via host response)

how do bacteria cause damage

direct: toxins, enzymes

indirect: triggering host immune responses

bacterial virulence factors ex.

- LPS

- heat shock proteins

- extracellular proteolytic enzymes

- fimbriae

- outer membrane proteins

- leukotoxin

- flagellum

- capsule

what are the first-line defenses in gingiva (innate and structural)

- activated rapidly (within mins)

- junctional epithelium + sulcular epithelium: intact barrier

- gingival crevicular fluid (GCF)

- neutrophils + macrophages in sulcus (phagocytose bacteria)

- antibodies (in GCF)

increase in plaque + host response = inflammation

role of gingival crevicular fluid (GCF)

- flushes bacteria

- delivers immune cells

- increases in inflammation

* outflow of GCF from sulcus has dilution effect and flushing action*

inflammatory cells involved in innate immunity "professional"

- neutrophils/PMN/polymorphonuclear → phagocytosis

- macrophages → phagocytosis + signaling

- dendritic cells → antigen presentation & activate adaptive immun.

- NK cells → kill infected cells; host cells that are altered (ex. tumor)

"non-professional" inflammatory cells involved in innate immunity

fibroblasts

osteoblasts

epithelial cells

what do fibroblasts and osteoblasts do in inflammation

produce:

- variety of cytokines (IL-6)

- MMPs

- prostaglandins (E2)

- RNAKL

*fibroblasts = constantly making & breaking down collagen*

epithelial cells

junctional or sulcular epithelium

initial point of contact with microbial-associated molecular pattern (MAMPs)

what characterizes healthy gingiva histologically

CT:

-densely packed collagen fiber bundles

-few inflammatory cells (neutrophils)

-balanced host-bacteria interaction

- gingival crevicular fluid in small amounts

what is unique about junctional epithelium

- non-keratinized

- "leaky" = allows immune cells to pass; neutrophils & macrophages from CT to sulcus

get ingress of bacterial products and antigens

- weak attachment via hemidesmosomes

where does gingival crevicular fluid originate

from postcapillary venules

GCF

- flushing action in gingival crevice

- brings blood components of the host defense into sulcus

- fluid flow increases in inflammation (edema/swelling)

- neutrophils are important component

saliva

-prevents attachment of bacteria to teeth and oral mucosa

- inhibit virulence factors, bacterial cell growth

- provide IgA antibodeis to peridontal pathogens

what happens to GCF during inflammation

increases → contributes to edema

what recognizes bacteria

pattern recognition receptors (PRRs)

especially toll like receptors (TLRs)

detect MAMPs (microbial associated molecular patterns)

patterns recognition receptors

on macrophages & dendritic cells

recognize MAMPs including:

-LPS

-bacterial lipoproteins/ lipoteichoic acids

- flagellin

- CpG DNA of bacteria and viruses

- ds RNA

- ss viral RNA

* to signal an immune response*

toll like receptors

pathogen related receptors

regulate apoptosis, inflammation, and immune responses leading to production of cytokines, chemokines, & anti-microbial peptides

expressed by epithelial cells, dendritic cells, lymphocytes, osteoclasts, and osteoblasts

neutrophil function

- feature of healthy gingiva

- forms barrier between subgingival plaque and gingival tissues

- phagocytes

-secrete enzymes = degradation of junctional epithelium BM

- migrate from gingival plexus to CT in response to chemotactic gradient (pathway to bacteria)

steps of neutrophil migration (1-4)

1. margination-- injury slows down blood flow, neutrophils move to periphery of blood vessel

2. adhesion-- neutrophils attach to adhesion molecules within endothelial wall (ICAM-1, ELAM-1, CMP-140)

3. emigration-- neutrophils exit vessel and go into CT

4. chemotaxis-- move toward bacteria; move through CT to BM and then junctional epithelium to bacteria

steps of neutrophil migration (5-8)

5. opsonization-- recognition & attachment to the target

6. phagocytosis-- engulfing target

7. killing-- respiratory burst or vacuole degranulation

8. digestion of dead bacteria/cells

what causes tissue damage from neutrophils

oxygen free radicals

enzymes

HOST causes damage (collateral damage)

what is chemotaxis (neutrophil migration)

movement of a cell in response to a chemical stimulus

complement dependent:

- C3a, C5a

complement independent:

- leukotriene

- products of bacterial metabolism

- endotoxin = activated macrophage = IL-8

- tissue injury

visual of neutrophil migration & chemotaxis

vessels getting closer to sulcular epithelium in disease

neutrophil granules and contents

azurophil (primary):

- large, dense

- lysosomal enzymes

- peroxidase ("myeloperoxidase")

- lysozyme (33%)

- cationic proteins

specific (secondary):

- smaller, less dense

- alkaline phosphatase

- lysozyme (67%)

- lactoferrin

ex. of genetic disease affecting periodontitis

leukocyte adhesion deficiency:

-↓ neutrophil migration → severe disease

papillon-lefevre syndrome:

- causes severe, aggressive periodontitis resulting in early, rapid tooth loss

*not enough PMNS... have more progressive inflammatory reaction b/c takes longer for other cells to arrive*

histopathology of gingival disease stages

stage 1 = initial lesion

stage 2 = early lesion

stage 3 = established lesion

stage 4 = advanced lesion

*know what cell present, inflammatory response, and how many days*

histopathology of gingival disease visual

initial lesion time frame

2-4 days

dominant cell in initial lesion

neutrophils

initial lesion

- clinically = looks healthy

- microroganisms in sulcus activate resident leukocytes

- migration of leukocytes into sulcus via chemotaxis

- increase in flow of gingival fluid into the sulcus

initial lesion vascular changes

- vasodilation of capillaries

- increased blood flow/permeability

- stimulation of endothelial cells

- GCF increase

- increased vascular permeability allows PMN and monocytes to migrate through CT to bacteria

initial lesion visual

early lesion (4-7 days)

- changes in initial lesion continue to intensify

-proliferation of capillaries, formation of capillary loops

- increased migration of PMNs to epithelium

-phagocytosis of bacteria

- release of lysosomes

-collagen destruction as by product apical & lateral to junctional and sulcular epithelium

-proliferation of basal cells in order to maintain in tact barrier

dominant cell in early lesion

T-lymphocytes

key features of early lesion

-collagen breakdown

-rete peg formation; epithelium proliferates into collagen depleted areas of CT

-capillary proliferation

clinical signs -- early lesion

redness

first clinical signs of eryhtema, edema

bleeding on probing

gingivitis (early)

no attachment loss

blood vessels forming capillary loops to get closer to epithelium

established lesion (14-21 days)

- changes in early lesion worsen

- continued breakdown of collagen, vascular prolfieration, developed/elongated formation of rete pegs

- moderately to severely inflamed gingiva

-changes in color, size, texture, consistency, contour of gingiva

-NO attachment loss

-gingival lesion is reversible

dominant cell in established lesion

plasma cells

is established lesion reversible

yes-- still in gingivitis stage

advanced lesion (periodontitis)

- extension of lesion into alveolar bone

- apical migration of junctional epithelium

bone loss:

- RANK/RANKL

-loss of attachment

-clinical signs of acute and/or chronic sings of inflammation may be present

periodontitis visual

-- in 2 diff teeth.. changes are dependent for localized area (site specific)

-- not all pt respond to bacteria same way

microbial virulence factors.

LPS

bacterial enzymes

microbial invasion

inhibition of antimicrobial peptides/ IL-8

- initiate inflammatory response

- contribute directly to tissue damage by release of noxious substances

LPS

- outer membrane of gram -

- aka endotoxin

- elicits strong immune response

- host recognizes LPS via toll-like receptors (TLRs)

what does TLRs recognizing LPS result in

- increased production of inflammatory mediators (cytokines)

- differentiation & recruitment of immune cells

- increased vasodilation & vascular permeability

bacterial enzymes and waste products

- ammonia

- hydrogen sulfide

- butyric acid-- apoptosis of T, B, fibroblasts, & epithelial cells

- proteases

proteases

breakdown of CT components (ex. collagen, elastin, and fibronectin)

gingipains produced by P. gingivalis reduce [ ] of cytokines and inactivate TNF-a

microbial invasion

- bacteria invade intercellular spaces of epithelium & CT (Aa, P.g, F. nuc)

- bacteria invade epithelial cells & allow other bacteria to enter tissue

- bacteria in tissues may act as a "reservoir" for reinfection

*important to maintain treatment b/c bacteria present always & periodontitis is chronic*

cytokines

-key mediators in periodontal disease

-proteins that act as messengers to transmit signals from once cell to another

- bind to receptors on target cells, initiate intracellular signaling, results in gene expression (alteration of cell behavior OR secretion of more cytokines)

- produced by many cells: neutrophils, macrophages, lymphocytes, fibroblasts, epithelial cells

*ex. induce fibroblasts & osteoclasts to produce enzymes to break down CT and bone*

main pro-inflammatory cytokins

IL-1β

TNF-α

IL-6

innate & adaptive

IL-1β functions

↑ prostaglandins

↑ inflammation

↑ bone resorption

- stimualtes synthesis of prostaglandin E2 (PGE2)- vasodilation, bone resportion via RANKL

- increase blood flow to site of infection

- facilitates migration of neutrophils from blood vessel

-increase GCF [ ] in gingivitis/periodontitis

-regulates development of antigen-presenting T cells

what produces IL-1β

monocytes

macrophages

neutrophils

fibroblasts

keratinocytes

epithelial cells

B cells

osteocytes

TNF-α funcitons

↑ neutrophil activity

↑ MMPs (mediates cell & tissue turnover)

↑ osteoclasts & limits tissue repair by osteoblasts

↓ tissue repair

facilitates neutrophil recruitment, IL-1β production, secretion of PGE2

*shares many actions of IL-1β*

*antagonists of IL-1β and TNF-α = ~80% reduction in inflammation and 60% reduction in bone loss*

what is RANK (receptor activator of nuclear factor-Kappa beta)

receptor expressed by osteoclast progenitor cells

RANKL

cytokine produced by osteoblast and bone marrow stromal cells

activates osteoclasts → bone resorption

RANKL + RANK = regulate osteoclast differentiation and activation

______ is a membrane-bound protein that binds to ____ receptors on osteoclast precursors to stimulate their differentiation, activation, and survival

RANKL, RANK

osteoprotegrin (OPG)

decoy receptor, secreted by osteoblasts

opposes RANKL to downregulate osteoclast activation

blocks RANKL = protects bone

IL-1 & TNF-α regulate the balance between RANKL and OPG

interleukin-6

stimulated by IL-1 β, TNF- α

secreted by many immune cells & osteoblasts to stimulate bone resorption and development of osteoclasts

matrix metalloproteinases (MMPs)

in health, MMP1 (collagenase) secreted by fibroblasts to maintain CT homeostasis

MMP production upregulated by IL-1 β, TNF- α and also produced by bacteria

in disease = MMPs secreted in excessive quantities and cause collagen and CT breakdown

when does adaptive immunity start

initiated in early lesion → dominant in established lesion (plasma cell)

if innate immunity fail to eliminate infection, then cells of adaptive immune are activated BUT innate doesn't turn off

adaptive immunity involves...

interactions between APC and T/B cells

non-progressing peridontal lesion

dominated by T cells

progressing periodontal lesion

dominated by plasma cells

TH1 vs TH2

TH1:

- cell mediated (APC)

-macrophages- phagocytose baceria

- NK cells & CD8 cytotoxic cells kill infected host cells

TH2:

- antibody- mediated (humoral)

- B cells produce plasma cells

- plasma cells produce antibody

- release of pro-inflammatory cytokines that lead to tissue destruction (bone loss in advanced lesion)

APC

macrophage:

- phagocytic from myeloid lineage

- ingest particulate antigen

- express MHC class II molecules to induce costimualtory activity on T cells

- homeostasis and defense

does gingivitis always become periodontits

no (despite poor oral hygiene)

depends on host susceptibility

Sir Lankan study

test laborers who had no access to dental care

3 groups:

- rapid progression (8%)

- moderate (81%)

- no progression (11%), only gingivitis but no periodontitis

same plaque, different outcomes → HOST RESPONSE matters

the major determinant of susceptibility to disease i the nature of the ____-_____ response

immune-inflammatory

*not everyone has same response to plaque bacteria*

host susceptibility

-patients with periodontal inflammation have a high concentrations of

TNF-α, IL-1β, RANKL and MMP-13

- immune responses to bacterial challenge take place in the context of other host and environmental factors that influence these responses and determine progression of disease

- more susceptible = excessive, or dysregulated, immune-inflammatory breakdown compared to those with a normal response

- bacterial threshold btwn stable and active disease that varies person to person

_____ ____ increase susceptibility to periodontal disease

risk factors

ex. smoking, diabetes, stress, genetics

why is smoking tricky

vasoconstriction → ↓ bleeding

disease may be present but masked

______ _____ may result in hyperinflammatory traits, increasing susceptibility (same bacterial challenge elicits a greater inflammatory response, increased tissue breakdown)

genetic polymorphisms

how gum disease affects body

1. alzheimers

2. heart disease

3. diabetes

4. pregnancy, health of fetus

5. overall inflammation

periodontal disease & heart

presence of periodontal disease may be associated with heart attacks, strokes, kidney disease, diabetes etc.

goal of periodontal therapy

reduce inflammation & biofilms

methods:

- plaque control

- mouthwash

- antibiotics

-scaling/ root planing

-surgery