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When a m.o. enters the body, it begins as a low level in terms of number of m.o. If it is a successful pathogen, it multiplies, and eventually it’s going to reach a point where there is a threshold level reached that activates the adaptive immune system. That threshold level that stimulates the adaptive immune system is typically greater than the threshold needed to activate the innate immune system. That’s somewhat lower and not shown on this graph. Eventually the number of m.o. peak and within this time there is activation of the adaptive immune system. The time it takes from the time the threshold is reached to the time you see the appearance of antibodies is usually about 10-14 days, closer to 10. This correlates with the fact that most of us recover from colds in 10-14 days. The correlation is due to the amount of antibody that is produced is released in this time period. Eventually the adaptive immune system is successful at eliminating the pathogen. Later of course there is immunological memory produced.

1. An organism that attaches to epithelium
2. If the pathogen is successful in breaking through the epithelium, it will simulate wound healing
3. There will be a release of various innate immune factors, such as antimicrobial proteins, phagocytes, the complement system, activation of certain types of T cells
4. Eventually the pathogen multiplies and is taken up (phagocytized) by an antigen presenting cell (APC), such as a dendritic cell, a Langerhan's cell, or a macrophage
5. APC that has phagocytized on of the pathogens is transported to an adjacent lymph node
6. The lymph node serves as a filtering organ which takes the antigen from the APC and presents it to B cells and T cells where there is induction of the adaptive immune system and subsequently there is induction of memory T cells and B cells
7. Ultimately these B and T cells migrate back to site of infection, they will release specific antibodies which will combine with the pathogen and destroy it

host factors are present all the time, or they are activated very rapidly after the first presentation of antigen

non-specific

Specific Host Defense Factors

more specific it is, the longer it will take to generate an immune response

very specific (antibodies, T cell, etc.)

Biochemical Innate Defense System Factors

Lactoferrin (LF)

Peroxidases (PO)

Lysozyme (LZ)

Mucins (MG1 and MG2)--mucin 1 is much larger than mucin 2 and, therefore, better at agglutinating mo to be cleared from the area

Salivary Agglutinin (SAG)

Cystatins

Amylase

Histatin

Many salivary proteins free in saliva, in general, will inhibit bacterial colonization to hard surfaces by binding to critical sites on bacteria, blocking their attachment.

Conversely, many of these same salivery proteins if first immobilized on hard surfaces (the salivary pellicle) will increase bacterial colonization.

H₆Lactoferrin + 2Fe³⁺ + 2HCO^- ↔ Fe₂Lactoferrin (HCO₃)₂ + 6H⁺

Close cousin of transferrin found in the blood. 

Binds ferric iron (Fe³⁺) making it unavailable for microbes.

This eliminates a nutrient that bacteria need to live (nutritional immunity).

Some microorganisms (e.g. E. coli) have adapted to this mechanism by producing enterochelins--bind more effectively than lactoferrin; iron-rich enterochelins are then reabsorbed by bacteria

Lactoferrin,with or without bound iron, can be degraded by some bacterial proteases.

In iron-bound state, a direct bactericidal effect (bacteria are killed) if high enough concentration.

In iron-unbound state, a bacteristatic effect (inhibition of bacterial growth)

Sialoperoxidase (SP, salivary peroxidase)

• produced in acinar cells of parotid glands
• also present in submandibular saliva
• readily adsorbed to various surfaces of the mouth--enamel, salivary sediment, bacteria, dental plaque

Myeloperoxidase (MP)

• From leukocytes entering via gingival crevice (produced by neutrophils--can also be found in machrophages and mast cells)
• 15-20% of total peroxidase in whole saliva

Lactoperoxidase

• Found in milk

1. Peroxidase enzymes (SP or MP)
2. Hydrogen peroxide (H₂O₂)--oral bacteria (facultative aerobes/catalase negative) produce large amounts of peroxide--S. sanguis, S. mitis, S. mutans
3. Thiocyanate ion (SCN^-) which is converted to hypothiocyanite ion (OSCN^-) by peroxidase--salivary concentration is related to diet and smoking habits

Salivary Glands

Leukocytes (Neutrophils)

Bacteria

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Oxygen (O₂)--WEAKEST

Superoxide radical (O₂·^-)

Hydrogen peroxide (H₂O₂)

Hydroxyl radical (·OH)

Hydroxyl ion (OH^-)

Nitric oxide (NO·)

Nitric oxide radical (NO₂·)

Hypothiocyanite (OSCN^-)

Hypothiocanous acid (HOSCN)

Singlet oxygen (¹O₂)

Ozone (O₃)

Hypochlorous acid (HOCl)--STRONGEST

• can oxidize sulfhydryl groups of enzymes
• block glucose uptake
• inhibit amino acid transport
• damage inner membrane, leading to leakage of cell
• disrupt electrochemical grradients

Enzyme that acts on primarily gram-positive bacteria cells (lots of layers of PG)

Present in numerous organs ans most mucosal secrtions

Oral LZ is derived from at least four sources: major and minor salivary glands, phagocytic cells, and gingival crevicular fluid (GCF)

Biological function:

• Classic concept of anti-microbial activity of LZ is based on its muramidase activity (hydrolysis of β(1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in the PG layer)
• Gram-negative bacteria generally more resistant than gram-positive because of outer LPS layer and because gram-negative bacteria have ~4 layers of PG and gram-positve bacteria have ~30 layers of PGb
• Punches a hole in the cell wall, which creates an osmotic imbalance in the bacterial cell (water rushes in and eventually the cell explodes)

Other Anti-Microbial Activites of LZ:

• Cationic-dependent activation of bacterial autolysins (disrupts membranes)
• Aggregation of bacteria
• Inhibition of bacterial adhesion to the tooth surfaces
• Inhibition of glucose uptake and acid production
• De-chaining of streptococci--more exposure of the cells to innate factors in saliva

Group of very small histidine-rich proteins

Potent inhibitors of Candida albicans growth

Major innate inhibitor of yeast growth (problem in immunocompromised patients or those recieving large amounts of antibiotics)

Histatin 1, when phosporylated, prevents precipitation of calcium phosphates and stabilizes soluble CaPO₄ molecules preventing calculus

Lack precise folded structure of globular proteins

Asymmetrical molecules with open, randomly organized structure

Polypeptide backbone (apomucin) with CHO side-chains--creates the adhesiveness of mucins

Side-chains may end in negatively charged groups, such as sialic acid and bound sulfate

Hydrophillic, entraining water (resists dehydration)

Unique rheological properties (e.g. high elasticity, adhesiveness, and low solubility)

Two major mucins (MG1 [larger] and MG2)

Mucin Functions:

• Tissue Coating:  protective coating about hard and soft tissues; primary role in formation of acquired salivary pellicle; concntrates anti-microbial molecules at mucosal interface
• Lubrication:  align themselves iwth direction of flow (characteristic of asymmetric molecules); increases lubricating qualities (film strength); film strength determines how effectively opposed moving sufaces are kept apart
• Aggregation of bacterial cells:  bacteria adhered to mucins may result in surface attachment or mucin-coated bacteria may be unable to attach to the surface
• Bacterial adhesion:  mucin oligosaccharides mimic those on mucosal cell surface; react with bacterial adhesins, therby blocking them

Large (340 kDa) salivary protein found in pellicle and saliva--about the size of IgA

Binds to antigen I/II on surface of many oral streptococci (including S. mutans)

Calcium metalloenzyme

Hydrolyzes α(1-4) bonds of starches such as amylose and amylopectin

Several salivary isoenzymes

Maltose is the major end-product (20% is glucose)

Has digestive function (degrades starches)

Found in all mucosal secretions (tears, serum, bronchial fluids, and urogenital secretions) so it must have another function--possibly has an effect on bacterial adherence

Anti-microbial activity: Potent inhibitor and specific inhibitor of N. gonorrheoeae and Legionella pneumonophila; modulates adhesion of certain oral species (S. gordonii and S. mutans) to teeth and other body surfaces

Marker of stress: amylase levels increase during periods of stress (when individuals are more susceptible to illnesses)

Inhibitors of cysteine-proteases such as cathepsins

Ubiquitous in many body fluids

Considered to be protective against unwanted proteolysis (bacterial proteases and lysed leukocytes)

May inhibit proteases in periodontal tissues

Also have an effect on calcium phosphate precipitation and stabilizes soluble CaPO₄ molecules preventing calculus

Like statherin and mucins, PRPs are also highly asymmetrical

Inhibitors of calcium phosphate crystal growth and stabilizes soluble CaPO₄ molecules preventing calculus

Inhibiton due to first 30 residues of negatively-charged amino-terminal end

Present in the initially formed enamel pellicle and in "mature" pellicles

Strong promoters of bacterial adhesion (amino terminal - control calcium phospate chemistry; carboxy terminal - interaction with oral bacteria)

Interactions are highly specific: depends on proline-glutamine carboxy-terminal dipeptide; PRPs in solution do not inhibit adhesion of bacteria

Asymmetrical

Also have an effect on calcium phosphate precipitation and stabilizes soluble CaPO₄ molecules preventing calculus

Tightly binds to enamel surfaces

Promotes bacterial adhesion

Lactoferrin-IgA (up to 85% bound to IgA in saliva)

Lysozyme-IgA

Peroxidase-IgA

Thicyanate-IgA

In this theory, IgA targets the antigen and bound protein kills the bacteria

High molecular weight glycoproteins (parotid saliva glycoproteins, mucins)

Secretory IgA

Other compounds (lysozyme, β₂-microglobulin, fibronectin, amylase)

Proteins or protein complexes produced by bacteria

Antagonistic to the same or related species

Commonly found in strains of mutans streptococci (40-90%)

Important role in transmission of mutans streptococci from mother to child

Important role in oral ecology

The strategy of innate factor recognition is based on the detection of constitutive and conserved products of microbial metabolism

Because the targets of innate factor recognition are conserved molecular patterns, they are called pathogen-associated molecular pattern (PAMPs)

The receptors that recognize PAMPs are termed pattern-recognition receptors (PRR), primarily Toll-like receptors (TLR) such as TLR4 for LPS (gram-negative bacteria) and TLR2 for LTA (gram-positive bacteria)

Soluble TLR are found in saliva suggesting they scavenge bacterial products and help in bacterial clearance

PRRs that have unique and essential function in animal immunity

Comprise a family of type I transmembrane receptors, which are characterized by an extracellular leucine-rich repeat (LRR) domain and an intracellular Toll/IL-1 receptor (TIR)

TIR activation causes adaptive immune system induction through the NFκ-β pathway and subsequent secretion of pro-inflammatory cytokines (IL-1, TNF-α, IL-6, IL-8)

Functions as the signal-transducing receptor for LPS

Recognizes a broad range of microbial products including peptidoglycan from gram-positive bacteria, bacterial lipoprotein, mycobacterial cell wall, etc.  It also functions as a receptor for atypical LPS produced by Leptospira interogans and P. gingivalis

Capable of either stimulating and immune response or reacting with products of immune responses

Can be protein, carbohydrate, lipid-containing or nucleic acid

Antigens that stimulate an immune response are termed immunogens 

Antigens that cannot stimulate an immune response but can react with products of an immune response are termed haptens

Carriers are components that when coupled to a hapten stimulate an immune response to the hapten, carrier, and haptin-carrier complex

The best immunogens are large and complex (i.e. proteins)

Antibody specificity can be removed by a 1 amino acid change

Simple anitgens do not require T cell involvement, and take a shorter time to reach maximum response by reach a lower response than responses to complex antigens

Complex antigens typically require T cell involvement, and take longer to reach maximum response by reach a higher response than responses to simple antigens

Surface components:

• surface immunoglobulin (Ag recognition)
• immunoglobulin Fc receptor
• class II major histocompatability complex (MHC) molecule (Ag presentation)

Function:

• direct antigen recognition
• differentiation into antibody-producing plasma cells
• antigen presentation within class II MHC

Surface components:

• CD3 molecule
• T-cell receptor (TCR, Ag recognition)

Function:

• involved with both humoral and cell-mediated responses

Surface components:

• CD4 molecule

Function:

• recognizes antigen presented within class II MHC
• promotes differentiation of B-cells and cytotoxic T-cells
• activates macrophages

Surface components:

• CD8 molecule

Function:

• downregulates the activites of other cells

Surface components:

• CD8 molecule

Function:

• recognizes antigen presented within class I MHC
• kills cells expressing appropriate antigen

Surface components:

• variable

Function:

• phagocytosis and cell killing

Surface components:

• immunoglobulin Fc receptor
• complement component C3b receptor
• class II MHC molecule

Function:

• bind Fc portion of immunoglobulin (enhances phagocytosis)
• bind complement component C3b (enhances phagocytosis)
• antigen presentation within class II MHC
• secrete IL-1 (macrokine) promoting T-cell differentiation and proliferation
• can be "activated" by T-cell lymphokines

Surface components:

• class II MHC molecule

Function:

• antigen presentation within class II MHC

Surface components:

• immunoglobulin Fc receptor
• complement compnent C3b receptor

Function:

• bind Fc portion of immunoglobulin (enhances phagocytosis)
• bind complement component C3b (enhances phagocytosis)

Surface components:

• variable

Function:

• direct cell killing

Surface components:

• unknown

Function:

• kills variety of target cells (e.g. tumor cells, virus-infected cells, transplanted cells)

Surface components:

• immunoglobulin Fc receptor

Function:

• bind Fc portion of immunoglobulin
• kills antibody-coated target cells (antibody-dependent cell-mediated cytotoxicity, ADCC)

Surface components:

• high affinity IgE Fc receptors

Function:

• bind IgE and initiate allergic responses by release of histamine