Microbiology 532: Microbiology 532: ImmunologyImmunology

Dennis E. Lopatin, Ph.D.Dennis E. Lopatin, Ph.D.Dept. of Biologic and Materials SciencesDept. of Biologic and Materials Sciences

4209 Dental Building4209 Dental Building

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Phone: 647-3912 Phone: 647-3912

Electronic mail: lopatin@umich.eduElectronic mail: lopatin@umich.edu

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Lecture 1Lecture 1ImmunologyImmunology

Introduction & Innate immunityIntroduction & Innate immunity

Why Does a Dentist Need to Why Does a Dentist Need to Understand Immunology?Understand Immunology?

Many of the oral diseases have an immune Many of the oral diseases have an immune componentcomponent Periodontal diseasePeriodontal disease CariesCaries Sjögren’s SyndromeSjögren’s Syndrome

Current and future therapeutics affect the immune Current and future therapeutics affect the immune system and oral healthsystem and oral health

Systemic and Oral diseases are interrelatedSystemic and Oral diseases are interrelated Cooperation with other health care professional Cooperation with other health care professional

requires a common languagerequires a common language

What is immunity?What is immunity?

““Protection” from infection, tumors, Protection” from infection, tumors, etc.etc.

Innate immunity is always availableInnate immunity is always available Adaptive immunity distinguishes “self” Adaptive immunity distinguishes “self”

from “non-self” and involves immune from “non-self” and involves immune system “education”system “education”

Responses that may result in host Responses that may result in host tissue damagetissue damage

Two types of immunityTwo types of immunity Innate immunity (not antigen-specific)Innate immunity (not antigen-specific)

Anatomical barriersAnatomical barriers MechanicalMechanical BiochemicalBiochemical

Non-specific (eg. Low pH in stomach)Non-specific (eg. Low pH in stomach) Receptor-driven (eg. PAMP-recognition)Receptor-driven (eg. PAMP-recognition)

Adaptive immunity (antigen-specific)Adaptive immunity (antigen-specific) Receptor-drivenReceptor-driven Pre-existing clones programmed to make a Pre-existing clones programmed to make a

specific immune response (humoral/cellular)specific immune response (humoral/cellular)

AntigenAntigen

A substance (antigen) that is capable of A substance (antigen) that is capable of reactingreacting with the products of a specific with the products of a specific immune response, e.g., antibody or immune response, e.g., antibody or specific sensitized T-lymphocytes.specific sensitized T-lymphocytes.

A “self” component may be considered an A “self” component may be considered an antigen even though one does not antigen even though one does not generally make immune responses generally make immune responses against those components.against those components.

Characteristics of Adaptive Characteristics of Adaptive ImmunityImmunity

Immune response is highly specific for the antigen that Immune response is highly specific for the antigen that triggered it.triggered it. Receptors on surface of immune cells have same specificity as the Receptors on surface of immune cells have same specificity as the

antibody/effector activity that will be generatedantibody/effector activity that will be generated Exposure to antigen creates an immunologic “memory.”Exposure to antigen creates an immunologic “memory.”

Due to clonal expansion and creation of a large pool of cells Due to clonal expansion and creation of a large pool of cells committed to that antigencommitted to that antigen

Subsequent exposure to the same antigen results in a rapid and Subsequent exposure to the same antigen results in a rapid and vigorous responsevigorous response

Components of the Components of the immune systemimmune system

Cells Cells involved involved

in in immunityimmunity

platelets platelets

megakaryocyte megakaryocyte eosinophil eosinophil

neutrophil neutrophil

basophil basophil

mast cell mast cell

common common myeloid myeloid progenitor progenitor

monocyte monocyte

macrophage macrophage

NaturalNaturalKiller cellKiller cell

plasma cell plasma cell

B LymphocyteB Lymphocyte

T LymphocyteT Lymphocyte

common common lymphoid lymphoid progenitor progenitor

Pluripotent Pluripotent hematopoietichematopoieticstem cellstem cell

BloodBloodBloodBloodSerum or Serum or PlasmaPlasma

Leukocytes, Leukocytes, Platelets and RBCPlatelets and RBC

Serum ProteinsSerum ProteinsSerum ProteinsSerum Proteins Mononuclear Mononuclear CellsCells

Mononuclear Mononuclear CellsCells

Polymorphonuclear Polymorphonuclear leukocytes (or leukocytes (or Granulocytes)Granulocytes)

Polymorphonuclear Polymorphonuclear leukocytes (or leukocytes (or Granulocytes)Granulocytes)

•ImmunoglobulinsImmunoglobulins•ComplementComplement•Clotting factorsClotting factors•Many othersMany others

•ImmunoglobulinsImmunoglobulins•ComplementComplement•Clotting factorsClotting factors•Many othersMany others

•NeutrophilsNeutrophils•EosinophilsEosinophils•BasophilsBasophils

•NeutrophilsNeutrophils•EosinophilsEosinophils•BasophilsBasophils

•Lymphocytes Lymphocytes (T cells, B cells (T cells, B cells & NK cells)& NK cells)•MonocytesMonocytes

•Lymphocytes Lymphocytes (T cells, B cells (T cells, B cells & NK cells)& NK cells)•MonocytesMonocytes

Where is that stuff?Where is that stuff?

Lymphoid OrgansLymphoid Organs

Primary or central lymphoid organsPrimary or central lymphoid organs bone marrow and thymusbone marrow and thymus where lymphocytes are generatedwhere lymphocytes are generated

Secondary or peripheral lymphoid organsSecondary or peripheral lymphoid organs where adaptive immune responses are where adaptive immune responses are

initiatedinitiated

Distribution of Lymphoid TissuesDistribution of Lymphoid Tissues

Response to Initial Infection Response to Initial Infection

Stages of Response to InfectionStages of Response to Infection

Course Course of Typical of Typical

Acute Acute InfectionInfection

Innate Host Defense MechanismsInnate Host Defense Mechanisms

Anatomic FactorsAnatomic Factors Mechanical FactorsMechanical Factors Biochemical FactorsBiochemical Factors

SkinSkin

Stratified and cornified epithelium provides a Stratified and cornified epithelium provides a mechanical barriermechanical barrier

Indigenous microbiota competes with pathogensIndigenous microbiota competes with pathogens Acid pH inhibits growth of disease producing Acid pH inhibits growth of disease producing

bacteriabacteria Bactericidal long chain fatty acids in sebaceous Bactericidal long chain fatty acids in sebaceous

gland secretionsgland secretions

Respiratory TractRespiratory Tract Upper Respiratory TractUpper Respiratory Tract

Nasal hairs induce turbulenceNasal hairs induce turbulence Mucous secretions trap particlesMucous secretions trap particles Mucous stream to the base of tongue where material is swallowedMucous stream to the base of tongue where material is swallowed Nasal secretions contain antimicrobial substancesNasal secretions contain antimicrobial substances Upper respiratory tract contains large resident floraUpper respiratory tract contains large resident flora

Lower Respiratory TractLower Respiratory Tract Particles trapped on mucous membranes of bronchi and bronchiolesParticles trapped on mucous membranes of bronchi and bronchioles Beating action of cilia causes mucociliary stream to flow up into the pharynx Beating action of cilia causes mucociliary stream to flow up into the pharynx

where it is swallowedwhere it is swallowed 90% of particles removed this way. Only smallest particles (<10µ in 90% of particles removed this way. Only smallest particles (<10µ in

diameter) reach alveolidiameter) reach alveoli

AlveoliAlveoli Alveolar macrophage rapidly phagocytize small particlesAlveolar macrophage rapidly phagocytize small particles

Alimentary TractAlimentary Tract General defense mechanismsGeneral defense mechanisms

Mucous secretionsMucous secretions Integrity of of mucosal epitheliumIntegrity of of mucosal epithelium Peristaltic motions of the gut propel contents downwardPeristaltic motions of the gut propel contents downward Secretory antibody and phagocytic cellsSecretory antibody and phagocytic cells

StomachStomach Generally sterile due to low pHGenerally sterile due to low pH

Small IntestineSmall Intestine Upper portion contains few bacteriaUpper portion contains few bacteria As distal end of ilieum is reached flora increasesAs distal end of ilieum is reached flora increases

ColonColon Enormous numbers of microorganismsEnormous numbers of microorganisms 50-60% of fecal dry weight is bacteria50-60% of fecal dry weight is bacteria

Genitourinary TractGenitourinary Tract MaleMale

No bacteria above urethrovesicular junctionNo bacteria above urethrovesicular junction Frequent flushing action of urineFrequent flushing action of urine Bactericidal substances from prostatic fluidBactericidal substances from prostatic fluid pH of urinepH of urine Bladder mucosal cells may be phagocyticBladder mucosal cells may be phagocytic Urinary sIgAUrinary sIgA

Female (Vagina)Female (Vagina) Large microbial population (lactobacilli)Large microbial population (lactobacilli) Microorganisms produce low pH due to breakdown of glycogen produced by Microorganisms produce low pH due to breakdown of glycogen produced by

mucosal cellsmucosal cells

EyeEye

Flushing action of tears which drain through the Flushing action of tears which drain through the lacrimal duct and deposit bacteria in nasopharynxlacrimal duct and deposit bacteria in nasopharynx

Tears contain a high concentration of lysozyme Tears contain a high concentration of lysozyme (effective against gram positive microorganisms(effective against gram positive microorganisms

ReceptorsReceptors

Almost all of biology occurs because Almost all of biology occurs because recognitionrecognition Enzymatic actionEnzymatic action Interactions between cells Interactions between cells

(cooperation/activation)(cooperation/activation) Communication between cellsCommunication between cells

Innate and adaptive immunity requires itInnate and adaptive immunity requires it

Innate Immune RecognitionInnate Immune Recognition All multi-cellular organisms are able to All multi-cellular organisms are able to

recognize and eliminate pathogensrecognize and eliminate pathogens Despite their extreme heterogeneity, Despite their extreme heterogeneity,

pathogens share highly conserved molecules, pathogens share highly conserved molecules, called “pathogen-associated molecular called “pathogen-associated molecular patterns” (patterns” (PAMPsPAMPs))

Host cells do not share PAMPs with pathogensHost cells do not share PAMPs with pathogens PAMPs are recognized by innate immune PAMPs are recognized by innate immune

recognition receptors called pattern-recognition receptors called pattern-recognition molecules/receptors (recognition molecules/receptors (PRMs/PRRsPRMs/PRRs))

Typical PAMPsTypical PAMPs

LipopolysaccharidesLipopolysaccharides PeptidoglycansPeptidoglycans Certain nucleotide sequences unique to Certain nucleotide sequences unique to

bacteriabacteria Other bacterial componentsOther bacterial components

Endogenous Signals Induced by PAMPsEndogenous Signals Induced by PAMPs

Mediate inflammatory cytokinesMediate inflammatory cytokines Antigen-presenting cells recognize Antigen-presenting cells recognize

PAMPsPAMPs Same APC processes pathogens into specific Same APC processes pathogens into specific

pathogen-derived antigens and presents them pathogen-derived antigens and presents them with MHC encoded receptors to T-cellswith MHC encoded receptors to T-cells

T-cell responds only when presented with both T-cell responds only when presented with both signalssignals

Different Effector Cytokines in Response to Different Different Effector Cytokines in Response to Different Pathogens (Th1 vs. Th2)Pathogens (Th1 vs. Th2)

Antimicrobial Antimicrobial Peptides/DefensinsPeptides/Defensins

Four hundred peptides described to dateFour hundred peptides described to date Defensins (3- 5-kD, four families in eukaryotes)Defensins (3- 5-kD, four families in eukaryotes)

-defensins (neutrophils and intestinal Paneth cells)-defensins (neutrophils and intestinal Paneth cells) -defensins (epithelial cells)-defensins (epithelial cells) Insect defensinsInsect defensins Plant defensinsPlant defensins

Defensins appear to act by binding to outer Defensins appear to act by binding to outer membrane of bacteria, resulting in increased membrane of bacteria, resulting in increased membrane permeability.membrane permeability.

May also play a role in inflammation and wound May also play a role in inflammation and wound repairrepair

Complement SystemComplement System

Three pathways now knownThree pathways now known ClassicalClassical AlternativeAlternative Lectin or MBL pathway (binding to mannose-Lectin or MBL pathway (binding to mannose-

containing carbohydrates)containing carbohydrates) Host cells have complement regulatory Host cells have complement regulatory

proteins on their surface that protect them proteins on their surface that protect them from spontaneous activation of C3 moleculesfrom spontaneous activation of C3 molecules

Inflammatory Mediators in Innate Inflammatory Mediators in Innate ImmunityImmunity

Cytokines secreted by phagocytes in response to Cytokines secreted by phagocytes in response to infection include:infection include: IL-1 IL-1

activates vascular endothelium and lymphocytesactivates vascular endothelium and lymphocytes Increases adhesiveness of leukocytesIncreases adhesiveness of leukocytes

IL-6IL-6 Induces B-cell terminal maturation into Ig-producing plasma cellsInduces B-cell terminal maturation into Ig-producing plasma cells

IL-8IL-8 Induces expression of b2 integrin adhesion molecules on Induces expression of b2 integrin adhesion molecules on

neutrophils, leading to neutrophil migration to infection siteneutrophils, leading to neutrophil migration to infection site IL-12IL-12

Activates NK cells and induces Th1-cell differentiationActivates NK cells and induces Th1-cell differentiation IL-18IL-18 TNF-TNF-

Activates vascular endothelium and increases vascular permeability, Activates vascular endothelium and increases vascular permeability, leading to accumulation of Ig and complement in infected tissuesleading to accumulation of Ig and complement in infected tissues

Other Mediators and MoleculesOther Mediators and Molecules

PhagocytesPhagocytes Toxic oxygen radicalsToxic oxygen radicals PeroxidesPeroxides Nitric oxide (NO)Nitric oxide (NO) Lipid mediators of inflammationLipid mediators of inflammation

ProstaglandinsProstaglandins LTB4LTB4 Platelet activating factorPlatelet activating factor

Complement component C5aComplement component C5a Stimulates mast cells to release histamine, serotonin and LTB4Stimulates mast cells to release histamine, serotonin and LTB4

IL-1, IL-6 and TNF-IL-1, IL-6 and TNF- Induce acute-phase response in liverInduce acute-phase response in liver Induce feverInduce fever

IL-1 and IL-18 signaling pathways activate NF-IL-1 and IL-18 signaling pathways activate NF-B, important in B, important in innate immunityinnate immunity

Immune Cells and Innate ImmunityImmune Cells and Innate Immunity

PhagocytesPhagocytes NeutrophilsNeutrophils Moncyte/macrophageMoncyte/macrophage Eosinophils (to a lesser extent)Eosinophils (to a lesser extent)

NK cells NK cells (large granular lymphocytes)(large granular lymphocytes) Antibody-dependent cell-mediated cytotoxicity Antibody-dependent cell-mediated cytotoxicity

(ADCC)(ADCC) Have two major functionsHave two major functions

Lysis of target cellsLysis of target cells Production of cytokines (IFN-Production of cytokines (IFN- and TNF- and TNF-))

Act against intracellular pathogensAct against intracellular pathogens HerpesvirusesHerpesviruses LeishmaniaLeishmania Listeria monocytogenesListeria monocytogenes

Act against protozoaAct against protozoa ToxoplasmaToxoplasma TrypanasomaTrypanasoma

Immune Cells and Innate Immunity (cont’d)Immune Cells and Innate Immunity (cont’d)

// T cells T cells Two types of T cell receptorsTwo types of T cell receptors

One composed of One composed of and and chains (basic T cell antigen receptor) chains (basic T cell antigen receptor) One composed of One composed of and and chains (minor population of T cells) chains (minor population of T cells)

Two groups of Two groups of // T cells T cells One group found in lymphoid tissuesOne group found in lymphoid tissues One group located in paracellular space between epithelial cellsOne group located in paracellular space between epithelial cells

Recognizes unprocessed target antigen in absence of APC helpRecognizes unprocessed target antigen in absence of APC help B-1 cells (minor fraction of B cells, do not require T-cell help)B-1 cells (minor fraction of B cells, do not require T-cell help) Mast cellsMast cells

Located in serosa, under epithelial surfaces and adjacent to Located in serosa, under epithelial surfaces and adjacent to blood vessels, nerves and glandsblood vessels, nerves and glands

Capable of phagocytosisCapable of phagocytosis Process and present antigen using MHC class I or II receptorsProcess and present antigen using MHC class I or II receptors LPS can directly induce release of mast cell mediatorsLPS can directly induce release of mast cell mediators Complement (C3a and C5a) induce mast cells to release Complement (C3a and C5a) induce mast cells to release

mediatorsmediators Chemotaxis, complement activation, inflammationChemotaxis, complement activation, inflammation TNF-TNF- secreted by mast cells results in neutrophil influx into infected secreted by mast cells results in neutrophil influx into infected

sitesite

Summary of Innate ImmunitySummary of Innate Immunity

External and mechanical barriersExternal and mechanical barriers Receptors for pathogen motifsReceptors for pathogen motifs Soluble antimicrobial proteinsSoluble antimicrobial proteins Pattern of cytokines produced Pattern of cytokines produced

influences adaptive responseinfluences adaptive response