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Microbiology 532: Immunology. Dennis E. Lopatin, Ph.D. Dept. of Biologic and Materials Sciences 4209 Dental Building Office Hours by Appointment Phone: 647-3912 Electronic mail: [email protected] Helpful Hints. Readings in text are beneficial

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Microbiology 532 immunology l.jpg
Microbiology 532: Immunology

Dennis E. Lopatin, Ph.D.

Dept. of Biologic and Materials Sciences

4209 Dental Building

Office Hours by Appointment

Phone: 647-3912

Electronic mail: [email protected]


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Helpful Hints

  • Readings in text are beneficial

  • I expect you to read the relevant chapters in Nester.

  • Understanding the concepts is not optional

  • Think, rather than memorize

  • Test questions are based on concepts

  • Ask questions

  • Don’t wait until the last minute to study

  • Check the website


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Lecture 1Immunology

Introduction & Innate immunity


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Why Does a Dentist Need to Understand Immunology?

  • Many of the oral diseases have an immune component

    • Periodontal disease

    • Caries

    • Sjögren’s Syndrome

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

  • Systemic and Oral diseases are interrelated

  • Cooperation with other health care professional requires a common language


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What is immunity?

  • “Protection” from infection, tumors, etc.

  • Innate immunity is always available

  • Adaptive immunity distinguishes “self” from “non-self” and involves immune system “education”

  • Responses that may result in host tissue damage


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Two types of immunity

  • Innate immunity (not antigen-specific)

    • Anatomical barriers

    • Mechanical

    • Biochemical

      • Non-specific (eg. Low pH in stomach)

      • Receptor-driven (eg. PAMP-recognition)

  • Adaptive immunity (antigen-specific)

    • Receptor-driven

    • Pre-existing clones programmed to make a specific immune response (humoral/cellular)


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Antigen

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

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


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Characteristics of Adaptive Immunity

  • Immune response is highly specific for the antigen that triggered it.

    • Receptors on surface of immune cells have same specificity as the antibody/effector activity that will be generated

  • Exposure to antigen creates an immunologic “memory.”

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

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



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Cells involved in immunity

platelets

eosinophil

megakaryocyte

T Lymphocyte

Pluripotent

hematopoietic

stem cell

neutrophil

B Lymphocyte

common lymphoid progenitor

basophil

common myeloid progenitor

plasma cell

mast cell

Natural

Killer cell

monocyte

macrophage


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Where is that stuff?

Blood

Serum or Plasma

Leukocytes, Platelets and RBC

Mononuclear Cells

Polymorphonuclear leukocytes (or Granulocytes)

Serum Proteins

  • Immunoglobulins

  • Complement

  • Clotting factors

  • Many others

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

  • Monocytes

  • Neutrophils

  • Eosinophils

  • Basophils


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Lymphoid Organs

  • Primary or central lymphoid organs

    • bone marrow and thymus

    • where lymphocytes are generated

  • Secondary or peripheral lymphoid organs

    • where adaptive immune responses are initiated






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Innate Host Defense Mechanisms

  • Anatomic Factors

  • Mechanical Factors

  • Biochemical Factors


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Skin

  • Stratified and cornified epithelium provides a mechanical barrier

  • Indigenous microbiota competes with pathogens

  • Acid pH inhibits growth of disease producing bacteria

  • Bactericidal long chain fatty acids in sebaceous gland secretions


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Respiratory Tract

  • Upper Respiratory Tract

    • Nasal hairs induce turbulence

    • Mucous secretions trap particles

    • Mucous stream to the base of tongue where material is swallowed

    • Nasal secretions contain antimicrobial substances

    • Upper respiratory tract contains large resident flora

  • Lower Respiratory Tract

    • Particles trapped on mucous membranes of bronchi and bronchioles

    • Beating action of cilia causes mucociliary stream to flow up into the pharynx where it is swallowed

    • 90% of particles removed this way. Only smallest particles (<10µ in diameter) reach alveoli

  • Alveoli

    • Alveolar macrophage rapidly phagocytize small particles


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Alimentary Tract

  • General defense mechanisms

    • Mucous secretions

    • Integrity of of mucosal epithelium

    • Peristaltic motions of the gut propel contents downward

    • Secretory antibody and phagocytic cells

  • Stomach

    • Generally sterile due to low pH

  • Small Intestine

    • Upper portion contains few bacteria

    • As distal end of ilieum is reached flora increases

  • Colon

    • Enormous numbers of microorganisms

    • 50-60% of fecal dry weight is bacteria


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Genitourinary Tract

  • Male

    • No bacteria above urethrovesicular junction

    • Frequent flushing action of urine

    • Bactericidal substances from prostatic fluid

    • pH of urine

    • Bladder mucosal cells may be phagocytic

    • Urinary sIgA

  • Female (Vagina)

    • Large microbial population (lactobacilli)

    • Microorganisms produce low pH due to breakdown of glycogen produced by mucosal cells


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Eye

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

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


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Receptors

  • Almost all of biology occurs because recognition

    • Enzymatic action

    • Interactions between cells (cooperation/activation)

    • Communication between cells

  • Innate and adaptive immunity requires it


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Innate Immune Recognition

  • All multi-cellular organisms are able to recognize and eliminate pathogens

  • Despite their extreme heterogeneity, pathogens share highly conserved molecules, called “pathogen-associated molecular patterns” (PAMPs)

  • Host cells do not share PAMPs with pathogens

  • PAMPs are recognized by innate immune recognition receptors called pattern-recognition molecules/receptors (PRMs/PRRs)


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Typical PAMPs

  • Lipopolysaccharides

  • Peptidoglycans

  • Certain nucleotide sequences unique to bacteria

  • Other bacterial components


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Endogenous Signals Induced by PAMPs

  • Mediate inflammatory cytokines

  • Antigen-presenting cells recognize PAMPs

    • Same APC processes pathogens into specific pathogen-derived antigens and presents them with MHC encoded receptors to T-cells

    • T-cell responds only when presented with both signals

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


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Antimicrobial Peptides/Defensins

  • Four hundred peptides described to date

  • Defensins (3- 5-kD, four families in eukaryotes)

    • a-defensins (neutrophils and intestinal Paneth cells)

    • b-defensins (epithelial cells)

    • Insect defensins

    • Plant defensins

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

  • May also play a role in inflammation and wound repair


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Complement System

  • Three pathways now known

    • Classical

    • Alternative

    • Lectin or MBL pathway (binding to mannose-containing carbohydrates)

  • Host cells have complement regulatory proteins on their surface that protect them from spontaneous activation of C3 molecules


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Inflammatory Mediators in Innate Immunity

  • Cytokines secreted by phagocytes in response to infection include:

    • IL-1

      • activates vascular endothelium and lymphocytes

      • Increases adhesiveness of leukocytes

    • IL-6

      • Induces B-cell terminal maturation into Ig-producing plasma cells

    • IL-8

      • Induces expression of b2 integrin adhesion molecules on neutrophils, leading to neutrophil migration to infection site

    • IL-12

      • Activates NK cells and induces Th1-cell differentiation

    • IL-18

    • TNF-a

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


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Other Mediators and Molecules

  • Phagocytes

    • Toxic oxygen radicals

    • Peroxides

    • Nitric oxide (NO)

    • Lipid mediators of inflammation

      • Prostaglandins

      • LTB4

      • Platelet activating factor

  • Complement component C5a

    • Stimulates mast cells to release histamine, serotonin and LTB4

  • IL-1, IL-6 and TNF-a

    • Induce acute-phase response in liver

    • Induce fever

  • IL-1 and IL-18 signaling pathways activate NF-kB, important in innate immunity


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Immune Cells and Innate Immunity

  • Phagocytes

    • Neutrophils

    • Moncyte/macrophage

    • Eosinophils (to a lesser extent)

  • NK cells (large granular lymphocytes)

    • Antibody-dependent cell-mediated cytotoxicity (ADCC)

    • Have two major functions

      • Lysis of target cells

      • Production of cytokines (IFN-g and TNF-a)

    • Act against intracellular pathogens

      • Herpesviruses

      • Leishmania

      • Listeria monocytogenes

    • Act against protozoa

      • Toxoplasma

      • Trypanasoma


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Immune Cells and Innate Immunity (cont’d)

  • g/d T cells

    • Two types of T cell receptors

      • One composed of a and b chains (basic T cell antigen receptor)

      • One composed of g and d chains (minor population of T cells)

    • Two groups of g/d T cells

      • One group found in lymphoid tissues

      • One group located in paracellular space between epithelial cells

        • Recognizes unprocessed target antigen in absence of APC help

  • B-1 cells (minor fraction of B cells, do not require T-cell help)

  • Mast cells

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

    • Capable of phagocytosis

    • Process and present antigen using MHC class I or II receptors

    • LPS can directly induce release of mast cell mediators

    • Complement (C3a and C5a) induce mast cells to release mediators

      • Chemotaxis, complement activation, inflammation

      • TNF-a secreted by mast cells results in neutrophil influx into infected site


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Summary of Innate Immunity

  • External and mechanical barriers

  • Receptors for pathogen motifs

  • Soluble antimicrobial proteins

  • Pattern of cytokines produced influences adaptive response


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