Microbiology 532: Immunology

1. 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: lopatin@umich.edu

2. 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

3. Lecture 1Immunology Introduction & Innate immunity

4. 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

5. 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

6. 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)

7. 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.

8. 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

9. Components of the immune system

10. 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

11. 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

12. 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

13. Distribution of Lymphoid Tissues

14. Response to Initial Infection

15. Stages of Response to Infection

16. Course of Typical Acute Infection

17. Innate Host Defense Mechanisms • Anatomic Factors • Mechanical Factors • Biochemical Factors

18. 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

19. 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

20. 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

21. 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

22. 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

23. Receptors • Almost all of biology occurs because recognition • Enzymatic action • Interactions between cells (cooperation/activation) • Communication between cells • Innate and adaptive immunity requires it

24. 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)

25. Typical PAMPs • Lipopolysaccharides • Peptidoglycans • Certain nucleotide sequences unique to bacteria • Other bacterial components

26. 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)

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. Summary of Innate Immunity • External and mechanical barriers • Receptors for pathogen motifs • Soluble antimicrobial proteins • Pattern of cytokines produced influences adaptive response