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Introduction to The Immune System • Pin Ling (凌 斌), Ph.D. ext 5632; [email protected] • References: 1. Male D., J. Brostoff, D. B Roth, and I. Roitt Immunology, 7th ed., 2006. 2. Abbas, A, K. et.al, Cellular and Molecular Immunology (6th ed., 2007), Chapters 1 & 2 Keys toward Learning Immunology • Lectures => Deliver the “Key Concepts” of Immunology. 1. What we teach is the current knowledge about • Workbook => Apply the “Knowledge” from Immunology. Immunology to the “Solutions” of clinical 2. Some may stand forever and Some may change in the problems. future. • SoTextbook reading learn theOne to 3. Keep your mind Open! => You Help could be the next details and build up the comprehensive make a breakthrough in Immunology. knowledge of immunology Outline • The Origin of the Immune Concept • Overview of Immunity to Microbes • Features & Components of Innate & Adaptive Immunity • Summary & Question The Origin of Immune Concept-I 1. The term “Immunity” => Latin word “Immunitas” => Protection from legal prosecution (Roman senators) Biological definition => Protection from infectious diseases 2. The concept of immunity => existed in ancient Greek & Chinese => Vaccination the experienced viewcalled Immunization) Vaccinia => (also 3. The scientific view of immunity => Edward Jenner (1796) Observation => Milkmaids generally get No Smallpox Hypothesis => Pus from vaccinia (cowpox) => Protect milkmaids from smallpox Test => Inoculate materials from cowpox pus => Protect a young boy from smallpox (Protective immunity) The Origin of Immune Concept-II 4. The concept of “Immunity” developed gradually over time through many scientific findings: => Robert Koch (1905 Nobel Laureate) => Infectious diseases caused by microorganisms => Louis Pasteur => Vaccines against cholera & rabies => These clinical successes => The search of underlying mechanism of “Protection of Infectious Diseases” => The development of “Immunology” 5. Advances in technology (e.g., Cell culture, Monoclonal Ab, Flow cytometry, Genetic engineering…etc) have facilitated our understanding of the immune system and its functions. “Descriptive Science” => “Experimental Science” The first vaccination against smallpox Exudate from a cowpox pustule on the hand of milkmaid Sarah Nelmes was inserted into scratches on the arms of James Phipps, May 14, 1796. Adopted from www.ebinrushed.com/history/images/history_7.jpg Eradication of smallpox Edward Jenner Vaccines for common infectious diseases Still no effective vaccines for many infectious microbes, e.g., HCV, HIV, Dengue virus…..etc Outline • The Origin of Immune Concept • Overview of Immunity to Microbes • Features & Components of Innate & Adaptive Immunity • Summary & Question Intracellular & extracellular pathogens Immune responses are adapted to different types of pathogen. Key concepts about immunity-I 1. The immune system has evolved to serve two major functions: (1) Protect against the invading pathogens (or foreign substances) (2) Maintain tissue homeostasis (damaged cells or cancer). Meanwhile, microbes (outside) and tumors (inside) have evolved to survive in the host. 2. The immune system (in mammals) consists of (1) Innate immunity and (2) Adaptive immunity => An integrated system of host defense => Cells & molecules function cooperatively Antigen-presenting cells => Lymphocytes => Effector cells 3. Innate immunity is evolutionally the more conserved host defense system: (1) Existed in both Invertebrates & Vertebrates; (2) Provides the first line of defenses against infections, and (3) “Activates” and “Programs” adaptive immune responses Key concepts about immunity-II 5. Adaptive immunity evolved later: - Existed only in Vertebrates - Provides the more potent and diverse defenses against infections - Develops as a response to infection and adapts to the Better Understanding of Immunology infection Help manipulate immune responses 6. The immune may problems fail => Immunodeficiency, Solve thesystem medical Hypersensitivity, & Autoimmune diseases. 7. Normal immune responses can be obstacles in medical cases, e.g., organ transplantation Overview of immune responses Innate vs Adaptive immunity The immune system has the ability to recognize some self components: - The Normal condition => prevent self-recognition - The “Pathological Conditions” => occur self-recognition Phagocytosis by innate immunity-I 1. Cells w/ phagocytic ability: Macrophage, Neutrophil, & Dendritic cells. 2. Phagocytosis serves two key functions: (1) Killing microbes (2) Antigen (Ag) Presentation Elie Mechnikoff:The Pioneer of Innate Immunity 1. The Discovery of Phagocytes & Phagocytosis 2. The Nobel Laureate in Medicine 1908 Adopted from Nature Immunology, July 2008 Paul Ehrlich: One of the pioneers of humoral adaptive immunity 1. The Discovery of Antibody functions 2. The Nobel The development of modern Immunology in 20th century Laureate in mainly centers on understanding the Adaptive Medicine 1908 Immune System. Adopted from Nature Immunology, July 2008 Interaction between innate and & adaptive immunity 1. Innate immunity => Ag presentation (by Dendritic cells) 2. Adaptive immunity => Ag recognition (by T & B lymphocytes) Interaction between innate and & adaptive immunity 1. Innate immunity => Ag presentation (by infected cells) 2. Adaptive immunity => Ag recognition (by T & B lymphocytes) Overview of adaptive immune responses Outline • The Origin of Immune Concept • Overview of Immunity to Microbes • Features & Components of Innate & Adaptive Immunity • Summary & Question The principle cells of the immune system Cellular components of the immune system will be discussed extensively in Lecture #2. Features of Adaptive immunity (107 ~ 109) (vaccination) Specificity, Memory, and Homeostasis of Adaptive Immunity Principle of Vaccination Clonal expansion of lymphocytes Antigens, Epitopes, & Antibodies 1. Antigens (immunogens) initiate adaptive immune responses. 2. Antigens may contain several different Epitopes for recognition by lymphocyte receptors or antibodies Types of adaptive immunity 1. Humoral immunity => Molecules in body fluid, e.g. Antibody (Ab) => Key player => B cells => Target extracellular microbes & toxins 2. Cell-mediated immunity => Key player => T cells => regulate other immune cells => Target intracellular microbes, e.g. viruses, bacteria Functions of different types of lymphocyte Active vs. Passive immunity Active immunity => A host response to a microbe (Ag) => specific and long-term immune defense (memory) Passive immunity => Adoptive transfer of Ab or lymphocytes specific for a microbe (or Ag) => specific, instant but transient immune defense Serum therapy => Humoral immunity & Passive immunity Serum (Ab) from animals recovered from diphtheria infection => Naïve animals => Resistant to diphtheria infection Innate vs. Adaptive Immune Recognition Adaptive immune recognition: 1. Antigen (Ag) receptors on T & B lymphocytes. 2. These Ag receptors generated by “somatic gene recombination” 3. They recognize diverse Antigens (peptides) from microbes or non-self. Innate immune recognition: Q: How do host cells recognize invading pathogens at the first place? Scientists have no answer to this until the end of the 20th century. The “Renaissance” of innate immunity In 1989, Janeway => Immune recognition of microbes => Detection of conserved molecular patterns, referred to PAMPs (Pathogen-Associated Molecular Patterns) with features: Charles A. Janeway, M.D. Yale Univ. 1. Invariant among a given class of microbes. 2. Have essential roles in microbial physiology. 3. Recognized by receptors of the innate immune system, called PRRs (Pattern-Recognition Receptors). 4. Innate immunity regulates adaptive immunity The Discovery of Toll and Toll-like receptor (TLR) Cell. 1996 Sept 20; 86(6):973-83 The dorsoventral regulatory gene cassette spatzle/Toll/cactus controls the potent antifungal response in Drosophila adults. Lemaitre B, Nicolas E, Michaut L, Reichhart JM, Hoffmann JA. Institut de Biologie Moleculaire at Cellulaire, UPR 9022 du Centre National de la Recherche Scientifique, Strasbourg, France Nature 388, 394 - 397 (24 July 1997) A human homologue of the Drosophila Toll protein signals activation of adaptive immunity. Medzhitov R, Preston-Hurlburt P, Janeway CA Jr. Section of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA. Key concepts in innate immunity 1. The innate immune system mainly recognizes common structures shared by classes of microbes, => Pathogen Associated Molecular Patterns (PAMPs), e.g., LPS, Peptidoglycan, Microbial DNA & RNA. 2. Host receptors that recognize PAMPs are called PatternRecognition Receptors (PRRs), which are encoded in “Germline” DNA=> limited Diversity. 3. Innate immunity not only provide the first line of defenses but link to the program of adaptive immunity. 4. PRRs may also recognize components from injured or dead host cells => Autoimmune diseases Toll-like Receptors Locations of Different PRRs Body fluids -Soluble PRRs Cellular PRRs - Cell surface - Endosomes - Cytosol Soluble Pattern Recognition ReceptorsComplement activation pathways Functions of Complement Epithelial barriers prevent the entry of microbes Failure of the immune system 1. Ineffective response - Immunodeficiency 2. Overactive response - Hypersensitivity 3. Auto-reactive response - Autoimmunity Outline • The Origin of Immune Concept • Overview of Immunity to Microbes • Features & Components of Innate & Adaptive Immunity • Summary & Question SUMMARY 1. Protective immunity against microbes is mediated by the early response of innate immunity and the later response of adaptive immunity. 2. Innate immune responses are initiated by recognition of common microbial structures (PAMPs) by PatternRecognition Receptors (PRRs) on innate immune cells. - Provide the first line of host defense - Activate and regulate the adaptive immunity 3. Adaptive immune responses are initiated by recognition of foreign antigens by specific lymphocytes. - Provide more potent, specific (Ag), & broad protection - Develop immune memory for the next exposure - Feedback regulate innate immunity Questions 1. Why is it necessary to vaccinate against tetanus only every 10 years, though antibodies against the toxoid disappear from the circulation within a year? 2. Why is the vaccine against tetanus always effective, whereas the vaccine against influenza protects on some epidemics but not others? The End & Thank you Phagocytosis during innate immunity-II Inflammation: 1. A “Hallmark” of innate immune response (Call for help) 2. Local accumulation of immune cells & molecules against microbes 3. Function to eliminate infections but often cause tissue damage & diseases 4. Link to the development of many diseases, e.g., Cancer, Cardiovascular disease, ….etc.