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The Immune System

The Immune System. What are the major functions of the Immune System?. Regulation and Protection Fight disease Prevent future infections. What are the major components of the immune system?. Lymphatic System Leukocytes (White Blood Cells). What is a pathogen?. Any disease causing agent

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The Immune System

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  1. The Immune System

  2. What are the major functions of the Immune System? • Regulation and Protection • Fight disease • Prevent future infections

  3. What are the major components of the immune system? • Lymphatic System • Leukocytes (White Blood Cells)

  4. What is a pathogen? • Any disease causing agent • Ex: bacteria, viruses, parasites, toxins, fungi

  5. What is the difference between innate and adaptive immunity? • Innate immunity – target any pathogen (nonspecific); found in all organisms • Adaptive immunity – targets one specific pathogen (specific) – varies from individual to individual (genetics!)

  6. What are some examples of external innate defenses? (1st line) • Skin – water-proof barrier • Sweat • Tears • Cilia – respiratory tract • Mucous membranes • Acids in stomach • Commensal microbes living on the skin

  7. What are some internal vertebrate innate immune defenses? • Macrophages – large phagocytic white blood cells • Natural Killer (NK) cells – WBCs that target cancer cells • Interferons – proteins produced by viral infected cells to limit spreading of viral infection • Complement System - ~30 different proteins that circulate in the blood and can act together with other defenses

  8. How Interferons Work:

  9. Phagocytes • White blood cells that patrol the circulatory and lymphatic system • Engulf any material they do not recognize • Act as “Antigen Presenting Cells” following phagocytosis for possible specific response

  10. Inflammatory Response

  11. Inflammatory Response (2nd Line) • FUNCTION: to disinfect and clean injured tissues; prevent spreading of infection • Triggered by any damage to tissue • Can be localized or widespread • Results in Redness, Heat Production, Swelling • 1. Damaged cells release histamines (chemical alarm signals) • 2. Blood vessels dilate, blood flow to area increases, blood plasma passes out of blood vessels into interstitial fluid • 3. Phagocytes recruited by other complement proteins and engulf pathogens

  12. Why is the inflammatory response considered to be innate immunity? • The response is the same regardless of whether the invader has been previously encountered

  13. How is the lymphatic System involved in immunity and what are the major components? • Involved in innate and adaptive immunity • Network of vessels, lymph nodes (packed with WBCs), and lymph (fluid)

  14. What are the two major functions of the lymphatic system? • To return fluid from the interstitial spaces to the circulatory system (filtration) • To combat infection

  15. How does the lymphatic system aid in combating infection? • Lymph (fluid) carries microbes, parts of microbes, and toxins to the lymph nodes • Macrophages may engulf them • May trigger specific adaptive immune response

  16. What is adaptive immunity? • “custom-tailored” defenses to each specific invader • Provides a strong and long lasting defense

  17. What is an antigen? • Any molecule that elicits an adaptive (specific) immune response • Ex: parts of microbes, proteins on microbes, toxins, mold, pollen • Foreign Molecules!

  18. What are the two types of lymphocytes involved in adaptive immunity? • B-lymphocytes (B cells) – humoral immune response • T-lymphocytes (T cells) – cell-mediated immune response

  19. Which lymphocytes are responsible for the humoral immune response? • B-lymphocytes • Produce antibodies to fight against pathogens • Also produce memory cells

  20. What is an antibody? • “Y-shaped” protein produced by B-cells • Attaches to one specific antigen and helps counter its effects **One gene can synthesize millions of Different antibodies via alternative splicing**

  21. How is the “perfect” antibody found and produced? (clonal selection)

  22. Finding the perfect antibody… • Inside the lymph nodes… • Each B-cell is capable of producing a different antigen receptor (prior to exposure to any antigen) • B-cell antigen receptors “sample” antigens in the lymph nodes (does it fit?) • Only B-cells with reactive antigen receptors are allowed to divide (clonal selection) • Once the perfect match has been found, the B-cell undergoes rapid cell division, forming plasma cells, which produce and secrete 2,000 antibodies/second into the blood plasma (PROTEIN SYNTHESIS)

  23. Antibodies do not kill pathogens, what do they do? • Neutralization: bind to surface proteins preventing ability to infect; easily recognized by macrophages

  24. Antibodies do not kill pathogens, what do they do? • Agglutination: (clumping together); antibodies bind to the antigen on multiple cells; easy for macrophages to identify

  25. Antibodies do not kill pathogens, what do they do? • Precipitation: antibodies link dissolved antigen molecules together causing them to solidify; recognized by macrophages

  26. Antibodies do not kill pathogens, what do they do? • Activation of complement system: Complement proteins attach to foreign cell, and act together to poke holes in the membrane, causing the cell to rupture

  27. How does the production of memory cells help promote long lasting immunity? • B-lymphocytes (and some T-lymphocytes) produce memory cells which last for a very long time in the lymph nodes • Activated by a second exposure to the antigen to produce the antibodies to fight it • Stronger and faster response

  28. What is the purpose of a vaccine? How are vaccines produced? • To prevent infection from a specific pathogen by introducing the antigens of the pathogen to the immune system • Two types of vaccines: • Live-attenuated viruses (weakened) • Dead viruses

  29. What happens in your body when you receive a vaccination? • Humoral immune response is triggered • Production of antibodies and memory cells • **Why is it that vaccines do NOT always provide life-long lasting immunity?** • Mutations in the pathogens DNA changes their antigens, making the produced antibodies ineffective

  30. What is the difference between active and passive immunity? • Passive Immunity: receiving premade antibodies; short lasting • Ex: breastmilk, antibody injection; antivenom • Active Immunity: the person’s own immune system actively produces antibodies; long lasting • Ex: vaccine, natural exposure to a pathogen

  31. What types of cells are involved in the cell-mediated immune response? • Antigen-Presenting Cells (Macrophages/Phagocytes) • T-helper Cells • Cytotoxic T Cell (Killer T cells)

  32. What is the role of antigen-presenting cells in the cell-mediated immune response? • After ingesting a pathogen, APCs display antigens on their cell membrane • “Major Histocompatibility Complex” = self protein and foreign antigen • Expressed in all phagocytes, infected cells, and many cancer cells

  33. How do APCs activate T-helper cells? What do the T-helper cells do following activation?

  34. How do APCs activate T-helper cells? What do the T-helper cells do following activation? • T-helper cells interact with the “Major Histocompatibility Complex” on the APC (receptor recognition) • T-helper cells will then activate specific B cells and T cells

  35. How do cytotoxic T cells destroy infected cells? • Following recognition and bindingto the MHC/antigen complex on infected cells, T-cells will “shoot” a perforin complex into the membrane of cells which triggers cell death via lysis or apoptosis

  36. What about Allergies? • Immune response to non-pathogenic foreign molecules (allergens) • Inflammatory response activated (often in the respiratory system) due to release of histamine • Treatment: antihistamines, epinephrine

  37. What is an autoimmune disease? • Immune response to populations of body cells • Treatments: immunosuppressant drugs; alleviation of specific symptoms • Ex: Type 1 diabetes mellitus: cytotoxic T cells attack insulin producing cells • Ex: MS: T cells react against myelin sheath • Ex: Rheumatoid arthirtis: antibodies target cartilage and bone cells at joints

  38. HIV/AIDS • HIV destroys helper T cells – uses the cells as virus producing factories (~1,000 per day) and eventually killing the cell • Greatly impairs the humoral and cell-mediated immune defenses • AIDS patients are more susceptible to cancers and opportunistic infections • Rapid evolution of HIV complicates treatment

  39. Prokaryotes Immune Systems • Restriction Enzymes! • Cut up foreign DNA (of a bacteriophage) at specific restriction site sequences • Protect their own DNA by adding methyl groups to the same restriction sites (preventing cutting) • Bacteriophages have evolved mechanisms to evade this defense

  40. Prokaryotic Immunity • A: Restriction Enzyme is successful • B: Evolved mechanisms in bacteriophages to evade degradation

  41. Fungi and Plants Immunity • Rely on the production of a wide variety of chemicals that can cause unpleasant effects in would-be pathogens and predators

  42. Fungi – Death Cap Mushroom • If consumed, can cause irreversible liver failure in humans

  43. Fungi – Penicilium genus • Produce antibiotics (like penicillin) to protect against bacterial infections

  44. Plants – Defenses against Pathogens • First line of defense – physical barrier of epidermal cells • If that fails, plant cells are damaged by infection… • In response, plants… • Seal off the infected areas • Release microbe-killing chemicals to signal local cells to do the same -> infected and local cells induce cell death • Plant hormones also secreted to prevent systemic spreading of the pathogen to other parts of the plant AND to stimulate production of defense chemicals

  45. Figure 33.13B_s6 5 3 Signal transduction pathway Enhanced local response 1 Binding of the pathogen’s Avr protein to the plant’s R protein R protein 6 Additional defensive chemicals 4 Avirulent pathogen 2 Hormones Signal transduction pathway Avr protein Recognition between R and Avr proteins, leading to a strong local response Systemic acquired resistance

  46. Plant defenses against herbivores • Herbivores are animals that mainly eat plants. • Plants use chemicals to defend themselves against herbivores and pathogens. • Plants counter herbivores with • physical defenses, such as thorns, and • chemical defenses, such as distasteful or toxic compounds.

  47. Figure 33.13A_s5 Plant defense against herbivores 4 5 Wasp is attracted The wasp lays eggs 3 Synthesis and release of chemical attractants Plant cell 1 Damage to plant and chemical in caterpillar saliva 2 Signal transduction pathway

  48. Animals – Invertebrates - Insects • Innate Immunity Only (LACK adaptive immunity) • Examples of Physical Barriers: • Exoskeleton • Low pH • Lysozyme enzyme secretion to break down bacterial cell walls • Immune cells capable of phagocytosis • Production of antimicrobial proteins to help destroy invaders

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