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Immune System Overview

Immune System Overview. Why an immune system?. We are outnumbered! Viruses and bacteria are everywhere! Humans offer limitless resources for pathogens Energy Reproductive potential Getting into the body isn’t easy!. Meet the enemy. Bacteria Free-living Not all are bad!

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Immune System Overview

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  1. Immune System Overview

  2. Why an immune system? • We are outnumbered! Viruses and bacteria are everywhere! • Humans offer limitless resources for pathogens • Energy • Reproductive potential • Getting into the body isn’t easy!

  3. Meet the enemy • Bacteria • Free-living • Not all are bad! • Pathogenic ones produce toxins that damage human tissue • Viruses • Obligate parasites • Hijack human cells; convert to virus-producers, killing host cell in the process • (And fungi, protozoa too…)

  4. A human fortress • Skin is thick – hard to penetrate • Produces substances that deter invasion: • Skin pH (not favorable) • Mucus (sticky trap) • Lysozymes (digest bacteria) • Specialized traps around vulnerable areas (Eyes, noes, mouth) • Cilia sweep away invaders that are trapped • Stomach acid kills ingested invaders

  5. …but we do get sick! • Enter through weak points: • Food • Nose • Break in skin/scrapes • Cells are damaged/destroyed • Dying cells release distress chemicals (histamine) • Triggers inflammation (blood vessel dilation, increased blood flow) • Draws defensive cells to area (generalized white blood cells)

  6. How do we tell “friend” from “foe”? • All cells present antigens– surface protein molecules that identify identity • (antigen = antibody generator) • Immune system reacts to foreign antigens

  7. A complex system! Several “lines” of defense: • Barriers (First line of defense) • Generalized defenders (Second line of defense) • Specific defenders AND memory (Third line of defense) Consist of: • Several types of cells • Proteins

  8. The Complement System • Part of second line of defense • Free-flowing proteins found in blood • Quickly reach site of invasion • React to antigens • When activated, can • Trigger inflammation • Attract “eater cells” (macrophages) • Coat pathogen (make macrophages’ job easier) • Kill intruder directly

  9. Phagocytes • Find and “eat” bacteria, viruses, dead/injured body cells by phagocytosis • 3 types: • Granulocytes • Macrophages • Dendritic cells

  10. Granulocytes • Often first to site of infection • Numerous • Short lifespan • “Pus” in infected wounds chiefly composed of granulocytes

  11. Macrophage • “Big eaters” • Slower to respond to invader than granulocyte • Larger, longer-lived, more capable • Help alert rest of immune system to invader • Start as monocytes; become macrophages when entering bloodstream

  12. Dendritic cells • “Eater” cells • Help with immune system activation – act as antigen-presenting cells • Filter bodily fluids to clear foreign organisms and particles

  13. Lymphocytes • T and B cells • Originate in bone marrow • Migrate to lymph nodes, spleen, thymus to mature • Lymph vessels • transport, store lymphocytes • Feeds cells into body • Filter out dead cells/invading organisms

  14. Receptors • Each lymphatic cell contains surface receptors • Recognize foreign antigens as cells pass by… • Specialized for a particular antigen

  15. T cells – Cell-mediated immunity • Primary focus = infected cells • Two types: helper and killer • T = thymus (site of maturation)

  16. Helper T cell • Main regulator of third line of defense • Primary task: activateother cells (B and killer T cells) • Usually activated by macrophages/dendritic cells (during antigen presentation)

  17. Killer T cell • Directly attacks body cells infected by pathogen, cancer cells • Receptors used to determine if each cell encountered is self/non-self (compare to accepted receptors, MHC)

  18. B lymphocyte cell – Humoral immunity • Searches for intact antigens matching receptor • If a match is found… • Connects to antigen • Triggering signal set off… • T helper proteins help fully activate B cell • Produces 1000’s of clones: differentiate into plasma cells or B memory cells

  19. Plasma Cell • Produces antibodies • Responds to same antigen matched by B cell receptor • Seek out intruders, help destroy them • Release tens of thousands/second

  20. Antibodies • Y-shaped • Attach to matching antigens • Enhance phagocytosis of macrophages (label for capture) • Neutralize toxins • Incapacitate viruses (coat surface proteins) • Group pathogens by linking (agglutination)

  21. 5 types of antibodies (Ig’s):

  22. Memory cells • Prolonged lifespan • “Remember” specific intruders • Both B and T cells have memory cells • Helps trigger immune system to respond more quickly if invader reappears

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