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The Immune System

The Immune System. Primary Functions. The immune system provides a series of layered defenses against pathogen s including: -bacteria -viruses -tumors -parasitic worms -fungi -protozoa. Pathogen = any disease causing agent. Key Culprits: Bacteria and Viruses.

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The Immune System

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  1. The Immune System

  2. Primary Functions • The immune system provides a series of layered defenses against pathogens including: -bacteria -viruses -tumors -parasitic worms -fungi -protozoa Pathogen = any disease causing agent

  3. Key Culprits: Bacteria and Viruses • Bacteria are single celled microbes which exist almost everywhere. Much smaller than eukaryotic cells, bacteria can replicate very quickly.

  4. Believe it or Not… • There are about 10 million bacteria cells on the palm of you hand right now!

  5. A Generic Bacterium

  6. Key Culprits: Bacteria and Viruses • Unlike bacteria, viruses are non-living infectious protein complexes which can only survive and reproduce inside a host cell.

  7. What is a “Virus?” • Viruses are microscopic particles composed of a DNA or RNA core wrapped in a protein coat. • Most viruses are so small, they require a powerful electron microscope to be seen. • Simple in design, viruses can contain anywhere from a few to over 100 genes.

  8. Viruses:Gaining Entrance via the Capsid • A viruses protein coat is called the capsid. The capsid contains specialized proteins designed to bind to receptor sites on host cells, tricking them to allow access inside…

  9. Virus Structure

  10. Viruses:Hijacking the Host Cell • Once inside the virus then “hijacks” the host cell, using its machinery to transcribe and translate its genetic information and make new viruses.

  11. Viruses: Highly Specialized Invaders • Because viruses must bind so precisely to specific proteins on cell surfaces, and then use the host’s genetic system to replicate themselves, most viruses are highly specific to the cells they infect. • Plant viruses infect plant cells • animal viruses only infect specific species of animals • bacterial viruses only infect specific kinds of bacteria (these are called bacteriophages)

  12. Viruses:2 Types of Infection Strategies • There are 2 slightly different means by which viruses invade & replicate inside host cells. These include “lytic Infection,” and “Lysogenic Infection.”

  13. Retroviruses: Working Backward… • When a virus contains RNA instead of DNA as its genetic blueprint, it is called a retrovirus. These viruses work backward inside the host cell by producing a DNA copy of their RNA, then incorporating it into the host cell’s DNA. • HIV is a retrovirus • Many retroviruses are linked to cancer in humans and other animals

  14. Viruses: Living or Nonliving? • Because of their unique characteristics, viruses are often debated as to whether they’re living or non-living entities… Can you explain the opposing arguments?

  15. In Summary…

  16. Organs of the Immune System • Thymus– glandular organ near the heart – where lymphocytes learn their jobs • Bone marrow – Phagocyte producing tissue located inside certain bones • Spleen– serves as a filter for the blood by removing old and damaged red blood cells • Lymph nodes/ vessels – Storage sites for immune cells, dead cells, and other immune components.

  17. The 1st Line of Defense: The Innate Immune System • Your skin prevents nearly all pathogens from entering, however sometimes they find a way…. • When this happens, an immediate, non-specific cellular response is triggered.

  18. Challenge Question: • What is the name of the water resistant oily substance on your skin that keeps it dry and largely microbe free?

  19. The 2nd Line of Defense: The Innate Immune System cont. • Phagocytes (made in bone marrow) recognize surface proteins on pathogens called antigens and destroy them. • 2 main types include macrophagesand Granulocytes…

  20. The 2nd Line of Defense: The Innate Immune System cont. • Granulocytes(also called neutrophils)are the first to attack foreign invaders, they recognize pathogens and “eat” until they die. • These cells make up 50-70% of your total “white” Blood cell count.

  21. The 2nd Line of Defense: The Innate Immune System cont. • Macrophagesare phagocytes which engulf and destroy pathogens as well as dead cell remains.

  22. Signs You’ve Triggered an Immune Response… • Redness, soreness, inflammation, and/or the presence of “pus” all indicate that phagocytes are present and doing their job.

  23. The 3rd (and final) Line of Defense:The Adaptive Immune System • When the phagocytes cannot overcome a pathogen, a new line of immune cells become involved called lymphocytes. • Unlike the passive immune response, Adaptive immunity is permanent, pathogen specific, and involves the production of antibodies.

  24. The 3rd (and final) Line of Defense:The Adaptive Immune System • There are 2 categories of lymphocytes generated in bone marrow: B Cells and T Cells (these mature in the Thymus). There are different types of each.

  25. The Adaptive Immune System B-Cells: 2 Types • Plasma B Cells- These lymphocytes (partially activated by macrophages) recognize antigens on foreign invaders and create antibodies which attach to pathogens and target them for destruction. antibody B Cell Pathogen Antigen

  26. The Antibody: A Closer Look The top portions of antibodies are highly variable and pathogen-specific (they bind tightly to foregin antigens like a lock and key). The heavy chain region at the base of the molecule is much more generic.

  27. The Adaptive Immune System B-Cells: 2 Types • Memory B Cells are Long-lived cells (they can persist for 10 years on average) that reside in lymph nodes and “remember” certain antigens and can react quickly in response to a future exposure.

  28. You have millions of unique Memory B Cells working for you every day!

  29. Memory B Activation A Naïve B cell has never been exposed to a foreign antigen and will become either a plasma B cell or a Memory B cell when “Activated.” T Cells and cytokines play an important role in activating and designating B Cell activities.

  30. The Adaptive Immune System T-Cells: 3 Types • Helper T Cells- Although they cannot kill microbes directly, these cells are crucial in activating and directing B-cells as well as maximizing the efficiency of macrophages. • These cells themselves must be activated…

  31. Macrophage

  32. Did you Know?... • T Cells can both activate and stop B cells from generating antibodies.

  33. The Adaptive Immune System T-Cells: 3 Types • Killer T Cells- Also called cytotoxic T-Cells, these lymphocytes target and destroy virally infected cells and tumor cells

  34. The Adaptive Immune System T-Cells: 3 Types Suppressor T Cells Slow down and/or regulate the activities of B and T cells once the infection is under control. Slowing down or stopping cell division and antibody production.

  35. In Summary…

  36. Initiating an Immune Response… Cytokines are small, simple ‘cell-signaling’ proteins that are secreted by the glial cells of the nervous system as well as various immune cells. The term "cytokine" is a general term for any immunomodulating agent, 2 key cytokines include interleukins and interferons. These are key in activating phagocytes to respond to local infections.

  37. Special Immune Cells: Natural Killer Cells Similar to Killer T cells, Natural Killer cells recognize and respond to virally infected cells and/or tumor cells. They do not bind to MHC or antibodies to function, they simply recognize and destroy “Stressed” cells that are not functioning properly.

  38. Special Immune Cells: Dendritic Cells As “antigen-presenters,” Dendritic Cells activate T Cells as messengers between the innate and the adaptive immune systems. Dendritic cells reside in tissues that are in contact with the external environment, such as the skin (where they are called “Langerhans cells”) and the epithelial lining of the nose, lungs, stomach and intestines.

  39. Did you Know?... • HIV attacks and kills Helper T Cells, significantly weakening the lymphatic response to infection.

  40. Being “Sick”…. • Typical symptoms like inflammation, stuffy nose, sore throat, and fever are a result of the body’s immune system trying to “get rid” of invading pathogens; not the pathogens themselves!

  41. Antibiotics • Antibiotics are compounds which kill or inhibit the growth of bacteria. They are prescribed to aid the immune system in either to fighting or preventing infection.

  42. Allergies An allergy is an exaggerated immune response or reaction to substances that are generally not harmful.

  43. Allergies and Histamines Histamines are molecules involved in local, innate immune responses. These simple molecules trigger an immediate inflammatory response to pathogen exposure. Histamines are produced by specialized granulocytes called basophils, and by mast cells found in connective tissues. Histamine increases the permeability of the capillaries to white blood cells, allowing them better access to pathogens. When triggered, mast cells, initiate a cascade of cellular processes which result in an ‘allergic’ response.

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