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Lecture 19

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  • 1. Lecture 19: Immune System Covers Chapter 36
  • 2. The world is teeming with microbes!!! • When microbes cause disease, they are called pathogens. • Four types that can invade humans: – Bacteria – Viruses – Protists – Fungi
  • 3. Modes of Transmission • Direct Contact – Shake hands with someone who is sick • Indirect Contact – Touch a contaminated object: telephone, doorknob • Vector-Borne Transmission – Intermediate organism gives it to you: mosquitos (malaria), bat (rabies) • Inhalation – Someone sneezes on you • Ingestion – Usually food poisoning: salmonella (chicken), beef (E.Coli)
  • 4. The Lymphatic System • A large part of the Immune System is the Lymphatic System • Purpose of the Lymphatic System*: – 1.) Removal of excess fluid from the tissues (Conducting System) • Via lymph vessels, capillaries, ducts. Carries fluid back to heart from the body. – 2.) Production of immune cells (Lymphoid Tissue) • Made in Bone Marrow and Thymus Gland and housed in lymph nodes, spleen, nodes and glands
  • 5. thymus spleen bone marrow thoracic duct valve prevents backflow lymph node chambers packed with white blood cells lymph vessels lymph nodes The Lymphatic System Contains Much of the Immune System Fig. 36-5
  • 6. Lymph Node Close-up
  • 7. Lymphatic System Components • Tonsils: a specialized lymph node around the pharynx • Thymus gland: small gland in chest below breastbone. Lymphatic cells mature here • Bone Marrow: produces some lymphatic cells • Spleen: fist-sized organ on left side of body. It filters blood, exposing it to lymphatic cells stores and purifies blood, high concentration of lymph cells
  • 8. The Body’s Immune Response to Pathogens* • Three lines of defense: 1.) Non-specific External Barriers (skin and mucus membranes) 2.) Innate Immune Response (WBC’s, Proteins, Inflammation) 3.) Adaptive Immune Response (Lymphocytes: T cells and B cells)
  • 9. Levels of Defense Against Disease Fig. 36-1 If these barriers are penetrated, the body responds with If the innate immune response is insufficient, the body responds with Adaptive Immune Response cell-mediated immunity, humoral immunity Nonspecific External Barriers skin, mucous membranes Innate Immune Response phagocytic and natural killer cells, inflammation, fever
  • 10. 1.) Non-specific external barriers (Skin and Mucus Membranes)* • NON-SPECIFIC DEFENSE (does not distinguish one pathogen from another-fight all pathogens the same way) – Skin: low pH of skin & sweat from skin glands helps repel pathogens – Saliva, tears, & mucus membranes in respiratory/GI/urinary/reproductive tract secrete enzymes that: • Slow growth of pathogen • Break down pathogens • Trap pathogens so they can be washed out of body
  • 11. The Protective Function of Mucus Fig. 36-2 Bacteria trapped by mucus and cilia
  • 12. 2.) Innate Immune Response (WBC’S, PROTEINS, INFLAMMATION)* • Also a NON-SPECIFIC line of defense: If a pathogen gets through the first line of defense, then 2nd line goes to work: –TWO types of WBC’s –TWO types of proteins –The Inflammatory Response
  • 13. WBC’s* Macrophages: move through lymph fluid, kill pathogens through phagocytosis** (engulf & kill with enzymes then eject material.) Discarded material causes inflammation and swelling of lymph nodes when we are sick. Natural Killer Cells: kill human cells invaded by pathogens via cell lysis** (poke holes cell membrane and pump in enzymes to kill the cell.)
  • 14. The Attack of the Macrophages Fig. 36-3
  • 15. Proteins* Interferons: secreted by cells infected by viruses. They act as a coating on nearby healthy cells to protect them from getting attacked.*** Complement Proteins: circulate in the blood. They coat the surface of a pathogen, making it “easier” for the macrophage to see.**
  • 16. Inflammatory Response • Damaged cells release chemicals that start a cascade, resulting in – Redness, swelling and pain • Histamine relaxes smooth muscle in vessels, allowing more blood flow to area and causing capillary walls to become leaky: redness, swelling, pain – Macrophages attracted to the area of damage – Blood clotting (if skin broken)
  • 17. The Inflammatory Response
  • 18. 3.) Adaptive Immune Response Lymphocytes: T & B Cells • This is a SPECIFIC line of defense* • T & B cells go after specific pathogens* • T&B cells start as stem cells in Bone Marrow • B cells remain in bone marrow until mature then emerge • T cells leave bone marrow, travel to thymus gland to mature. Then they emerge.. • Mature T & B cells “hang out” in lymphatic system: lymph nodes, glands and spleen.
  • 19. How do T & B cells recognize pathogens* • Pathogens have unique molecules on their surface, which human immune cells can recognize. These molecules are called antigens (proteins, polysaccharides or glycoproteins). • B cells and T cells (and macrophages) have ANTIGEN RECEPTORS on their surface. They recognize antigens on surface of pathogens OR placed on the surface of an infected human cell (pathogens can “hijack” cells and “paste” an antigen on a human cell.) – The antigen receptors belonging to B cells are called antibodies. – The antigen receptors belonging to T cells are called T-cell receptors. – These receptors are y-shaped proteins whose “ends” serve as antigen receptor sites
  • 20. Antigen Receptors on T & B cells
  • 21. Antibodies on B Cells Fig. 36-7 (a) Antibody receptor function B cell antibody antigen m icrobe
  • 22. T cell receptor
  • 23. B-Cells: Antigen-Antibody Response Pathogen enters body and B-cell encounters it B cells kill mostly small pathogens (bacteria or fungi usually)* FOUR THINGS HAPPEN: • 1.) B-cell will cause destruction of pathogen.* B-cell antigen receptor (antibody) recognizes an antigen on the pathogen and this interaction signals complement to come in and coat the pathogen, making it a target for macrophage.
  • 24. B-Cells: Antigen-Antibody Response • 2.) B cell will be stimulated to replicate itself* at high numbers with the same antigen receptor (antibody) placed on the surface of the new B cells (called plasma cells)
  • 25. B-Cells: Antigen-Antibody Response • 3.) B cells secrete antibodies* (free-floating copies of the antigen receptor) • 4.) In addition, memory B-cells are created* so that a faster immune response will happen if pathogen attacks body again
  • 26. B Cell Antigen-Antibody Response Fig. 36-10 Invading antigens bind to antibodies on one B cell (dark blue) 1 The B cell “selected” by the antigen multiplies rapidly 2 A large clone of genetically identical B cells is produced 3 These B cells differentiate into plasma cells and memory B cells 4 Plasma cells release antibodies into the blood 5 endoplasmic reticulum memory B cell plasma cell antibodies antigensantibodies
  • 27. T Cells • T Cells- attack HUMAN CELLS that have been infected by microorganisms AND LARGE microorganisms (viruses usually)*
  • 28. T-Cells* • There are 3 different kinds: 1.) Cytotoxic T-cells • Virus enters one of our cells • VIRUS WILL PLACE ITS ANTIGEN ON SURFACE OF CELL • Cytotoxic T-cells recognize antigen and attack cell (punch holes & pump in enzymes) 2.) Helper T-Cells • Send chemical “message” to other Cytotoxic T-cells & B-cells about the presence of the pathogen 3.) Memory T-Cells • These cells are created for faster immune response if same pathogen attacks again
  • 29. T Cells Fig. 36-13, 1 of 2 B cell helper T cell cytotoxic T cell cytokines infected cell dendritic cell or macrophage antibody viral antigen Targets invaders outside cells (e.g., viruses, bacteria, fungi, protists, and toxins) Stimulate both humoral and cell-mediated immunity by releasing cytokines Targets defective body cells (e.g., infected cells and cancer cells), transplants HUMORAL IMMUNITY CELL-MEDIATED IMMUNITYHELPER T CELLS B-cell antibodies bind to viral antigens and stimulate the B cells to divide and differentiate Viral antigens presented on the surfaces of dendritic cells or macrophages, and infected cells T-cell receptors bind to viral antigens Cytokines released by helper T cells stimulate B cells and cytotoxic T cells virus
  • 30. T Cells Fig. 36-13, 2 of 2 memory cytotoxic T cell memory helper T cell memory B cell infected cell cytotoxic T cellplasma cell Plasma cells secrete antibodies into the blood and extracellular fluid Memory cells confer future immunity to this virus Cytotoxic T cells release pore-forming proteins that destroy infected cells B cell helper T cell cytotoxic T cell cytokines antibody Targets invaders outside cells (e.g., viruses, bacteria, fungi, protists, and toxins) Stimulate both humoral and cell-mediated immunity by releasing cytokines Targets defective body cells (e.g., infected cells and cancer cells), transplants HUMORAL IMMUNITY CELL-MEDIATED IMMUNITYHELPER T CELLS Cytokines released by helper T cells stimulate B cells and cytotoxic T cells