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The Immune System

The Immune System. AP Biology Unit 6. Types of Immunity. Innate Immunity = non-specific protection against many different microbes Acquired Immunity = specific protection against microbes. Nonspecific Defenses. Target a wide range of pathogens (non-specific foreign body)

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The Immune System

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  1. The Immune System AP Biology Unit 6

  2. Types of Immunity • Innate Immunity = non-specific protection against many different microbes • Acquired Immunity = specific protection against microbes

  3. Nonspecific Defenses • Target a wide range of pathogens (non-specific foreign body) • Examples include: skin, mucous membranes, inflammatory response, phagocytic cells

  4. Nonspecific Defenses: Lymphatic System • “filters” interstitial fluid and blood continually • immune system cells in the lymph (in lymph nodes) take care of foreign particles and microbes

  5. Phagocytosis • phagocytes are white blood cells (leukocytes) that ingest microbes • neutrophils and macrophages are the most common

  6. Antimicrobial Proteins • Complement System • Series of 30 proteins that are usually present in the blood (inactive) • Activated when microbes are present (by molecules on the surface of microbes) • Creates a cascade of reactions  results in the microbe cells bursting • May also trigger inflammatory response (by attracting phagocytes)

  7. Antimicrobial Proteins: Interferons • Secreted by cells infected by viruses • Causes nearby cells to inhibit viral reproduction/replication • Not virus-specific • Because of these, you aren’t as likely to get 2 viral diseases at the same time

  8. Inflammatory Response • A non-specific way to protect tissues from possible infection by destroying invading bacteria

  9. Signs of Inflammation • Redness • Due to the dilation of blood vessels • Swelling • Due to extra fluid in the area • Heat • Due to dilation of blood vessels (increased blood flow) • Pain • Extra fluid presses on nerves

  10. Inflammatory Response • Chemokines are small proteins that guide macrophages and signal them to increase lysosome contents

  11. Natural Killer Cells • Recognize virus-infected cells and cancer cells • They directly release lethal chemicals, leading to apoptosis Image taken without permission from http://www.news.utoronto.ca/images3/killercells.jpg

  12. Specific Defenses • Antigen = foreign body recognized by acquired immune system • Examples of antigens include viruses and bacterial toxins • Antibodies in the immune system bind antigens

  13. Specific Defenses • B cells and T cells are lymphocytes with receptors that each recognize a specific antigen. • Ex. Specific B and T cells recognize the cold virus, but not the chicken pox virus. • After recognizing the specific antigen, certain cells are activated to eliminate that antigen or infected cells

  14. B and T Cell Receptors • The receptors on B and T cells and antibodies are formed from the random rearrangement of gene segments • Like different combinations of the letters in the alphabet make different words

  15. Humoral Immune Response • Involves the actions of antibodies • Antibodies • Proteins also known as Immunoglobulins • Tremendous Diversity—there are thought to be millions (1015) of different specific antibodies

  16. B cells • Each B cell has a different antigen receptor on it- recognizes specific antigen only • Mature in the bone marrow • Differentiate to become Memory cells or Plasma (Antibody-Secreting) cellsafter binding to the appropriate antigen

  17. B cells • “Anti-self” cells are destroyed before fully differentiating (Clonal Selection) • This has to occur since the antigen receptors are formed from RANDOM gene rearrangements  could accidentally produce a receptor that recognizes a body cell/molecule • Autoimmune diseases result when clonal selection fails

  18. Steps of the Humoral Response • Macrophage presents antigen on Class II MHC and binds to Helper T Cell • MHC proteins are on the surface of cells and bind antigens

  19. Steps of the Humoral Response 2. Helper T Cell & Macrophage secretes cytokines Cytokines activate Helper T Cells

  20. Steps of the Humoral Response 3. B cell with specific antibody binds to antigen (at the same time Helper T cells are being activated) 4. Cytokines activate B cell to divide and differentiate into: Plasma Cells and Memory B cells 5. Antibodies combine with antigens all over body and help to facilitate phagocytosis

  21. Plasma Cells • Secrete loose antibodies into the bloodstream • Like antibody factories  • Plasma cells have a lot of ribosomes and Rough ER– WHY? • Antibodies are proteins  these are the organelles needed for protein synthesis & secretion

  22. Image taken without permission from http://bcs.whfreeman.com/thelifewire/default.asp?s=&n=&i=&v=&o=&ns=0&uid=0&rau=0

  23. Actions of Loose Antibodies • Surround virus/bacteria  prevent it from binding to and infecting cells • Antibodies can bring together multiple bacteria or antigens, making them much larger  more noticeable for destruction by macrophages or phagocytes – clumps them together

  24. Cell-Mediated Response • Involves the action of Cytotoxic T Cells • Eliminates infected cells, cancer cells, and transplanted cells Slide 24 of 46

  25. T cells • Arise from lymphocytes maturing in the thymus gland • Differentiate to become Cytotoxic T Cell or Helper T Cell • Helper T cells also participate in Humoral Response • Differentiate to become Memory cells or Effector cells • Effector cells will act immediately, memory cells act later if the microbe returns Slide 25 of 46

  26. T Cells • The receptors on each T cell are specific to an antigen • T cell receptors can also recognize antigen fragments Slide 26 of 46

  27. Steps of the Cell Mediated Response • Infected cell presents antigen on Class I MHC • Cytotoxic T Cell recognizes antigen and binds to it Slide 27 of 46

  28. Steps of the Cell Mediated Response 3. Cytotoxic T Cell reproduces (clones itself) 4. Cytotoxic T Cells bind to antigen bound to infected cells and release perforin to lyse infected cells Slide 28 of 46

  29. Primary versus Secondary Response • Primary Response = initial immune response to antigen • Secondary Response = immune response when exposed the same antigen a second time (carried out by Memory cells) Slide 29 of 46

  30. Primary vs. Secondary Response • The secondary response is much faster than the primary response • More antibody & T cell production in a shorter amount of time Secondary Response Primary response Slide 30 of 46

  31. Helper T cells • Participate in both the Humoral and Cell-Mediated Immune Responses • the HIV virus attacks Helper T cells Slide 31 of 46

  32. Immunizations • Active immunity = immunity due to exposure to an antigen (produces memory cells) • Immunizations (vaccinations) allow an individual to develop active immunity to an antigen without actually getting “sick” during initial exposure • Vaccines are usually made up of weakened viruses or microbes Slide 32 of 46

  33. Immune Responses to Donor Tissue • There are 3 kinds of antigens associated with blood: A, B, and Rh • Antibodies are produced that react to the wrong blood type (Anti A and Anti B) • This causes agglutination (clumping of RBCs) and lysis (bursting) of RBCs which can lead to serious conditions Slide 33 of 46

  34. Blood Donors and Recipients • What blood type is the Universal donor? • Type O  does not have any surface antigens (A or B) so the donor’s body will not attack it • What is the blood type of the Universal recipient? • Type AB  no anti A or B, so it won’t attack any of the other blood cells Slide 34 of 46

  35. Rh factor • The Rh factor is another surface protein that is found on the surface of red blood cells • An individual either has the Rh factor on RBC (+) or doesn’t (-) – genetically determined • Individuals who are Rh- will produce antibodies that attack Rh+ cells • This is particularly dangerous if a mother is Rh- and her fetus is Rh+ (she produces antibodies against Rh) Slide 35 of 46

  36. Tissue Donors • In tissues, the body looks at MHC molecules to identify self from non-self. • What is the best source of tissue you might need for a transplant? • Yourself  or someone very closely related to you (identical twin would be ideal) Slide 36 of 46

  37. Allergies • When the immune system “overreacts” or becomes hypersensitive to certain antigens • Most allergies involve the actions of IgE antibodies • This causes mast cells to release histamine Slide 37 of 46

  38. Allergies • Histamine triggers inflammatory responses  leads to allergy symptoms such as runny nose, tearing eyes, etc. • Many allergy medicines are antihistamines to block the receptors for histamine Slide 38 of 46

  39. Autoimmune Disorders • When the immune system fails to recognize a body cell as a self cell and attacks it • Could be due to a failure in clonal selection • Examples include: • Lupus (attacks a variety of body cells) • Rheumatoid Arthritis (attacks cartilage and joints between bones) • Type I Diabetes (attacks beta cells in pancreas that produce insulin) • Multiple Sclerosis (attacks myelin sheaths on nerves) Slide 39 of 46

  40. HIV: the Basics • The Human Immunodeficiency Virus attacks Helper T Cells • HIV progresses to AIDS when white blood cell counts reach a certain low • HIV is a retrovirus (RNA is the nucleic acid inside) Slide 40 of 46

  41. HIV: the Basics • Mutations to the HIV surface antigen occur each time the virus replicates, which is why finding a cure is difficult. • Drugs can help slow HIV reproduction but some drug resistant strains have now been generated from mutations during viral replication Slide 41of 46

  42. ELISA • ELISA = Enzyme Linked Immunosorbent Assay • This is a test that detects the presence of specific antibodies in the blood to determine if an individual has a certain condition • Ex. If the person was infected with Swine flu then they would have lots of specific antibodies against swine flu in their bloodstream (from the humoral response) Slide 42 of 46

  43. ELISA antigens • The ELISA plate is coated with antigens specific to the antibody being tested for (ex. Chicken pox) • Blood is added that may contain the antibodies (present only if the person has the disorder) • Only the specific antibody will bind to the antigen on the plate Slide 43 of 46

  44. Secondary Antibody After washing ELISA • Unbound antibodies are washed away • A secondary antibody (anti antibody) is added that will bind to the antibody already bound to the antigen • The secondary antibody has an enzyme attached to it Slide 44 of 46

  45. ELISA • After washing away unbound secondary antibody, a substrate is added • If there is secondary antibody in the well (bound to the antibody), there will also be enzyme present to break apart the substrate • Breaking apart the substrate causes a color change  antibody present Slide 45 of 46

  46. ELISA and Pregnancy tests • Home Pregnancy tests use the same principles as home pregnancy tests. Slide 46 of 46

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