Understanding the Immune System: Types, Functions, and Importance

1. Warm-Up (Review) • Compare bacteria vs. viruses. • When you think about your immune system, what are 5 words that come to your mind? • Think about this year’s flu epidemic. Why didn’t getting the flu shot last fall help many people who got sick with the flu?

2. Chapter 35 Warm-Up Define the following terms: • Pathogen • Antigen • Antibody • Allergen • Vaccine

3. Ch. 35 Warm-Up • What is the difference between innate vs. adaptive immunity? • Where are B and T cells produced and matured? • What is the role of antigen-presenting cells?

4. Ch. 35 Warm-Up • Contrast the functions of B cells and T cells. • What are memory cells? • How do vaccines work? • How does HIV affect the immune system?

5. THE IMMUNE SYSTEM Chapter 35

6. Gross Science:Everything you didn’t want toknow about SNOT Running time: 4:25 min

7. Types of Immunity

8. Plant Defenses • Nonspecific responses • Receptors recognize pathogen molecules and trigger defense responses • Thicken cell wall, produce antimicrobial compounds, cell death • Localize effects

10. Innate Immunity (Nonspecific)

11. Barrier Defenses: • Skin • Secretions (pH 3-5 hostile condition) • Mucous membranes • Lysozyme (digestive enzyme in tears, saliva, mucus) • Antimicrobial Proteins: • Interferons (inhibit viral replication) • Complement system (~30 proteins, membrane attack complex  lysis) Innate Immunity (non-specific) • Natural Killer Cells: • Kill virus-infected and cancer cells • Inflammatory Response: • Macrophages release cytokines (signal molecules) • Mast cells release histamine • Blood vessels dilate, increase permeability (redness, swelling) • Deliver clotting agents, phagocytic cells • Fever • Phagocytic WBCs: • Neutrophils (engulf & destroy) • Macrophage (“big eaters”) • Dendritic cells (stimulate adaptive response) • Eosinophils (fight parasites)

12. Inflammatory Response

13. TLRs • Toll-like receptors (Toll: innate immunity activator in insects) • Binds to fragments of molecules from foreign pathogens • Increase efficiency of phagocytosis

14. Phagocytosis • Engulf and destroy • Video: White blood cell chasing bacteria

15. Bone marrow = blood cell & platelet production Main production areas = pelvis, femur, sternum (RBC) (platelets)

16. The Immune System Explained Running time: 6:48 min

17. Adaptive Immunity (Specific)

18. Lymphatic System: involved in adaptive immunity

19. Adaptive Response Lymphocytes (WBCs): produced by stem cells in bone marrow • T cells: mature in thymus • helper T, cytotoxic T • B cells: stay and mature in bone marrow • plasma cells  antibodies

20. Antigen: substance that elicits lymphocyte response

21. Antibody(immunoglobulin – Ig): protein made by B cell that binds to antigens

22. B and T Cell Diversity • Millions of differentB and T cells are produced by the immune system • Each unique cell has a specific antigen receptor

23. How different antigen receptors are made

24. Origin of Self-Tolerance • Undifferentiated B cell: • Ig (antibody) gene: DNA rearrangement + alternative splicing = different antigen receptors! • 1 million different B cell antigen receptors • 10 million different T cell antigen receptors • As lymphocytes mature in bone marrow or the thymus, they are tested for self-reactivity • B and T cells with “self” receptors programmed for cell death or nonfunctional

26. Antigen-presenting cell Humoral Immune Response (antibodies) display antigen fragments Cell-Mediated Immune Response (T Cells) Helper T cell activates activates B cell Cytotoxic T cell divides releases cytokines Plasma cell Identify and destroy secretes tag for destruction Infected cell Antibodies pathogen

27. Antigen-presenting cell Engulf pathogen, break up molecules and displays foreign molecules on surface

29. Role of Helper T cells: “HELP!” (cytokines) activates B cells and cytotoxic T cells Clonal selection: produce thousands of cells specific to antigen (effector cells, memory cells)

30. Clonal Selection (B cells) • Antigen binds to B cell receptor • Activation enhanced by cytokines • Millions of clones of B cells are made specifically for a specific antigen • Plasma cells: produce antibodies specific to that antigen • Memory cells: same receptor, but long-lived and can quickly mount immune response in future infections

31. Clonal Selection (B cells)

32. B cell  plasma cell  produce antibodies

33. Antibodies mark pathogens for destruction Antibodiesbind to antigens and: Prevent viruses/toxins from entering cells Tag infected cells for destruction

35. Cytotoxic T cells (Tc) kill infected cells disrupt membrane & trigger cell death

37. Immunological Memory • Primary immune response: 1st exposure to antigen • Memory cells • Secondary immune response: repeat exposure  faster, greater response

38. BioFlix: Immunology Running time: 6:51 min

39. Major Histocompatibility Complex (MHC) • MHCs display proteins on cell surface • Responsible for tissue/organ rejection (“self” vs. “non-self”) • B and T cells bind to MHC molecule in adaptive response • MHC Class I: all body cells (except RBCs) • MHC Class II: displayed by immune cells; “non-self”

40. Active vs. Passive Immunity Active immunity: exposure to antigen leaves behind memory cells Immunizations/vaccines: induce immune memory to nonpathogenic microbe or toxin Passive immunity: mom’s antibodies in breast milk passed to baby

41. Immune System Disuptions • Allergies: hypersensitive responses to harmless antigens • Autoimmune Diseases: • Lose tolerance for “self” and turn against molecules in body; cytotoxic T cells attack and damage own cells • Lupus, rheumatoid arthritis, type I diabetes, multiple sclerosis • HIV: infect Helper T cells • AIDS = severely weakened immune system • Cancers: viruses involved in 20% of cancers; need to develop vaccines in fight cancer

42. TED-Ed Video:Why it’s so hard to cure HIV/AIDS Running time: 4:31 min