Lecture 13 – Ch. 43: Immune System

1. Lecture 13 – Ch. 43: Immune System • I. Overview • Innate Immunity • A. components • B. cells • IIII. Adaptive/acquired immunity • A. Lymphocytes • i. B-cells • ii. T-cells • B. humoral vs. cell-mediated immunity • C. Antibodies • D. MHC molecules • IV. Immune memory • V. Immune System Problems • VI. Preparation for next lecture

2. Thought Question: Why do we not get sick EVERY time someone near us sneezes?

3. cilia of tracheal cells pollen dust Overview Irritants Pollen Dust Pathogens Viruses Bacteria Macroparasites For example…

4. Disease Defenses A Way In? • Mucus membranes • Eyes • Nose • Mouth • Vagina • Urethra • Skin breeches (cuts, punctures, scrapes) Antigens = foreign molecules specific to the invader

5. Immunity Overview

6. Which cells are exclusively part of the adaptive immune system? • Dendritic cells • Macrophages • B cells • Natural killer cells • White blood cells

7. External Barriers Skin Dry dead cells Constantly sloughed off Secretions Contain natural antibiotics Mucus physically traps microbes Innate Immunity Internal Barriers Dendritic cells – detect foreign particles alert innate and adaptive immune systems Mast cells – cause inflammation and alert of damaged tissues

8. Innate Immunity Leukocytes • Phagocytes - ingest foreign particles & cellular debris • Macrophages – consume many cells • Neutrophils – die upon consumption Natural killer cells Attack cancerous or infected body cells Use proteins & enzymes to lyse cells

9. Inflammation Initiated by damaged or infected cells Histamine release by mast cells Capillary flow and permeability increased Phagocytes drawn to area Innate Immunity Cytokines – recruit more lymphocytes  leads to pus, swelling, redness, heat

10. Inflammatory “Symptoms” Warm, red, painful Result of leaky capillaries Increased fluid secretions Removal of dead cells and waste Pain Swelling, chemical response Alerts injured organism Innate Immunity NSAIDs Leukocytes and fluid = pus

11. Innate Immunity Antimicrobial peptides first discovered in insects (like Drosophila). Antimicrobial peptides in vertebrates: the complement – family of proteins, inactivate and lyse infected cells Interferons – cytokine made by host cells, boosts immune response

12. One immune similarity between insects and humans is….. • Both use B and T cells • Both have skin as a barrier • Both engage antimicrobial peptides • Both have adaptive immunity

13. Adaptive Immune System Acquired/ adaptive immunity –consists of lymphocytes  B cells and T cells Responsible for circulating antibodies, remembering pathogens, destroying infected cells

14. B cells Made and mature in bone marrow Lymphocytes that make antibodies – either secreted or embedded in B cell membrane Humoral immunity B cells and antibodies attack pathogens before they enter cells After encounter pathogen, B cells differentiate into memory B cells and plasma cells Adaptive Immune System

15. Adaptive Immune System Clonal Selection:

16. Adaptive Immune System B cell  Plasma cell Plasma cells make and secrete TONS of antibodies, as opposed to memory B cells

17. Which is NOT a function of B cells? • Produce memory cells • Secrete antibodies • Attack infected cells • Make clones of plasma cells

18. Antibody action Defend against pathogens in blood or fluid Can inactivate pathogens by binding to epitopes Can stimulate phagocytosis Can neutralize toxins or block adhesion Can trigger complement system where blood proteins destroy invaders Adaptive Immune System

19. Antibodies Produced by B cells Each composed of two heavy chains and two light chains Constant region is same Variable region is unique to antibody Bind antigens at each end of “fork” Adaptive Immune System Genes are unique in that can recombine into millions of combinations in different B cells. Transmembrane antigen receptors inserted in B cells

20. Immunospecificity Antibodies are “pieced together” from many genes Random combinations allow for millions of possibilities Adaptive Immune System Each B cell produces unique antibodies Over 100 million different antibodies in body  chances of an antigen encountering one that fits are high

21. How does our body mount an immune attack to a new pathogen (not previously encountered)? • By using memory B cells • By chance encounter with a B-cell receptor • By attacking with macrophages • Both (b) and (c) • Both (a) and (c)

22. Adaptive Immune System T cells Made in bone marrow, mature in thymus Lymphocytes that cozy up to infected cells – two types: Helper T cells – recognize and bind infected cells Cytotoxic T cells – bind and lyse infected cells Cell-mediated immunity T cells find and attack pathogen-infected cells

23. Cell-mediated immunity Cytotoxic T cells: Insert pores in infected cells, enzymes break down cells Helper T cells stimulate lymphocyte division Some T cells develop into memory cells – future protection Adaptive Immune System

24. Adaptive Immune System T cell receptors – recognize pathogen epitopes ‘presented’ on infected cells Composed of one alpha chain, one beta chain Have a variable and constant region, similar to B-antibodies

25. Adaptive Immune System Self-tolerance MHC = major histocompatibility complex All cells have MHC molecules – most body cells have class I (lymphocytes have class II) MHC molecules displayed on cell surface – each binds a specific peptide foreign fragment then “displays” it on surface.

26. Adaptive Immune System Self-tolerance T-cells (cytotoxic or helper T) bind to MHC presented antigens Self-reactive lymphocytes with receptors to self epitopes are eliminated before they leave bone marrow and mature

27. Which cells have MHC molecules displayed? • Most body cells • Cancerous cells • Immune system cells • Transplanted cells • All white blood cells

28. Adaptive Immune System Immune system must remember past victories... • Memory cells “remember” specific antigens • May survive for years • Respond faster and larger to repeat invasion

29. Memory Memory B and T cells are able to recognize pathogens and fight off infections immediately Adaptive Immune System • Then why do you keep catching a cold every year? • 100+ rhinoviruses • Cold viruses can mutate quickly Vaccinations take advantage of the immune response Body is exposed to antigens to stimulate memory cells

30. Antibiotics aid disease fight Reduce growth and reproduction of living pathogens (not viruses) Give immune system time to fight infection Humans have misused antibiotics  “superbugs” Overuse of antibacterial products Failure to complete full course of antibiotics Non-medicinal use of antibiotics Antibiotics

31. Allergies Immune overreaction to harmless antigens Histamine triggers inflammation Extreme response can trigger anaphylaxis Immune System Problems Autoimmune Disorders • Immune system attacks healthy body cells • Lupus, Rheumatoid Arthritis, Multiple Sclerosis, Type 1 Diabetes, Celiac disease, Crohn’s disease

32. Immune Deficiency Syndromes Severe Combined Immune Deficiency (SCID): Few/no immune cells produced  genetic Acquired Immune Deficiency Syndrome (AIDS): Due to Human Immunodeficiency Virus (HIV) Destroys helper T cells Immune System Problems Immune rejection When tissue without “self” MHC molecules (aka HLA) contact immune system, response mounted Can be countered by immunosuppressive drugs

33. Thought Question: What can you do to fortify your immune system?

34. Things To Do After Lecture 13… • Reading and Preparation: • Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. • Ch. 43 Self-Quiz: #1 – 7 (correct answers in back of book) • Read chapter 43, focus on material covered in lecture (terms, concepts, and figures!) • Skim next lecture. • “HOMEWORK” (NOT COLLECTED – but things to think about for studying): • Compare and contrast: T cells and B cells, the humoral response compared to the cell-mediated immune response. • Explain the function and parts of the human innate immune system. • Describe the problem with each of the following: allergies, autoimmune disorders, immune deficiency syndromes. • Why are people concerned about over-use or misuse of antibiotics?