Immunity

1. Immunity Chapter 38 Part 1

2. Impacts, IssuesFrankie’s Last Wish • Infection with a common, sexually transmitted virus (HPV) causes most cervical cancers – including the one that killed Frankie McCullogh

3. 38.1 Integrated Responses to Threats • Immunity • The capacity to resist and combat infection by pathogens such as viruses, bacteria, and fungi • In vertebrates, innate and adaptive immune systems work together to combat infection and injury

4. Evolution of the Body’s Defenses • Proteins in eukaryotic cell membranes have unique patterns that the body recognizes as self • Cells of multicelled eukaryotes have receptors that recognize nonself cues (PAMPs) on or in pathogens, and trigger defense responses

5. Innate Immunity • Binding of a receptor with a PAMP triggers immediate, general defense responses that are part of inborn innate immunity • Complement • Proteins that destroy microorganisms or flag them for phagocytosis • An innate immune response

6. Adaptive Immunity • Adaptive immunity is a system of defenses that specifically targets billions of different antigens an individual may encounter during its lifetime • Antigen • PAMP or other molecule the body recognizes as nonself that triggers an active immune response

7. Three Lines of Defense 1. Physical, chemical, and mechanical barriers • Keep pathogens outside the body 2. Innate immunity • General responses destroy invaders inside the body before they become established 3. Adaptive immunity • Huge populations of white blood cells form to target and remember a specific antigen

8. Mucus and Cilia: Physical Barriers

9. Comparing Innate and Active Immunity

10. The Defenders • White blood cells (leukocytes) specialized for different tasks carry out all immune responses • Phagocytes (neutrophils, macrophages, dendritic cells) • Secretory cells (eosinophils, basophils, mast cells • Lymphocytes (B and T lymphocytes, natural killer cells)

11. The Defenders • All white blood cells secrete chemicals, including cell-to-cell signaling molecules (cytokines) that coordinate all aspects of immunity • Interleukins • Interferons • Tumor necrosis factors

12. White Blood Cells

13. Fig. 38-3a, p. 661

14. Fig. 38-3b, p. 661

15. Chemical Weapons of Immunity

16. 38.1 Key ConceptsOverview of Body Defenses • The vertebrate body has three lines of immune defenses • Surface barriers prevent invasion by ever-present pathogens • General innate responses rid the body of most pathogens • Adaptive responses specifically target pathogens and cancer cells

17. 38.2 Surface Barriers • Normal flora • Billions of microorganisms normally live on human surfaces, including interior tubes and cavities of digestive and respiratory tracts • A pathogen can cause infection only if it enters the internal environment by penetrating skin or other protective barriers at the body’s surfaces

18. Some Normal Flora

19. Vertebrate Surface Barriers • Physical, chemical, and mechanical barriers keep microorganisms outside body tissues • Skin • Mucus and cilia • Lysozyme • Gastric fluid and bile salts • Normal flora • Urination

20. Vertebrate Surface Barriers

21. Skin • Healthy, intact skin is an effective surface barrier

22. skin surface epithelial cells die and become filled with keratin as they are pushed toward skin surface epidermis dividing epithelial cells 0.1 mm Fig. 38-5, p. 663

23. 38.3 Remember to Floss • Dental plaque • A thick, sticky biofilm of glycoproteins, bacteria, and their products that contribute to tooth decay and gum disease (periodontitis) • Nine of every ten cardiovascular disease patients have serious periodontal disease • Oral bacteria associated with periodontitis are also found in atherosclerotic plaque

24. Plaque

25. 38.2-38.3 Key Concepts Surface Barriers • Skin, mucous membranes, and secretions at the body’s surfaces function as barriers that exclude most microbes

26. 38.4 Innate Immune Responses • Innate immune mechanisms nonspecifically eliminate pathogens that invade internal tissues before they become established • Phagocytes • Complement • Inflammation • Fever

27. Phagocytes • Macrophages • Large phagocytes that patrol interstitial fluid and engulf and digest pathogens • Secrete cytokines when receptors bind to antigen • Cytokines attract more macrophages, neutrophils, and dendritic cells to infection site

28. Complement • Complement proteins become activated when they encounter antigen • Cascading enzyme reactions concentrate activated complement at infection site • Complement attracts phagocytes to infection site and tags pathogens for destruction • Forms attack complexes that puncture bacteria • Helps mediate active immunity

29. Complement Attack Complexes

30. activated complement antibody molecule A In some responses, complement proteins become activated when antibodies (the Y-shaped molecules) bind to antigen—in this case, antigen on the surface of a bacterium. Fig. 38-7a, p. 664

31. activated complement bacterial cell B Complement also becomes activated when it binds directly to antigen. Fig. 38-7b, p. 664

32. activated complement C By cascading reactions, huge numbers of different complement molecules form and assemble into structures called attack complexes. Fig. 38-7c, p. 664

33. attack complex that causes a pore to form through the lipid bilayer of the bacterium D The attack complexes become inserted into the target cell’s lipid envelope or plasma membrane. Each complex makes a large pore form across it. E The pores bring about lysis of the cell, which dies because of the severe structural disruption. Fig. 38-7de, p. 664

34. Inflammation • Inflammation • A local response to tissue damage characterized by redness, warmth, swelling and pain, triggered by activated complement and cytokines • Mast cells release histamine, increasing capillary permeability • Phagocytes and plasma proteins leak out, attack invaders, form clots, and clean up debris

35. Inflammation Response to Bacterial Infection

36. A Bacteria invade a tissue and release toxins or metabolic products that damage tissue. D Complement proteins attack bacteria. Clotting factors also wall off inflamed area. E Neutrophils and macrophages engulf invaders and debris. Macrophage secretions kill bacteria, attract more lymphocytes, and initiate fever. B Mast cells in tissue release histamine, which widens arterioles (causing redness and warmth) and increases capillary permeability. C Fluid and plasma proteins leak out of capillaries; localized edema (tissue swelling) and pain result. Stepped Art Fig. 38-8, p. 665

37. Fever • Fever • A temporary rise in body temperature – above the normal 37°C (98.6°F) – that often occurs in response to infection • Cytokines stimulate brain cells to release prostaglandins, which act on the hypothalamus • Fever enhances the immune response by speeding up metabolism and phagocyte activity • Fever over 40.6°C (105°F) can be dangerous

38. 38.4 Key Concepts Innate Immunity • Innate immune responses involve a set of general, immediate defenses against invading pathogens • Innate immunity includes phagocytic white blood cells, plasma proteins, inflammation, and fever

39. 38.5 Overview of Adaptive Immunity • Vertebrate adaptive immunity adapts to different antigens it encounters during its lifetime • Lymphocytes and phagocytes interact to effect four defining characteristics: Self/nonself recognition, specificity, diversity, and memory

40. Self/Nonself Recognition • Self versus nonself recognition • Each kind of cell or virus has a unique identity • MHC markers • Plasma membrane self-recognition proteins • T cell receptors (TCRs) • Antigen receptors that recognize MHC markers as self, antigens as nonself

41. Specificity and Diversity • Specificity • Defenses are tailored to target specific antigens • Diversity • There are potentially billions of different antigen receptors on T and B cells

42. Memory • Memory • The capacity of the adaptive immune system to remember an antigen • If the same antigen appears again, B and T cells make a faster, stronger response

43. First Step – The Antigen Alert • Once a B or T cell recognizes and binds to a specific antigen, it begins to divide by mitosis • All descendent cells recognize the same antigen • T cells do not recognize an antigen unless it is presented by an antigen-presenting cell • Macrophages, B cells, and dendritic cells digest particles and display antigen-MHC complexes

44. Cell Types • Effector cells • Differentiated lymphocytes (B and T cells) that act at once to fight infection • Memory cells • Long-lived B and T cells reserved for future encounters with the same antigen

45. Antigen Processing

46. Fig. 38-9a, p. 666

47. cell engulfs an antigen-bearing particle particle is digested into bits lysosome fuses with endocytic vesicle antigen–MHC complexes become displayed on cell surface MHC markers bind fragments of particle endocytic vesicle forms Stepped Art Fig. 38-9b, p. 666

48. Two Arms of Adaptive Immunity • Antibody-mediated immune response • B cells produce antibodies that bind to specific antigen particles in blood or interstitial fluid • Cell-mediated immune response • Cytotoxic T cells and NK cells detect and destroy infected or altered body cells

49. Interactions Between Antibody-Mediated and Cell-Mediated Responses

50. Intercepting and Clearing Out Antigen • After engulfing antigen-bearing particles, dendritic cells or macrophages migrate to lymph nodes, where T cells bind and initiate responses • During an infection, lymph nodes swell due to accumulation of T cells • Antibody-antigen complexes bound by complement are cleared by the liver and spleen