Defenses Against Disease

1. 36 Defenses Against Disease 0

2. Chapter 36 At a Glance • 36.1 How Does the Body Defend Itself Against Disease? • 36.2 How Do Nonspecific Defenses Function? • 36.3 What Are the Key Components of the Adaptive Immune System? • 36.4 How Does the Adaptive Immune System Recognize Invaders? • 36.5 How Does the Adaptive Immune System Attack Invaders?

3. Chapter 36 At a Glance (continued) • 36.6 How Does the Adaptive Immune System Remember Its Past Victories? • 36.7 How Does Medical Care Assist the Immune Response? • 36.8 What Happens When the Immune System Malfunctions? • 36.9 How Does the Immune System Combat Cancer?

4. 36.1 How Does the Body Defend Itself Against Disease? • The environment teems with microbes, which include microscopic living organisms such as bacteria, protists原生生物,单细胞生物,and many fungi,真菌and viruses, which are usually not considered to be alive • Some microbes are pathogens病原体, a term derived from Greek words meaning “to produce disease” • Pathogens reproduce and seek new hosts • When you have a cold, sneezing broadcasts viruses to everyone around you

5. 36.1 How Does the Body Defend Itself Against Disease? • Most microbial diseases, such as cholera霍乱, measles麻疹, plague鼠疫, tetanus破伤风, and chicken pox水痘, have been with humans for thousands of years • Viruses in the news include • HIV • Ebola virus • West Nile virus • Swine (H1N1) flu • Avian (H5N1) flu

6. 36.1 How Does the Body Defend Itself Against Disease? • We are also endangered by deadly, often new strains of bacteria • The intestinal bacterium Escherichia coli，（ E. coli）大肠杆菌is usually harmless, indeed beneficial, because it produces vitamin K in our large intestines • However, one strain, called O157:H7, usually acquired by eating undercooked ground beef, causes food poisoning, sometimes with fatal consequences

7. 36.1 How Does the Body Defend Itself Against Disease? • We are also endangered by deadly, often new strains of bacteria (continued) • Staphylococcus aureus金黄色葡萄球菌bacteria (“staph”) occur frequently on the skin and in the nasal passages, but some strains cause fatal toxic shock syndrome or prolonged infections if they penetrate through the skin or mucous membranes • Staphylococcus aureus and Mycobacterium tuberculosis结核杆菌(which causes TB) have become resistant to most antibiotics抗生素

8. 36.1 How Does the Body Defend Itself Against Disease? • Vertebrate animals have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses • Vertebrates have evolved three major forms of protection against disease 1. Nonspecific external barriers非特异性的外部屏障prevent most disease-causing microbes from entering the body • The anatomical 解剖的structures include skin and cilia • Secretions include tears, saliva, and mucus

9. 36.1 How Does the Body Defend Itself Against Disease? • Vertebrate animals have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses (continued) • 1. Nonspecific external barriersprevent most disease-causing microbes from entering the body (continued) • These barriers cover the external surfaces of the body and line body cavities that open to the external environment, including the respiratory, digestive, and urogenital

10. 36.1 How Does the Body Defend Itself Against Disease? • Vertebrate animals have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses (continued) 2. Nonspecific internal defenses非特异性的内部防御are collectively called the innate immune response天然免疫反应and swing into action if external barriers are breached • Some white blood cells engulf foreign particles or destroy infected cells

11. 36.1 How Does the Body Defend Itself Against Disease? • Vertebrate animals have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses (continued) 2. Nonspecific internal defenses are collectively called the innate immune response and swing into action if external barriers are breached (continued) • Chemicals released by damaged body cells and proteins released by white blood cells trigger inflammation and fever

12. 36.1 How Does the Body Defend Itself Against Disease? • Vertebrate animals have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses (continued) 3. Specific internal defenses特异性的内部防御, the final line of defense, comprise the adaptive immune response适应性免疫反应, in which immune cells selectively destroy the specific invading toxin or microbe and then “remember” the invader, allowing a faster response if it reappears in the future

13. Figure 36-1 Levels of defense against infection Nonspecific External Barriers skin, mucous membranes If these barriers are penetrated,the body responds with Innate Immune Response phagocytic and natural killer cells,inflammation, fever If the innate immune response is insufficient,the body responds with Adaptive Immune Response cell-mediated immunity, humoral immunity

14. Table 36-1 Innate and Adaptive Immune Responses to Invasion

15. Table 36-2 The Body’s Cellular Arsenal Against Disease

16. 36.1 How Does the Body Defend Itself Against Disease? • Invertebrate animals possess the nonspecific lines of defense • Invertebrates are protected only by nonspecific external barriers and nonspecific internal defenses • Different invertebrates possess an enormous range of external barriers, ranging from exoskeletons外骨骼to slimy粘液状的secretions • Internally, invertebrates have white blood cells that attack pathogens and secrete proteins that neutralize invaders or the toxins they release

17. 36.2 How Do Nonspecific Defenses Function? • The ideal defenses are barriers that prevent invaders from entering the body in the first place • If these barriers are breached, however, the body has several nonspecific methods of killing a wide variety of invading microbes

18. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion • In animal bodies, the first line of defense consists of the surfaces with direct exposure to the environment • The skin • The mucous membranes of the digestive, respiratory, and urogenital tracts

19. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • The skin and its secretions block entry and provide an inhospitable environment for microbial growth • The skin is a barrier to microbes • The outer surface of the skin consists of dry, dead cells filled with tough proteins that do not allow the microbes to obtain the water and nutrients they need to survive

20. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • The skin and its secretions block entry and provide an inhospitable environment for microbial growth (continued) • The secretions from sweat and sebaceous glands contain natural antibiotics, such as lactic acid乳酸, that inhibit the growth of many bacteria and fungi

21. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes • Mucous membranes deploy利用several defenses against infection • First, mucous membranes secrete mucus, which traps microbes that enter the nose or mouth

22. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes (continued) • Mucus contains proteins, including lysozome溶酶体, which kills bacteria by digesting their cell walls, and defensin 防御素, which makes holes in bacterial plasma membranes

23. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes (continued) • Finally, cilia on the membranes sweep up the mucus, microbes and all, until it is either coughed or sneezed out of the body or is swallowed

24. Figure 36-2 The protective function of mucus Bacteria trappedby mucus

25. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes (continued) • If microbes are swallowed, they enter the stomach, where they encounter protein-digesting enzymes and extreme acidity; both are often lethal to them • Intestines contain bacteria that are harmless to people but secrete substances that destroy invading bacteria

26. 36.2 How Do Nonspecific Defenses Function? • The skin and mucous membranes form nonspecific external barriers to invasion (continued) • Mucus, antibacterial proteins, and ciliary action defend the mucous membranes against microbes (continued) • The slight acidity of urine inhibits bacterial growth • In females, acidic secretions and mucus help protect the vagina • Fluids released by the body, including tears, urine, diarrhea腹泻, and vomit呕吐, help expel invaders

27. 36.2 How Do Nonspecific Defenses Function? • The innate immune response nonspecifically combats invading microbes • Despite the many defenses, many disease-causing microbes enter the body through the mucous membranes or through cuts in the skin • Pathogens that get through the external barriers encounter three types of nonspecific innate immune responses • Protection by white blood cells • The inflammatory response • Fever

28. 36.2 How Do Nonspecific Defenses Function? • The innate immune response nonspecifically combats invading microbes (continued) • Protection by white blood cells • The body has a standing army of white blood cells, or leukocytes, many of which are specialized to attack and destroy invading cells or the body’s own cells if they have been infected by viruses

29. 36.2 How Do Nonspecific Defenses Function? • The innate immune response nonspecifically combats invading microbes (continued) • The inflammatory response • A wound provokes an inflammatory response, which recruits leukocytes to the site of injury and walls off the injured area, isolating the infected tissue from the rest of the body

30. 36.2 How Do Nonspecific Defenses Function? • The innate immune response nonspecifically combats invading microbes (continued) • Fever • If a population of microbes succeeds in establishing a major infection, the body may produce a fever, which slows down microbial reproduction and enhances the body’s own fighting abilities

31. 36.2 How Do Nonspecific Defenses Function? • Phagocytic leukocytes and natural killer cells destroy invading microbes • The body has several types of leukocytes, collectively known as phagocytes吞噬细胞, which ingest foreign invaders and cellular debris by phagocytosis吞噬作用Three important types of phagocytes are • Macrophages 巨噬细胞 • Neutrophils 中性粒细胞 • Dendritic cells 树突状细胞

32. 36.2 How Do Nonspecific Defenses Function? • Phagocytic leukocytes and natural killer cells destroy invading microbes (continued) • These cells travel within the bloodstream, ooze 渗出through capillary walls, and patrol巡查the body’s tissues, where they consume毁灭bacteria and other foreign substances that have penetrated the skin or mucous membranes

33. Figure 36-3 The attack of the macrophages Bacteria visiblethrough a hole inthe macrophage’splasma membrane A macrophage leaves acapillary and enters a wound A macrophage stuffed withbacteria that it has ingested

34. 36.2 How Do Nonspecific Defenses Function? • Phagocytic leukocytes and natural killer cells destroy invading microbes (continued) • Nonspecific defense against viruses is the job of another type of leukocyte, called the natural killer cell自然杀伤细胞 • Viruses enter body cells and use the cells’ own metabolism to manufacture more viruses • Natural killer cells destroy virus-infected cells • Killing infected cells before the viruses have had enough time to reproduce and spread to other cells can stop viral infections before they do damage to the body as a whole

35. 36.2 How Do Nonspecific Defenses Function? • Phagocytic leukocytes and natural killer cells destroy invading microbes (continued) • The surfaces of normal body cells display a set of proteins, collectively called the major histocompatibility complex (MHC)主要组织相容性复合体 • MHC proteins differ from species to species, and in fact, differ from individual to individual within a species • Most cancerous cells have missing or altered MHC proteins • NK cells kill the non-self cells.

36. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue • The inflammatory response causes tissues to become warm, red, swollen, and painful • The inflammatory response begins when damaged cells release chemicals that cause certain cells in the connective tissue, called mast cells,肥大细胞to release histamine组胺

37. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Histamine relaxes the smooth muscle surrounding arterioles, increasing blood flow and causing capillary walls to become leaky • Extra blood flowing through leaky capillaries drives fluid from the blood and into the wounded area, causing redness, warmth, and swelling

38. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Other chemicals released by the wounded cells, mast cells, and some substances produced by the microbes themselves attract macrophages, neutrophils, and dendritic cells • These cells squeeze out through the leaky capillary walls and ingest bacteria, dirt, and cellular debris • In some cases, pus脓may accumulate

39. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Other chemicals released by injured cells initiate blood clotting to reduce blood loss and prevent more microbes from entering the bloodstream • Swelling and some of the chemicals released by the injured tissue cause pain, which usually leads to protective behaviors that reduce the likelihood of further injury

40. Animation: The Inflammatory Response

41. Figure 36-4 The inflammatory response dead celllayer Tissue damage carriesbacteria into the wound epidermis Wounded cellsrelease chemicals (red)that stimulate mast cells Mast cells releasehistamine (blue) dermis Histamine increases capillaryblood flow and permeability Phagocytes leavethe capillaries and ingestbacteria and dead cells

42. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Fever combats large-scale infections • If invaders breach these defenses and mount a full-blown充分发展的infection, they may trigger a fever • The onset of fever is controlled by the hypothalamus, the part of the brain housing temperature-sensing nerve cells that serve as the body’s thermostat • In humans, the thermostat is set at about 97 to 99F

43. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Fever combats large-scale infections (continued) • Certain types of bacteria, as well as the phagocytic cells that respond to an infection, produce chemicals called pyrogens致热原 • Pyrogens travel in the bloodstream to the hypothalamus and raise the thermostat’s set point

44. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Fever combats large-scale infections (continued) • The body responds with increased fat metabolism, constriction of blood vessels supplying the skin, and behaviors such as shivering and bundling under blankets

45. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Fever combats large-scale infections (continued) • An elevated body temperature increases the activity of phagocytic white blood cells while simultaneously slowing bacterial reproduction • Fever causes the cells of the adaptive immune system to multiply more rapidly, hastening the onset of an effective adaptive immune response

46. 36.2 How Do Nonspecific Defenses Function? • The inflammatory response attracts phagocytes to injured or infected tissue (continued) • Fever combats large-scale infections (continued) • Fever also stimulates cells infected by viruses to produce a protein called interferon干扰素, which travels to other cells and increases their resistance to viral attack • Interferon also stimulates natural killer cells that destroy virus-infected body cells

47. 36.3 What Are the Key Components of the Adaptive Immune System? • If the nonspecific defenses are breached, the body mounts a highly specific and coordinated adaptive immune response directed against the particular organism that has successfully colonized the body • The essential features of the adaptive immune response were recognized by the Greek historian Thucydides修昔底德more than 2000 years ago • He observed that sometimes a person would contract a disease, recover, and never catch that disease again

48. 36.3 What Are the Key Components of the Adaptive Immune System? • The adaptive immune system consists of cells and molecules dispersed throughout the body • The adaptive immune system (or simply the immune system) is distributed throughout the body, with concentrations of cells in certain locations

49. 36.3 What Are the Key Components of the Adaptive Immune System? • The adaptive immune system consists of cells and molecules dispersed throughout the body (continued) • The adaptive immune system consists of three major components 1. Immune cells • The adaptive immune response is produced by interactions among several types of white blood cells, including macrophages, dendritic cells, and lymphocytes

50. 36.3 What Are the Key Components of the Adaptive Immune System? • The adaptive immune system consists of cells and molecules dispersed throughout the body (continued) 1. Immune cells(continued) • Unique to the adaptive immune response are specialized white blood cells called lymphocytes • B cells and T cells are two types of lymphocytes that arise from dividing stem cells in the bone marrow