CHAPTER 24 The Immune System

1. CHAPTER 24The Immune System Modules 24.1 – 24.2

2. The Continuing Problem of HIV • Acquired immune deficiency syndrome (AIDS) is epidemic throughout much of the world • 14,000 people are infected with the AIDS virus every day • HIV is the virus that causes AIDS • HIV is transmitted mainly in blood and semen • Former L.A. Laker Magic Johnson is one of 900,000 Americans who are HIV-positive

3. It backs up several mechanisms of nonspecific resistance • HIV attacks the immune system • It eventually destroys the body’s ability to fight infection • Our immune system is a specific defense system

4. NONSPECIFIC DEFENSES AGAINST INFECTION 24.1 Nonspecific defenses against infection include the skin and mucous membranes, phagocytic cells, and antimicrobial proteins • The body’s first lines of defense against infection are nonspecific • They do not distinguish one infectious microbe from another

5. They “eat” any bacteria and virus-infected cells they encounter • Macrophages wander in the interstitial fluid Figure 24.1A

6. Viral nucleic acid VIRUS • Interferon and complement proteins are activated by infected cells 6 Antiviral proteins blockviral reproduction 1 New viruses Interferongenesturned on 2 mRNA Interferonstimulatescell to turnon genesfor antiviralproteins 5 3 Interferonmolecules HOST CELL 1 Makes interferon;is killed by virus 4 HOST CELL 2 Protected against virusby interferon from cell 1 Figure 24.1B

7. 24.2 The inflammatory response mobilizes nonspecific defense forces • Tissue damage triggers the inflammatory response Skin surface Swelling Pin Phagocytes Bacteria Phagocytes andfluid moveinto area Chemicalsignals Whiteblood cell 1 Tissue injury; release ofchemical signals such ashistamine 2 3 Dilation and increased leakinessof local blood vessels; migrationof phagocytes to the area Phagocytes (macrophages andneutrophils) consume bacteriaand cell debris; tissue heals Figure 24.2

8. disinfect tissues • limit further infection • The inflammatory response can

9. 24.3 The lymphatic system becomes a crucial battleground during infection • The lymphatic system is a network of lymphatic vessels and organs • It returns tissue fluid to the circulatory system • It fights infections

10. LYMPHATICVESSEL Adenoid Tonsil VALVE Right lymphaticduct, enteringvein Tissue cells Lymph nodes Interstitialfluid Bloodcapillary Thoracic duct,entering vein Thoracicduct Thymus LYMPHATICCAPILLARY Appendix Spleen Masses oflymphocytes and macrophages Bonemarrow Lymphaticvessels Figure 23.3

11. It will return it as lymph to the blood • Lymph contains less oxygen and fewer nutrients than interstitial fluid • This lymphatic vessel is taking up fluid from tissue spaces in the skin LYMPHATICVESSEL VALVE Tissue cells Interstitialfluid Bloodcapillary LYMPHATICCAPILLARY Figure 23.3B

12. They are packed with lymphocytes and macrophages • Lymph nodes are key sites for fighting infection Masses oflymphocytes and macrophages Outer capsule oflymph node Macrophages Lymphocytes Figure 23.3C, D

13. SPECIFIC IMMUNITY 24.4 The immune response counters specific invaders • Our immune systems responds to foreign molecules called antigens • Infection or vaccination triggers active immunity • The immune system reacts to antigens and “remembers” an invader • We can temporarily acquire passive immunity

14. 24.5 Lymphocytes mount a dual defense BONE MARROW Stem cell • Two kinds of lymphocytes carry out the immune response • B cells secrete antibodies that attack antigens • T cells attack cells infected with pathogens THYMUS Viablood Immaturelymphocytes Antigenreceptors T cell B cell CELL-MEDIATEDIMMUNITY HUMORALIMMUNITY Viablood Lymph nodes,spleen, and otherlymphatic organs Final maturation of B and T cellsin lymphatic organ OTHER PARTSOF THELYMPHATICSYSTEM Figure 24.5

15. 24.6 Antigens have specific regions where antibodies bind to them Antibody Amolecules • Antigenic determinants are the molecules to which antibodies bind Antigen-bindingsites Antigenicdeterminants Antigen Antibody Bmolecule Figure 24.6

16. 24.7 Clonal selection musters defensive forces against specific antigens • When an antigen enters the body, it activates only lymphocytes with complementary receptors • B and T cells multiply into clones of specialized effector cells that defend against the triggering antigen • This is called clonal selection

17. Antigen molecules Variety ofB cells in a lymph node Antigen receptor(antibody oncell surface) Cell growth division, and differentiation Clone of manyeffector cellssecretingantibodies Endoplasmicreticulum Antibodymolecules Figure 24.7

18. 24.8 The initial immune response results in a type of “memory” • In the primary immune response, clonal selection produces memory cells • These cells may confer lifelong immunity Figure 24.8A

19. Unstimulated lymphocyte First exposure to antigen • When memory cells are activated by subsequent exposure to an antigen, they mount a more rapid and massive secondary immune response FIRST CLONE Memory cells Second exposure to antigen Effector cells SECOND CLONE More memory cells New effector cells Figure 24.8B

20. 24.9 Overview: B cells are the main warriors of humoral immunity • Triggered by a specific antigen, a B cell differentiates into an effector cell • The effector cell is called a plasma cell • The plasma cell secretes antibodies

21. PRIMARY RESPONSE (initial encounter with antigen) Antigen Antigen receptoron a B cell Antigen binding to a B cell Cell growth, division, and differentiation Clone ofcells Memory B cell Plasma cell Antibody molecules Later exposure to same antigen SECONDARY RESPONSE (can be years later) Cell growth, division, and further differentiation Larger clone of cells Plasma cell Memory B cell Antibody molecules Figure 24.9

22. 24.10 Antibodies are the weapons of humoral immunity • An antibody molecule Figure 24.10A

23. An antibody molecule has antigen-binding sites specific to the antigenic determinants that elicited its secretion Antigen-binding sites Light chain Heavy chain Figure 24.10B

24. 24.11 Antibodies mark antigens for elimination • Antibodies may • block harmful antigens on microbes • clump bacteria or viruses together • precipitate dissolved antigens • activate complement proteins

25. Binding of antibodies to antigens inactivates antigens by Neutralization (blocks viral binding sites; coats bacterial toxins) Agglutination of microbes Precipitation of dissolved antigens Activation of complement Complement molecule Bacteria Virus Antigen molecules Bacterium Foreign cell Hole Enhances Leads to Phagocytosis Cell lysis Macrophage Figure 24.11

26. 24.12 Connection: Monoclonal antibodies are powerful tools in the lab and clinic Antigen injected into mouse Tumor cells grown in culture • These molecules are produced by fusing B cells specific for a single antigenic determinant with easy-to-grow tumor cells B cells (from spleen) Tumor cells Cells fused to generate hybrid cells Single hybrid cell grown in culture Antibody Hybrid cell culture, producing monoclonal antibodies Figure 24.12A

27. Example: home pregnancy tests • They are also useful in the treatment of certain cancers • These cells are useful in medical diagnosis Figure 24.12B

28. 24.13 T cells mount the cell-mediated defense and aid humoral immunity • Helper T cells and cytotoxic T cells are the main effectors of cell-mediated immunity • Helper T cells also stimulate the humoral responses

29. An antigen-presenting cell (APC) first displays a foreign antigen and one of the body’s own self proteins to a helper T cell Microbe Macrophage (will become APC) • Cell-mediated immunity 1 Antigen from microbe(nonself molecule) Self protein Self protein displaying antigen T cell receptor Bindingsite for self protein 3 2 Helper T cell 4 Binding site for antigen APC Figure 24.13A

30. The interaction activates the helper T cells • The helper T cell can then activate cytotoxic T cells with the same receptors • The helper T cell’s receptors recognize the self-nonself complexes on the APC Self protein displaying an antigen Cell-mediated immunity (attack on infected cells) Cytotoxic T cell Interleukin-2 stimulates cell division T cell receptor Interleukin-2 activates other T cells and B cells APC HelperT cell Humoral immunity (secretion of antibodies by plasma cells) B cell Interleukin-1 activateshelper T cell Figure 24.13B

31. 1 2 Cytotoxic T cell bindsto infected cell Perforin makes holesin infected cell’s membrane 3 Infected cell is destroyed • Cytotoxic T cells bind to infected body cells and destroy them Holeforming Foreignantigen INFECTED CELL CytotoxicT cell Perforinmolecule Figure 24.13C

32. 24.14 Cytotoxic T cells may help prevent cancer • Cytotoxic T cells may attack cancer cells • The surface molecules of cancer cells are altered by the disease Figure 24.14

33. 24.15 The immune system depends on our molecular fingerprints • The immune system normally reacts only against nonself substances • It generally rejects transplanted organs • The cells of transplanted organs lack the recipient’s unique “fingerprint” of self proteins

34. DISORDERS OF THE IMMUNE SYSTEM 24.16 Connection: Malfunction or failure of the immune system causes disease • Autoimmune diseases • The system turns against the body’s own molecules • Immunodeficiency diseases • Immune components are lacking, and infections recur • Physical and emotional stress may weaken the immune system

35. 24.17 Connection: Allergies are overreactions to certain environmental antigens • Allergies are abnormal sensitivities to allergens in the surroundings B cell (plasma cell) Histamine Mast cell Antigenic determinant Antibodies attach to mast cell Allergen binds to antibodies on mast cell Histamine is released, causing allergy symptoms Allergen (pollen grain) B cells make antibodies SENSITIZATION: Initial exposure to allergen LATER EXPOSURE TO SAME ALLERGEN Figure 24.17

36. 24.18 Connection: AIDS leaves the body defenseless • The AIDS virus attacks helper T Cells • This cripples both cell-mediated and humoral immunity • So far, AIDS is incurable • Drugs and vaccines offer hope for the future • Practicing safer sex could save many lives