Talk Twelve: The Immune System Chapter 20

1. Biology Today (BIOL 109) Talk Twelve: The Immune System Chapter 20

2. The Immune System • Immunity is the ability to react to antigens so that the body remains free of disease. • Disease is a state of homeostatic imbalance. • Can be due to infection or failure of the immune system.

3. Primary Lymphatic Organs • Lymphatic organs contain large numbers of lymphocytes (White Blood cells). • Primary organs are:- • Red Bone Marrow. • Site of stem cells. • Source of B lymphocytes. • Thymus Gland. Lymphocytes from bone marrow pass through to form T-lymphocytes • Produces thymic hormones (thymosin). • Aids in T lymphocyte maturation.

4. Secondary Lymphatic Organs • Secondary lymphatic organs are places where lymphocytes encounter and bind with antigens. • Spleen. • Lymph nodes. • Tonsils. • Peyer’s patches.

5. Lymphatic Organs

6. Secondary Lymphatic Organs • Spleen – upper left of abdominal cavity behind stomach. Sectioned off by connective tissue- white pulp & red pulp. • White pulp – lymphocytes • Red pulp – filters blood. Blood entering the spleen passes through red pulp before it leaves (network of sinuses) • FRAGILE

7. Secondary Lymphatic Organs • Lymph Nodes – occur along lymphatic vessels. Formed from connective tissue. • Packed full of B-lymphocytes • As lymph courses through sinuses it is filtered by macrophages, which engulf pathogens and debris. • Also present- T-lymphocytes – fight infection and attack cancer cells

8. Secondary Lymphatic Organs • Tonsils – patches of lymphatic tissue. • Perform the same function as lymph nodes • First line of defense • Peyer’s Patches – on the intestinal wall and appendix. Attack pathogens that ender the body by way of the intestinal tract.

9. Nonspecific Defenses • Barriers to Entry. • Mucous membranes • Line respiratory, digestive, and urinary tract. • Oil gland secretions. • Chemicals that kill or weaken bacteria on skin • Ciliated cells. • Sweep mucus & particles into throat • Bacteria • Both in stomach and vagina, prevent pathogens from gaining a foot-hold. • Acid

10. Innate Immunity • One important function of the immune system is to promote growth and repair after injury • Either via physical damage or microorganisms • The mobilization of innate immune cells to get rid of damaged cells or microorganisms is called inflammation • Small molecules called cytokines are also involved

11. Innate Immunity • Inflammatory Reaction. • Tissue damage causes • tissue cells and mast cells to release chemical mediators.

12. Innate Immunity • Inflammatory Reaction. • Histamine and kinins. • Capillaries dilate and become more permeable. • Skin reddens and becomes warm. • Proteins and fluids escape from tissue. Swelling occurs

13. Innate Immunity • Inflammatory Reaction. • Proteins and fluids escape from tissue and cause swelling. • Swelling stimulates free nerve endings, causing the sensation of pain.

14. Innate Immunity • Neutrophils and Monocytes migrate to site of injury. • Amoeboid – can change shape – squeeze through capillary walls and enter tissue fluid. • Neutrophils engulf pathogens –destroyed by hydrolytic enzymes when fused to a lysosome

15. Innate Immunity • Macrophages: Monocytes change into these as they leave the blood and enter the tissues. • These are phagocytic cells • Can eat many (100’s) of pathogens and survive. • Eat old blood cells and bits of dead tissue • Stimulate the immune response. • Increase production of white blood cells in bone marrow.

16. Innate Immunity • Macrophages: Monocytes change into these as they leave the blood and enter the tissues. • Macrophages enter lymph vessels carring bacteria fragments to lymph nodes • This starts a specific immune response

18. Protective protein system • Known as Complement proteins • Are activated when pathogens enter the body. • Complement certain immune responses.

19. Protective protein system • Attract phagocytes. • Form holes in bacteria. • Interferon binds to receptors of non-infected cells causing them to prepare for possible attack

20. Specific immunity • Antigen--shape on cell, allows recognition of self and detection of foreign cells. • Antibody--protein that recognizes and binds antigens. • Specific defenses respond to antigens. • Lymphocytes recognize an antigen due to antigen receptors whose shape allows them to combine with a specific antigen. • Immunity is primarily the result of the action of B lymphocytes and T lymphocytes.

21. White blood cells • Granular Leukocytes • Neutrophils: Most abundant. Have multilobed nucleus. • They are the first to respond to infection, and engulf pathogens duringphagocytosis. • Eosinophils: Have bilobed nucleus • Known to increase in number in the event of parasitic worm infection and during allergic reaction. • Basophils: U-shaped or lobed nucleus. • In connective tissues release histamines along with Mast Cells

22. White Blood Cells • Agranular Leukocyles • Monocyles: Largest of the white blood cells. • Differentiate into even larger Macrophages • Phagocytize pathogens, old cells and debris • Stimulate production of other white blood cells • Lymphocytes: Two types: • T-lymphocytes – Destroy any cell with foreign antigens • B-lymphocytes – Produce antibodies that combine with antigens • Target pathogens for destruction

23. Natural Killer Cells • Natural killer cells kill virus-infected cells and tumor cells by cell-to-cell contact. • Large, granular lymphocytes.

24. T Cells • Provide cell-mediated immunity. • Produced in bone marrow, mature in thymus. • Antigen must be presented in groove of HLA molecule. • Cytotoxic T cells destroy non-self protein-bearing cells. • Helper T cells secrete cytokines that control the immune response.

25. B Cells • Provide antibody-mediated immunity against bacteria. • Produced and mature in bone marrow. • Reside in spleen and lymph nodes. • Circulate in blood and lymph. • Directly recognize antigen and then undergo clonal selection. • Clonal expansion produces antibody-secreting plasma cells and memory B cells.

26. Clonal selection Theory • The antigen selects which lymphocyte will undergo clonal expansion and produce more lymphocytes with the same type of antigen receptor. • Some become memory cells – long term immunity to the same infection. • B-cells become plasma cells – fight infection • Apoptosis – when danger of infection is over, all plasma cells undergo programmed cell death

27. Specific Defenses • Antibodies are proteins shaped like an antigen receptor and capable of combining with, and neutralizing, a specific antigen.

28. Antibodies • Classes. • IgG - Enhances phagocytosis. • IgM - Activates complement proteins. • IgA - Prevents attachment of pathogens. • IgD - Antigen receptors on virgin B cells. • IgE - Immediate allergic response.

29. Induced Immunity • Active Immunity. • Immunization involves use of vaccines. • Contain an antigen to which the immune system responds. • Primary response. Secondary (booster) response. • Dependent upon the presence of memory B and T cells capable of responding to lower antigen doses.

30. Induced Immunity • Passive immunity • occurs when an individual is given prepared antibodies. • Temporary. • No memory cells. • Primary and secondary injections

31. Issue - Allergies • Occurs when your immune system reacts atypically to some antigens to which the host does not need protection. • Pollen, dust mites, cats, a hard days work! • Called Allergens • The atypical response produces a special antibody • IgE • A form of innate immunity

32. Allergies • IgE binds to mast cells. • When a person later encounters the same allergen, the allergen binds to the IgE on the mast cell • This triggers the explosive release of histamine • Capillaries dilate and become more permeable. • Skin reddens and becomes warm. Proteins and fluids escape from tissue. Swelling occurs

34. Allergies • The large amounts of histamines released in an allergic reaction cause strong symptoms • Runny eyes, sneezing, or shortness of breath • Depends upon the tissue in which the mast cells were triggered

35. Allergies • As allergy symptoms are caused by histamines, taking antihistamines stops the build up of histamines in the cells of blood vessels. • However, antihistamines do not stop the immune response or the release of histamines in mast cells • Other allergies are mediated by T-cells • Latex, poison ivy, dyes or chemicals in cosmetics or clothing • Antihistamines do not help in these allergic reactions

36. Allergies • As each allergy is an antigen-specific immune response it shows memory and a greater response on the next exposure • This is why allergies get worse over time • Thousands of different substances can produce allergies in people – each triggered by a specific antigen-specific response • Why people are usually bothered by only a few • Appears to be inherited • Remember human genetics and meiosis!!!!

37. The End. Any Questions?