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Immunity  Vocabulary: Pathogen, antigen, antibody, artificial, natural, active, passive, specific, nonspecific, monoclonal, vaccination, phagocyte, macrophage,

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Presentation on theme: "Immunity  Vocabulary: Pathogen, antigen, antibody, artificial, natural, active, passive, specific, nonspecific, monoclonal, vaccination, phagocyte, macrophage,"— Presentation transcript:

1 Immunity  Vocabulary: Pathogen, antigen, antibody, artificial, natural, active, passive, specific, nonspecific, monoclonal, vaccination, phagocyte, macrophage, clotting, antibiotic, T-Cell, B-Cell, thrombin, prothrombin, fibrinogen, fibrin, platelets, innate, inflammation, fever, mucous, cell-mediated, humoral, effector cell, virus, bacteria

2 INNATE DEFENSES AGAINST INFECTION Innate defenses against infection include the skin, mucous membranes, and phagocytic cells Innate immunity is the body’s first line of defense against all invaders – Skin provides tough barrier and general chemical defenses – Mucous membranes – Stomach acid – Hairs, cilia

3 Pathogens that get past the body's external defenses are met by innate defensive cells – Found in blood and interstitial fluid – Macrophages are large phagocytic cells – Natural killer cells release chemicals – Specific proteins attack microbes or impede their reproduction Interferons help cells resist viruses The complement system – Initiated by microbes, can lead to lysis of invaders

4 Bacteria Colorized SEM 3,800 

5 VirusViral nucleic acid New viruses Interferon genes turned on DNA mRNA Interferon molecules Host cell 1 Makes interferon; is killed by virus Host cell 2 Protected against virus by interferon from cell 1 Interferon stimulates cell to turn on genes for antiviral proteins Antiviral proteins block viral reproduction

6 The inflammatory response mobilizes nonspecific defense forces Tissue damage triggers the inflammatory response – Can disinfect tissues and limit further infection Steps of the inflammatory response 1.Tissue injury releases chemical signals such as histamine 2.Local blood vessels dilate and leakiness increases; phagocytes migrate to the area

7 3.Phagocytes consume bacteria and cell debris; tissue heals The inflammatory response may be widespread as well as localized – White blood cells may increase – Fever may stimulate phagocytosis – Septic shock Overwhelming systemic inflammatory response May cause death

8 Pin Skin surface Bacteria Chemical signals White blood cell Blood vessel Tissue injury; release of chemical signals such as histamine Dilation and increased leakiness of local blood vessels; migration of phagocytes to the area Phagocytes (macrophages and neutrophils) consume bacteria and cell debris; tissue heals Phagocytes and fluid move into area Swelling Phagocytes

9 The lymphatic system is activated during infection The lymphatic system is involved in both innate and acquired immunity – Branching network of lymphatic vessels – Lymph nodes packed with macrophages and white blood cells – Tonsils and adenoids – Appendix – Spleen – Bone marrow and thymus – Lymph, similar to interstitial fluid

10 Main functions of the lymphatic system – Return tissue fluid to circulatory system Lymphatic vessels take up fluid from tissue spaces Lymph reenters circulatory system through two large lymphatic vessels – Fight infection Microbes picked up from infection sites travel in lymph through lymphatic organs packed with white blood cells

11 Adenoid Tonsil Lymph nodes Right lymphatic duct, entering vein Thoracic duct, entering vein Thymus Thoracic duct Appendix Spleen Bone marrow Lymphatic vessels Lymphatic capillary Interstitial fluid Tissue cells Blood capillary Lymphatic vessel Valve Masses of lymphocytes and macrophages Lymph node

12 ACQUIRED IMMUNITY* The immune response counters specific invaders The immune system recognizes and defends against invading microbes and cancer cells – Can distinguish one infectious agent from another Acquired immunity develops only after exposure to a specific foreign substance (antigen) – System produces a specific type of antibody that helps counter the antigen's effects – Primed system remembers the antigen and reacts to it in the future

13 Immunity is usually acquired by natural exposure to antigens but may be achieved by vaccination* – Active immunity Person's own immune system actively produces antibodies – Passive immunity Person receives premade antibodies, as a fetus does from its mother Immunity lasts only as long as the antibodies do

14 Natural v. Artificial*  Natural immunity is defined as that being acquired from having gotten the pathogen w/out being injected or inoculated.  Artificial immunity is defined as having being given through an injection or inoculation  Being exposed to Chicken Pox when young is “natural”, while getting the chicken pox vaccine is considered “artificial”.

15 Lymphocytes (WBC’s) mount a dual defense Lymphocytes originate from stem cells in the bone marrow Humoral immunity – B cells secrete antibodies that circulate in blood and lymph to sites of infection – Defends primarily against bacteria and viruses present in body fluids

16 Cell-mediated immunity – In the thymus, immature lymphocytes specialize into T cells – T cells attack cells infected with pathogens, fungi and protozoans, cancer cells – T cells also promote phagocytosis and production of antibodies

17 Functioning of B and T cells – Certain genes in the cell are turned on – Cell synthesizes specific protein molecules, which are incorporated into the plasma membrane – Antigen receptors sticking up from cell surface recognize specific antigens and mount a defense Millions of diverse B and T cells stand ready to recognize and bind virtually every possible antigen

18 Bone marrow Stem cell Immature lymphocyte Via blood Thymus Antigen receptors B cell Humoral immunity Via blood T cell Cell-mediated immunity Final maturation of B and T cells in lymphatic organ Lymph nodes, spleen, and other lymphatic organs Other parts of the lymphatic system


20 Antigens have specific regions where antibodies bind to them Antigens are usually molecules on the surface of viruses or foreign cells Antigenic determinants are the specific regions on an antigen to which antibodies bind – Antigens may have several different determinants – Immune system may direct several distinct antibodies against one antigen

21 Antibody A molecules Antigen- binding sites Antigen molecule Antigenic determinants Antibody B molecule

22 Clonal selection musters defensive forces against specific antigens* Primary immune response: lymphocytes exposed to antigen for the first time – Antigen activates a small subset of lymphocytes (B cells) bearing complementary receptors – The selected B cells multiply into clones of effector and memory cells

23 Effector (plasma) cells* – Combat the antigen – Secrete antibody molecules that circulate in blood and contribute to humoral immunity – Last only 4 or 5 days Memory cells – Remain in lymph nodes – May last for decades, sometimes confer lifetime immunity

24 Secondary immune response* – Memory cells exposed to same antigen a second time – Second round of clonal selection ensues – Secondary response is faster and stronger; produces very high levels of antibodies Animation: Role of B Cells Animation: Role of B Cells

25  Comparison of primary and secondary immune response  Primary response  Takes several days to occur, during which the individual may become ill  Antibody level peaks in about two weeks, activated cells die out  Secondary response  Occurs quickly  Is of greater magnitude and lasts longer

26 Acquired immunity is specific: the body's response to a second antigen is not influenced by its response to the first one

27 Second exposure to antigen X, first exposure to antigen Y Secondary immune response to antigen X Primary immune response to antigen X Primary immune response to antigen Y First exposure to antigen X Antibodies to X Antibodies to Y Antibody concentration 0714212835424956 Time (days)

28 Antibodies are the weapons of humoral immunity Antibody molecules are secreted by plasma (effector) B cells Antibody molecule structure – Y shaped, made of two identical "heavy" and two identical "light" polypeptide chains – A C (constant) and a V (variable) region on each chain – Antigen-binding sites specific to the antigenic determinants that elicited its secretion

29 Antibody functions in humoral immunity – Binds its antigen at the antigen-binding site – Assists in elimination of the antigen, at the C region of the heavy chains


31 Antibodies mark antigens for elimination Involves a specific recognition-and-attack phase followed by a nonspecific destruction phase Antibodies mark invaders by forming antigen- antibody complexes Binding triggers ways to eliminate the invader – Neutralization – Agglutination of microbes – Precipitation of dissolved antigens – Activation of complement system

32 Binding of antibodies to antigens inactivates antigens by Neutralization (blocks viral binding sites; coats bacteria) Agglutination of microbes Virus Bacterium Bacteria Precipitation of dissolved antigens Antigen molecules Activation of complement system Complement molecule Hole Foreign cell Cell lysisPhagocytosis Enhances Macrophage Leads to

33 Monoclonal antibodies are powerful tools in the lab and clinic Antibodies are used in clinical diagnosis, treatment, and research (pregnancy tests, cancer) Monoclonal antibodies – All cells producing the antibodies are descendants of a single cell – Harvested from cell cultures rather than from animals

34 Production of monoclonal antibodies* – Animal injected with antigen that stimulates its B cells to make specific antibodies – B cells fused with tumor cells – Hybrid cells make antibodies specific for the desired antigenic determinant Can multiply indefinitely in culture - Harvest antibodies

35 Antigen injected into mouse B cells (from spleen) Tumor cells grown in culture Tumor cells Cells fused to generate hybrid cells Single hybrid cell grown in culture Antibody Hybrid cell culture, producing monoclonal antibodies

36 Helper T cells stimulate humoral and cell-mediated immunity Cell-mediated immunity produced by T cells battles pathogens that have entered body cells T cells respond only to antigens present on the surface of the body's own cells – Cytotoxic T cells attack infected cells – Helper T cells Help activate T cells, B cells, and macrophages Interact with antigen-presenting cells

37 Precise interaction of antigen-presenting cells and helper T cells – Antigen-presenting cell self protein binds antigen nonself molecules and displays them on the cell surface – Helper T cells recognize and bind to the self-nonself complex Depends on highly specific receptors in the T cell's plasma membrane – Binding activates helper T cells Enhanced by other signals

38 Activated helper T cells promote the immune response, particularly secretion of stimulatory proteins – Make helper T cells grow and divide, producing memory cells and additional helper T cells – Help activate B cells, stimulating humoral immunity – Stimulate activity of cytotoxic T cells

39 Microbe Macrophage Self-nonself complex Antigen from microbe (nonself molecule) Self protein Antigen-presenting cell T cell receptor Interleukin-1 stimulates helper T cell Binding site for antigen Binding site for self protein Helper T cell Interleukin-2 stimulates cell division B cell Interleukin-2 activates other B cells and T cells Cell-mediated immunity (attack on infected cells) Cytotoxic T cell Humoral immunity (secretion of antibodies by plasma cells)

40 Cytotoxic T cells destroy infected body cells Like helper T cells, cytotoxic T cells recognize and bind with self-nonself complexes on infected cells Mechanism of cytotoxic T cell action – Binding to infected cell stimulates cytotoxic T cell to synthesize perforin – Perforin makes holes in infected cell's membrane, and T cell enzymes enter – Infected cell is destroyed

41 Cytotoxic T cell binds to infected cell Self-nonself complex Perforin molecule Cytotoxic T cell Enzyme that can promote apoptosis Hole forming Perforin makes holes in infected cell’s membrane and enzyme enters Foreign antigen Infected cell is destroyed Infected cell

42 Cytotoxic T cells may help prevent cancer Genetic changes leading to cancer can result in new proteins displayed on cell surfaces T cells identify these tumor antigens as foreign and destroy the affected cells

43 Allergies are overreactions to certain environmental antigens Allergies are abnormal sensitivities to antigens (allergens) in the surroundings Allergic reactions occur in two stages – Sensitization: initial exposure to allergen Allergen enters bloodstream B cells make antibodies Antibodies attach to mast cells that produce histamines and trigger the inflammatory response

44 – Later exposure to same allergen Allergen binds to antibodies on mast cell Histamine is released, causing allergy symptoms Anaphylactic shock is a severe allergic reaction – Causes severe drop in blood pressure – Potentially fatal

45 B cell (plasma cell) Mast cell Antigenic determinant Allergen (pollen grain) enters blood stream B cells make antibodies Histamine Antibodies attach to mast cell Sensitization: Initial exposure to allergen Allergen binds to antibodies on mast cell Histamine is released, causing allergy symptoms Later exposure to same allergen

46 Blood Clotting Crazy

47 Blood Clotting Better

48 Blood Clotting Best*

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