Dynamic Defense System

1. Dynamic Defense System Ch 43 Notes

2. Pathogens • Infectious Agents that cause disease • Viruses, bacteria, protists and fungi may be pathogens • Animals fight back using immune cells

3. Innate Immunity • Found in all animals • Active immediately upon infection • Includes: barriers (skin), internal defenses • Made of preset group of receptors that binds to a molecule absent from animal bodies but found in microbes

4. Acquired Immunity • Found only in vertebrates • Activated after innate immune defense • Enhanced by previous exposure to pathogen • Very specific

6. Innate Immunity of Invertebrates • Exoskeleton – first line of defense • Chitin effective against most pathogens • Lysozyme – enzyme that digests microbial cell walls – blocks pathogens in digestive system • Phagocytosis – Ingestion and digestion of bacteria/foreign substances – fights pathogens that get through exoskeleton • Antimicrobial peptides – circulate through insect bodies to kill fungi and bacteria

7. I. Innate Immunity of Vertebrates • A. Barrier Defenses • 1. Intact skin – barrier that can’t normally be penetrated by microbes • 2. Mucous membranes – line digestive, respiratory and urogenital tract • a. Mucus – fluid secreted by mucous membranes – traps microbes and is removed from body by cilia (tiny hairs) • b. Acid – produced in stomach destroys microbes before they go into the digestive tract • Lysozyme – destroys bacteria in respiratory tract and eyes • Sweat and oil glands have low pH to kill bacteria

8. Cellular Innate Defenses • 1. Phagocytic white blood cells • Use TLR receptors to recognize pathogens • TLR triggers internal defenses • Phagocyte traps microbe, engulfs it, makes a vacuole, fuses with lysozyme, kills microbe • Neutrophils • Most numerous WBC • Infected tissue sends signals which call out neutrophils • Neutrophils engulf and destroy

10. Cellular Innate Defenses • Monocytes • enter into damaged tissue and form macrophages • attach to microbe’s surface, “eat” it and destroy it using lysosomes – YUM!! • macrophages live permanently in lungs, liver, kidney, brain, lymph nodes and spleen • If microbe is in blood – trapped in spleen • If microbe is in interstitial fluid – trapped in lymph

12. Cellular Innate Defenses • c. Eosinophils • *defend against large parasites (eeww)

13. Antimicrobial Peptides and Proteins • Interferons – proteins that provide defense against viral infections • Cells infected with virus sends out interferons • Cause uninfected cells nearby to produces substances to fight off virus • Limits cell to cell spread

14. Antimicrobial Peptides and Proteins • Complement System- 30 proteins in blood plasma • Fight infections • Circulate in an inactive state • Get activated by microbes • Causes cascade of reactions leading to lysis of invading cells

15. Inflammatory Responses • Response to tissue damage (from injury) or to entry of microorganisms • Histamine – released by mast cells at site of tissue damage • Arterioles dilate (open) and venules constrict (shrink) so that the blood supply increases in the area (swelling and redness) • *aid in blood clotting and repair • *block spread of microbes

16. Inflammatory responses • During inflammation – signals sent out • Antimicrobial proteins go to site • More histamine is released • Phagocytes attracted • Neutrophils and macrophages are called in • Ends with accumulation of Pus – filled with WBC’s, dead microbes and cell debris – YUM!!

18. Natural Killer Cells • Help recognize and eliminate certain diseased cells in vertebrates • Cells have class I MHC molecules on their surface • When a virus infects or cell becomes cancerous, cells stop expressing the MHC protein • Natural Killer cells attach to these damaged cells and cause them to die preventing spread

19. Evasion by Pathogens • Some pathogens can avoid being destroyed • Some bacteria have capsules that hide polysaccharides in the cell walls and don’t get recognized (like strep pneumoniae) • Some bacteria are resistant to breakdown after phagocytosis (like TB)

20. Acquired Immunity • Pathogen specific response • Specific response to an invader (not general defense like innate defenses

21. Acquired Immunity • Lymphocytes – WBC’s • 2 Types – B lymphocytes (B cells) and T lymphocytes (T cells) • circulate through blood and lymph and are concentrated in lymph nodes and spleen • Contribute to Immunological Memory– recognize and respond to a specific foreign invader that has been encountered previously

22. Acquired Immunity • Antigen – foreign molecule that causes a response by lymphocyte • can be found on viruses, bacteria, fungi, protozoa, parasitic worms • also found on pollen (allergies) and transplanted tissue (like heart transplant) • B cells and T cells recognize antigens using Antigen Receptors

23. Acquired Immunity • B Cells (form and mature in Bone marrow) • Produce antibodies that are specific to a particular antigen • *5 classes of antibodies (IgA, IgD, IgE, IgG, IgM) • *Structure of antibodies is basically the same except for a variable region that makes the antibody recognize specific antigens • *Antibody binds to intact antigen and inactivates it • *Macrophage comes and eats it

25. II. Specific Line of Defense – IMMUNE SYSTEM • T Cells (form in bone marrow and mature in Thymus gland) • Only bind to antigen fragments that are on the surface of host cells • recognize nonself cells • if nonself cell is identified, T cells divide rapidly and produce • Cytotoxic T cells (killer T cells) that puncture non-self cells and make them burst • Helper T cells – stimulate more B cells and killer T cells to form to help fight the invader faster

26. Acquired Immunity • T Cell receptors • Have alpha and beta chain • Also have constant region and variable region

27. Acquired Immunity • MHC – Major Histocompatability Complex • Helps immune system tell the difference between self (you) and nonself (invader) • MHC is unique to all individuals (except identical twins or clones ) • Class I • found on almost all cells of body • Bind peptide fragments of foreign antigens • If body cell is infected or cancerous, it makes foreign antigens and displays them • Cytotoxic T cells recognize these antigens and kill the infected cells

28. Acquired Immunity • MHC II • Made by dendritic cells, macrophages and B cells • Bind to foreign materials that have been taken in by phagocytosis • Cytotoxic and Helper T cells recognize them

29. Amplifying Lymphocytes Binding of an antigen receptor to its specific antigen initiates events that activate the lymphocyte B Cells and T cells amplify the response Effector cells – short lived – attack the antigen and the pathogens that are making it Memory Cells – long lived – bear receptors specific for the antigen Clonal Selection – proliferation (making lots) of clone cells in response to an antigen -Presenting of an antigen to a receptor leads to lots of cell division = thousands of cells to fight pathogen

30. Clonal Selection • Primary Immune Response- takes 10-17 days (when you get sick) • invader attacks a body cell • antigens from invader bind to a B cell with the correct receptor • B cell proliferates (makes lots of copies of itself) and makes two types of cells (effector and memory)

31. Clonal Selection • Secondary Immune Response – takes 2-7 days (usually don’t get sick) • Individual is attacked by same invader at a later time • T and B memory cells recognize the antigen much faster and produce a stronger response (2-7 days)

33. E. Categories of Immune Responses • Humoral Response • involves most body cells • responds to antigens or pathogens circulating in the blood or lymph fluid • B cells produce plasma cells • Plasma cells release antibodies that bind to invading antigen • B cells produce memory cells for future immunity • Used for Extracellular pathogens

36. Cell Mediated Response • Cell-mediated response • uses mostly T cells and responds to any nonself cell triggering the following events:

37. Cell Mediated Response • Antigen presenting cell stimulates Cytotoxic T cell • Cytotoxic T cell becomes activated • Secretes proteins to cause cell rupture and cell death • Used for Intracellular pathogens and cancer • Also makes memory T cells for future infection

40. Role of Antibodies • Bind to antigen • Interfere with pathogen in different ways • Bind to pathogen and block it’s ability to enter host • Bind to toxins released by pathogen and neutralize them • Made it easier for macrophage to recognize invader • Use a membrane attack complex to make a hole in the membrane of the foreign object – cause it to swell and burst