1. The Immune System Joshua Asiaban Imelda Hernadez AP Biology 4-26-14

3. Difference between Invertebrates and Vertebrates Invertebrates have only: Innate Immunity Vertebrates have both: Innate and Acquired Immunity

4. Innate Immunity of Invertebrates Mostly composed chitin-based barriers that provides defense against infection. Lysozymes: enzymes that digest microbial cell walls Some hemocytes use phagocytosis to ingest and digest bacteria and bacteria and secrete anitmicrobials to kill bacteria.

5. Innate Immunity of Vertebrates Barrier Defenses – Skin: Block entry of microbes – Mucous membranes: Line the digestive, respiratory, urinary, and reproductive tracts that trap bacteria. – Saliva, tears, and mucous membranes washes out microbes. Also, there are high amount of lysozymes in these substances which kill bacteria.

6. Innate Immunity of Vertebrates Cellular Innate defenses – Toll-like receptors (TLR): recognize fragments of molecules that have characteristics of pathogens. – Neutrophils: signals from infected tissues attract these which engulf and destroy microbes. – Macrophages: an even more effective phagocytic defense.

7. Innate Immunity of Vertebrates – Eosinophils: low phagocytoic activity but are important for defending against mulitcellular invaders such as parasite worms by using destructive enzymes. – Dendritic cells: populate tissues and stimulate acquired immunity.

8. Innate Immunity of Vertebrates Antimicrobial peptides and proteins: – Interferons: when body cells are infected, they secrete interferons which inhibit viral reproduction. – Complement system: about 30 proteins in the plasma that fight infections. Important in Inflammation.

9. Inflammation Occurs when some type of tissue is cut or damaged. Histamine, an important signaling molecules is secreted by mast cells and white blood cells near the site of damage. This triggers nearby blood vessels to dilate and become more permeable. This allows the entry of antimicrobial peptides and also attracts more phagocytic cells.

11. Natural Killer cells Recognize and eliminate certain diseased cells in vertebrates using MHC molecules (we will talk about them later.

12. Acquired Immunity of Vertebrates Lymohocytes: either B or T cells that come from bone marrow and develop in the thymus. They recognize antigens (any foreign molecules, but are usually polysaccarides and peptides. B and T cells can recognize these antigens based on their epitopes (antigenic determinants.

13. Antigen Receptors B and T cells each have their own receptors

14. Antigen receptors We have about 1 million different B cells and 10 million T cells with different receptors, how? Well, each variable region has about 40 different segments, and there are also joining regions between the chains that have 5 segments, so: 40 X 5 = 200 combinations. They are combined together during early development where a recombinase enzyme binds a V and J gene segments randomly.

15. Antigen Receptors; Self and Nonself Because antigen receptor genes are randomly rearranged, some lymphocytes produce receptors specific for epitopes on the body's own molecules. However, to fix this; lymphocytes are tested for self-reactivity and are destroyed by apoptosis or rendered nonfunctional.

16. How do B cells recognize antigens? B cells will only bind to an intact antigen, whether the antigen is free or on the surface of a pathogen.

17. How do T cells recognize antigens? T cells will recognize antigen fragments that are displayed or presented on the surface of host cells. The host cells will use MHC (major histocompatibility complex) that is produced by the host cell when it has an antigen fragment in order to present the antigen to a T cell. There are two types of MHC molecules: – Class I: bind to peptide fragments of foreign antigens synthezies within the cell. Only cytotoxic T cells bind to this.

18. Cont. – Class II: made only by dendritic cells, macrophages, and a B cells. They bind to antigen famgens derived from foreign materials that have been internalized by phagocytosis or endocytosis.

19. What happens when B and T cells interact with antigens? Clonal selection occurs which: B or T cells will proliferate (duplicate) and create: – Effector cells: short-lived, attack the antigen and any pathogens produced – Memory cells: long-lived but less numerous and bear receptors specific for the antigen.

20. Clonal selection

21. Primary vs. Secondary Response Primary immune response: takes about 10-17 days to defeat since it takes time to clone the lymphocytes and make memory cells Secondary immune response: takes about 2-7 days to defeat since there are already previous memory cells that have receptors for the antigen.

22. Humoral Immune Response vs. Cell- mediated Immune Response Humoral immune response: when B cells are activated which start the clonal of effector B cells (called plasma cells) which secrete antibodies that circulate in the blood and lymph. Cell-mediated immune response: when T cells are activated and clones cytotoxic T cells (the effector cells).

23. Helper T cells Helper T cells aid with the activation of both humoral and cell-mediated immune response. The Helper T cell will recognize a Class II MHC molecule on an antigen- presenting cell and will also proliferate to create activated helper T cells which then secrete cytokines that can stimulate either a B cell or a T cell.

24. Helper T cells

25. Cell-mediated Immune Response When T cells are activated through the help of helper T cells, they attach to an antigen-presenting cell and they destroy the infected cell by the secretion of proteins that cause cell rupture and cell death.

26. Humoral Immune Response A B cell can either be activated through the aid of Helper T cell's cytokines or through a direct attachment to an antigen fragment. It produces plasma cells and memory cells. d

27. Plasma Cells Equivalent to the effector cells produced by clonal selection of B cells. Create antibodies that will flow in the plasma that will damage or kill antigen-presented cells. There are different types of Antibodies: – IgM: First Ig class produced and is important by promoting neutralization (antibodies bind the pathogen's surface and prevents it from entering and infecting cells).

28. Plasma cells cont. – IgG:Most abundant in blood and some in tissue fluids; promotes opsonization (increased phagocytosis of the antigen), neutralization. -- IgA: Present in tears, saliva, mucus, and breast milk; provides defense of mucous membranes by neutralization -- IgE: Present in blood in low concentrations; triggers release from mast cells of histamine that cause allergic reactions. -- IgD: Present mostly on the surface of B cells that have not been exposed to antigens; acts as a antigen receptor in the proliferation of B cells (clonal selection).

30. Effects of Antibodies Neutralization: antibodies bind to the surface proteins of a virus or bacteria inhibiting it. Opsonization: the biding of antibodies to antigens on the surface of bacteria to promoe phagocytosis. Activation of complement system: activates the proteins from the complement system to open a pore in the cell's membrane to kill it through lysis.

33. Active vs. Passive Immunity Active immunity: when acquired immunity develops naturally through either infection or vaccination. Passive Immunity:when an individual receives antibodies such those passed through the fetus.

34. Spleen It filters blood, destoryes old or damaged blood vesseld through the use of T cells that look for foreign particles while the blood is flowing.

35. Lymphatic System Equivalent of the spleen, but instead it filters Lymph (fluids from tissues). This lymph is collected at various locations and circulates through lymph nodes which will eventually come back to the blood for circulation. The lymph nodes contains the same cells found in the spleen also.

37. Allergies Hypersensitivity reaction to a particular allergen When you get allergies a class of immunoglobulin called IgE triggers release from mast cells and basophils of histamine and other chemical that causes allergic reaction It's the histamine that causes sneezing, running nose, tearing eyes, and smooth muscle contractions that can result in breathing difficulty Drugs called antihistamine takes ways the allergy symptoms by blocking receptors for histamine.

38. Autoimmune Diseases Def: An immunological disorder in which the immune system turns against itself. Systemic lupus erythematosus also know as lupus, the immune system generates antibodies against histones and DNA released by the normal breakdown of body cells. -> causes skin rashes, fever, arthritis, and kidney dysfunction. - rheumatoid arthritis leads to damage and pain inflammation of the cartilage of the bone joints

39. Autoimmune Diseases cont. Multiple sclerosis -- T- cells infiltrate the central nervous system leading to destruction of the myelin sheath that surrounds parts of many neurons

40. Immunodeficiency Diseases A disorder in which the ability of an immune system to protect against pathogen is defective or absent - AIDS/ HIV -> the pathogen causing this escapes and attacks the acquired immune response -> virus binds specifically to the cells CD4 molecules. Takes over the host cell. If not treated HIV infection will attack and destroy the immune responses in your body. -> causing death

41. Questions 1. Which statement best describes the difference in responses effector B cells (plasma cells) and cytotoxic T cells ? a. B cells confer active immunity; cytotoxic T cells confer passive immunity. b. B cells kill viruses directly; cytotoxic T cells kill virus infected cells. c. B cells secrete antibodies against a virus; cytotoxic T cells kill virus- infected cells d. B cells accomplish the cell- mediated response; cytotoxic T cells accomplish the humoral response. e. B cells respond the first time the invader is present; cytotoxic T cells respond subsequent times.

42. Questions cont. 2. Which of the following is not true about helper T cells? a. They function in cell-mediated and humoral responses. b. They are activated by polysaccharides fragments. c. They bear surface CD4 molecules. d. They are subject to infection by HIV. e. When activated, they secrete cytokines Answers on next slide >>>>

43. Answer to Multiple Choice 1. C 2. B

44. Free Response Question Explain how the immune system achieves the following: a)Provides an immediate nonspecific immune response b)activates T and B in response to an infection c) responds to a later exposure to the same infection agent d)Distinguishing self from nonself.

45. Bibliography Reece, Jane B., and Neil A. Campbell. Campbell Biology. Boston: Benjamin Cummings / Pearson Education, 2011. Print.