Immunity Chapter 48

1. ImmunityChapter 48 April Sike AP Biology April, 2011

2. Summary We survive because we have evolved a variety of defenses against constant attack. The first line of defense consists the mechanisms for preventing bacteria from entering the body. The second line of defense consists mechanisms for dealing with any foreign substances in the body. All organisms have the mechanics to protect themselves from the onslaught of smaller organisms and viruses.

3. Evolutionary development • Invertebrates • Vertebrates

4. Invertebrates • In 1882 Elie Metchnikoff became the first to recognize that invertebrate animals have immune defenses. • The invertebrate immune response shares several elements with the vertebrate one.

5. Phagocytes • All animals have phagocyticcells that attack invading microbes. • These cells travel through the animal’s circulatory system. • In animals that do not have a circulatory system the phagocytic cells roam inside the mesoglea.

6. Distinguishing Self from Nonself • The ability to recognize the difference between cells of your own body and cells from another individual seems to have evolved early in the history of life. • Sponges, thought to be the most ancient animals, attack tissues from other sponges just like insects and starfish. • None of these invertebrates seem to show any evidence of having an immune system. • Apparently the humoral immune defense did not evolve until vertebrates.

7. Lymphocytes • Lymphocyte – A type of white blood cell responsible for the immune responses, two classes; B cells and T cells. • Invertebrates do not have complementary proteins or lymphocytes. • But annelid earthworms and other invertebrates do have lymphocyte-like cells that may be evolutionary precursors of lymphocytes.

8. B and T cells • B cells: B cells respond to helper T cells by interleukin-1. B cells have receptor proteins on their surface, one type of receptor for each type of B cell. • T Cells: protect the body from virus infection and cancer, by killing abnormal cells.

9. B Cells: The Humoral Immune Response • In this response, the immune system triggers specific B cells to make large amounts of their specific antibodies. These antibodies can fight viruses and stop infection. • http://bcs.whfreeman.com/thelifewire/content/chp18/1802004.html

10. T Cells: Cellular Immune Response • Cells of this system kill cells of the body that are cancerous. This response relies on the lethal cytotoxic T cells. They contain molecules, called perforin, that they release into target cells. The perforin pokes holes in the target cells and kills them. • http://bcs.whfreeman.com/thelifewire/content/chp18/1802003.html

11. Vertebrates • The earliest vertebrates, the jawless lampreys first evolved some 500 million years ago. • They have an immune system based on lymphocytes. • At this early stage of vertebrate evolution, however, lampreys lack distinct populations of B and T cells that are found in all higher vertebrates.

12. The modern vertebrate immune system first arose with the evolution of fish with jaws. • The oldest surviving group of jawed fishes are the sharks, which evolved 450 million years ago. By then the vertebrate immune defense had been fully evolved. • Sharks have an immune response similar to mammals, with a cellular response carried out by T cell lymphocytes and humoral response carried out by B cells.

13. Necessary • The Immune system is necessary for survival because without it organisms would not be able to protect themselves against viruses or diseases. We would be subject to every infection and disease and not survive. • There is no example in the world of an organisms functioning without an immune system, but there are examples of organisms being born without specific parts of their immune system, making them susceptible to infection by certain types of viruses.

14. Structures and functions of the system • Skin: The first line of defense • Cellular Counterattack: 2nd line of defense • The Immune Response: 3rd line of defense

15. Skin: 1st line of defense • The largest organ of the vertebrate body, provides nearly impenetrable barriers and reinforces defenses with surface chemical weapons. • Mucus membranes of the digestive, and reparatory help trap and get rid of microorganisms before they invade the body’s tissue.

16. Cellular counterattack: 2nd line of defense • Macrophages – big phygocytic cells that can digest invading bacteria. • Cellular and chemical defenses respond to any microbial infection. • Neutrophils (capable of engulfing microorganisms and other foreign particles) kill cells of the body infected with viruses.

17. The Immune Response: 3rd line of defense • The pathogen enters the body. • Macrophages with antigen fragments displayed on their surfaces are called antigen-presenting cells. An antigen-presenting macrophage interacts with a T-helper cell that can recognize the same antigen. • During the interaction, the macrophage releases a chemical alarm signal called interleukin-1, which stimulates the T-helper cell to secrete interlukin-2.

18. The Immune response

19. 1.) Damaged tissues release histamines, increasing blood flow to the area. 3.) Phagocytes engulf bacteria, dead cells, and cellular debris. 2.) Histamines cause capillaries to leak, releasing phagocytes and clotting factors into the wound. 4.) Platelets move out of the capillary to seal the wounded area.

20. Interdependence of this system with other body systems The immune system works closely with the circulatory system for transportation needs by means of blood cells, allowing the immune cells to travel throughout the body and survey the body for infection. The nervous system uses the brain to help stimulate the defense mechanisms against infection, and the skeletal system provides the blood cells that the immune system needs.

21. The immune System & The Lymph  System • Lymph organs include the bone marrow, lymph nodes, spleen, and thymus. Bone marrow contains tissues that produce lymphocytes. • B-cells mature in the bone marrow. • T-cells mature in the thymus gland. • Other blood cells like monocytes and leukocytes are made in the bone marrow. • The thymus makes the hormone; thymosin, that causes T-cells to mature in the thymus.

22. 3 types of diseases or disorders of the system • T Cell Destruction • Antigen Shifting • Autoimmunity and Allergy

23. T Cell Destruction • Many helper T Cells and inducer T cells are CD4+ T cells. Therefore, any pathogen that inactivates CD4+ T cells leave the immune system unable to mount a response from any foreign antigen.

24. Antigen Shifting • A pathogen may escape recognition by the immune system if it changes its surface antigens. Such antigen shifting is an example of evolution by natural selection.

25. Autoimmunity and Allergy • Autoimmunity diseases are produced by failure of the immune system to recognize and tolerate self-antigens, and can result from a variety of mechanisms. • Allergies can be divided into immediate hypersensitivity and delayed hypersensitivity, both of which can cause the release of histamine. • In extreme cases, the widespread release of histamine can lead to anaphylactic shock.