Understanding the Immune System in Animals

1. By:Diana Marzulli, Sony Abraham andLindsay Davenport

2. Introduction The immune system is a complex, highly developed system. The function of this system is to protect the animal from intruders that could potentially harm them Animals have two major forms of immunity: innate immunity and acquired immunity

3. Innate Immunity Provides a broad defense against infection. An animal passes these defenses onto offspring. It is a non-specific defense: all antigens are attacked equally. Divided into two parts: external defenses and internal cellular and chemical defenses.

4. External Defenses: Skin and the Mechanical Response to Pathogens Skin is the most important of the external defenses. Normally, bacteria and viruses cannot penetrate the skin. However, if there is an opening in the skin (such as a scratch or a cut) then the pathogens may enter. That is where the other forms of external defenses kick in. Pathogens are expelled from the lungs by ciliary action. As the tiny hairs move in an upward motion, coughing and sneezing abruptly eject both living and nonliving things from the respiratory system. Tears, saliva, and urine flush pathogens from the body.

6. External Defenses: Mucous Membranes and Secretions • Mucous membranes line the digestive, respiratory, and genitourinary tracts. They stop the entry of potentially harmful microbes. • Certain cells produce mucus: a fluid that traps microbes and other particles. • Bodily secretions cause an environment that is hostel to microbes. • The body produces lysosomes which destroy susceptible bacteria as the enter the upper respiratory tract or other openings.

7. Internal Cellular and Chemical Defenses: Phagocytotic Cells The microbes that do manage to break through the external defenses are then attacked by the internal defenses. These defenses mainly rely on phagocytosis: the ingestion of invading microorganisms by certain types of white blood cells. These white blood cells, called phagocytes, attach to the microbes via surface receptors found on microorganisms but not normal body cells. The cell then engulfs the microbes it has attached to and forms a vacuole that fuses with a lysosome. The lysosome then destroys the microbe through poisoning or degradation.

8. Internal Cellular and Chemical Defenses: Inflammatory Response Tissue damage by either physical injury or the entry of pathogens leads to the release of chemical signals that trigger an inflammatory response. Histamine is a chemical secreted during an inflammatory response that dilates the capillaries, causing more blood to flow to the area. This increased blood supply causes the redness, heat, and associated with inflammation. This increased blood flow delivers antimicrobial proteins and other healing elements to the site. The body may also initiate a systemic response in which a fever or increase in white blood cell count. The most severe of systemic response is septic shock, which often causes death.

9. Acquired Immunity: An overview of Lymphocytes The key cells of acquired immunity that provide specific defenses against infection. Activated by the cytokines excreted by the phagocytes. Any foreign molecule recognized by the lymphocytes is known as an antigen. The lymphocyte recognizes and then binds to only a small region known as the epitope. There are two types of lymphocytes: B lymphocytes (B Cells) and T lymphocytes (T Cells). A single B or T cell contains about 100,000 antigen receptors which specific to one epitope.

10. Acquired Immunity: B Cells and T Cells B Cells are produced in the stem cells of the bone marrow. They produce antibodies (also known as immunoglobulin) and oversee humoral immunity. The recognize and bind to intact antigens. T Cells are also produced in the bone marrow, but migrate to the thymus later. Unlike the B cells, they do not produce antibodies and they recognize small fragments of antigens bound to MHC molecules. There are two types of T cells: cytotic T cells and helper T cells. Cytotic T cells eliminate infected cells from the body as well as eliminate cancer cells and transplanted cells. Helper T cells detect antigens and stimulate the activation of B cells and cytotic T cells.

11. Acquired Immunity: Humoral and Cell-Mediated Immunity The humoral immune response involves both the activation and clonal selection of B cells. This results in the production and secretion of antibodies that travel in the blood and the lymph. Cell-mediated immune response involves the activation and clonal selection of T cells to destroy target cells.

12. The Immune System and Transplants The immune system has the ability to recognize the body’s own cells from those of another individual. This can lead to problems if a transplant is ever needed. Blood transfusions need to be done with either a donor that matches the person’s exact blood type or with blood that is type O (the universal donor). In order for a tissue or organ transplant to take place, the recipient has to be matched with a donor that has MHC molecules that closely resemble those of the recipient. The recipient is also given medication that suppresses immune responses. This can leave the recipient more susceptible to disease during the treatment.

13. Diseases That Affect The Immune System Allergies are responses to a certain type of antigen called an allergen. During an allergy attack, histamines are released and the usual reaction takes place (sneezing, watery eyes, coughing, etc.). Antihistamines diminish the symptoms. An attack can sometimes lead to anaphylactic shock, a severe drop in blood pressure upon being exposed to an antigen. This can cause death within a few minutes. Autoimmune diseases occur when the immune system loses tolerance for itself and turns on the body. Examples of autoimmune diseases include lupus, rheumatoid arthritis, and multiple sclerosis) Immunodeficiency diseases are caused by the inability of the immune system to protect the body from pathogens. They can either be inborn (primary immunodeficiency) or develop later in life (acquired immunodeficiency). Acquired immunodeficiency can be temporary and is often caused by stress. An example of a disease in this category is AIDS.

14. How the Lymphatic and Immune Systems are Connected • White blood cells attack any bacteria or viruses they find in the lymph as it flows through the lymph nodes. If cancer cells break away from a tumor, they often become stuck in the nearest lymph nodes. This is why doctors check the lymph nodes first when they are working out how far a cancer has grown or spread. • Filtering the blood is the job of the spleen. It filters the blood to take out all the old red blood cells and then destroys them. They are replaced by new red blood cells that are made in the bone marrow. The spleen also filters out bacteria, viruses and other foreign particles found in the blood. White blood cells in the spleen attack bacteria and viruses as they pass through.

15. Continued… • When people say "I'm not well, my glands are up" they are really saying they have swollen lymph nodes because they have an infection. The lymphatic system helps fight infection in many ways such as • Helping to make special white blood cells (lymphocytes) that produce antibodies • Having other blood cells called macrophages inside the lymph nodes; which swallow up and kill any foreign particles, for example germs • This function of the lymphatic system is really part of the immune system.

16. Activity

17. Activity 2 Match the description on the top with the terms on the bottom by writing the correct letter in each blank. _____ 1. a disease that destroys the immune system _____ 2. disease-causing bacteria _____ 3. traps pathogens in respiratory system _____ 4. contains weakened antigens _____ 5. immunity occurring when your body makes its own antibodies _____ 6. immunity occurring when antibodies are introduced from an outside source _____ 7. cells attacked by AIDS virus Word Bank a. active b. passive c. mucus d. lymphocytes e. pathogens f. vaccine g. AIDS

18. Activity 3 Pathogens play a vital role protecting your body. A virus is a preparation of a weakened or killed pathogen which is used to create antibodies. Neutrophils and lymphocytes can engulf foreign bodies by the process called phagocytosis. Serotonin is a chemical secreted during an inflammatory response. 5.Autoimmune diseases occur when the immune system loses tolerance for itself and turns on the body.

19. ANSWER KEY Matching Column: 1.G 4. F 7.D 2.E 5. A 3.C 6.B True and False: 1. F 5. T 2. F 3. T 4. F

20. Works Cited Campbell, N., Reece, J. (2005) A P Edition Biology 7th Ed., San Francisco Pearson Education http://uhaweb.hartford.edu/BUGL/immune.htm#innate http://www.cancerhelp.org.uk/about-cancer/what-is-cancer/body/the-lymphatic-system#role http://www.cancerhelp.org.uk/about-cancer/what-is-cancer/body/the-lymphatic-system#role Pictures • http://www.allthingsbeautiful.com/all_things_beautiful/2005/12/index.html • www.learner.org/courses/biology/archive/images/1924_d.html • course1.winona.edu/kbatesImmunology/chapter1.htm • course1.winona.edu/kbatesBio241/immunolo.htm • web.ukonline.co.uk/ecrbio_diag4.html • http://www.accessexcellence.org/RC/VL/GG/antibodies.php