Immune System

1. Immune System Chapter 21

2. Immune System • Elaborate defense system that protects the body from pathogens • Also provides protection from other foreign agents including pollens, toxins and cancer cells • Classified as specific and nonspecific immunity; divided into three lines of defense

3. Nonspecific Immunity • Nonspecific immunity protects the body against many types of foreign agents • Body does not recognize specific foreign agents • First line of defense • Mechanical and chemical barriers, reflexes • Second line of defense • Phagocytosis, inflammation, fever, protective proteins, natural killer cells

4. First Line of Defense • Mechanical barriers • Intact skin and mucous membranes • Chemical barriers • Tears, saliva and perspiration help wash away microorganisms; tears secrete lysozyme • Stomach acid & digestive enzymes create a hostile environment • Mucus creates a sticky environment; traps particles in the respiratory tract which are swept away by cilia

5. First Line of Defense • Reflexes • Sneezing and coughing help remove pathogens from the respiratory tract • Vomiting and diarrhea help remove pathogens from the digestive tract

7. Second Line of Defense • Phagocytosis • Leukocytes ingest and destroy pathogens and other foreign substances • Can be motile or fixed • Motile cells respond to injury; sense chemical signals sent out by injured cells (chemotaxis) • Fixed cells- macrophages (“big eater”); remain in certain organs and filter blood as it passes through (liver, spleen, lungs)

8. Second Line of Defense • Inflammation • Response the body makes when confronted by an irritant (pathogens, friction, excessive heat or cold, radiation, injury, chemicals) • If the irritant is a pathogen, the inflammation is called an infection • Characterized by redness, heat, swelling and pain (rubor, calor, tumor, dolor)

9. Inflammation • When tissues are injured, the cells release histamine (and other substances) • Cause blood vessels near the site to dilate and bring more blood to the area • Histamine causes blood vessel walls to leak fluid into the tissue space • Fluid and irritating chemicals accumulate at the injured site

10. Inflammation • Increased blood flow carries more phagocytes to injured site • Phagocytes may be killed in the process of destroying foreign particles; the accumulation of dead leukocytes, pathogens, injured cells and tissue fluid is called pus • Clotting factors are also secreted- helps to prevent the spread of infection

12. Second Line of Defense • Fever • Also known as pyrexia (fever reducers are known as antipyretics) • Pyrogens are released by phagocytes as they are doing their job • Pyrogens stimulate the hypothalamus to increase the body temperature • Elevated temperature stimulates phagocytosis and diminishes reproduction of some pathogens

13. Second Line of Defense • Protective Proteins • Interferons • Secreted by cells when those cells are infected with a virus; diffuse to surrounding cells to prevent viral replication • Complement proteins • Circulate in the blood in an inactive state; when activated against a bacterium, the proteins attack the cell and punch holes in the cell membrane; the bacterium bursts and dies

14. Second Line of Defense • Natural Killer (NK) Cells • Specialized lymphocyte that acts nonspecifically to kill a variety of cells • Effective against many microbes and certain cancer cells • Work with the other lines of defense to increase their protective properties

15. Natural killer cells attacking an infected cell (Image: Jerry G Johnson from The World of Biology)

17. Specific Immunity • Third Line of Defense • Provides protection against one specific substance and no other • Most important cells in this type of immunity: • B lymphocytes • T lymphocytes • Macrophages

18. Antigens • Antigen is a substance that stimulates the formation of antibodies • Generally large molecules, usually proteins; found on the surface of pathogens, RBCs, pollens, food, toxins & cancer cells • Antigenic substances are attacked by lymphocytes

19. Self vs. Non-Self • Before birth, the cells of the body learn to recognize what cells are “you” (self) and what cells are “not you” (non-self- foreign agent) • Body perceives non-self cells as antigenic and tries to get rid of them (the basis of autoimmune diseases)

20. Lymphocytes • T lymphocytes • Originate from the thymus gland • B lymphocytes • Originate from bone marrow • Both attack antigens, but through different mechanisms

21. Lymphocytes • T lymphocytes • Attack antigens directly, through cell to cell contact • This mechanism is referred to as cell-mediated immunity

23. Lymphocytes • B lymphocytes • Interact with the antigen indirectly, through the secretion of antibodies • Process is called antibody-mediated immunity (or, humoral immunity) • Activated B cells produce antibodies which react against specific antigens (individual cells can produce millions of antibodies)

25. Helper T cells • Both T and B lymphocytes depend on helper T cell activity • HIV attacks these helper T cells, which severely affects the immune system • Helper T cells are also called CD4+ T cells (named for a protein on their surface); a CD4 count is a marker for the function of the immune system; as AIDS progresses, the CD4 count decreases

26. Antibodies • Antibodies secreted by the B cells are called immunoglobulins; found primarily in the plasma • Most abundant in the body are • Immunoglobulin G (IgG) • Immunoglobulin A (IgA) • Immunoglobulin M (IgM)

27. Antibodies • Antibodies destroy antigens • Antibodies either destroy antigens directly by attacking the membrane, or indirectly by activating complement proteins • Direct attacks are called antigen-antibody reaction • Indirect attacks promote chemotaxis, agglutination (clumping), lysis and phagocytosis

28. Primary & Secondary Response • Primary Response • When exposed to an antigen, B cells produce plasma cells and memory cells • Plasma cells secrete antibodies • Slow development of response and low blood levels of antibodies

29. Primary & Secondary Response • Secondary Response • If the same antigen is presented again, the body responds much faster and produces a large number of antibodies • Stimulated by memory cells (live for a long time in the plasma) • Provides immunity from certain diseases (if you had measles as a child, for example, you cannot get it again); the levels of antibodies in the blood is called an antibody titer

30. Types of Immunity • Genetic Immunity • Inherited immunity to certain diseases • Based on genetic makeup • Also called innate, inborn or species immunity • Means you cannot get certain diseases that affect other species (canine heartworm, for example)

31. Acquired Immunity • Naturally Acquired Immunity • Active Immunity (achieve immunity by getting the disease, as in the secondary response) • Generally long-lasting • Passive immunity (acquired before birth from mother; also passed through breastmilk) • Provides only about six months protection

32. Acquired Immunity • Artificially Acquired Immunity • Vaccine (an antigen-bearing substance injected into a person to stimulate antibody production) • Vaccines containing a pathogen that is first weakened or killed is called attenuated (still cause antibody production, but too weak to cause disease) • Vaccines can also be made from toxins secreted by the pathogen (still produces immunity); called toxoids

33. Acquired Immunity • Artificially Acquired Immunity • Immune globulin (obtained from a donor; contain antibodies to respond to a specific antigen) • Provide immediate protection, but not as long-lasting • Available for diseases like rubella (German measles, hepatitis A and B, rabies and tetanus)

34. Acquired Immunity • Artificially Acquired Immunity • Antitoxins (contain antibodies that neutralize the toxins secreted by the antigens; do not affect the actual pathogen) • Antitoxins include tetanus antitoxin, diptheria and botulism • Antivenoms contain antibodies that protect from the effect of venom from poisonous snakes

36. Other Immunologic Responses

37. Allergic Reactions • Delayed reaction allergy • Usually about 48 hours to occur • Usually results from repeated exposure, resulting in a contact dermatitis • Include reactions to things like cleaning chemicals, poison ivy, soaps, cosmetics, latex, etc…

38. Allergic Reactions • Immediate hypersensitivity reaction • Occurs immediately, involves IgE • Allergen (antigen) activates a B cell; forms clones- plasma cell secretes antibodies; plasma cell secretes large amounts of IgE; IgE binds to mast cells in body tissues; mast cells release large amounts of histamine, leukotrienes and other substances that cause systemic effects…

39. Allergic Reactions • Immediate hypersensitivity reaction • Anaphylaxis is the most severe form of hypersensitivity reaction; results in massive vasodilation, hypotension and bronchoconstriction; anaphylactic shock may result • Certain antibiotics (especially penicillin) cause anaphylaxis, also food (peanuts) and insect stings (bee venom)

40. Examples of allergic reactions to medications

41. Anaphylaxis

42. Autoimmune Disease • Occurs when a person’s own T cells attack their body • Diseases that result from these attacks are called autoimmune diseases • Include systemic lupus erythematosis (SLE), rheumatic fever, rheumatoid arthritis

43. Hand deformity from rheumatoid arthritis Hallmark “butterfly rash” of SLE

44. Organ Rejection • When organs are transplanted, the patients body perceives the tissue as foreign, so it attacks the tissue with its defenses • If the immune attack is successful, the organ is said to be rejected • Organs are selected that are immunologically similar and drugs are given to suppress the patient’s immune system