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Bio6Immune.doc Bio6Immune.doc Document Transcript

  • Immune system (chapters 13 and 15) Immune system The parts of the body that guard against pathogens (disease-causing organisms, such as bacteria and viruses) • Infection = An invasion of the body by a pathogen • The body’s defenses against pathogens also defend against certain cancers • The immune system distinguish pathogens from normal body cells by the antigens present on each cell type √ Antigens = Molecules (usually proteins, carbohydrates and fats on the surface of a cell) that the immune system can interact with - Self antigens = Antigens that are made naturally as part of the body - The immune system does not attack cells displaying only self antigens - Foreign antigens = Antigens that are not a natural part of the body (such as antigens of viruses and bacteria) - The immune system attacks cells displaying foreign antigens White blood cells (WBC) (leukocytes) The blood cells that are part of the immune system • There are five basic types of WBCs, each with its own role in the defending the body WBC cell type Function Neutrophils Phagocytosis Eosinophils Phagocytosis Basophils Release histamine Monocytes Phagocytosis √ (become macrophages) Lymphocytes Roles in specific √ (There are two types: immune system B cells and T cells) Fig 13.13
  • Phagocytosis One cell engulfing (eating) another cell • Neutrophils and monocytes (macrophages) are the two most active phagocytes Fig 15.2 The “battlefields” where the body defenses fight pathogens are usually the blood and the lymphatic system Lymphatic system A network of vessels and ducts throughout the body that (a) return lymph (excess tissue fluid) back to the circulatory system, and (b) filter the lymph to cleanse it of pathogens • Lymph nodes = Hollow structures located at the points where lymphatic vessels converge √ The lymph is filtered at the lymph nodes √ Many immune system cells are stationed at the lymph nodes • All lymph vessels eventually converge into either the thoracic duct or the right lymphatic duct √ These two large lymph ducts drain the lymph back into the circulatory system Fig 13.37, 13.38, 13.39 Lymphoid organs that filter/cleanse non-lymph fluids • Tonsils = filter/cleanse fluids in upper respiratory system • Peyer’s patches = filter/cleanse fluids in digestive system • Spleen = filters/cleanses blood The body has two defensive systems: • The non-specific (innate) immune system • The specific immune system
  • The non-specific immune system The defense system that makes the body less accessible and less hospitable to pathogens in general (but does not target specific pathogens) • Skin = Physically blocks pathogens from entering the body • Phagocytes = WBCs that engulf pathogens √ The three phagocytic WBCs: Neutrophils, Eosinophils, and Monocytes/Macrophages • Interferons = Proteins that inhibit viruses from entering cells • Fever = Elevated body temperature √ Inhibits bacterial growth √ Speeds up body defenses • Complement = Blood proteins that rupture pathogen cell membranes • Inflammation = The redness, heat, swelling, and pain in injured tissues √ The redness and swelling are caused by basophil WBCs releasing histamine, a molecule that makes the capillaries leaky so WBCs can exit the blood vessel to attack pathogens in the injured tissue √ Injured cells release molecules that attract WBCs and activate pain receptors Fig 15.5, tables 15.1 and 15.5 The specific immune system The defense system that makes precise attacks against individual specific pathogens by recognizing their foreign antigens • Cells of the immune system: Lymphocytes (T cells and B cells) • The immune system has “memory”: It attacks pathogens more effectively if it has encountered them before • The immune system has two branches: The humoral immune system and the cell mediated immune system • The humoral immune system attacks pathogens using antibodies (proteins that bind to the pathogen’s antigens) √ B cells make the antibodies and release them into the lymph and blood • The cell mediated immune system attacks pathogens using cells √ T cells (activated by macrophages) destroy pathogens Table 15.4
  • Humoral (antibody-mediated) immune system function • Each B cells makes and coats its surface with an antibody against only one specific foreign antigen √ We have thousands of different B cells so we have antibodies against thousands of different foreign antigens • If the surface antibody binds its antigen, the B cell divides repeatedly √ This produces thousands of identical clones of the B cell • Most of the clones release their antibodies, allowing the antibodies to circulate widely in the body • Memory B cells = The clones that retain their antibodies √ Memory cells remain ready to divide in future encounters with the antigen • Circulating antibodies coat the outside of any pathogen cell that has the antigen √ Complement proteins rupture (“fix”) antibody-coated cells √ The antibody coat prevents the pathogen cell from functioning properly √ The antibodies link together (“agluttinate” or “precipitate”) the pathogen cells, which helps the body eliminate them Figs 15.7, 15.12, 15.13, 15.22, 15.23
  • The cell mediated immune system • The first step is when a macrophage engulfs a pathogen √ The pathogen’s foreign antigens are displayed by the macrophage on its surface • Each T cell is programmed to attack only one specific foreign antigen √ We have thousands of different T cells, each programmed to attack a different foreign antigen • T cells become activated only after they encounter a macrophage displaying their specific foreign antigen • Once activated, T cells divide repeatedly, producing thousands of clones of themselves The clones of the activated T cell come in three types: √ Killer T cells = They attack the pathogen directly √ Helper T cells = They make B and T cells divide √ Memory T cells = They remain ready to divide in future encounters with the pathogen Fig 15.18, 15.19 Detrimental immune system reactions • Autoimmune diseases = Any disorder caused by the immune system attacking self antigens in specific tissues or organs √ Examples: Multiple sclerosis, rheumatoid arthritis, lupus • Allergies = Excessive (tissue damaging) responses to harmless antigens in the environment √ Effects = Rash (hives), watery eyes and nose, itching, asthma √ Anaphylactic shock = A life-threatening allergic response to allergens that enter and circulate within the body • Rejection of organ transplants √ Immune suppressive therapy reduces rejection, but increases patient’s susceptibility to pathogenic diseases Table 15.10
  • Immunodeficiencies Disorders that weaken or eliminate the immune system • SCID (Severe combined immunodeficiency disease) = a congenital (genetically inherited) absence of the immune system • AIDS (Acquired immune deficiency syndrome) = An acquired disease in which the HIV virus destroys Helper T cells √ Helper T cells are needed to make B and T cells divide √ There is a months to years delay between viral infection and onset of immune system deterioration √ AIDS is spread by exchange of bodily fluids √ 1 million victims in US; 40 million worldwide