Chapter 21: The Immune System Flashcards
The 3 Lines of Defense Against Pathogens:
o External Barriers (innate) o a) skin o b) mucous membranes o Non-specific (innate) Internal Body Defenses o a) antimicrobial proteins o b) antimicrobial CELLS o c) fever o d) inflammatory process o Specific Immune System = “immunity”
Characteristics of Innate Defenses:
o Present at birth.
o Act instantly or very quickly.
o No prior exposure necessary.
o Response is the same EACH TIME the body is exposed to any foreign thing.
o Responses are effective against a wide range of pathogens, even pathogens our body has never seen before!
o Reduces the workload for our SPECIFIC defense mechanisms.
First Line of Defense:
External Barriers
o Skin:
o Hostile surface (dry, low pH, keratin).
o Closely packed cells; shed periodically.
o Coated with antimicrobial chemicals.
• Defensins (peptide that pokes holes).
• Lactic acid & dermcidin (from sweat).
• Lysozyme (from sweat, tears, mucus, saliva).
o Mucous Membranes:
o Mucus (sticky trap).
o Lysozyme (enzyme that is disruptive to pathogen cell walls).
o Cilia in respiratory tract.
o Coughing and sneezing.
o Tears.
o Cerumen.
o Low pH of gastric juice.
o Emesis.
o Diarrhea.
o Acid secretions of vagina.
o Acid pH of urine + periodic flow of urine.
Second Line of Defense:
Non-Specific Internal Body Defenses (4 Categories)
o 1. Antimicrobial Proteins.
o 2. Antimicrobial cells.
o 3. Pyrexia (fever).
o 4. Inflammatory process.
Second Line of Defense:
Antimicrobial Proteins
o Interferons. o Complement proteins. o Epithelial cell-derived chemicals. o Bacterial-derived chemicals (normal flora). o Proteins secreted by epithelial cells: o Cathelicidins. o Defensins. o Collectins. o Proteins secreted by bacteria that normally populate our mucous membranes.
Antimicrobial Proteins:
Interferons
o Small proteins that provide protection against viruses.
o Secreted by your own body cells that have become infected by a virus.
o These infected body cells (especially lymphocytes) secrete interferons into the IF (interstitial fluid), they bind to surface receptors on neighboring cells.
o Neighboring cells receive the signal and make anti-viral substances.
o Interferons also activate macrophages and NK cells.
o Alpha-Interferons: Produced by cells infected with viruses. Attract and stimulate NK cells and enhance resistance to viral infection.
o Beta-Interferons: Secreted by fibroblasts, slow inflammation in a damaged area.
o Gamma-Interferons: Secreted by T cells and NK cells, stimulate macrophate activity.
Antimicrobial Proteins:
Complement Proteins
o The complement system = 30 or more antimicrobial proteins that circulate in the blood in an inactive state.
o Many ways to activate the complement system!!!!
o When activated, 3 important effects:
o Inflammation.
o Enhanced Phagocytosis via opsonization.
o Cytolysis via membrane attack complexes (MACs).
Second Line of Defense:
Antimicrobial Cells
o Natural Killer Cells (NK Cells): o Immune surveillance. o Secrete perforins and granzymes. o Phagocytes: o Microphages: • Neutrophils. • Eosinophils. • Basophils. o Macrophages, from monocytes. o (Most lymphocytes are involved in specific defense mechanisms).
Antimicrobial Cells:
Natural Killer Cells
o Destroy bacteria, viruses, cancer cells, and cells of transplanted organs and tissues.
o The cells within a primary tumor may grow rapidly, and if the tumor has a surrounding capsule, the cells within may not provoke a massive response by NK cells.
o As a malignant tumor cells begin migrating into surrounding tissues, they can be detected and destroyed by NK cells.
o Sometimes a daughter cell will be produced that either doesn’t display tumor-specific antigens, or that secretes chemicals that destroy NK cells. Such as a cell will survive and be free to grow and divide.
o Once immunological escape has occurred, cancer cells can multiply and spread without interference by NK cells. They can even move throughout the body, establishing potentially lethal secondary tumors.
Antimicrobial Cells:
Phagocytes
o Neutrophils: Abundant, mobile, and quick to phagocytize cellular debris or invading bacteria. They circulate in the bloodstream and roam through peripheral tissues, especially at sites of injury or infection.
o Eosinophils: Less abundant than neutrophils. Phagocytize foreign compounds or pathogens that have been coated with antibodies.
o The two major classes of macrophages derived from the monocytes of the circulating blood.
o Fixed macrophages: Permanent residents of specific tissues and organs and are scattered among connective tissues. Normally don’t move within these tissues.
o Free macrophages: Travel throughout the body, arriving at the site of an injury by migrating through adjacent tissues or by recruitment from the circulating blood.
Neutrophils:
o Most abundant of the microphages. o First to arrive; usually first to die. o Really good at killing bacteria. o Phagocytosis (eating one/few at a time). o Respiratory burst (via degranulation). • Superoxide anions. • Hydrogen peroxide. • Hypochlorite ion. o Unfortunately, they kill just about everything in the vicinity (including themselves, and our body cells).
Eosinophils:
o Weak but useful phagocytes (antigen- antibody complexes).
o Surround much bigger parasites.
o Round worms, tapeworms, etc.
o Produce superoxide, hydrogen peroxide, and even a neurotoxin.
o Do induce inflammation, but then seem to modulate the inflammatory response by secreting the enzyme histaminase to limit allergic and inflammatory responses.
Basophils:
o Help out other WBCs.
o Release histamine (vasodilator).
o Release heparin (inhibits formation of clots, making it easier for WBCs to move around the infection site).
o Involved in hypersensitivity reactions, such as anaphylactic shock.
Monocytes:
o Monocytes emigrate from the blood in the tissue spaces to become MACROPHAGES (5X normal size).
o Fixed macrophages:
o Kupffer cells of liver.
o Alveolar dust cells of lung alveoli.
o Many fixed in spleen, lymph nodes and red bone marrow.
o Wandering macrophages (lookin’ for trouble).
o Not the first to arrive (8-12 hr), but they are deadly to pathogens and also “clean up”.
Macrophages are APCs (tattle-tales):
o Macrophages: o 1. Eat the pathogen. o 2. Digest the pathogen. o 3. Recycle/spit out parts of pathogen. o 4. Insert fragments of the pathogen into their own membrane.
Second Line of Defense:
Pyrexia
o Fever = abnormal elevation of body temp from many different causes.
o Exogenous pyrogens (e.g., endotoxins).
o Endogenous pyrogens (e.g., our own neutrophils and macrophages secrete “pyrogens” when they eat bacteria).
o IL-1 and IL-6 (interleukins).
o TNF-alpha (tumor necrosis factor).
o Pyrogens stimulate the hypothalamus (via release of prostaglandins) to raise the set point for body temp.
o 1. Pyrogens stimulate the hypothalamus to release PGE (prostaglandin E).
o 2. PGE increases the Hypothalamic set point.
Benefits of Moderate Fever:
o Intensifies effects of interferons.
o Enhances phagocytosis.
o Increases lymphocytic activity.
o Elevates metabolic rate, which accelerates tissue repair.
o Causes liver and spleen to sequester iron, zinc & copper (needed for bacterial replication).
o Kills and/or inhibits the growth of some microbes (but many like heat).
Dangers of High Fever:
o Proteins denature at high temps, including ENZYMES.
o Proteins in cell membranes can coagulate.
o Nerve damage begins at 41Degrees C (105.8 degrees F).
o Greater than 103 Degrees F: danger of heat stroke.
o Greater than 105 Degrees F: delirious/convulsions/coma.
o Greater than 110 Degrees F: irreversible brain damage or death.
