Foundations in Microbiology
Sixth Edition
Chapter 14Nonspecific Host
Defenses
Lecture PowerPoint to accompany
Talaro
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Defense Mechanisms of the Host• To protect the body against pathogens, the
immune system relies on a multilevel network of physical barriers, immunologically active cells, and a variety of chemicals.– first line of defense – any barrier that blocks invasion
at the portal of entry – nonspecific– second line of defense – protective cells and fluids;
inflammation and phagocytosis – nonspecific– third line of defense – acquired with exposure to
foreign substance; produces protective antibodies and creates memory cells – specific
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Physical or Anatomical Barriers: First Line of Defense
Skin and mucous membranes of respiratory, urogenital, eyes and digestive tracts– outermost layer of skin is composed of epithelial cells
compacted, cemented together and impregnated with keratin; few pathogens can penetrate if intact
– flushing effect of sweat glands– damaged cells are rapidly replaced– mucous coat impedes attachment and entry of bacteria– blinking and tear production– stomach acid– nasal hair traps larger particles
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Nonspecific Chemical Defenses• Sebaceous secretions• Lysozyme, an enzyme that hydrolyzes the cell wall of
bacteria, in tears• High lactic acid and electrolyte concentration in sweat• Skin’s acidic pH• Hydrochloric acid in stomach• Digestive juices and bile of intestines• Semen contains antimicrobial chemical.• Vagina has acidic pH.
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Genetic Defenses• Some hosts are genetically immune to the
diseases of other hosts.• Some pathogens have great specificity.• Some genetic differences exist in
susceptibility.
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Structure and Function of the Organs of Defense and Immunity
• The study of the body’s second and third lines of defense is called immunology.
• Functions of a healthy immune system:1. Constant surveillance of the body2. Recognition of foreign material3. Destruction of entities deemed to be foreign
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Immune System
• Large, complex, and diffuse network of cells and fluids that penetrate into every organ and tissue
• Four major subdivisions of immune system are:
1. Reticuloendothelial system (RES)2. Extracellular fluid (ECF)3. Bloodstream4. Lymphatic system
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Reticuloendothelial System (RES)• Network of connective tissue fibers that
interconnects other cells and meshes with the connective tissue network surrounding organs
• Inhabited by phagocytic cells – mononuclear phagocyte system – macrophages ready to attack and ingest microbes that passed the first line of defense
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Origin, Composition, and Functions of the Blood
• Whole blood consists of plasma and blood cells – red blood cells and white blood cells.– Serum is the liquid portion of the blood after a
clot has formed-minus clotting factors.• Plasma – 92% water, metabolic proteins,
globulins, clotting factors, hormones and all other chemicals and gases to support normal physiological functions
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White Blood Cells• Neutrophils- 55-90% - lobed nuclei with lavender
granules; phagocytes• Eosinophils – 1-3% - orange granules and bilobed
nucleus; destroy eucaryotic pathogens• Basophils, mast cells – 0.5% - constricted nuclei, dark
blue granules; release potent chemical mediators• Lymphocytes – 20-35% - large nucleus B (humoral
immunity) and T cells (cell-mediated immunity) involved in the specific immune response
• Monocytes, macrophages – 3-7%- large nucleus; phagocytic
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Lymphatic System
1. Provides an auxiliary route for return of extracellular fluid to the circulatory system
2. Acts as a drain-off system for the inflammatory response
3. Renders surveillance, recognition, and protection against foreign material
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Lymphatic Fluid• Lymph is a plasma-like liquid carried by
lymphatic circulation• Formed when blood components move out
of blood vessels into extracellular spaces• Made up of water, dissolved salts, 2-5%
proteins• Transports white blood cells, fats, cellular
debris and infectious agents
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Lymphatic Vessels• Lymphatic capillaries permeate all parts of
the body except the CNS.• Thin walls easily permeated by extracellular
fluid which is then moved through contraction of skeletal muscles
• Functions to return lymph to circulation; flow is one-direction-toward the heart-eventually returning to blood stream
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Lymphoid Organs and Tissues• Classified as primary and secondary• Primary lymphoid organs – sites of lymphocytic
origin and maturation – thymus and bone marrow• Secondary lymphoid organs and tissues –
circulatory-based locations such as spleen and lymph nodes; collections of cells distributed throughout body tissues – skin and mucous membranes – SALT, GALT, MALT
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Lymphoid Organs• Thymus – high rate of growth and activity
until puberty, then begins to shrink; site of T-cell maturation
• Lymph nodes - small, encapsulated, bean-shaped organs stationed along lymphatic channels and large blood vessels of the thoracic and abdominal cavities
• Spleen – structurally similar to lymph node; filters circulating blood to remove worn out RBCs and pathogens
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Actions of the Second Line of Defense
• Recognition• Inflammation• Phagocytosis• Interferon• Complement
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Recognition • Protein receptors within cell membrane of
macrophages, called Toll-like receptors• Detect foreign molecules and signal the
macrophage to produce chemicals which:– stimulate an inflammatory response
(nonspecific) – promote the activity of B and T cells (specific)
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Inflammatory ResponseClassic signs and symptoms characterized by:• Redness – increased circulation and vasodilation in
injured tissue in response to chemical mediators and cytokines
• Warmth – heat given off by the increased blood flow
• Swelling – increased fluid escaping into the tissue as blood vessels dilate-edema; WBC’s, microbes, debris and fluid collect to form pus; helping prevent spread of infection
• Pain – stimulation of nerve endings• Possible loss of function
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Insert figure 14.13Events in inflammation
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Unique Characteristics of Leukocytes
• Diapedesis – migration of cells out of blood vessels into the tissues
• Chemotaxis – migration in response to specific chemicals at the site of injury or infection
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Fever• Initiated by circulating pyrogens which reset the
hypothalamus to increase body temperature; signals muscles to increase heat production and vasoconstriction– exogenous pyrogens – products of infectious agents– endogenous pyrogens – liberated by monocytes,
neutrophils, and macrophages during phagcytosis; interleukin-1 (IL-1) and tumor necrosis factor (TNF)
• Benefits of fever: – inhibits multiplication of temperature-sensitive
microorganisms– impedes nutrition of bacteria by reducing the available iron– increases metabolism and stimulates immune reactions and
protective physiological processes
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Phagocytes and Phagocytosis3 main types of phagocytes:
1. Neutrophils – general-purpose; react early to bacteria and other foreign materials, and to damaged tissue
2. Eosinophils – attracted to sites of parasitic infections and antigen-antibody reactions
3. Macrophages – derived from monocytes; scavenge and process foreign substances to prepare them for reactions with B and T lymphocytes
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Phagocytosis
General activities of phagocytes:1. To survey tissue compartments and
discover microbes, particulate matter and dead or injured cells
2. To ingest and eliminate these materials3. To extract immunogenic information from
foreign matter
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Interferon• Small protein produced by certain white blood
cells and tissue cells– alpha interferon- lymphocytes and macrophages– beta interferon – fibroblasts and epithelial cells– gamma interferon – T cells
• Produced in response to viruses, RNA, immune products, and various antigens
• Bind to cell surfaces and induce expression of antiviral proteins
• Inhibit expression of cancer genes
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Complement• Consists of 26 blood proteins that work in
concert to destroy bacteria and viruses• Complement proteins are activated by cleavage.• Classical pathway – activated by the presence of
antibody bound to microorganism• Alternative pathway – begins when complement
proteins bind to normal cell wall and surface components of microorganisms
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