Lecture PowerPoint to accompany
Foundations in
Microbiology
Sixth Edition
Talaro
Chapter 14
Nonspecific Host
Defenses
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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 body
2. Recognition of foreign material
3. 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.
2.
3.
4.
Reticuloendothelial system (RES)
Extracellular fluid (ECF)
Bloodstream
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 hearteventually 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 Tcell maturation
• Lymph nodes - small, encapsulated, beanshaped 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 Response
Classic 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 14.13
Events 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 Phagocytosis
3 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 materials
3. 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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