Lecture PowerPoint to accompany
Foundations in
Microbiology
Seventh Edition
Talaro
Chapter 14
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14.1 Defense Mechanisms of the Host
• Host Defenses
– Innate, natural defenses: present at birth,
provide nonspecific resistance to infection
– Adaptive immunities: specific, must be
acquired
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14.1 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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Figure 14.1
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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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Figure 14.2
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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 an 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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14.2 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 functioning
immune system:
1. Surveillance of the body
2. Recognition of foreign material
3. Destruction of entities deemed to be foreign
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Figure 14.3
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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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Immune System Definitions
• White blood cells (leukocytes) – innate capacity
to recognize and differentiate any foreign material
• Nonself – foreign material
• Self – normal cells of the body
• Pathogen-associated patterns (PAMPs) –
molecules shared by microorganisms
• Pathogen recognition receptors (PRRs) –
receptors on WBCs for PAMPs
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Body Compartments that Participate
in the Immune System
• The reticuloendothelial system
• The spaces surrounding tissue cells that
contain extracellular fluid
• The bloodstream
• The lymphatic system
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Figure 14.4
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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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Figure 14.5
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Origin, Composition, and Functions
of the Blood
• Whole blood consists of plasma and formed
elements (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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Figure 14.6
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A Survey of Blood Cells
• Hemopoiesis – production of blood cells
• Stem cells – undifferentiated cells,
precursor of new blood cells
• Leukocytes – White blood cells
– Granulocytes: lobed nucleus
– Agranulocytes: unlobed, rounded nucleus
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Figure 14.7
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Granulocytes
• Neutrophils – 55-90% - lobed nuclei with
lavender granules; phagocytes
• Eosinophils – 1-3% - orange granules and
bilobed nucleus; destroy eukaryotic pathogens
• Basophils – 0.5% - constricted nuclei, dark
blue granules; release potent chemical
mediators
– Mast cells: nonmotile elements bound to
connective tissue
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Agranulocytes
• Lymphocytes – 20-35%, specific immune response
– B (humoral immunity)
• Activated B cells produce antibodies
– T cells (cell-mediated immunity)
• Activated T cells modulate immune functions and kill foreign cells
• Monocytes, macrophages – 3-7% - largest of WBCs,
kidney-shaped nucleus; phagocytic
– Macrophages: final differentiation of monocytes
– Dendritic cells: trap pathogens and participate in immune
reactions
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Erythrocytes and Platelet Lines
• Erythrocytes: develop from bone marrow
stem cells, lose nucleus, simple biconcave
sacs of hemoglobin
• Platelets: formed elements in circulating
blood that are not whole cells
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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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Figure 14.8
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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, bone, placenta, and thymus
• 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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Figure 14.9
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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
• Miscellaneous – GALT, Peyer’s patch
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14.3 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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Figure 14.11
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Inflammatory Response
Classic signs and symptoms characterized by:
• Redness – increased circulation and vasodilation in
injured tissues 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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Figure 14.12
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Figure 14.13
Insert figure 14.13
Events in inflammation
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Figure 14.14
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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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Figure 14.15 Diapedesis and chemotaxis of leukocytes
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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 phagocytosis;
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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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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Phagocytes and Phagocytosis
Main types of phagocytes:
1. Neutrophils – general-purpose; react early to
bacteria and other foreign materials, and to
damaged tissue
– Eosinophils – attracted to sites of parasitic
infections and antigen-antibody reactions
2. Macrophages – derived from monocytes;
scavenge and process foreign substances to
prepare them for reactions with B and T
lymphocytes
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Figure 14.16 Developmental stages of monocytes
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Figure 14.17 Site-specific macrophages
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Mechanisms of Phagocytic
Recognition, Engulfment, and
Killing
• Chemotaxis and ingestion: phagocytes migrate
and recognize PAMPs
– Phagosome
• Phagolysosome: lysosome fused with phagosome
(death ~30 minutes)
• Destruction and elimination
– Oxygen-dependent system (respiratory burst)
– Liberation of lactic acid, lysozyme, and nitric oxide
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Figure 14.18
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Interferon
• Small protein produced by certain white blood
cells and tissue cells
– Interferon alpha – lymphocytes and macrophages
– Interferon beta – fibroblasts and epithelial cells
– Interferon gamma – 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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Figure 14.19
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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
(cascade reaction)
• Pathways
– Classical – activated by the presence of antibody bound to
microorganism
– Lectin pathway – nonspecific reaction of a host serum protein
that binds mannan
– Alternative – begins when complement proteins bind to
normal cell wall and surface components of microorganisms
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Stages in the Complement Cascade
•
•
•
•
Initiation
Amplification and cascade
Polymerization
Membrane attack
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Figure 14.20(a)
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Figure 14.20(b, c, d)
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Figure 14.21
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