Innate Immunity Chapter 15

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Innate ImmunityChapter 15
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First Line of Defense

• Structures, chemicals, processes that work to
  prevent pathogens entering the bodyBarriers to
  Entry
• Nonspecific defenses
• Includes the skin and mucous membranes of the
  respiratory, digestive, urinary, and reproductive
  systems

Animation Host Defenses
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Skin Physical Components of Defense

• Epidermis
• Outer layer composed of multiple layers of
  tightly packed cells
• Few pathogens can penetrate these layers
• Shedding of dead skin cells removes attached
  microorganisms
• Epidermal dendritic cells (Langerhans cells)
• These are able to phagocytize pathogens
• Dermis
• Contains protein fibers collagen
• Give skin strength and pliability to resist
  abrasions that could introduce microorganisms

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Skin Chemical Components of Defense

• Perspiration secreted by sweat glands
• Salt inhibits growth of pathogen by drawing
  water from their cells
• Antimicrobial peptides sweat glands secret
  dermicidins
• Lysozyme destroys cell wall of bacteria
• Sebum secreted by sebaceous (oil) glands
• Helps keep skin pliable and less likely to break
  or tear
• Lowers the pH of the skin to a level inhibitory
  to many bacteria

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Mucous Membranes

• Line all body cavities open to the outside
  environment
• Epithelium
• Thin, outer covering of the mucous membranes
• Unlike surface epidermal cells, epithelial cells
  are living
• Tightly packed to prevent entry of pathogens
• Continual shedding of cells carries attached
  microorganisms away

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Microbial Antagonism

• Normal microbiota help protect the body by
  competing with potential pathogens
• Various activities of the normal microbiota make
  it hard for pathogens to compete
• Consumption of nutrients makes them unavailable
  to pathogens
• Create an environment unfavorable to other
  microorganisms by changing pH

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Other First-Line Defenses

• Many body organs secrete chemicals with
  antimicrobial properties
• Lacrimal glands that bathe the eye

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More First Line Defenses
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Second Line of Defense

• Operates when pathogens succeed in penetrating
  the skin or mucous membranes
• Nonspecific defense
• Composed of cells, antimicrobial chemicals, and
  processes but no physical barriers
• Many of these components are contained or
  originate in the blood

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Blood

• Composed of cells and portions of cells within a
  fluid called plasma
• Plasma is mostly water containing electrolytes,
  dissolved gases, nutrients, and proteins
• When the clotting factors (a group of plasma
  proteins) are removed from plasma, the remaining
  fluid is called serum
• Other plasma proteins include complement proteins
  and antibodies
• The cells and cell fragments in plasma are called
  formed elements

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Formed Elements

• Three types of formed elements
• Erythrocytes carry oxygen and carbon dioxide in
  the blood
• Platelets involved in blood clotting
• Leukocytes involved in defending the body
  against invaders
• Two groups
• Granulocytes
• Agranulocytes

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Granulocytes

• Contain large granules that stain different
  colors based on the dye used
• Basophils stain blue with the basic dye
  methylene blue
• Eosinophils stain red/orange with the acidic
  dye eosin
• Neutrophils stain lilac with a mixture of
  acidic and basic dyes
• Neutrophils and eosinophils can phagocytize
  pathogens
• Neutrophils and eosinophils are capable of
  diapedesis

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Agranulocytes

• Cytoplasm appears uniform under a light
  microscope
• Two types
• lymphocytes most involved in adaptive immunity
• monocytes leave the blood and mature into
  macrophages

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Macrophages

• Phagocytic cells of the second line of defense
• Wandering macrophages leave the blood via
  diapedesis and phagocytize throughout the body
• Fixed macrophages do not move throughout the body
  and often phagocytize within a specific organ
• Include alveolar macrophages (lungs), microglia
  (central nervous system), Küpffer cells (liver)
• All macrophages, plus monocytes attached to
  endothelial cells, constitute the mononuclear
  phagocytic system

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Lab Analysis of Leukocytes

• The differential white blood cell count (the
  diff) can signal signs of disease
• Increased eosinophils can indicate allergies or
  parasitic worm infection
• Bacterial diseases often show increase in
  leukocytes and in neutrophils
• Viral infections show increase in lymphocytes

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Components of the Second Line of Defense

• Phagocytosis
• Extracellular killing by leukocytes
• Nonspecific chemical defenses
• Inflammation
• Fever

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Phagocytosis

• Cells capable of phagocytosis are called
  phagocytes

Animation Phagocytosis
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Extracellular Killing by Leukocytes

• Three Cell types that kill extracellularly
• Eosinophils
• Mainly attack parasitic helminths (worms) by
  attaching to their surface
• Secrete toxins that weaken or kill the helminth
• Natural killer lymphocytes (NK cells)
• Secrete toxins onto the surface of virally
  infected cells and tumors
• Neutrophils
• Produce chemicals that kill nearby invaders

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Nonspecific Chemical Defenses

• Augment phagocytosis
• Some attack pathogens directly
• Some enhance other features of innate immunity
• Includes various chemicals
• Lysozyme
• Complement
• Interferon
• Defensins

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Complement System

• Set of serum proteins designated numerically
  according to the order of their discovery
• Complement activation results in lysis of the
  foreign cell
• Complement can be activated in several ways
• Classical pathway
• Complement named for the events of this
  originally discovered pathwaythe various
  complement proteins act nonspecifically to
  complement the action of antibodies
• Alternate pathway
• Activation occurs independent of antibodies

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Complement Two Pathways
Figure 15.10
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Inactivation of Complement

• Bodys own cells withstand complement cascade
• Membrane-bound proteins on many cells bind with
  and break down activated complement proteins

Animation The Complement System
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Interferons

• Protein molecules released by host cells to
  nonspecifically inhibit the spread of viral
  infections

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Inflammation

• Nonspecific response to tissue damage resulting
  from various causes
• Characterized by redness, heat, swelling, and
  pain
• Two types
• Acute
• Chronic

Animation Inflammation
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Acute vs. Chronic Inflammation

• Acute inflammation
• Develops quickly and is short lived
• Is usually beneficial
• Important in the second line of defense
• Dilation and increased permeability of the blood
  vessels
• Migration of phagocytes
• Tissue repair
• Chronic inflammation
• Develops slowly and lasts a long time
• Can cause damage to tissues

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Increased Vascular Permeability during
Inflammation
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Events in Inflammation
Figure 15.17.1
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Events in Inflammation
Figure 15.17.2
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Fever

• A body temperature over 37?C
• Results when chemicals called pyrogens trigger
  the hypothalamus to increase the bodys core
  temperature
• Various types of pyrogens
• Bacterial toxins
• Cytoplasmic contents of bacteria released by
  lysis
• Antibody-antigen complexes
• These signal for the production of interleukin-I
  (IL-1)

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Fever Production

• IL-1 production causes the hypothalamus to
  secrete prostaglandin which resets the
  hypothalamic thermostat
• Communication with the brain initiates muscle
  contractions, increased metabolic activity, and
  constriction of blood vessels which raises the
  bodys temperature
• Chills associated with fever are due to the
  reduced blood flow of constricted vessels
• Decrease in IL-1 production results in the bodys
  temperature returning to normal

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Benefits of Fever

• Enhances the effects of interferons
• Inhibits growth of some microorganisms
• May enhance the performance of phagocytes, cells
  of specific immunity, and the process of tissue
  repair

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A Summary of Some Nonspecific Components of the
First and Second Lines of Defense
Table 15.5