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Innate Immunity

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					   Innate Immunity:
Nonspecific Defenses of
       the Host
• Susceptibility: Lack of resistance to a disease.
• Immunity: Ability to ward off disease.
• Innate immunity: Defenses against any
  pathogen.
• Adaptive immunity: Immunity, resistance to a
  specific pathogen.
Host Defenses




 Host defenses

                 Figure 16.1
                Physical Factors
• Skin
• Epidermis consists of tightly packed cells with
  – Keratin, a protective protein
                 Physical Factors
• Mucous membranes
• Ciliary escalator:
  Microbes trapped in mucus
  are transported away from
  the lungs.
• Lacrimal apparatus:
  Washes eye.
• Saliva: Washes microbes off.
• Urine: Flows out.
• Vaginal secretions: Flow out.
                                    Figure 16.4a
              Chemical Factors
• Fungistatic fatty acid in sebum.
• Low pH (3-5) of skin.
• Lysozyme in perspiration, tears, saliva, and tissue
  fluids.
• Low pH (1.2-3.0) of gastric juice.
• Transferrins in blood find iron.
• NO inhibits ATP production.
          Normal Microbiota
• Microbial antagonism/competitive exclusion:
  Normal microbiota compete with pathogens.
                 Phagocytosis
• Phago: from Greek,
  meaning eat
• Cyte: from Greek,
  meaning cell
• Ingestion of microbes
  or particles by a cell,
  performed by
  phagocytes.

                    Phagocytosis

                                   Figure 16.6
Phagocytosis




               Figure 16.7
   Microbial Evasion of Phagocytosis
Inhibit adherence: M protein,   Streptococcus pyogenes, S. pneumoniae
  capsules
Kill phagocytes: Leukocidins    Staphylococcus aureus

Lyse phagocytes: Membrane       Listeriamonocytogenes
 attack complex
Escape phagosome                Shigella

Prevent phagosome-lysosome HIV
 fusion
Survive in phagolysosome        Coxiella burnetti
                   Inflammation
• Redness
• Pain
• Heat
• Swelling (edema)
• Acute-phase proteins activated (complement, cytokine,
  and kinins)
• Vasodilation (histamine, kinins, prostaglandins, and
  leukotrienes)
• Margination and emigration of WBCs
• Tissue repair
  Chemicals Released by Damaged Cells
Histamine        Vasodilation, increased permeability
                 of blood vessels
Kinins           Vasodilation, increased permeability
                 of blood vessels
Prostaglandins   Intensity histamine and kinin effect

Leukotrienes     Increased permeability of blood vessels,
                 phagocytic attachment
Inflammation




               Figure 16.8a–b
Inflammation




               Figure 16.8c–d
       Fever: Abnormally High Body
               Temperature
• Hypothalamus normally set at 37°C.
• Gram-negative endotoxin cause phagocytes to
  release interleukin–1 (IL–1).
• Hypothalamus releases prostaglandins that reset
  the hypothalamus to a high temperature.
• Body increases rate of metabolism and shivering
  which raise temperature.
• When IL–1 is eliminated, body temperature falls
  (crisis).
                              Fever
• Advantages                     • Disadvantages
   – Increase transferrins          – Tachycardia
   – Increase IL–1 activity         – Acidosis
                                    – Dehydration
       The Complement System
• Serum proteins
  activated in a
  cascade.




                               Figure 16.9
  Effects of Complement Activation
• Opsonization or
  immune
  adherence:
  Enhanced
  phagocytosis.
• Membrane attack
  complex: Cytolysis.
• Attract
  phagocytes.

               Complement System   Figure 16.10
Effects of Complement Activation




                              Figure 16.11
Classical Pathway




                    Figure 16.12
Alternative Pathway




                      Figure 16.13
Lectin Pathway




                 Figure 16.14
 Some Bacteria Evade Complement
• Capsules prevent C activation.
• Surface lipid-carbohydrates prevent MAC formation.
• Enzymatic digestion of C5a.
              Interferons (IFNs)
• Alpha IFN and Beta IFN: Cause cells to produce
  antiviral proteins that inhibit viral replication.
• Gamma IFN: Causes neutrophils and
  macrophages
  to phagocytize bacteria.
Interferons (IFNs)




                     Figure 16.15
                Innate Immunity
• Transferrins          • Antimicrobial peptides
   – Bind serum iron       – Lyse bacterial cells

				
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posted:1/23/2013
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