Immune Responses to Infectious Disease

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Immune Responses to Infectious Disease

• Reading Chapter 17

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• Infection pathogens vs. the immune response
• Overview of protective mechanism
• Overview of pathogen evasion
• Risk of infectious disease
• Environmental factors
• Increased travel
• Poverty
• Fear of vaccination
• Bioterrorism

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• Immune response to viruses
• Innate response
• Production of interferons
• Stimulated by dsRNA
• Activation of JAK/STAT pathway and genes
  transcription
• Activation of NK cells
• Lytic function enhanced by interferons and
  cytokines

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• Humoral response
• Antibodies recognize viral proteins
• Function well to inhibit initial infection or
  block viral spread during acute phase
• Block adhesion to, or penetration of, cell
  membrane
• Importance of secretory IgA
• Cell-mediated response
• Important defense following infection (cell types
  involved, cytokines, adoptive transfer)

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• Examples of viral evasion
• Hepatitis C virus
• Blocks PKR
• Herpes simplex viruses
• Inhibition of TAP by viral ICP47 and elimination
  of CD8 T-cell response
• Adenovirus and cytomegalovirus
• Reduce expression of class I MHC
• CMV, measles, HIV
• Reduce expression of class II MHC
• Vaccinia virus and HSV
• Block complement pathways
• Influenza, rhonoviruses, HIV
• Antigenic variation
• Paramyxoviruses, measles, EBV, cytomegalovirus,
  HIV
• Immunspression by directly infecting lymphocytes
  or macrophages

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• Influenza a major challenge for the immune system
• Ovoid or spherical virions, 90-100 nm
• Surrounded by hosts lipid bilayer plus
  hemagglutinin and neuraminidase
• Inner layer of matrix protein and nucleocapsid
• Three types A, B, C
• Differ in nucleoprotein and matrix proteins

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• Types of influenza
• Designation
• Ex. A/Sw/Iowa/15/30 (H1N1)
• Variability
• Changes in matrix proteins
• Antigenic drift
• Antigenic shift
• Genetic reassortment
• Inhibits memory
• Strain differences within a subtype
• Re-emergence of viral strains

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• Serum antibodies against HA molecules
• Antibody directed against domains flanking the
  sialic-acid-binding cleft
• peaks within a few days and slowly decreases over
  6 mo. , reaches a plateau titer
• CTLs also important
• Antigenic drift
• Avoidance of antibody for the HA molecule
• Amino acid substitutions in the antigenic domain

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• Bacterial Infections
• Phagocytosis or Antibody mediated immune response
• Exception intracellular growing bacteria
• DHT response
• Source of antibody
• Function to remove bacteria and inactivate
  bacterial toxins
• Endotoxins vs exotoxins
• Opsonin function with complement pathway
• Production of inflammation with complement
  proteins

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• Steps in bacterial infection
• Attachment
• Proliferation
• Invasion
• Toxin-induced damage to host cells

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Neisseria gonorrhoeae

• Increased ability for viral attachment
• Presence of pili and pilin
• Secretory IgA avoidance

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• Pathogenesis of the immune response
• Endotoxins (Diptheria) and exotoxins and cytokine
  production
• Generation of superantigens, activation of T
  cells and cytokine production
• Chronic activation of CD4T cells and the
  formation of granulomas
• Tuberculosis and the immune response

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