Adapted and Evolved Immune Systems


How are Reptiles Different to Other Species?

  • Only ectothermic amniotes (cold blooded and produce eggs)
  • Increasingly terrestrial lifestyle
  • Generally long-lived
  • nnate, cell-mediated and humoral compartments
  • Heterophils = neutrophils
  • IgM and IgY
  • Possibly IgA - identified in leopard gecko
  • Thymus, spleen, GALT and bone marrow
  • No lymph nodes
  • Cannot produce pus - instead produce a caseous mass (almost like a hard lump) of degranulated and degenerated heterophils)
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Does Temperature Affect the Immune System of Ectot

  • Able to respond over a wide range of temperatures
  • Phagocytic activity of macrophages can be affected
  • Wall lizards have highest macrophage activity at 25*C
  • Temperatures can also affect pathogen and therefore prevalence

What Happens to the Immune System During Hibernation?

  • Especially in mammals and reptiles
  • Immunity decreases as metabolic rate decreases
  • Thymic involution occurs (fewer T cells)
  • In the Spring: redevelopment of the thymus reconstitutes their T cell population
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How Can Animals Eat Carcasses and Not Get Ill?

  • Seen in vultures and alligators
  • Microbioata of vertebrates break down after death --> toxic metabolites --> hazardous
  • Issue for vultures as they insert their head into the decaying body (additional risk). However, to make sure they don't get infected they have:
    • An acidic gastric passage which kills the pathogen
    • A less diverse hind-gut flora of pathogenic bacteria
  • Ig against toxins
  • Most animals know not to eat dead animals that they haven't killed themselves due to possible contamination
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Are Vultures Carriers of Disease?

  • Griffon vultures almost always eat already dead organisms
  • Travel long distances when searching for food
  • They can pass on disease through the following ways:
    • Excretion (faeces, saliva)
    • AI tract and excreted
    • Mechanical transmission eg. on feet
    • Regurgitation of pellets
  • They spread disease but also prevent it as they eat wild dugs and rodents who would carry other diseases
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Parasites as Alternative Treatments

  • Certain worms and parasites can be used to help manage certain conditions such as gluten intolerance and asthma
  • Exposure to helminth:
    • Induce strong TH2 response --> development of allergen specific TH2 cells
    • Increased eosinophils
    • Mechanical irritation at location --> inflammation
    • Allergens are more accessible to uptake and presentation by antigen presenting cells
  • How could exposure to helminths potentially prevent allergies?
    • Induction of alternatively activated macrophages - directly T cell functions
    • IgE blocking hypothesis - protects against mast cells or basophil degranulation by saturating the IgE binding sites of the cell
    • Induction of immunosuppressive B cells -
    • Presentation of allergens by dendritic cells (needed for TH2 activation) is suppressed
  • If using parasites as an alternative treatment need to ensure there's the correct balance - enoguh to have an effect but not enough to become ill
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How Do Parasites Survive the Immune Response?

5 main things:

  • Antigenic variation - changing their appearance
  • Avoidance strategies - covering their bodies in host antigens
  • Molecular mimicry - linking with host MHC
  • Host immunosuppression
  • Enzymatic role - reducing host inflammation reaction
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