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Innate vs. Adaptive Immunity

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Topic updated on 05/20/17 2:13pm

Overview
 

 
Introduction
  • The human immune system is designed to deal with a variety of insults including
    • acute exposure to new infectious agents such as bacteria and viruses
    • re-exposure to the same infectious agent after clearance of the initial infection
    • chronic infection by fungi and parasites
  • In order to have a variety of responses to infection, the immune system is divided into
    • the innate immune system that is responsible for
      • fast recognization and clearance of initial infections
      • destruction of fungi and parasites
    • the adaptive immune system that is responsible for
      • immunological memory and rapid responses to re-infection
      • recognition of pathogens that have defences against innate immunity
Differences Between Innate and Adaptive Immunity
 
Differences Between Innate and Adaptive Immunity
Feature Innate Immunity Adaptive Immunity
Genetics
  • All components encoded in germline
  • May vary between individuals but does not change over course of an individual lifetime
  • Inherited from parents 
  • Encoded as variable V, D, and J regions
  • Immunity is generated by recombination of these regions and further hypervariation
  • Not inherited from parents
Components
  • Myeloid lineage white blood cells such as
    • neutrophils
    • monocytes
    • macrophages
  • Natural killer (NK) cells
  • Complement system
  • Physical barriers (such as mucus membranes)
  • Killer CD8+ T-cells
  • Helper CD4+ T-cells
  • B-cells
  • Antibodies
Recognition
  • Uses receptors that recognize conserved pathogen-associated molecular patterns (PAMPs)
  • Examples linclude
    • LPS
    • flagellin
    • nucleic acids
  • Uses recombined B- and T-cell receptors that recognize specific antigens on pathogens
  • Can recognize aspects of almost all pathogens
Response
  • Nonspecific recognition
  • Occurs rapidly from minutes to hours
  • Does not confer memory
  • Specific recognition that can be refined
  • Occurs over days to years
  • Confirms immunological memory
Resistance
  • Caused by pathogenic virulence factors
  • Often involves disabling the conserved pattern recognition used by innate system
  • Caused by mutation of the recognized antigen
  • Can be overcome by further maturation of the receptor
 
Interactions between Innate and Adaptive systems
  • These two branches of the immune system can cooperate in several ways including
    • opsonization
      • coating pathogens with antibodies in order to activate
        • antibody dependent cellular cytotoxicity
        • antibody dependent cellular phagocytosis
    • complement activation
      • activation of the C3 convertase by the
        • classical complement pathway
        • interaction of antibodies with C1q
    • cytokine secretion
      • release of signaling molecules by helper T-cells causes
        • additional production of innate immune cells
        • synthesis of circulating factors such as the complement system

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