Summary: Immunobiology

Read the summary and the most important questions on Immunobiology

• 1 Chapter 1: Elements of the immune system and their roles in defense

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• What three pathways are there to kill a pathogen by antibodies of B cells?

  Neutralization: blocks toxins from entering the cells, by binding them
  Opsonization:
  1. Bind to the bacteria on the surface --> signal to get rid of the cell through macrophages
  2. Bind to the bacteria on the surface and bind to a complement compound --> also gives a signal
  

• What is the difference between primary lymphoid tissues and secondary lymphoid tissues?

  Primary lymphoid tissues are the sites where lymphocytes develop and mature, whereas secondary lymphoid tissues are the sites where lymphocytes become stimulated.

• 2 Chapter 2: Innate Immunity: the immediate reponse to infection

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• Which three pathways form the complement system from the innate immune system, when are they activated? And what do they have in common?

  
  1. Alternative pathway --> recruitment of inflammatory cells
  2. Lectin pathway --> opsonization of pathogens facilitating uptake and killing by phagocytes
  3. Classical pathway --> perforation of pathogen cell membranes
  All have a common component: the thioester bond of C3 or C3b becomes susceptible to nucleophilic attack, resulting in C3b being bound covalently to the pathogen surface

• What key element is is essential in the complement system to activate the alternative and classical pathway? And how does work?

  C3 cleavage, which leads to C3a that recruits phagocytes and C3b that tags bacteria for destruction. 
  

• What happens after C3b binds on the surface of the pathogen?

  There are two options:
  
  1. Pathogen can be eliminated by phagocytic cells, e.g., Macrophages. Many innate cells have receptors for C3b: macrophages take up the bacterium by endocytosis because the C3b can bind to a receptor on the macrophages cell surface.
  2. Terminal component proteins make pores on the pathogen surface. Making pores: C5 activation by the alternative C5 convertase --> C5 binds to the C3b2Bb complex, which causes cleavage and forms C5a and C5b. C5b with C6 t/m 8 form a complex, that recruits C9 and form pores (= MAC)

• How do we prevent making pores on healthy cells?

  On human cells, CD59 binds to the C5b678 complex and prevents recruitment of C9 to form the pore (also on infected cells).

• What two functions does the complement system have?

  1. Fighting infectious diseases
  2. Tissue maintenance

• 3 Chapter 3: Innate Immunity: The induced Response to Infection

• What do the innate immune cells recognize in order that they don't recognize self-peptides?

  PAMP is any molecule that is common among large group of microorganisms. PAMPs are only found on pathogens, not on human cells. A PAMP doesn’t need to be taken up by the cell, it could also be extracellular.

• How do neutrophils function at the site of infection?

  Neutrophils express receptors for bacterial and fungal constituents -->  neutrophils bind and engulf pathogen, then destroy them with toxins from their granules. Then kill themselves via explosion.

• How do macrophages inhibit the complement system?

  Induce expression of inflammtory cytokines by NFkB (transcription factor)