The Specific Immune Response

When foreign invaders (such as potential pathogens) gain entry to the human body the specific immune system is called to action.  The specific immune system is also described as the Adaptive or Acquired Immune System because its ability to function is a result of experience with exposure to pathogens.  There are two branches of the Adaptive or Acquired Immune System:  The Humoral or Antibody-Mediated Response and the Cell-Mediated Response.  

 

Antibody-Mediated  Cell-Mediated
  • Seeks out and destroys specific pathogens that are free-floating in the body
  • Produces Antibodies to identify and help in the destruction of the pathogen
  • Effective against Bacteria
  • Seeks out and destroys specific cells that have been infected by specific pathogens
  • Produces Cytotoxic T cells to destroy infected cells
  • Effective against Viruses

 

These two branches will be described separately at first, but it is important to understand that they work together to defeat different pathogenic infections. 

 

Both branches begin with some work that is completed by the Macrophage ...

 

Antigen-Presentation

We have already discussed the mechanism by which macrophages identify, engulf, and digest potential pathogens.  However, macrophages also do something else.  In this process macrophages do not entirely digest the pathogen, but rather break off the piece of the pathogen that identifies it (the antigen) and displays this protein on its surface.  In the diagram below you can see this mechanism.  This process is called Antigen-presentation Download presentation.  

 

Life10e-Fig-42-15-0.jpg

 

Essentially what the macrophage is doing is it is telling the rest of the cell that it has just found something suspicious in the body and that there could be more of this suspicious entity out there ... so the body should be on alert!  One important part of this mechanism is the MHC II molecule with which the Antigen is presented.  This MHC II molecule is one of your self markers and it tells the other cells in your body "Don't worry.  I belong to you."  If the Antigen was presented without the MHC II molecule then other white blood cells might recognize the macrophage as non-self (it is presenting a non-self protein) and try to destroy it.