02.03 Host defenses

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Included In This Lesson



  1. Two main Types of Immunity in Vertebrates
    1. Innate- immune responses that an organism is born with
      1. Physical barriers such as skin, sweat, mucus, saliva, digestive enzymes, tears
      2. Inflammatory response- triggers increased blood flow, swelling, increase temp,
      3. White blood cells like mast cells secrete histamines, macropages start eating pathogens, neutrophils, basophils and eosinophils secrete toxins to bacteria/fungi and parasites, dendritic cells of the skin and mucousal lining link the innate to the adaptive immune system, Natural killer cells attack compromised or infected host cells.
    2. Adaptive- the immune response aka the aquired immune response is a very specific response to a particular pathogen.
      1. Pathogen-specific details are obtain and stored for the life of the organism.
      2. Macrophages (from innate system) that bind with the pathogen engulf it and present pieces on its membranes. This stimulates helper T cells to activate B cells to become plasma cells and make specific antibodies against the pathogen.
      3. Cells infected with the virus “present” fragents of the virus on their cell membranes.
      4. Helpter T cell that match these fragments (like a puzzle piece) are activated and release cytokines.
      5. These cytokines recruit and activate B cells and cytotoixc T cells with matching receptors (puzzle pieces)


Today we’re going to be talking about host defenses.

As a vertebrate organisms humans have two main types of defense mechanisms to fight off foreign invaders. The innate response which is one you are born with and this is shared across kingdoms of plantae, fungi,and animal kingdoms. The second type happens to be exclusive to vertebrates is known as the adaptive immune response that is like the special forces of the military that gathers intel about the foreign agent and designs specific tactical response never to be forgotten. 

So within the innate response, there are different levels. The first one involves the physical barriers that attempt to prevent any foreign agent from entering the organism in the first place. Your skin, mucous lining membranes that allow entry points into the body attempt to trap pathogens like quicksand. Sweat with it’s pH, saliva, tears, and digestive enzymes try and break down the culprit before entering the body as well. And should any of those barriers be penetrated next up the inflammatory response is triggered. Blood flow increases to the area, swelling is induced and temperatures may rise as the area warms with the rush of blood. White blood cells monitoring the entire surface begin ingesting these foreign unwelcome guests. Toxins are secreted to attack bacterial, fungal or parasitic nuisances and the dendritic cells of the skin and membranes communicate with cells to trigger the adaptive immune response while NKC’s attack cells that have already fallen prey to the bad guy. 

So when all else fails the adaptive response, will eventually take over and more than likely win this war. Here specific details about the antigens worn on the cell membranes of the pathogen are dealt with in a manner that is quite impressive. Macrophages from the innate system that binds with the pathogen devour it like a PacMan and then disassemble the bad guy and actual present pieces of the pathogen on its membrane. This presentation stimulates what are known as helper T cells to activate B cells to make specific antibodies that will bind up and block the pathogen from invading more cells.  And even more amazing is that some of these cells stick around as memory and lie in waiting ready to ramp up a quicker and stronger response should a return visit ever occur.

So vertebrates have evolved to have an immune response that is innate and adaptive. innate is inborn and nonspecific and adaptive is acquired through exposure to the pathogen and specialized development of antibodies to ward off and create a memory of that bad guy should it ever revisit. 

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