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What is Immune System?

                                      Immune System


Our body has a powerful immune system that protects it from various types of threats. These threats can come in the form of mechanical injuries,  entry of germs, or the entry of other foreign particles like dust.  Every day, we encounter a huge number of bacteria, viruses and other diseasecausing organisms.   However, we don't fall ill every other day.   which is due to our immune system an army of cells that is always roaming our body,  ready to ward off any attack.  
What is Immune System?


 The immune system can be broadly divided into two parts innate and adaptive immunity. Innate immunity or nonspecific immunity is the body's first natural defense to any intruder.   This system doesn't care what it's killing.  Its primary goal is to prevent any intruder from entering the body, and if it does enter,   then the immune system kills this intruder. 

First line of Defence:

  It doesn't differentiate between one pathogen and another.   The first component of this defensive system is your skin.  Any organism trying to get into the body is stopped by the skin, our largest organ, which  covers us. 

Second line of Defence:

 Second line of defence,  is the mucous lining of all our organs.   The sticky, viscous fluid of this lining traps any pathogens trying to get past it.  These are the physical barriers.   However, we also have chemical barriers, such as the lysozyme in the eyes, or the acid in  the stomach, which kill pathogens trying to gain entry. 

  Genitourinary tract:

The genitourinary tract and other places have their own normal flora, or microbial community.  These compete with pathogens for space and food, and therefore also act as a barrier.  The next line of defense is inflammation, which is done by mast cells.  These cells are constantly searching for suspicious objects in the body.   When they find something, they release a signal in the form of histamine molecules.   These alert the body, and blood is rushed to the problem area.  This causes inflammation and also brings leukocytes, or white blood cells, which are soldiers in   our body's cellular army.  Once they come, all hell breaks loose!
   Sometimes however, the intruder may not be germ, but rather a harmless thing like a dust  particle.  The body still causes a full immune reaction to this intruder, which is how allergic reactions occur.   In the fortress of our body, the leukocytes are VIPs.  They have an allaccess pass to the body, except, of course, to the brain and spinal cord.   Our leukocytes come in many types.   Those that belong to the innate system are the phagocytes.   These cells can either patrol your body, like the neutrophils, or they can stay in certain  places and wait for their cue.

Most Abundant Cells of Immune system:

   Neutrophils are the most abundant cells.   They patrol the body and can therefore get to a breach site very quickly.  These cellular soldiers kill the infectious cell and then die, which leads to pus formation.   There are also the big bad wolves, or the macrophages.  These cells are like hungry, ravenous monsters who simply engulf unwanted pathogens.   Instead of roaming freely in our blood, they are collected in certain places.   These cells can consume about 100 pathogens before  they die, but they can also detect our own cells that have gone rogue, such as cancer cells, and kill them too.  

Natural Killer Cells:

We also have the Natural Killer Cells.   These cells can efficiently detect when our own cells have gone rogue, or are infected  with, say, a virus.   NKCs detect a protein produced by normal cells, called the Major Histocompatibility Complex  or MHC.  Basically, whenever a cell isn't normal, it stops producing this protein.   The NKCs move around constantly, checking our cells for this type of deficiency, and   when they find an abnormal cell, they simply bind to it and release chemicals that will  destroy it.   

Dendritic cells:

The last cells of our innate immune system are the dendritic cells.   These are found in places that come in contact with the outside environment, such as the  nose, lungs, etc.  They are the link between our innate and adaptive immune systems.  They eat a pathogen, and then carry information about it to our adaptive immune system cells.   This information is produced and shared in the form of antigens.   Antigens are the traces that pathogens leave around.   They are molecules found on the surface on pathogens that can be detected by our adaptive  immune system for recognition.  The dendritic cells pass on this information to our T cells.  However, macrophages can also perform this function.  

Now, there is also the adaptive or acquired immune system.  This system is more efficient, as it can differentiate between different types of pathogens. 
 It has 2 main components T lymphocytes and B lymphocytes:
  •  Tcells come into play when an infection has already occurred, thus bringing about the  cellmediated immune response.   
  • Bcells join the fight when the pathogens have entered, but haven't yet ca
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