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A fact of life is that, at some point, we all get sick. Catching a cold is as commonplace as morning coffee.  In an effort to stay healthy, people take vitamin C, get good exercise, and even consume herbal concoctions in an effort to keep their “resistance” up.  However, do they know what their “resistance” entails?  It is true that when your resistance is low, you can become sick. But, what is “resistance” and how does it work?

Your resistance is better known as your immune system.  The immune system is your body’s defense mechanism against illness.  The system enables your body to know the difference between yourself, germs, and the outside world.  Your body sees any illness or outside nuisance, such as pollen, as a foreign substance.  The body does not like foreign substances because they result in illness, pain, and other physically negative phenomena.  That is why your body is set up to battle against what it perceives as an invader.

Your immune system is like a community or team.  This team is comprised of many different cells that work together to keep you healthy.  They all have specialized functions and ways of communicating with each other.  The two important tasks of the immune system are to kill and to remember.  Killing and remembering involves recognizing foreign invaders.  Nature is teeming with invaders ready to infect our bodies.  Thus, our immune system is equipped to specifically recognize the differences between different invaders referred to as pathogens.  All pathogens release certain chemicals and proteins that our immune defense recognizes. Recognition triggers a kill response.  The cells responsible for killing actually eat and digest the pathogen. Eating the pathogen allows some of the killer cells to process the bad guys and package them so that the other members of the immune team recognize them if the same invaders return.

When an invader returns, the team members responsible for remembering past invasions sense the invader’s chemical signals. The signal stimulates them to produce and excrete chemical tags called antibodies.  These antibodies stick to the invaders and enable the killer cells to recognize and kill again.  Cells whose duty it is to patrol and report do another form of recognition.  Sometimes invaders succeed in invading and they hide and make their victim cells sick from the inside.  When this happens, the victim cells ask for help by displaying proteins on their exteriors that are flags for help.  The patrolling team recognizes these flags and goes into action.  They kill the infected cells and alert the other immune cells that there is an invader in the area.  This way, the invaders inside infected cells are killed and the invaders that have not yet had a chance to infect are also killed.

Whenever a person actually catches a cold, it’s not because the members of the team forgot the plays.  One reason sickness occurs is because the team doesn’t always recognize a new invader fast enough to react.  A new invader may be able to do enough damage to cause illness before the immune response is complete.  Another scenario is a low number of players.  The body may be in the process of recovering from fighting a foreign invader.  Thus, the body is in the process of gaining new team members and building back up to full strength.  This would be a time when resistance is down and there is not enough manpower to handle invaders.  Viruses, clandestine foreign invaders, form a special threat to the immune team.  They can actually hide dormant inside cells for a long time.  Without warning they come out of hiding and begin attacking our bodies.  When they are hiding inside our cells, the immune team doesn’t see them.  So while they are undercover, they multiply and assemble to kill the cells in which they hide.  After killing, they go out and infect more.

The immune system is very complex and effective.  There are many different cells, many different chemicals, and many different ways of chemical communication.  What is important to remember is that the immune system relies on intricate teamwork.  All the members know the plays and how to execute them.  If a person eats well, exercises, and gets good rest, they can keep their immune team at its best.  It’s just that simple!

The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful to the body. The immune system protects the body from potentially harmful substances by recognizing and responding to antigens.  Antigens are molecules (usually proteins) on the surface of cells, viruses, fungi, or bacteria.  Non-living substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter) can be antigens.  The immune system recognizes and destroys substances that contain these antigens.

Even your own body cells have proteins that are antigens. These include a group of antigens called HLA Antigens.  Your immune system learns to see these antigens as normal and does not usually react against them.

Innate Immunity

Innate immunity is immunity that you are born with.  Innate immunity involves barriers that keep harmful materials from entering your body.  These barriers form the first line of defense in the immune response. Examples include:

  • Cough Reflex
  • Enzymes in tears and skin oils
  • Mucus which traps bacteria and small particles
  • Skin
  • Stomach acid

If an antigen gets past the external barriers, it is attacked and destroyed by other parts of the immune system.

Acquired Immunity

Acquired immunity is immunity that develops with exposure to various antigens.  Your immune system builds a defense that is specific to that antigen.

Passive Immunity

Passive immunity involves antibodies that are produced in a body other than your own.  Infants have passive immunity because they are born with antibodies that are transferred through the placenta from the mother.  These antibodies disappear between 6 and 12 months of age.

Passive immunization involves transfusion of antiserum, which contains antibodies that are formed by another person or animal.  It provides immediate protection against an antigen, but does not provide long-lasting protection.  Gamma globulin and equine (horse) tetanus antitoxin are examples of passive immunization.

Blood Components

The immune system includes certain types of white blood cells. It also includes chemicals and proteins in the blood, such as complement proteins and interferon. Some of these directly attack foreign substances in the body, and others work together to help the immune system cells.

Lymphocytes are white blood cells which include B cells and T cells.

  • B cells produce antibodies.  Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen.
  • T cells attack antigens directly and help control the immune response.

As lymphocytes develop, they normally learn to tell the difference between your own body tissues and substances that are not normally found in your body.  Once B cells and T cells are formed, a few of those cells will multiply and provide "memory" for the immune system.  This allows the immune system to respond faster and more efficiently the next time you are exposed to the same antigen and in many cases will prevent you from getting sick.  For example, an individual who has had chickenpox is immune to getting chickenpox again.

Inflammation

The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause.  The damaged tissue releases chemicals including histamine, bradykinin, and serotonin.  These chemicals cause blood vessels to leak fluid into the tissues, causing swelling. This helps isolate the foreign substance from further contact with body tissues.

The chemicals also attract white blood cells called phagocytes that "eat" microorganisms and dead or damaged cells.  This process is called phagocytosis.  Phagocytes eventually die.  Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.

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