When you are born you enter into a very hostile environment full of nasty little microorganisms with the capability of injuring and even killing you.
Fortunately you arrive equipped with a powerful defense system known as your immune system. It works around the clock watching for, attacking, and eliminating the foreign invaders that endanger your body. This ongoing process is called the immune response
. For this to work properly your immune system must be able to distinguish between an invading infectious organism and the cells that comprise your body. However, all the cells in your body are marked so your immune system can recognize "you" from foreign invaders. So for as long as you live your immune system keeps you healthy by destroying the invaders. But, there are times when it fails. If the invader is stronger it can overpower your immune system. Or your immune system, in the process of fighting off the foreign substance, can injure your own tissues.
These microorganisms are designed by nature to perform two functions: reproduce and stay alive
. To accomplish their goals they need the nourishment your body can provide. And obtaining this nourishment can make you very ill and perhaps even kill you. However, the organism must first gain access to your body. There are many ways for it to do this. They can enter through your nose as you inhale, through your skin if there is a break in the skin, and through your mouth via the water you drink and the food you eat. Your body has many sentinels standing guard to repel these organisms such as the hairs in your nose, tears in your eyes, cells on the linings of you throat, esophagus and windpipe, and acids in your stomach and intestines.
The organism that does manage to get past the sentinels and into your body has to then attach itself to your tissues
. Only then can it strive and reproduce. Some of these organisms need to gain entry to your cells in order to survive. However, the minute these organisms access your body, the immune system mobilizes for attack. The attack mechanism operates something like an army. The main soldiers are the lymphocytes or white blood cells. There are different kinds of these with different jobs. One kind of T lymphocyte directions the action. Some become killer cells and others become memory cells.
Your immune system employs two defense strategies:
the development of killer cells and the development of anti-bodies. The first strategy involves sending killer T lymphocytes to attack the infected cells. The second strategy requires B lymphocytes to manufacture substances known as antibodies. These antibodies attach themselves to a germ and immobilize it thereby bringing about its destruction. The killer T cell strategy is employed against viruses. Viruses hide themselves within some of your body cells and can only survive as long as the host cell survives. The antibody strategy is used for bacterial infections. A third important defense mechanism involves the production of memory cells. The lymphocytes remember past infections. If the same infection should return, the memory cells prompt the immune system to respond more quickly and more aggressively.