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Your immune system is often compared to an army. This army defends your body from infection and disease. Your skin and the mucous that lines your respiratory and gastrointestinal tracts help block bacteria from entering or staying in your body. If foreign substances somehow make it through these barriers, your immune system kicks into gear with two defensive systems: innate and adaptive.

The innate system exists in your body before you are exposed to foreign substances like bacteria, viruses, fungi, or parasites. These substances, which are called antigens, can invade your body and make you sick. The components of the innate system include:

-WHITE BLOOD CELLS - White blood cells form your first line of defense against infection.They surround and swallow foreign bodies quickly.

-NATURAL KILLER (NK) CELLS - Natural Killers are special white blood cells that detect and destroy cells infected with cancer or viruses.

-CYTOKINES - White blood cells send out these chemical messengers directly to an infected site. Cytokines trigger inflammatory responses, like dilating blood vessels and increasing blood flow to the affected area. They also call on more white blood cells to swarm an infected area.

The adaptive system kicks in after you are exposed to an infection for the first time. The next time you encounter the same infection, your adaptive system fights it off even faster and more efficiently than the first time. The components of the adaptive system include:

-T-LYMPHOCYTE CELLS - T-cells reinforce the work of white blood cells by targeting individual foreign substances.T-cells can identify and destroy a vast array of bacteria and viruses.They can also kill infected cells and secrete cytokines.

-B-LYMPHOCYTE CELLS - B-cells produce antibodies that fight off harmful substances by sticking to them and making them stand out to other immune cells.

-ANTIBODIES - After B-cells encounter antigens, they produce antibodies.These are proteins that target specific antigens and then remember how to combat the antigen.


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