One of the most important players in our immune systems is the white blood cell, also called a leukocyte. Leukocytes patrol the blood and tissues throughout the body in search of intruders. When they detect a foreign substance, they send out signals and launch an immune attack. These disease-fighting cells are made in the bone marrow and are stored in many different places in the body such as the tonsils and adenoids.

There are two types of leukocytes: phagocytes and lymphocytes. Phagocytes engulf the intruders, break them down and chew them up. Lymphocytes are further broken down into two more types. The B lymphocytes (or B-cells) create antibodies and alert the T lymphocytes (or T-cells) to kill the pathogens.

White blood cells are a part of the lymphatic system, a network of lymph vessels that collect excess fluids from tissues throughout the body and then return them to your bloodstream. The lymphatic system and lymph nodes (small bean-shaped organs clustered in the neck, armpits, abdomen and groin) act as filters and trap harmful germs. If immune cells in the lymph node recognize pieces of a germ, they will activate, replicate and leave the lymph node in search of those harmful germs. Lymph nodes often become swollen due to an active immune response, which is why doctors check them for signs of infection.

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