The lymph system is a network of vessels that carry lymph, a watery fluid containing white blood cells, throughout the body. Lymph drains from the blood vessels and body tissues, carrying away waste products. The waste products are filtered out of the lymph by small structures called lymph nodes. Within the lymph nodes, harmful microorganisms are trapped, attacked, and destroyed by white blood cells. This is one of the body's primary and most efficient lines of defense.
Antibodies are manufactured in the lymph system. Antibodies are protective substances that the body produces in response to invasion by a hostile organism or the presence of a foreign substance. Antibodies counteract some invading bacteria and viruses by inactivating them so that they are powerless. Antibodies that neutralize toxins (poisons) produced by bacteria are called antitoxins.
The body's production of white blood cells and antibodies in response to an invading organism is called the immune reaction. Immunity is the body's ability to resist an invasion of disease-causing bacteria and viruses. Once antibodies have been made to fight a certain type of microorganism, that microorganism usually no longer poses a threat to the body. That is why one attack of a disease often prevents its recurrence down the road. The first attack causes antibodies to be produced, and these antibodies protect the system against future attacks.
There are ways to help the body's own defenses work. One is immunization, something all of us have experience with. Read about it in the next section.