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Definition - What does Immune System mean?

The immune system is the complex network of cells, proteins, and organs that protect the body from infection. Bacteria, viruses, fungi, and parasites that attack the body are fended off by the immune system. Most of the body's immune system cells are produced as stem cells in the bone marrow and later differentiate themselves into various types of cells required to protect the body.

SureHire explains Immune System

The immune system's response to the threat of infection is to recognize and identify the threat and initiate the appropriate processes required to fight off the infection. The cells produce specific chemicals that allow the immune system to focus on attacking the problem and distinguish the infected cells from the healthy ones. These cells travel through the bloodstream and lymphatic system. The immune system is comprised of the liver, tonsils, spleen, thymus, bone marrow, bloodstream and lymph nodes.

The immune system responses are what make immunoassay drug testing possible.