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The immune system is your body’s defense against intruding foreign organisms that cause disease. White blood cells called leukocytes seek out and destroy threatening organisms.
Chemotherapy and treatments to prevent rejection of grafts or transplants or control autoimmune diseases can suppress or weaken the immune system. Hematological cancers, such as leukemia, suppress normal immune system function.
You can inherit a genetic conditon that weakens your immune system. Collectively, this is called immunosuppression.
The Immune System
In order to comprehend the significance of immunosuppression, it is important to understand how the immune system functions.
The immune system is made up of white blood cells called leukocytes, which are produce and stored in many locations including the thymus, spleen and bone marrow.
Lymphoid tissue, primarily the lymph nodes, store leukocytes. Leukocytes circulate through the body between the organs and lymph nodes via blood vessels and lymphatic vessels. They continuously monitor for harmful germs and substances.
The two basic types of leukocytes are phagocytes, which digest the invading organisms, and lymphocytes. Bone marrow and the thymus are called lymphoid organs, because they store lymphocytes. Both are organs of the immune system. The two types of lymphocytes are B and T lymphocytes.
B lymphocytes remain in the bone marrow and produce antibodies. T lymphocytes leave the bone marrow and travel to the thymus. They destroy antigens identified by the antibodies or cells that have become infected or altered. (1)
The Immune Response
A healthy immune system distinguishes the body’s own cells from foreign cells. But, when foreign intruders, called antigens, are detected, the immune system attacks. This is called the immune response. An antigen is any substance that can trigger the immune response.
Viruses, bacteria, tissue grafts and organ transplants acts as foreign antigens. In some situations, allergens such as tree pollen, triggers an immune response.