Immune System, Health and IAQ
What the immune system is and its role
Conditions or substances that can weaken the immune system
Resource for additional infomration
What the Immune System Is and Its Role
The immune system consists of several varieties of white blood cells such as lymphocytes, antibodies, and other substances that fight off infections in the body. The white blood cells are produced in different areas of the body including the bone marrow, the thymus, the lymph nodes, and spleen. Some white cells travel throughout the body in the blood and lymph systems in order to recognize "self" cells from "non-self" cells. They do this by locating markers found on the surface of every cell in the body. Those substances that are recognized by the immune system when introduced into the body are called antigens. The T cells from the thymus make this distinction. Some of these cells in the immune system are part of the general body defenses while others seek out specific targets. The reaction of the immune system to foreign substances is called an immune response.
As early as the 5th century BC, Greek physicians noted that people who had recovered from some diseases, like the plague, never got it again. This is because, whenever T cells and B cells (another lymphocyte) are activated, some of the cells become "memory" cells. Then, the next time that an individual encounters that same antigen, the immune system is ready to destroy it quickly.
This kind of "immunity" from disease after having had the disease became known as acquired or active immunity. The degree and duration of immunity depend on the kind of antigen, its amount, and how it enters the body. An immune response is also dictated by heredity with some individuals responding strongly to a given antigen, others weakly, and some not at all. In addition to actually having a particular disease, active immunity can also be acquired through vaccinations.
Vaccines contain microorganisms that have been altered so they will produce an immune response but will not be able to cause the disease. Some vaccines are made from microbes that have been killed. Others use microbes that have been changed slightly so they can no longer produce infection. Some vaccines are made from a live virus that has been weakened by growing it for many cycles in animals or cell cultures.
Infants are born with rather weak immune responses, but they are protected during the first months of their lives by means of antibodies they receive from their mothers either when they were in their mother's uterus or by drinking their mother's breast milk. Whatever the mothers are immune to, their babies are immune to during these first critical months. This is called passive immunity. Passive immunity typically lasts only a few weeks.
Sometimes the immune system responds to a false alarm. This is what happens with allergic reactions such as hay fever, some kinds of asthma, and hives. In a susceptible person, a normally harmless substance, such as grass pollen or house dust, is perceived as a threat and is attacked. Such allergic reactions are related to the antibody known as immunoglobulin E (IgE). Like other antibodies, each IgE antibody is specific, reacting only to one particular antigen.
The first time an allergy-prone person is exposed to an allergen, there may be no response. With subsequent exposures, however, large amounts of the corresponding IgE antibody may be produced. These IgE molecules attach to the surfaces of mast cells (in tissue) or basophils (in the circulation). Mast cells are plentiful in the lungs, skin, tongue, and linings of the nose and intestinal tract. When an IgE antibody comes across its specific allergen, the IgE antibody signals the mast cell or basophil to release powerful chemicals that are stored within these cells. Among these chemicals are histamine and other substances that result in the usual symptoms of allergies including wheezing, sneezing, runny eyes and itching.
If some parts of the immune system are missing, this is referred to as an immunodeficiency. Immune deficiencies can be inherited, acquired through infection or other illness, or produced as an inadvertent side effect of certain drug treatments such as chemotherapy.
Conditions or Substances That Can Weaken the Immune System
Examples include:
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People with advanced cancer that develop immune deficiencies as a result of the disease process or from extensive anticancer therapy (such as chemotherapy or radiation).
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Common viral infections, including influenza, infectious mononucleosis, and measles
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Bacterial or parasitic infections
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Blood transfusions
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Surgery
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AIDS
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Stress
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Age
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Malnutrition
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Toxins
People with immune system problems are more likely to suffer health problems such as:
Resource For Additional Information
Horner WE, Lehrer SB, Salvaggio, JE. Aerobiology. In: Lockey RF, Burkhartz SC. Allergens and Allergy Immunotherapy, 2nd ed. New York, NY: Marcel Dekker, 1999:53-72. (212) 696-9000