In immunodeficiency disorders, part of the body's immune system is missing or defective, thus impairing the body's ability to fight infections. Asa result, the person with an immunodeficiency disorder will have frequent infections that are generally more severe and last longer than usual.

The immune system is the body's main system to fight infections. The normal immune system involves a complex interaction of certain types of cells that can recognize and attack "foreign" invaders, such as bacteria, viruses, and fungi. It also plays a role in fighting cancer. People are born with certain parts of the immune system; such parts are called innate immunity. Otherparts of the immune system people develop over time, which is called adaptiveimmunity.

The innate immune system is made up of the skin (which acts as a barrier to prevent organisms from entering the body), white blood cells called phagocytes, a system of proteins called the complement system, and chemicals called interferon. When phagocytes encounter an invading organism, they surround and engulf it to destroy it. The complement system also attacks bacteria. The elements in the complement system create a hole in the bacterium's outer layer ofthe target cell, which leads to its death.

The adaptive component of the immune system is extremely complex and still not entirely understood. Basically, it has the ability to recognize an organismor tumor cell as not being a normal part of the body, and to develop a response to attempt to eliminate it.

Defects can occur in any component of the immune system or in more than one component (combined immunodeficiency). Different immunodeficiency diseases involve different components of the immune system. The defects can be inheritedand/or present at birth (congenital) or acquired.

Congenital immunodeficiency is present at birth, and is the result of geneticdefects. Even though more than 70 different types of congenital immunodeficiency disorders have been identified, they rarely occur.

Disorders of innate immunity affect phagocytes or the complement system. These disorders also result in recurrent infections.

Acquired immunodeficiency is more common than congenital immunodeficiency. Itis the result of an infectious process or other disease. For example, the human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS). However, this is not the most common cause ofacquired immunodeficiency.

Acquired immunodeficiency often occurs as a complication of other conditionsand diseases. For example, the most common causes of acquired immunodeficiency are malnutrition, some types of cancer, and infections. People who weigh less than 70% of the average weight of persons of the same age and gender are considered to be malnourished. Examples of infections that can lead to immunodeficiency are chicken pox, German measles, measles, tuberculosis, chronic hepatitis, lupus, and bacterial and fungal infections.

Sometimes, acquired immunodeficiency is brought on by drugs used to treat another condition. For example, patients who have an organ transplant aregiven drugs to suppress the immune system so the body will not reject the organDuring the period of time that these drugs are being taken, the risk of infection increases. It usually returns to normal after the person stops takingthe drugs.

People with an immunodeficiency disorder tend to become infected by organismsthat don't usually cause disease in healthy persons. The major symptoms of most immunodeficiency disorders are repeated infections that heal slowly. These chronic infections cause symptoms that persist for long periods of time. People with chronic infection tend to be pale and thin. They may have skin rashes. Broken blood vessels, especially near the surface of the skin, may be visible, resulting in black-and-blue marks in the skin.

There is no cure for immunodeficiency disorders. Therapy is aimed at controlling infections and, for some disorders, replacing defective or absent components.

Common variable immunodeficiency also is treated with periodic injections ofgamma globulin throughout life. Additionally, antibiotics are given when necessary to treat infections.

In most cases, immunodeficiency caused by malnutrition is reversible.The health of the immune system is directly linked to the nutritional healthof the patient. Among the essential nutrients required by the immune system are proteins, vitamins, iron, and zinc.

For people being treated for cancer, periodic relief from chemotherapydrugs can restore the function of the immune system.

In general, people with immunodeficiency disorders should maintain a healthydiet because malnutrition can aggravate immunodeficiencies. They should alsoavoid being near people who have colds or are sick because they can easily acquire new infections. For the same reason, they should practice good personal hygiene, especially dental care. People with immunodeficiency disorders should also avoid eating undercooked food because it might contain bacteria that could cause infection. This food would not cause infection in normal persons, but in someone with an immunodeficiency, food is a potential source of infectious organisms. People with immunodeficiency should be given antibiotics at the first indication of an infection.

There is no way to prevent a congenital immunodeficiency disorder. However, someone with a congenital immunodeficiency disorder might want to consider getting genetic counseling before having children to find out if there is a chance they will pass the defect on to their children.

Some of the infections associated with acquired immunodeficiency can be prevented or treated before they cause problems. For example, there are effectivetreatments for tuberculosis and most bacterial and fungal infections. HIV infection can be prevented by practicing "safe sex" and not using illegal intravenous drugs. These are the primary routes of transmitting the virus. For people who don't know the HIV status of the person with whom they are having sex,safe sex involves using a condom.

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