Immune Deficiencies

Immune deficiencies (ih-MΥΟΟN dih-FIH-shen-seez), or immunodeficiencies, are conditions that impair the body's immune system so that it is less able to fight infection.

Immune deficiencies arise when one or more parts of the immune system are missing or not working correctly, leaving the body less able to fight disease-causing agents. There are two types of these deficiencies: primary (inherited) immune deficiencies and secondary (acquired) immune deficiencies.

The immune system has many parts that work together to protect the body from foreign invaders such as microorganisms * and toxins * . When any segment of the immune system is absent or breaks down, it can lead to an immune deficiency. Given that there are so many parts in the human immune system, it is not surprising that there are more than 250 different types of primary immune diseases. They range from those that have severe and sometimes fatal effects to mild disorders that cause people few (if any) problems. About 1 person in every 1,200 in the United States has some type of primary immune deficiency, with more boys than girls affected by these conditions.

Secondary immune deficiencies are much more common than inherited deficiencies. Unlike patients with primary immune deficiencies, people with secondary immune deficiencies are born with a healthy immune system, but at some point in later life, the system becomes weakened or damaged. Both primary and secondary deficiencies typically lead to frequent infections and sometimes to additional medical problems, including certain cancers. People with immune deficiencies often experience a variety of skin, respiratory, and bone issues, and are more likely to have autoimmune diseases * .

The immune system consists of a group of organs, cells, and a specialized system called the lymphatic (lim-FAH-tik) system that helps clear infectious agents from the body. Together, they guard the body against infectious diseases. The lymphatic system is a major part of the immune system: it consists of lymphatic vessels, lymph nodes * , the thymus (THY-mus) gland, and the spleen. Lymph nodes and lymphatic vessels transport lymph, a clear fluid that contains white blood cells called lymphocytes (LIM-fo-sites) throughout the body. The lymphocytes mature in the thymus, a gland located behind the breastbone. The spleen, an organ that is the center of certain immune system activities, is found in the upper left side of the abdomen. Lymphatic tissue is also found in other locations throughout the body, including the tonsils * and the appendix * .

When a foreign substance or microorganism enters the body, phagocytes (FAH-go-sites) often are the first cells at the site. These large scavenger white blood cells patrol the bloodstream, looking for possible invaders. When they find one, they engulf, digest, and destroy the intruder.

Other components of the immune response react when presented with specific antigens * . The most important agents in this fight are two types of lymphocytes that learn to recognize and destroy the foreign invaders.

B cells, the first type, are white blood cells that produce antibodies * * to the site of an infection and move them into action against the antigens.

T cells, the second type of lymphocyte, are specialized white blood cells that have several different functions. They monitor and coordinate the entire immune response, which includes recruiting many different cells to take part in that response. Some T cells, the T helper cells, signal the B cells to start making antibodies. Other T cells, the T killer cells, attack and destroy substances that they recognize as foreign. Once the foreign antigens have been neutralized, cleanup crews of scavenger phagocytes called neutrophils (NU-tro-fils), a type of white blood cell that can surround and destroy invading organisms, and macrophages (MAH-krofay-jez), another form of engulf-and-destroy cell, arrive to clear up the remains of the infection.

A genetic * abnormality in any type of cell of the immune system can lead to a primary immune deficiency. Some of these deficiencies produce no symptoms, whereas others cause severe symptoms and may even be fatal. Although primary immune deficiencies are present at birth, some patients do not begin to show signs of the condition until later in childhood or even in the early adult years.

There are several well-known primary immune deficiencies. About 1 person in 500 is born with selective IgA deficiency, a mild disease that most often affects those of European ancestry. People with this condition lack immunoglobulin (IH-myoo-no-GLAH-byoo-lin) A (IgA), a class of antibodies that fight organisms that can infect the mucous membranes that line the mouth, airways, and digestive system * . Many patients with this disorder experience few symptoms, but some may have frequent infections.

The effects of common variable immunodeficiency, also known as hypogammaglobulinemia (HY-po-gah-muh-gloh-byoo-lih-NEE-me-uh), can range from mild to severe. Its symptoms occasionally affect infants but often do not appear until early adulthood. Those symptoms include frequent bacterial infections of the ears, sinuses * , bronchi * , or lungs brought on by low levels of various immunoglobulins, including IgA and IgG.

Caused by defective genes on the X chromosome * , X-linked agammaglobulinemia (a-GAH-muh-gloh-byoo-lih-NEE-me-uh) is uncommon, affecting only about 1 person in every 250,000, and occurs only in males. Patients have very low levels of mature B cells as well as low levels of immunoglobulins, which can result in pus * collecting in the lungs, sinuses, and ears, in addition to other signs of infection.

Other primary immune deficiency diseases may involve other components of the immune system, including neutrophils and phagocytes. There may be fewer of these cells produced, as occurs in a condition known as neutropenia (NU-tro-PEE-nee-uh), which is marked by low levels of neutrophils in the blood. Chronic * granulomatous (gran-yooLO-muh-tus) disease is an immune disorder in which bacteria-fighting phagocytes are present but do not work properly. Genetic defects also can impair the complement system, a series of 30 or more proteins that come together during the body's immune response to complement (support) the work of antibodies. These conditions and defects in other parts of the complex immune system cause problems with the body's immune response, often making a person more susceptible to a variety of infections.

Secondary immune deficiencies are acquired rather than inherited disorders. Many chronic conditions, such as diabetes * , cancer, and cirrhosis * of the liver, make a person more susceptible to infections. Patients who have had their spleens removed or whose spleens do not work properly, as occurs in sickle cell disease * , for example, are especially vulnerable to infection by certain bacteria that the spleen normally fights. In addition, radiation therapy for cancer as well as some medications, particularly corticosteroids * and drugs used to treat cancer, may suppress the immune system. Malnutrition, especially when there is a lack of protein in the diet, also may weaken the immune response. Lastly, older adults are more likely to have certain disorders or take certain medications that suppress the immune system, which has already been weakened by the aging process.

The human immunodeficiency virus (HIV), a virus that attacks the immune system and is the cause of acquired immunodeficiency syndrome (AIDS), is responsible for a sharp increase in the number of people with secondary immune deficiencies. HIV destroys T cells, which are crucial to the normal functioning of the human immune system. This condition can lead to overwhelming infections. People can contract the virus through contact with blood, semen, vaginal secretions, and breast milk.

Immune deficiencies may be characterized by frequent, recurrent, or prolonged infections. In some cases, there may be an overwhelming or unusual infection. In others, organisms that typically do not cause problems in a person with a healthy immune system may produce an opportunistic infection * in a person with an immune deficiency. These infections are seen in people infected with HIV and often mark the onset of AIDS.

Other immune deficiencies are characterized by chronic opportunistic infections. Depending on the condition, patients may experience recurrent lung and sinus infections, weakness, tiredness, a lingering cough, diarrhea (dye-uh-REE-uh), skin rashes, and hair loss. Many patients simply look and feel sick. Signs of immune deficiencies also include poor response to treatments; incomplete or slow recovery from illness; fungal or yeast infections that keep coming back; and certain specific infections, such as pneumonia caused by Pneumocystis jirovecii (NU-mo-SIS-tis JEE-roh-VEK-ee-eye).

Although symptoms of opportunistic infections may suggest an immune deficiency, laboratory tests are needed to diagnose the specific deficiency. These include blood tests to measure levels of white blood cells, red blood cells, and platelets * , and to measure the presence of specific types of cells such as B cells and T cells. Other blood tests can measure the levels or function of antibodies (such as IgA, IgG, and IgM) and complement proteins. Skin tests may be done to check the responsiveness of T cells. Other more specific tests of the immune system's competency depend on the type of deficiency suspected.

The primary goal in treating immune deficiencies is to prevent infections. Although it is a good idea for some people who have immune deficiencies to avoid contact with people who have infections, doing so is not always practical. Many patients take daily medication to prevent certain infections, and patients with antibody deficiencies may receive regular doses of the immunoglobulins they lack. People who have HIV or AIDS take combinations of drugs to keep the virus from making more copies of itself and destroying more T cells. Bone marrow * transplantation, to replace the absent or poorly functioning immune system cells of the affected person, is necessary for some patients with severe immune deficiencies such as SCID. Prompt recognition and treatment of infections, including opportunistic infections, is essential.

See also AIDS and HIV Infection • Genetic Diseases: Overview • Immune System and Other Body Defenses: Overview • Immunoglobulin Deficiency Syndromes • Infection • Meningitis • Pneumonia • Sepsis • Toxoplasmosis

* microorganisms are tiny organisms that can be seen only under a microscope. Types of microorganisms include fungi, bacteria, protozoa, and viruses.

* toxins are poisonous substances produced within living cells or organisms.

* autoimmune diseases (awtoh-ih-MYOON) are diseases in which the body's immune system attacks some of the body's own normal tissues and cells.

* lymph nodes (LIMF) are small bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

* tonsils are paired clusters of lymphatic tissue in the throat that help protect the body from bacteria and viruses that enter through a person's nose or mouth.

* appendix (ah-PEN-diks) is the narrow, finger-shaped organ that branches off the part of the large intestine in the lower right side of the abdomen. Although the organ is not known to have any vital function, the tissue of the appendix is populated by cells of the immune system.

* antigens (AN-tih-jens) are substances that are recognized as a threat by the body's immune system, which triggers the formation of specific antibodies against the substance.

* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms such as bacteria and viruses.

* complement proteins are proteins that circulate in the blood and play a role in the immune system's response to infections. More than 30 complement proteins had been identified as of 2016.

* genetic (juh-NEH-tik) refers to heredity and the ways in which genes control the development and maintenance of organisms.

* digestive system is the system that processes food. It includes the mouth, esophagus, stomach, intestines, colon, rectum, and other organs involved in digestion, including the liver and pancreas.

* sinuses (SY-nuh-ses) are hollow air-filled cavities in the facial bones.

* bronchi (BRONG-kye) are the large tube-like airways that carry air in and out of the lungs.

* chromosome (KRO-mo-zom) is a unit or strand of DNA, the chemical substance that contains the genetic code to build and maintain a living being. Humans have 23 pairs of chromosomes, for a total of 46.

* pus is a thick, creamy fluid, usually yellow or ivory in color, that forms at the site of an infection. Pus contains dead infectionfighting white cells and other substances.

* chronic (KRAH-nik) means lasting a long time or recurring frequently.

* diabetes (dye-uh-BEE-teez) is a condition in which the body's pancreas does not produce enough insulin or the body cannot use the insulin it makes effectively, resulting in increased levels of sugar in the blood. Diabetes can lead to increased urination, dehydration, weight loss, weakness, and a number of other symptoms and complications related to chemical imbalances within the body.

* cirrhosis (sir-O-sis) is a condition that affects the liver involving long-term inflammation and scarring, which can lead to problems with liver function.

* sickle cell disease is a hereditary condition in which the red blood cells, which are usually round, take on an abnormal crescent shape and are less able to carry oxygen throughout the body.

* corticosteroids (kor-tih-ko-STIRoyds) are chemical substances made by the adrenal glands that have several functions in the body, including maintaining blood pressure during stress and controlling inflammation. They can also be given to people as medication to treat certain illnesses.

* platelets (PLATE-lets) are tiny disk-shaped particles within the blood that play an important role in clotting.

* bone marrow is the soft tissue inside bones where blood cells are made.

* opportunistic infections are infections caused by organisms that usually do not produce disease in people with healthy immune systems but can cause widespread and severe illness in patients with weak or faulty immune systems.