What are immunoglobulins?

Immunoglobulins or antibodies are substances produced by the body's immune system in response to bacteria, viruses, or other foreign substances, such as fungus, allergens or cancer cells. Antibodies attach to the foreign substances, causing them to be destroyed by other immune system cells.

Antibodies are usually specific to each type of foreign substance. For example, antibodies produced in response to a tuberculosis infection attach only to tuberculosis bacteria. Antibodies also play a role in allergic reactions. Occasionally antibodies may be produced against a person's own tissues. This is called an autoimmune disease.

A person whose immune system produces low levels of antibodies may be at an increased risk of developing repeated infections. A person may be born with an immune system that produces low levels of antibodies, or the immune system may produce low levels of antibodies in response to certain diseases, such as cancer.

The five major types of antibodies are:

IgA. IgA antibodies are found mainly in areas of the body such the nose, breathing passages, digestive tract, ears, eyes, and vagina. IgA antibodies protect body surfaces that are exposed to the outside from foreign organisms and substances. This type of antibody is also found in saliva and tears. About 10% to 15% of the antibodies usually present in the body are IgA antibodies. A small percentage of people do not make IgA antibodies.

IgG. IgG antibodies are found in all body fluids. They are the smallest but most abundant of the antibodies, normally comprising about 75% to 80% of all the antibodies in the body. IgG antibodies are considered the most important antibodies for fighting bacterial and viral infections. IgG antibodies are the only type of antibody that can cross the placenta. Therefore, the IgG antibodies of a pregnant woman can also help protect her baby (foetus).

IgM. IgM antibodies are the largest type of antibody. They are found in blood and lymph fluid and are the first type of antibody produced in response to an infection. They also cause other immune system cells to produce compounds that can destroy invading cells. IgM antibodies normally comprise about 5% to 10% of all the antibodies in the body.

IgD. IgD antibodies are found in small amounts in the tissues that line the abdominal or chest cavity of the body. The function of IgD antibodies is not well-understood. They appear to play a role in allergic reactions to some substances such as milk, some medications, and some poisons.

IgE. IgE antibodies are found in the lungs, skin, and mucous membranes. They cause the body to react against foreign substances such as pollen, fungus spores, and animal dander. IgE antibody levels are often high in people with allergies.

The levels of each type of antibody can give your health professional information about the cause of a medical problem.

Clinical Implications of Human Immunoglobulin Classes
Adapted and abridged from:F.T. Fischbach in "A Manual of Laboratory
Diagnostic Tests," 2nd Ed., J.B. Lippincott Co., Philadelphia, PA, 1984.

IgG

1. Increases in:

a) Chronic granulomatous infections

b) Infections of all types

c) Hyperimmunization

d) Liver disease

e) Malnutrition (severe)

f) Dysproteinemia

g) Disease associated with hypersensitivity granulomas, dermatologic

disorders, and IgG myeloma

h) Rheumatoid arthritis

2. Decreases in:

a) Agammaglobulinemia

b) Lymphoid aplasia

c) Selective IgG, IgA deficiency

d) IgA myeloma

e) Bence Jones proteinemia

f) Chronic lymphoblastic leukemia

IgM

1. Increases (in adults) in:

a) Waldenström's macroglobulinemia

b) Trypanosomiasis

c) Actinomycosis

d) Carrión's disease (bartonellosis)

e) Malaria

f) Infectious mononucleosis

g) Lupus erythematosus

h) Rheumatoid arthritis

I) Dysgammaglobulinemia (certain cases)

Note: In the newborn, a level of IgM above 20 ng./dl is an indication

of in utero stimulation of the immune system and stimulation by the

rubella virus, the cytomegalovirus, syphilis, or toxoplasmosis.

2. Decreases in:

a) Agammaglobulinemia

b) Lymphoproliferative disorders (certain cases)

c) Lymphoid aplasia

d) IgG and IgA myeloma

e) Dysgammaglobulinemia

f) Chronic lymphoblastic leukemia

IgA

1. Increases in:

a) Wiskott-Aldrich syndrome

b) Cirrhosis of the liver (most cases)

c) Certain stages of collagen and other autoimmune disorders such as

rheumatoid arthritis and lupus erythematosus

d) Chronic infections not based on immunologic deficiencies

e) IgA myeloma

2. Decreases in:

a) Hereditary ataxia telangiectasia

b) Immunologic deficiency states (e.g., dysgammaglobulinemia,

congenital and acquired agammaglobulinemia, and hypogammaglobulinemia)

c) Malabsorption syndromes

d) Lymphoid aplasia

e) IgG myeloma

f) Acute lymphoblastic leukemia

g) Chronic lymphoblastic leukemia

IgD

1. Increases in:

a) Chronic infections

b) IgD myelomas

IgE

1. Increases in:

a) Atopic skin diseases such as eczema

b) Hay fever

c) Asthma

d) Anaphylactic shock

e) IgE-myeloma

2. Decreases in:

a) Congenital agammaglobulinemia

b) Hypogammaglobulinemia due to faulty metabolism or synthesis of immunoglobulins