Immunoglobulin

and Eva Rudolf-Müller, doctor

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

More about the experts All content is checked by medical journalists.

Immunoglobulin (Ig) refers to various proteins that play an important role in the body's defense against foreign substances. They are also called antibodies and come in different forms with different functions, such as immunoglobulin D or immunoglobulin G. Read everything you need to know about antibodies here: definition, division into different classes, tasks and the possible causes of an immunoglobulin deficiency.

What is an immunoglobulin?

The immunoglobulins (antibodies) are protein structures that belong to the specific immune system. Specific means that they can specifically identify, bind and fight certain components of a pathogen. This is possible because they were each “programmed” beforehand for a specific pathogen. Another common term for immunoglobulin is gamma globulin, or g-immunoglobulin.

While some antibodies circulate in the blood, other immunoglobulins are membrane-bound: They sit on the surface of certain immune cells (B lymphocytes).

Antibodies: structure and function

Immunoglobulins are so-called glycoproteins. This means that they have both a protein and a sugar content.

Immunoglobulins have a y-shape, consisting of two so-called heavy and light chains (H and L chains), of which there are different types. They have two binding sites for antigens. These are characteristic surface structures of foreign substances such as pathogens. By binding the antigens, the immunoglobulin effectively traps the pathogen and thus neutralizes it.

In addition, the antibody-antigen binding is a signal for certain white blood cells (leukocytes) to "swallow" the intruder and thus eliminate it.

Another important antibody function is the activation of the complement system. This is a system of cascade-like activated proteins of the immune system, which act unspecifically against foreign substances and eliminate them.

The various immunoglobulin classes have different tasks in detail. While the specific antibody function of immunoglobulin classes A, E, G and M has been well researched, not much is known about the biological tasks of immunoglobulin D so far.

Which antibody classes are there?

There are five different immunoglobulin subgroups:

• Immunoglobulin A (IgA)
• Immunoglobulin D (IgD)
• Immunoglobulin E (IgE)
• Immunoglobulin G (IgG)
• Immunoglobulin M (IgM)

The classification is based on the type of the two heavy chains. For example, immunoglobulin A has two so-called alpha chains.

Further information: Immunoglobulin A

If you would like to know where this class of antibodies occurs and what tasks it fulfills, read the article Immunoglobulin A.

Further information: Immunoglobulin E

If you want to know how the class E antibody fights parasites and is implicated in allergies, read the post Immunoglobulin E.

Further information: Immunoglobulin G

If you want to know more about the role of these antibodies and what they mean for newborns, read the article Immunoglobulin G.

Further information: Immunoglobulin M

If you want to know where type M antibodies are found in the body and what their function is, read the article Immunoglobulin M.

When are immunoglobulins determined?

The doctor determines the immunoglobulin values ​​if an immunodeficiency is suspected. This exists, for example, in patients who are very susceptible to infections. The immune system can also be disturbed in patients in whom a normally uncomplicated infection is particularly long or severe. Other diseases that are suspected to be diagnosed with antibodies are:

• Autoimmune diseases such as Crohn's disease
• Diseases with increased antibody production (so-called monoclonal gammopathies)
• chronic liver diseases such as cirrhosis or chronic hepatitis

The antibody determination helps to diagnose these diseases and also to estimate their prognosis. It is also used in the aftercare of diseases.

Immunoglobulin: normal values

Immunoglobulins are determined from the blood serum. The following normal values ​​apply to adults:

IgA	IgD	IgE	IgG	IgM
70-380 mg / dl	<100 U / ml	up to 100 IU / ml	700-1600 mg / dl	Women: 40-280 mg / dl Men: 40 - 230 mg / dl

Different reference values ​​apply to children depending on their age.

When are immunoglobulins decreased?

The following diseases lead to a reduced production of antibodies:

• Cushing's Syndrome
• Diabetes mellitus
• Underactive thyroid (hypothyroidism)
• bacterial infections
• Blood poisoning (sepsis)

Therapies that suppress the immune system also inhibit immunoglobulin production. This applies, for example, to chemotherapy and radiation therapy for cancer patients.

Other diseases such as nephrotic syndrome do not affect the production of antibodies, but lead to their increased loss. The same happens with severe burns.

Congenital antibody deficiency

In rare cases, the immunoglobulin deficiency is congenital. If there is a deficiency in all antibody classes, the doctor calls this agammaglobulinemia. However, only individual antibody subgroups can be affected, which is called selective immunoglobulin deficiency. The most common congenital immune disorder is selective IgA deficiency, which affects up to 0.1 percent of the population. Selective IgG or IgM deficiency, for example, is less common.

When are immunoglobulins increased?

An increased antibody level is based on an increase in immunoglobulins and is known as hypergammaglobulinemia. A distinction is made between polyclonal and monoclonal hypergammaglobulinaemia:

Polyclonal hypergammaglobulinaemia

Many different immunoglobulins are increased here. This happens, for example, in the following cases:

• acute and chronic infections
• Autoimmune diseases (such as systemic lupus erythematosus, rheumatoid arthritis)
• Liver diseases such as cirrhosis

Monoclonal hypergammaglobulinaemia

Only a certain type of antibody is increased less frequently. Examples of such monoclonal hypergammaglobulinemia are:

• Plasmacytoma (multiple myeloma)
• Waldenström's disease (immunocytoma)

What to do if the immunoglobulin values ​​change?

In the case of an acquired lack of antibodies, the underlying disease is treated first. For example, the doctor can prescribe insulin therapy for diabetes mellitus or hormone replacement therapy for hypothyroidism.

If there is a congenital antibody deficiency, the patient is given a lifelong substitution with immunoglobulins. These are given into a vein (intravenously) or under the skin (subcutaneously).

If the doctor has diagnosed monoclonal hypergammaglobulinemia, he must investigate the cause. For example, bone marrow and urine examinations or imaging (CT, MRT or scintigraphy) are used. Once the underlying disease has been identified, it will be treated accordingly.

Even if more than one immunoglobulin type is elevated (polyclonal hypergammaglobulinemia), the cause is found out so that appropriate therapy can then be initiated.

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