What is an immunoglobulin?
Immunoglobulins (antibodies) are protein structures that belong to the specific immune system. Specific means that they can recognize, bind to and fight specific components of a pathogen. This is possible because they have each been “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 component.
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 captures the pathogen, so to speak, and thus neutralizes it.
In addition, antibody-antigen binding is a signal for certain white blood cells (leukocytes) to “swallow” the invader and thus eliminate it.
The different 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 subclasses:
- Immunoglobulin A (IgA)
- Immunoglobulin D (IgD)
- Immunoglobulin E (IgE)
- Immunoglobulin G (IgG)
- Immunoglobulin M (IgM)
The classification is made according to the nature 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 performs, read the article Immunoglobulin A.
Further information: Immunoglobulin E
If you want to learn how antibody class E fights parasites and is involved in allergies, read the article Immunoglobulin E.
Further information: Immunoglobulin G
If you want to know more about the roles of these antibodies and their importance to 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 do you determine immunoglobulins?
- Autoimmune diseases such as Crohn’s disease
- diseases with increased antibody formation (so-called monoclonal gammopathies)
- Chronic liver diseases such as cirrhosis of the liver or chronic hepatitis
The determination of antibodies helps to diagnose these diseases and also to estimate their prognosis. It is also used in the follow-up of these diseases.
Immunoglobulin: Normal values
Immunoglobulins are determined from blood serum. For adults, normal values are as follows:
|
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 |
For children, other reference values apply depending on age.
When are immunoglobulins decreased?
The following diseases lead to a decreased production of antibodies:
- Cushing’s syndrome
- Diabetes mellitus
- hypothyroidism (underactive thyroid gland)
- bacterial infections
- blood poisoning (sepsis)
Therapies that suppress the immune system also inhibit immunoglobulin production. This is true, for example, of 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
When are immunoglobulins elevated?
An elevated antibody level is due to an increase in immunoglobulins and is referred to as hypergammaglobulinemia. A distinction is made between polyclonal and monoclonal hypergammaglobulinemia:
Polyclonal hypergammaglobulinemia.
Here, many different immunoglobulins are increased. This occurs, 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 hypergammaglobulinemia
Less commonly, only one particular type of antibody is increased. Examples of such monoclonal hypergammaglobulinemia are:
- Plasmocytoma (multiple myeloma)
- Waldenström’s disease (immunocytoma)
What to do in case of altered immunoglobulin levels?
In the case of an acquired deficiency of antibodies, the underlying disease is treated first. For example, the physician may prescribe insulin therapy for diabetes mellitus or hormone replacement therapy for hypothyroidism.
If there is a congenital antibody deficiency, the patient receives a lifelong substitution with immunoglobulins. These are administered into a vein (intravenously) or under the skin (subcutaneously).
Even if more than one type of immunoglobulin is elevated (polyclonal hypergammaglobulinemia), the cause is investigated so that appropriate therapy can then be initiated.