THE BEAUTIFUL IMMUNE SYSTEM LESSON 6: Antibody Classes and the Immunoglobulins Test

The body’s immune system makes antibodies in response to something it believes needs to be destroyed. Most often, antibodies are made to attach to foreign substances, “immunogens”, such as bacteria, viruses, fungi, parasites, animal dander, cancer cells…and the list goes on. Occasionally antibodies are made to our own body’s tissues, as is the case with auto immune diseases.

Antibodies are made by the immune system and are basically just chains of proteins. Because they are formed in response to an immunogen and are made up of proteins–glycoproteins, rather–they are also called immunoglobulins in the scientific community.

Scientists use the short hand “IgY” when expressing immunoglobulins. The “Y” is replaced with a letter to signify the antibody class. The immunoglobulins can be divided into five different classes. These classes are based on the differences in the amino acid structure in specific regions of part of the antibody’s protein chains.

As you may recall from earlier lessons, antibodies are made in response to SPECIFIC foreign substances. For example, the only substance the diphtheria antibody attaches to is a specific site on the diphtheria bacterium, Corynebacterium diphtheriae.

All of these specific antibodies also fall into one of the five classes of antibodies, which all have different functions in different places in the body.

These five different classes of antibodies are:

IgAIgA, Alpha:  This class of antibody is important in protecting the body’s surfaces (mucosal and secretory immunity) that are exposed to the outside world. Because of this, IgA antibodies are found in particular areas of the body, such as the nose, breathing passages, digestive tract, ears, eyes, and vagina, as well as in secretory bodily fluids such as saliva, tears, colostrum, mucus, and blood. It is the second most common antibody found in blood serum. And about 10-15% of the antibodies found in the body are of this class.1 However, a small number of people do not make IgA antibodies.

IgGIgG, Gamma: These antibodies are found in all body fluids and are the power house antibodies, capable of carrying out ALL of the functions that immunoglobulins are able to do. They are the smallest and most common (75% to 80%) of all the antibodies in the body.1 IgG antibodies play a fundamental role in fighting bacterial and viral infections.  And they are the only antibody class that can cross the placenta to give a growing fetus antibody protection in early life.
IgM
IgM, Mu: This class is found in the blood and lymph fluids. They are the third most common antibody in blood serum, and comprise about 5-10% of the antibodies in the body.1 IgM’s are the largest antibodies and are the first type of antibody to be made in response to an infection. They also are they type of antibody to form when an infection occurs in the body for the first time, and because of this, are the first immunoglobulin molecules made by a fetus’s own body. IgM’s are very efficient in destroying foreign substances and are important in the clumping of microorganisms for eventual elimination from the body.
IgD
IgD, Delta: This class of antibodies is found in very low levels (1%) in the blood serum, as well as in the tissues that line the belly/chest. IgD’s function is currently unclear, however it is known that they are mostly found on the surfaces of B cells.
IgE
IgE, Epsilon: IgE’s are found in the lungs, skin, and mucous membranes, and are the least common antibody in blood serum. This class is involved in allergic reactions, as well as eliminating parasitic worms from the body. You would find high levels of IgE’s in someone who has allergies.

The level of antibodies in the blood can be measured by a test called the immunoglobulins test. The amount and type of antibodies in the blood tells us so many things. It can tell if you have an autoimmune disease, allergies, certain types of cancer, an infection (particularly from low levels of IgG), can tell if you have immunity to a disease or have had a certain disease in the past, and can be important in checking for responses/treatments for certain diseases.

I’m not going to post the “normal” values for these antibody classes, because “normal” varies from lab to lab, person to person, and also with age. But, if you should have particularly high or low values of a class of antibody, here is what it may tell your physician:

IgA

  • High IgA may indicate: Multiple myeloma, an autoimmune disease such as rheumatoid arthritis or systemic lupus erythematosus, and some liver diseases such as cirrhosis of the liver or chronic hepatitis.
  • Low IgA may indicate:  Some types of leukemia, kidney damage, problems with the intestines, a rare inherited disease that affects muscle coordination (ataxia-telangiectasia), and an increased chance of developing an autoimmune disease. Also, some people are just born with very low levels or no IgA antibodies.
IgG
  • High IgG may indicate: This often indicated a long-term infection, such as with someone who has HIV. High IgG may also indicate multiple myeloma, chronic hepatitis, and multiple sclerosis (MS).
  • Low IgG may indicate: Macroglobulinemia, a disease that inhibits the growth of cells that make IgG. Also seen in some types of leukemia and a type of kidney damage (nephrotic syndrome). Rarely, people are born with a low level of IgG antibodies, and these people are more prone to developing infections.
IgM
  • High IgM may indicate: early viral hepatitis, mononucleosis, rheumatoid arthritis, kidney damage, and sometimes parasitic infection. They also indicate a NEW infection–something the body has never seen before. When a newborn has high levels of IgM, it means that an infection has started in the infant’s body before birth.
  • Low IgM may indicate: Multiple myeloma, some types of leukemia, and some inherited types of immune diseases.
IgD
  • High IgD may indicate: Multiple myeloma.
  • Low IgD may indicate: Hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS).
IgE
  • High IgE may indicate: This most often indicates a parasitic infection or allergies. People with normally high IgE antibodies have allergic reactions, asthma, atopic dermatitis, some types of cancer, and certain autoimmune diseases.
  • Low IgE may indicate: Ataxia-telangiectasia, a rare inherited disease that affects muscle coordination.

 

 

Resources:

  1. Webmd.com
  2. Fischbach FT, Dunning MB III, eds. Manual of Laboratory and Diagnostic Tests. 8th ed. Philadelphia: Lippincott Williams and Wilkins. 2009.
  3. Microbiology and Immunology Online. University of South Carolina School of Medicine. Nov. 2009. Link.
  4. Abbas, Abul K., Andrew H. Lichtman, and Shiv Pillai. Cellular and Molecular Immunology. Philadelphia: Saunders Elsevier, Inc., 2010.

 

 

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