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Immunoglobulins are simply proteins that act as antibodies! These proteins are produced by a type of blood cells known as B cells in response to an immunogen. Their role is to identify and neutralize antigens
Immunoglobulins are among the most abundant proteins in the blood since they comprise about 20% of total plasma proteins.
They derive their name from the fact that when the serum that has got antibodies is subjected to a process of electrophoresis, five main peaks of proteins are identified. These are based on their differential ability to migrate in an electric field.
Antibodies are generally drawn as a ‘Y’ shaped structure and when they are in this conformation the heavy chain can be thought of as being ‘inside’ the light chain.
The five classes or isotypes of immunoglobulins are: IgA,IgE,IgD,IgG and IgM
An immunoglobulin has:
In this article, we are specifically looking at the causes of elevated immunoglobulin levels
Immunoglobulin A exists in three forms which are:
A monomer, a dimer, and dimer plus a secretory piece.
The dimer form is transported across respiratory and intestinal mucosal barriers into the lumen by the secretory piece which is the receptor for immunoglobulin A Fc portion on the epithelium of the mucosa.
There exist two subclasses of IgAα1 and α2.
This immunoglobulin is found in high concentration in serum
It exists mainly as a dimer with a half-life of 6 days.
IgA Protects mucosal tissues, tears, saliva, and colostrum by blocking bacteria, viruses, and toxins from binding to host cells.
Immunoglobulin A is increased in lymphoproliferative disorders such as;
Immunoglobulin A is decreased in:
Immunoglobulin E has four C domains with a molecular weight of 188000d.
It is unstable at 56 degrees and is called a reagin.
There is a very low serum concentration of immunoglobulin E because its Fc region binds avidly to mast cells and basophils.
This immunoglobulin binds to circulating basophils and tissue-bound mast cells via a receptor on their surface. The binding of an antigen to these IgE sensitized cells trigger the release of vasoactive amines mainly histamines. This results in atopic disease characterized by a local reaction known as hives and a systemic reaction known as anaphylaxis.
This immunoglobulin does not cross placenta nor fix complement via a conventional pathway.
Immunoglobulin E levels are elevated in conditions such as;
IgE is decreased in:
Of all the immunoglobulins, immunoglobulin G has the highest concentration in serum with a half-life of 18-25 days.
It is elevated in the following conditions:
IgG is decreased in:
Immunoglobulin M exists in two structural forms. A monomer form is synthesized by B cells and retained also on the membrane of B cells. It serves as the B cell receptor specific for a single antigenic epitope.
Secreted immunoglobulin M exists as a pentamer. This simply means that it exists as five monomeric IgM molecules that are joined together by a J chain.
The pentamer is secreted following antigen and cytokine activation of plasma cells, with hypervariable regions on the pentamer same as those on the membrane-bound monomeric receptors.
IgM has four constant domains on the H and L chains, therefore, its pentamer form has the highest molecular weight of the immunoglobulins.
It’s the first antibody to appear after the antigenic stimulus and fixes the complement avidly.
Immunoglobulin M is elevated in;
Only immunoglobulins M and G are able to fix complement.
Only immunoglobulin G crosses the placenta.
Immunoglobulin M has the highest number of antigen binding sites – 10 sites.
immunoglobulin G has the highest concentration in serum -80%.
immunoglobulin E has the lowest concentration in serum.