What Are the Five Classes of Immunoglobulins?

By Bryan Cohen; Updated April 24, 2017
Scientist looking through microscope

Immunoglobulins, also referred to as antibodies, are proteins that are located in the bodily fluids and blood of vertebrates that regulate the immune system. These immunoglobulins help to determine what foreign objects are and to neutralize them. Some examples of foreign objects in the blood stream are viruses and bacteria. Immunoglobulins are created by a white blood cell called a plasma cell and can be classified into five different classes based on their antigenic properties.


Immunoglobulin A is the major antibody found in the membranes of the respiratory and gastrointestinal tract. The second most common immunoglobulin in the human body, IgA can also be found in tears, saliva, mucus, and colostrums. IgA is one of the most important immonoglobulins in local immunity. The two subclasses of IgA are IgA1 and IgA2.


This immunoglobulin class is present in the blood serum in tiny amounts. Immunoglobulin D can be found on B cell surfaces and it is used as a receptor for antigen. It helps to anchor to cell membranes with its abundance of amino acids. It is not completely determined why IgD is found in serum, making this the least understood antibody.


Immunoglobulin E can be found protecting the body in the mucous membranes and skin. IgE is the least common antibody found in the blood stream. It is the antibody that triggers allergic reactions, which occur when IgE bind to cells to which the body is allergic. IgE also functions during problems with parasites, and the amount of IgE is sometimes measured to determine if the body has a parasitic infection.


This major class of immunoglobulins is the body’s main defense against bacteria. IgG makes up around 75 percent of all human immunoglobulins and this is the only class that can cross the placenta to protect newborns against infections. Immunogloblin G is the most versatile of all the antibodies because it can carry out functions of the other types of antibodies as well. The four subclasses of IgG are IgG1, IgG2, IgG3, IgG4.


These immunoglobulins fight blood infections and help to trigger additional production of immunoglobulin G. Like IgD, these antibodies are present on lymphocyte cells. Of all immunoglobulins 10 percent are IgM. Immunoglobulin M is the first antibody made by the fetus. These immunoglobulins are well-suited for clumping microorganisms and helping them to be removed from the body.

About the Author

Bryan Cohen has been a writer since 2001 and is a graduate of the University of North Carolina at Chapel Hill with a double degree in English and dramatic art. His writing has appeared on various online publications including his personal website Build Creative Writing Ideas.