Learn About Antibodies and Antigens

Understanding what antigens and antibodies are and their roles in your body. Learn more.

Antibodies, or immunoglobulins, are proteins made by the body that help fight against foreign substances called antigens. When an antigen enters the body, it stimulates the immune system to produce antibodies. The antibodies attach, or bind, themselves to the antigen and inactivate it.

Antigens are any substance that stimulates the immune system to produce antibodies. Antigens can be bacteria, viruses, or fungi that cause infection and disease. They can also be substances, called allergens, that bring on an allergic reaction. Common allergens include dust, pollen, animal dander, bee stings, or certain foods.

 How bispecific monoclonal antibodies work. Image courtesy of SinoBiological.com

The Five Classes of Antibodies

There are five different kinds of antibodies, IgG, IgA, IgM, IgD, and IgE. Ig is the abbreviation for immunoglobulin, or antibody. Laboratories use Serological Testing to identify these antibodies in samples.

IgG antibodies are the most common and the most important. They circulate in the blood and other body fluids, defending against invading bacteria and viruses. The binding of IgG antibodies with bacterial or viral antigens activates other immune cells that engulf and destroy the antigens. The smallest of the antibodies, IgG moves easily across cell membranes. In humans, this mobility allows the IgG in a pregnant woman to pass through the placenta to her fetus, providing a temporary defense to her unborn child.

IgA antibodies are present in tears, saliva, and mucus, as well as in secretions of the respiratory, reproductive, digestive, and urinary tracts. IgA functions to neutralize bacteria and viruses and prevent them from entering the body or reaching the internal organs.

IgM is present in the blood and is the largest of the antibodies, combining five Y-shaped units. It functions similarly to IgG in defending against antigens but cannot cross membranes because of its size. IgM is the main antibody produced in an initial attack by a specific bacterial or viral antigen, while IgG is usually produced in later infections caused by the same agent.

IgD is present in small amounts in the blood. This class of antibodies is found mostly on the surface of B cells—cells that produce and release antibodies. IgD assists B cells in recognizing specific antigens.

IgE antibodies are present in tiny amounts in serum and are responsible for allergic reactions. IgE can bind to the surface of certain cells called mast cells, which contain strong chemicals, including histamine. When an allergen such as pollen binds with its specific IgE antibody, it stimulates the release of histamine from the mast cell. The irritating histamine causes the symptoms of an allergic reaction, such as runny nose, sneezing, and swollen tissues.

Image courtesy of Compoundchem.com Creative Commons License. Click to enlarge

Can we produce antibodies in a laboratory?

Yes. Antibody production is carried out in the body by B cells. There are various methods for antibody production in the laboratory. Monoclonal antibodies can be produced through the use of hybridoma cells in vitro. Polyclonal antibodies are typically manufactured in rabbits.

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