What Are the Classes of Antibodies?

Antibodies watch for, and guard against, bodily invaders such as viruses and bacteria. The adaptable structure of antibodies includes four chains and multiple binding sites, allowing the antibody to bind to a wide range of antigens. Antigens are anything that enters the body and triggers the release of antibodies. The names of the five classes of antibodies are prefaced with the letters Ig, which stand for immunoglobulin, another term for antibody.

IgG

IgG, the most common class, makes up 80 percent of antibodies, according to Dr. Gary Kaiser of Community College of Baltimore County. Traveling through bodily fluids, including blood, IgG structures are small and able to cross the membranes of cells, making them easy to transport. Different portions of the IgG structure can bind to different kinds of antigens.

IgM is much larger than IgG and is incapable of crossing the membranes of cells, limiting its movement. According to Science Clarified, this limited movement motivates the body to deploy IgM as a first line of defense, leaving IgG as a backup to go after antigens in case of IgM failure.

IgM accounts for 13 percent of antibodies.

IgA, which accounts for 6 percent of antibodies, travels in bodily secretions that include tears, mucus, saliva and urine. IgA serves to neutralize the bacterial or viral antigens, blocking their paths at bodily entry and to the organs. IgA protect internal organs by preventing antigen binding to the mucous membranes of the organs.

Blood-borne IgD resides on B cells, the cells that create the antibodies. IgD can identify antigens for the cell, instructing it what antibodies to release to combat the invader. IgD only account for 0.2 percent of antibodies.

IgE antibodies bind to mast cells, which produce histamines. Histamines are chemical substances released in response to an allergic reaction. The binding of allergens to IgE creates the allergic reaction.

Though IgE account for only 0.002 percent of antibodies, the functions extend beyond allergies. IgE blocks parasitic worms and may inflame mucous membranes to allow protective substances such as IgG to enter the tissue.