The five classes of immunoglobulins are IgA, IgG, IgE, IgD and IgM. Immunoglobulins are substances made by the immune system in response to specific diseases or illnesses in the body, according to WebMD. They are also known as antibodies, and they identify and attach to invading bacteria, viruses, fungus or cancer cells so the immune system can destroy the foreign organism.
IgA immunoglobulins are found in saliva, tears, blood and in the exposed airways. They are also found in the nose, digestive tract, vagina, eyes and ears. Approximately 10 to 15 percent of all human antibodies are IgA antibodies, which in general protect body surfaces that are exposed to foreign environmental organisms. IgG immunoglobulins are found on body surfaces and are important in fighting viral and bacterial infections. Although small in size, IgG antibodies make up the greatest percentage of all immunoglobulins, accounting for 75 to 80 percent of the immunoglobulins in the human body, explains WebMD. IgE immunoglobulins are found in the lungs and on the skin and mucous membranes, and they are involved in the allergic response.
The function of IgD immunoglobulins is not well understood, but they are found in the linings of the abdomen and chest, WebMD notes. IgM immunoglobulins are the largest in size and account for 5 to 10 percent of all antibodies. They are found in blood and lymph fluid. IgM antibodies are the first type of immune cell made when an infection begins and trigger other immune cells to destroy foreign organisms. Antibody levels in the blood are analyzed to determine the cause of medical problems.