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Lymphatic System

Specific Defenses

Classes of Immunoglobulins

There are five classes of antibodies, known as immunoglobulins (Igs).

Class Description
IgG Accounts for 80% of all antibodies in the blood; found in blood, lymph, and the intestines; the only antibody that crosses the placenta from mother to fetus; provides resistance against many viruses, bacteria, and bacterial toxins
IgA Accounts for 10% to 15% of all antibodies in the blood; found mostly in secretions such as sweat, tears, saliva, and mucus; attack pathogens before they enter internal tissues; levels reduce under stress lowering resistance
IgM Accounts for 5% to 10% of all antibodies in the blood; found in blood and lymph; first antibody secreted after exposure to an antigen; includes the anti-A and anti-B antibodies of ABO blood, which bind to A and B antigens during incompatible blood transfusions
IgD Accounts for 0.2% of all antibodies in the blood; found in blood, lymph, and the surfaces of B cells; plays a role in the activation of B cells
IgE Accounts for less than 0.1% of all antibodies in the blood; found on the surfaces of mast cells and basophils; stimulates cells to release histamine and other chemicals that accelerate inflammation; plays a role in allergic reactions


Antibodies, antigens, and lymphocytes work together to fend off disease. (From Smeltzer, S. C., and Bare, B. G. Textbook of Medical-Surgical Nursing. 9th Ed. Philadelphia: Lippincott, Williams & Wilkins, 2000.)
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