Immunoglobulins (Ig) or antibodies are proteins produced by white blood cells. They are important in maintaining the body’s immune system since they attach to bacteria, viruses, and other foreign bodies and help in destroying them.
There are five classes of immunoglobulins: Immunoglobulin A (IgA), Immunoglobulin G (IgG), Immunoglobulin M (IgM), Immunoglobulin D (IgD), and Immunoglobulin E (IgE).
IgA antibodies are the ones in saliva, tears, sweat, and other secretions including those in the gastrointestinal, genitourinary, and respiratory tracts. IgG antibodies are the most common as they are located in all bodily fluids. They fight infections and are the only ones which can cross the placental barrier and assist the developing fetus. IgM antibodies are located in the blood and lymph fluid; they are the first responders to infections. IgD antibodies are only present in small quantities and their exact function is not yet clear. IgE antibodies are essential in allergic responses as they fight allergens.