Often referred to as gamma globulins or immunoglobulins, antibodies are divided into five main classes. By far the most common variety is immunoglobulin G, otherwise known as IgG. IgG antibodies in the bloodstream are largely responsible for the protection produced by-immunizations, such as those against measles and rubella.

Immunoglobulin A (IgA), which is found in stomach and nasal secretions and in breast milk, is the second class of immunoglobulins. IgA serves as the first line of defense against attack to the mucus membranes of the respiratory and digestive tracts.

The third class of immunoglobulins, immuniglobulin E, IgE, is a major weapon in your body's natural defense against assault by large organisms, such as parasitic worms. To allergy sufferers, however, this antibody is better known for its critical role in sensitizing people to specific allergens and for inducing allergy attacks (discussed below). For these reasons IgE has earned the dubious reputation of being the primary allergy antibody.