Study type: Blood collected in a gold-, red-, or red/gray-top tube; related body system: Circulatory/Hematopoietic, Immune, and Respiratory [IgE] systems.

Immunoglobulins A, D, E, G, and M are made by plasma cells in response to foreign substances. Immunoglobulins neutralize toxic substances, support phagocytosis, and destroy invading microorganisms. They are made up of heavy and light chains. Immunoglobulins produced by the abnormal proliferation of a single plasma cell (clone) are called monoclonal. Polyclonal increases result when multiple cell lines produce excessive amounts of antibody.

IgA is found mainly in secretions such as tears, saliva, and breast milk. It is believed to protect mucous membranes from viruses and bacteria.

The function of IgD is not well understood, but it is believed to interact directly with microorganisms and participate in the activation of B lymphocytes, mast cells, and monocytes.

IgG is the predominant serum immunoglobulin and is important in long-term defense against disease. It is the only antibody that significantly crosses the placenta.

IgM is the largest immunoglobulin, and it is the first antibody to react to an antigenic stimulus. IgM also forms natural antibodies, such as ABO blood group antibodies. The presence of IgM in cord blood is an indication of congenital infection.

IgE is an antibody whose primary response is to allergic reactions and parasitic infections. Most of the body’s IgE is bound to specialized tissue cells; little is available in the circulating blood. IgE binds to the membrane of special granulocytes called basophils in the circulating blood and mast cells in the tissues. Basophil and mast cell membranes have receptors for IgE. Mast cells are abundant in the skin and the tissues lining the respiratory and alimentary tracts. When IgE antibody becomes cross-linked with antigen/allergen, the release of histamine, heparin, and other chemicals from the granules in the cells is triggered. A sequence of events follows activation of IgE that affects smooth muscle contraction, vascular permeability, and inflammatory reactions. The inflammatory response allows proteins from the bloodstream to enter the tissues. Helminths (worm parasites) are especially susceptible to immunoglobulin-mediated cytotoxic chemicals. The inflammatory reaction proteins attract macrophages from the circulatory system and granulocytes, such as eosinophils, from circulation and bone marrow. Eosinophils also contain enzymes effective against the parasitic invaders. A nasal smear can be examined for the presence of eosinophils to screen for allergic conditions. Either a single smear or smears of nasal secretions from each side of the nose should be submitted, at room temperature, for Hansel staining and evaluation. Normal findings vary by laboratory, but generally, greater than 10% to 15% is considered eosinophilia or increased presence of eosonophils. Results may be invalid for patients already taking local or systemic corticosteroids.