Immune Hypersensitivity Reactions
Two of the antibodies involved in an allergic reaction are immunoglobulins E (IgE) and immunoglobulin G (IgG). IgE production occurs right after ingestion or inhalation of an allergy and is referred to as a Type I Immediate Hypersensitivity Reaction. Type I reactions are usually seen in acute allergies like hives, sneezing, itchy eyes and a runny nose. IgG antibodies are produced for several hours or days after exposure to an allergen are called Type III Delayed Hypersensitivity Reactions. The IgG-IgE Allergy Serum test measures for immediate and delayed reactions to allergens through IgE and IgG respectively. Inhalant allergies are assessed through IgE only. The IgG-IgE Allergy-Serum test only measures immune reactions that result in production of antibodies and inflammatory mediators.
IgE Delayed Onset Allergies
IgE mediated hypersensitivities occur in approximately 20% of the population. IgE is produced in response to allergen/antigen and binds to the mast cells and basophils. This triggers the release of a compound called histamine which triggers other inflammatory reactions resulting in a very quick allergic reaction. The effects of histamine can cause the following reactions
- dilation of blood vessels leading to redness and swelling of the skin
- increased capillary permeability causing swelling and heat
- constriction of airways causing asthma and breathing problems
- stimulation of mucous secretion leading to phlegm, runny nose and itchy watery eyes
- stimulation of nerve endings leading to pain and itching on skin surface
- severe type I hypersensitivity reactions can lead to anaphylaxis due to circulatory effects from blood vessel dilation and increased capillary permeability
IgE is measured in the serum and not the blood because there are similar amounts of IgE in blood relative to IgG, therefore a larger sample is required.