In the blood of healthy people, IgE antibodies make up less than 0.001% of all immunoglobulins. These IgE antibodies are key in triggering allergic responses when people sensitive to allergens come into contact with them.
Structurally, IgE resembles other antibodies, having two light chains and two heavy chains. The heavy chains have a special region that determines the antibody's specificity to antigens. Measuring IgE levels is clinically significant mainly because of its role in allergic reactions, even though IgE myeloma is a very rare condition.
IgE antibodies typically attach to mast cells and basophils in the bloodstream. When these cells interact with specific allergens, they release histamines and other compounds that start the allergic reaction. Around half of the people suffering from allergic rhinitis or asthma show high IgE levels, but it's also common for individuals with allergies and specific allergen sensitivity to have normal total IgE levels.
Research has found that people with atopic dermatitis often have raised total IgE levels, which appears to align with the severity of their eczema. Besides, elevated IgE can be indicative of parasitic infections, allergic bronchopulmonary aspergillosis, or certain immune deficiencies.
References:
Portnoy JM. Appropriate allergy testing and interpretation. Mo Med. 2011 Sep-Oct;108(5):339-43. PMID: 22073491; PMCID: PMC6188374.
Fadal RG. IgE-mediated hypersensitivity reactions. Otolaryngol Head Neck Surg. 1993 Sep;109(3 Pt 2):565-78. PMID: 8414585.
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